P-51 Airfoil and Turn Performance

[Scherf]

God, not Gaston again.

Fargin necro.

[drgondog]

The use of flaps to improve turn performance was useful only briefly in order to gain a short lived tighter turn in order to get a better deflection shot.  The 51 Flap was a big beast compared to the maneuvering flap on say a 109 or even a P-38.

There are many 8th AF encounter reports of good pilots chasing 109s that deployed flaps for small temporary improvement accompanied with a decided loss of speed.  John C. Meyer had just such an encounter on May 12 in which the 352nd FG attacked a German force north of Frankfurt.  The encounter report is on Spitfireperformance.com website within the P-51 Merlin tab. scroll to the bottom for Encounter Reports and go to 352nd FG

http://www.spitfireperformance.com/mustang/combat-reports/352-meyer-12may44.jpg

[Gard06]

What we should be asking, "Why is the p51D under modeled in this game". 
Here are the true numbers for the pony....  HTC is way off and below these.

Flight Test Engineering Branch
Wright Field, Dayton, Ohio
15 June 1945

Flight Tests on the North American
P-51D Airplane, AAF No. 44-15342

Summary

       Fuel consumption and speed data listed in the flight operation instruction chart have been spot checked by duplicating in the test program some of the power settings shown in the T. O. By comparing the results obtained with the T. O. figures, a quick estimate of the validity of the T. O. may be made.

       High speed and climb performance have been obtained on this airplane at a take-off gross weight of 9760 pounds. Performance was obtained up to an altitude of 35,000 feet in increments of 5000 feet in a clean configuration. The clean configuration included one external bomb rack on each wing. Additional configurations were flown at 5000 and 15,000 feet including two 110 gallon tanks, two 500 pound bombs, and two 250 pound bombs. The principal results are as follows:

       A.  Clean Configuration (with bomb racks).

   1.   Maximum speed at critical altitudes   
       
      High Blower   
   
      War Emergency power (3000 RPM and 67") 26000'   442 MPH
      Military power (3000 RPM and 61") 28000'   439 MPH
      Normal Rated power (2700 RPM and 46") 29400'   420 MPH
   
      Low Blower   
   
      War Emergency power (3000 RPM and 67") 10000'   417 MPH
      Military power (3000 RPM and 61") 13200'   413 MPH
      Normal Rated power (2700 RPM and 46") 16200'   387 MPH
   
   2.   Maximum speed at sea level   
       
      War Emergency power (3000 RPM and 67")   375 MPH
      Military power (3000 RPM and 61")    364 MPH
      Normal Rated power (2700 RPM and 46")    323 MPH
       
   3.   Rate of climb at critical altitude.
       
      War Emergency power (3000 RPM and 67") high blower (19,000')   3200 ft/min.
      War Emergency power (3000 RPM and 67") low blower (4,800')   3600 ft/min.
       
   4.   Time to climb to service ceiling, war emergency power
3000 RPM and 67") (41600')   28 minutes.

       B.  True speed loss, MPH from clean configuration due to external load items (2700 RPM and 46").

2-110 Gal. Tanks   2-500 Lb. Bombs   2-250 Lb. Bombs
5000 ft. 45   36   25
25000 ft. 47   33   2



Notice in Aces High the spec's on the p-52d at sea level doesn't even go over 360mph....   Why is that HTC?   

[Widewing]

In game, the P-51D can reach 367 mph at 50 ft ASL with 25% fuel.

Less than 375 mph, but speeds varied with the aircraft as not all aircraft are maintained the same. There was and always would be some normal variation from plane to plane....

[Skull-1]

The Mustang is undermodeled because if it weren't.....everyone would fly it.

It is a legendary and iconic airplane.  That's one of the main reasons people fly it.  Visibility is a factor.  The ability to disengage as well.

Still, as porked as it is, the real deal is overrated.   Pony pilots say they could turn with the Germans all day long.  German pilots say the opposite.

At the end of the day, my friend Chris Avery (CAF Hawg pilot) says the F4U can beat anything with the Sea Fury being the toughest opponent.   That's his opinion as I recall it.  I could be wrong.

[DaveBB]

Pilot skill is such a huge variable, that the only way to compare two aircraft is to compare the test data.  Chuck Yeager flew against some USAF Colonel in mock dogfights when they captured a Mig-15.  Chuck beat him both in the Mig-15, and when they switched, he beat him again in the F-86.

