CFS1 Curtiss-Wright AT-9 "Jeep" Work In Progress.

[aleatorylamp]

Hi all, and Hi Ivan!
I have started this new thread for the Curtiss Wright At-9 "Jeep" I have under construction. It was also called "Fledgeling", and the manufacturer´s number was CW25.
The model is available here for anyone to look at, try out and if possible, comment on and maybe even cooperate with:
http://www.sim-outhouse.com/sohforum...id=19&id=19844
My idea is not only to facilitate questions and answers regarding the progress of this WIP - work in progress - open on its own thread, but possibly also issue an invitation to anyone wishing to cooperate.
In fact, it could be maybe even a joint hobby venture, if you like!

At the moment, the model is roughly at 75%.
- There is neither a hollow, transparent cabin, nor instructor and student pilot.
- I´m still curing little bleedthroughs and gaps between parts in certain places.
- Because of moving control surfaces, perhaps other groupings are more effective, but cause bleedthrough elsewhere, specially in the tail.
-Textures are a bit simplistic as yet, and I need more expertise.
-The greatest problem is the flight dynamics - the FS98 FD work great! ...not so the CFS1 ones.

CFS1 FD:
It must have been quite a handfull for pilots, and the FD are by no means correct.
I have found comments like:
-I had great fun doing acrobatics.
-A quick snap of the yoke could generate a high speed stall.
-Approach and landing: Always maintain air speed=110-120mph!
-On power off landings you viewed the air strip through the upper window!
-A dead stick landing was done at a 45 degree angle as there was little if any gliding ratio.
-One told of losing an engine and barely making it back to the field, ruining the good engine in the process.
-They wouldn't fly on one engine.
-Full flaps were never set as speed went down too far, risking stall.

The Propeller (tables 511 and 512):
I´m trying to adjust the CV prop for the AT-9 Jeep. As the engines are 295 Hp radials, presumably non-supercharged, I´m having difficulty in adjusting the props to the engines.
I managed to make AAM work on my computer, by putting it into the C: directory, and the visual display of the propeller graphs seems more meaningful than the numbers in AirEd.
All stock aircraft have really strong, large multi-cylinder engines, above 1000 hp, and the propeller graphs (511 and 512) appear to be the same for all, there being no example for a 300 hp engine.
My experience on tables 511 and 512 is reduced to the 25 degree column for fixed pitch props, and as I was getting about 90 hp after putting in the engine details, I patiently lowered all the propeller thrust and efficiency graphs, and I got upp to 230 or 240 hp, but to get the required power, I had to put the torque graph up to 85 and reduce the friction to 36, which is not really correct, I believe.
I´ve managed to get top speed correct, but accelleration is very slow, and as soon as a climb is started, speed falls off very quickly.
Also, ailerons and turning are sluggish - not so on the FS98 FD!

So the bottom line is, I would indeed appreciate some help and guidance!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

That was about as clear an invitation as I have seen.

Regarding Propeller Tables:
My recommendation as before is to tune the Engine output and Propeller Tables separately.
With the Engine, you want to get your proper output at full RPM at various altitudes.
If the existing Propeller will not allow you to reach full RPM, then adjust the Propeller Diameter or Pitch until it does.
The Propeller Tables go down to 15 Degrees and the Diameter can get as small as you like.
Don't worry about actual aircraft performance to start.

Regarding all those 1000-2000 HP stock CFS Engines, The actual Horsepower isn't really all that important and isn't a good determination as to whether the Propeller Tables will work with your aeroplane.
The important factor is Propeller POWER Coefficient and those vary quite a lot.
(From memory, I believe the Hawker Hurricane has the lowest Cp and the Me 109G has the highest.)

If that still doesn't quite work out, you can simply reduce all entries by a constant amount.
I wrote my own utility to do the AIR File dump, but Jerry Beckwith has a utility that does it a bit nicer than mine.

As for pilot's reports, it sounds like some of those anecdotes are probably a bit exaggerated.
My understanding from what little I have read about this aeroplane is that the speed range is very low.
Also, when you do single engine testing, you should get radically different performance depending on whether the dead engine is the critical one.

Cool Looking Project!
- Ivan.

