Turn Performance and Lift Coefficient

[USARStarkey]

I am a novice when it comes to calculating turn performance on planes and I was wondering if there was anyone here who could help me with this. From doing some internet searches on P-51 lift coefficients I have not been able to turn up any definitive results. I have found that the subject of turn performance regarding this aircraft is a hotly debated subject. From what I have been able to glean from reading peoples arguments, there is considerable disagreement regarding what the actual CLmax of the P-51 is when going into a turn. The source of contention seems to be that that the CLmax charted in wind tunnel tests isn't necessarily applicable to real-life turning. There also seems to be alot of disagreement on which tests are valid. I dont really know much about this and I am interesting in hearing from knowledgeable people of the subject.

My own search for Cl-Max got me a value of 1.8: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA800868

 

I also found charts showing values as low as 1.6 at approximately 16 degrees AoA.

 

MY guess as why there seems to be such disagreement is that is might have something to do with the aircraft as a whole creating disconnect from the wings performance on its own. Just guessing. Just as an experiment I did some turn tests in DCS at combat weight of 9550lbs and used TACVIEW to check the results. I did the tests a 500ft at full power without flaps. I made about 5 circles AFTER obtaining a sustained turn.

 

Turn Radius was about 890 feet. Turn rate was about 17.5 degrees a second. Turn time obviously being 20.5 seconds. The most interesting thing is that I reached a sustained AoA of about 22-24 degrees, which is much higher than some Cl Max charts show the P-51's wing stalling at. This is easily the best performing mustang modeled in any game. It is also almost certainly the most accurate given that this sim goes to a far higher level of detail than others. That being said, what changed? Why does the P-51 in this sim perform so much better?

[BitMaster]

Hey,

 

I was just digging through my pile of books trying to help that other topic in identifying a P-51 when I read this which might help you a little bit:

 

Flying Legends; Page 112; ISBN 0-7603-0563-3

 

"Ell's Belle/Ginny was a P-51B-10 and I flew all of my missions with her. In June of 1944 I was offered a P-51D, but I preferred to keep the B-10. I checked out the D and flew a number of mock combat missions in it, but to me it didn't have the delicate response of the B-10, which had four 0.50 calibre guns. When they built the D they added another gun to each wing. To do so, they had to alter the configuration of the wing. I maintain this caused a small reduction in maneuverability. I guess it was a personal thing, for obviously most pilots thought otherwise"

 

Lt. Elmer O'Dell, 363rd FG, Azeville, 1944

 

 

It seems like the P-51 changed it's behavior, to the better or worse, depending on the skills and liking but one can almost be certain those planes didn't fly exactly the same.

 

Bit

[gavagai]

This is easily the best performing mustang modeled in any game. It is also almost certainly the most accurate given that this sim goes to a far higher level of detail than others. That being said, what changed? Why does the P-51 in this sim perform so much better?

 

Funny that there are so many threads that complain about the DCS P-51's turn and stall behavior.

[HotTom]

Funny that there are so many threads that complain about the DCS P-51's turn and stall behavior.

 

Gav, my guess is those complaints are from folks who haven't flown it enough to really get a feel for it. It takes a long time flying it every day to get the muscle memory working.

 

My log book has just gone over 100 hours and I'm just starting to feel comfortable and confident.

 

TTT (HT)

Edited March 23, 2014 by HotTom

[USARStarkey]

Yeah this thing is very agile. Much more in line with what pilots said about it during the war than it is in other "sims." I can't believe people would complain that they cant turn it in this! Just don't try to yank back on the stick so abruptly. You "notch" this plane into a turn, and you can feel it accelerate faster and faster around the turn until you reach equilibrium for a sustained turn.

[HotTom]

Yeah this thing is very agile. Much more in line with what pilots said about it during the war than it is in other "sims." I can't believe people would complain that they cant turn it in this! Just don't try to yank back on the stick so abruptly. You "notch" this plane into a turn, and you can feel it accelerate faster and faster around the turn until you reach equilibrium for a sustained turn.