[drgondog]

The Mustang is undermodeled because if it weren't.....everyone would fly it.

It is a legendary and iconic airplane.  That's one of the main reasons people fly it.  Visibility is a factor.  The ability to disengage as well.

Still, as porked as it is, the real deal is overrated.   Pony pilots say they could turn with the Germans all day long.  German pilots say the opposite.

Turning with another fighter in a sky full of predators is over rated, but I have listened to two sides of a conversation between my father, Henry Brown (Who out turned five 109s in a Lufberry with no ammo to distract them from two of his 354FS buddies, forcing each one to bail as he closed on the next one) Gunther Rall and Steinhoff while 109 vs 51 attributes were discussed.  As you might expect, highly respectful and detailed shared experiences. To my knowledge Rall engaged with but never filed a claim for a 51.  The outcome of the discussion is that at low to medium speeds the 109 had an advantage in acceleration (slight and hard to measure), turn and climb (also hard to measure- but Marshall and Brown both agreed that if a good pilot was in the 109 he could make a steep rh climbing turn that the 51 couldn't match. The 51 was faster to much faster until the 109K, could roll and turn better at high speed/high G and outdive (slightly) the 109. 

Conclusion - best pilot with equal or better tactical position has advantage with agreement that the 51 could 'do it' everywhere in Europe from England and Italy while the 109 has to seriously disengage if possible after 90 minutes.

At the end of the day, my friend Chris Avery (CAF Hawg pilot) says the F4U can beat anything with the Sea Fury being the toughest opponent.   That's his opinion as I recall it.  I could be wrong.

At the Joint Fighter Conference - Oct 1944 at Patuxent, MD over 200 reps from AAF, USN, USMC, RAF and test pilots from all the manufacturers flew YP-59, P-51D, P-63, F4U-1, F4U-4, P-47D-30, F4F, F6F, P-40N, P-39Q, P-38L, Vampire, Mosquito, P-61, F7F, Spit XIV, A6M, XF8-F and included such folks as Lindbergh, Tom Lanphier, Boone Guyton.

The rankings for Best All Around Fighter above 25,000 feet were P-47D (45%), P-51D (39%), F4U-1 (7%), F6F and F4U-4 (3% each), Seafire (2%) and P-38 (1%) in that order.

The rankings for Best All Around Fighter below 25,000 feet were F8F (30%), P-51D (29%), F4U-1 (27%), F7F (7%), F6F (2%), F4U-4 and F2G (2% each).

Best Fighter Bomber
F4U-1 (32%), P-47D (19%), Mosquito (14%), F6F (12%), F7F (11%), P-51D (7%), P-38 (5%)

Having voted and tallied opinions from so many reps of both the contractors and different Services might not be perfect - but far better than one person's opinion.

[Gaston]

The use of flaps to improve turn performance was useful only briefly in order to gain a short lived tighter turn in order to get a better deflection shot.  

  Not quite. This short-lived turn superiority was true for the P-51 aircraft as a whole (it resembled the Spitfire in that respect): It could gain lead on a Me-109G, but then shuddered and stalled if the flaps were up, this happening repeatedly over a single 360 (a condition which the Spitfire could tolerate better, since it was in a very stable speed-decaying "rumble", during which it could fire accurately "accross the circle", probably the only way the Spitfire could "out-turn" anything at all...)... For the P-51 this difficulty in gaining was likely because the turn rate was similar, but over a larger diameter at a slightly higher speed, which made leading difficult.

  To exploit the flaps, they had to stay down:

   Sq. Lt. Hearner (No 19 Sq) commenting 11 April 1945 battle over Lister airfield (P-51 Mk IV vs late Me-109Gs or Ks):
 
  "The 109s we encountered were obviously an experienced bunch of boys. Their turning circle is decidedly better than ours at low speed. The lowering of 20 degrees of flaps may just enable us to hold them in the turn, although I feel they could outclimb us."

  G.

[FLS]

  Not quite. This short-lived turn superiority was true for the P-51 aircraft as a whole (it resembled the Spitfire in that respect): It could gain lead on a Me-109G, but then shuddered and stalled if the flaps were up, this happening repeatedly over a single 360 (a condition which the Spitfire could tolerate better, since it was in a very stable speed-decaying "rumble", during which it could fire accurately "accross the circle", probably the only way the Spitfire could "out-turn" anything at all...)... For the P-51 this difficulty in gaining was likely because the turn rate was similar, but over a larger diameter at a slightly higher speed, which made leading difficult.

