Quote:
Originally Posted by WildBoar44
I do know that bigger engines need bigger prop's, the Corsair is good example, prop so big that the wings were canted to accomodate it without huge undercart legs. The twin props fitted to Precious Metal are short cropped paddle type and I think it helps reduce frontal area , reduced torque effect, allow's them to spin faster and there is some vortec thing that happens with the second rear prop i dont understand.
hope someone can step in and give the difinitive answer !!! 
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The main problem with a long prop is that the tips go supersonic, which leads to a tremendous drop in efficiency and an increase in vibration. Even a little Cessna can make the tips go supersonic if you leave the RPM up too high. Twin counter rotating props would theoretically allow for more thrust to be produced at lower tip speeds, but I'm not sure if this would compensate for the added mechanical complexity. Seems like there would be a lot more counter rotating engines around if it really worked as advertised. Gotta admit though, that Griffon is mighty bad assed