This is a model of an air rocket. All measurements are in the MKS system. You may wish to play around with the amount of water in your bottle rocket, which can vary from a fill fraction (fillfraction) of 0 (no water) to 1 (all water). The pressure is in Pascals, with 101,000 pascals being about atmospheric pressure. Roughly 15 psi = 100,000 Pa. This is set with "pumpPressure", which is initially 200,000 Pa, or about 30 psi. The water fires only briefly (blue part of the trajectory), the rest is coasting. It seems crudely correct, reaching 100 ft or 33 meters in altitude, but errors may be present.
Physics: Bernoulli used to calculate water exit velocity. With bottle opening area, that can be volume flow rate. Density gives us mass flow rate, m-dot. m-dot x velocity of the water is rocket thrust m-dot can also be used to calculate the loss of water and expansion of air. This changes the pressure in the bottle, using an adiabatic approximation. DVAT equations are used to model flight.
