FAA Powerplant Written Practice Test

What is the angle-of-attack of a rotating propeller blade measured between?

1. The blade chord and the relative airstream

2. The blade tip and the hub

3. The pitch angle and the airspeed

4. The leading edge and the trailing edge

The correct answer is: The blade chord and the relative airstream

The angle-of-attack of a rotating propeller blade is defined as the angle between the blade chord line and the relative airstream. This measurement is crucial as it directly influences the aerodynamic forces acting on the blade, affecting the lift and drag produced as the propeller rotates. The blade chord line is an imaginary line that runs from the leading edge to the trailing edge of the blade. The relative airstream refers to the airflow around the blade due to the forward motion of the aircraft combined with the action of the rotating propeller. Understanding this angle is essential for optimizing propeller performance and efficiency. Other options, while related to propeller dynamics or blade design, do not accurately describe the specific angle used to determine the angle-of-attack. For instance, measuring between the blade tip and the hub does not relate to angle-of-attack, nor does the relationship between pitch angle and airspeed pertain to the angle definition. Similarly, the leading edge and trailing edge describe physical locations on the blade but do not relate to the context of angle-of-attack measurement.