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If both have the same dimension, same amount of fan blade, and supplied by the same amount of energy, which one would product bigger thrust and less total drag (the drag on the blade and the "tube" they are in)? What other characteristic would they differ at? Clarify: duct fan is driven by a shaft, a shaftless propeller is driven at the rim using electromagnetic force like this "http://www.popsci.com/china-new-submarine-engine-revolutionize-underwater-warfare" or normal mechanical force. Don't mind the fact the shaftless propeller is using on a submarine, I am thinking that if it can propell water it could propell air.

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  • $\begingroup$ There was a question about this not long ago, but I can't find it. The problem is that the bearing losses in the outside race track are going to be huge.The propeller has to impart the force of thrust to the aircraft fuselage somehow, those outside bearings become a big issue. $\endgroup$ – Ron Beyer Jun 6 '17 at 15:16
  • $\begingroup$ First of all you need to specify a speed. Also a prop is not a fan. A prop does not generate force by moving air backwards, but by generate lift, which is why its efficiency is heavily affected by the ratio of air speed and blade speed, which is why prop is only usable for lower speed planes because blade speed is limited by the speed of sound. $\endgroup$ – user3528438 Jun 6 '17 at 15:47
  • $\begingroup$ @user3528438: Lift produces downwash by accelerating the flow downwards. Now turn this concept around by 90°, and the downwash becomes a prop blast. Of course do both accelerate air backwards and create lift in the opposite direction. The physics of both is the same. $\endgroup$ – Peter Kämpf Jun 6 '17 at 19:08