What is a limitation of increasing RPM for greater power in a piston engine?

In a piston engine, increasing RPM (revolutions per minute) can significantly affect performance and efficiency. One of the limitations of operating at higher RPM is the concern regarding excessive propeller tip speed. As engine RPM increases, the rotational speed of the propeller tips also increases.

When propeller tip speed approaches or exceeds the speed of sound (approximately 343 meters per second or 1,125 feet per second), it can lead to compressibility effects, resulting in problems such as increased drag, loss of efficiency, and potentially the onset of shock waves on the propeller blades. This can lead to a reduction in thrust and can cause vibrations and structural stresses that might compromise the integrity of both the propeller and the engine.

Maintaining an optimal propeller tip speed is crucial for ensuring that the engine operates efficiently and safely. If the design limits for tip speed are exceeded, not only is performance adversely affected, but it can also potentially lead to failures or significant damage, thus significantly constraining the operational parameters of the aircraft engine. This illustrates the importance of managing RPM to balance power output while remaining within safe operational limits.