[aleatorylamp]

Hi Ivan,
Once again, thanks very much for your support and interesting answer!
Yes, they exaggerated with looking at the runway through the top window on a dead-stick approach... but what they mentioned about it being like a hotrod must have been no joke!
I forgot to mention the prop diameter - it´s 8 ft, and there should be 295 hp at 2300 RPM, and at the moment what I´m getting is quite close, although with the torque graph too high at 85, the friction graph too low at 36, and Manifold pressure too high at 40 (even though it´s not supercharged), but it´s very slow on accelleration. Entering more normal values for these values only makes it even worse as it loses 25% power.
I was changing the values on the prop thrust graphs for the 15 to the 65 degrees and found the more or less working combination in the present .air file: Values range from 0.023 to 0.75. Lower combinations starting at 0.015 and going to 0.33, and then others starting higher at .04 and going upto 0.65 were both worse. The next one I´ll try is one starting at 0.023 and make it go up to 1 and see if it improves.
Cheers,
Aleatorylamp

[aleatorylamp]

A new entry has been added to Add-Ons Library, category CFS 1 Aircraft Add-Ons

Description: CFS1 Curtiss Wright AT-9 "Jeep" Work In Progress.

Work in progress upload: Unfinished visual model, textures and FD. Suggestions and cooperation welcome!

Advanced 1941-43 twin-engined WWII trainer, built to prepare pilots for the new generation, high performance aircraft like the B25, B26 and P38. Deliberately designed unforgiving and difficult to fly and land, it was however reported as delightful by some - like a hotrod. It was powered by two 295 hp Lycoming R680-9 9-cyl radials, and had a top speed of 171 kt (197 mph). 792 units were built. By Stephan Scholz.

To check it out, rate it or add comments, visit CFS1 Curtiss-Wright AT-9 "Jeep" Work In Progress.zip
The comments you make there will appear in the posts below.

[aleatorylamp]

Hi Ivan,
Just to confirm, extrapolating from the Giant´s list of "J" values
to complete it for the Jeep, would this be correct?

8 Foot Propeller Advance Ratios:
0.0 - Zero MPH as you would expect
0.2 - 26 mph
0.4 - 53 mph
0.6 - 79 mph <-- Giant´s Target Speed is 85 mph (just a little above this).
0.8 - 105 mph
...now continuing your list:
1.0 - 131 mph
1.2 - 157 mph
1.4 - 183 mph
1.6 - 206 mph <-- Jeep´s Target speed is 197 mph (just under this).

Also, from your previous post, as a provisional measure, I gather you were suggesting using the Hurricane´s propeller graphs, but using a much smaller propeller, e.g. 5 ft?

Thanks and cheers,
Aleatorylamp

[aleatorylamp]

Hi Ivan,
Probably good news:
I was wondering if I could bounce a few things off you:
I managed to find a couple of graphs related to Cessna engines and propellers, all rather generic, but more within the size/power range than the powerful CFS1 stock aircraft.
I entered the new data into tables 511 and 512 and immediately things improved noticeably, especially the acceleration, which is now close to what one would expect from this aircraft.
The aim is 171 kt at 500 ft, with 295 Hp at 2300 RPM, so the next steps were the friction and torque graphs. (Drag was already OK from before).
For the friction graph, AirEd info mentions 12% of the Hp, so I put in 295x12/100=35.
Then I brought down the torque graph from 85 to 81 to get my 295 hp. and it´s all bang on except the RPM, which is still 11 RPM too slow at 1289, as before, but I´d say that´s fine.
Would you say this is criteria is reasonable?
Cheers and thanks,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I believe your calculations for Advance Ratio are a bit off.
Without doing a whole lot of research, here is what I get for general information on the AT-9 and its Lycoming R-680 engine:

Propeller Diameter - 8.0 feet - I just took the value you gave.
Propeller Gearing - 1:1 - Direct Drive - This is from Jane's. The aeroplane isn't there, but the Lycoming R-680 description is there.
Maximum RPM - 2200 - Some versions were up to 2300 RPM.

From this, I get the following:
J ---- MPH
0.0 - 0
0.2 - 40
0.4 - 80
0.6 - 120
0.8 - 160
1.0 - 200

At 2300 RPM, J=1.0 only changes to 209 MPH. I wonder why we are getting such different numbers?

