So I need to know the equations for finding the size and angle for a conical nozzle. I am making a rocket engine and I decided the conical nozzle would be the easiest to build. The rocket is going to be used at ground level(a stable altitude), so you don't need to worry about finding the best nozzle shape for a range of altitudes.
Overall, I need an equation that gives me specifically the nozzle length and the nozzle wall angle, and this equation needs to find those two things based on a stable altitude not a range of altitudes.
If there is a generally good nozzle angle online, then please send me that too.