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

[Ivan]

Hello Aleatorylamp,

I only pulled out the AIR file from the last version you sent. I didn't even check for the improved visual model or for a DP file.
I believe in looking at some drawings that the reason the AT-9 was so unstable was because it typically had a CoG that was pretty far aft. That was indicated by the position of the aircraft lifting lugs on the wing roots. They were a bit far back from where I would have expected to find the wing's center of lift.

I finally got my version of the AT-9 off the ground.
I am following my own "Process" for creating a new AIR file in starting with a stock P-51D
I found one glaring error in my instructions thus far: I forgot to list editing the Fuel Tanks.

The engine power is still down around 236 HP at 500 feet and I have done no performance testing at all.
Interestingly, I have no trouble getting near 2300 RPM (actually around 2298 until pilot sets prop for maximum RPM).
The handling is a bit twitchy at the moment since I have not changed any non-essential parameters from the P-51D.
Another interesting thing is that the cockpit POV from the P-51D was good enough to fit your model.

I am following my own recommendations for Engine Tuning first and THEN Propeller Tuning.
By the way, can you figure out WHY the performance dropped when you increased the Propeller Diameter?

It will be a while yet.
- Ivan.

 

[aleatorylamp]

Hi Ivan,
Thanks for your comments - it´s very interesting to follow the process - not only the result.
So your engine´s slightly faster than mine... very good!
I suppose the 6-inch-increase in prop-diameter caused a power drop due to increased drag, so zero-lift-drag had to be lowered, perhaps?
I think I did my tanks calculating MTOW minus Empty-Weight minus Crew-Weight, as I had no extra info.
OK, then,
Cheers,
Aleatorylamp

 

[Ivan]

Status Update

Hello Aleatorylamp,

The actual fuel tank arrangement of the AT-9 is a single 130 Gallon tank in the wing center section under the cockpit.
That would put this at very near 0,0,0 in relation to the aircraft center of gravity. I will see if I can post the data sheet I did.
Most of the data comes from drawings by Paul Matt. The drawings actually have an incredible amount of information which I tried to capture in text form for easy reference.

I swapped the MDL and the DP file from the last version you sent me. The Propeller Animation seems to be a bit strange. There also appear to be a fair number of bleeds of the propeller when seen from the rear. You might want to check this out.

With a bit more tuning, I now have engine power up to 298 HP at Take Off (elevation about 265 feet). At 500 feet, it is only making 295 HP. Speed is too high still, but that is easy to fix and I don't want to fix it until I have the basic Propeller tuning finished

Interesting thing about the Propeller thus far is that I am getting around 25 degrees pitch at 200 MPH which is only a touch lower than where I would want it. (I was going for 30 degrees.) I CAN leave it the way it is, but realistically, this is a tiny little propeller with only two blades, so the power coefficient should be a bit less.

Regarding the 8.5 foot versus 8 foot propeller change: I believe the real reason is that the advance ratios changed with a larger diameter propeller and didn't change in the direction you would have wanted. Another possibility is that the new advance ratio puts the efficiency into a "dip" in the curve. There are dips in various places which I was planning to discuss in a new thread once I finished up my revised propeller tables.

- Ivan.

P.S. The attached data sheet is pretty typical of what I try to get before starting a project. I could not find the propeller pitch range but 15 to 45 degrees sounds workable for now. If I wanted a bit better Take-Off performance, I would change the range to something like 10 to 35 or 40 degrees.

 

[aleatorylamp]

Hi Ivan,

Wow! Very interesting progress and extra information in your compiled Data-sheet - very diligent!
I´ll correct the angles of incidence, MOI´s, weights and tank right away. Thanks a lot!

Update: I´ve just put in the new data.
This is very pleasing: The roll and pitch issues have ceased. I never expected that the MOI´s would be so low - so "light". Only with this, it makes all the difference, and the .air file is now completely useful and usable.

It is also interesting to see that the initical climbing rate of 1325 fpm is stated at full combat power. Are we led to believe that this is equivalent to a 100% Throttle position, or is it with WEP, for which WEP will have to be implemented in the .air file first? In this case, without WEP, initial climb would maybe be about 1200 fpm?

The prop animation bleedthrough is a bit complicated because of the different grouping-places for the nacelle, cowling and engine parts. I´m still working on that, apart from some cracks in the skin-welding.
Update: I think I´ve managed to fix the prop-animation issue: The prop-blurs are now components (I still had some left), and I used some glue. I also put in a wing-nose template on each side which may also be helping. It´s much better now!

