Question

If an engine fails to reach its rated wide-open throttle (WOT) RPM, what specific change to propeller pitch should be made?

Accepted Answer

If an engine fails to reach its rated wide-open throttle RPM, you must decrease the propeller pitch. Wide-open throttle, or WOT, refers to the condition where the throttle is fully open, allowing the engine to produce maximum power. Rated RPM is the specific speed at which the engine manufacturer guarantees the engine will produce its peak rated horsepower. Propeller pitch is the distance a propeller would move forward in one full revolution if it were cutting through a solid medium, similar to how a screw moves through wood. Increasing the pitch makes each blade cut a larger angle into the air, which increases the load or resistance on the engine. If the load is too high, the engine cannot spin fast enough to reach its rated RPM, similar to how a bicycle is harder to pedal in a high gear. By decreasing the pitch, you reduce the blade angle, which lowers the resistance on the engine. This allows the engine to spin more freely and reach its rated RPM under full throttle conditions. Essentially, reducing the pitch acts like shifting to a lower gear, allowing the engine to reach its intended operating speed by making the propeller easier to turn.

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If an engine fails to reach its rated wide-open throttle (WOT) RPM, what specific change to propeller pitch should be made?