P-38 Lightning vs P-51 Mustang: Which was the Better Fighter?

[drgondog]

KK - you will note that I posed 'inboard wing body' considerations re: shock wave and or 'masking the elevator'.. out board of nacelle should not be much of an issue regarding the elevator issues?

You will also note I passed on your 'Flap' comments and focused on the dive/speed brake.. virtually the same approach used on the F7F.

NOBODY deploys flaps at high speed although a 51 could deploy 10 degrees at high speed to a.) lose a lot of energy, and b.) cut a turn - but it better get the result the pilot was looking for because it negated a lot of energy maueverability advantage it may have had..

[renrich]

My reference states that the P38 was limited to the equivalent of a dive speed of .65 Mach and that was placarded in the cockpit.

[kool kitty89]

And I think it was raised to .68 Mach with the dive flaps intalled.

[HJERIA]

P 51 Was faster and more maneuverable, The Lightning was stronger and had better volume of fire, with its guns in the nose.... I guess always the hands make the difference, but I think the Mustang was a little superior.

[kool kitty89]

Maneuverability depends on the context and models each having advantages, though overall maneuverability of the pre-G P-38 had mediocre maneuverability in every respect. (the G model received combat flaps which nearly doubled the turn rate)

And initial roll rate was rather poor until the boosted ailerons on the late J models.

[parsifal]

one thing that does not appear to be brought up in this thread. The P-38 cost, on average about $91000 US dollars to build, wheras the P-51D only cost $51000. For comparison, the P-47 cost about $67000 per unit.

[trackend]

P51 for me, one lump, lower maintenance time, easier to keep flying, easier to manufacture these go towards IMO making it a better fighter. a fighter on the deck and not in the air is not a fighter Impressive though the Lighting undoubtedly was I believe the Mustang to be more suited to the task.

[drgondog]

Originally Posted by parsifal

one thing that does not appear to be brought up in this thread. The P-38 cost, on average about $91000 US dollars to build, wheras the P-51D only cost $51000. For comparison, the P-47 cost about $67000 per unit.

And that reflects 1945 unit costs. The 51 went from 12,000 hours to build the A-36 to 2200 hours for the P-51.

IIRC the P-38 in 1943 was around 111K and the 51 was near 59K? The P-47 was around 80K in 1943 I think.

Syscom had the actuals on all three by tables on one of the other posts.

[drgondog]

Originally Posted by kool kitty89

Maneuverability depends on the context and models each having advantages, though overall maneuverability of the pre-G P-38 had mediocre maneuverability in every respect. (the G model received combat flaps which nearly doubled the turn rate)

And initial roll rate was rather poor until the boosted ailerons on the late J models.

The P-38L was the only version that finally approached manuevering equivalency in several, better than some, and worse than a few factors vs P-51

[kool kitty89]

Yeah, the roll rate was a major limiting factor (which had continually degraded up to the J model, particularly with full LE tanks, until the boosted ailerons were added)

And Bill, you do understand I was talking about dive flaps (dive recovery flaps) which are mounted outboard of the nacelles under the main spar. They obvioulsy would have a significant drag effect, but the main purpose was to prvent the pitch-down behavure iirc. Granted that earlier statement about shock-wave reduction/delay doesn't make sense.

And AFIK the P-38 never had actual airbrakes/dive-brakes.

Wikipedia seems to have gotten it right:

The dive flaps were installed outboard of the engine nacelles and in action they extended downward 35° in 1½ seconds. The flaps did not act as a speed brake, they affected the center of pressure distribution so that the wing would not lose its lift

[drgondog]

Originally Posted by kool kitty89

Yeah, the roll rate was a major limiting factor (which had continually degraded up to the J model, particularly with full LE tanks, until the boosted ailerons were added)

And Bill, you do understand I was talking about dive flaps (dive recovery flaps) which are mounted outboard of the nacelles under the main spar. They obvioulsy would have a significant drag effect, but the main purpose was to prvent the pitch-down behavure iirc. Granted that earlier statement about shock-wave reduction/delay doesn't make sense.

And AFIK the P-38 never had actual airbrakes/dive-brakes.

Wikipedia seems to have gotten it right:

KK - I DO realize that. That is why I call them dive brakes instead of flaps - based on loaction. And I do agree (not that it matter what I agree) that it was to keep the dive speed in the .68 to .70 range - where the P-38 was both manueverable and still controllable.

Now, controlling the pitch down tendency is all about preventing compressibility which in turn masks the elevator, which in turn, prevents the pilot to offset the pitch down effect by pulling back on the stick (meaning an 'up' elevator deflection). He needs to have effective 'up' elevator to give negative lift force at tail (relative to wing positive lift).

