My motors tend to have a convergent-divergent nozzle slid into the casing
with an o-ring and retained with a clip or something that prevents them
from being ejected, but would allow it to slide further up into the motor.
Obviously the pressure is trying to push it out, right? That's how rocket
motors work!
Except the interaction of the expanding gas with the convergent part of the
nozzle is actually where the magic happens, accelerating the exhaust by
trading pressure and temperature for velocity.
I'm ready to be wrong here, but wouldn't a large proportion of the total
thrust be pushing the nozzle IN TO the motor? All the forces have to
balance, and you can't accelerate the gas without something to push against
(I do NOT mean that like the question "how do rockets work in space with no
ground to push against?")
I haven't sat down to work out the net force on the nozzle of an example
motor, any of you ever done so, or suspect that the answer might be
surprising?
-Bill
