Warhawk

[Ivan]

I originally built a P-40E and released it in January 2005.

Since then, it has had a couple slight modifications such as improved exhausts.
Some of the parts were re-used to make the P-40C aircraft.
The idea of making a long tail version (P-40K, P-40M) is the first real "modification" to the basic design.
Attached are some screenshots illustrating the differences.

There is still something not quite right about the shape of the Tail Fin and I believe the panel lines need some additional attention, but it seems to fit together fairly well at this point.

- Ivan.

[Ivan]

Sometimes design choices for the original project (P-40E) cause problems when trying to modify it into a new project.

In this case, the scale of the Fuselage was consistent across files but a little odd at 11.6 feet to 256 pixels.
This makes aligning textures a bit difficult in certain circumstances. The lack of a camouflage pattern on this aircraft makes this not terribly important, but if I were to repaint with a pattern extending across different parts of the aircraft, precise work may be difficult.

Another issue was that the textures were laid out VERY tight within the files so that for a 20 inch longer tail, there needed to be at least one more texture file because the extended parts would not fit onto the same files.
There also wasn't room to texture any additional parts using the existing files.

These days, I am a bit smarter and don't lay things out quite as tight because using an additional file may simplify the matching of parts pairs such as landing gear, guns, etc.
The assembly sequence was also a touch strange at places, but I chose not to change things because the original sequence was working well enough.
Many parts were reshaped from just aft of the Cockpit, but the parts count is identical to the original which I believe is rather amusing.

The Curtiss Company designation for the P-40E and P-40K were the same; both were Hawk 87B's.
Next comes the new markings.....

- Ivan.

[Ivan]

I created the P-40E from a set of drawings by William Wylam.
These were drawings derived from Curtiss company specifications for the aircraft with dimensions stated.
I had noticed when building the model that sometimes the stated dimensions could not actually line up, but the differences were not great and the result looked like a short tailed P-40.
I had also noticed that my model differed a bit from photographs but wasn't quite sure where the differences were.

Attached are two images derived from overlaying the wire frame from my model with a drawing and a photograph.
There is of course the possibility that the photograph isn't lined up, but the differences are a bit more extreme than a slight misalignment would create.

The interesting thing is that the mismatch does not appear in the Fin as I was expecting. It is mostly in the Canopy and Keel area.

The big question now is whether or not I should continue trying to develop this model or not.
The Wylam drawing is the only dimensional reference I have at this point and my model agrees pretty well with that.

What do you all think of the mismatches?

- Ivan.

[Ivan]

42-10343 happens to be a P-40K-15-CU.

- Ivan.

[No Dice]

Ivan,
I do see the difference you are talking about, BUT I can not help looking at the shadows under the wings. If the shadows were lined up
that may compensate for a lot of what we see. Do you think ?? I am just not so sure that you are that off of the mark.

Dave

[smilo]

as always, the decision to change
or live with the discrepancies is up to you.

as my wife likes to say when i point out project deficiencies,
nobody would notice, if you didn't say something.

but, then again, it's your project.
not hers.

[Ivan]

Hello Smilo, No Dice,

To me, the shape of an aircraft model is very important. It isn't enough to get a general representation, at least not for me.
It has to have "The Look". This one just doesn't quite look right at this point.

I went back to check the drawings I was working from (by William Wylam). The drawing lengths add up about 4 inches short of the stated length of the aircraft. The greatest deviation from the stated measurements was around 1/2 inch at the rear of the keel fairing. So.... From the dimensions I have, it is "Correct".

So now what?
- Ivan.

[arfyhun]

Ivan, I can see your point, but from one who can barely keep the things flying I would be very happy with it 'as-is'. BUT...knowing me as I do, if I were in your position and spent the hours you have in developing it as far as you have I would not be able to stop until complete satisfaction is achieved.

Unfortunately, I do not have the ability to build anything at all so the notes you have produced are going over my head a lot better than the planes I fly!

If I had not been privvy to this thread the A/C would have looked brilliant; and now you have shown me the tiny inaccuracies that exist I can honestly say to me it makes no difference....but I am not Ivan.

In a small way that makes me glad as I do not have to worry.

As the Irishman once said; 'I'm just grateful for small Murphys'.

I would love to be in your position but glad I'm not!

Best wishes,

Graham.

[Ivan]

Thanks Arfyhun,

Last night I had a bit of trouble sleeping and I found an aircraft diagram of the P-40N in the book America's Hundred Thousand. The odd thing abour this drawing is that it has a scale below the drawing showing distances from the aircraft datum line which happens to be about 1/3 of the way back on the spinner from the tip.

I spent about an hour or so using a clear straight edge and measuring the locations of various aircraft pieces from the reference line. This morning, I took those measurements and compared them to the P-40K that I have been building.

Surprise, surprise, there isn't an item that is more than about 1/2 in off on my model as compared to the drawing except for the rudder hinge line and I already knew about that.

So now I can honestly say that I have not a clue as to where the problem is except that it does not match photographs....
Still looks wrong but I have no idea where to fix things.

- Ivan.

[smilo]

just a guess.
is it possible that the photograph perspective is off?
i have a hard time imagining that the photo view angles
are as precise as a, say, side view drawing.

it would seem to me, that a slight variance in the view angle
would change the perceived part distance.

especially for parts farthest from center,
ie; tail parts would appear to be farther from center
than they would be in a flat drawing.

build the model to drawing specs...no small task,
load it up, go into spot/chase view and pan around.
how does the tail look when viewed from slightly forward/up and down?

then there is the monitor resolution variations.
but, that's another subject all together.

[Ivan]

Thanks for the insight, Smilo.

I pretty much have finished the visual model, but it just doesn't look quite right.
The Chinese insignia will be replaced with standard USAAF stars of a style suitable for late 1942.
The fuselage stars will displace the tactical number and there will be few additional markings.

This is such a common aircraft that I am surprised that even the drawings don't agree with each other.
Since I don't have a good drawing to work from, I can't really make reasonable adjustments.

There were some problems with the Wylam drawings:
The stated overall length was 31' 7".
The sum of the lengths of all the parts was only 31' 3", so in order to use the dimensions, I had to arbitrarily add the extra 4 inches SOME PLACE on the aircraft. I did this by adding an inch here and there an eyeballing the result.

Another issue is that the book "America's Hundred Thousand" specifies the K and N models as being 33.22 feet.
The P-40N Erection and Maintenance Manual specifies the length as 33 feet 3.7 inch. Yet another source claims the length to be 33 feet 3.75 inch or 33 feet 4 inch.
I will probably use the number from the E&M manual because I believe those tech manuals the most against the other sources.

Still wondering which is right.

- Ivan.

[arfyhun]

Ivan, I can only say that when you come to your final decision the Hawk will look brilliant.

Don't lose sleep, take a deep breath and 'amble along'. I'm sure that way all things will fall into place.

Oftentimes, it's the tension inside which gets in the way. Easy for me to say, I know!

Ask your son which looks better, a lot of times a fresh pair of eyes can see the wood for the trees.

Good luck,

Graham.

[No Dice]

Ditto, It will be one fine bird.

Dave

[Ivan]

Over the last week or so, I decided to finally revisit the P-40 Long Tail.
I started with a dimensional confirmation of the original Short Tail version of the P-40E and found that apparently I had misread Wylam's Drawing. The dimensions actually don't have a 4 inch discrepancy if it is interpreted correctly. I also found that my P-40E is a bit off in places but generally close enough to the drawing not to matter much (about 3/4 inch off at the worst and generally under 1/4 inch off or dead on).
I also found that my copying of the panel lines around the Rudder and Fin area was quite poor.

The Long Tail configuration that I am building as a model looks like either a late P-40K or P-40M. The E&M manual lists 33 ft 3.7 in, so that would make it 20.7 inches longer.
In looking over a LOT of photographs, it finally occurred to me that I had handled the Fuselage Extension incorrectly:
Yes, it is 20.7 inches longer, but there is also a vertical shift that isn't so precisely defined.
Another VERY interesting thing is that the Rudder has the exact same visual appearance between the two versions!
Most of the panel lines on the Fin also appear to match with that exception that there is a new panel at the root of the Fin which apparently extends it.

Extending the Fin upwards made it look more proportional but also made it not fit into its original texture file. This little change cascaded through a couple texture files because now the Tail Cone also needed moved which affected the Landing Gear.... While updating textures, I found that the Rudder had an incorrect number of Ribs and didn't match the real aeroplane's hinge lines.
Another major change was that the Razorback area behind the Cockpit apparently had a subtle bump which I also added. (It is now around 2 scale inches higher which changed all the contours in the Aft Fuselage. The wider and higher Aft Fuselage also affects the Quarter Windows, Framing and the cutout underneath. Without going into even more detail, the changes and fixes took 3-4 evenings....

The changes are not entirely obvious and I am sure they still disagree with photographs, but they do seem to agree with the drawings and have "The Look" I was trying to get.

- Ivan.

[smilo]

looks very good.
nicely done.

[Ivan]

looks very good.
nicely done.

Thanks Smilo, I didn't want to respond before I actually had completed something substantial on the project.

The Tail got yet another redesign. It is entirely by eyeball at this point and a couple polygons were added to the leading edge of the fin. The textures are redone a bit to look more like the actual aircraft. The first SCASM pass has been done to the model and it should make future texturing easier. An interior view of the canopy framing for the virtual cockpit has been built but it hasn't been textured yet. The nice thing is that the canopy framing is identical between the E, K, and M models so it only needs to be done once for those aircraft. The frame still needs to be flipped inside out after disassembly to SCASM. Quite a lot of effort goes into the model that isn't even visible from an external screenshot.

- Ivan.

[smilo]

as always, we look forward
to seeing the fruits of your labor.

[Ivan]

Thanks Smilo.

Here's the process I am using:
1. I copy all the pieces from the Canopy Frame Component (CFrame-something).

2. I then narrow them down a bit (50% in this case) so that they will not block too much visibility from the cockpit (to be discussed later).
At this point it is an untextured Component (IFrame) which I modify to remove bleeds and sparklies where the pieces don't quite meet up.

3. Next it is textured to be Dark Green. One side is textured Red for better visibilty for the screenshot.
When it is textured and changed to be a "Smooth" AF99 Component, it disappears from the Interior View.
The Red is easily seen against the real canopy frame to show how the widths compare.

4. Now HERE is the cool part: Next, I extract the SCASM code for the Component and run it through a little C program I wrote which reverses all the Polygons directions.
The result is a "Component" which faces inward and isn't visible from outside. Editing the SCASM code by hand would take a couple hours with great potential for error. Using this conversion program takes about 2-3 seconds!

The result is amusing to look at. The Exterior View screenshot shows the Canopy Frame looking like it is facing you 7 or 8 o'Clock.
In Reality, it is facing 10 or 11 o'Clock along the same direction as the runway markings.

....

[smilo]

i wish i could come up with
a comment besides my standard,
very nice or that's cool, but for now,
it will have to do.

thanks for the shots.

[Ivan]

Hello Smilo,

Actually I like your responses because I am sure that if you saw something that didn't look quite right, you would tell me. Hubbabubba also can be counted on for an honest critique.

Here is what happens when the Internal Canopy Frame gets put into the rest of the model.
There is a slight problem though because the Canopy Frame then chops off part of the Pilot's Shoulder. The P-40 has a very low Cockpit Wall as compared to many other aircraft. One pilot remarked that it felt like the glass came down to around your waist.
The solution after leaving it overnight was simply to redraw the Pilot's Shoulder yet again.

Since I took these screenshots, I increased the width of the front section of the windshield frame by 50% and it looks a bit better to me now. I also adjusted the display range of the Flaps and Flap Wells so that continue to display until fully retracted. I had to do a little guessing here and also to remove the entire model except for the Flap parts to see what was actually happening when all the parts opened and closed.

Perhaps I am terribly out of practice, but flying this beast is a bit more difficult than I remembered. It also changes Directional Trim with Airspeed changes like the actual aircraft does though I didn't intentionally do this. Another goofy thing is that CFS doesn't have lockable Tail Wheels so there is lots of overcontrol at low taxiing speeds.

- Ivan.

- Ivan.

[Ivan]

I have also been considering doing ALL of the P-40 versions from the P-40B/C all the way out to the P-40N. The Q also is a consideration, but it would require a substantial rebuild (which is what the real one was) and I am lazy.

In order to do this, the textures need to be able to support long and short Fuselage variants, AND the monstrously ugly Fin Fillet on the mid series K. I also want the texture layouts to be as close to the same as possible between variants. I had originally arranged the textures VERY tight for the P-40E with almost no wasted space.
When the increased length Tail Cone needed to be fitted in, the Fin could no longer fit onto the same texture file as the Tail Cone. This wasn't a big deal because I had no room to put the texture for the interior of the Canopy Frame for the Virtual Cockpit. Thus one more texture file was added. A couple things like landing gear pieces also needed moved around to fit.
What I had not considered was that the extra length Fin Fillet on the earlier K series would need more room than I had originally planned. A bit more reworking and now I believe I can handle from the D model out through the N model using the same basic layout with some small component variations.

The P-40K also had a minor trip through the Paint Shop and hopefully looks better. I could not find a definitive source for paint standards, so I used a bit of artistic license.

- Ivan.
P.S. My son calls this aeroplane "Rudolf" for fairly obvious reasons.

[smilo]

....and I am lazy.

sorry, i don't buy it.
you are far from lazy.
maybe, a little over extended, but, not lazy.

I have also been considering doing ALL of the P-40 versions from the P-40B/C all the way out to the P-40N. The Q also is a consideration, but it would require a substantial rebuild (which is what the real one was)

this would be a major undertaking,
but, when completed, an interesting package.
i, for one, would like to see it happen.

[Ivan]

We had a visitor from Alaska visit our shop today. She claimed to be an artist and wanted to look over the P-40K. She spent a lot of time looking at the P-40 from different angles and drawing and making notes in her sketch pad.

When we stepped out of the shop to analyse results of recent engine tests, she sneaked into our paint booth and tried her hand with our spray guns. By the time we came back into the shop, she was so far along that we decided to let her finish.

We decided it wasn't worth repainting back to the original colours just for flight testing today, so here is the result. The paint wasn't even on long enough to dry when these shots were taken.

We are still trying to decide whether to throw her in jail or hire her for future work.
;-)
- Ivan.

[Ivan]

Over the last few days, the AIR file of the P-40K gradually took shape. There are a few things about it that surprise me, but I believe that a lot of it is due to the conflicting information about the aircraft.

Maximum Speed at 5000 feet
Actual 320 mph
Model 341 mph

Maximum Speed at 15,000 feet
Actual 362 mph
Model 357 mph (Maximum Speed 363 mph @ 10,000 feet)

Service Ceiling
Actual 28,800 feet (Unknown climb rate. Was it 500 feet/min or 100 feet/min?)
Model 29,900 feet (100 feet/min with 50% fuel and 100% ammunition)

Initial Climb
Actual 2600-2800 feet/min depending on source
Model 2990 feet/min

The general handling seems to be quite good. In watching Air Show performances on video, it appears to me that P-40 pilots actually are willing to do more with their aircraft than just low level passes and a few slow rolls. They move much more enthusiastically than your typical WW2 fighter.

Smilo,
A complete set of P-40 models is actually not that far away:
The early P-40 through P-40C have been done.
The P-40D,E, and early K without the fillet are done.
Adding a Fin Fillet gets the mid production short tail K.
The P-40K,M are my current project.
The P-40N isn't that much of a departure from the K.
The P-40F,L with Merlin engines are basically either E or K models with a revised cowl and intake.

Problem is that I can see all the P-40s I have could use some improvements.

- Ivan.

[Ivan]

The paint schemes took a bit longer than I thought they would.
The Disney Flying Tiger image didn't quite turn out as well as I had hoped, but the fuselage seemed a bit bare without it.
I am not sure which set of textures I like better.

I had always thought of these mid production P-40s as rather drab, Sad Sack kind of aeroplanes. In doing a little basic research to work on this project, I found that these P-40Ks were probably the hottest version of the aircraft at low altitudes. The Allison engine tolerated boost pressure well above what the manual specified. It became bad enough in practice that the limits in the manuals were adjusted higher (after GM / Allison Division's agreement) though not as high as some pilots were already using.
The Merlin installations had much better altitude performance but were not even close in power at low altitudes. Later Allison engines also reduced maximum manifold pressures because their higher geared superchargers would not stand up to as much boost down low.

I still believe this project could use some improvement but is pretty much releasable as it stands.

- Ivan.

[smilo]

.....
The Disney Flying Tiger image didn't quite turn out as well as I had hoped, but the fuselage seemed a bit bare without it.
I am not sure which set of textures I like better.

.....................

I still believe this project could use some improvement but is pretty much releasable as it stands.

- Ivan.

if i might offer an opinion, or two;

ship it, she's a beauty!

as for the textures, i have to disagree.
but first, i need to qualify....
i have always been partial to the Plane Jane,
everyday workman style paint schemes.
i don't think the fuselage seemed a bit bare without it.
i like it. she looks great!

as for the Disney Tiger and the Aleutian Tiger motifs,
i prefer the Disney Tiger.

i've never really appreciated the Aleutian Tiger.
to me, it just looks like a muddled glob of yellow.
a bit harsh, yes. please don't take offense.
i can see that you've spent a lot of time on it.
this does not apply to just your paint.
i have thought that since the first time
i saw the scheme many years ago.
maybe, if i was stationed in the Aleutians,
i would feel differently about it.

as i said above,
SHIP IT!!

[Ivan]

Hi Smilo,

I actually uploaded it last night....
;-)

The Disney Flying Tiger was a poster sized print that was sent to the AVG in China. They pasted them onto the sides of their aircraft. The problem is that in CFS, the pixels are kinda large so if the image is about the right size on the aeroplane, it looks a bit pixelated up close.... I may work on it again, but not for a while.

- Ivan.

[smilo]

good, good...well done
did you send Dave a copy for your page
at the freefflight site?

here's the link for download here;
http://www.sim-outhouse.com/sohforums/local_links.php?catid=19

[Ivan]

Smilo,

You're right. I should have sent a copy to No Dice. Last night, I was just a bit too tired after trying to write something descriptive for the P-40K.
My son had my computer most of the day for online games and right now, the ZIP file is on a flash drive that I can't get to without waking up Anna Honey. Doing THAT would not be wise....

FWIW, Tonight, I thought I would demonstrate proper flying technique for a simple take-off, once around the island and landing to my son after his online games. He was sitting still and watching so intently (which is unusual). I executed a proper take-off while staying near the center of the runway.
On the approach to land, I was dragging it in pretty slow for a nice three-pointer, found I was a touch low and managed to stall and crash in a nice looking fireball just short of the runway....

I had forgotten that at low speed, the P-40 has all kinds of trim changes.

- Ivan.

[Ivan]

Now that the Workshop's Assembly Line is cleared of the P-40K (at least for a little while), What should take its place in the P-40 series?
For a Long Tail, we can go next to a P-40N. For the Short Tail, we can go next to either a revised P-40E with WEP and some graphical fixes or a P-40F with a Merlin, or even a Short Tail P-40K with a Fin Fillet. Or perhaps the Hawk 81s also need a canopy frame?

- Ivan.

[hubbabubba]

Now that the Workshop's Assembly Line is cleared of the P-40K (at least for a little while), What should take its place in the P-40 series?
For a Long Tail, we can go next to a P-40N. For the Short Tail, we can go next to either a revised P-40E with WEP and some graphical fixes or a P-40F with a Merlin, or even a Short Tail P-40K with a Fin Fillet. Or perhaps the Hawk 81s also need a canopy frame?

- Ivan.

Any P-40/Merlin version would be great. It would also give you an opportunity to explain to us why it was not as successful a pairing than it was for the P-51. Was the P-51 lines so superior to the Curtiss? After all, North American bought the plans of the P-40 before building their pony. Some even accused them of copying, which is absurd in face of the greatly enhanced performances of the Mustang, Allison or RR versions.

[womble55]

Off the top of my head, I think it was down to the aerodynamics. The P51 had much better streamlining and that all important laminar flow wing whereas the P40 was fairly modern but still old technology. The P40Q tried to address these problems which to some extent they did but there was no point changing production over to something that was just as good as what they already had...the P51. As quoted in several books, the P40 was a damn good second choice.

[Ivan]

Any P-40/Merlin version would be great. It would also give you an opportunity to explain to us why it was not as successful a pairing than it was for the P-51. Was the P-51 lines so superior to the Curtiss? After all, North American bought the plans of the P-40 before building their pony. Some even accused them of copying, which is absurd in face of the greatly enhanced performances of the Mustang, Allison or RR versions.


Off the top of my head, I think it was down to the aerodynamics. The P51 had much better streamlining and that all important laminar flow wing whereas the P40 was fairly modern but still old technology. The P40Q tried to address these problems which to some extent they did but there was no point changing production over to something that was just as good as what they already had...the P51. As quoted in several books, the P40 was a damn good second choice.

I was debating on which message to reply to. Hopefully this looks OK.

Hubbabubba,

The actual plans that North American were REQUIRED to buy were not those of the P-40, but rather of the P-46 which was a more recent development that showed promise. The big problems with the P-46 were that the airframe was a bit on the heavy side and that the Allison engine didn't have enough power to haul that mass around but it was still a faster aeroplane on the same engine power as the P-40. Although North American bought the plans, there is no evidence that they influenced the Mustang / Apache design at all.