I´d be quite happy with any changes in the criteria that you were to decide, as regards for example prop-pitch at high speed or pitch-angle range for take-off.

Definitely interesting developments!
Cheers,
Aleatorylamp

 

[aleatorylamp]

New development files

Hi Ivan, Hi all!
Being a "work in progress" thread, I thought a post including the new model and .air files which implement Ivans new discoveries and corrections would be very much in order, as perhaps there may be other members of the forum who may be interested...
It flies much better now, and includes propeller-blurs, correcting their bleedthrough.
Also, the aileron hinges are better placed.
Enjoy! - Just for eye-candy there´s an extra screenshot of this hot and cool plane!
Cheers,
Aleatorylamp
P.S. Now for the transparent cabin...

 

[Ivan]

Hello Aleatorylamp,

I just emailed you my first cut on the AT-9 AIR file.

I forgot to tell you that with the data sheet, the MOI was formula based.
I tried these numbers out and they actually didn't work well in the Flight Model: The aeroplane had a bounce that would not go away until the Pitch MOI was raised to about that of the stock P-51D.
I also significantly increased the Roll MOI because the aeroplane was much too agile.

In the MOI calculations, I had a choice of "Light Twin" or "Prop Bomber 2 Engine" and the two "different" configurations give significantly different results.

There is still a lot of tuning that I want to do with the AIR file version that I am working on, but here is what it does now:
Maximum Speed: 199 MPH at 500 feet. (I like it a touch high. It will actually stabilize at 200 or 201 with enough time.)
Initial Climb Rate: Slightly over 1400 feet/minute at 200 feet altitude. (This is easy to increase.)
Service Ceiling with nearly full fuel is about 19,400 feet. (Changing the initial climb will likely affect this significantly.)

I changed the propeller pitch range to 10-35 degrees.
The Power Coefficient Table (512) is exactly half that of the stock Hurricane Mk.I.
(There is a lot of flexibility with Table 512 on this aeroplane.)

Regarding Prop Blurs: Why not do them as a single Part instead of as a Component? That is actually what I do on my aeroplanes.
The actual weirdness I was observing with the Propeller Animation was that the Propeller Blur actually was shown as soon as the Propeller started moving.

Glad things are working.
- Ivan.

 

[aleatorylamp]

First cut airfile

Hello Ivan,
The .air file is really becoming a very good one now!
The plane flies much more smoothly - very nice! Movements aren´t half as brusque, and it doesn´t shake on the runway anymore.
I have an old FS98 MOI table for all sorts of different aircraft, but these MOI´s are too high for CFS1, which obviously processes this data differently.
I understand what you mean about the prop-blur. I´ve now done it as one part, saving 2 components, and regulated it so that it appears from 35-100% RPM as you suggested in a post some time ago.
I´m now working on the transparent canopy, but there are interferences with wing fairings and the central flap below. I´ll try different grouping approaches. For the moment the fairings are glued to the body, but so are the left and right middle flap halves.
Personally, I prefer the more sobre or secretive look of texture-shaded opaque cabin windows. ...it also eliminates all kinds of bleedthrough complications. I´ll see how it goes.
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

I tried out your AIR file and here is what I have found thus far:
I already mentioned the bounce on the runway.
Setting the Pitch MOI up to about 8000 seems to cure the problem.
There is also a noticeable vibration at high speed (around 190 mph).
The propeller pitch at maximum speed seems to be way low: I see only 18 degrees at maximum level speed.
If your minimum pitch angle is still 15 degrees, then there is only a three degree operating range.
For a constant speed propeller, this seems a bit odd.
I still think that the Elevator Control is way too high.

That is all I have found thus far.
I still like my version of the AIR file better, but as usual, that is probably mostly because it IS mine.
I will poke around a bit more but we are going out soon, so I won't have a chance until much later tonight.

I haven't had a chance to look at your model yet.

- Ivan.

 

[aleatorylamp]

Yours better any day!

Hi Ivan,
I like your .air file much more as well, and I am using it!
My reason for posting the previous one was that your suggested corrections made such a huge difference that I thought it worthwhile to do so. The new visual model is not really so important. Both are only interim improvements, as obviously further FD improvements on your part will be coming, as well as model improvements on my part. The transparent cabin is as yet no good yet, and we shall see.
The propeller tables in your new .air file look far more coherent than what I had - my insight into the meaning behind them is rather limited (just as the limited 18 degrees pitch in my table!), so it is a great help, what you are doing!
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

Thanks for the praise!

