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I know airplanes and helicopters fly thanks to the same principle, the Bernoulli Principle. The wings and blades are designed so that the air travels faster across the up side than it does on the bottom side, generating an upward pressure, or lift. My question is... if the propeller rotates in reverse, does the pressure becomes downward? The distance the air has to travel from point A to B of the wing/blade is still the same so I would think that the way air moves around it do not matter. From the airplane perspective, I think this reverse rotation of the propeller would be equivalent to the airplane flying backward. So, what is the case here?

Thank you very much.

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    $\begingroup$ The Bernoulli principle isn't why planes fly. That's a common misconception. The majority of the lift comes from the angle of the wings/propellor blades. Run a helicopter propeller in reverse and it will accelerate downwards. $\endgroup$ – John Rennie Aug 29 '17 at 16:13
  • $\begingroup$ It can be done, but as John says, not by reversing the rotation: youtu.be/SIOGuidZuew $\endgroup$ – user167453 Aug 29 '17 at 17:50
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As John Rennie said, it's mainly the angle of attack. The Bernoulli effect keeps the air following the upper surface. As it is pulled down, it provides some lift. The Bernoulli effect is caused by the fluid stream carrying surrounding fluid away, leaving a low pressure zone, & effectively sucking a nearby surface onto the stream, or the stream onto it. It makes the top of the wing, or rotor do it's bit to help lift the aircraft. That's why some planes have turned up wing tips, to stop air leaking back into the low pressure zone from the side.

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