Author Topic: P-51 Airfoil and Turn Performance (Read 34027 times)

Stoney74 · « **on:** August 17, 2007, 09:18:01 AM »

I know the Pony was supposed to have a "laminar flow" wing, but I don't know what airfoil it had exactly. What I do know is that some of the uncambered 6-series NACA airfoils at low thickness/chord ratios have some relatively poor Clmax numbers. I'm assuming that someone knows the airfoil used on the Pony, and also the t/c ratio for the wing.

If my above thoughts are true, can it be safe to assume that the airfoil shape/type may have one of the reasons that the Pony's slow speed turn performance in the game is comparitively poor?

From a general aviation perspective, I know Mooney's and Grumman's with 6-series airfoils have some quirky/poor slow-speed handling and stall characteristics, even though they use 15% t/c with design lift coefficients of .4. If the Pony used a thinner airfoil with less camber, seems like it may suffer drag penalties at slower speeds or high AoA maneuvers.

(I've been geeking out on airfoil books lately)...

gripen · « **Reply #1 on:** August 17, 2007, 01:21:07 PM »

Some sources (like NACA papers) claim the profiles of the P-51 as "North American-NACA compromise" sections while some others claim sections as NACA 45-100. AIAA-91-3288 by Lednicer&Gilchrist gives t/c 16,55% at root (without leading edge extension) and 11,44% at tip.

Theoretically the first laminar profiles had a lower Clmax values than the earlier profiles but in practice the P-51 reached quite similar Clmax values at low mach numbers as other WWII fighters ie around 1,3. At higher mach numbers the P-51 did relatively well.

But read your self:

http://hdl.handle.net/2060/19930092575

http://hdl.handle.net/2060/19930093805

http://hdl.handle.net/2060/19930084610

And there is a bit more but I'm too lazy to dig them out...

AquaShrimp · « **Reply #2 on:** August 17, 2007, 01:32:37 PM »

Translate this into laymans terms please. What is clMax?

gripen · « **Reply #3 on:** August 17, 2007, 01:36:57 PM »

eeh...

Cl = lift coefficient
Clmax = maximum lift coefficient

clMax = second cousin of the Mad Max

dtango · « **Reply #4 on:** August 17, 2007, 01:49:35 PM »

I lean toward the Lednicer/Gilchrist airfoil quotations that Gripen notes.

In their modern CFD eval of the P-51 as they tried to identify the airfoil they eventually ended up spending time with Ed Horker (sp??) who was a NAA designer for the Mustang and provided them the definitive answer on the Mustang airfoil along with the engineering drawings. The airfoil was an NAA airfoil modified from a NACA spec.

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On the turn performance complaint I'm not sure the issue is the Mustang's turn performance clean, but sustained turn with flaps deployed. Widewing will have to clarify.

With all due respect to Widewing, I'm not ready to agree there is a problem in this regard. I think HiTech has stated that it's an issue of which data source to use in this particular case.

The funny thing is that there are other things I've mulled over (for a long long time now!) from a turn performance standpoint for the Mustang that gripen is aware of but alas I've not reached any definitive conclusion on it!

Tango, XO
412th FS Braunco Mustangs

Widewing · « **Reply #5 on:** August 17, 2007, 02:46:13 PM »

Quote

Originally posted by dtango

On the turn performance complaint I'm not sure the issue is the Mustang's turn performance clean, but sustained turn with flaps deployed. Widewing will have to clarify.

With all due respect to Widewing, I'm not ready to agree there is a problem in this regard. I think HiTech has stated that it's an issue of which data source to use in this particular case.

The funny thing is that there are other things I've mulled over (for a long long time now!) from a turn performance standpoint for the Mustang that gripen is aware of but alas I've not reached any definitive conclusion on it!

Tango, XO
412th FS Braunco Mustangs

Have a look at this graphic and tell me if you think that a 13,457 lb P-47D-25 should out-turn a fuel light, 8,604 lb P-51B.

That's 44.9 lb per sq/ft wing loading fighter turning smaller circles than a 36.9 lb per sq/ft wing loading fighter.

I can't find a single test reference that supports what we see here. Something is clearly incorrect.

My regards,

Widewing

evenhaim · « **Reply #6 on:** August 17, 2007, 02:52:19 PM »

Would this have to do with last year's FM update?

cheers
-freezman

Benny Moore · « **Reply #7 on:** August 17, 2007, 02:54:11 PM »

Quote

Originally posted by Widewing
That's 44.9 lb per sq/ft wing loading fighter turning smaller circles than a 36.9 lb per sq/ft wing loading fighter.

While such things can easily be explained by differences in flaps, power, wing shape, and other factors, you're quite right; all of the tests I've seen say that the P-51 should definitely out-turn a P-47 and should turn almost as well as a Spitfire, though not as tight as a P-38 (provided that the P-38 is using the maneuver setting for its Fowler flaps).

Widewing · « **Reply #8 on:** August 17, 2007, 03:02:51 PM »

Quote

Originally posted by evenhaim
Would this have to do with last year's FM update?

cheers
-freezman

Several updates have contributed... The last one around June of 2006 was the capper.

My regards,

Widewing

SteveBailey · « **Reply #9 on:** August 17, 2007, 03:11:00 PM »

Quote

Originally posted by Widewing
Several updates have contributed... The last one around June of 2006 was the capper.

My regards,

Widewing

I'd like to know why HT ignores this... any answers?

Kweassa · « **Reply #10 on:** August 17, 2007, 03:15:37 PM »

Quote

I'd like to know why HT ignores this... any answers?

They need definate proof, Steve.

bozon · « **Reply #11 on:** August 17, 2007, 03:32:42 PM »

WW are these circles with full flaps? Is this how the P51 turns or is it just effect of the flaps?

My gut feeling is that our flap drag penalty is too low for the extreme settings. Perhaps too much stability near stall and easy recovery too. I hate the flap-o-rama that dogfighting has become. In a way, I'd wish that all planes would get the old 109 instability and the Mosquito's tail slide stall. That would put an end to the silly hanging on the prop with full flaps till you fall backwards, and the full flaps 80 mph turning circles while eating a sandwich.

Widewing · « **Reply #12 on:** August 17, 2007, 03:39:25 PM »

Quote

Originally posted by SteveBailey
I'd like to know why HT ignores this... any answers?

Well, here's the same test done in AH1 (1.11 patch 4) added to the graphic. Yes, I still AH1 on my machine.

Note the smaller circle and faster turn rate (overlap of the trail). Note that the issue is magnified by the P-51s getting worse, and many of the other fighters getting better.

My regards,

Widewing

Widewing · « **Reply #13 on:** August 17, 2007, 03:49:09 PM »

Quote

Originally posted by bozon
WW are these circles with full flaps? Is this how the P51 turns or is it just effect of the flaps?

These tests were done at about 50 feet ASL, and with flaps fully deployed. At least 6 full circles were flown to stabilize the aircraft at their limits.

My regards,

Widewing

gripen · « **Reply #14 on:** August 17, 2007, 04:03:15 PM »

BTW here is something tested on the P-47 as well.