What is the function of moveable counterweights on engine crankshafts?

The function of movable counterweights on engine crankshafts is primarily to reduce torsional vibrations in an aircraft reciprocating engine. Torsional vibrations occur when there is a twisting force on the crankshaft as it rotates; these forces can cause stress and wear on the engine components. Moveable counterweights are designed to adjust their position in response to these vibrations, effectively balancing the crankshaft's rotational forces and minimizing the amplitude of torsional vibrations. This helps to ensure smoother operation of the engine, enhancing its reliability and performance.

In contrast, while dynamic vibrations are a concern for engine performance, they are typically managed through other design features such as engine mounts, exhaust systems, or fixed counterweights. Resonation at the natural frequency of the crankshaft is also a phenomenon that can cause issues but is not the primary purpose of movable counterweights. Their specific role is focused on mitigating torsional vibrations, which is critical for maintaining the structural integrity of the engine components during operation.