Womble55,

Aerodynamics was certainly ONE factor but in my opinon was not the DOMINANT factor. Aerodynamic / streamlining generally affects maximum speed but perhaps not much more. With the same engine, the Mustang was superior in speed to the P-40 but it was just as superior to the Spitfire when equipped with the same engine:

The Mustang Mk.I and P-40E were both equipped with the Allison V-1710-39 (F3R) with the same horsepower ratings. The maximum speed of the P-40E was around 345 mph while the Mustang I could hit about 380 mph on the same power. The climb rates of the two aircraft were quite similar as were their weights.

The Mustang Mk.III (P-51B/C) and Spitfire Mk.IX were both equipped with Merlin 60 series engines of nearly the same power. The maximum speed of the Mustang III was about 440 mph while the Spitfire IX could only achieve about 410 mph. The Spitfire could climb over 600 feet per minute faster mostly because it was significantly lighter.

An even more interesting comparison is the Lavochkin La-5FN and La-7. Both aircraft had the same engine. Their planforms and size are nearly identical. The La-5FN could hit about 405 mph. The La-7 with a laminar flow wing and repositioned oil cooler (!) could hit about 425 mph.

A bit off topic, but WHY was the Mustang so much faster on the same engine power?
First, it did have a laminar flow wing section and that probably helped a lot but also cost something as well. The Mustang was less agile than the P-40 or the Spitfire probably because the Laminar Flow Wing had a significantly lower maximum Lift Coefficient when compared to the older designs.
A second aerodynamic factor was the Coolant Radiator which used something called the "Meredith Effect" to add thrust on the exhaust side to offset most of the cooling drag. I believe this was the more significant factor.

The prototype P-40 ALSO had a rear mounted Coolant Radiator which was moved forward because of fears that it would be vulnerable to debris from the the propeller wash. The Lavochkin La-7 moved its Oil Radiator back from under the cowling to under the rear fuselage even though it would make it more vulnerable with longer oil lines to weapons fire.

....

[Ivan]

The most significant reason the P-40 didn't get as much of a gain as the Mustang did with the installation of the Merlin engine was simply that the two aircraft did not get the same version of the Merlin:

The P-40E had an Allison V-1710-39 (F3R) engine with a Single Stage - Single Speed Supercharger.
Its critical altitude was 12,000 feet at which it could produce 1150 HP at Military rating.

The P-40F received the Packard Merlin V-1650-1. This had a SINGLE Stage - Two Speed supercharger.
Its critical altitude at low speed was 10,800 feet at which it could produce 1240 HP at Military rating.
Its critical altitude at high speed was 18,000 feet at which it could produce 1050 HP at Military rating.
At 18,000 feet, it was making about 200 HP more than the Allison F3R did at the same altitude.

The P-51B received the Packard Merlin V-1650-3. This had a TWO Stage - Two Speed supercharger.
Its critical altitude at high speed was 26,000 feet at which it could produce 1210 HP at Military rating.
Its significantly higher critical altitude was the main reason it gained so much performance.

The Merlin installed in the P-40 was pretty similar to the one installed in the late Hurricanes while the Merlin in the Mustang was most similar to that of the 60 series Merlin Spitfire. The Hurricane was never noted for great altitude performance either.

As a side note, The P-51A which was easily the best performing Allison Mustang had the Allison V-1710-81 (F20R).
It also had a Single Stage Single speed supercharger but with the critical altitude increase to 14,600 feet (1125 HP Military rating).
It was considerably less capable at lower altitudes than the earlier Allison F3R and F4R engines and had a WEP MP limit of 57" Hg instead of the earlier engines' 60" Hg.

The Merlin Mustang was apparently a bit less aerodynamic than the Allison Mustang as well. The Merlin 60s produced a bit more power at low altitudes than the Allison F20R, but the Allison Mustang was a bit faster up to 10,000 feet at which it was making about 390 MPH.

- Ivan.

[Ivan]

I created the P-40E from a set of drawings by William Wylam.
These were drawings derived from Curtiss company specifications for the aircraft with dimensions stated.
I had noticed when building the model that sometimes the stated dimensions could not actually line up, but the differences were not great and the result looked like a short tailed P-40.
I had also noticed that my model differed a bit from photographs but wasn't quite sure where the differences were.
....
The interesting thing is that the mismatch does not appear in the Fin as I was expecting. It is mostly in the Canopy and Keel area.
....
The Wylam drawing is the only dimensional reference I have at this point and my model agrees pretty well with that.

- Ivan.

I decided to go back and do another comparison between the drawings' dimensions and my own. The Vertical offset is 0.75 feet because I selected the CoG to be 0.75 feet below the Engine Thrust Line, 12.08 feet from the Spinner Tip and 19.00 feet from the back edge of the Rudder. As you can see from the attached screenshot, the differences are VERY VERY slight.
The worst discrepancy is at the aft end of the Keel which is slightly less than 0.2 feet aft of where it should be. I did this intentionally to make the Fuselage join easier. The other area is the Rudder Aerodynamic Balance at the top of the Fin which is about 0.06 too far forward.

....Yet it still does not quite look right.......
- Ivan.

[Ivan]

Hello Arfyhun,

I just noticed the reply in the Warbirds Library forum.
It isn't often that we see an actual reply in that forum

Thanks for the Comment.
- Ivan.

[Ivan]

Hello All,

I finally managed to find a Fuselage Station diagram for the short tail Allison P-40 about a week ago.
It isn't a great drawing for quality, but is quite useable for at least laying out many things longitudinally.

I found where the Longitudinal and Vertical Datum lines were and am now able to adjust photographs accordingly.
The Longitudinal Datum (Station 1) happens to be at the airframe's Firewall.
The Vertical Datum or Fuselage Reference Line happens to be at the seam where the top half of the Fuselage joins the Bottom half.

From these drawings, the BIGGEST problem with the drawings by William Wylam is that he appeared to be confusing the Engine Thrust Line with the Fuselage Reference Line. This alone would have accounted for a 3.75 inch shift from the front end of the aircraft to the tail. There are MANY other listed dimensions in the drawings which simply do not make sense.

Also from these drawings (along with a couple other P-40 Manual references), I can conclude that the overall length of the P-40E was 31' 8.75" instead of the 31' 7" as stated in the Wylam drawings.

Here is what I have for general longitudinal locations:
Station 1 at the Firewall is the reference.
The front end of the Cowl is 87" ahead of Station 1.
The Rudder Line (Middle Portion) appears to coincide with Station 16 at 226.5" aft of Station 1.
The Rudder End is 262.5" aft of Station 1.
The Fin and Stabilizer appear to attach slightly behind Station 13 at 188" aft of Station 1.
Assuming the OAL listed earlier is correct, that would put length of the Spinner at 31.25" which is very close to the 31" listed in the Wylam drawings.

In comparison to the drawing, the CoG of my model is 2.35 feet aft and 0.44 feet below the aircraft Datum.
I have already started on a rebuild that looks to be quite tedious.

I would post the drawing here but it happens to be several megabytes in size and is hard enough to read even at that resolution.

- Ivan.

[Ivan]

After a couple days of looking over the station diagram and rescaling and combining another tech drawing of the P-40 Cowl, I now have a pretty good representation of the fuselage of the P-40E series. It is still missing the fin and rudder, but I had already scaled those dimensions from several photographs.

Today, I finished entering those dimensions into AF99 to compare with the AF99 model I have of the P-40E. First, I took the resulting part which I believe is as correctly dimensioned as I can get and compared it to the original Warhawk model.
I then took that same part and compared it to the Warhawk model I have been reworking. Attached are screenshots of the results.

I found that the offsets from the aircraft datum point to my AF99 model were not optimal.
The longitudinal offset of -2.35 feet is good, but I found that a vertical offset of 0.55 feet has more matching points than the 0.44 feet offset I used earlier. The engine thrust line now needs to be moved 0.10 feet higher.

The entire front fuselage has already been moved 0.12 feet forward. The horizontal stabilizer has been moved down and will also need moved forward to be even with the fin. I will be ignoring the 2 degree angle of incidence.

It seems like almost everything except for the cockpit and wings will get some kind of adjustment or re shaping. The end result (if I ever finish) will be as close to dimensionally accurate as I can make it which should cure some of the shape issues. I wonder if anyone else will ever notice the changes.

- Ivan.

[smilo]

I wonder if anyone else will ever notice the changes.

you will

[Ivan]

I did a fair amount of review of the shape changes from what the Warhawk looks like now to where it should be but can't do a thing for the next week or so. Am out in Cape Cod, MA for vacation.

Before we left for vacation, I tried to look at what the outline of the entire aircraft should be to best match the drawings I have. This involved estimating the line of the lower fuselage under the Cowl fairing based upon the angles of the wing fillets extended to the aircraft centerline. What I found was that the projected centerline was actually much more consistent than I would have expected even though the line was not shown in the reference templates I had built with the original aircraft. The points were all where I would put them now with the except of the aft-most template. The last template is incorrect because the angle of the tail is quite different between Wylams drawings and my current drawings.

It is a pity that so little of the original aircraft will be retained.

Screenshot comparisions will be posted when I am able.

- Ivan.

[Ivan]

We got back from vacation this weekend.

While on vacation, I had quite a bit of time to look for photographs of the P-40 and found quite a few though I did not have the capability to actually do any modifications to my project.

One of the things I noticed was that the P-40 actually had a wing tip with a flat underside and I had missed that completely in my model. This is actually a very easy and quick fix which I did the night we got back.

Other changes have been from starting from the wing trailing edge and moving forward. (I believe I have completed everything behind the wing.) My process here is to rework the reference parts (the equivalent of Jigs and Fixtures) while checking how they align with other existing pieces and THEIR Templates which may also get reworked.

An interesting thing to observe is the relationship between the cowl fairing on the bottom of the fuselage and the line of the lower fuselage as it continues back to the rudder. On the real aircraft, the underside of fuselage at the cockpit is where the two wings are joined to be covered by a fairing. On my model, this line is just imaginary because there are no actual polygons under the fairing. The light blue reference part shows a fairly consistent line between the tail and the cowl and is used to confirm that the polygons forming the wings are aligned with the wing fillet polygons and their projected endpoints are in alignment at the fuselage centerline. The cowl fairing polygons must also meet along the projected line.

Next step is to rebuild the front half of the Warhawk....

- Ivan.

[Ivan]

The rework of my P-40E is finally nearing completion. It turned out to be MUCH more extensive than I had first expected.

As an example, the last thing I found which was only a couple days ago was that the maximum fuselage width was quite a bit off.
William Wylam's drawing lists it as 1' 9" (1.75 feet in AF99 Units) from the centerline.
I had already done a correction (to 1.66 feet) some time back because it simply didn't look right
When I reworked the radiator intake (Shark Mouth), the shapes still didn't look right.
I found that I had a pretty good technical drawing and re-scaled it down to 1 pixel = 0.01 foot.
The tech drawing showed a maximum width of 1.60 feet and an upper cowling that was also 1.60 feet above the propeller centerline.
This is very unlike the Spitfire or Mustang that do not have constant radii in their cowling.
A P-40N Erection & Maintenance manual lists the fuselage maximum width as 38.3 inches in a 3-View drawing and 38.32 inches in a dimensions table.
38.32 inches overal width works out to 1.5966667 feet from the centerline.

Seems like a pretty reliable number to me!

At this point, I have most of the polygons reworked. There are a couple wing polygons and the pilot and canopy that haven't been changed and that is about it! This turned out to be more work than building an entirely new design.

Next comes the texturing and animations and minor revisions to the AIR file.
The screenshot shows a rather disturbing state I saw earlier.

- Ivan.

[Ivan]

Latest changes were the following:
Added Gun Ports to the model. They were only a texture before. They should be stubs but are just black ports. The locations (offset from centerline) came from the P-40N E&M manual.

Modified DP file to match the new outline of the model. Relocated the weapons slightly to match the locations from E&M manual. Changed the bomb load from 1x500 lb to 3x500 lb. There are still a few more things to check here.

Modified the AIR file for new contact points for the longer landing gear struts. Moved the propeller location about 1 inch up and 1 inch forward to match the model which hopefully matches the tech drawings.

Next comes a majpr rework of the layout of textures and some edits to the textures themselves.

So far, I can say that with the same paint job and even knowing where to look, I don't see much detail difference other than the increased depth of the aft fuselage. The entire cowl is about 1 or 2 inches higher, but it isn't very obvious. The 1.5 inch narrower fuselage isn't very obvious either.

I have been changing the painting templates and from those, it becomes apparent that somewhere around 95% of the polygons were altered and for components of the aircraft, it is closer to about 98%.

- Ivan.

[Ivan]

After about three evenings of relocating textures and panel lines, here is what I have.
A wire frame comparision shows LOTS of changes, but a screenshot doesn't show up much difference at all.
I suppose the comparison is to that of an "Eyeball Scale" model versus a dimensionally correct scale model.

Still need to relocate some textures, but the basic shapes are done. The dimensions and layout are as accurate as I can make them with the information I have accumulated with the exception of the area just behind the radiator exhaust.

Besides the visuals, there is plenty more to do. I figure this beast deserves to have the WEP rating that I didn't know about when I first built it way back.

- Ivan.

[Ivan]

Hello All,

The rebuild is pretty much finished. I am not quite satisfied with the shape of the Radiator Exhaust, so that area will get rebuilt again. Besides that, there are a couple panel lines that need to get moved around a bit after the polygons under them got shifted.

In looking at the screenshots, I KNOW that just about everything on this aeroplane got moved around, but the general appearance does not appear to have changed much at all. The shape of the Radiator Intake took a few tries. I finally decided to open a Otaki (?) 1:48 P-40E model kit I had to see how the shapes looked in 3D. I believe I got the shape fairly close to the model. Hopefully it is close to the actual aircraft.

The only new obviously new thing is the textured Radiators.

- Ivan.

[smilo]

she's a real beauty.
nicely done.

at the risk of sounding like an obnoxious sob,
have you considered bringing the project full circle
and building the p-40 precursor, the p-36 hawk?

might be interesting.

[Ivan]

Hi Smilo,

Thanks for the suggestion.

Actually I have had a P-36 / Hawk 75 project going for a couple years now.

From my line of reasoning, after I had the first P-40E (the current "Warhawk" project), I thought there would not be too many changes to get to a P-40C.
It turned out to a LOT of changes to get to a P-40C "Hawk 81" project. (Fewer though than my current revisions to the Warhawk.)
From the Hawk 81, it should have been "easy" to get to a Hawk 75 since everyone KNOWS the P-40 was just a P-36 with a new engine. Turns out that there aren't that many shared pieces between the two. Although the general construction is the same, everything was moved around a bit to put the Allison inline in place. The prototype P-37 and P-40 might have been simple engine swaps, but production stuff was a lot dfferent.

The cockpit is located in a different place. The main gear fairings are different. The tail gear is also located differently.
Internally, even the fuel tanks are quite different. There may be more that I haven't seen yet.

I COULD re-engine a P-40C and get something looking a lot like a P-36, but dimensionally it would be quite wrong. I am also not sure the Paul Matt drawings I have are correct.

With the latest drawings on the P-40, I could probably get a bit further than I have before though. It at least gives a common reference point between the different airframes.

The idea of this "Thorough Rebuild" was to get to a good point for further P-40 releases though I will probably change direction again before that happens because I don't have a very long attention span.

- Ivan.

[Ivan]

Revised the Radiator Exhaust to look more like the real thing.

I also found a pretty serious bleed in the nose from an "improvement" I had made.
Turns out I usta be a bit smarter than I am now.
After removing the bleed, I'll need to adjust the textures on the parts that were reshaped.

The remaining screenshot shows the revised wingtip.

- Ivan.

[smilo]

'twas just a thought
inspired by an Aviation History article
about the USS Ranger based F4F Wildcats
taking on Vichy French H-75A Hawks
during Operation Torch in November 1942.

was almost considering setting up
invasion Task Force 54 off Morocco.

oh well...sorry to interrupt.
back to topic.

[Ivan]

Hi Smilo,

That discussion seemed very much ON topic to me. The Hawk 75 is a natural progression when working on the P-40. It seems less and less likely now that I will actually do a P-40Q. It just seems like way too much work and is a hard thing to comtemplate when I have spent the the last few weeks essentially building a new P-40E that looks almost exactly like the original one. I felt I needed to do that to own a really "Good" P-40 which I have always wanted.

If I am planning on building more P-40s I needed to have as good a starting point as I can create.

Another thing to consider is that just about all of this group of fighters has the same basic wings, stabilizers and fin though the pieces get moved around a bit. With that in mind, hopefully the next Curtiss fighter project will just be a matter of moving a few correctly dimensioned pieces around and connecting the dots.

Status update:
After the last post, I was thinking this aeroplane was ready for the SCASM treatment. I started the process and then decided to check on JUST ONE MORE THING....

As Background:
Although this P-40E has almost everything altered from the original to one extent or another, the build secquences and file naming are nearly all the same. The actual parts themselves sometimes are simply moved or hava vertex moved or have nothing of the original except for the purpose.

To cure bleeds, I often duplicate the same part in several assemblies. When the part is re-shaped, it sometimes doesn't fit in all of the original assemblies any more. Also, AF99 has a single directional display polygon called an "insignia". These work pretty well for addresing specific bleeds.
The problem is that if a part is reshaped, often the insignia parts display in the wrong direction. You don't even need to change the sequence of vertices. Now, you have a bleed from a direction that you were not checking to build the new part or the insignia part itself becomes a bleed because it is facing the wrong direction.

Glue (viewing planes) are also very often located in reference to existing parts. When those parts are re-shaped or moved, sometimes the glue part itself needs to be re-shaped.

Another issue is that all the rebuilding adds up to quite a few more polygons. At the moment, I am up from 1042 ro 1112. When the parts count gets higher, sometimes AF99 starts to behave badly.

....

[Ivan]

The first screenshot shows the main gear struts bleeding through the flaps. Note that the same thing is happening from the far side strut as well. A workable solution in the original model was to add flap parts to the landing gear but as insignia displaying up and aft. When the flaps were reshaped, the insignia flipped to facing forward and down which made them useless. When a couple extra parts were added in other areas and the insignia direction was flipped, the texturing here completely fell apart. I ended up removing the pieces because with the texturing incorrect, it was worse than the bleed it was trying to cover up.

The second screenshot shows a couple of the reasons for the extra parts count. The spinner on a P-40 doesn't really come to a sharp point. The end is spherical with a 1.5 inch radius. Adding one more section to the spinner structure added 12 polygons. Building the wing guns as parts rather than as texture added one more part for each gun and one for glue to attach each one to the wing.

The third screenshot shows a notch or cutout at the trailing edge of the flaps. The flap on each side is made up of 4 separate parts. To have a cutout like this on a textured piece generally requires at least 3 parts. The earlier Warhawk had the inboard edge of the cutout aligned with the join between wing and fillet.
The wing / fillet join needed to be moved slightly 0.15 foot inboard to cure another bleed and required that an additional part be added to the flap on each side along with the glue part to locate it.

I don't know if I found all the issues yet....
- Ivan.

[Ivan]

The front of the landing gear fairings got a bit of a rework to cure a small sparkly where the panels did not overlap.
I finished the SCASMing this morning and adjusted the collision bubble. I did some minor texture tweaks this afternoon also. It seems like even some of the references I am using do not agree with photographs. The photographs are guaranteed accurate, but don't show enough detail to get all the major panel lines.

Sometimes for animation tests, it helps to have a slow computer so that the transitions don't just flash by.

This afternoon, my 10 year old nephew took it for a fighter intercept mission. I believe he was chasing B-17s. The sim remains paused on one of the game machines in the living room.

- Ivan.

[Ivan]

The military rating for the V-1710-39 was 1150 HP at Sea Level with a Manifold Pressure of 45.5 inches Mercury.
In the last releases of this aeroplane, I had not included any War Emergency Power but since then, I have found a manual that does give a WEP rating. In addition, there is the document from Allison which permits up to 60 inches Mercury on the -39 engine.

The aircraft manual gives the WEP rating as 1470 HP at Sea Level with MP of 56 inches Mercury. In preparation for tweaking, I first added the WEP change to the AIR file and bumped the critical altitude (I don't this field does anything) down to 12,500 ft. Since it is pretty much impossible to actually test at Sea Level, I run at a minimum altitude of 500 ft for consistency. Generally this means that the engine power will be around 5 HP or so above the SL rating.
I was a bit surprised when the first test showed 1487 HP which is close enough for my purposes. All that remains is checking the power at each altitude and conducting a bunch of performance tests.

Sometimes we get lucky.
- Ivan.

[Ivan]

Although the latest version of the P-40E is more dimensionally correct, there was something about the look that was not as good as the original.
I believe that tonight I fixed one of the issues.

It isn't easy to see and depends a bit on the angle of the photograph, but there is a very slight rounding of the underside of the Radiator Fairing before forward of the cooling flaps. The open flaps often disguise this because with the flaps even slightly open, the underside looks quite flat.

Fixing this added another 4 Parts to the project
Unfortunately, the textures also needed a slight modification and the Animation needed to be redone.
The worst part is that this aeroplane needs another trip through the rather tedious SCASM process.

- Ivan.

[Ivan]

There was something about the shape of the Carb Scoop that bothered me.
I believe this version is a bit closer to the actual shape. It may not show it, but I spent a bit over two hours building and re building to see if I could get the shape the way I thought it should be.
I don't know how good of a match it is now, but it looks closer to me.

I was wondering why I was having such trouble staying on the runway at take-off.
After a few tries, it finally occurred to me that the issue was mostly my lack of understanding:
We all know that steerable tail wheels (which the P-40 has) do not lock in CFS.
As such, they are VERY sensitive at the start of the Take-Off run.
As soon as the Tail Wheel lifts, the torque swing must be counter-acted by the Rudder.
I was not catching the change quickly enough. When I did catch this, I found that very little Rudder input is required to hold the aeroplane straight while in reality, there should have been barely sufficient control.
Next task is to reduce the control effect at low airspeeds.
Elevator control seems too high as well.

