A couple of points.
When Johnson said during my interview that he saw 300 mph IAS at 32,000 ft, I immediately compared that to the P-38 (which I been extensively researching). At 30k and 300 mph IAS, the P-38 would have been well into compressibility. Estimating in my mind, I figured that at 32k, 300 mph IAS is about 455 mph. I responded to Bob with "That's well above 450 mph". Bob then said, "Closer to 470."
I thought a speed just above 450 mph was reasonable, and I still think that it is. And believe me, there was nothing that Johnson was going to encounter in December of 1943 that could get within 60 mph of his Jug at altitude anyway.
After reviewing various data sheets for the R-2800-21 and -59, as well as power and speed charts for the above, I conclude that Henning isn't really out of line here, 32,000 feet is really pushing the limits to pull 72" of MAP with a "B" series engine and related turbo.
When I examine the power curve for the P-47M-1-RE, I see that it could reach 475 mph at 32,600 feet, pulling 72" Hg. However, the P-47M used the -57 "C" series engine and the more efficient CH-3 turbo. This turbo provided greater boost pressure without overspeeding. According to G.E., the C-21 and C-23 turbos suffer serious efficiency problems at 22,000 RPM, as well as great risk of overheating, which will eventually cause the lubricating oil to coke, which in turn works like a lapping compound that will rapidly destroy the bearings. This is why the turbos (C-21 and C-23)were regulated to 18,250 RPM in normal use, it provided a adequate cushion for limited overspeed. The Turbo impeller/compressor assembly could handle rotational speeds up to 26,000 RPM, but due to the backpressure caused by their inherent inefficiency, boost pressure would drop dramatically, and temperature would rise dangerously within the turbo housing. This would eventually lead to heat related failure as described above. Catastrophic failure could seriously damage the airplane and cause it to become unflyable. It is interesting to note that Republic did design in more than enough duct capacity for even the CH-3 turbo.
Now about comparing drag between the P-47D/N and F4U-3. In terms of drag coefficient, the P-47D-25 thru M is lower than the the F4U-1D. The Jug comes in at .0235 and the Corsair at .0267. The F4U-3 was built from the F4U-1A, which didn't have the rocket stubs. However, the F4U-3 did incorporate a large intake scoop under the fuselage (as engine induction air was no longer taken in from the inboard leading edge openings). So, I imagine drag was probably consistant with the F4U-1D.
It may be interesting to note that the P-47B came in at .0213, even lower than the P-39N! Adding the under wing pylons and bubble canopy bumped drag up. Johnson's Jug had neither, so it should be somewhere between the P-47B (which lacked even the belly shackles) and the P-47D-25. Probably close to .0218 give or take a tiny bit. That will certainly aid in relation to maximum speed. Comparing flat plate area using a Cdo for the P-47D-5 of .0218, the F4U-1D calculates at 8.58 sq/ft, the P-47D-5-RE at 6.54 sq/ft. (Drag data from NACA L5A30 and ACTR 4677). Considering the size of the Thunderbolt, and the diameter of the engine, its Cdo is remarkably low.
For comparison's sake, the P-51D comes in at .0176, the P-63A at .0203 and the P-40E at .0242.
My regards,
Widewing
