Has any propeller driven aircraft ever achieved and sustained supersonic speed? If not, why can't propeller airplanes achieve that speed?
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4$\begingroup$ In controlled horizontal flight? $\endgroup$– mjsMay 17, 2014 at 6:41
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$\begingroup$ @mjs yes.in a steady controlled horizontal flight $\endgroup$– KatzMay 17, 2014 at 6:57
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3 Answers
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Supersonic level flight? No.
The fastest propeller-driven aircraft is either the turboprop-powered TU-114 with a measured top speed of Mach 0.73 or the turboprop-powered XF-84H "Thunderscreech" with a design top speed of Mach 0.9 and an actual top speed of either Mach 0.83 or Mach 0.7 (sources disagree). The latter is an indication of why supersonic propeller-driven aircraft are unlikely: the continuous sonic boom coming off the propeller tips made the Thunderscreech the loudest airplane in the world.
The record for piston-engine aircraft is slightly lower, at Mach 0.71.
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$\begingroup$ Why would there be a continuous sonic boom coming off the propeller tips? If it was turning fast enough with the tips supersonic and the hub subsonic I'd agree (some part of the prop would always be precisely at Mach 1) but in this case the entire prop would be supersonic wouldn't it? $\endgroup$– falstroMay 17, 2014 at 9:14
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14$\begingroup$ @falstro: The sonic boom is not only occurring at Mach 1, but at all speeds above it. When a body travels faster than the sound, the forward-moving sound waves are compressed and will form a cone. When this cone moves over the ear of an observer, he will hear the pressure changes across the boundary of this cone as a sonic boom. Theoretically, a properly designed propeller will still work at supersonic speeds, but the efficiency will be so horrible that nobody has tried that seriously. $\endgroup$ May 17, 2014 at 10:24
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7$\begingroup$ @falstro more of a boom? The Thuderscreech never went above mach as a whole system. The propeller turned such that the tips were above mach. As soon as they did so they were radiating a sonic boom. Each blade was. When a blade passed the plane (level/altitude/height of your ears) of your hearing you would hear it's boom, then when the next blade's boom came across your ears, you would hear it's boom. Many booms per second, which to you would "sound like" one long continuous boom, but in fact were waves of booms radiating out. $\endgroup$ May 17, 2014 at 13:11
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3$\begingroup$ @falstro - If you read the wikipedia article you'll see that the XF-84H's propellor tips were going supersonic even when it was on the ground. Causing aaaallll sorts of havoc for ground operations. The inability to get to a designated "supersonic" zone before unleashing a huge sonic boom seems like quite the show stopper. Further, the sonic waves coming from the tips (when the rest of the craft was subsonic) appeared to mess with the aircrafts general stability. I'd think those two reasons together are sufficient to explain that sentence. $\endgroup$– Jae CarrMay 18, 2014 at 16:19
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1$\begingroup$ @falstro: I would think that a larger crosssection (due to the propeller) would make for a louder boom. $\endgroup$– user7241Feb 20, 2015 at 21:17
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According to Wikipedia: "The tip of the propeller on many early aircraft may reach supersonic speeds, producing a noticeable buzz that differentiates such aircraft. This is particularly noticeable on the Stearman, and noticeable on the North American T-6 Texan when it enters a sharp-breaking turn. This is undesirable, as the transonic air movement creates disruptive shock waves and turbulence. It is due to these effects that propellers are known to suffer from dramatically decreased performance as they approach the speed of sound. It is easy to demonstrate that the power needed to improve performance is so great that the weight of the required engine grows faster than the power output of the propeller can compensate. This problem was one that led to early research into jet engines..."
So basically the performance drops so badly that you better switch to jet engines. In fact when designing the blades, a max tip Mach of ~.9 is a hard limit of design. The text continues to say that nevertheless some propeller aircrafts were able to approach speed of sound in a dive.
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1$\begingroup$ What if you had a jet that pushed the plane above Mach 1 and then turned on the propellers? Impractical, I know, but just for the sake of the argument? $\endgroup$– d-bApr 24, 2017 at 20:07
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No propeller-driven aircraft has ever exceeded Mach 1. The Brits did high-Mach dive tests in Spits out to high Mach numbers but never to Mach 1. In the US, Herb Fisher did high-Mach dive testing in a modified P47 and never reached Mach 1.
The problem is propeller over-speed and high drag rise on the propeller disk. It simply can't be done.