As I mentioned earlier, the stock aeroplane with the lowest Cp is the Hawker Hurricane Mk.I and the Cp of the AT-9 is about 84% that of the Hawker Hurricane.

Do you happen to know the propeller pitch range for the AT-9? If your engine is not achieving full RPM at maximum speed, it means that it is still lugging and hasn't come off the low pitch stops which should not be happening at maximum level speed.

I still recommend that you do your Engine Performance Tuning and Aeroplane Performance Tuning (Propeller Stuff) independently and in that order. The alternative is that because everything is inter related, you can't adjust one parameter without messing up other stuff.

Using this method, doing the Engine Tuning for the P-38F Lightning only took about two hours in all and that included three service ceiling tests which are fairly time consuming AND doing power readings every 2500 feet up to 40,000 feet.

- Ivan.

[aleatorylamp]

Hi Ivan,
Thank you very much for the extra information on the AT-9´s engines.
Thanks also for correcting the J factor numbers for this engine. They differ so much from mine because I forgot to take into account that your 8 ft Prop J factor list I´d extrapolated was only for the slow Giant´s engines, so that was useless! Too silly!
With the new entries I put into tables 511 and 512, everything seems to be fine now.
Power at different altitudes also seems to coincide with what would be expected, but I´ll check that just to make sure. Rate of climb is much better too, and I was just about to test that.
For the moment, I have sea level specs looking quite good:
-197 mph with 295 Hp = 100% perfect.
-1289 RPM instead of 2300 RPM = 0.5% too low, but I wouldn´t call it lugging...
-Max. Manifold pressure is at 30 - I needed 40 before, so that´s also perfect now.
-Friction is at 35 (according to AirEd´s 12% of the Hp recommendation).
-Torque goes up to 81%. I was looking at torque in engine performance graphs, and from what I saw, this also seems OK at .81.
Nevertheless I´ll try and do the tuning like you mention, starting with the Hurricane data.
Cheers,
Aleatorylamp

[aleatorylamp]

These would be the new graph tables.
The red dot on the graph has the value given in the boxes below, so this gives an idea of the size of the entries.
Cheers,
Aleatorylamp
P.S. The rate of climb is a little low - the average for 0-10000 ft was 1162 fpm and I´m getting about 1200 fpm at sea level and only about 400 at 9000 ft.
Anyway, I´ll try the other tuning method!

[Ivan]

Hello Aleatorylamp,

If you cannot achieve full Engine RPM at maximum speed with a constant speed propeller, then something is definitely wrong.
It still means that you can't get off the Minimum Pitch Angle.

If *I* was building this flight model, I would do a lot of pretty quick calculations first:
With 295 HP, and assuming about 85% Propeller Efficiency, How much thrust would you be generating at 200 MPH?
What is the Propeller Pitch Range? At Maximum Level Speed, you should be much closer to the Maximum Pitch Limit than the Minimum Pitch Limit. Actually 85% is a value I would use for a generic aeroplane if I didn't know anything else about it. With this one, I would guess that 70% would be closer to reality because of the very low Advance Ratios.

Although the Propeller Power Coefficient (Cp) is about 84% that of the Hurricane, it doesn't mean as much as you might expect because the Air Speeds are so different for the two Aircraft. The AT-9 never gets above an Advance Ratio of 1.0 in level flight while the Hurricane is way above that.

My suggestion for a Table 511 and 512 is to tune it accordingly because this aeroplane will never see an Advance Ratio above about 1.5 and certainly never see 2.0 even in a terminal speed power dive.
My next guess about Table 512 is that you need use values that are only around 1/2 or 1/3 those of the Hurricane, but that is a guess.

Looks like I may have to find out a bit more about the AT-9 to see what it really did.
- Ivan.