I did a few more updates to my version of the AIR file last night.
The aeroplane had the following issues I was trying to address:
1. Really an experimentation thing: It seemed to be so responsive in directional control that I was wondering if perhaps my original conclusion that the Propeller Effect on Rudder didn't work with twins was correct.
I removed the Steerable Tailwheel and Directional Control pretty much disappeared. Steerable Tailwheel went back on....

2. Although the aeroplane WAS fully aerobatic, a Loop took a lot more care than I had wanted and pulling out was difficult.
I changed the Elevator Response at higher speeds and the issue is better. It should still exist though because this is not a high powered aeroplane.

3. The aeroplane was a bit too tail heavy at high speeds, so I adjusted the Trim so that it is pretty much neutral longitudinally at about 180 MPH.

4. Although the Paul Matt information states that initial climb was only 1300-someting FPM, I wanted it a touch higher, so now it is just a touch under 1600 FPM at about 128-133 MPH TAS.

5. I thought about it a bit more and it didn't make much sense to have a Propeller Pitch Range of 10-35 degrees because the tables only go down to 15 degrees. I changed it to 15-40 degrees.
Propeller Pitch at maximum speed of 199 MPH is 24-25 degrees which is fairly reasonable in my opinion.
Pitch at the start of Take-Off run is obviously 15 degrees.
Propeller comes off Low Pitch at about 80 MPH which means that is where it hits Full 2300 RPM (299 HP @ 245 feet).

So.... Now we have an aeroplane that Takes Off at about 125 MPH, Climbs at about 130 MPH and should be flown now lower than about 110-115 MPH on the approach. It isn't quite the 120-120-120 as the pilots claim, but it's close.

I absolutely positively did NOT do any time to altitude tests but I expect that to be a bit lower than the earlier data.

Check your email....

- Ivan.

 

[smilo]

"How can one edit the post title? I wanted to say "normal" instead of "norlal"..."

from my experience,
sorry, you can't...
at least, i've never been able to do it.

 

[aleatorylamp]

A very nice .air file for the AT-9

Hi Ivan,
I hardly expected such good results in so little time! The plane is now fantastic to fly, thanks very much! I tested if for manoueverability, power, climbing etc., and it performs very well all round! It is very nicely balanced - so much better than I was able to manage.
The climbs are also coherent with the specs as far as I could tell, and it´s interesting now how the pitch behaves at the different speeds you mention. Indeed an achievement, which I´m sure a lot of simmers will appreciate!
In another order of things, however, the transparent canopy is giving me trouble with bleedthrough, which is by no means down to an acceptable minimum yet. We shall see!
Cheers,
Aleatorylamp

 

[aleatorylamp]

Title mistakes are forever!

"How can one edit the post title? I wanted to say "normal" instead of "norlal"..."

from my experience,
sorry, you can't...
at least, i've never been able to do it.

Hi Smilo!
Here I was so absorbed with the .air file back-and-forth, I almost overlooked your post - so there´s no backing away from a mistake there! Ha! I´m glad I didn´t put an "i" instead of an "l" in the word "title" in the title...
Hope all´s well with the new computer!
Cheers,
Aleatorylamp

 

[Ivan]

Hello Smilo,

I guess changing a post title is different from changing a thread title because I know you have done that before.
I take it you didn't see the email I sent to you a couple weeks ago about finding a lot of drawings of he Martin Baltimore.

Take Care.
- Ivan.

 

[Ivan]

Hello Aleatorylamp,

Glad you like the almost complete AIR file. Please feel free to use it. It WAS intended for your aircraft.
Keep in mind though that it isn't quite done yet

It also should not have War Emergency Power as it does now.
The overspeed and dive characteristics have still not been tested.
I believe the trim should be slightly more nose up so that it is neutral at about 175 mph or so.
The Flap values should be adjusted a bit so that the drag is higher and so that the aircraft pitches down more when flaps are deployed.

It seems a bit easier to fly than it should but I am not really sure what its nasty characteristics were.

