When a two-blade propeller is checked on a balancing beam, what will vertical imbalance cause?

• A. the blade to rise to a vertical position
• B. the blade to stay at mid-position
• C. the blade tends to come to rest in a horizontal position
• D. the blade to move unpredictably

Answer: (C)

Vertical imbalance means one blade is heavier than the other in the plane of rotation, shifting the prop’s center of gravity away from the hub. That creates a gravitational torque about the balancing supports. The system will rotate until that torque is neutralized, settling in the orientation that minimizes potential energy. For a two‑blade propeller, the stable equilibrium under gravity is when the blade pair lies in a horizontal plane, with the heavier blade positioned at its lowest point. This makes the torque zero and prevents further rotation. Hence, the blade tends to come to rest in a horizontal position.

The other outcomes would not produce a stable, gravity-free state given the uneven mass distribution: a persistent vertical tilt or continual motion would imply ongoing torque, while a mid-position rest would indicate balance, which vertical imbalance does not provide.