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Liquid-fulled rocket engine efficency.

  1. Jul 20, 2009 #1
    "Acceleration increased during S-IC flight for two reasons: decreasing propellant mass; and increasing thrust as F-1 engine efficiency improved in the thinner air at altitude."

    This is from Wikipedia, so who knows. Why would a thiner atmosphere increase the thrust efficency of the engine? Something to do with the ullage space in the tanks not needing to be filled with atmosphere?
  2. jcsd
  3. Jul 20, 2009 #2


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    I don't know whether or not this would be considered 'engine efficiency', but obviously aerodynamic drag decreases with altitude.
    Also, rocket nozzles have specific air-pressure ranges at which they work best. Bell-shapes work better lower, while conical ones are better in thinner air.
  4. Jul 20, 2009 #3


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    It's mostly due to the pressure thrust. As altitude increases and atmospheric pressure decreases, there is a contribution to the thrust due to static pressure at the exit of the nozzle. Both thrust and Isp increase with altitude.
  5. Jul 22, 2009 #4
    Ah, this makes sense. You can imagine a 1atm pressurized container. Opening this on the ground does nothing. Opening this in space would create thrust. Thanks!!
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