FAA Aviation Mechanic Powerplant (AMP)PropellersEasy
A mechanic examines a propeller blade and notices the blade angle gradually decreases from root to tip. What is the purpose of this design feature?
- ATo equalize the angle of attack along the blade span since tip speed is greater than root speed
- BTo increase the structural strength at the blade tip
- CTo allow the blade to feather more quickly during engine failure
- DTo reduce the overall weight of the propeller blade
Show answer & explanationAnswer & explanation
Correct answer: A. To equalize the angle of attack along the blade span since tip speed is greater than root speed
Because the tip of the blade travels faster through the air than the root (due to greater radius at the same RPM), the blade is twisted so that each section maintains a more uniform, efficient angle of attack along its length.
Why the other options are wrong
- B. Twist is not primarily a structural feature.
- C. Feathering rate is unrelated to blade twist design.
- D. Twist is aerodynamic, not primarily for weight savings.
Blade Twist (Washout)
A design feature where blade angle decreases from root to tip to equalize angle of attack, since tip speed exceeds root speed at a given RPM.
- Tip travels faster than root due to greater radius
- Twist keeps angle of attack more uniform along span
- Improves overall aerodynamic efficiency
Memory trick: Twist tames the tip's extra speed