Define Resultant relative wind.

• A. Rotational relative wind added to forward speed
• B. Free stream wind
• C. Rotational relative wind modified by induced flow
• D. Induced flow only

Answer: (C)

The airspeed a rotor blade element experiences is not just the air coming from the front; it’s the combination of three parts: the tangential velocity from the blade’s rotation, the axial flow from forward flight (free stream), and the downwash created by the rotor’s lift (induced flow). The blade’s relative wind is this vector sum, so the resultant relative wind is the rotational relative wind modified by induced flow. This means you’re accounting for the spinning motion and how the rotor’s wake changes the axial component of the wind the blade sees. For example, in hover there’s no forward free stream, but there is rotation plus induced downwash, still yielding a resultant wind that’s rotational relative wind adjusted by induced flow.