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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)
delcyros said:after a look-araouns I found some additional critical Mach-speed figures:
From Lunatic (compare P-47 vs. F4U):
Spitfir MK IVX: 0.89*
Hawker Tempest: 0.83*
F4U: 0.73 (windtunnel tested)
P-51B: 0.84*
P-38: 0.65
P-47C: 0.69
P-47N: 0.83*
*) All Mach figures, for planes with an airscrew in front of the plane, above 0.80 are highly debatable. It could happen, that a prop driven plane exceed this Mach number but the airscrew would render most controls useles (maybe except the wing). That would result in terminal dive. (terminal means not unrecoverable, but the normal use of controls is out of order. Inverted controls, buffeting, no response and other aspects)For example, the original MiG-9, the soviets first jet fighter had only a critical Mach number of 0.79. Later versions had Mach 0.81.
delcyros said:Interesting. The shockwave effects were not very well understood in the early 40´s. It is a good question how to rate the P-38. 0.65 seems to me a bit to little, too. I will have to check mathmaticly...
There are two questions remaining: A) Could the wing design sustain the stress and B) had the tail design enough stiffness for a Mach speed of, lets say 0.70?
The loose of control is a problem, too. I think the Brits did got a major breakthrough with their free bending rudder design (look at the Spit for example). I don´t know how the others tried to manage it...
wmaxt said:delcyros said:after a look-araouns I found some additional critical Mach-speed figures:
From Lunatic (compare P-47 vs. F4U):
Spitfir MK IVX: 0.89*
Hawker Tempest: 0.83*
F4U: 0.73 (windtunnel tested)
P-51B: 0.84*
P-38: 0.65
P-47C: 0.69
P-47N: 0.83*
*) All Mach figures, for planes with an airscrew in front of the plane, above 0.80 are highly debatable. It could happen, that a prop driven plane exceed this Mach number but the airscrew would render most controls useles (maybe except the wing). That would result in terminal dive. (terminal means not unrecoverable, but the normal use of controls is out of order. Inverted controls, buffeting, no response and other aspects)For example, the original MiG-9, the soviets first jet fighter had only a critical Mach number of 0.79. Later versions had Mach 0.81.
According to Lockheed the P-38 is .68 but evedence suggests that .70 was reachable when conditions were right the P-51D is rated closer to .80.
An interesting fact is that as the Mach is achieved Stabilizer/elevator effectivness is lost. The key to controlable supersonic speed was twofold a) lose the prop and b) an all flying stabilator to eliminate the shock-stall that rendered the elevator useless.
RG_Lunatic said:wmaxt said:delcyros said:after a look-araouns I found some additional critical Mach-speed figures:
From Lunatic (compare P-47 vs. F4U):
Spitfir MK IVX: 0.89*
Hawker Tempest: 0.83*
F4U: 0.73 (windtunnel tested)
P-51B: 0.84*
P-38: 0.65
P-47C: 0.69
P-47N: 0.83*
*) All Mach figures, for planes with an airscrew in front of the plane, above 0.80 are highly debatable. It could happen, that a prop driven plane exceed this Mach number but the airscrew would render most controls useles (maybe except the wing). That would result in terminal dive. (terminal means not unrecoverable, but the normal use of controls is out of order. Inverted controls, buffeting, no response and other aspects)For example, the original MiG-9, the soviets first jet fighter had only a critical Mach number of 0.79. Later versions had Mach 0.81.
According to Lockheed the P-38 is .68 but evedence suggests that .70 was reachable when conditions were right the P-51D is rated closer to .80.
An interesting fact is that as the Mach is achieved Stabilizer/elevator effectivness is lost. The key to controlable supersonic speed was twofold a) lose the prop and b) an all flying stabilator to eliminate the shock-stall that rendered the elevator useless.
Figures I have are 0.84 for for the P-51B, 0.82 for the P-51D because of the slightly thicker wing and the bubble canopy. I also recently found the mach number of the Bf-109G was about 0.78, the 109F was about 0.80.
The P-38 mach number is so low because it has a very thick (by proportions) conventional wing with the maximum chord well toward the front. Also, the shock wave from the wings and fuselage directly impead the function of the tail fin. Basically the P-38 was designed before any knowlege of mach was understood, and they just got unlucky in this one respect. Raising the tail plane to the top of the fin might have relieved a lot of this problem.
=S=
Lunatic
redcoat said:going off memory
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, and its propellor fell offFortunately the pilot managed to land OK
RG_Lunatic said:redcoat said:going off memory
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, and its propellor fell offFortunately the pilot managed to land OK
Umm, in test trim (no guns, pitot tube, etc.., all such holes covered over) the Spitfire was able to dive to 0.89 mach and make a full recovery. In combat trim this would probably be more like 0.83-0.85.
=S=
Lunatic
KraziKanuK said:No pitot tube? It carried a pitot comb 14" wide.
Standard practice was to tape over the gun ports. There was also a pitot added at each wing tip. The P-51, tested at the same time, had its guns and radio removed. It had its normal pitot removed, and as on the Spit, one added at each wing tip. The Spit reached M 0.89 while the P-51, M 0.80.
delcyros said:0.89 is for the Spit is overated. Even it´s smaller (in diameter) airscrew caused schockwaves and they did interfere with fuselage and tail (I agree, 33 inches are not enough to ensure no interfere and shockwave effects caused by the airscrew). And it lost its aircrew on that dive. Recovering alone doesn´t proove that it was no terminal dive Mutke´s claim to break Mach 1 in a Me-262 dive (which I don´t believe) underlines that. He was able to recover from his terminal dive at very high subsonic speed (but not Mach 1, the airframe of the Me-262 couldn´t sustain the stress). Anyway I believe the spit has the highest critical Mach number of prop driven planes. What about any pusher-prop layouts? Any datas?