Had a little project a while back, created some 'coke bottle' rockets. The ideais simple, use compressed air to push out an incompressible liquid, water creating some thrust for the bottle rocket to fly into the sky. there are plenty of tutorials for making bottle rockets out there, but i wanted a more realistic effect of a rocket. Here is where some physics comes in. I personaly dont see this effecting lift off performence but i am no professor. I want to replace the water, with a volatile liquid. And, when launched, the air forces the liquid out as it would do to water thus creating some thrust, but then the fuel coming out is ignighted, creating a rocket like effect on the ground and while it flies into the air. As its ignighted outside the bottle, it wouldnt increase the thrust would it? If it were ignighted inside the bottle (well thats a generalisation), it would, as the expansion of gases would make a good little rocket. Just somthing i want to test out to make the bottle rockets a tad more interesting. I fear that each rockets lifetime would drop dramaticly. That and i would be replacing launch pads quite a few tmes before i upgraded to a copper.