P-38 Ideas & Questions

[KJ_Lesnick]

I was thinking about the P-38 and I was wondering why it had such high aspect ratio wings and not simply larger wings.  Look at the DH Mosquito and the Lighting...

[Mr.Creak]

With such high wing-loading, the P-38 should have been a dog in all but top speed.  It wasn't because of two other factors.
One is its aspect ratio (span to chord ratio; that is, the relationship of the length of the wing to its width).  Another, related, factor is its span loading (ratio of airplane weight to wingspan).
In turns or climbs, a plane's drag tends to increase and its speed to decrease.
A way to counter this is to increase the wingspan.  For any given wing area, increasing the span decreases the chord, providing a higher aspect ratio.  For structural and other reasons, most WWII-era fighters had aspect ratios of 6 or less.  The P-38 had an amazing aspect ratio of 8, meaning that it could gain the advantage of high wing loading for speed and still not lose in maneuverability, climb or ceiling.

http://yarchive.net/mil/p38.html

[KJ_Lesnick]

Mr. Creak

I was always under the impression the P-38 had poor turning performance at altitude...

[Mr.Creak]

I suppose they meant that the high AR gave a better manoeuvrability than would have been the case had it stuck with a more "normal" one.

Same link:
"As the plane approached 30,000 ft, speeds over Mach 0.60 could be sustained in level flight. Thus, manuevering could quickly give the plane compressibility problems.  At Mach 0.65 (290 mph IAS, 440 mph TAS at 30,000 ft.; 360 mph IAS, 460 mph TAS at 20,000 ft.) drag began to soar as the plane began to encounter compressibility.  At Mach 0.67 shock waves began forming and buffeting began at Mach 0.675.  At Mach 0.74 tuck under began. Buffeting developed at a lower Mach number in any maneuver exceeding 1 g."
T/C doesn't relate in any particular way to AR.
Although if they'd had the same area for a smaller AR then, of necessity the chord would have been greater, and that would have given a more favourable T/C. Presumably someone, somewhere made that choice... (Not that T/C re compressibility was much of a consideration at the time).

[KJ_Lesnick]

Mr. Creak

So turning problems was due to compressibility (air accelerating too fast over the top of the wing)