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What air pressure is required?
I have seen a rocket driven by compressed air. It is made from a plastic bottle and is a children's toy.
If you build a rocket one the same principle that can carry one person to the moon, how much air and what pressure does it need?
What kind of treadmill would be suitable for that?
asked in aircraft, pressure, sci fi



ndm20 answers:

This is a very complex calculation - given that the escape velocity for earth is 11km/s, and this is over the speed of sound, you'd need a converging-diverging nozzle at the exit. If we have the exit velocity of the air at mach 3 (as that's what my tables go up to) this is roughly 1/11 of the speed required of the rocket. This means you'd need an internal pressure of 110 bar, and thus (assuming the tank was thick enough to hold the pressure - 20cm steel, but you built it, somehow, to have a mass of half a tonne) to accelerate the rocket the required amount you'd need a tank to hold 15million litres of compressed air (1.7billion litres uncompressed). This equates to a cylinder 100m in radius by 500m tall - more so the heavier the craft is as this doesn't take into account the mass of the air!!

Now, with a foot-pump you can get about 0.5l/s of air (if you work quickly). This means that it would take you 108 years to fill it.

With a treadmill it all depends on the mechanism used - if you can a massive 10l/s, it would still take you just over 5 years... At least you'd get fit!!


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