FAA Aviation Mechanic Powerplant (AMP)PropellersMedium
A propeller shop technician places a removed propeller on knife-edges to check for balance before installation. This test primarily checks for what type of imbalance?
- AStatic imbalance caused by unequal weight distribution when the propeller is at rest
- BAerodynamic imbalance caused by blade twist variations
- CTorsional imbalance caused by uneven pitch change forces
- DDynamic imbalance caused by uneven mass distribution around the axis while rotating
Show answer & explanationAnswer & explanation
Correct answer: A. Static imbalance caused by unequal weight distribution when the propeller is at rest
A knife-edge balance stand checks static balance, meaning the propeller assembly at rest should not rotate to any particular position, indicating that its weight is evenly distributed around the hub axis. Dynamic balance, by contrast, requires the propeller to be spinning and is typically checked with electronic balancing equipment.
Why the other options are wrong
- B. Aerodynamic imbalance is not a standard balance category checked with knife-edges.
- C. Torsional imbalance relates to pitch-change forces, not knife-edge static balance.
- D. Dynamic imbalance requires the propeller to be rotating; knife-edges test static balance.
Static Balance (Knife-Edge Test)
A propeller balance check performed at rest using knife-edges to verify even weight distribution around the hub axis.
- Performed with the propeller not rotating
- Checks for heavy spots that cause the assembly to rotate
- Dynamic balance requires spinning and specialized equipment
Memory trick: Static sits still on the knife edge