The Mustang Mk I was delicate compared to a Spitfire. It had specific procedures to care for the painted wing surface that have been posted here, including covering the pilots boots and using rubber covers when working on it. But "delicate" is subjective, this isnt a reflection on the Mustang or the Spitfire it is a recognition that the game had changed. soon after the war this type of care would be normal, and the methods used on the Mustang Mk I seen as primitive and brutal. The USA wanted lighter faster fighters and as drgondog has described, they investigated how RAF fighters were lighter than USA fighters, it wasnt cheating or below standard it was how standards were decided and applied.
P-47N/M vs P-51H
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Mustangtmg
Airman
- 58
- Mar 8, 2014
The turbocharger as shown above is not, AFAIK, representative of ANY turbocharged engine on any of the WWII aircraft engines. I'm saying that the turbo was always (once again, AFAIK) the first stage of a two-stage supercharger "system" ... if fuel injection was used, fuel was injected into the pressurized air at a point before reaching the intake system of the engine itself. If a carburetor was used, the carb was "downwind" from the intercooler, in between the intercooler and the "eye" of the 2nd stage - the engine-drive supercharger.
The image above look like a turbo setup on the engines on today's GA aircraft (and turbocharged cars) - maybe there would be an intercooler, or two turbos, but they were "parallel" and not in "series" such as those on P-38s, B-17s, B-24s, B-29s and a couple other WWII piston/prop aircraft.
Thumpalumpacus
Major
The problem is drag. A one-ounce feather drops slower than a one-ounce rock because of drag. But the acceleration under one G is a steady 32 feet per second per second regardless of the weights involved. Relative drag gets involved because it can and does slow down one object over another depending on its form.
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Another problem is that drag increases with speed. An extra 100 BHP is useful, but it is pointless making engines with an extra 100BHP if it is put in something with flaky paint and big gaps between panels that eat up that 100HP.
An example I like to suggest, take two sheets of identical paper, crumble one up and presto, it falls faster.
Regarding the subject at hand, I dimly remember reading something, maybe here, that both the P-47 and P-38 had low "Mach numbers" compared to the P-51 and especially the German fighters either or both the Me-109 or Fw-190.
I just found out that my understanding of mach number was rather wrong, instead of the wikipedia article on mach number in general, the one about Critical Mach number seems more useful to us: Critical Mach number - Wikipedia
tommayer
Airman
Why would you think a turbo reduces power at low alt? Carefully avoid believing any further information from the source that lead you to that supposition. You might spend an hour or two at Greg's Airplanes, watch his vids on various supercharging systems. He'll answer your turbo v mechanical supercharger questions clearly and simply. 47N faster way up high cause the critical altitude on its turbosupercharged system was considerably higher than the critical altitude on the mechanically supercharged 51. To understand this stuff it might be useful and interesting to you get an E-6B, or an electronic flight calculator, Set in different density altitudes and see what indicated airspeeds are needed for a given true airspeed. Quick and dirty example. Say your 51H was rated at 475 true @ 25K. That's a shade less than 320 indicated. Say your 47N is supposed to go 480 at 35K. 480 true is about 265 indicated. Your North American v Grumman question gets into aerodynamics but also has pretty simple explanations.
tommayer
Airman
For sake of completeness here, EB was not God, just a great pilot, and his critical mach estimates for the 47 were at odds with NACA's. He may have been right, but there is much credible evidence from respectable sources to the effect that he was not this time.
drgondog
Major
I had a long running correspondence with him back in the 70s. His recollections of critical mach values for P-51 and P-47 were too low and his recollection that FW 190 had Mcr higher than P-51was incorrect. I sent him a variety of tests performed by both AAF and RAF corroborating 0.75 for Limit with 0.80 Vne. Never heard back. Reams of wartme testing at Wright Field, Eglin Field and post war Wright Field validated the .75 M placard values for limit dives. Both the the P-47D and P-51D were tested to 0.84M - both experienced signicant damage including local buckling due to Q loads.
Howard Gibson
Senior Airman
It takes significant horsepower to drive a centrifugal compressor at the pressures and airflows required for WWII superchargers. That power can come directly from the driveshaft. It can come from pumping exhaust air out of the cylinder and through a turbine. I just had a fun Google search for "electric superchargers". There is no free lunch.
Spitfires and Mustangs could easily have a higher critical altitude. Just use a higher gear ratio for the supercharger. When you do this, you lose low altitude performance. Two and three speed superchargers are somewhat of a work-around for this. If you want to build a low altitude beast, you want a single stage supercharger, like on the Hawker Tempest.
Just twincharge it like Audi did with the quattro and like Lancia did the S4 the tubro feeds the supercharger making more power without changing displacement and without the lag of a turbo having slow throlle response so imganie the R-2800 or the Merlin or even the Juno in the FW-190 twincharged to make more power than normal then if you add overboost or water methol injection or nitrous you could 3k plus horsepower without changing he main engine design
Engine-driven supercharger was ... engine thing, that engine might be installed on this or that aircraft.
If you want a low altitude beast, you want a big-displacement engine, that also turns good/great RPM? Sabre was of 1/3rd greater displacement vs. Merlin, and made extra 25-30% RPM - we know that on same fuel and both with 1-stage S/C it will beat Merlin easily.
swampyankee
Chief Master Sergeant
- 4,020
- Jun 25, 2013
All turbocharged aircraft engines of the WWII era had the turbocharger "feed the supercharger"; the turbo was the low-pressure stage of a two-stage supercharging system, very often with an intercooler between stages and an aftercooler after the second (mechanical) stage. Many US fighter engines also had water injection (actually, a water-alcohol mixture to prevent freezing) and many German engines used nitrous oxide injection. Other than EFI and a concern for emissions, there's not much being done to car engines that wasn't done to aircraft engines by 1945.
Structuraly, the Mustang is a robust beast that functioned as a passable dive bomber. The 'delicate' was the over expectation of the performance of the laminar flow wing, it wasn't built well enough to function as the 'aerodynamically perfect' wing, and the surface damage they fretted about actually had almost no effect.
Hard to argue either way, although even today if you want to maximise performance you make sure the wings are clean and polished. The way the RAF used the Mustang needed to maximise speed, economy and timing, having a big disparity between aircraft on a mission increased the chances of things going FUBAR.
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- Thread starter
- #96
I have a question though, how come P-47N dive so much faster than p-51D? How come P-51H dive limit is similar to P-51D eventhough their wing are different?
Metrallaroja
Airman
- 97
- Nov 21, 2020
Wings have no influence on the dive limit, the flight controls like the elevator do instead.
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FLYBOYJ
"THE GREAT GAZOO"
Have you ever heard of compressibility?
It is a brave man who states "wings are not important" in anything to do with an aircrafts speed, I can sense Drgondog warming up his keyboard as we speak.
