FAA Powerplant Written Practice Test

What are the rotational speed and blade pitch angle requirements of a constant-speed propeller during takeoff?

1. Low speed, high pitch angle

2. High speed, low pitch angle

3. Medium speed, adjustable pitch

4. Variable speed, constant pitch

The correct answer is: High speed, low pitch angle

During takeoff, a constant-speed propeller is designed to achieve maximum efficiency and performance, which is primarily influenced by the rotational speed and blade pitch angle. The correct answer emphasizes high speed and low pitch angle. In a constant-speed propeller system, the pitch angle of the blades can be adjusted to maintain optimal engine performance at varying speeds. During takeoff, the goal is to generate the maximum thrust possible. To achieve this, the propeller blades are set to a low pitch angle. A low pitch angle allows the blades to "bite" into the air more aggressively, which increases thrust. At the same time, a high rotational speed is necessary to produce sufficient power. During this phase of flight, engine RPM (Revolutions Per Minute) is controlled to ensure that the engine operates efficiently and generates the necessary thrust for takeoff. The combination of high RPM and low pitch angles allows for the proper balance between thrust production and engine performance. This relationship between pitch angle and rotational speed is critical in understanding how a constant-speed propeller works during various phases of flight, particularly during takeoff when maximum performance is required.