How is the angle of incidence measured in a rotary-wing aircraft?

How is the angle of incidence measured in a rotary-wing aircraft?

• A. Measured from chord line to rotational relative wind
• B. Measured from leading edge to trailing edge of the airfoil
• C. Measured from the airfoil surface to the relative wind
• D. Measured from the center of pressure to the relative wind

Answer: (A)

Angle of incidence on a rotor blade is the angle between the blade’s chord line and the relative wind the blade sees. In a helicopter, the air the blade cuts through comes from its own rotation (the rotational relative wind) and any forward or vertical motion of the aircraft (induced flow). The pitch setting changes this angle by rotating the chord line relative to that relative wind, which directly affects lift generated by the blade section. So the reference is the chord line, measured to the direction of the relative wind produced by the blade’s motion through the air. The other options don’t reflect how the blade actually interacts with the moving air: the leading/trailing edge is just geometry, measuring from the surface is not the standard reference for incidence, and the center of pressure is a force point, not an angular reference.

Angle of incidence on a rotor blade is the angle between the blade’s chord line and the relative wind the blade sees. In a helicopter, the air the blade cuts through comes from its own rotation (the rotational relative wind) and any forward or vertical motion of the aircraft (induced flow). The pitch setting changes this angle by rotating the chord line relative to that relative wind, which directly affects lift generated by the blade section. So the reference is the chord line, measured to the direction of the relative wind produced by the blade’s motion through the air. The other options don’t reflect how the blade actually interacts with the moving air: the leading/trailing edge is just geometry, measuring from the surface is not the standard reference for incidence, and the center of pressure is a force point, not an angular reference.