  To exploit the flaps, they had to stay down:

   Sq. Lt. Hearner (No 19 Sq) commenting 11 April 1945 battle over Lister airfield (P-51 Mk IV vs late Me-109Gs or Ks):
 
  "The 109s we encountered were obviously an experienced bunch of boys. Their turning circle is decidedly better than ours at low speed. The lowering of 20 degrees of flaps may just enable us to hold them in the turn, although I feel they could outclimb us."

  G.

In other words, the 109 and Spitfire had a lower stall speed than the P-51, and flaps lower your stall speed.

[drgondog]

As I re-read this thread I noticed several incorrect assumptions:
First the NACA/NAA 45-100 airfoil remained throughout the XP-51, 51A/B/C/D/K and A-36.
The Wing dropped about 3" from the A to the B/C/D/K but the leading edge plan view from ~WS 61 to Root Chord steepened with the D/K wing and also changed LE incidence in that region.  The outboard twist remained the same all the way to the tip chord. For the B the washout was -0.5degree at root, 0.75 at ~ WS 50, thence to -0.85 degree at tip. For the D the washout was +0.25 degree at Root, 0.6 degree at ~ WS 61, thence constant to -0.85 degree at tip.

The two D CLmax for the NACA/NAA 45-100 was about 1.6 but of course reduced as function of Aspect Ratio. The wind tunnel and flight tests demonstrated a CLmax at approximately 1.4+ for high Reynolds no and about 1.5 for wheels up level flight Stall (Clean - no flaps) While the CLmax with Flaps was close to 1.7 (2-D), the CD of NACA/NAA 45-100 was significantly higher at CLmax. (I don't have my notes in front).

I have not seen any publication of any test that suggest a change in Oswald efficiency for any of the P-51 series including the XP-51F/G/J and P-51H with straight leading edge NACA 66-(1.8) 15.5 (at root chord) and 12% at tip.

I've read all the informed opinions and have a few thoughts based on research, knowledge of Flight Dynamics factors related to conventional aircraft, and opinions based on the above.  First - I have no idea regarding the modeling but I agree just about everything I have read by Dtango and Widewing.

The primary distinctive unknown factor between the B and D is how does the difference in Inboard wing incidence as a result of the Leading edge difference in Incidence between the Root and the intersection with the common wing around WS 61?  The second question in my mind is what the difference in yaw behavior at low to medium speeds might be between turtledeck B and teardrop canopy D versions?

In real life high G turns at corner speeds the application of yaw correction, finite and undefinable, should result in delta trim drag (Ditto and even moreso for a 109 with slats deployed - the local wingtip CL for the high wing is greater than lower wing in greater proportion I would think than for a P-51 which in turn requires slightly more rudder input (and drag) to carve the turn)?

After those considerations, the model (IMO) requires derivation with respect to time the following:
Change of drag (dominated by pressure drag as function of lift/AoA) as function of CL as change to velocity and angle of attack occurs from the velocity entering the turn to steady state sustainable velocity in a constant altitude, constant speed turn.
Change to propeller efficiency as the aircraft reduces speed. Shouldn't be much but worth exploring along with trim drag contributions to the T=D equations.

As to some of the other stuff commented on here.  A Bf 109 (and FW 190) terminal dive speed was less than that of a 51 and a 47. Having said that, with a head start it might get away but the test docs state that 475mph at ~ .72M for 1G dive limit was about all the average 109 should attempt. In addition, the 51 did not suffer the lower speed (than .65 to .72M) compressibility issues that all conventional NACA 23xxx in same 12 to 15% T/C conventional airfoils suffered.  The laminar flow wing with T/C at ~ 39% made a huge difference in the drag rise regime.

The other complications when modeling dissimilar engines is the plug of HP as a function of altitude and gear stages when comparing say a P-51 and a Bf 109 or FW 190.. as well as stick forces for both roll and high G/high speed turns...It seems the gamers need to input a reasonable (and constant) stick force table for each separate combatant.
 