- Ivan.

[aleatorylamp]

Hi Ivan,
It does look rounder!
Rounder is always nicer in AF99 if one has the parts to do it!
Cheers,
Aleatorylamp

[aleatorylamp]

Hi Ivan,
Your Warhawk not only looks really cool with interesting details, but also flies with lots of character - quite a challenge!
Nice work!
Cheers,
Aleatorylamp

[Ivan]

Thanks Aleatorylamp,

The Warhawk is one of my favourites. I am still not quite sure WHY it flies as well as it does, but it does fly as I intended.
The beast does have its peculiarities, so reading the Pilot's Manual (in this case, the ReadMe File and CheckList) is worthwhile.

The appearance isn't greatly different than the original from 2005, but this one has much more accurate dimensions.
Was it worthwhile to spend weeks to rebuild EVERYTHING? Maybe and maybe not, but I like this aeroplane so much I had to do it.

The latest Panel Line addition is a strange one and Smilo is the fellow to blame here!
He commented earlier than he liked "Plain Jane" P-40s without all the gaudy paint.
I didn't quite do that with my U.S. Army paint scheme, but I did think a bit about what would happen if one were to paint the Spinner the same colour as the Fuselage / Cowl. I had never done this but realised that there was no separation line between the Spinner and Cowl. Most P-40s probably left the factory painted that way.

Adding a line was easy, but I also tried a small (0.01 ft) gap which I did not include in the final model in this release because I am not sure I like it. The gap is probably smaller than the real one but is a bit distracting.

The screenshots show what I mean. Imagine if the Spinner and Cowl didn't have a line for separation.

- Ivan.

[aleatorylamp]

Hi Ivan,
About the spinner colour I just looked on the net and found spinners in red, yellow, beige, dark green, light green, brown, red and khakhi together... There were even a couple of colour shots with the plain factory colour that you mention, where the separating line is hardly noticeable at all. They actually all look good. Was the spinner colour then a matter of taste for each individual pilot? As they say in Spanish "for tastes, they made colours" - Para gustos, se hicieron colores!

The shark´s mouth seems to have been one of the most popular nose-arts for this plane - beat the enemy by scaring the **** out of them when they only see you coming! It was even on some sent to China. The tiger one was rather tame, I thought.

By the way, I am mystified as to how you avoided bleedthrough with the 3-pointed star-shaped division in the air intake? I am also mystified as to how you got the plane to fly so temperamentally in the .air file... I wonder if you could possibly indicate where in the .air file one can define the strength of the torque effect that pulls the aircraft to the left.
For example, would it be technically possible to eliminate it for the case of either concentric counter-rotating propellers or a tandem mounted push-pull setup?

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

There were so many different ways the Spinners were painted that if you think of a combination, it was probably done.
The only things I don't believe I have ever seen on a P-40 are Spiral designs and non symmetrical designs that would require an animated Spinner to display properly.
Colonel Robert Scott of the AVG was reported to have had his Spinner repainted between missions to give the Japanese the impression that they were being attacked by more aircraft than there really were.

Regarding the Tiger Shark mouth design, it started with RAF 112 Squadron in the African Campaign. It was covered in Life Magazine and the AVG apparently got the idea from those photographs. The AVG became famous. Fewer people have heard of 112 Squadron.
Some of the Shark mouth designs look "Fierce" as my son calls it. Some just look silly like a smiling drunk. My designs are not copied off of any particular aircraft. I just drew them to represent my impression of what one SHOULD look like.
The same applies to the Hawk 81 P-40 I released a while back.
A Frontal view of the Shark Mouth is particularly interesting to me because I have seen a photograph of a modern P-40 from that angle and my version looks VERY close in my opinion. To get that view right requires not just the paint to match but the nose contours have to be pretty close as well.

Regarding the Intake Dividers, I like the way they turned out. This version actually has textured Radiator faces unlike prior versions. The way this was done was VERY expensive from the AF99 resource standpoint.
IIRC, the Radiator Face, Intake Interior Walls, and the Dividers AND the roof of the Shark Mouth area are all in the Body, Main group with the display priorities set so that from Foreground to Background we have

Dividers
Roof
Interior Walls
Radiator Face

They are all Glued at the Radiator Face
The exterior is in both the Body, Main group AND in the Nose Group
If you try out the Aeroplane without texture files, it will become much more apparent what I actually did.

It is actually a touch more complicated, but the basic idea is that if you are behind the CoG, the display order of the interior parts doesn't matter because all will be hidden by the exterior of the cowl.
If you are ahead of the CoG, the interior parts are displayed in proper order and then covered by the duplicated exterior.

This is one of the goofy things about AF99 in that there is no way to specify something as ALWAYS in the background.
AF99 always expects a viewing plane spec to make the determination and will add one if there isn't one.

Regarding "Temperamental" flight characteristics, This beast is tuned to the best of my abilities to match pilots reports. It wasn't always the nicest handling aircraft especially with all the trim changes, but the combination wasn't bad. If you watch airshow displays, P-40 pilots fly a lot more maneuvers (especially vertical maneuvers) than a typical high speed pass that you see with other warbirds.
The very "Pointable" characteristic is just a side effect and I wish I knew how exactly to quantify and reproduce it. Strange thing is that my FW 190A also has this characteristic but even more so (as it should).

- Ivan.

[aleatorylamp]

Hi Ivan,
Very interesting, thanks, and psychologically effective, no doubt!
Thanks also for the description of your air intake construction.
I´ll investigate in the .air files and look for indications as regards the "Pointable" characteristic. I remember you once asked a rhetoric question on what to do with concentric counter-rotating props.
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

In one of your earlier replies you commented that rounder is better.... Usually it is, but some things are supposed to be angular instead of curved. I found a P-40 model for another simulator that had probably 10 times the polygons of mine but had enough general shape problems that I believe it is a much inferior model. The author should have looked at more photographs and done a bit more than just making a "Tube" and squishing it into a shape resembling parts of a P-40.

I think it is about time to take this P-40E out for some more test flying and experiments.

- Ivan.

[Ivan]

Hubbabubba made a very good suggestion a while back that the next P-40 perhaps should be a Merlin powered version.
Since I have what I believe to be a pretty well dimensioned P-40E, the next one might be a Short Tail Merlin P-40F.

The first step with any of these modifications is to do a little research to note what the changes might be.
The most obvious change is the removal of the Carb Scoop, but there are many more changes than that.

This again is where we run into the issue of contradictory data from different sources. If they contradict, which do you trust?

The P-40E that was just completed was built to an overall length of
31.73 Feet or 31 feet 8.75 inches. This does not agree with William Wylam's drawings, but was listed in a couple technical manuals and also in "America's Hundred Thousand" by Francis Dean.

The P-40F Pilots manual lists the
Early P-40F at 31 feet 7 23/32 inches
Late P-40F and all P-40L at 33 feet 3 23/32 inches.
The P-40F Service Manual lists the length of
Early P-40F at 31 feet 7 3/4 inches which is close enough to be considered identical.

So far so good. Multiple sources state that the Extension to the Tail was 20 inches and this is an exact match.

Now comes the fun part:
The P-40N Erection and Maintenance Manual states that the overall length of the P-40N was 33 feet 3.7 inches
Other Long Tail Allison P-40s are also listed as 33 feet 3 23/32 inches or 33 feet 4 inches.

The problem is this:
If the Tail Extension on a Merlin P-40 iw 20 inches, then does it make sense than the Tail Extensions on Allison P-40s is only 19 inches?

Or is the nose section on later P-40s shorter which is not supported by photographs. If anything, the later Allision P-40s had LONGER noses..... Now if the Nose is longer, something else must be shorter, but where?

Hmmm.... Makes you wonder.
- Ivan.

[Ivan]

.....And just when you thought it was safe, I just found that one of my reference drawings probably had a slight error.
The actual drawing wasn't bad. The annotation on it was incorrect.

The drawing listed the P-40E Thrust line to be 3.75 inches above the FRL
The newer drawing found in looking for data for the P-40F states that it should be 3.078 inch.
The really ironic thing is that this is pretty much the difference between the current model and the prior model so I am putting things back the way they were before.... Sheesh!

The change would not really be visible (about 0.06 foot difference) but I have to do it anyway for the P-40F.....
Corrections in the quest for perfection. It never ends....

- Ivan.

[aleatorylamp]

Hi Ivan,
Yes, it is annoying when one´s annotations on a blueprint have a glitch, but small ones often go unnoticed on the visual model.
What causes more of a problem though, and that´s when you have to "eyeball" it, is when factory blueprints are not available. I have often found the drawings and sketches available for any given model to have some differences, not only depending on the author if there are several sketches available, but differences with photos of the planes.
These differences, can mostly only be corrected by comparing the photos with screenshots of the model - if you get angles and distances right. I have sometimes had to correct rudder height, nose or chin curves, and even elevator widths and lengths this way. Of course by how far the result is accurate with reality is impossible to tell and it is only the general impression I can go by.
But I can understand your strive to get it perfect! I get similar sensations when I am building something!
The best of luck!
Cheers,
Aleatorylamp

[Ivan]

In looking over the Drawings and the mismatch, what I see now is that the actual change to make a correction to the Thrust Line from 3.75 inch above the FRL to 3.078 inch above the FRL is actually only 0.04 feet.
It is a little less because of the rounding errors necessary to represent items listed in Thousandths of an Inch to the AF99 resolution which is only 0.01 Foot or 0.12 Inch.

The next step is to actually make the correction and fix everything else this will break.
It doesn't look like much of a change in the screenshot, does it?
I am almost tempted not to do it except my eyeball has been telling me since I built this version that the nose was a touch too high.

The quest for "Perfect" dimensions never ends!
- Ivan.

[aleatorylamp]

Hi Ivan,
Usually the pixels on the drawings that I have to work on for old models are thicker than the differences in your blueprint! Quite honestly, if my humble opinion serves, such small differences for me would qualify as negligible, and I really woudn´t worry.
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I know the feeling of working with very imprecise drawings.
That is how my first models started and even more recently, some of the models were created from much less than perfect drawings.
The issue here is that I KNOW the correct dimension here and this discrepancy is the largest one that I know about thus far.
The Carb Scoop that I most recently worked on was a result of this. I could not get the shape right with trying to keep a smooth curve and keeping within the dimensions and now I know WHY I had that issue.

Not knowing is a good excuse, but here I DO know. It also appears that ALL of the P-40s had the same Thrust Line so correcting it once here corrects it for all the descendants as well. It may take a while to get there though....

- Ivan.

[Ivan]

This screenshot shows a slightly revised Template for the new Parts locations and moving some of the actual pieces of the aeroplane.
Shifting the Thrust Line down 0.05 feet appears to be the best solution.

There are four basic areas to address:
1. The Carburetor Scoop (Probably the best reason to shift so many Parts)
2. The Contour Line of the entire Fuselage back past the Cockpit to ensure there are no strange bends
3. The actual Cowl Panels.
4. The Radiator Intake and pieces on the lower side of the Cowl.

This looks quite tedious, but hopefully this will not take too long.

- Ivan.

[aleatorylamp]

Hi Ivan,
An aircraft with such an appealing design as this one is definitely worth the effort to get as exact as possible if within the capability of the modeller and the limits of his patience!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I don't really know if it is worthwhile, but it is what I am doing. I need a break from the Gauge Project because I am pretty much stuck. I have changed the code to what I understand it needs to be and yet I am not getting the results I want. I will continue at some point, but several days of zero results tells me I should change subjects.

Here is a comparison of the revised nose with a set of factory drawings.
The match isn't too bad at this point but there are a couple changes that are pretty obvious.

1. The Cowling Flaps are way too short in my model
2. The contour of the Carb Scoop is quite a bit off. Mine has too much of an arch.
The opening on mine agrees better with photographs than the factory drawing does though.
3. The Front of the Radiator needs to be significantly deeper.
4. The Rear of the Radiator has a gradual sweep upward that my model does not.

There are many more small mismatches, but the major components line up pretty well with the rest of the drawing.
A very interesting issue here is that my model lines up much better with these drawings han they do with photographs of actual aeroplanes! It also looks much better in the simulator than here in these screenshots.

- Ivan.

[aleatorylamp]

Hello Ivan,

There is something that I have recently been asking myself when it comes to factory drawings and actual photos of planes: To what extent could changes be introduced into a given production batch, differing from the factory drawings of the initial design? These changes would perhaps only have drawings, if any, reflected on supplementary subsections to the main ones.

With the different photos available of any given model I sometimes have the uncanny sensation that I am being tricked by optical illusions, ...or are the small differences from one unit to another in effect real?

Moreover, to what degree would a factory engineer be capable of simply adjusting certain panels on a specific unit, to fit over some alternative part being fitted that was different just because of a logistics problem, especially in the wartime production rhythm?

So then, what are we doing as virtual modellers? Producing models as per factory specification drawings, or producing the planes that actually flew? ... or are we just splitting hairs?

I would muse that it is something in-between: We can apply our own "magic", to use your expression, so that suddenly, Presto!: Our models fit both concepts!

Cheers,
Aleatorylamp

[Ivan]

My goal as usual is to produce "My Own Impression" of the aeroplane in question.
When possible, use all resources available but NOTHING is infallible other than a photograph but those are subject to a lot of factors and to interpretation.

My latest issue is that I am hitting a place where the drawing and a couple specified dimensions do not match. Which should I believe? I am also getting small inconsistencies depending on where I get the wire frame image from. The one from DPED and the one from AF99 seem to differ slightly in proportions.

Again, it will be a best judgment thing. Flight models have always been a best judgment thing for me.

- van.

[aleatorylamp]

Hi Ivan,
I´ve just checked the difference you mentioned in the Dped and AF99 blueprints, and I was quite shocked when I saw the magnitude of this difference!
Just to show, I made a comparative joint screenshot, and compared it to Paul Matt´s drawings. It appears that the AF99 blueprint is quite a bit too long, and that the Dped one matches the drawings. I hate to think about what connotations this could have in all these years...
Good luck!
Aleatorylamp

[aleatorylamp]

Hi Ivan,
I just thought I´d investigate the Aircraft Animator blueprint too, and it turns out that dimensions coincide 100% with Dped blueprints and Paul Matt´s drawings in the case of the AT-9.
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

So you also see the differences between AF99 and DPED....
....and you can confirm that AA agrees with DPED.

Now the next trick is to figure out which is the most correct and if the difference is constant or distorted.
I have a couple ideas as to how to do that, but until then, the Warhawk is on hold because I suspect I may be making unnecessary corrections.

- IIvan.

[aleatorylamp]

Hi Ivan,
I remember that the reason I´d almost given up on the AT-9 before resuming construction was that suddenly the height started to go off somehow. Now I realize that it was when I was adjusting the AF99 wireframe to side-view photo. As the wireframe was too long, the adjustment reduced the height - it was driving me crazy.
My first impression is that both the Dped and the AA wireframes are trustworthy, but I´ll have to make some more exact measurements.
I´ll keep you posted!
Cheers,
Aleatorylamp

[Ivan]

Hello All....

Here is a little comparison between Wire Frame Models in
Aircraft Factory 99
Aircraft Animator
and
DPED.

The model here is very simple. I just took one of the Workshop Projects I had and added a 12-sided Circle imported Part.
A screenshot of the saved Assembly in AF99 was then taken.
After producing the project, I then took a screenshot from AA and from DPED.
The results were interesting....

DPED
Height = 127 to 651 = 524 Pixels
Width = 250 to 774 = 524 Pixels

AA
Height = 165 to 574 = 409 Pixels
Width = 389 to 798 = 409 Pixels

So far, so good.....

AF99
Height = 111 to 695 = 584 Pixels
Width = 205 to 819 = 614 Pixels

Hey! The numbers don't match!!!
So the stretching is obviously not imagined.
There actually is just over a 5% difference.

Next step is to figure out if this can be fixed.

- Ivan.

[Ivan]

So, now that we know which screenshot NOT to use, how does the Warhawk compare to the drawings?

The attached screenshot shows an overlay.
I believe it is pretty close but there are still a couple issues as noted by the arrows.
The worst section is on the Radiator scoop as expected.
The Carburetor scoop needs its contours adjusted a bit.
The Windscreen should also be moved back slightly. I believe the difference is under one inch.

- Ivan.

[aleatorylamp]

Hi Ivan,

It is interesting that the AF99 wireframe distortion now has been nailed down to a definite dimension in pixels!!

At least using DPed or AA´s wireframes allows reliable, undistorted shapes, and is a relief for trustworthy adjustments after comparisons to drawings or convenient photos. With the latter, of course, there is also the added factor of distortion which you have mentioned too, due to excessive camera proximity, and the best photos I suppose would be those taken with tele-objective from a certain distance.

I certainly miss some kind of intelligent image recognition program for airplanes, similar to those available for face-recognition in virtual photo albums, which would allow a rotation to create a 3-view set in the X, Y, Z axes! ...Wishfull thinking.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello All, Hello Ivan,

Just to check on AF99´s top and front view wireframes as well:
Comparing these to the Dped and AA ones, and it turns out that both of these are also too low in proportion.
The top view shows a shorter wingspan and the front view, a lower height.

Cheers,
Aleatorylamp

[Ivan]

Sometimes the degree of precision in the drawing is not matched by the degree of accuracy in the wire frame that one can get from DPED or Aircraft Animator or even Aircraft Factory 99.

Over the last few days, I tried to check the wire frame screenshots against the tech drawing.
The results were a bit less consistent than I would have wanted.

The large errors that are over about 0.07 foot are noticeable but anything less is a rather random thing as far as screenshots are concerned.
With one screenshot, I was able to get very good alignment but with offsets that were a bit different than I had calculated.
One the next screenshot, I was able to get some pretty good matches with the original alignment.
The lines themselves are around 0.05 feet wide which isn't very very bad considering that the scale means the lines are only 5 pixels wide.

I also found areas that could use a slight curve but I can't put them in because I don't have vertices there.
So.....

I just found with the latest screenshot that my model's Center of Gravity is
2.35 feet behind the Firewall (as before)
and
0.55 feet below the Fuselage Reference Line.....

- Ivan.

[Ivan]

Hello All,

After a couple hours yesterday to make sure my template drawings match up with the tech drawing, I decided to start hammering on the virtual metal....

The Canopy Frame and Glass took an hour last night and a couple hours this morning.
I believe it looks fairly reasonable and I even improved the shape a touch.

Now here is the nasty part:
Way back when I designed this aeroplane, I tried to line up as many things as was reasonable to do so.
The front of the Canopy lines up with a major partition line in the Fuselage AND THE major reference line in the Wings.
Moving the Canopy front edge from 1.21 Feet to 1.11 Feet ahead of the CoG affects how the Fuselage would line up with the Wings.
Although the reference line on the Wings doesn't need to line up wit the reference line on the Fuselage, it is / WAS nice to know that I took the care to arrange things this way when first laying out the project. Pity the dimensions were not quite right.

At this point, with a mismatch of the Wing reference and Fuselage reference, the difference needs to be made up via adjustments to the Wing Fillet.

Note that in these screenshots, the lower edge of the Windscreen has been moved back 0.10 feet and the upper edge has been moved back around 0.18 feet.

The other screenshot is a reference part I found that shows the degree of change of the Aft Fuselage between the original Wylam drawing model and the current model. Looks similar from a distance but obviously the shape is quite different.

- Ivan.

[Ivan]

Most of the changes to the AF99 model are now done.
The cropped screenshot shows that the alignment is pretty close.

There still needs to be a minor shape adjustment on the Carb Scoop.

After that, the texture files need adjusted to fit all the changes to the model underneath.
The biggest issue will be the Radiator Intake which has a lot of textured pieces within.

THEN comes the fun part with SCASMing.
Note that I will need a new Canopy Interior because the pieces below the texture have changed shape.
Most of the Canopy Frame interior is adjusted to be narrower, so this will need to be done again.
There are also a few animation changes from the version that Aircraft Animator generates.

- Ivan.

[Ivan]

This is the correct screenshot. The differences are on the bottom of the Radiator Intake.

Note that the vertical mismatch of the Cowl is due to the incorrect offset of the Thrust Line in the tech drawing which I assembled using the notes on the drawing itself.
This drawing listed 3.75 inch from FRL.
The factory drawing lists 3.078 inch....
....which is what started off this latest rebuild cycle.

- Ivan.

[Ivan]

Luckily none of the textures required any significant remapping.
Some of them needed a bit of re-drawing though, so one more step is finished.... Maybe.

There was also a minor adjustment in assembly sequence and adjustment of Glue to reduce a bleed.
It was only reduced, not cured.

Next is another dimensions check. I found something a bi strange on the lower part of the Cowl.
Hopefully I won't find anything significantly wrong.

Still playing....
- Ivan.

[Ivan]

The lower part of the Cowl was re shaped to make the sides more parallel at the opening.
One very interesting thing was that I first tried to draw some of the contour lines for the Cowl and could not get them the way I wanted.

I then decided to try copying the contour of the lower edge of the Cowl / Radiator Housing and by rotating it 30 degrees, I came up with a reasonably pleasing line that was shaped pretty close to the way I wanted.

There was a moment of panic when rebuilding when the resulting model showed a coloured stripe extending off to the horizon.
This was strange because I was only using 1127 Parts of 1200 allowed. Usually this is enough margin to avoid AF99 failures.
My development machine crashed shortly after and strangely enough, after a reboot, the subsequent builds all were clean.

