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Proper Thrust Formula

  1. Apr 9, 2013 #1
    I would like to get some help if possible. I am trying to determine the correct formula to calculate the velocity of the exit stream in an aircraft. I know the thrust, the velocity of the intake, inlet diameter, and air density (ρ). Thanks for any help.

  2. jcsd
  3. Apr 9, 2013 #2


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    Thrust is momentum per time - with the known mass flow (mass per time: you have density, velocity and area), you can calculate the velocity difference between intake and exit.
  4. Apr 13, 2013 #3
    It depends on the propulsion mechanism. Is this a jet engine? Because if you are considering a jet engine I don't think you have enough information. The temperature of the exit stream is significantly higher than the inlet temperature which means the density is different between intake and exit. So you can determine the mass flux but you do not have sufficient information to determine the velocity. In addition, if the exit stream is supersonic and is not perfectly expanded then the pressure difference between intake and exit will also be contributing to the thrust.
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