Which term describes the variation in blade incidence from root to tip?

Which term describes the variation in blade incidence from root to tip?

• A. Blade Twist
• B. Blowback
• C. Center of Gravity
• D. Chord

Answer: (A)

Blade twist describes how the angle of incidence changes along the length of a rotor blade from root to tip. As the rotor spins, the tip moves through the air much faster than the root, so if the pitch were the same along the blade, the tip would encounter a higher angle of attack and produce more lift than the root. To keep lift more evenly distributed and improve performance and stability, the blade is designed with twist—the pitch angle varies from root toward the tip. In many designs this means the pitch is reduced toward the tip (negative twist) so the effective angle of attack stays more uniform along the span. The other terms don’t describe this spanwise variation: blowback isn’t about how incidence changes along the blade, center of gravity refers to the aircraft’s balance, and chord is the blade’s width from leading to trailing edge, not how the incidence changes from root to tip.

Blade twist describes how the angle of incidence changes along the length of a rotor blade from root to tip. As the rotor spins, the tip moves through the air much faster than the root, so if the pitch were the same along the blade, the tip would encounter a higher angle of attack and produce more lift than the root. To keep lift more evenly distributed and improve performance and stability, the blade is designed with twist—the pitch angle varies from root toward the tip. In many designs this means the pitch is reduced toward the tip (negative twist) so the effective angle of attack stays more uniform along the span.

The other terms don’t describe this spanwise variation: blowback isn’t about how incidence changes along the blade, center of gravity refers to the aircraft’s balance, and chord is the blade’s width from leading to trailing edge, not how the incidence changes from root to tip.