I believe that a lot of the issues you ran into with your version of the AIR file were caused by some strange characteristics that were in the Zep-R6 AIR file that you started from. That is why I thought it was a good idea to start from the stock P-51D. (It was also an opportunity to run through the build process for the first time and not everything was listed that needed to be done.)

Things are still evolving....
- Ivan.

 

[aleatorylamp]

new .air file

Hi Ivan,

Yes, not to worry, I realize it´s not the definitive .air file yet, and I´ll fine-adjust the attitude for 175mph and the flaps pitching effect as you say.
I´m actually quite pleased that it doesn´t have the nasty characteristics it was reputed to have, so that´s fine too!
Also, as regards WEP, I mistakenly thought the aircraft had WEP as I´d mis-read an ex AT-9 trainees´ comment about an instructor who on final approach had suddenly simulated an emergency in combat by pulling the power on one of the engines. I´d thought he´d pulled the WEP on one of the engines, but he just pulled one of the throttles, de-stabilizing the aircraft instantly.

OK, thank you for your continued efforts. When I upload the plane it will be with your .air file!
Regarding the transparent cabin... Oh dear! The more I muck around with it, the more I like my textured shading on the windows!!
Cheers,
Aleatorylamp

 

[Ivan]

Messing Around with AIR Files

Hello Aleatorylamp,

I also did some messing around with the AIR File last night. Check your email again.
Added is the Pitch Down effect of deploying Flaps, so on final approach, it is distinctly nose down though not as bad as looking out the top window. With such a short nose on this aeroplane, I bet it DID look like it was pitched down a bit more than it really was.
I started to increase the Flap Drag as well, but stopped way short of making the aeroplane unable to maintain altitude at maximum power. The numbers I had to use were getting a bit unrealistic.
At 70% power, it barely maintains altitude and even above that setting, it is very difficult to gain altitude with full flaps though it is possible to take off with full flaps deployed.

I adjusted the trim slightly so that now it has neutral pitch trim at 175 MPH which it achieves with 75% Throttle and full RPM.
In case I forget to tell you later, the Trim adjustments are the following:

Lateral: 2 Notches Right Wing Down.
Directional: 1 Notch Right Rudder
Longitudinal: Varies a lot more with Airspeed. It is NOT easy to trim to fly hands off which is the way I thought it should be.

I also adjusted the High Speed controls a bit, especially for the Elevator and made some Low Speed adjustments for the Ailerons.

Hopefully this is an improvement.
It seems such a shame to intentionally screw up a nicely flying flight model though....

- Ivan.

 

[aleatorylamp]

Hi Ivan,
Thanks for the newest .air file. I´ve just tried it out a bit more:
1) Full-power take-off with 1 notch of flaps, slight rotation and lift-off at 120 mph.
2) Approach with 50% power and last-but-one flap notch at 135 kt
Keeping the same settings:
3) Final approach at 130 kt
4) Raise nose slightly and touch-down at 120 mph
5) Throttle back to idle-power
6) Retract flaps to prevent lifting off again
7) Slowly lower tail
Touchdown can also be at lower speeds, with the advantage of not having to retract flaps before lowering the tail to prevent lift-off, but at higher speeds control is better, which is completely realistic.
The .air file I feel fits the air craft very well!
Thanks again
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

Seems like it works well for you. As I commented in the email, I typically used lower power settings when landing.
I also try to a full stall 3-point lading so there isn't enough lift for a serious bounce. With full flaps this isn't very easy because the aeroplane starts to get very wobbly at the stall.

Loops are not very easy even now because at the top of the loop, there is very little airspeed. The loop has to be started at very near the maximum level speed to go over the top easily.

The general maneuverability is what I will be checking out now though I really don't have much to use as a guide other than a comment that it was fully aerobatic.

Let me know if you find other issues.

- Ivan.

 

[aleatorylamp]

AT-9 Handling

Hi Ivan,
I was further trying out the new .air file, and everything seems to be ship-shape.
With loops it usually makes it over the top between 90 and 105 kt, which seems fine, and then it comes out nicely at the bottom without losing too much height, which is also good. Rolls and inverted flight are fine too.
Depending on the approach angle, I found 20% throttle to be good for steeper angles with 3 points of flap, as otherwise height loss is too much - which on the other hand is fine if you are close to the threshhold. Anyway, the need for power on approach is definitely consistent from the reports on the plane.
The .air file is very good all round, so I´d say it is the definitive version!!
Cheers,
Aleatorylamp