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| | Propeller - Wikipedia, the free encyclopedia |
 | | A propeller is a device which provides thrust for propulsion of a vehicle such as an airplane, ship, or submarine though a fluid such as water or air, by rotating two or more twisted blades about a central shaft, in a manner analogous to rotating a screw though a solid. |
 | | However, the blades of a propeller don't push directly on the fluid, but rather act as rotating wings, and produce force via Bernoulli's principle, generating a difference in pressure from the forward and rear surfaces of the airfoil-shaped blades. |
 | | Contra-rotating propellers involve a second propeller rotating in the opposite direction immediately 'downstream' of the main propeller so as to recover energy lost in the swirling motion of the air in the propeller slipstream. |
| en.wikipedia.org /wiki/propeller (2006 words) |
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