Question

How does induced flow primarily affect the angle of attack on a rotor blade?

Accepted Answer

Induced flow primarily decreases the effective angle of attack on a rotor blade. Induced flow is the downward movement of air caused by the rotor blades pushing air downwards to generate lift. The angle of attack is the angle between the rotor blade&#x27;s chord line (an imaginary line from the leading edge to the trailing edge of the blade) and the relative wind (the direction of the air flowing past the blade). Without induced flow, the relative wind would be nearly horizontal. However, because the rotor blades push air downwards, this downward moving air combines with the horizontal airflow to create a relative wind that is angled downwards. This downward angled relative wind reduces the angle between the blade&#x27;s chord line and the relative wind, thereby decreasing the effective angle of attack. A decreased angle of attack reduces the amount of lift produced by the blade. The pilot must compensate for this reduction in lift by increasing the blade&#x27;s pitch angle (the angle of the entire blade relative to the horizontal plane of rotation), which in turn increases the angle of attack back to the desired level to maintain the needed lift.

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How does induced flow primarily affect the angle of attack on a rotor blade?