Here is the current status. I still see a minor shape problem at the lower rear of the Cowl by the Radiator Flaps.

- Ivan.

[aleatorylamp]

Hi Ivan,
Interesting to follow!
Glad the improvement is turning out the way you want!

I had recently found a much clearer, larger and more detailed 3-view drawing for the P-3 Orion that I thought looked wonderful, and promptly widened the fuselage width by about 1.5 ft accordingly, but alas!, the result was disgusting because the plane got all fat and ugly!!

So I put it all back to what it was, which was not hard to do as the fuselage was all structures.
This just shows how difficult it can get as regards reliability of some expectedly reputed sources.

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

The obvious question is: How reliable were the drawings you found? If the dimensions are correct, perhaps the aeroplane really is not as nice and sleek as you might want to build. If so, then you have the choice of building it accurately or to appear the way you want.
I say use the correct dimensions and the shapes should fall into place. If they do not, then your shapes need to be reworked until they DO fall into place.

I ran into a similar problem with the drawings by William Wylam which is what started this thread a while back. The dimensions were all labeled out and were "derived from Curtiss factory drawings", but the shapes in the drawings did not match the numbers sometimes. Also, I found out later that a rather large portion of the labeled dimensions were simply wrong.

Correct dimensions and shapes is what started the last couple rebuild cycles for the Warhawk.... Which incidentally are not done yet.

- Ivan.

[Ivan]

Reworking the lower rear of the Cowl was not terribly painful, but it involved changing a LOT of pieces.

After making changes, I found a bleed with the Carburetor Scoop........
THAT required some Glue Part changes and upon closer examination, I found another bleed which required more changes.
A few hours later, I finally arrived at a shape I was satisfied with... and then noticed another mismatch of vertices.
I had missed a couple Parts that connected with those I had changed.

The untextured model is what I often use to check on bleeds. A simple dark colour overall paint scheme can hide a great number of sins.

The other screenshots show some of the changes. If you know where to look, there ARE differences though some are not so obvious.

Time to flip it around in the simulator to make sure there are not bleeds or shape issues I do not yet know about.

- Ivan.

[aleatorylamp]

Hi Ivan,
Given dimensions are usually no more than wingspan, overall length and height.
Fuselage width is not really mentioned very often, unless the info is on a publicity pamphlet for a passenger plane. I´ll have to do some serious photo-studying, because on some drawings, the Orion looks fat, but not on the photos.
Anyway, slowly we are progressing.
Cheers,
Aleatorylamp

[Ivan]

After adjusting the front of the Canopy / Canopy Frame backwards by around 0.10 foot, the Internal Canopy Frame would need to be changed also.
The problem is that I could not find it....
I know I had called it "IFrame-Something" but could not find any of the related files.

As I commented earlier on Post #18
http://www.sim-outhouse.com/sohforums/showthread.php?80890-Warhawk
Most of the pieces of the Internal Canopy Frame were narrowed a bit and I did not want to have to make the same edits since the majority of the Parts had not changed.
After a while, I found it (In the directory for the P-40K Project) and was able to do the edits pretty quickly.

Most of the SCASMing was done last night and I believe all that is left is to reset the Collision Bubble and change the Animations a bit.

- Ivan.

[aleatorylamp]

Hi Ivan,
Interesting! - I´m looking forward to being able to see your resulting new model!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I was debating whether or not to release a new copy of the P-40E. The differences are not even visible to ME and I know where I made the changes. The differences are so little that I don't think even the Flight Model has to change.

Other than the model, nothing else is different yet.

I needed this model as accurate as possible mainly to serve as a starting point for other versions.

- Ivan.

[aleatorylamp]

Hi Ivan,
Not to worry, then we´ll preferably wait for a new offspring derived from this modification!
Cheers,
Aleatoryamp

[Ivan]

Only a couple days after I thought the P-40E Warhawk was done, it is heading back into the Workshop again.

In looking at reference drawings for a P-40F, I found that my interpretation of Drawings / Photographs for the E model was not correct.
I noted earlier that the Carb Scoop was bothersome because the shape which was done from Photographs a while back did not line up well with the Factory Drawings. Most notable was that the Scoop extended much further forward on the actual aeroplanes than it did in the drawings.

Now I know why: Apparently the longer Scoop was a characteristic of the later P-40M/N. There is also more of an arch on the later aircraft.
The P-40E/K had a Scoop Inlet that nearly lined up with the Radiator Scoop and also had less of an arch.
This explains why I kept seeing something different every time I looked.
The most clear and largest resolution photographs are of modern aircraft and I suspect that the pieces are interchangeable between the E and the M/N models. Perhaps some of the modern P-40Es are wearing later pieces.

So.... Photographic evidence is great but knowing what is original is important and in this case I clearly did not know.

- Ivan.

[aleatorylamp]

Hello Ivan,
Philosophically speaking, if the real aircraft of the different editions that you mention could wear either type of pieces, you´d be correct both times!
One thing would be a pristine model just run out of the factory, and another, a unit that has already had quite a few flying and combat hours.
It just occurred to me, now that you´ve discovered what´s going on: If you were to depict a certain unit with a certain registration number and a certain type of scoop seen on a photo, it could be an interesting detail to be able to mention something to that effect in the readme!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

My preference is to build them as they were when they made their reputations.
They should be as close to fresh from the factory as possible.

I don't really care to represent aircraft that are full of replacement parts, worn or damaged.
I figure the Virtual Pilots deserve aeroplanes in the best condition consistent with the time period.
I know there are plenty of P-40E that served until they were war weary or have even lasted to modern times, but I am not interested in depicting those.

What sense does it make to build a P-40E with Pieces from late wartime P-40Ns? By that time they would most likely serving as Trainers instead of Fighters. The ones then in combat would be P-40Ns. To use the mixed parts P-40E earlier in the was would be an anachronism and I do not like those. To create those accidentally is an indication of poor research.

I will correct the P-40E eventually. It is a simple fix but the re-SCASM may take a while.
I have a new set of reference drawings to work on first.

- Ivan.

[aleatorylamp]

Hello Ivan,
I see your point. It could be seen as an excuse for skiving and not working the correct part into position. Pacience then, to put it right!
I´m trying not to bend the parts too much to force them into position on the Orion. I have all the Fuselage Station points lined up correctly now, all nicely measured out from the nose, but some of the Waterline ones are giving me a hard time now. Pacience here too!
Cheers,
Aleatorylamp

[Ivan]

In doing a lot more poking around, I am finding that there were at least TWO different length Carb Scoops on the wartime P-40E on the assumption that the photograph captions are reliable. Often they are not.

The very short Scoop appears to have been standard on the early aircraft. There are even a couple surviving P-40Es with that scoop today.
This scoop can be recognized by the large gap between the Spinner and the opening of the scoop. It appears to be nearly inline with the Radiator Opening. (It is actually slightly ahead.) It appears to be slightly under 6 inches from the Spinner line.

Next there was the long Scoop which with an opening about 1-3 inches behind the Spinner line. This can be recognized in photographs as being distinctly ahead of the Radiator Opening. I have found a few war time photographs of Short Tail P-40s (captioned as P-40E) with this scoop. One photograph shows several in a flight with the same scoop so it is unlikely to have been retro fitted.
The USAF Museum's P-40E has this scoop and I would imagine that they have the resources to put it the way it should be.
The Smithsonian's P-40E (Lope's Hope) also has this length Scoop and again, I expect they would have the resources to make it the way it should be even if they needed to fabricate pieces

There may be variations on the longer Scoop. Some look like they extend all the way to the Spinner while others have a noticeable gap there. There really should not be a gap between the Spinner and Cowl because on the real aircraft, there was actually a bevel in the Cowl and a slight overlap but it is not easy to be subtle with AF99.

So.... It appears that the current Carb Scoop on my P-40E isn't necessarily incorrect for a War Time P-40E.
This is not to say there are not other errors because I know there are at least a couple which I have chosen not to fix because of resource limitations in AF99.

I wonder if any of my other projects would hold up at this level of examination.

Here is a little comparison between the way it is today and the outline of the way it was a couple years ago.
Although overall dimensions are the same, many things are obviously shifted.

- Ivan.

[Ivan]

Now that I have a pretty reasonable P-40E as a starting point, the Conversion / Duplication Process for the Merlin powered P-40F begins.
This model will be a bit more difficult because the scans of the Factory Drawings for the F-model Cowl section is much worse quality and appears to have some distortions.

There are also some disagreements in dimensions between the various models:
The P-40E as modeled is 31 feet 8.75 inch or 31.73 feet in AF99 units.

The length varies a bit depending on the source. The most plausible dimensions are 31 feet 8 inch to 31 feet 9 inch with 31 feet 8.75 inch being the most likely value in my opinion.

The length of the P-40F also has a similar variation ranging from 31 feet 7 9/16 inch to 31 feet 7.75 inch depending on the aircraft manual. The variation is actually much higher than this from sources other than the manuals.

The Datum Point as stated earlier is at Station 1 (The Firewall) longitudinally and at the Fuselage Reference Line vertically.
The Forward End of the Cowl is 87.0 inches ahead of the Datum for most Hawk 87 models.
For the Hawk 87D (Merlin Powered) P-40F / P-40L, the End of the Cowl is only 85.75 inches ahead of the Datum.

The Merlin was a heavier engine than the Allison and I believe the difference in engine location was to maintain a consistent CoG without having to add ballast.

Another feature worthy of note is that the forward edge of the Cowl had a slight bevel and the Spinner actually overlapped the Cowl slightly. The visible gap that is in my model is really just a line on the real aeroplane.

When I scaled the Factory Drawing of the F-model Cowl to match the 85.75 inch (7.1458 or 7.15 feet) dimension, I found that the top of the Cowl did not quite match the other drawings and the length of the Spinner was about 1/2 inch too short as compared to the E-model Spinner.

Now comes the fun part of measuring offsets for the new 3D model.
(The CoG of the model remains at 2.35 feet Aft and 0.55 feet Below the Aircraft Datum Point.)

- Ivan.

[aleatorylamp]

Hi Ivan,
Sounds great, and I´m glad you sorted that out. It´s amazing how many details one can unearth during an in-depth investigation. It makes modelling all the more interesting!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I don't know that I really have sorted anything out yet.
I suspect the mismatches will become more obvious as I build further
The length discrepancy is between 1/16 inch and 1/2 inch depending on the sources.
Unfortunately I don't happen to have a P-40F that I can go measure.
I also would not have a method of measuring such a large object so precisely anyway.

- Ivan.

[Ivan]

The most obvious difference between the P-40E and P-40F is the lack of a Carburetor Scoop on the F model.
The Allison used a down-draft Carburetor which is why the airflow had to come from the top.
The Merlin on the other hand used an up-draft Carburetor which is why its airflow came from the bottom.

The first and most obvious step was to remove the Carburetor Scoop.
This served two purposes.
The primary purpose was to get some instant gratification and see something closer to the final version.
The secondary and more important purpose was to free up two Components and about 50 Parts to use in new construction.
It is pretty obvious already that the Merlin Warhawk will be less complicated and probably also less resource intensive.

Note that there is a dark spot on the upper rear of the Cowl. This was there to provide a shading difference between the Cowl and Carburetor Scoop on the earlier aeroplane.
It is easily removed.
There are certain to be other less simple texturing differences.

The second step which I only partially completed last night was to move the Nose Pieces 0.10 feet Aft.
In reality, the difference should be 1.25 inch which is really 0.104-something feet so the Cowl Pieces were only moved 1.200 inches Aft. The Propeller, Spinner and associated Glue Parts also need to be moved.
This granularity in AF99 dimensions also serves to hide the 1/16 inch discrepancy I was unable to resolve.

Here are a couple screenshots of the current status. The Spinner to Cowl Gap is 1.32 inches here. I plan to leave it at 0.12 inch when completed.

- Ivan.

[Ivan]

Here are a few screenshots from last night.
The Radiator Housing area of the Merlin Warhawk are very different.
The Radiator Inlet is much narrower and also much deeper.
The entire Radiator Housing is also much shorter

The division line between the "Forward Fuselage" and "Cowl" sections is right at the Radiator Exhaust and that will need to be moved forward.
The Warhawk lost two Components for the Carburetor Scoop, but will likely use them up with the new Cowl Fairing on the underside of the Fuselage.

The Steps for the entire Conversion were the following:
1. Remove the Carburetor Scoop and adjust panels to close the upper Cowl area. - Completed
2. Move the Spinner / Propeller / Cowl pieces to shorten by 1.25 inches. - Completed
3. Re Shape the Cowl / Radiator Housing - Working
4. Add a Bulkhead at +4.35 feet to be the new dividing line - Working
5. Replace Cowl Interior pieces - Waiting
6. Redesign the Radiator Exhaust - Waiting
7. Modify Textures to fit new pieces - Exact Tasks Unknown so far

- Ivan.

[Ivan]

The Steps for the entire Conversion were the following:
1. Remove the Carburetor Scoop and adjust panels to close the upper Cowl area. - Completed
2. Move the Spinner / Propeller / Cowl pieces to shorten by 1.25 inches. - Completed
3. Re Shape the Cowl / Radiator Housing - Completed
4. Add a Bulkhead at +4.35 feet to be the new dividing line - Completed
5. Replace Cowl Interior pieces - Working
6. Redesign the Radiator Exhaust - Working
7. Modify Textures to fit new pieces - Exact Tasks Unknown but looks worse than I thought it would.

My first try at a Carburetor Intake Duct wasn't too bad as a structure but I found that there is actually a slight tilt to the opening which means it cannot match up very well with a Structure.
Another issue is that the Carb Ducting is not the same height from front to rear and this really causes a shape problem when represented by a Structure.

The Radiator Exhaust area required a LOT of reworking on the Lower Fuselage / Cowl Fairing area.
This has been the most difficult part thus far, but it was finished a couple nights ago.
Note that the Cowl / Radiator Housing is MUCH shorter. The area formerly occupied by Cowl Flaps has been almost entirely removed and the Cowl Flaps will be moved forward.
The Cowl looks a bit strange at the moment because very few of the Textured Panel Lines actually match up to reality.
In fact the Texture needs to be shifted up a bit because it extends all the way to edge of the file.
(I like to have a 1 Pixel border around all the Textures.)
Luckily there is no longer a Carb Scoop over the Cowl, so there is room to shift things a bit upward.

This shifting of Textures brings up a problem which I didn't know enough to address very early on.
The entire Fuselage is textured to a scale of 256 Pixels == 11.6 feet.
Although I can shift from 1 to 12 pixels, there is no amount I can shift the texture that does not cause a different mapping onto the pieces of the aeroplane.

- Ivan.

[aleatorylamp]

Hello Ivan,

Very interesting, the description of what you are doing. I´m taking a few notes for myself along the way.

Modifications always catch me out. Initially one doesn´t expect complications: "Oh, nothing! - piece of cake!", It NEVER is! Modifications invariably branch out, affecting a cascade of other parts, and it ALWAYS gets far more complicated.

Now that I´ve got everything lined up on the Orion, the only ("only" - good grief!) job left is a thicker wing. BUT, now the three wing sections won´t fit the engine-nacelle structures so well. The nacelle walls now sometimes take display priority over the upper and lower wing surfaces. If I can´t get that out with some decent glue, I´ll have to try out radically different strategies. It´s always back to square one, isn´t it?, but one gets there eventually.

It´s also interesting how textures affect surfaces. They can either enhance a bulge, or create a physically inexistent one, or completely disguise one! Truly amazing.

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Actually this Merlin modification is much less complicated and labour intensive than the last two major rebuilds:
(The Wylam Drawings to Current Drawings and Thrust Line from 3.75 inch to 3.078 inch.)

I actually haven't documented as many of the changes here as I have done in the past. I don't think there is actually much of an audience. Notice how far apart the posts are spaced? Sometimes there really isn't anything going on and sometimes there is a lot.

Regarding Orion, I would have taken a different approach to the aeroplane.
I still think the best (or least painful) approach would have been to build each engine as two Components and the Wing as a single Component.

You might have noticed that I don't tend to take up other designs and modify them.
I believe the payoff is much less and the frustration level is probably about equal to that of a new design.
The end result is also my aeroplane rather than someone else's.
I have a pretty predictable system to naming and it helps me find things faster on my own projects.

- Ivan.

[Ivan]

These two screenshots show what I call the Intake Fairing added to the underside of the Fuselage.
I WOULD have taken another screenshot from further aft, but my computer locked up and I didn't care to wait for it to reboot and go through the File System Checks.

- Ivan.

[Ivan]

After an hour or so of editing, I saw this result right after I textured the Intake Fairing.
I suspected the issue was not an AF99 error and I had also been experiencing some strange issues, so I rebooted the computer.
These issues went away with the next build.

The computer is definitely misbehaving a bit.
- Ivan.

[aleatorylamp]

Hi Ivan,

Thanks for the suggestion on the Orion Wing issue. I´ll address that further on the other thread.

As regards texture issures, missing bulkheads, or sometimes missing insignia intakes, when CFS1 starts up and loads a plane initially, I find it often gets fixed by simply re-loading the plane, and won´t go away by re-starting the computer, but perhaps it´s not the same bug that you are experiencing.

Talking about bugs: A few months back my AF99 started giving an error message every time I compile a plane, saying that the model is currently loaded into the simulator - and CFS1 isn´t even running! So I just ignore it, re-click the compiling button, and it proceeds correctly!

Yes, I suppose the audience for FS98 and CFS1 is rather limited nowadays, and any new people go directly for the new flight simulators and aeroplane building programmes, but I just can´t get myself to like Gmax or Fsds - although I have tried several times each. If CFS2/3, FS2004 and FSX at least had kept up the backwards-compatibility with the old style Autocad files of AF99, it may have been a different matter. Apparently it would not have hampered anything, and the incompatibility was totally intentional after FS2002. If FS2002 could handle both new and old model files, why not the subsequent ones? Too bad...

Cheers,
Aleatorylamp

[Ivan]

....And just when you thought it was safe....

From the first drawing of the entire Cowl, the length from the Datum to the forward end of the Cowl appeared to be 85.75 inch.

In looking over some of the other drawings, it appears that my interpretation of the earlier drawing was incorrect.
The number really should be 86.75 inch as can be seen in the detail on the lower Cowl drawing.

It appears that a few pieces will get shifted around a bit yet again.
Luckily there appears to be no significant difference with either the Cowl Opening or line of the Upper Cowl.
Time for another rework....

- Ivan.

[Ivan]

In re-shaping the nose of the Merlin Warhawk, I reached the point where the 3D Model extended past the edge of the texture file.
That meant that the mapping of the texture file would have to be changed.

The Warhawk uses a scale of 11.60 feet per 256 Pixels.
The mapping of the texture was right up to the edge of the file.
It needed to be moved at least 2-3 pixels to leave a slight margin to the edge.
There was enough room to move it up to 13 Pixels before the opposite edge was hit.

I wanted the alignment of the panel lines to be EXACTLY the same between the Merlin and the Allison versions.
The problem is that with a scale of 11.60 feet per Pixel, there is no shift between 2 and 13 Pixels that would produce the same alignment.
The end result is that it is not quite an exact match but fairly close.

As can be seen from the screenshots, some parts of the Cowl still need to be adjusted and obviously the Carburetor Inlet still needs a texture. The texture for the Cowl Flaps at the bottom is not ideal, but is probably as good as it will get at this scale of texturing.

At this point, the panel lines are a pretty fair match to my references for a P-40F.

The folks in the paint shop chose a very light coloured primer to make the panel lines more distinct at this stage.

- Ivan.

[Ivan]

A few things were moved around last night and the holes in the Cowl got fixed.
The Carburetor Opening appears to have a Choke or diverter of some kind that tends to be closed for Take-Off or Landing but appears to normally be open in flight.

Plenty more to do before it is finished.

- Ivan.

[aleatorylamp]

Looks very intriguing...
I was already wondering what it was. It´s a cool detail on the model.
What I like about it is how it fits behind the cowl walls without bleedthroughs. You´d already explained how that was done with the "Y" separators in the cowl on the other model.
Cheers,
Aleatorylamp

[Ivan]

Here is the latest on the Merlin Warhawk from a couple days ago:

The Radiator Exhaust area took a few tries but is finally shaped about the way I wanted.
It isn't completely faithful to the original because of AF99 resource and assembly limitations.
To look correct, the textures need a lot of adjustments.
Although the general appearance looks not very different from the Allison birds, there actually have been a lot of pieces reshaped here.

Along the way, I was looking over the rest of the changes and noticed..... A BLEED!!!!
Hopefully this will not be difficult to eliminate and also will not burn up many more Parts.
I suspect it is a consequence of my shifting of various pieces back and forth and forgetting to shift the Glue Parts at the same time.

We shall see.

- Ivan.

[aleatorylamp]

A little bleed is like a fly you try to swat,
but just manages to get away, aided by
the air pressure from the fly swatter...

Cheers,
Aleatoryplamp

[Ivan]

This Bleed is actually not hard to fix and I already know where it came from.
It will just cost about 10-12 more Parts to the model.

The original P-40E was designed with its Frames located where major contour changes occurred on the Fuselage.
This can be seen in the first screenshot.
Note that the second Frame from the Spinner coincides with the Radiator Opening.
This was chosen so that it would work as a Glue position to separate pieces behind from pieces in front.

With the modifications from the original design (Wylam Drawings) to the better Fuselage Station diagram the Radiator Opening was moved Forward a little bit. The Intake Walls were also moved forward at the same time of course.
I chose not to move the Frame location forward on the upper Cowl area because I did not want to rebuild the Cowl.
I did not see any bleeds resulting from that change...... But there WERE some.
They just were not as visible because the move of the Radiator Opening was very slight and the angle for the bleed was very small.

