FAA Powerplant Written Practice Test

What is the primary factor that increases the blade angle of non-feathering propellers during operation?

1. Oil pressure

2. Fuel flow

3. Air pressure

4. Blade design

The correct answer is: Oil pressure

The primary factor that increases the blade angle of non-feathering propellers during operation is oil pressure. In non-feathering propellers, the blade pitch is controlled by a hydraulic mechanism that adjusts according to oil pressure changes. When the engine is running and oil pressure is applied to the propeller control mechanism, it causes the blades to change their angle to a higher pitch, optimizing the propeller's performance for various flight conditions. This adjustment is crucial for maintaining efficient thrust and handling different loading conditions during flight. Increased oil pressure, which typically results from the engine's operation, directly influences the propeller's pitch control system, allowing for changes in thrust and improving performance during takeoff, climb, and cruise phases of flight. While fuel flow, air pressure, and blade design can impact a propeller's operation, they do not play a direct role in actively changing the blade angle in non-feathering systems. Specifically, fuel flow affects combustion and power output, air pressure can influence the aerodynamic forces acting on the blades, and blade design defines performance characteristics but does not adjust the blade angle during operation.