If you went supersonic in a plane that has no pressurized cockpit, would you be completely deaf (because of flying faster-than-sound)? Would it be dangerous to the pilot even if he/she was in an enclosed cockpit, and if so, is this the reason why we still don't have supersonic maglev trains? Did anyone ever attempt or conduct a supersonic flight in a non-pressurized plane?
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$\begingroup$ It would be as safe as any other non pressurised plane at that altitude $\endgroup$– AbdullahMar 21, 2021 at 10:26
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$\begingroup$ @Abdullah I didn't specify an altitude. Would one be deaf when supersonic? $\endgroup$– GiovanniMar 21, 2021 at 10:28
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1$\begingroup$ No, one would not be deaf, because the air in the cabin is moving with you. On a related note, if you jump from a Boeing 737MAX and hit another Boeing 737MAX flying the other way, you would break the windshield, then break the sound barrier. $\endgroup$– AbdullahMar 21, 2021 at 10:39
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$\begingroup$ @Abdullah But the cabin isn't pressurized, and some general aviation aircraft have tiny open holes/windows where you can stretch your handpalm out. If a plane with such windows flew supersonic, would the air still move with you so to not be deaf(er)? $\endgroup$– GiovanniMar 21, 2021 at 10:41
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$\begingroup$ May be a duplicate. Answered here: aviation.stackexchange.com/questions/17056/… $\endgroup$– John KMar 21, 2021 at 14:31
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3 Answers
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When you're in the cockpit, the sound you are hearing is vibrations of the skin and canopy/windows induced by the outside flow, transmitted through the air within the cabin to your ears. A very loud hiss/roar (even in a normal jet, if you speed up to near Vmo, say .85 M, the noise level in the flight deck gets unpleasantly loud. Go faster, and it's the same hiss/roar but the more energy being imparted means the sound level transmitted to your ears goes up).
When Chuck Yeager was going supersonic in the X-1, he could only tell he was supersonic was by the Mach Meter, not by the noise level.
If the cockpit was unpressurized, this doesn't really change because it's still just noise transmitted from vibrations of the skins/windows transmitted through air that is stationary relative to objects it's in contact with, so you're still just hearing a hiss/roar of the outer airstream passing by, supersonic flow or not. Just way louder, I'm sure, because of less sealing and insulation.
Any other sounds originating outside you would also hear to the extent that the sound waves from that sound impacted that skin and caused a change in the sound character being transmitted through the stationary air in the cockpit. If the wave was intense enough, you should hear a thump sound of some sort, whatever was the result the pressure wave of the sound origin changing the transmitted energy passing through the still air in the cockpit at the instant it reaches the fuselage.
The key part is that the air within the cockpit is not moving with any speed, so it will transmit any vibration from the skins, windows, engines, pumps, etc to your ears whether you are supersonic or not.
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1$\begingroup$ And if your cockpit wasn't enclosed, you'd sit in open air instead, you wouldn't hear anything as Arkhem stated, unless there was a sound in front of you, right? $\endgroup$– GiovanniMar 22, 2021 at 6:08
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$\begingroup$ @Giovanni: if you were sitting in the open air with it moving past you at > 1235 km/h, I'd say you would have more pressing things to worry about than the sounds you hear. But yeah, I guess you wouldn't hear sounds generated behind you, unless they are transmitted through the fuselage... $\endgroup$– rob74Mar 22, 2021 at 7:59
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$\begingroup$ @rob74 What things to worry about exactly? I'm assuming here the pilot flies below the Death Zone altitude (< 26,000 ft), and even above that altitude you don't necessarily need a pressurized or enclosed cockpit, just artificial oxygen supply. $\endgroup$– GiovanniMar 22, 2021 at 9:07
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$\begingroup$ @rob74 The 1235 kmh number is just for 20°C. In the upper troposphere sound is considerably slower. Since your planet's mean surface temperature is 14°C, I don't get why the speed of sound is usually specified at 20°C. $\endgroup$– GiovanniMar 22, 2021 at 9:12
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1$\begingroup$ @Giovanni A lot of scientists are past 50 years of age, and their fingers get too stiff to take good notes when the room is down to 14C. Yes, I know, that's what post-grads are for, and they're generally in their 20s. It's mostly a joke, anyway... $\endgroup$ Mar 22, 2021 at 11:09
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I refer you to Thrust SSC, a supersonic car.
The sonic boom is left behind you as you are by definition going faster than the sound. It’s the people around you who are damaged by it. Hence why no supersonic flight over land - and news articles when it does happen for security reasons - and no supersonic vehicles in general.
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$\begingroup$ But one is deaf when driving or flying supersonic in a non-pressurized cabin? $\endgroup$– GiovanniMar 21, 2021 at 10:38
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$\begingroup$ Do you mean “are you deafened” (the noise damages your ears) or “is all sound left behind you so that there is nothing for your ears to hear?” If there were sound being generated in front of you then you would pass through the waves and hear it. However you would not hear sound behind you. A greatly simplified example: If you are riding your bicycle next to someone in a car at speed and they throw some water in front of you from their window you would get wet as you would catch up with it. If they throw from behind you you would not get wet as you are moving forward faster than the water is. $\endgroup$– ArkhemMar 21, 2021 at 10:45
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$\begingroup$ I mean your 2nd question, all the sound is left behind you. So your answer is yes, you'd be deaf because the sound (the water in your example) would remain behind you? $\endgroup$– GiovanniMar 21, 2021 at 10:47
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$\begingroup$ @Giovanni I wouldn’t use the word ‘deaf’ as that implies you are incapable of hearing because your body is damaged or defective. You aren’t deaf, there’s just nothing to hear unless you pass through the sound wave of something in front of you. I suspect it would sound odd through doppler shift but I defer to physicists for that. $\endgroup$– ArkhemMar 21, 2021 at 10:50
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I believe the Bell XS-1 was unpressurized. As John K points out, pressurization will not have an effect on sound levels in the cockpit.
In regards to your comments about supersonic trains, the energy consumption at low levels would be prohibitive in order to overcome exterior parasite drag and there are significant problems keeping and maintaining a vehicle on a track at those speeds. Attempts such as the Hyperloop in order to combat parasite drag by operating the vehicle inside of an evacuated tunnel are being experimented with, but in my opinion do not show a whole lot of promise, as the entire system would be cost prohibitive to operate, not to mention riddled with design difficulties. It has nothing to do with a pressurized cabin versus an unpressurized cabin.
answered Mar 22, 2021 at 6:38
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$\begingroup$ I also wonder what is it like to drive or fly supersonic while you're in open air (such as a cabriolet and its counterpart among airplanes). $\endgroup$– GiovanniMar 22, 2021 at 6:49