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Jet propulsion efficiencies

  1. Aug 21, 2011 #1
    Let's suppose one wanted to move a wheeled, land-based vehicle. Generally, which would be more efficient, and why? Using a jet of air straight out the back (like the Batmobile seen in the 1989 Batman movie) or absorbing most of jet's thrust through a turbine and delivering that force to the wheels? So, pushing on air or pushing on a turbine connected to a wheel?
     
  2. jcsd
  3. Aug 21, 2011 #2

    cjl

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    Generally, applying the power to the wheels will be more efficient.
     
  4. Aug 22, 2011 #3

    sophiecentaur

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    This would be because the Kinetic energy transferred to the Earth would be vanishingly small, when you use a wheel, (the Earth doesn't move backwards, measurably) whereas there is a lot of (much more) kinetic energy transferred to the very fast moving exhaust gases. So the efficiency for the wheels is nearly 100% and the efficiency for the jet would be, initially (before the car is actually moving) 0%.
     
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