How does propeller efficiency change for an aircraft with a fixed pitch propeller?

For an aircraft equipped with a fixed pitch propeller, propeller efficiency is influenced by the operating speed and the angle of attack. Fixed pitch propellers are designed for a specific range of operating conditions, meaning they cannot adjust their blade angle to optimize performance across all speeds.

At low speeds, a fixed pitch propeller often operates inefficiently due to its design, which may not provide the ideal blade angle for such conditions. Conversely, as speed increases, the propeller can experience increased drag and reduced effectiveness due to the inability to change blade pitch, causing further reductions in efficiency.

The peak efficiency typically occurs at cruising speed, where the propeller can efficiently convert engine power into thrust without excessive drag losses. Thus, it is at cruising speed that the propeller operates with the highest efficiency, while both low and high speeds result in lower efficiency due to mismatches between the propeller characteristics and the aircraft's speed.

This dynamic makes the assertion about efficiency being low at both low and high speeds while reaching its peak at cruising speed accurate for a fixed pitch propeller.