The Merlin P-40 required an additional forward move of the Radiator Opening and with this move, the angle became greater, thus I was able to see it better with this version of the model.

The two additional screenshots show the views from ahead and behind the CoG plane.
The fix is actually fairly easy.
The first row of Cowl Parts just needs to be added to the main Cowl (Dark Olive) which will cost between 10 and 12 more Parts depending on how I choose to do it.

I should probably go back and edit the P-40E for the same change.

- Ivan.

[Ivan]

The small Cowl bleed was fixed this morning.
The CowlMain Component now has 12 more Parts than it did before.
The view from Forward of the CoG is unchanged.
The additional Parts in CowlMain should block the bleeds from Aft of the CoG.
The contrasting colours made this little problem very easy to find and give an idea of the actual assembly sequence for this project.

Parts Count is now 1109.

- Ivan

[aleatorylamp]

Hello Ivan,
Looks good! Parts count is not giving a nightmare either.
I´m going to adopt your way of using provisional coloured un-textured sections to discover bleedthroughs!
So then, forward cowl ring parts are now duplicated into the main cowl component (body-Main?), and the first cowl ring, is that grouped in Nose then, with spinner and prop?
Cheers,
Aleatorylamp

[Ivan]

The Merlin Warhawk model is pretty close to completion at this point.
It will represent a P-40F-1. The F-5 was the first Long Tail version.

A couple days ago, I started gathering information for the Flight Model for the F-1.
As one might expect, the majority of the changes are to the Engine Parameters considering that this was basically just an engine swap from the P-40E.

The following are the obvious changes:
The Allison was also designated the V-1710.
The Merlin was designated the V-1640 in US service.

The slight difference in displacement was due to the slightly lesser Bore of the Merlin.
5.4 inch on Merlin versus 5.5 inch on Allison. For the AIR file, each Cylinder would have 137.41326 Cubic Inches displacement.
There was also a difference in Compression.
The Merlin typically used a 6.0:1 Compression while the Allison was typically 6.65:1.
This difference in compression might explain why it was easier to supercharge the Merlin.

Both engines had a maximum of 3000 RPM which makes the next item a bit surprising.
The Propellers appear to be the same across the two models, but....
The Reduction Gearing on the Allison was 0.500 while the Merlin installed in the Warhawk was 0.447
The Pitch Range also differed slightly from 24.5 to 54.5 degrees in the Allison P-40 to 26.5 to 56.5 degrees for the Merlin.

Take-Off Rating
54.3 inches Hg - 1300 HP - 3000 RPM

Military Rating
48.2 inches Hg - 1240 HP - 3000 RPM

WEP Rating
51.0 inches Hg - 1300 HP - 3000 RPM.

There is a lot more data for power settings available. They differed slightly in British as versus American service.

Listed Climb Rates are barely over 2000 ft/min but typically not for full power operation (48 inches Hg - 2850 RPM)
Maximum speeds are 355-365 MPH but again are not at maximum power settings. One test recorded a maximum speed of just over 370 MPH which was probably done at maximum power.

To Be Continued.....

[No Dice]

Ivan,
It will be another great addition to your collection, beautiful work.

http://www.thefreeflightsite.com/Ivans.htm

Happy Holiday Sir,

Dave

[Ivan]

Hello Aleatorylamp,

Your description of the assembly sequence for the Nose section is pretty much correct.
The multi colour assembly sequence isn't a new idea.
I have been using it pretty much since I started and Womble55 commented on it a few years back when I was explaining why I was doing it.

Hello No Dice,

Thanks for the compliment. I do think this will look nice eventually. There is still quite a lot to do.
At the moment, I don't know of anyone else who has actually built a Merlin Warhawk or even a proper Long Tail Warhawk for Combat Flight Simulator. Just removing the Carburetor Scoop isn't really enough to do a real conversion in my opinion but that is all that I have seen out there thus far.

The K model released earlier will probably get thrown out eventually because the Tail isn't quite right and it has inherited all the goofy shapes from the Wylam drawings. That it would be thrown out was expected once I started reworking the E model.

When I have a basic K model Long Tail, the next step will probably be the N model with a cut down Cockpit area. You wanted one by the time of your Birthday, so it will only be a couple years late.

Even the E model will get released again once I correct the theoretical Cowl bleed and a couple texture issues.

This whole Warhawk business and how much time I have spent on it is actually quite funny considering how reluctant I was to even begin working on the first Warhawk because I did not think it was a hot enough fighter.

- Ivan.

[Ivan]

.....

But for the Engine, Coolant Radiator, and Oil Coolers, the P-40E and P-40F are pretty much identical in equipment and disposable loads.

The Zero Fuel Weight of the P-40F Merlin Warhawk may be calculated from the following information:

7089 lbs - Basic Weight. This includes Trapped Fuel, Trapped Oil, Military Equipment, etc.
180 lbs - Pilot. I believe this is a bit light but this is what is in the manual.
98 lbs - Engine Oil. Some of this will be burned in flight so only 75% (73 lbs) is added.
---------
7342 lbs <--- This will be the value for the AIR File.

+ 888 lbs - Full Internal Fuel.
+ 423 lbs - Ammunition.
-----------
8678 lbs - Loaded Weight.

As a comparison, this is the information for the P-40E:
6702 lbs - Basic Weight. (387 lbs LESS for what is basically just an Engine Change.)
97 lbs - Engine Oil. Negligible difference.

- Ivan.

[Ivan]

A couple days ago, I plugged in the known changes to a copy of the P-40E AIR File to begin working on one for the P-40F.
Last night was a fairly long tuning and testing session to try to get some initial performance numbers.

There are actually several problems with performance modelling the Merlin Warhawk:

First of all, the Merlin's performance advantage over the early Allison was due to its Two Speed Supercharger.
CFS does not really handle multi speed superchargers very well. It really models only a Single Speed Supercharger and does not do that very well.
Multiple Speed Superchargers typically have an altitude at which each speed will achieve its greatest output. Between those peak output altitudes, the power drops lower until the next blower shift creates the next peak.
Unfortunately, CFS only models one peak, so the power output will be much higher than it should at altitudes between the peaks.

Another issue is that the listed performance values are not consistent for throttle settings. Some values are listed for Climb Power, some are for Take-Off Power and some are for Military Power.

Yet another issue is that a few of the numbers simply do not make sense.
The P-40F is listed as achieving a maximum speed at Sea Level of barely over 300 MPH.
This is slower than for the Allison P-40s even though there is more engine power even at Military Rating.
At its critical altitude of 20,000 feet, it was quite a bit faster than the early Allison P-40s with a speed between 355 MPH and 375 MPH depending on the source of data.

My version of the P-40F is now getting the following:
319 MPH at 500 feet with 1252 HP. (Take-Off and WEP is 1300 HP, Military is 1240 HP.)
369 MPH at 12,500 feet with 1394 HP. (A bit too high. There should be a Supercharger Gear Shift here.)
369 MPH at 15,000 feet with 1295 HP. (High Speed Supercharger should not be peaking until much higher.)
358 MPH at 20,000 feet with 1052 HP. (Not quite enough HP and slightly low speed here.)

My testing protocol was to record a speed as maximum if it did not increase in 15-20 seconds.
If testing allowed more time for speeds to stabilise, the numbers would be 1-2 MPH higher but then again, I am doing this with an autopilot which is not available on the actual aeroplanes.

This isn't a great match but I believe it fairly reasonable for what can be done in CFS.

Next comes the Climb and Service Ceiling tests.....

- Ivan.

[aleatorylamp]

Hello Ivan,
I´m not able to contribute much here because the technical info is rather high level, but you seem to have achieved quite a good CFS1 approximation!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Regarding Flight Models, usually I get the match much closer than this.
I am not really expecting responses here or suggestions.
I am just documenting some changes to an aeroplane project.
These Technical Descriptions during a build tend to be mostly monologues which is fine.

This isn't really all that high level. You needed the same information on your builds so you should be pretty familiar with it.

- Ivan.

[Ivan]

My version of the P-40F is now getting the following:
319 MPH at 500 feet with 1252 HP. (Take-Off and WEP is 1300 HP, Military is 1240 HP.)
369 MPH at 12,500 feet with 1394 HP. (A bit too high. There should be a Supercharger Gear Shift here.)
369 MPH at 15,000 feet with 1295 HP. (High Speed Supercharger should not be peaking until much higher.)
358 MPH at 20,000 feet with 1052 HP. (Not quite enough HP and slightly low speed here.)

My testing protocol was to record a speed as maximum if it did not increase in 15-20 seconds.
If testing allowed more time for speeds to stabilise, the numbers would be 1-2 MPH higher but then again, I am doing this with an autopilot which is not available on the actual aeroplanes.

This isn't a great match but I believe it fairly reasonable for what can be done in CFS.

Next comes the Climb and Service Ceiling tests.....


The Merlin Warhawk got some more tuning this morning.
Mostly it was to adjust the Service Ceiling a bit higher than the 32,000 feet I was getting originally.

The new numbers are as follows
318 MPH at 500 feet with 1252 HP.
368 MPH at 12,500 feet with 1388 HP. (Still A Bit Too High.)
373 MPH at 15,000 feet with 1344 HP.
371 MPH at 17,500 feet with 1221 HP.
367 MPH at 20,000 feet with 1102 HP. (This is about where I wanted it to be.)

Maximum Climb is 2790 feet/minute at 7,000 feet.
This is about 300 feet/minute higher than the target but there is a lot more power at medium altitudes than there should be because there is no blower shift point.

Service Ceiling is 34,100 feet which is about where it should be but absolute ceiling is barely over 34,200 feet.
This was done by autopilot and the aeroplane is very unstable above 32,000 feet so the service ceiling when flown without autopilot should be a lot lower.

In my opinion, this is probably very near the target performance. It can certainly be tuned a bit more but the differences would not be very meaningful.

- Ivan.

[Ivan]

I believe this post was lost with the recent crash:

The Merlin Warhawk's textures were also adjusted a bit especially around the Radiator and Oil Coolers.
At this point, the aeroplane really needs a more appropriate paint scheme. I doubt any Merlin Warhawks ever carried Chinese Nationalist insignia.

- Ivan.

[Ivan]

Recent changes to the Merlin Warhawk have been to begin the SCASM process in order to use BMP textures which accept more tools for editing.

After doing the initial SCASM conversion, I found that the Carb Intake appeared a bit small, so that was also increased in size followed by another SCASM treatment followed by another model edit followed by.... (You get the picture...)

The USAAF paint scheme for the Merlin Warhawk was updated over the last few days which was a lot easier to do using PCX and BMP textures. There is one more paint scheme in the works and that one will be a bit more complicated.

There are quite a few things left to complete:
Completion of the SCASM process
A new Control Panel
Checklist
Performance Testing and Documentation.

- Ivan.

[Ivan]

Last night, the Interior Views were corrected.
What remains now for SCASM is just to adjust the animations.
No point in posting screenshots since nothing changed from an exterior view.

The process taken with the Merlin Warhawk seems to be pretty good. It is still based on least commitment but allows a choice of tasks to make progress without forcing a single course of action.

- Ivan.

[aleatorylamp]

Hello Ivan,
It is certainly turning out beautifully clean and accurate!
Cheers,
Aleatorylamp

[Ivan]

The last couple of days has been spent working on a better looking Instrument Panel for the Warhawk.

I had been using a slightly modified stock P-51D Panel up to this point.
Although the panel is functional, the appearance has never been quite right.
I do not believe it is possible to get both functionality and appearance in a good Panel for CFS for some aircraft.
The biggest issue is that the various instruments and controls are distributed in many locations in the cockpit but typical CFS aeroplanes only have a Main Instrument Panel and an Engine Control Panel.
Many instruments also do not have an equivalent in the stock gauges and some do not make sense to include.

This Control Panel is based on the background for the stock Spitfire Mk.IX with instruments selected based on functionality and appearance.

Here are a few characteristics I know are incorrect and likely will remain so:

1. The Fuel Selector does not look like the one here and is not in this location on the real aircraft.
2. There is a Suction / Vacuum Gauge that has not been included.
3. The Magneto and Starter Switch are not on the upper / visible part of the panel on the actual aircraft.
4. There is no Trim Gauge on the control panel.
5. The Clock is located where the Compass would have been and the location of the Clock is taken by the Magneto Switch.
6. There is no Landing Gear Warning Light. I could not find an equivalent in the stock gauges.
7. The Panel Background colouring is not as good a match as I would like. Perhaps this can be fixed....

- Ivan.

[Ivan]

Here is an updated version of the Warhawk Control Panel with Gauge sizes and locations modified slightly and a heavily edited Background. Only stock Gauges are used at this point. The Canopy Frame colour is a best try at this point and perhaps will yet be modified in the future.

I believe that at this point, it is a pretty good combination of functionality and appearance.
Note that for appearance, most of the Gauges came from the P-47D.

Next step is to make some changes to the panel for Test Flying....

- Ivan.

[aleatorylamp]

Hello Ivan,
Wonderful! Apart from the useful looking layout, I really like the Curtiss sign.
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

In reality, there probably was no "Curtiss" signature in that location.
We don't really know because where I put it is the sheet metal UNDER the actual Black Control Panel and that area would normally be hidden under the Gun Sight.
The Spitfire Gun Sight is much smaller so there is the space underneath.

I also believe this is pretty good balance between functionality and authentic appearance.
There are actually lots of little missing things such as Coolant Warning Lights, and a bunch of little things added,
The tag "FUEL" should really read "FUEL SIG." for fuel signal but I could not keep the size of lettering if I added a S or G.
The only change I am still contemplating is increasing the size of the Artificial Horizon.

I believe this will be used in future versions of the P-40 and possibly even retrofitted back to the P-40E as an update.

- Ivan.

[Ivan]

The Technicians in the Paint Booth have been busy over the last few days.
Last night was a marathon session where the Camouflage was matched up between various pieces of the Aeroplane.

This may not be the best way to do it, but essentially the painters have to paint each piece before it is fitted to the Aeroplane and when there is a mismatch as there usually is, the piece is removed to be repainted and reassembled.

This result is actually pretty close to the typical Desert scheme used by the RAF and USAAF though I have taken a few liberties which I believe improve the appearance.
Other personal and unit insignia still need to be applied.

- Ivan.

[aleatorylamp]

Hello Ivan,
Nicely fitting camo patterns! I feel they always give a very professional look.
As regards names on the instrument panel, I also like putting them in, just to add a bit of ambience, even if on the real aircraft they weren´t there or as visible.
Cheers,
Aleatorylamp

[Ivan]

The first paint scheme was a Generic US Army Olive over Neutral Gray.
The second scheme was US Army Desert Sand and Dark Earth over Sky (Gray)
The third and final scheme which I just finished is RAF Desert Sand and Dark Earth over Sky (Gray).

The RAF Desert scheme is actually the hardest because there were so many little changes over time and it is quite possible to get a combination that could never have happened.

There were a few others, but I think this combination should be good enough for release.
Should I release just one version with all three schemes or two versions with contrasting schemes as I did with the P-40C?
I am tending towards two.....

- Ivan.

[Ivan]

There are a couple parts of the camouflage pattern that are questionable.
Some are intentional and done under artistic license.

ONE section is pretty close to the painting guide for P-40 models:
The port side of the Tail under the Horizontal Stab clearly shows as Dark Earth, but....
in photographs, This shape appears to resemble a dark shadow rather than dark paint.

The Wing Root and Fillet on the starboard side should also have the dark pattern moved forward a bit.

- Ivan.http://www.sim-outhouse.com/sohforums/attachment.php?attachmentid=34150&stc=1

[smilo]

beautiful, Ivan, simply beautiful.
well done.

as for uploading number preference,
it's your call, sir.

[aleatorylamp]

Hello Ivan,
Very good this 3rd. texture of yours with the Pegasus detail - Definitely upload that one!
If one were forced to choose between the other two, it would be very difficult, because both have their advantages: Well done camo versions always look striking, and are rarer on models than plain coloured ones for their texturing difficulty. Dark, plain-coloured versions I feel have a no-nonsense atmosphere to them which is also appealing.
I know what I would do (all 3!), but it´s your creation... So, as Smilo says... it´s your call!
Cheers,
Aleatorylamp

[Ivan]

Thanks Smilo.

Glad you approve. I am also a bit surprised at how nice the Merlin version looks.
Although I had not planned it that way, it still appears to be quite agile and performance appears to be very good.

Thanks also, Aleatorylamp,

The plan was actually to do something pretty similar to what I did earlier with the Hawk 81s.
There were two uploads even though they were basically the same project; One would have the Green US Army paint scheme set up as default and the other would have the RAF Desert paint scheme as default. Both would have all three textures included.

I don't think the USAAF Desert scheme looks too bad either.
Note that the US Army Desert paint scheme had a LOT of variations with some seriously strange combinations such as Pink overall.

I was also debating on doing a CheckerTail, Shark Mouth 112 Squadron, or Monochrome Tan as was originally used.
There are also at least two Camouflage patterns used in the desert.
For now, I am staying generic.

- Ivan.

[Ivan]

Hello Hubbabubba,

I just finished uploading the Merlin Warhawk that you suggested back in Post #31 a while back.
Hopefully this meets your expectations.
It is certainly a bit more than just leaving the Carburetor Scoop off a regular Allison P-40.

My technicians are waiting for the upload to be approved before sweeping up the metal scraps from the workshop.

Although I like the RAF paint scheme, the reality is that very few P-40Fs actually served with the RAF.
Some were also used by the French and sent to Russia of all places.

- Ivan.

[aleatorylamp]

Hello Ivan,
I´ve just downloaded and tried out your new plane!
Definitely a very beautiful job, and exciting and precise to fly.
Very nice!
Thanks!
Cheers,
Aleatorylamp

[Ivan]

Thanks Aleatorylamp,

I like the result of this project also.
It still has the nice handling of the prior versions of the Warhawk despite the extra 300 pounds of weight.

The climb rate is actually a bit higher than the Allison versions in my models, but that isn't proof of anything since my flight modelling is not necessarily accurate.

The odd thing that I believe I found is that down low, the Merlin Warhawk was a bit slower than a contemporary Allison even though the Merlin would have more power. Perhaps it is because of restrictions on power settings, but to create this effect, I had to turn up the Drag Coefficient quite a bit. This would imply that the bigger radiator scoop caused a LOT more drag.

So now the Workshop is officially clear. I think the technicians are actually working on tools to make the next project easier.

- Ivan.

[aleatorylamp]

Hello Ivan,

Given the limitations in the .air file for the two different turbo superchargers for the Allison and Merlin engines, it´s most probably as good as it gets.

Currently, and for a totally different era and performance envelope, I´m tweaking the two different Benz Bz.III (165 hp) and Bz.IV (230 hp) engines performances on the Albatros G.II and G.III (1916 and 1917) that I want to upload as soon as possible, to clear my own workshop and see what´s on otherwise.

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Yes, As far as I know, there are limitations on SUPERchargers are handled in CFS.
Neither the Allison nor the Merlin as installed in the P-40s ever had a TURBOcharger.
The Allison installation in the P-38 Lightning did have a Turbocharger and differences in plumbing are pretty serious.

Next step in the evolutionary process of my P-40s is going to be a revisit of the P-40E Warhawk to correct the not so obvious bleed problem in the Cowl area and to remap a couple textures that might be located less than optimally.

The underside behind the Cowl also needs an examination for faults as I found in the Merlin Warhawk.
I don't know for sure that there are any that were not caused by the numerous changes for the Merlin installation though.

It seems almost a shame to chop up such a nice looking Warhawk to correct a few things that are barely visible under a directed examination, but that is what I need to do to have a solid basis for any follow-ons because any errors will be propagated forward.
What I hate the most about this is the need to go through the SCASM adjustment process again.

On the next release, the P-40E will also have a RAF Desert texture available because with just a minor exception, just about everything maps the same between the P-40E and P-40F.

- Ivan.

[aleatorylamp]

Hello Ivan,
Sorry, yes... I meant just superchargers - the word "turbo" keeps slipping in as in my mind SUPERchargers ARE a kind of turbine, with vanes like a pump, or helicoidal or whatever, even though they aren´t driven by an exhaust-turbo, but by a belt or gears...
...I MUST get into the habit of calling things correctly!

Re: Re-visiting models: I was just thinking... I find re-visiting a model for alterations or upgrading after some years does indeed have its nice aspects. With the familiarity on one hand, and the added experience on the other, with perhaps additional data available, the result is usually quite successful and often includes the satisfaction of improvements or corrections that weren´t planned or expected.

Cheers,
Aleatorylamp

[Allen]

I must say that the models look good!

[Ivan]

Thanks Allen,

I do think this one turned out looking pretty nice with the Desert Camouflage.
I believe this is this (surprisingly) is the first actual Merlin Warhawk that is more than just the Allison version with the Carburetor Intake removed.


Hello Aleaorylamp,

A Supercharger is just a pump installed before the intake system. Some are turbine driven thus Turbo Supercharger (or Turbocharger for short).
The actual pump on these aero engines is an Impeller (Centrifugal) or kind of a reverse turbine, but there are many forms of supercharger. Impellers are not positive displacement but there are many such as the Roots type that are positive displacement and work regardless of input shaft speed. Spiral Superchargers I believe are also positive displacement.
Positive Displacement Superchargers have the advantage that their output is linear with input shaft speed AND also that there is typically no Lag when the throttle is applied.
Turbo Superchargers may have a delay between Throttle opening and power increase which is referred to as "Turbo Lag" and happens because it may take some time for the (possibly heavy) turbine to come up to speed to supply extra air.

