P-39 and P-63 Data

drgondog said:

ThomaP - if the FTH of the Turbosupercharged engine (at 37,800 ft) was 1700BHP, the Hp would have reduced considerably by the time it reached 42K?

I suspect that the prop tip velocities would also been supersonic to add considerable drag. Uness a Cd vs RN plot is available as well as a CD vs CL for increasing pressure drag as a function of increasing altitue/lower density, more data elements are absent to estimate Vmax at that altitude which would be deep into compressibility drag rise?

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I would also add that even to this day with wind tunnels and supercomputers airflow is still a bit of a mystery. I disagree with the statement that the F-4U airframe was well understood. I don't believe that given the tools of the day we can state that any aircraft of that era was well understood. In particular as aircraft speeds approached the speed of sound localized airflow could reach near supersonic increasing drag dramatically. The kangaroo pouch on the bottom of the FG-3 is far different aerodynamically than a streamlined drop tank mounted outside of the boundary layer of the fuselage. Turbulent flow is still not well understood. As Heisenberg (whose PhD thesis was on turbulent flow and who was instrumental in the development of quantum mechanics) is supposed to have said "When I meet God, I'm going to ask him two questions: why relativity? And why turbulence? I really believe he'll have an answer for the first."

Hey drgndog,

re the reduced power vs altitude

I know you know most of this, but for anyone not familiar with the effects altitude density & temperature have on the efficiency of the supercharger or turbocharger.

Below the Tropopause (~36,000 ft), as you increase altitude the engine/SC combination will become more efficient (due the temperature drop) at a faster rate than the decrease in air density will reduce the engine power - at least this is the case up to the engine critical altitude. Above the Tropopause the temperature stays the same up way past the altitude where a piston engine can operate, so the engine/SC installation will no longer gain in efficiency. This means that everything else being equal, the engine BHP will start to decrease above 36,000 ft in comparison to what it would be if the temperature kept decreasing. But RAM effect can slow down the loss of power to a degree. And contrary to what is commonly thought, a turbocharger can see gain from RAM effect, though in WWII to a lesser degree (I think) than a straight supercharger. Still (if I did my math right) the gain due to RAM effect would be about +.5 lb boost at ~40,000 ft and 450 mph, which is about the difference in altitude density between 37,800 and 42,600 ft. I have been assuming that this RAM effect accounts for the Vmax occurring at 42,600 ft (the aircraft critical altitude) rather than 37,800 ft (engine critical altitude) if there were no RAM effect.

So although I cannot say for sure whether the lesser Vmax in the chart vs what I calculated is due to the engine installation/RAM effect vs altitude effects, I do not think it would be enough to reduce the BHP by ~243 BHP - which is what would be needed to reduce the Vmax by 20 mph at those speeds (ie 440 vs 460).

I figure you are probably correct that it is due to reduced propeller efficiency and increased airframe drag due to Mach effects.

drgondog said:

Multiple reasons. The RAF gave up completely on the P-400 before the first Merlin 61 was installed on a Spit V for test (and Mustang I). Second reason is that both R-R and Packard were under capacity for demand of the Merlin 60 series - and the P-51B received highest priority which cut Curtiss, Lockheed and Bell completely out of the loop. An example includes the killing of Kelsey's 'dream' for Merlin powered P-38K in late spring 1944 by 'higher authority'. Next, the Merlin 60 series a.) did not fit, b.) wold have required the same re-design of wing attach to account for aft cg as the P-63.

The P-40 cooling requirements increased for Packard 1650-1 and would have 'jumped' agin by approximately 30%+ to accomodate cooling requirements. It would have been interesting to listen to the re-design options for cooling system - almost certain to resolve to increase of frontal radiator area and susequent drag - negating signiicant improvement in top speed at high blower.

The build quality was fine, not as good as NA surface quality, but still good for 1930s production design and processes. P-39 parasite drag was nearly equivalent to P-51 when full scale wind tunnel testing was performed at Langley. Superior to P-38, P-40 and P-47.