[aleatorylamp]

Hi Ivan,
I´ve studied your post, and it makes sense for improving the new Hurricane adaptation - thanks a lot!
I made a new table 512 using 84% of the Hurricane´s values, but used my 85% Prop efficciency ones because with the Hurricane´s 91% ones, performance was far too low.
Even so, it´s still not getting me where I need, although I did increase torque again to 85 instread of 81. Even lowering Friction to 27 (too far for my liking) and increasing Zero Lift Drag to from 68 to 74, won´t make the numbers tally: Speed is 4 kt too high, RPM is still 11 RPM too low and Hp is now 5 Hp too low too!
Question: Was it really that bad when everything coincided except that RPM was 2289 instead of 2300?
Now, to your questions and comments:
- Thrust with 295 Hp @ 85% prop efficiency: I had 413 before, and now it´s at 475.
- Prop Pitch Range: as yet unknown, but I´ve entered 15-65 (I can´t find it anywhere)
- OK! I´ll try reducing the prop eff. table to 70%
- OK! I´ll progressively reduce the 84% Hurricane values to 50% or even 33% and see how it goes.

As regards performance specs apart from the 197 mph top speed (presumably at sea-level) the only other data I could find is the average rate of climb from 0 to 10000 ft being at 1162 fpm (8.6 minutes climb). Should you manage to dig up any more details, that would be fantastic!
Thanks very much again!
I´ll keep you posted.
Cheers,
Aleatorylamp

[aleatorylamp]

Hi Ivan,
OK, I reduced table 512 to 50% of the Hurricane values, and Table 511 to 70%, but performance was terrible until I adjusted as follows:
- increase propeller efficiency table 511 back to 85%
- reduce friction graph from 35 to 30
- increase torque graph from .81 to .825
Performance returned with this, but speed was too high, so:
- increase 0 lift drag from 68 to 77
Now sea level performance is as follows:
297 Hp (2 Hp too high)
172 Kt (1 Kt too high)
2289 RPM (STILL 11 RPM too low)
Thrust is at 476
This is very similar to what I was getting yesterday.
So, next I´ll try with Table 512 values at 33% of the Hurricane´s and see what happens there.

Update:
Results with 33% of the Hurricane table 512, (table 511 as before at 85%):
I kept everything else as it was except:
- 0 lift drag reduced from 77 to 73
- torque graph reduced from .825 to .822
With this, performance at sea-level is:
295 Hp (perfrect)
172 Kt (1 Kt too high)
2289 RPM (STILL 11 RPM too low)
Thrust is at 449
This is very similar to the 50% Hurricane 512 table trial, but I have the feeling that the plane doesn´t climb so good.

Thanks in advance for your attention!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

My son and I did a few calculations on a spreadsheet based on the following information:
Climb from Sea Level to 10,000 feet in 8.0 Minutes.
Service Ceiling 19,000 feet (100 feet per minute).

Assumption: Climb Rate varies linearly with altitude changes.

Initial Climb Rate: 1720 feet per minute.
Climb Rate at 10,000 feet: 867 feet per minute.
Absolute Ceiling: slightly over 20,100 feet.
Time to Service Ceiling: 33:15.

Now keep in mind that a sustained climb will not be at full power but at a much lower throttle setting.
That would put a full power initial climb probably somewhere over 2000 feet per minute.
Perhaps that is why this was considered a "Hot Rod".

Also keep in mind that these were trainee pilots. I have read accounts by trainees that commented on how the Brewster Buffalo (!) was a hot rod as well.

I still believe that you need to finish engine tuning before messing with propeller setting and flight performance.
Just out of curiosity, what propeller pitch angle are you getting at maximum speed?

- Ivan.

[aleatorylamp]

Hi Ivan,
I just spent most of the afternoon to no avail, trying to find precisely a breakdown of the rates of climb for different altitudes. It´s fantiastic that you should come up with precisely that - what a coincidence! Thank you! - and of course, thank your son too for his calculation - it´s a huge help.

What I did find, is a fine illustrated account of this plane - the best yet:

http://www.letletlet-warplanes.com/2...ery/thumbnails

Your question on the prop pitch angle at maximum speed I´m getting: It´s about -.80
Incidentally, the thrust reading is at 416 and the torque reading, at 677.

Of all the table 512 and 511 trials, the one that gives me the best rates of climb is still the "generic" one I copied from the Cessna engine tables which may be almost like the ones you mention today, although I´m having have a hard time to establish it - it´s difficult to see what the aircraft can sustain, as it ´s always slowing down, dropping off, speeding up and rising again. I`ll have to implement the autopilot for that, as
I have to see exactly what RoC I´m getting before proceeding any further.
I´ll then perhaps establish where in table 512 I can squeeze out a little more power, i.e. in the significant J numbers you mentioned in one of your previous posts.