Revisiting older projects is sometimes fun and sometimes discouraging for me. My build standards and practices are evolving with every project and some of the very old ones need so much tedious work that I am hesitant to do any modifications.
As you stated, the nice thing about reworking our own models is that the naming schemes are fairly predictable and things are not hard to find and if they were built once before, there was probably a reason for doing it at the time.

At the moment, models being considered for rework / completion are the SBD Dauntless, FW 190A, Spitfire IX, Ki 61-I, La-5FN, Thunderbolts and of course the Corsairs. All have some aspect that I don't feel like dealing with. The P-40E needs to be updated before any of the others though because it is likely to be the pattern for further development into a Long Tail model.
I don't believe I have ever seen a Long Tail P-40 for Combat Flight Simulator other than my K model and that one has shape problems inherited from the Wylam drawings.

- Ivan.

[Ivan]

Here are a couple screenshots of the P-40E wearing a RAF Desert paint scheme.
The textures are not quite a direct replacement, especially around the Cowl area (of course) but were not difficult to create.

Note also that the Radiator scoop extends barely past where the original line was.
That is why the bleed at the Cowl was only really visible when the Radiator opening was extended forward on the Merlin version.
There are a couple different ways to correct the bleed (which I can't see but know is there):
1. Move one frame the top of the Cowl slightly forward to match the cowl opening.
2. Extend the Main Cowl Component to include the next row of polygons as was done on the Merlin.
This would cost a bit more than on the Merlin because it is likely the Carb Scoop would also need extended forward.

Best I get to work on it soon.

- Ivan.

[Ivan]

Note the difference between the E and F Radiator openings.

It turned out that the changes to the P-40E actually needed 20 extra Parts.
The P-40F only needed 12 Parts but the top Part of the first cowl ring is split into two pieces to allow for the Carb Scoop on the P-40E to make it 14 Parts.
The Carb Scoop also needed to be extended forward which cost another 6 Parts.
Total Parts Count is now 1143 for the P-40E as versus 1111 for the P-40F.
Hopefully there is still enough room for further changes for later P-40s.

- Ivan.

[aleatorylamp]

Hello Ivan,
Interesting, the intricate details. They make each model quite unique.
Cheers,
Aleatorylamp

[Ivan]

Here is a screenshot of a panel on a very nice repaint of my Warhawk.
The artist's name escapes me at the moment.
Heck, I wish I knew enough to do what he does on these paint jobs.

My version is also included for comparison.
His gunsight is more correct.
My fuel selector is more functional.

- Ivan.

[Ivan]

Here is a screenshot illustrating some of the issues I was chasing with the Warhawk:

The Cowl Fairing had a non-planar polygon that put a weird dent in the underside.
I fixed it in the Merlin version but had not made the same changes in the Allison version.

There is also a slight line in the underside of the Cowl by the intake that looked like a mapping problem but didn't go away wen I remapped this area. I still don't know what it is, but the problem looks small enough I will just leave it for now.

The SCASM process was done very late last night. The really amazing thing is that most of the changes to the SCASM SCX source when copied from the prior version actually compiled without error. Even with 20 extra polygons, most of the SCASM code didn't change.

The second screenshot shows the outline of the previous P-40K model and shows why I am just going to start over from the P-40E. This picture only shows the profile. A plan view would show even more issues.

- Ivan.

[Ivan]

The Curtiss P-40 is the subject of a great amount of literature and documentation.
There are many surviving examples in museums and there are even many flyable examples.

With this being the case, one has to wonder why there are so much conflicting data.
Is it because there were that many variations in the actual aircraft or just that inaccurate numbers were recorded and propagated forward? Is it because of rounding errors?

From what I have been able to gather, the Wing Span of the P-40 series was pretty much constant.
Some sources show 37 feet 4 inches. Some show 37 feet 3.5 inches.
My belief is that this is a simple rounding issue and that the actual dimension is 37 feet 3.5 inches.

The Stabiliser Span is also fairly consistent at 12 feet 9 5/8 inches (also listed as 9.625 inches and 9.62 inches)
The differences are very small and most likely just a rounding issue.

With the Fuselage Length, there were at least five distinctly different airframes:
P-40 through P-40C (The Long Nose P-40s)
P-40D, P-40E, and early P-40K (Short Tails)
Early P-40F Merlin versions (Short Tail Merlins)
Late P-40K, P-40M, P-40N (Long Tails)
Late P-40F, P-40L (Long Tail Merlins)

For this discussion, I will ignore the P-40Q which bore little resemblance to anything before it.
I would also limit this discussion only to the P-40D through P-40N because that is where most the disagreements are.

Here is what I have found in decreasing degree of certainty:

The Overall Length of the P-40N, and other Long Tail Allison P-40s is often stated as 33 feet 4 inches.
The manual states this as 33 feet 3.7 inches.
Yet another source states this as 33 feet 3 23/32 inch.
These numbers are all quite consistent and in this case, I believe the most precise is also likely to be the most accurate (33 feet 3 23/32 inch).

The P-40L is also listed in the manuals as having the same length as the Long Tail Allison P-40s, but we will come back to that later.

The P-40D/E is listed as having several different overall lengths:
31 feet 7 inches
31 feet 8 1/2 inches
31 feet 8 3/4 inches
31 feet 9 inches
The Maintenance Manual states that the overall length with thrust line level is 31 feet 8 3/4 inches.
Technical Drawings appear to confirm this number.

The P-40F Service Manual lists its overall length as 31 feet 7.75 inch.
A book about Curtiss aircraft states the overall length as 31 feet 7 9/16 inch which is very close.
There are actually some discrepancies between the E and F service manuals regarding Thrust Line and Propeller Clearance and Overall Height. The number from the E manual works out mathematically. The specification for the F does not.

So..... Here is where the numbers stop adding up properly.
The Thrust Line according to Curtiss Factory drawings is the same across the D,E,F,K,L,M,and N aircraft at 3.078 inch above the Fuselage Reference Line. (This is why I spent so much time rebuilding the model to match this number.)
The numbers therefore cannot be different between the E and F despite the manual's contents which again confirms that there is at least one incorrect number in the F Service Manual.

There is a 1 inch length difference between the E and F but although the Curtiss drawings specify that the difference in length between Allison and Merlin Cowls is only 1/4 inch shorter for the Merlin.
Now if we go back to the E-F difference as -1.0 inch and the L-N difference as ZERO, then there is some difference in the fuselage length on the long tail versions which does not make sense.

From a modelling standpoint, we need to pick some definite number to build toward.
So.... My Merlin P-40F is therefore only 1/4 inch shorter than the P-40E regardless of its stated dimensions.
The shape appeared to be consistent with Factory Drawings though it is admittedly just a guess.

With the Long Tail Allison P-40, I am finding that although the commentary shows a 20 inch extension, the overall lengths only allow for an extension slightly under 19 inches.
These numbers are not consistent but again are a best guess from the available and contradictory information.

- Ivan.

[aleatorylamp]

Hello Ivan,

Your reasoning sounds sound, and your argumentation and conclusions in this case are the only solution for accurate building.

Apart from the decimal rounding issues, obviously the numbers should work out mathematically, and I agree that discrepancies would be due to someone´s mistake writing down something along the line.

The human being is famous for practical adaptation, with a heuristic as well as analytical brain. Depending on the person this tends more towards one or the other, and includes other things like skiving and covering up mistakes, also depending on the person. Some people would just call it incompetence, and others, fixing things the quickest way.

The differences you found between service manuals and factory drawings, could perhaps imply slight adjustment-modifications undertaken during a production run, and then not fully recorded in all their details, giving rise to differences between units of the same model - maybe not so much for performance reasons, but for practical ones such as fitting of parts, etc.

This does not help someone trying to decipher accurate measurements!

Anyway, your deductions would be the only solution, I´d say!
Cheers,
Aleatorylamp

[Ivan]

There are a lot more strange things that I have not brought up yet, but here is one fairly clear difference.
These images are both for the P-40N. I pulled one as a scan from America's Hundred Thousand.
The other is from the P-40N E&M Manual.

The aft end of the Rudder is positively located by the overall length of the aeroplane.
The vertical shift is not so positively located but note that these images do not agree as to the location of the top of the Fin / Rudder from the ground line.

- Ivan.

[aleatorylamp]

Hello Ivan,

It´s frustrating, isn´t it... one of the artist wasn´t too careful, and in this case it´s quite difficult to confirm which one is correct by means of photos. (Going to the museum to measure it would also be impossible... ha ha!).

It happens so often! One of the reasons I´ve delayed re-work on yet another WW1 twin biplane - i.e. the Rumpler G.II/G.III - is that the G.II is said to have had unstaggered wings perpendicular to the fuselage like the G.I, and that only the G.III had refinements like backwards stagger and backwards slanting wings - like an arrow - I don´t remember the term used. It´s not "taper", as the wings have the same width at root and tip.

Anyway, then, in the drawings, I see the G.II´s wings also slanting backwards from the perpendicular line! So... the next step is to try and delucidate this from the few availble photos.

Never a dull moment - and good luck with your deductions!
Cheers,
Aleatorylamp

[Ivan]

A couple days ago, (Actually before my last two posts) I decided to try shifting the Tail pieces from the P-40E to produce a P-40K.
I did this by trying to project the lines that I already had for the existing Tail. The end result was very interesting because it produced a model that had a Fin / Rudder that was 12 feet 4.8 inches above the underside of the Main Wheels.
This is why I was looking for the drawings that specified that dimension
One of the drawings is an exact match. The other obviously is not.

Although I don't know the dimensions are absolutely correct, I believe this may be as good as I am going to get and probably good enough to build with.

- Ivan.

[Ivan]

The actual dimensional change to convert MY Warhawk from a Short Tail to a Long Tail is to move the Fin / Rudder
0.20 Feet Up
and
1.58 Feet Back.

This was shown in the screenshots for the prior post.
This post shows the adjustments of the Textures and all the messy stuff inside.

The Fin and upper half of the Rudder is done as a single Component.
Its location in the AFA file was moved back 1.58 Feet.
That alone isn't enough; The actual paint needs to be shifted up by 4.41 Pixels.
(Since we can't shift a fraction of a Pixel, it was moved up by 5 Pixels.)
The lower half of the Rudder is part of the Tail Cone Component.
It does not get adjusted in the AFA File.
I moved the paint from just ahead of the Rudder Hinge Line Up 5 Pixels and Back 35 Pixels.
(It really should be 34.87 Pixels.)

The screenshots show the result.
There is also something else worth noting in the screenshots:
The Ribs on the Rudder and Elevators are plainly visible in the Texture Files but not visible at all in the screenshots from the Simulator, at least not as .?af (R8 format) files. As BMP files, they become visible.

- Ivan.

[Ivan]

Hello All,

In the last post, I included an overhead view of the Long Tail Warhawk which didn't really fit in with the theme.
The original intent was to comment about the center frame at the top of the canopy.
Many illustrations of the Warhawk (P-40D through P-40M) do not show this center frame.
I have several P-40 model kits and some show the center frame and some do not.
The paint guide I used for the Merlin Warhawk did not show this frame but a restored P-40F has it.

I spent a fair amount of time trying to find photographs of original wartime aeroplanes to see if they actually had this frame or not. As stated earlier, sometimes modern photographs are not reliable. Many aeroplanes have been converted with modern instrumentation, a passenger seat, additional antennas and possibly combining parts from later birds.

My conclusion now is that this frame was a part of every standard canopy from the P-40D through the P-40M.
(The P-40N had a radically different canopy.)
The reason for this conclusion is that I found parts manuals for the P-40E-1 and the P-40M/N.
They both show the center frame in the Canopy Frame. Perhaps things changed mid production but until I find conflicting evidence, this is how I will be building the models.

- Ivan.

[Ivan]

Yesterday, I went through a marathon session with the Long Tail Warhawk.
The Tail Cone needed an almost complete redesign (actually done in two tries) and some of the Glue Parts needed to be adjusted.
The end result is that by the end of the evening, I had a pretty fair (in my opinion) 3D model even though the textures needed to be adjusted more.....

*******

[Ivan]

The shape of the Tail Cone just in front of the Fin is a bit of a compromise.
I really would like to put in a Fillet as on the real aircraft but the problem is that it would either cost resources I do not have or cause some bleeds from below that are more unsightly.
I believe that the compromise is probably the best that I can do at this point and I don't dislike the result.

The next part was to adjust the textures and panel lines to fit the new tail.
I found here that I may have made a mistake earlier with the textures.
They did not line up between the top and bottom halves of the Rudder.
The new location of the dividing line also splits the Rudder Trim Tab which resulted in a bit more work in matching.

Panel lines are always a compromise of some kind. Plastic modelers have the same problem.
On the actual aeroplane, the skin panels are usually butt joints and cannot be seen from more than a few feet away.
The rivet detail also cannot be seen.
The problem is that without panel lines, the model starts to look like a shapeless blob.
This is particularly noticeable with Combat Flight Simulator because the rendering engine doesn't get very sophisticated with shading and highlights and shadows simply do not exist.
Adding all the panel lines starts to make the model look like patchwork and full of scars.
....So a decision has to be made regarding which lines are significant and need to be represented.

The contrasting colours here are to make the panel lines more obvious so they can be easily adjusted.
The model has since been painted Army Olive Green and doesn't look quite as strange.

- Ivan.

[Ivan]

Animating the Long Tail Warhawk started off strangely.
None of the original moving parts were visible.
It finally occurred to me that the new P-40K or Hawk87B was closer to the P-40E than the earlier release of the P-40K.
Copying the moving parts file from the Warhawk project and renaming it solved most of the animation issues.
Flaps of course still needed attention.

An interesting observation can be made about the Short Tail versus the Long Tail P-40:
No functional pieces other than the Rudder actually moved.
All the Landing Gear pieces remained where they were.
Even the Elevator did not move.
From an AIR file and texture mapping standpoint, that makes things much easier.

This profile view gives an idea of the shape issue in front of the Fin. As with most Aircraft Factory 99 models, the resource limitation may mean that this will not be changing.

From this Long Tail P-40K, a minor texture change and a slightly more curved Carburetor Scoop are the only changes needed to get to the P-40M. To build the P-40L requires grafting the new pieces onto the Merlin Warhawk and removing one of the Wing Guns from each side. Only with the P-40N do things become significantly different.

- Ivan.

[Ivan]

I wrote prematurely....

Just because I did not see a solution to a problem does not mean that there was not one and a fairly easy one at that.
I had an idea while cooking dinner tonight and will see tonight whether it will work or not.
That is the danger of a running commentary: Sometimes given enough time, a better idea becomes obvious.

- Ivan.

[Ivan]

The Tail Cone adjustment actually worked better than expected.
The Parts Count is now back to 1145 which is the same as the P-40E.

My original distraction was that I didn't see that adding a Fin Fillet (which would normally cost an additional Component that I didn't have) would actually allow the blending of the Fin with lowered Tail Cone WITHOUT an additional Component.

At this point I am reasonably satisfied with the shape.

Last night, one computer crash actually destroyed my AFA Project file and I had to restore a backup to continue.
Over the last few days, the crashes and blue screens have become quite frequent.

The screenshots show a comparison between the two versions of the lengthened Tail and views from the simulator.

- Ivan.

[Ivan]

SCASM Process has just been complete. It was almost exactly the same as the P-40E Warhawk so very little real work had to be done. It was mostly a matter of copying SCASM source from the Warhawk project.
Surprisingly, the Pilot Shoulder Component was slightly relocated but nothing else in the SCASM process was affected.

Next step is to select a paint scheme for release.

- Ivan.

[aleatorylamp]

Hello Ivan,

Very interesting, the Long-Tail development of your Warhawk, and the results of your meticulous research.

A question for the .air file: I would expect the effectivity of the CFS1 air file to be able to perhaps reflect the small changes in behaviour for the Long Tail. Would this be achieved by simply adjusting the further aft positioning of the fin/rudder, or would you think any extra adjustments elsewhere would be needed, like rudder effectivity or something?

BTW I thought you´d remedied the computer crashes. I´m sorry to hear that your machine is playing up again. I have managed to speed up my wife´s old Pentium Dual Core XP workhorse laptop with some extra memory and a faster CPU from E-Bay, and it is turning out to be a very stable and fast platform, and I even got a new battery for it.

Cheers,
Aleatorylamp.

[Ivan]

Hello Aleatorylamp,

Currently, all I am doing with the AIR file for the Long Tail K model is to move the Rudder back.
There were some other things that were done but until I am more familiar with how to do things in the AIR file, I am not putting those in just yet.

There are also some low speed handling issues on ALL my P-40s that need to be addressed at some point.
At the moment, there are several areas I need to work on: Gauges, 3D Models, and a few effects in AIR files that need some research / experimentation.

No, I never really addressed the machine that is having problems. Sometimes it is fairly stable and sometimes it is not.
I also need to get a KVM switch at some point to bring another machine online next to the current development machine.

- Ivan.

[aleatorylamp]

Hello Ivan,
Step by step then, with quite a full to-do list!
I like using a KVM switch too, as it helps keeping 2 computers apart and simplifies having them together.
With modernities now though, my fast computer only has 1 PS2 socket, for either a mouse or a keyboard (it won´t take a "Y" splicer to have both), so I have to use a USB mouse on it and a SP2 Mouse on the paralell Pentium-4 Of course a new KVM switch with USB ports would be perfect, but it´s not worth the money just for that.
Anyway, KVM´s are practical!
Cheers,
Aleatorylamp

[Ivan]

Some time during the production run of the Curtiss Hawk 87 series of aircraft, the Propeller was switched.
The early Propeller Blades were fairly narrow which was all that was necessary to handle the power from the early engines.
As engine power increased, a Wide Chord Propeller was fitted.
When exactly this occurred is hard to pin down.
It is also hard to determine whether earlier Hawk 87s were retrofitted.

One can be fairly certain that the early P-40E had a Narrow Chord Propeller as original equipment.
One can be fairly certain that by the time the P-40M was built, the Wide Chord Propeller was standard.

General belief is that some time during the production run of the P-40K, the Wide Chord Propeller was fitted.
My belief was that it happened fairly early in the production because of the efforts made to enhance directional control of the aircraft:
First, an extended Fin Fillet was added and later, the Tail was lengthened. Note that this was not retrofitted to P-40Es

I have not found an explicit statement to this effect, but believe that the Wide Chord Propeller was also fitted some time during the production run of the P-40F or P-40L as well.

Creating a Wide Propeller Blade from the Narrow version w.as actually quite easy.
First, the original Blade Template was widened by 31% which brought the maximum chord to a touch over 11 inches.
This created a blade with a tip that appeared too wide and rounded.
Next, the tip was reduced in width by 10% and the two section were blended which resulted in what I consider to be a fairly reasonable shape.
After the Blade Template was updated, it was rotated 26.5 degrees in Yaw to add pitch and saved as Propeller Blade #1.
Propeller Blades 2 and 3 were created by rotating Blade 1 in Bank and relocating to a common center point.

This is just the first of the changes required to produce the P-40M and P-40N. Many more changes will be necessary.
Perhaps I will retro fit this to the P-40K project.

- Ivan.

[Ivan]

The following changes were needed to get from the P-40K to P-40M:

Wide Chord Propeller - As noted earlier, they may have been fitted or retrofitted to earlier models
Filtered Intake Openings - Holes in front of Exhaust Manifold
Antenna Mast - Although earlier aircraft may have had them, they became much more common on later versions
Vent Window - A Small Window was added to the Left Side of the Windscreen. This could be opened slightly for ventilation

I believe that was all that was visibly different with the P-40M.
The P-40M also introduce a new version of the Allison with changes to the supercharger to increase high altitude performance.
The power rating went from 1150 HP to 1300 HP, but actual maximum power was considerably lower because the new supercharger did not tolerate higher boost pressures that were successfully used on the earlier engines.

Interestingly enough, the P-40M production was intended for export and never used operationally by American forces.
They served with Australia, New Zealand, The Soviet Union and possibly others.

The first screenshot shows a problem that luckily went away by itself.
The second screenshot shows the visible differences

- Ivan.

[aleatorylamp]

Hello Ivan,
I find the well researched small details that you introduce into you models as the versions progress from one to the next, fascinating, as well as the information you provide to explain the variations.
Cheers,
Aleatorylamp

[Ivan]

Thanks Aleatorylamp,

The evolution of the P-40 series is actually quite interesting though not necessarily a happy one.
We are certainly getting near the end of the P-40 line. I have already started work on dimension checks for the P-40N.
When I am done there, I will likely take a little break and then go back to the ancestor of the series: The P-36 / Hawk 75.

Consider how this story evolved:
A fairly good 1930's design, The P-36 / Hawk 75, makes a nice transition from Biplane fighters to Monoplane and retains the flying qualities of the Biplane with performance of contemporary (for 1935) monoplanes.

A couple years later, the US Army sees the developments in Europe with inline engines and wants the improved performance.
Curtiss responds by fitting the Allison V-1710 to the Hawk 75 an eventually gets to the Hawk 81.
The level speed is improved but everything else suffers: Climb Rate, Maneuverability and Handling are all noticeably worse with the Hawk 81 which is actually a fairly competitive design but for Altitude performance which can be blamed entirely on the engine.

A few years later, Curtiss does a major redesign to fit the new Allison F series engines and arrives at the P-40D/E (Hawk 87) series.
Firepower and Protection are better but engine power is actually very nearly the same and performance actually doesn't change much.
If anything, climb rate is worse because of the increased weight.
One of the major changes in the Allison engine was in the reduction gearing (which raised the thrust line). The new gearing could handle output that the old gearing could not. Some folks figured out that the Allison could actually take much more boost than was claimed.
They managed to get an engine rated at 1150 HP to put out around 1550 to 1600 HP.

