Opening the throttle on a reciprocating engine when the propeller is in the constant-speed range with the engine at cruise power does what to the blade angle?

Opening the throttle on a reciprocating engine when the propeller is in the constant-speed range with the engine at cruise power does what to the blade angle?

• A. Decreases it
• B. Increases it
• C. Keeps it the same
• D. Oscillates

Answer: (B)

In a constant-speed propeller system, the governor controls the blade angle to keep engine RPM at the set value as load and power change. When you open the throttle at cruise power, you’re putting more power into the engine. The governor detects a tendency for the RPM to rise, so it moves the propeller to a higher pitch (increase blade angle) to absorb that extra power. A higher pitch increases drag on the propeller, which slows the engine back toward the desired RPM, so the blade angle ends up increased. In short: opening the throttle causes the blade angle to increase.

In a constant-speed propeller system, the governor controls the blade angle to keep engine RPM at the set value as load and power change. When you open the throttle at cruise power, you’re putting more power into the engine. The governor detects a tendency for the RPM to rise, so it moves the propeller to a higher pitch (increase blade angle) to absorb that extra power. A higher pitch increases drag on the propeller, which slows the engine back toward the desired RPM, so the blade angle ends up increased. In short: opening the throttle causes the blade angle to increase.