FAA Powerplant Written Practice Test

What purpose do moveable counterweights serve in a radial engine aircraft?

1. To increase engine speed

2. To adjust fuel-air mixture

3. To reduce dynamic vibrations in the reciprocating engine

4. To enhance the cooling of the engine

The correct answer is: To reduce dynamic vibrations in the reciprocating engine

Moveable counterweights in a radial engine aircraft are specifically designed to help reduce dynamic vibrations that can occur due to the reciprocating motion of the engine's pistons. In radial engines, the arrangement of the cylinders and the movement of the pistons can produce significant forces that lead to vibrations. These vibrations can have detrimental effects on the aircraft's performance, structure, and can lead to pilot fatigue. The moveable counterweights adjust in response to the changing conditions and positions of the pistons during operation. By counterbalancing the forces generated, they effectively minimize the vibration levels. This adjustment is crucial as it enhances the overall smoothness of engine operation, improves engine efficiency, and reduces wear on engine components. Additionally, while other options may suggest functions that could theoretically relate to engine performance or operation, they do not pertain to the primary purpose of the counterweights in a radial engine context. Thus, their integral role in vibration reduction makes them essential for maintaining the overall integrity and efficiency of radial engines.