At that speed (>.72-.75mach) the pitching moment of the airfoil/body combination tends to pitch down and the elevator cannot help because it is 'masked' by the turbulent flow between the nacelles during compressibily turbulence. This is why early recovery and nose up capability started with trim tab being the first control surface small enough for normal strength to move.. but very dangerous loading at that high speed.

Does that make sense?

[kool kitty89]

I know the "tuck under" was a result of the shockwave/tyrbulent flow causing the tailplane to lose downward pressure ("inverted lift"), but I also think that the dive flaps forced pitch up if control had been lost by increasing lift w/out changing AoA. (granted they would also have a braking, or speed limiting effect)


See what was mentioned here: http://www.ww2aircraft.net/forum/avi...t-13155-3.html (Elevator trim during Combat)


buzzard's comments also said that the tailplane actually exhibeted a positive lift, forcefully pitching the a/c down, and attempts to pull up on the elevator (if you had the strength) resulted in further pitch down, a kind of "control reversal."

[drgondog]

Originally Posted by kool kitty89

I know the "tuck under" was a result of the shockwave/tyrbulent flow causing the tailplane to lose downward pressure ("inverted lift"), but I also think that the dive flaps forced pitch up if control had been lost by increasing lift w/out changing AoA. (granted they would also have a braking, or speed limiting effect)


See what was mentioned here: http://www.ww2aircraft.net/forum/avi...t-13155-3.html (Elevator trim during Combat)


buzzard's comments also said that the tailplane actually exhibeted a positive lift, forcefully pitching the a/c down, and attempts to pull up on the elevator (if you had the strength) resulted in further pitch down, a kind of "control reversal."

The P-38, without an elevator at all, would pitch down due to the Center of Lift and Pitching Moment of the wing body combination relative to CG.

If masking the elevator by the turbulence caused by separation 'blanked' the elevator, from creating either positive or negative lift at the tail, it would pitch the nose down.

I haven't looked at the Force Diagrams for the P-38 but this would be common design practice.

Think of it this way - if the natural tendency for the P-38 was to pitch up when elevator control was lost during compressiblity, it would start to recover from the dive 'hands off'

[kool kitty89]

Blanking would make more sense (I haven't seen mention of control reversal elswhere either, except for accounts of pilots mistaking the "tuck under" for control reversal)

I do believe the dive flaps forced a pitch op though.

[kool kitty89]

from the site buzzard posted in the elevator trim thread:

Research in Supersonic Flight and the Breaking of the Sound Barrier

The general aeronautics community was suddenly awakened to the realities of the unknown flight regime in November 1941, when Lockheed test pilot Ralph Virden could not pull the new, high-performance P-38 out of a high-speed dive, and crashed. Virden was the first human fatality due to adverse compressibility effects, and the P-38, shown below, was the first airplane to Suffer from these effects. The P-38 exceeded its critical Mach number in an operational dive, and penetrated well into the regime of the compressibility burble at its terminal dive speed, as shown by the bar chart on page 80 .35 The problem encountered by Virden, and many other P-38 pilots at that time, was that beyond a certain speed in a dive, the elevator controls suddenly felt as if they were locked. And to make things worse, the tail suddenly produced more lift, pulling the P-38 into an even steeper dive. This was called the "tuck-under" problem. It is important to note that the NACA soon solved this problem, using its expertise in compressibility effects. Although Lockheed consulted various aerodynamicists, including Theodore Von Kármán at Caltech, it turned out that John Stack at NACA Langley, with his accumulated experience in compressibility effects, was the only one to properly diagnose the problem. The wing of the P-38 lost lift when it encountered the compressibility burble. As a result, the downwash angle of the flow behind the wing was reduced. This in turn increased the effective angle of attack of the flow encountered by the horizontal tail, increasing the lift on the tail, and pitching the P-38 to a progressively steepening dive totally beyond the control of the pilot. Stack's solution was to place a special flap under the wing, to be employed only when these compressibility effects were encountered. The flap was not a conventional dive flap intended to reduce the speed. Rather, Stack's idea was to use the flap to maintain lift in the face of the compressibility burble, hence eliminating the change in the downwash angle, and therefore allowing the horizontal tail to function properly. This is a graphic example of how, in the early days of high-speed flight, the NACA compressibility research was found to be vital as real airplanes began to sneak up on Mach one.36

Indeed, it was time for real airplanes to be used to probe the mysteries of the unknown transonic gap. It was time for the high-speed research airplane to become a reality. The earliest concrete proposal along these lines was made by Ezra Kotcher, a senior instructor at the Army Air Corps Engineering School at Wright Field (a forerunner of today's Air Force Institute of Technology). Kotcher was a 1928 graduate of the University of California,
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36. The "tuck-under" problem, and its technical Solution, is described in John D. Anderson, Jr., Introduction to Flight (New York, NY. McGraw-Hill Book Co., 3rd ed., 1989), pp. 406-08.