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My question is how can the angle of attack be changed when the wing is in the slipstream of a propeller, giving "enough air flow" to the wing. The propeller sends the flow of air in the same direction related to the wing no matter how the aeroplane is oriented in the space. So theoretically the angle of attack should never change.

UPD: The answer should not depend on how the plane is thrusted. Turbo engines are also pushing the plane in the same direction related to the fixed wing. ( I am not talking about engines that can change the vector of thrust).

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Not all planes have propellers and not all of the wing is behind the propeller.

In fact only a small part of the wing is behind the propeller. The rest will get clean air depending on the attitude (orientation) of the aircraft. The wing is also not perfectly straight behind the propeller either, usually dropping down a bit so there is a positive angle of attack.

Jet powered planes generally have their engines away from the wings.

In most planes, thrust is surprisingly small compared to the weight, an empty A380 only has a thrust to weight ratio of 0.47 and most of that thrust will be applied horizontally. So as the plane will sink rapidly should there be no lift from the wings. That sink tendency is what provides the angle of attack.

This will max out the sink rate should the wings be level, angle them up a bit and the plane will try to climb.

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  • $\begingroup$ The answer should not depend on how the plane is trusted. Engine are also pushing the plane in the same direction related to the fixed wing. $\endgroup$ – Boris Jan 29 '15 at 9:12
  • $\begingroup$ I believe that the question is about the washing up the top side by the way that's the airflow is formed behind that portion of the wings. $\endgroup$ – George Geo 22 hours ago
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The angle of attack, in relation to a propeller, probably affects yaw more than anything.

The way a plane is thrusted, propeller vs jets, significantly changes the dynamics of how the plane flies. Because of propeller torque and p-factor the plane tends to yaw more and will require more rudder input to compensate, especially as angle of attack is increased (on take off for example).

Look at this link to P-factor for more information. Here's an excerpt:

P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, that is responsible for asymmetrical relocation of the propeller's center of thrust when aircraft is at a high angle of attack. This shift in the location of the center of thrust will exert a yawing moment on the aircraft, causing it to yaw slightly to one side. A rudder input is required to counteract the yawing tendency.

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