[quote name='Francois424']
- Electric Propellers (I'd say 3 sizes: 0.625, 1.25 and 2.5 to fit existing fuel tanks)
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Why propellers? We already have jet engines for high efficiency atmospheric flight, and ion engines and nuclear engines for high efficiency space flight.
May I link you to a helpful topic on aerodynamics? http://forum.kerbalspaceprogram.com/threads/121615-In-praise-of-the-new-aerodynamics-and-rocket-flipping