Building the Better Rocket
Because the force driving the rocket depends on the pressure of the water spewing out the back, you can improve flight time and distance in two ways: Increase the pressure in the bottle or make the water transfer momentum more efficiently.
Start by experimenting with driving the cork farther into the bottle and using different launch angles. A deeper cork requires more pressure to pop, so you can expect longer flights. The limiting factor here is your pump; any old pump will be able to launch a rocket whose plug is inserted only to the safe point, but as you drive the cork deeper, you’ll need more pressure.
If you’re using a very cheap bike pump, the back pressure can overwhelm the seals on the pump before the rocket launches. ...