I thought I had already finished the engine tuning - With the correct engine data for compression ratio, cylinder displacement and manifold pressure, I thought that I had reached the best adjustments for friction and torque values. Others gave bad results. Even getting friction down to 27 didn´t help to squeeze the missing 11 RPM out.

OK, then. Today was my last day with enough free time... Tomorrow I´m starting to give a two-month intensive 5-hour-a-day crash course in German for Waiters. I´ve been designing the course for several months now, it´s a 90-page student´s illustrated student´s manual and it´s finally ready ...including the teacher´s manual and lengthy course description. Anyway, the pay will be good. The job is similar to the 8 years I had at the hotel-school here until 2007, only 3 times more intensive, but I´ll survive, no doubt.

Anyway, I´ll keep you posted. My next post will most probably be related to the rates of climb for different altitudes.

Thanks again for the RoC´s!!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

You stated in Post #11 that you didn't know the propeller pitch range so you were using 15 degrees to 65 degrees....

Yet in Post #14 you stated that propeller pitch at -.80. What does -.80 mean????
This part is actually fairly important.

Also, I didn't think you had the Engine Tuning done because even on Post #11, you were still tuning Torque and Friction graphs and commenting that it was 5 HP too low.

I actually found a couple PDFs online that include information about the AT-9. One of the comments was that the AT-9 was harder to fly than the operational types and that B-25s and B-26s could serve as trainers for the AT-9. Once the older models of the B-25 and B-26 were replaced by newer models, the older aircraft worked better as trainers than the AT-9 did.

Which model of AT-9 are you building? AT-9 or AT-9A?
Do you want me to run the same calculations with any adjustments such as 8.6 minutes to 10,000 feet instead of 8.0 minutes or with a different service ceiling? It doesn't take long to do this.

- Ivan.

[aleatorylamp]

Hi Ivan,
I had discarded my engine tuning as it always gave 2289 RPM readings, but I didn´t remember exactly what was going on, so I did it again:
With the stock 511 and 512 tables from the Hurricane, the best propeller size seemed to be 4.7 ft.
My Friction entries ranged from 29 to 35, Torque entries from .8 to .83.
I was getting Power readings between 287 and 307 Hp, all at 2289 RPM!
No combination of friction, torque or propeller diameter would give me the desired 2300 RPM.
Thrust readings were between 265 and 304 at the best of times.
Of course, the plane wouldn´t fly - it could only do 50 mph.

So I suppose that what I´d have to go for is a similar thrust readings at maximum speed on the working plane.

Now to your last post:
First of all, thanks again!
The plane I´m doing is the AT-9, but it could just as well be the AT-9A because the difference in performance - 5 Hp and 3 mph will hardly be noticeable. I think the 909 in the museum exhibit was an AT-9, but if it wasn´t, it´ll have to be the AT-9A.
The minus -.80 (zero point eighty) I mentioned is the pitch reading that I get at maximum speed at the bottom of the Beckwith gauge, but from your comment, now I doubt whether it refers to the propeller. As before, I´m using 15-65 degrees for that.
Re. pilots´ and instructors´comments, they actually said that the B25, B26 and P38 would have been good to train pilots for the AT-9 !!! Anyway, flown by the book they said it was great, and that it was fully acrobatic.

Update:
I misundestood your last question - It was 8.6 minutes instead of 8 - I had missed that. Yes, please, If you would be so good to re-run the calculation, that would be great, thanks!

OK, then! Now I have to get my nose on the grindstone for classes.
More later!
Cheers,
Aleatorylamp

[Ivan]

Assuming:
8.6 Minutes to 10,000 feet
Linear Climb Rate versus Altitude
Service Ceiling of 19,000 feet

New Initial Climb Rate is 1600 feet per minute
Climb Rate at 10,000 feet is 810 feet per minute
Time to 19.000 feet is 35.0 minutes
Absolute Ceiling would be 20,265 feet

Although I believe our calculations are correct, this problem is VERY oversimplified so I recommend using this as a basic estimate only.
Usually climb rate is highest not at sea level but more like a couple thousand feet up.
Also, remember that Climb Power is typically well below Maximum Power.

