S.R.B.M. idea

[deathbyDWV]

In this case S.R.B.M. doesn't stand for short range ballistic missile, but it stands for soda rocket bottle mortar. I was going to take an idea from this guy http://www.instructables.com/id/Gasolin ... her.-Desi/ but i wanted to use propane for the fuel and not have an air pump. Do you think it'll have good power at all or not really? I was thinking that his might just work much better because it is (kind of) a hybrid.

[Technician1002]

In this case S.R.B.M. doesn't stand for short range ballistic missile, but it stands for soda rocket bottle mortar. I was going to take an idea from this guy http://www.instructables.com/id/Gasolin ... her.-Desi/ but i wanted to use propane for the fuel and not have an air pump. Do you think it'll have good power at all or not really? I was thinking that his might just work much better because it is (kind of) a hybrid.

Propane provides a little less energy than gasoline. Using unpressurized instead of at 40 PSI shown in the video cuts the mass of fuel and oxidizer in the combustion chamber down to about 1/3. You can compensate some for the non pressurized chamber by making it a little larger and using a longer launch tube to accelerate over a longer distance using the lower pressure. In the dimensions given, the power will be considerably lower with propane and air if not under pressure.