Which term describes the resultant relative wind in the basic aerodynamic model?

• A. Induced flow
• B. Rotational relative wind
• C. Resultant relative wind
• D. Angle of Attack

Answer: (C)

In the basic aerodynamic model, the airspeed seen by a blade element is the vector sum of the rotation-induced speed (rotational relative wind) and the downwash created by the rotor (induced flow), plus any freestream speed if there’s forward flight. This combination gives the resultant relative wind—the actual wind the blade element experiences. Lift is produced according to the angle between this resultant relative wind and the blade’s chord, which is the angle of attack. So the term that describes the overall wind the blade sees is the resultant relative wind. The other terms describe parts of that motion: induced flow is the downward component, rotational relative wind is the tangential component from rotation, and angle of attack is measured relative to the resultant relative wind.