Model rocket propulsion

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If say hydrogen is ejected out of the tail of a model rocket and combusted with O2 of the surrounding air, will that propel the model rocket forward and will the propulsion be sustainable?
 
It is a fairly common method using propane. Try searching for pressure jet. Hydrogen will combust much faster so some adjustments will probably be needed.

To get any significant thrust you need a properly designed combustion chamber.
 
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Thank you for the reply.

So in effect, the expansion of hot gases is fast enough that it poses no significant barrier to the entry of oxygen in the combustion chamber from the outside air?

For a fairly large combustion chamber, is the process more efficient than say 40-50%?
 
The fuel must enter the combustion chamber at supersonic speed to pull in the air and generate the ram effect that makes it work. The propane ones I have seen had a very low efficiency.
 

enigma

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You are referring to bringing oxygen from the outside, mixing it with hydrogen in a combustion chamber and expelling that?

I see no reason why it wouldn't work. It's not a 'rocket' engine if you use that design, however. 'Rocket' implies both fuel and oxidizer are carried onboard.
 
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Bjørn Bæverfjord said:
The fuel must enter the combustion chamber at supersonic speed to pull in the air and generate the ram effect that makes it work. The propane ones I have seen had a very low efficiency.
what is "ram effect"?
 

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