Regarding your post: Every time you mention changing the Torque or Friction Graphs, I know you are retuning your engine.
Once you have the basic engine set, you should not be messing with it for performance reasons except perhaps to change the service ceiling.
The actual "airframe" you use to test your engine really does not matter much for basic engine performance.
It won't work so well for a setting the service ceiling which is why you might have to alter the engine to set ceiling properly.

This is the process I try to follow and it seems to work for me. Perhaps your method will work also, but I can't give you advice on what I don't know.

- Ivan.

[aleatorylamp]

OK, Ivan!
That´s very good of you, and a great help, at least as a rule of thumb, and thanks also the rest of your advice.
I think I´ll be able to manage quite nicely. I would expect a continuous climbing power to have the level cruise throttle setting for 175 mph. A normal climbing speed would probably be about 120 mph as per the comment that this aircraft "took off, climbed, approached and landed at 120 mph" - in other words, everything except level flight!
I´m still not sure about my rates of climb, but I think they are a bit low in principle, as at full power I´m getting about 1000-1500 fpm for the first 3000 ft, speeds being 120-130 mph, but as I say, it´s at full power.
Also, I´m still having trouble with steady flight - be it level or climbing - it needs constant trimming up or down, and the autopilot is useless even though elevator trim is at 0.25 and the horizontal stabilizer angle of incidence is disabled. Possibly at cruising power the plane will settle down a bit without rocking up or down all the time.
OK then. Good night! It´s late now, but more tomorrow!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I decided to try out the package you made available for download and found out a whole bunch of things that I believe will be of great interest to you.

Here Goes:
Perhaps you have changed some of these already and perhaps not from the discussions we have been having.

First of all, your "Release Point (?)" in the AIR File is quite a bit off. Your aeroplane is entering into the simulator below ground.
It needs to be released about 20,000 higher and the ground angle can be reduced about two degrees.

Next, the propeller pitch limits are way off. The low limit is actually 23 degrees in your AIR file The setting is actually in two places in the AIR file:
Record 510 as you might expect and also I believe in Record 500. I reset both to 15.0 Minimum to 45.0 degrees Maximum.
THAT will go a LONG way to addressing a lot of the problems you have been describing such as lack of climb and acceleration.
With this change, it has no problems hitting 2300 RPM and is making 314 HP at 500 feet. Idle speed also went up by around 100 RPM.

Next, I believe your damping values are way too high which gives a strange feel and might be causing other problems.

Finally, your problems with the autopilot can probably be cured by changing your value from 0.25 to 1.75. That value at least let the autopilot maintain altitude but I believe the damping values may be causing some of these issues.

I believe there are a bunch of other things that are not quite right and here's why: The high damping slows down changes in pitch. The problem with that is that when you stall the aeroplane (which is way too easy but we will get to that in a moment) The nose does not drop so the plane mushes into the ground. I believe that stalling is too easy because the Elevator control is too strong. It is so strong that you can prevent the nose drop at the stall as well.

I didn't want to make a whole lot more changes because this is your project and I doubt I have the latest version of the AIR file.
I CAN tell you that it became a whole lot easier to fly with a few of the changes I described.

- Ivan.

[aleatorylamp]

Hi Ivan,
Wow! That´s definitely a handful of great help! Thanks!
I had already noticed the 23 instead of 15 degrees prop-pitch, but had only limited success curing the damping issue on elevators and ailerons. These react react very differently from FS98, so I appreciate your comments immensely! I´ll have a look into your Lightning .air file - that will perhaps be useful as a guideline. The AT-9 was the initial trainer for it as the P-38 had no second seat for an instructor.
I´ll put it all this right and continue my testing from there, which should then be easier.

As I have this intensive course every evening (it´s going great!), my wife has let me off the housework and cooking, so I have my free mornings for this hobby in compensation.
Cheers,
Aleatorylamp

[aleatorylamp]