With the beginning of Merlin engine production at Packard in the United States, some of the engines which were intended for Bombers were installed in the P-40E series which resulted in the P-40F. Altitude performance was considerably improved.
About this time, the extra engine torque was causing directional controllability problems which were addressed by first adding a fillet to the fin and afterwards with a longer tail section which remained with all subsequent P-40s.

The P-40 was always a relatively heavy aircraft for its power and Curtiss tried to address this issue in a very interesting manner.
With the P-40L model, Curtiss reduced weight by decreasing the ammunition load and removing one internal fuel tank (the Forward tank).
Some other parts were also replaced with lighter and more poorly made pieces. The decreased operational capabilities and increased maintenance issues caused many of the changes to be reversed in the field. Thus these changes were ineffective.

The demand for Merlin engines was greater than the production capacity so the P-40 was forced to revert back to the Allison.
By this time, the P-40 was considered to be suited for use as a fighter-bomber or for places where the opposition was not very modern.
It was sent to China, Burma, India, to Australia and New Zealand, to the Mediterranean, and as an export aircraft to the Soviet Union.
An Allison engine with an improved supercharger also entered production at this time which is the main distinction between the P-40M being built now and the earlier P-40K. This also might explain why the P-40M never served operationally with US forces though Australia, New Zealand and the Soviets used them.
The "improved" supercharger gave better altitude performance but had much less capability at low altitudes.

My intention here was to use South East Asia Command insignia as carried by the RAF (not RAAF or RNZAF) but I don't know for sure that the RAF ever used the P-40M operationally either.

Just to complete this story:
The P-40N was a more successful attempt to produce a lightened version. The earliest version (P-30N-1) was visually the same as the P-40M other than having only two instead of three guns per wing. The changes which distinguish this model were all in internal equipment.
The next P-40Ns had the cut down rear fuselage that we typically associate with this model.
The P-40N was the fastest and possibly the best performing of the production models but even then, production was terminated at the end of 1944. By the end of the war, it was no longer serving as a front-line fighter in any of the major services.

- Ivan.

[smilo]

thanks for the history lesson.
i, for one, appreciate your research.

[aleatorylamp]

Hello Ivan,
So it appears that the airframe was very well capable of superior performances, limited only by the available engine technology, and it is very intesting to see how different strategies were experimented with varying degrees of success to try and get round the limitations.
Also interesting is how modifications to increase performance went in detriment of other factors - it happens so often, that compromises have to be reached!
Cheers,
Aleatorylamp

[Ivan]

Thanks Smilo,

This was obviously a somewhat informal summary just for general understanding.
It also reminded me of why I was so reluctant to build a P-40 to begin with, but it is way too late now!

Hello Aleatorylamp,

Here are my opinions based on a fair amount of reading:
As I mentioned in a much earlier post, the P-40 series was a rather heavy airframe.
Its durability and strength were quite good and by reputation was much better than either the Mustang or Spitfire.
Also by reputation, its maneuverability was probably between that of the Spitfire and Mustang.
Its aerodynamics was probably comparable to the Spitfire and much worse than the Mustang.

Its weight limited the climb rate as compared to the Spitfire and the Aerodynamics limited the speed as compared to the Mustang.
So what we have here is an aircraft that was always going to be slower than the Mustang even though it was more agile.
The Mustang in comparative testing was not a particularly maneuverable aeroplane and quite comparable to the Thunderbolt.
By that stage of the war though, the services were all looking for high climb rates and high maximum level speeds and didn't really care about nice handling and good maneuverability. The Mustang fit the requirements.

The Spitfire was never particularly fast for its power but it climbed well. When the Griffon engine was installed starting with the Mk.XIV, it became quite a lot faster.
(Yes, I know the Mk.XII was the first to carry a Griffon, but it was fast only at low altitudes; The Mk.IX was still faster up high.)
Remember that it was to be replaced after the war with the Spiteful / Seafang series which were much faster aircraft with the same engine.

Even when the P-40Q came along, it was still 20-30 MPH slower than the Mustangs so it made sense not to continue producing it.
Yes, they were improved during the war, but not enough to keep up with expectations.

- Ivan.

[Ivan]

After a couple nights, this is what sits in the Workshop.
There is still much to do and some of the textures needed to be remapped.

The Technicians will be fabricating more Canopy Frame Parts for the fixed sections on the Fuselage and also cutting a piece of Armour Plate to be installed behind the Pilot.
Other Technicians are gathering patterns for artwork to be used on the new aeroplane.
The artistic types in my shop are not particularly good or fast though.

- Ivan.

[aleatorylamp]

Hello Ivan,
From your comparison of the performance of the different aircraft, it is interesting to see how different top-notch manufacturers who were operating at cutting-edge technology, were successful in different areas, each being able to come out with peak performance in specific areas, and how it was extremely difficult or almost impossible to come out with a general all-round winner that beat all otheres in all aspects.
Cheers,
Aleatorylamp

[Ivan]

The P-40N model was pretty much completely last night and this evening most of the textures were adjusted.
My computer is still acting up rather badly which even made screenshots difficult.

What still remains is the SCASM processing, Flight Model, Damage Profile, and even a New Control Panel.
The N model used at least two Control Panels that were significantly different from earlier models.
The internal Canopy Frame also needs to be built and I will probably be adding another paint scheme before I am done.

-Ivan.

[Ivan]

The late model P-40s had a small vent window on the forward left side that could be opened in flight.
I have always thought this was a peculiar design and rather ugly but it was an obvious recognition feature.
This was an asymmetric design and only on the left which causes some issues when thinking of an aeroplane as a nice symmetrical object.

My development computer is misbehaving so it took a few tries to make things work.

Note that at this point, the Internal Canopy Frame Component is not reversed. It makes sense to stay in AF99 when just building the pieces.

Here is a comparison between the views with and without the Vent Window.
If this is any indication, then the additional framing did not greatly impact the view from the Cockpit.

Next come changes to the Instrument Panel background to add the new Frame and a bit of a redesign of the entire panel to more closely resemble the N version.

- Ivan.

[Ivan]

This Project being built for Combat Flight Simulator is intended to represent a "Generic" P-40N.
Besides the P-40N-1 and P-40N-40, the other models were quite similar and differing only slightly (from the CFS Viewpoint) in equipment.

The P-40N-1 was a lightweight version which didn't have a cut down rear fuselage and looked more like a P-40M.
Differences were in internal equipment and reduced armament.

The P-40N-40 did not look any different from the earlier versions but combined the engine controls into a single simplified control.
There were fewer options for the pilot. The problem with representing this design is the lack of panel instruments that can perform the proper functions of combining propeller pitch and throttle.

Depending on the source and variant, engine power differed a bit in the P-40N.
The Take-Off Power was 1200 HP at 3000 RPM and achieved with 52" Hg Manifold Pressure.
WEP from one source was 1360 HP at 3000 RPM.
The Pilot's Manual shows WEP as 1480 HP at 3000 RPM with 57" Hg Manifold Pressure at 10,000 feet. This is the number I will be aiming for.
Military Power was 1125 HP at 3000 RPM with 44.2" Hg achieved at 17,000 feet.

Cruise Power is specified at Auto Rich and Auto Lean settings which I don't know how to represent in CFS so although a number will be added to the Check List, it may have a bit less meaning than it would imply.

Armament will be a full 6 x .50 Cal MGs with the maximum ammunition loadout
Bomb Load will be 3 x 500 Pound as was typical for a late model P-40.
The model will have all three internal fuel tanks unlike some of the early Ns that had he forward tank removed.
Capacity may have varied slightly with fuel tank construction but that will not be taken into account.

Weights will be for the P-40N-25 which are pretty typical:
6717 Pounds Basic Weight
200 Pounds Pilot
60 Pounds Oil -- Note that this is less than for earlier variants.
423 Pounds Ammunition
954 Pounds Internal Fuel
------------------------------
8354 Pounds Gross Weight

The weight used for the AIR file will be
6717 Pounds Basic
200 Pounds Pilot
45 Pounds (75%) Oil
------------------------------
6962 Pounds.

- Ivan.

[aleatorylamp]

Hi Ivan,
Have you noticed the downloads on the 2 models?
Indeed remarkable for CFS1 in this day and age.
Cheers,
Aleatorylamp

[Ivan]

I also am surprised at the number of downloads.
I wonder what it is about this particular model that is so much more attractive than other earlier P-40s I have released because to me, the quality (or lack) is all pretty much equivalent.
After the P-40N model is finished (and before its release), I need to do some testing for the flight model because I see a few faults.
The P-40K with a fin fillet will likely wait until other more interesting projects are done.

- Ivan.

[aleatorylamp]

Hello Ivan,
Perhaps the high download numbers reflect the interest and expectation generated by the discussions in the thread on how you were improving the P-40, with special emphasis on design accuracy, realistic detail and the flight model, to get it as close as possible to the real plane.
With the amount of information on the aircraft that is mentioned in the posts, it makes downloading a model more enticing, I´d say.
Cheers,
Aleatorylamp

[Ivan]

I just take the higher download count as an oddity.
It doesn't remotely come close to the 10,000 downloads I had seen on other less detailed models years ago.

There is nearly the same discussion and information on just about every project I work on, so that probably isn't the reason.
As always, I build these models because I like doing it, and the download count really isn't that important (which is why I have never uploaded anything to Simviation or Flightsim.com.)

Not important but still nice to see because it is a form of compliment.....

:untroubled:
- Ivan.

[Ivan]

SCASM cockpit, texture and animation tweaks were completed last night.
Next comes some more texture modifications and then then comes a major revisit to the flight model.
I am also debating on a Russian and a RAF Desert texture for this export only version.

- Ivan.

[Ivan]

The prior post was about the P-40M export-only version.
Now we will continue with the P-40N which still needs SCASM Processing even after all this time.

One might wonder why I am jumping back and forth between the M and N versions.
It is because from a visual model standpoint, the M is only a very minor change from the prior K version.
To get the N, it is easier to modify the M model than the K model.
The problem with finishing the M is that there is much less performance and other data available as compared to the N.
Since both aeroplanes use the same V-1710-81 engine, it makes more sense to tune the engine and performance for the N and export the engine back to the M version.

The version that will be built is the P-40N-15-CU because it has the proper combination of features I intend for this project.
The P-40N-20 was equipped with the Allison V-1710-99 which had simplified engine controls and a simplified Instrument Panel.
At this time, the P-40s were still leaving the factory with camouflage paint; It was not until the production of the last P-40N-40s that no paint was applied at the factory.

As usual, there is a bit of conflicting information on the P-40N.
How fast was it really?
The P-40N-1 was able to reach 378 MPH at 10,500 feet but was also the lightest version with about 450 pounds less loaded weight than later versions.
This did not make it the most effective version because the weight was mostly fuel, ammunition and guns as was the case for the P-40L.
Later versions were supposedly quite a bit slower with one version reaching only 350 MPH at 17,000 feet.

Next step was to do some Engine Tuning starting with the V-1710 from the earlier P-40K Hawk 87B Project.

.......

[Ivan]

The earlier Allison V-1710-39 and -73 (F3R and F4R) engines were fairly tolerant of over boosting.
The Allison Engine company agreed to permit settings as high as 60 inches Hg at which point these early engines were putting out around 1570 HP.
Some operators claimed to be running near 70 inches Hg for around 1700 HP....
This was from an engine that was only rate at 1150 HP.


The V-1710-81 installed in the P-40M and P-40N had higher supercharger gear ratios and was not nearly as tolerant of over boosting.
Its maximum output was 1480 HP at 57 inches Hg from an engine rated at 1200 HP.

From the standpoint of balance, these over boosted settings should be limited in some way and should be considered "War Emergency" settings.

With War Emergency Power in Combat Flight Simulator, we have yet another problem: It is not implemented correctly.

A Supercharger is used to pump additional air into the intake of an Engine.
Engines because of structural strength limitations have maximum manifold pressure limitations.
At Sea Level, the supercharger is generally capable of pumping much more air than the engine can take.
As the aircraft gains altitude, the outside air pressure drops and the supercharger's excess capacity is reduced.
At some point, the outside air pressure is low enough that the supercharger operating at full capacity is only able to pump enough air for the engine to reach its maximum Manifold Pressure.
This is the Critical Altitude.

War Emergency Power is higher throttle setting than normally allowed.
This higher setting may be due to the use of an anti-detonant / charge cooler such as Water, Methanol-Water, or additional Fuel injected into the engine or
it may require no anti-detonant and just rely on the heat-soaking ability of the engine and its cooling system.

The crucial point is that with the exception of additional oxidizers such as Nitrous Oxide (GM1 or NoS), there is no additional supercharger capacity.
Above the Engine's Critical Altitude, there IS NO ADDITIONAL CAPACITY from the supercharger than can be made available with War Emergency Power.
Unfortunately Combat Flight Simulator's WEP does not work that way.
It adds additional manifold pressure regardless of altitude.

We shall see very shortly how this affects this flight model.

.......

[Ivan]

The Allison V-1710-81 had higher supercharger gearing than earlier engines.
As such one would have expected more power to be absorbed by the supercharger.
In this case, because I expected the power drop-off to be slower than for the earlier Allisons,
the Torque was reduced instead of increasing the Friction.

Here are the results:
Target: 1200 HP at 3000 RPM (52.0 inches Hg) at Sea Level (Take-Off Rating)
Actual: 1210 HP at 3000 RPM (52.0 inches Hg) at Sea Level (500 Feet)

Target: 1480 HP at 3000 RPM (57.0 inches Hg) at 10,000 feet (WEP)
Actual: 1479 HP at 3000 RPM (57.0 inches Hg) at 10,000 feet (WEP)

Target: 1125 HP at 3000 RPM (44.2 inches Hg) at 17,000 feet (Military Rating)
Actual: 1120 HP at 3000 RPM (43.2 inches Hg) at 17,500 feet (Normal Maximum)

Unfortunately because of CFS handling of WEP, we have this:
Actual: 1384 HP at 3000 RPM (51.0 inches Hg) at 17500 feet (WEP)

Speeds:
Max: 312 MPH @ Sea Level
WEP: 322 MPH @ Sea Level
These numbers are fairly reasonable but are a bit slower than the earlier Warhawks
Without WEP, this is slightly slower than the Merlin Warhawk but with WEP it is slightly faster.

WEP: 371 MPH @ 10,000 feet
This is about where I would have wanted it.

Unfortunately there is also the following:
WEP: 389 MPH @ 15,000 feet with 1528 HP....

Service Ceiling is around 32,700 feet with Absolute Ceiling near 33,500 feet with 50% Fuel.

Other than the high altitude WEP effects, this seems pretty close.
Since WEP is only available for 10 minutes, it is good for about 3 speed runs starting at maximum non-WEP speed.
With the extra power, this aeroplane would have much more agility than it should between 10,000 and 20,000 feet.

- Ivan.

[glh]

".....A Supercharger is used to pump additional air into the intake of an Engine.
Engines because of structural strength limitations have maximum manifold pressure limitations.
At Sea Level, the supercharger is generally capable of pumping much more air than the engine can take.
As the aircraft gains altitude, the outside air pressure drops and the supercharger's excess capacity is reduced.
At some point, the outside air pressure is low enough that the supercharger operating at full capacity is only able to pump enough air for the engine to reach its maximum Manifold Pressure.
This is the Critical Altitude. ....."

"At Sea Level, the supercharger is generally capable of pumping much more air than the engine can take." True, but I don't believe you can model the wastegate in the FS model. This is a proportional air valve that is left open at low altitudes to just dump most (if not all) of the (turbo)supercharger output as it is basically not needed at this point. Thus, the engine basically runs only in normally aspirated state at atmospheric pressure at sea level to a couple thousand feet altitude.

"As the aircraft gains altitude, the outside air pressure drops and the supercharger's excess capacity is reduced." My understanding of the process is that the (turbo)supercharger output remains constant at rated output by design through the altitude range. However, the wastegate now starts to close as the aircraft ascends in order to maintain the manifold pressure to contribute to engine power. Thus, the dumping is gradually closed off and the (turbo)supercharger output is now gradually applied to the engine.

"At some point, the outside air pressure is low enough that the supercharger operating at full capacity is only able to pump enough air for the engine to reach its maximum Manifold Pressure.
This is the Critical Altitude. ....."

When the wastegate is fully closed, the (turbo)supercharger is now applying rated output fully to the engine. Measured by the MP rating (and maintaining it) at some power setting (military power ?), the "Critical Altitude" has been reached. Any further increase in altitude will result in decreased MP/engine power as the (turbo)supercharger has now reached its limitation due to:
a.) the outside air pressure.
b.) the design parameters of the (turbo)supercharger.

[Ivan]

Hello GLH,

Welcome to Combat Flight Simulator.

Thanks for some additional explanations.

I was being deliberately vague with the mechanics of specific implementations because the actual implementations vary in lots of ways.
Your mention of a Waste Gate tells me that you are probably discussing Turbo Superchargers which are compressing only Charge Air.
Some of the Superchargers being discussed here are compressing Air and FUEL and would not be dumping the excess out the side.
Some others such as those on the Daimler Benz DB 600 series engines used a fluid clutch with slippage that varied with altitude.
Others are just throttle limited.

The major point in this whole supercharger discussion is that past the critical altitude, WEP cannot provide any more boost whether it is on or not.

- Ivan.

[aleatorylamp]

Hello Ivan,

For my current Baltimore Project, CFS1 WEP impementation and aircraft ceiling is also a problem.

After reading this latest interesting exchange on turbo-superchargers here on this thread, and also having noted the way that your MitchellC .air file includes WEP within the normal procedural maximum power, it occurred to me that this could be the most feasible solution. Without using the CFS1 WEP option, ceiling performance would remain unaffected.

Of course, it is not a new idea to include the full Manifold Pressure in the Engine Parameter Section, so as to get full HP at normal full throttle, leaving WEP without activation, but one could then edit the throttle gauge bitmap with a red area at the end of the Throttle Lever Travel: This would define the WEP area, not to be invaded in normal circumstances! Of course it would have to be carefully dimensioned using the Beckwith gauge to get the position right.

Also, simmers would obviously have to be careful using the throttle lever in order to maintain realism, because in this case, the engine would not break down after time runs out if the throttle lever stays in the WEP area. Basically, this would be the only drawback for this possible solution.

If this idea is useless, please ignore this post!

Cheers,
Aleatorylamp

[Ivan]

Hello All,

I had meant to acknowledge it, but forgot: GLH actually gave a pretty good explanation of the way Turbo Superchargers work.
The only disagreement I had with his comments were about Turbocharged aeroplanes just trying to maintain naturally aspirated power levels.
I believe that all the Turbocharged aeroplanes of the time were equipped with an additional mechanical supercharger and were running manifold pressures well above 30 inches Hg which means they were running higher than naturally aspirated settings.

Hello Aleatorylamp,

The problem with the bitmap "Gating" that you are describing is that the non-WEP throttle position limit would change with altitude.
Perhaps we can build a Throttle Gauge that would enforce this kind of setup?
That would also presume that the Engine Control Panel was the only control available.

- Ivan.

[aleatorylamp]

Hello Ivan,

The idea would only be valid if this were to be a better solution than to have a more-or-less inaccurately adjusted ceiling with WEP.

The only suggestion for a red WEP zone on the Throttle gauge bitmap, would be to have an additioinal initial orange zone which would mark the transition zone, depending on altitude, between maximum normal throttle and WEP positions. Here there could be three black lines indicating low, medium and high altitude for the beginning of the WEP position.

I suppose Take-off power, which is also a 5-minute affair, would be in the WEP area rather than within the normal maximum power range.

An ideal situation for this idea to work would be if normal maximum power were to coincide with an 80% or 90% throttle positions, because of the keyboard keys that can be used, so for example take-off would be with 90%, normal maximum with 80%, and WEP with 100%. That would be very convenient...

The first thing to do would be to see where the maximum normal power lies with the Beckwith gauge giving a normal Hp reading at low, medium and high altitudes. It will be curious to see what percentage Hp it would be.
Of course the equivalent of 100% normal power percentage changes because 100% would in this case include WEP.

Perhaps, as a starting point, I´ll experiment a bit changing the stock P47 air file and see how it affects power and how the throttle gauge position reacts, if WEP is included in the normal procedural performance range.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

I installed a duplicate of the stock P47D for comparison, with a modified .air file which included WEP within the normal throttle lever travel. I raised the MP parameter from 52 to 56, and set WEP at 0.

I conducted trials every 5000 ft, and noticed that normal maximum power with the modified .air file was at 92% of maximum throttle position, with 52.1 Mpsi.

This appeared to be consistent upto 25000 ft. The stock .air file maintained its 52-56 Mpsi values, and the modified one kept 52 Mpsi for 92% power, so a red zone on the throttle gauge bitmap may be of some use for this kind of WEP incorporation into the normal travel of the throttle gauge.

As of 30000 ft, however, the modified .air file could only provide the non-WEP power of the stock .air file, but needed 100% power to do so.
Update: As critical altitude for the P47D is 27000 ft, it´s logical.

This would mean that a red zone on the throttle gauge only indicates an effective and careful use of WEP upto this altitude, after which full power can be maintained with full forward throttle as WEP is no longer operative.

30000 ft: Stock .air file Mpsi fell to 45.1 and 49.6 (WEP).
Modified .air file, 92% throttle fell to 42.3 Mpsi, and 100% throttle was only with 44.7 Mpsi, and gave the non-WEP power of the stock .air file.

