What operational change affects performance in fixed pitch propellers?

The correct choice highlights the importance of coordinating manifold pressure adjustments with RPM changes in fixed pitch propeller operations. In fixed pitch propellers, the blade angle is set and cannot be altered during flight. This means that if the pilot wants to change the power output or performance, they must adjust the throttle and associated manifold pressure accordingly to maximize efficiency.

When reducing RPM, it is crucial to first ensure that the manifold pressure is set appropriately. Lowering RPM without first adjusting manifold pressure could lead to an inefficient engine operation, as the engine may not be able to achieve the desired power output effectively. Therefore, both RPM and manifold pressure adjustments are critical to maintaining optimal engine performance in conjunction with the fixed pitch propeller's limitations.

Other options do not encapsulate this relationship accurately. Only adjusting RPM without regard to manifold pressure can lead to suboptimal performance, while the notion that power output is unaffected by propeller type misunderstands the principles of power and thrust in aviation.