Hi Ivan,
After doing the necessary corrections, it was of course easier to test climbing on the plane, although it did porpoise a lot above 10000 ft. As expected, power is not at all up to par yet!
I tried to fix the throttle for a 175 mph level flight, which would be about 85% I suppose, but for the moment I settled for 90%, as that was easier to set, and also, 90% is usually possible as a continuous climb, if I´m not mistaken.
So, at 90% throttle, (sea-level horizontal flight equivalent of 180 mph - fast cruise...) I did a climbing test to see what rates of climb could be maintained at a constant 120 mph:
upto ft - fpm
3700 - 850
4800 - 750
5000 - 700
5500 - 600
6000 - 500
7000 - 450
7500 - 400
8000 - 350
8500 - 300
9000 - 250
10000 - 200
11000 - 100
12000 - 13000 ft, 100 fpm could be maintained only at 110 mph.
First I´ll try to reduce Induced Drag and increase Zero Lift Drag to get more speed higher up, keeping the 171 mph max. sea-level speed and then I´ll do another test, although that will only improve things a bit higher up.
After that I´ll try my luck at adjusting the thrust curves to get more power at 90%.

Update:
I´ve just done the Drag adjustments and it seems that as speeds are better at altitude, the RoC also improves noticeably - looks promising!
2nd update: Now it looks like this:
upto ft - fpm
2500 - 1400
3700 - 1200
4800 - 1100
5500 - 1000
6500 - 950
7500 - 900
8500 - 850
10000 - 800
11000 - 700
It was porpoising a lot and I had to stop, but it looks very close, I´d say!
Cheers,
Aleatorylamp

[aleatorylamp]

Hi Ivan,
Actually I had a mistake in the initial climb upto 2400 ft - it was only 1200 fpm, not 1400... but now,
I´ve just ever so slightly tweaked the J = 0.6 values in tables 511 and 512 corresponding to the 120 mph speed, and I got another 200 fpm out! (I´m amazed that it was so easy...).
So, it should be OK!

...IF, of course, a 90% throttle setting for continuous climb is correct!

Now it´s time for another more extensive test!
Update: Here it is:
upto ft: fpm:
2500 - 1600
4500 - 1400
6200 - 1200
8500 - 1000
9700 - 900
10000 - 800
11000 - 700
12000 - 600
13000 - 500
...by now it was bobbing up and down so bably I couldn´t continue.

I think I can leave it here, as it coincides nicely with the calculated expectations, I´d say!

Cheers,
Aleatorylamp

[Ivan]

Those numbers are not too far off. I hope 90% is the "Climb / 30 minute" power setting.
I believe with full power / military power, it should climb quite a bit faster.

You comment about bobbing and such brings up another point:
There is something about the controllability of this aeroplane that just isn't quite right.
It appears to fly much "heavier" than it should.
I modified the moments of inertia but that didn't completely cure the problem.

- Ivan.

[aleatorylamp]

Hi Ivan!
Thank you for your as always useful input!
The 90% I mention is simply pressing key "9", having 90% on the Beckwith gauge in the "Thrt" square.
This airplane indeed did have WEP, but I have no idea what type it was, so that´s why I haven´t implemented it as yet. If I can´t find out which it was, I´ll use Methanol-water, I suppose, because there is no mention of a supercharger that could have had extra boost for this plane.
Heaviness-stability-manoueverability:
OK, so there does seem to be something strange going on. I tried fiddling the MOI´s, the Stability Factor 2, the Damping... but it´s a mystery. As I´ve said before, an FS98 plane with similar entries performs really fine, but not here! Obviously the CFS1 .exe interprets the FD differently.

I´ll make another .air file then. I had simply copied over the FD from one of my FS98 German twin-engined courier planes into the CFS1 Hurricane FD I think it was, but I think I´ll repeat it, omitting the "funny" parts to do with stability and other "strange" things. ...or maybe the Hurricane FD is not the best one for this. Would the Mustang one perhaps do better?

Thanks again for your feedback!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

When I was starting out with AIR files, I chose the P-51D as a template because I believe it actually has more records than some of the others including the Hurricane. I don't remember what was missing so perhaps I am mis remembering. You CAN of course use which ever one you want to start.

With the stock P-51D, there are only two not so obvious gotchas and neither is all that serious:
The Wing Efficiency Factor in Record 1204 is WAY too low to be realistic. Basically it makes the aeroplane not have as much induced drag.
6000 to 7500 seems more reasonable to me.
The second issue I know about is Aileron Control Factors in Table 518. If you look carefully, one of those numbers doesn't fit the sequence.
These are in my notes but I am still adding to those notes as I go.
There are about 3 or 4 other things I have to experiment on.

- Ivan.