I asked this over at Physics, but no one seemed to know, so I'll try here:

If I fill a plastic bottle with a small amount of rubbing alcohol, shake it around and hold a match to the bottle neck, I'll get a flame wooshing out of the opening. This can easily be used to propel the bottle upwards, like a rocket. I tried it already, there are lots of youtube videos about this, and NASA has instructions for the experiment as well.

When trying to go for maximum speed or height of the rocket, there are a few factors influencing this experiment. Here are the ones that I can think of:

Some related to the bottle:

volume, shape, aerodynamics, weight, size of opening, possibly shape of the bottle (long and thin or short and fat) When the bottle neck is smaller it creates a stronger thrust.

Others related to the propellant:

How fast does it burn, how dense is it (especially compared to air), how heavily does it vaporize. If the vapor is denser then air it all floats out of the opening of my bottle before I can light it and I don't have as much fuel.

As you might be able to see, I don't know a lot about the propellants.

So here's my question:

What are the factors related to the propellant, that influence the launch height and speed of the woosh rocket.

What's the best propellant to choose for a woosh rocket, and why?

  • $\begingroup$ Related: Best Fuel for Potato Gun $\endgroup$
    – user7951
    Jul 20, 2015 at 14:15
  • $\begingroup$ Please don't crosspost. $\endgroup$ Jul 20, 2015 at 15:41

1 Answer 1


For home projects like this I believe one of the most important things is to ensure you have a good fuel to air (oxygen) ratio. It is surprisingly easy to use too much propellant which can take up air space within the combustion chamber. More fuel doesn't necessarily mean bigger bang.


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