 

[save]

As to some of the other stuff commented on here.  A Bf 109 (and FW 190) terminal dive speed was less than that of a 51 and a 47. Having said that, with a head start it might get away but the test docs state that 475mph at ~ .72M for 1G dive limit was about all the average 109 should attempt. In addition, the 51 did not suffer the lower speed (than .65 to .72M) compressibility issues that all conventional NACA 23xxx in same 12 to 15% T/C conventional airfoils suffered.  The laminar flow wing with T/C at ~ 39% made a huge difference in the drag rise regime.

The other complications when modeling dissimilar engines is the plug of HP as a function of altitude and gear stages when comparing say a P-51 and a Bf 109 or FW 190.. as well as stick forces for both roll and high G/high speed turns...It seems the gamers need to input a reasonable (and constant) stick force table for each separate combatant.
 
 

From P51 pilots accounts that  flew both the B and D model where in consensus that the D model had to break off when the B model P51 did not, catching 109G's in a high speed dive, due to instability.
If the 109g did not have a head start, they would die trying to dive into clouds below, experienced 109 pilots did not dive away knowing they would be easy meat.

Do you have any opinion of these accounts, Drgondog ?

 

[drgondog]

From P51 pilots accounts that  flew both the B and D model where in consensus that the D model had to break off when the B model P51 did not, catching 109G's in a high speed dive, due to instability.
If the 109g did not have a head start, they would die trying to dive into clouds below, experienced 109 pilots did not dive away knowing they would be easy meat.

Do you have any opinion of these accounts, Drgondog ?

Yes - one anecdotal and one flight test observations.

The Mustang laminar flow wing with max T/C at ~39% had the most benign drag rise characteristics of any fighter I am aware of save the Spitfire with the thinner wing... it did Not have a pitching moment tuck similar to the 109/190/P-38 and even the P-47 with classic airfoils with max T/C at ~25%. The late model P-47D (-30?) installed a similar dive flap at about 30% C to the P-38 to lessen the impact of the forward pitching moment at Mcr. It was tested on the P-51B, found to be slightly beneficial but not enough at the 505mph TAS Vne to warrant production introduction.

The undesirable dive characteristics of the P-51B (and D) were related to Yaw and an element of porpoising near Vne. The porpoising was directly related to the fabric elevators on BOTH the P-51B and D, which was fixed when the P-51D-15 was produced and metal elevators were retrofitted (as well as dorsal fins for the P-51D-5 and all P-51B/C to improve yaw - somewhat).

There are too many combat Encounter reports in which the 'winner' (the Mustang since that pilot survived the Encounter) dove after a 109 or 190 and destroyed it in a dive.  If a Mustang broke up in a dive (somewhat rare) then there was no Encounter Report to cede the advantage to the Bf 109. The Test reports I have seen for the Bf 109 indicate Vne= 475mph, about the same as the F4U but greater than the P-38.

My father destroyed six Bf 109s plus a Ju 87 and the victory credits were (2) in a Lufberry on June 20, 1944 over Rugen Island with one each Bf 109s in turning combat - both blown up, (1) in a terminal dive chasing a Bf 109 on July 28 near Mulhausen in which the fleeing 109 was observed out of control and dove into the ground, (1) September 11 near Giessen in which he pursued and caught a  109 in a dive and blew it up, (1) September 11 in which he chased and caught a 109 on the deck and shot it down, one on August 6 Sw Hamburg in a maneuvering fight from altitude in which he caught a diving 109 then engaged in a maneuvering fight on the deck. The outcome was decided when the 109 pilot attempted a split S from 2000 feet, my father dropped partial flaps - followed itinto the Split Ess but the 109 crashed as he brought his guns to bear.

The June 6, June 20 combats were P-51C-10NT, the July 28/Aug 6/Sept 11 were P-51D-5NA.

Anecdotal combats documented and affirmed by wingman, involving turning, diving, random maneuvering and split Ess from common low altitude.

[Mike Williams]

Good post Bill.

[save]

Nice post, thanks

[Charge]

Bf109 dive tests 1943:

max. Mach 0,805@7.0km
max. TAS 906km/h@5.8km
max. IAS 737km/h@4.5km

http://109lair.hobbyvista.com/techref/structures/tails/109.05e43_report/05e43-p2.htm

I cannot understand how yaw porpoising would be affected by fabric of metal elevators. AFAIK the porpoising of D was due to bubble canopy disturbing the flow around rudder assembly. The fillet cured the problem in level flight but not in dive.

-C+