WW2-fighter and critical Mach speed

asma18 · Jan 15, 2018

delcyros said:
How about the critical Mach speed of fighter during world war 2? Speed remained of highest value for fighterplanes of ww2. In the early 40´s fast diving planes reached extreme speeds, bringing them close to the sound barrier. We may discuss on this board Mach speed figures of different planes. The Spitfire could be the example of the prop driven fighter with the highest Mach number of all times. What was the earliest plane to encounter it´s critical Mach Speed? P-38? Spitfire? Me-262? Anything else? (no unmanned designs like Goddarts or v. Brauns supersonic rockets, please)

ARDU in WW2 was the only allied unit to have Machmeters.Eric Brown obtained the following Tactical Mach numbers P38-0.68, P47-0.71, P51- 0.78 Brown was always able to get 0.84 out of his Spit Mk XI but that was the limit of his strength Others iin the Team were getting 0.86 with Tony Martindale obtaining 0.92 in a uncontrollable dive. Bent winngs lost prop spinner and he had blacked out but the meter had recorded it.Source Eric Brown Wings on My Sleeve

Zipper730 · Mar 14, 2018

the lancaster kicks ass said:
apparently if the spit could be powered to such a speed, the airframe could withstand the stress of mach 1.3...........

Just to be clear here, would it be able to withstand just the aerodynamic forces, or would it be able to be trimmable for level flight?

Zipper730 · May 22, 2018

redcoat said:
The piston engined aircraft with the highest Mach speed is a late model Spitfire, which in the hands of a test pilot reached Mach 0.98 in a dive, though the aircraft almost fell apart

I did some checking and it turns out that 0.96 was achieved in 1952 by a reconnaissance pilot. He was flying over 50,000 feet and lost control.

GregP said:
Here is another pdf from the US Navy.: http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80t-80.pdf

If only you had that up before I bought the book -- I could have read through this for free

swampyankee · May 22, 2018

delcyros said:
Thanks Lunatic!

I found the Critical Mach number of the Yak-3 to be rated at 0.76 (OKM tested). The wing of the Mustang has some advantages, no doubt. The elliptical wing of the Spitfire and the swept back wing of Me-262/Me-163 were also very beneficial. I found some interesting calculations of the Ho-229 design: The V1 (unpowered glider) had a critical Mach number of 0.84, but the V-2 has to be redesigned because of the Jumo 004, which did not fit in the airframe. Horten estimated a critical Mach number of 0.79, so it´s recorded top speed of 607 mp/h seems to me suspicious. Depends on the altitude.

Dave Lednicer has written a couple of articles on CFD analyses of WWII fighters, including the Spitfire. The analysis showed the first shocks were near the canopy.

fubar57 · May 22, 2018

Zipper730 said:
Just to be clear here, would it be able to withstand just the aerodynamic forces, or would it be able to be trimmable for level flight?

Lanc hasn't been here for 6 years

Zipper730 · May 22, 2018

Oh, I didn't know that

pbehn · May 22, 2018

Zipper730 said:
Oh, I didn't know that

I believe that after the flight it had no prop and bent wings so the maximum speed is obviously below that quoted.

wuzak · May 22, 2018

pbehn said:
I believe that after the flight it had no prop and bent wings so the maximum speed is obviously below that quoted.

There were a number of test flights with a PR.XI with speeds up to ~Mach 0.92, one of which saw the propeller break off (the wings were damaged from very high G-forces after that), another where the supercharger exploded and others where the dive was completely successful.

A PR.XIX in the far east after the war recorded the highest altitude attained by a Spitfire. Over 50,000ft. At one point the aircraft went into an uncontrolled dive, the calculated maximum speed was Mach 0.96. But this was based on regular instruments, nut on special test instruments used in the earlier tests. I believe the aircraft survived that unscathed.

pbehn · May 23, 2018

wuzak said:
There were a number of test flights with a PR.XI with speeds up to ~Mach 0.92, one of which saw the propeller break off (the wings were damaged from very high G-forces after that), another where the supercharger exploded and others where the dive was completely successful.

A PR.XIX in the far east after the war recorded the highest altitude attained by a Spitfire. Over 50,000ft. At one point the aircraft went into an uncontrolled dive, the calculated maximum speed was Mach 0.96. But this was based on regular instruments, nut on special test instruments used in the earlier tests. I believe the aircraft survived that unscathed.

My point was that if bits fall off the aircraft you have exceeded a limit. Similarly if the plane goes into an uncontrolled dive, unless it is always recoverable you have exceeded a limit. The maximum speed must be always under control and always return with an aircraft completely serviceable.

WW2-fighter and critical Mach speed

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