Rocket Engine Thrust Formula Help

  • Thread starter mleesk
  • Start date
  • #1
3
0
hello,

does anyone know how to derive the ROCKET ENGINE THRUST formula:

T = P/R AV + (P-B)A

i know you need to use F=ma and Momentum flow rate equations to get the first place. but what do you do after that?

Any help would be greatly appreciated.

Thanks,
Michael
 

Answers and Replies

  • #2
FredGarvin
Science Advisor
5,066
8
Explain your variables. I see you are accounting for pressure difference across the nozzle in the second term, but I want to make sure of the variables in the first term.
 
  • #3
The thrust is the sum of the momentum change (mass flow) * (exit velocity) if the nozzle is over or under expanded than you will get extra thrust from the exit area times the pressure difference (Exit Plane Pressure - Ambient Pressure) * (Exit Area)

[tex]\dot{m} V+({V}_{exit} -{V}_{amb}){A}_{exit} [/tex]

The mass flow is density times velocity times area, by perfect gas law

[tex]\rho = \frac{P}{RT}[/tex]


[tex]\frac{P}{RT}V^{2}+({V}_{exit} -{V}_{amb}){A}_{exit} [/tex]

so it looks like there is a T missing and the velocity should be squared. CHECK YOUR UNITS!!
 
Last edited:

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