During forward flight, which blade has greater lift and why?

• A. The retreating blade has greater lift due to reduced forward speed.
• B. The advancing blade has greater lift because forward speed adds to rotor speed.
• C. Lift is identical on both blades.
• D. The rotor disc experiences no lift.

Answer: (B)

In forward flight, the blade that’s moving in the same direction as the aircraft’s travel (the advancing blade) experiences a higher relative wind than the blade moving opposite (the retreating blade). This happens because the forward velocity adds to the blade’s rotational speed on the advancing side, increasing the airspeed over that blade. Lift is proportional to dynamic pressure, which depends on the square of relative airspeed, so the advancing blade generates more lift than the retreating blade. The result is a dissymmetry of lift across the rotor disc, which is why rotor systems use cyclic pitch and other adjustments to balance the lift.