At 35000 ft: Stock .air file Mpsi fell to 35.5 and 39.1 (WEP).
Modified .air file, 92% throttle fell to 33.5 Mpsi, and 100% throttle was only with 35.5 Mpsi, and gave the non-WEP power of the stock .air file.

40000 ft: Stock .air file Mpsi fell to 27.9 and 30.7 (WEP).
Modified .air file, 92% throttle fell to 26.2 Mpsi, and 100% throttle was only with 27.9 Mpsi, and gave the non-WEP power of the stock .air file.

Although the ceiling is quoted as 42000 ft for the P47D, neither .air file was able to maintain this altitude.

At altitude, however, as one would have expected, the modified .air file seems to deal more realistically with the WEP power.

I thought this information is quite interesting, and may be of some use.

Update:
P.S. I did the same comparison with the P51D and here the normal max. was at 90% throttle if WEP was included in the throttle lever travel, and the altitude at which WEP started to dwindle was 25000 ft, as P51D critical altitude is 24000 ft. Actually the 90% position is quite convenient because of key "9" for normal maximum throttle.
In conclusion, this could perhaps mean that in CFS1, changes in altitude below critical altitude would not affect the throttle position at which WEP would start if WEP were implemented within the normal throttle lever travel, and hence would not require making a special throttle gauge which takes altitude into account for the threshhold between WEP and non-WEP.

Cheers,
Aleatorylamp

[Ivan]

SCASM edits are now finished for the P-40N.
Most of the Hawk 87 series has been nearly the same as far as location of pieces in the SCASM SCX source code.
Sometimes one or two pieces may need to be located because their address (and thus the Label) has changed from the prior project.
This project has had the most changes of any in the Hawk 87 series.

The Camouflage / Markings need a few edits and possibly an alternative paint scheme added.
The DP file is not significantly changed from any of the prior versions.

The most significant task remaining is to tune the low speed handling characteristics to remove some odd behaviour.

The screenshot shows what happens when the MDL is edited to use new textures and the new textures have not yet been created.....

- Ivan.

[Ivan]

A duplicate Allison V-1710-81 engine was built up for the P-40M as well.
There was a slight bit of difficulty when power readings were close but not exact.
It turns out the technician doing the final assembly had included some mismatched accessories which was soon corrected.

The aeronautical engineers are doing some testing on the P-40N for directional stability.

- Ivan.

[Ivan]

There hasn't been much activity on the Hawk 87W (P-40N) but there has been some.

The SCASM processing is now complete.
This means that further texture updates will be much simpler because the files are BMP format.
The animation changes are also complete.

One thing that has bothered me for a while is that the low speed handling of the P-40 seemed to be too good.
There appeared to be way too much control authority.

My task over the last couple days was to adjust the low speed control without compromising the generally excellent handling.
After creating spreadsheets to graph the control effect versus aerodynamic force (1/2 Rho V^2) and making adjustments,
I found that what I arrived at for new values was not significantly different from what is currently in place.
In other words, it appears to be pretty well tuned (or where I want it to be) now.

There was one area in which the values were different; My new values for Rudder Effect were a bit lower at low speed.
The question then becomes: Is the Rudder Effect too high or is the Propeller Torque Effect too low?
In any case, the Low Speed Rudder Effect is only noticeable if the Tail Wheel is made free castoring instead of steerable which means that in the actual flight model with a steerable Tail Wheel it is invisible.

The other minor change is to test a different texture pattern on the Spinner.
The later model P-40 especially when used by the RAF, RAAF, and RNZAF had a tendency to use two colours there.
The texture is a bit harder to apply than usual because it is Fore-Aft instead of Left-Right.

- Ivan.

[aleatorylamp]

Hello Ivan,
Sounds as though progress is being made!

At least you have done something, wheras in my case I´ve been totally inactive - with the German course for waiters there´s no energy left for building aircraft. The timetable is two hours daily at midday and it gets in the middle of cleaning, cooking and lunch and I´ve got a kind of buider´s block"! Perhaps when the private students have their holidays as of June or July I´ll have some free afternoons to pursue FS building.

Regarding the steerable tailwheel in FS, I find the way it is controlled in the opposite direction so confusing that I prefer not to have it.

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

Actually I have been working on other projects.
Some are even CFS related.
You might have seen my thread in "Other Hobbies".
There are a few things in that direction that needed pursued.

- Ivan.

[Ivan]

The Technicians and Test Pilots have been working on a little project with the P-40N which has finally come down to a matter of fine tuning.

Several of the staff were on the Me 109E Trop project and used that aeroplane to experiment with directional control parameters to try to fly a "Knife Edge". The lessons from that project were added to the P-40N where they are working as expected.

The screenshot shows the P-40N maintaining altitude though drastically losing airspeed while doing it.
The adjustments are needed to lower the amount of airspeed that is lost so that this maneuver can be flownfor longer.
Note the low airspeed and extreme yaw angle.

- Ivan.

-

[aleatorylamp]

Hello Ivan,
Wow! I believe the Germans call it the "hammerhead".
It is a very intriguing manouever, this one, how to have the fuselage and vertical stabilizer as sustaining surfaces... totally mind boggling!
Cheers,
Aleatorylamp

[Ivan]

It seems like CFS Superchargers have a bit more capability than I had thought.
Aleatorylamp came across an interesting supercharger power reduction by adjusting a parameter identified as

WEP Pressure Change Rate (0.528 or Zero)

This parameter apparently works as modifier to the SuperCharger Boost Gain parameter.
If set to Zero, there is no additional power when using WEP above the critical altitude.
By doing this, the high altitude WEP effect which was causing problems is gone.

Unfortunately, the testing also showed that the parameters which were modified to allow knife-edge flight affected lateral stability and control in a very unfavourable way so until I can compensate in the AIR file this feature will not be included.

- Ivan.

[aleatorylamp]

Hello Ivan,
I´m glad that regulating the WEP Pressure Change Rate has cured the P-40´s excessive WEP effect at altitude, and hopefully you´ll find a way of correcting the knife-edge lateral stability side-effects!
Cheers,
Aleatorylamp

[Ivan]

The P-40N didn't have the greatest problems with WEP at altitude; The P-40K and P-40E were quite a bit worse.

The P-40K also has a new visual model which may the excuse for an updated release.

In playing with the P-40N, it just did not look right without a shark mouth, so the last couple evenings were spent in repainting the cowl to put a shark Mouth there.

- Ivan.

[aleatorylamp]

Hello Ivan,
The Sharkmouth is definitely an asset for this model!
Cheers,
Aleatorylamp

[Ivan]

Last Night, I ran a test of the P-40N's Climb Performance.

Results are the following:
Best Climbing Airspeed is around 195 MPH TAS.
Yes, I know it varies in IAS with altitude.

While holding 195 MPH TAS, Climb Rate was
2800 feet / minute at 500-1,000 feet altitude
2885 feet / minute at 5,000 feet altitude
3000 feet / minute at 10,000 feet
3085 feet / minute at 12,000 feet

At 5,000 feet, 195 MPH works out to be about 180 MPH IAS, so that is the number I will use for record.
The climb rates seem to be where I would have wanted them.

The plan is to test again using IAS at some point to find the Indicated Air Speed at which I can get the best climb rate.

- Ivan.

[Ivan]

Starting with 55% fuel the P-40N Service Ceiling appears to be
32,700 feet with 509 HP at 293 MPH TAS which is pretty close to 180 MPH IAS.
Remaining fuel was 64.3 Gallons (73.5 Gallons would be 50%).

Absolute Ceiling appears to be just over 35,050 feet with 442 HP.

Unfortunately for me, I started this test fairly low at 27,500 feet, so the actual test took much longer and burned more fuel that I expected.
The Service Ceiling is a bit higher than I would have wanted, but this was done with autopilot.
A manually flown test would probably end up a bit lower but also would be a bit harder to reproduce.

I will probably repeat this test at some point to try to have it finish with 50% fuel.

- Ivan.

[aleatorylamp]

Hello Ivan,
Thanks for this useful information. It comes in very handy for my Baltimore Mk.V and MkIIIA/IV tests.
Cheers,
Aleatorylamp

[Ivan]

A second test of the Service Ceiling gave 32,400 feet with about 71.5 gallons fuel remaining.

Climb Rate specifications seem to vary quite a lot depending on the test conditions.
A test report of the P-40N-5 running at 44 inches Hg showed only a bit over 2200 feet / minute.
A test report of the P-40N-1 running at 57 inches Hg showed 3100 feet / minute.
My own test of my "P-40N-15" at 52 inches Hg gave about 2800 feet / minute which seems quite in line with the actual test reports.

It has been uploaded.

Hello No Dice,
You wanted a P-40N for your birthday a couple years back.
This version is either a few years late or a month or so early.
I will send you a copy shortly.
(Anna Honey says I need to prep for some guests now.)

- Ivan.

[aleatorylamp]

Hello Ivan,
A very nice quality-contribution, this long-tail, and a great flier too!
This time I was careful on take-off and my pride was left intact!
Cheers,
Aleatorylamp

[Ivan]

Thanks Aleatorylamp.

I liked the way it turned out also.

Next step is to go back and finish up a P-40M which should not be difficult and also to rework the P-40E and P-40K flight models.
Then there are the P-40C models..... The list is endless.

- Ivan.

[aleatorylamp]

Hello Ivan,
It´s turning out to be quite a unique collection!
Aleatorylamp

[Ivan]

am in Cambridge, MAssachusetts at the moment and on an iPad.
Not going to be on much for a few days.

- Ivan.

[Ivan]

Version 011 contains an updated AIR file.
There are no performance changes.
The Aircraft Type Identification has been changed.
The Length specification in the Description has also been changed.
(The earlier version listed the length of a Short Tail Warhawk.)

- Ivan.

[Ivan]

A while back, after receiving an email about No Dice, I was thinking about how he always had a way of giving praise for the projects I had released.
I went back and found one of the old threads: The one that described the Merlin P-40F, my latest project at that time.
As usual, he had some nice compliments.

I followed the thread a bit and my plan at the time was to work on a proper Long-Tail P-40 and then build the Long Tail versions of the Merlin P-40. I had actually gotten pretty far as detailed in THIS thread.
The P-40M was completed but not released because I could not decide on a good paint job.
The P-40K was also worked on though I cannot remember where I left it.
The P-40N was completed and released and even had an immediate update for an error in the description.

I never actually went back to the Merlin P-40.

A few months ago, on another forum, there was a very long running discussion about the merits of the Merlin P-40 and its relative performance as a fighter against its contemporaries. There was quite a bit of information presented and some of it resolved some contradictions that I had encountered when working on the original version of the flight model.
These discussions and the old thread "Ivan's Latest and Greatest" (http://www.sim-outhouse.com/sohforums/showthread.php/98532-Ivans-Latest-and-greatest) were the reason behind this latest round of updates.

The updates turned out to be quite easy.
The model updates were lifted from the P-40N; The longer tail was designed specifically so that the pieces would match easily to the current version of the Short-Tail Warhawk.
Texture updates were tedious as usual, but not as bad as they could have been because with the design of the Long-Tail, the textures were arranged so that only one mapping edit was needed and only one texture needed to be edited (in theory).

Attached are some images of the completed textures as applied on the model.
There are more images and historical information in the thread mentioned earlier.

- Ivan.

[Ivan]

As part of the updates to the flight model of the P-40F, I thought it would be a good idea to manufacture a custom propeller to replace the current propeller which probably came from the stock P51D.

None of the P-40 projects that I have released thus far have had anything but a stock propeller with all of its problems.
Doing a quick comparison showed that just about all the P-40s had pretty comparable propellers with only small variations because of engine output and critical altitude. The only real exceptions were the Merlin equipped versions which used a different reduction gear ratio.

With this in mind, it made more sense to build a propeller that was best suited for the Allison P-40 and adapt it to the Merlin as was probably done in real life. The P-40N was selected as the development aircraft because its flight model was the most recent and least likely to have other problems.

The First screenshot shows a speed run after testing to determine engine output at each altitude.
370 MPH @ 12,500 feet with 1351 HP on Military Power.
370 MPH can also be achieved at 10,000 feet with 1479 HP on War Emergency.
Critical Altitude is 12,850 feet.

Second and Third screenshots show current Propeller Tables 511 and 512 which have the standard Perpetual Motion curves.

- Ivan.

[Ivan]

As some folks may already know, a Propeller for Combat Flight Simulator is really composed of two Records:
Record 511 - Propeller Efficiency
and
Record 512 - Propeller Power Coefficient

In my opinion, just about any reasonable Propeller Efficiency Table is a suitable starting point as long as it doesn't have the "Perpetual Motion" curves AND as long as the Propeller Power Coefficient Table matches it.

For a starting point, I decided to use the original Record 511 with minimal but essential modifications.
The efficiency curve for each blade angle now drops to Zero when the Advance Ratio is high enough that the blade cannot maintain a positive AoA. Note that there is also a bit of an allowance for camber and also for the problem that 0.2 is a pretty large change in Advance Ratio but is the smallest increment we can represent in the table and still have a reasonably wide range of speeds.

To cover the practical range of speeds that the P-40 was capable of, the maximum Advance Ratio was extended to 2.8 which at 3000 RPM would be the equivalent of 525 MPH. This would be pretty close to the maximum speed expected in a power dive.

Note that the stock P-51D Record 511 only goes to J=2.2 or the equivalent of 402.6 MPH which doesn't even cover its entire level speed range much less its potential speed in a dive. This is actually a neat way to cheat. At the upper end of the speed range, Propeller Efficiency tends to drop very quickly but since the simulator uses the value for J=2.2 if J is above 2.2, your propeller would be providing much more thrust than it should.

The added columns for 2.4, 2.6, and 2.8 are what I believe are reasonable continuations of the curves.
If there are any mistakes, they should not affect the first round of testing which was at or below J=2.0 (375 MPH).

The original Record 512 had too many odd curves so I decided to use a replacement that I generated using a spreadsheet I wrote for the purpose a couple years ago. The curves are smooth because they are generated by parameters fed into a formula.
The highlighted cells show the places where I tried to match the original Power Coefficient curves.

Test Results to Follow.

- Ivan.

[Ivan]

The updated AIR file loaded into CFS without problems.
That was a good sign. Formatting errors in the past have caused load failures.
Engine started - Another good sign.
Idle Speed 496 RPM - Unchanged from original which made me suspect I might be using the wrong AIR file.
Sea Level Military Power (1210 HP)
312 MPH - same.
Propeller Pitch 35 Degrees - same
1230 Pounds Thrust - Higher! - Original was 1225 Pounds.

Sea Level War Emergency Power (1358 HP)
322 MPH - same.
Propeller Pitch 37 Degrees - same
1302 Pounds Thrust - same.....

10,000 feet War Emergency Power (1479 HP)
371 MPH - same.
Propeller Pitch 41 Degrees - same
1333 Pounds Thrust - Original value unknown, I didn't write it down.

12,500 feet Military Power (1351 HP)
372 MPH - Higher. Original was 370 MPH
Propeller Pitch 41 Degrees - same
1242 Pounds Thrust - Higher. Original was 1219 Pounds.

For a first attempt, this was a LOT closer than I was expecting.
I believe the slight differences are due to slight differences in propeller pitch (less than a degree) and my tuning of the Power Coefficient Table was done by eyeball. There are also limitations with trying to match the odd curves of the original tables (not that I want to) using math formulas.

The Efficiency Table definitely needs to have some of the mismatched curves smoothed out and adjusting the efficiency down slightly to reproduce the same maximum speed is pretty trivial.
The question is whether or not the adjustment is really necessary.....

- Ivan.

[Ivan]

Yesterday, I had to work with my Son on a writing assignment and didn't get much time with the simulator until fairly late in the evening.

As can be seen by the title of this post, there have been quite a few changes.
I was already pretty close, so the first set of changes (Mod2) was just to make some basic corrections to both Tables.
These changes were simple things such as smoothing out the curves where there were obvious continuity problems and adjusting the efficiency numbers at 0.0 Advance Ratio. (In theory this should be zero but that isn't how CFS works.)
The Power Coefficient Table was also adjusted at the coarse pitch angles to be closer to the original even though it should have no effect at the power levels and speeds reached by the P-40N.

There was quite a bit of flight testing especially for level acceleration during which I found that the low level maximum speed was achieved just past one of the dips in the Propeller Efficiency curve (caused by interpolating between 30 degrees and 35 degrees).
This created an interesting situation which I entirely missed in my previous test runs because I had been using War Emergency Power to get close to the maximum speed before switching back to Military Power to allow speed to climb the last couple MPH.
The WEP was pushing past the dip. Without WEP, maximum speed was barely above 300 MPH - Sometimes....

Why SOMETIMES?
My testing protocol is to record a speed as "maximum" if it has not increased by 1 MPH in 15 seconds.
The timing is done manually so I may be a couple seconds off at times.
Let's say that the acceleration slows at 304 MPH so that to reach 305 MPH SHOULD take 14 seconds.
If my timing is fast, I record it as 304 MPH and quit.
If my timing was a little slow, I might accept it as 305 MPH and then see how long it took to reach 306 MPH.
At certain parts of the Efficiency curve, the acceleration might actually increase and not slow down again until overcome by drag at 312 MPH.

Sea Level Military Power (1210 HP)
313 MPH - Higher
Propeller Pitch 34 Degrees - Finer Pitch
1235 Pounds Thrust - Higher! - Original was 1225 Pounds.

12,500 feet Military Power (1351 HP)
370 MPH - Same.... Back down to original speed
Propeller Pitch 41 Degrees - same
1222 Pounds Thrust - Higher. Original was 1219 Pounds. This is about as close as it gets.

In reality it took more than just three more versions of the Propeller Tables.
It was more like three major revisions and a dozen minor revisions for fine tuning.
I also found out that one of my tools was very unreliable and needs a bit more programming work.

Next comes the Climb and Service Ceiling Tests which are sure to be followed by further revisions.

- Ivan.

[Ivan]

This update really should be described as testing of Mod 5 version 65 or something along those lines.
There have been enough little changes that I haven't bothered to keep an accurate count.
The week has been very busy but most of it has not been related to flight simulators. Real life intrudes sometimes.

The Climb Test was pretty much a complete failure.
The Propeller would select way too coarse a pitch and climb rate was several hundred feet per minute too low.
My original intent was to hold the two endpoints of each curve in place and only adjust the curve as needed but that was not enough to come up with a working set of graphs for Table 512.

Altering the endpoint at Zero Advance Ratio seemed to be the best idea; I could significantly improve the shape of the curves and all that would happen is that the Idle speed would change.
This was done and the Climb Rate was greatly improved. Idle speed went from 496 RPM to 417 RPM.

The minor adjustments of the curves to improve Climb also seemed to make the Speed at 500 feet a bit worse.
The maximum was still 312 MPH most of the time, but Acceleration felt slow. This was not surprising because the Propeller Pitch only reached 33-34 degrees which coincided with where both the 30 degree and 35 degree curves dropped off just past J=1.6.
Adjusting the curves at J=1.6 didn't help much because the real value was J=1.664 and the 30 degree curve dropped to Zero at J=1.8.

The last idea I tried was to use the Power Coefficient Table to reduce the power requirements for 35 degrees at J=1.6 and even out the curves before and after and it seemed to solve the problem.

Test results have now changed to the following:

Sea Level Military Power (1210 HP)
317 MPH - Significantly Higher
Propeller Pitch 35 Degrees - Same
1264 Pounds Thrust - Significantly Higher - Original was 1225 Pounds.

12,500 feet Military Power (1351 HP)
370 MPH - Same.... Back down to original speed
Propeller Pitch 41 Degrees - same
1221 Pounds Thrust - Higher. Original was 1219 Pounds. Basically the same.

Climb Rate at 5000 feet is 2900+ feet / minute or pretty close to previous.
Actual climb rate is probably between 2950 and 3000 feet / minute but autopilot isn't that precise.
Speed is 180-185 MPH IAS.
Power is around 1260 HP.
Climb at WEP was not tried.

Climb Rate at 10,000 to 13,000 feet is about 3000 feet / minute at 175-185 MPH IAS.
Speed wasn't precise because it changes slightly during the climb and a couple MPH difference does not appear to make any significant difference.
Power is around 1323 HP.

Climbs were done with nearly full fuel so rates should be a bit higher with only partial fuel.

Now for a Service Ceiling Test

- Ivan.

[Ivan]

The slightly lower climb rate bothered me a little, so I made a small change to the Propeller Efficiency at J=0.8.
I also tried adjusting the Power Coefficients to be able to hit full RPM a little earlier but that did not work out well.
The new climb rates are nearly unchanged but they can be achieved at a wider range of speeds.

Climb Rate at 5000 feet is about 2950 feet / minute and increasing to almost 3000 feet / minute.
Speed is 175-185 MPH IAS.
Power is around 1260 HP.

Climb Rate at 10,000 to 13,000 feet is about 3000 feet / minute at 165-175 MPH IAS.
Power is around 1323 HP.

Climb Rate at 14,000 feet falls to around 2800 feet / minute at 165-175 MPH IAS.
Power is around 1275 HP and falling quickly.

Service Ceiling seems to give a range of values from 32,100 feet to 32,700 feet.
Typical Results:
Service Ceiling: 32,580 feet
Speed: 293 MPH TAS (174 MPH IAS) - Propeller Pitch: 35 Degrees.
Power: 514 HP
Remaining Fuel: 75.4 Gallons.

After the Service Ceiling test, I tried a high speed dive and then concluded with an actual landing without breaking the aeroplane. The wobbly landing tells me I need a LOT more practice.

Attached are the updated Propeller Efficiency Table and a Screenshot of a Warhawk that didn't miss the runway on landing.

- Ivan.