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I read that the scram jet has a theoretical maximum speed of Mach 24. What is the theoretical maximum speed of a rocket-powered aircraft designed to operate in the atmosphere?

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    $\begingroup$ Why do you think such a value exists? Given a big enough engine, there may well be no upper limit at all. $\endgroup$ – abelenky Feb 8 '18 at 18:54
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    $\begingroup$ @abelenky: Not entirely true. The speed of light is an absolute maximum, of course. I'd also guess that there's a maximum acceleration you can get from a rocket exhaust, so you'd be limited by how long that acceleration takes you to get out of the atmosphere. And of course you have practical considerations like how much fuel you can carry... $\endgroup$ – jamesqf Feb 8 '18 at 19:19
  • $\begingroup$ @jamesqf, the assumption is clearly that you accelerate in a way to stay in the atmosphere. And the thing with practical considerations is that they don't give you a theoretical limit, just a practical one. $\endgroup$ – Jan Hudec Feb 8 '18 at 20:15
  • $\begingroup$ @abelenky size of the engine alone doesn't buy you very much: a bigger engine will consume more fuel, which is heavy, requiring a bigger engine... it's the curse of the rocket equation. That still doesn't imply a theoretical hard limit though, just that it gets exponentially expensive to attain higher speeds. $\endgroup$ – leftaroundabout Feb 8 '18 at 22:19
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    $\begingroup$ This would depend on the altitude, (or should I say, the air density). At an arbitrarily high enough altitude, where the air is thin enough to be at whatever arbitrary density you choose, just about any speed is attainable. Or are you asking what is the maximum attainable indicated/calibrated airspeed? I'd guess that would be based on the dynamic pressure that would cause the best possible insulator (think space Shuttle Heat Shield tiles), to melt or break apart from heat stress. $\endgroup$ – Charles Bretana Feb 8 '18 at 22:25
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In theory the max speed within the atmosphere is the speed that makes the air resistance equal to the strenght of the material the rocket is build from.

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    $\begingroup$ Is this common knowledge? Do you have a source to reference? $\endgroup$ – bogl Sep 23 '18 at 10:12

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