Warhawk

[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