 

I wouldn't go so far as to say "agile." A Spitfire is agile. An ME109 is agile. This is still an energy fighter relying more on speed than ability to turn. It can turn a bit and the controls must be handled with some sensitivity. As with any plane, you have to find the edge and keep it there during a fight. I find a Force Feedback stick is a huge help. It starts twitching as soon as I get even close to a stall.

 

I think that accelerated stall is an unexpected and rude awakening to folks who expected to yank and bank. You have to develop a "touch" and that takes practice and flying it regularly.

Edited March 23, 2014 by HotTom

[USARStarkey]

OK. So after a very long and arduous process I was able to reverse calculate the CLMax for a sustained 500ft ASL turn.

 

ClMax = 1.8 which corresponds very well with this chart.....:http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA800868

 

not surprising really.

[ZaltysZ]

I wouldn't go so far as to say "agile." A Spitfire is agile. An ME109 is agile. This is still an energy fighter relying more on speed than ability to turn.

 

P51 pilot thinks that BF109 is more agile, when he is prop hanging, stall fighting or just normally dogfighting at up to 400km/h or so. BF109 pilot thinks that P51 is more agile when he has to follow P51 into high speed steep dive, but struggles keeping up with all the banking and pulling because of too heavy controls.

[RagnarDa]

I must commend the OP that tries to actually make a solid point about the simulation instead of quoting pilots which means next to nothing ("agile" - compared to what?).

[=Mac=]

I was simulating a Mach Loop, clean, 40 press average, 25 rpm, pulling hard often. One thing I learned: she makes a singing noise when turning hard. I don't know what the source is, but I used that to gauge how hard to pull and keep from dropping a wing. (TM Warthog has no FFB.) I'm sure there must be other methods to get close to max turning rate, but I'm happy with her little singing.

[effte]

Ran a quick test of my own, FWIW.

 

TOW 4419 kg, so GW probably around 4350 kg once I got to test altitude.

19°C/770 mmHG (1027 hPa) @ SL (FWIW)

Tests at 5000' pressure altitude

MAP 15-16"/2700 RPM

Clean a/c.

Very gradual approach to the stall, well below 1 mph/s I'd say.

 

Buffeting at 101 mph IAS

Stall break at 96-98 mph IAS

 

Reference area S = 240.1 ft^2 = 22.31 m^2, as per ADA800868.

 

Let's call Vs,1g at 97 mph IAS, 44 m/s IAS

Dynamic pressure corresponds to IAS, q = 1/2*rho,SLS*IAS^2 = 1,225/2*44^2 Pa = 1186 Pa (11.86 hPa)

 

L = 4350*9.82 = 42.7 kN = q*CL*S

 

CL,max = 42700/(1186*22,31) = 1.61

 

Compared to figure 8 in the linked paper, that's a bit on the high side. OTOH, can't exactly call the test methodology high science so not ready to call anything or draw any conclusions. Besides, someone will point out a calculation error shortly... :)

 

Cheers,

/Fred

[Topgun505]

Do you all mess with the curve values on your stick? It seems like I just BARELY pull back on my stick and one wing drops and I end up snap-turning (high speed stall?) almost immediately. And this happens at nearly any speed and engine setting. It just seems like I have to fly this thing like a grandma lest a wing drops and the thing spins out of control. Are there any videos of this aircraft in ACM with the control map display turned on so I could see how far the controls are moving compared to what I'm doing?

[NineLine]

Here are some posts that might be of interest as well:

 

http://forums.eagle.ru/showthread.php?t=87966

 

http://forums.eagle.ru/showthread.php?t=95479

[WildBillKelsoe]

The best I could achieve was 21°/sec at 6000 ft, 2700 RPM, 45 MP, under 3 Gs without porpoising.

[Crumpp]

Compared to figure 8 in the linked paper

 

 

Is a study of the effect of rate of angular change on CLmax and the buffet boundary.

 

Under the reports conditions, CLmax is a range of values. I would think it makes for a very confusing and somewhat frustrating comparison of CLmax values under a single set of conditions.

 

:smilewink:

 

Here is a excerpt from the P51 Operating Instructions on the maneuvering envelope. It actually includes a doghouse plot, too.

 

Anyway, you can calculate Clmax under a variety of conditions from this chart to get an idea of the 1G stall Clmax that is used for minimum radius of turn calculations.