So, what? The USN mission never included mandate for hgh altitude (>25K) performance during WWII. The superturbo charged F4U would not have superior performance over P-47D and have less Combat Radius, so never a consideration for long range escort for heavy bombers at high altitude. As to introducing a 'bug free' F4U-3 into combat ops in 1943? IMO - No chance that it replaces F4U-1 operationally and for a variety ofreasons - ever replace F4U as produced.

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1943 was never an option. F4U-3 didn't fly until 1944.

NevadaK said:

1943 was never an option. F4U-3 didn't fly until 1944.

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I think he was implying that the F4U-3 WOULD NOT be ready in 1943.

As to introducing a 'bug free' F4U-3 into combat ops in 1943? IMO - No chance that it replaces F4U-1 operationally and for a variety of reasons - ever replace F4U as produced.

FLYBOYJ said:

I think he was implying that the F4U-3 WOULD NOT be ready in 1943.

As to introducing a 'bug free' F4U-3 into combat ops in 1943? IMO - No chance that it replaces F4U-1 operationally and for a variety of reasons - ever replace F4U as produced.

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Thank you for the clarification FLYBOYJ.

02157 converted to XF4U-3 on change order O-3-15-42 (USN Record of acceptances), accepted on 15 August 1942, crashed 31 March 1943

17516 and 49664 diverted to XF4U-3 from contract NOa(s)-198 (The F4U-1, 1C and 1D order dated 30 June 1941, extended 14 December 1943) change dated 10 June 1943 for 2 XF4U-3 aircraft, 1 with R-2600-16B, one with R-2600-14C, (Production Program Naval Aircraft 31 May 1944, Part II, Navy Department, Bureau of Aeronautics). 17658 accepted on 11 August 1943.

Lot of web sites, with details mostly repeating each other.

Geoffrey Sinclair said:

02157 converted to XF4U-3 on change order O-3-15-42 (USN Record of acceptances), accepted on 15 August 1942, crashed 31 March 1943

F4U Corsair Bu. No. 02157 | New England Aviation History

newenglandaviationhistory.com

17516 and 49664 diverted to XF4U-3 from contract NOa(s)-198 (The F4U-1, 1C and 1D order dated 30 June 1941, extended 14 December 1943) change dated 10 June 1943 for 2 XF4U-3 aircraft, 1 with R-2600-16B, one with R-2600-14C, (Production Program Naval Aircraft 31 May 1944, Part II, Navy Department, Bureau of Aeronautics). 17658 accepted on 11 August 1943.

Lot of web sites, with details mostly repeating each other.

U.S. Experimental & Prototype Aircraft Projects

This book focuses on those American fighter projects of WWII that never reached combat forces, or only in a very limited manner. The book illuminates little known or minimally documented aircraft and projects that significantly advanced fighter design that never went into full-rate production...

books.google.com.au

Vought F4u Corsair [PDF] [47srhl9900j0]

Vought F4u Corsair [PDF] [47srhl9900j0]. This is a definitive technical guide to the Vought F4U Corsair. With over 12,500 produced, the Vought F4U Corsair is one...

vdoc.pub

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Thank you, Geoffrey. I grabbed this screen shot from the Vought F4U book you linked. From this it looks like no F4U-3's flew prior to 1944.

Regards,

Kk

Some crazy numbers of the F4U-3 already posted in another thread.


And an extract from AEL-867 Calibration of R-2800-14W Engine and XTT13-12 Turbo Supercharger

Note that tested GW at TO = 90% of combat load. Increased speed values for Vmax woul be enhanced by a.) lower contribution of pressure drag due to lower CL, and b.) lower CL would reduce Induced Drag.

Net - reported performance must be compared to other a/c in similar state,

An aircraft that supposedly flew at 480 MPH and no one has ever heard of it. As Maxwell Smart would say "Would you believe it?"
I also note that F6F with the same engine was credited with 413 MPH a very very big difference.
I found my copy of the NACA test of the Birmann turbocharger