What does the term blade angle refer to in propeller theory?

In propeller theory, the term "blade angle" specifically refers to the angle between the chord line of the propeller blade and the plane of its rotation. This angle is crucial in determining how effectively the propeller converts engine power into thrust. The chord line of a blade is an imaginary straight line connecting the leading edge and the trailing edge, while the plane of rotation is defined by the circular path traced by the tips of the blades as they rotate.

Understanding this relationship helps in analyzing the performance characteristics of a propeller. A correctly calibrated blade angle ensures that the propeller can produce the desired thrust while maintaining efficiency across various flight conditions. Adjusting the blade angle can dramatically affect the thrust generated by the propeller, influencing the aircraft's performance during takeoff, cruising, and climbing.

The other choices relate to different concepts in aerodynamics and propeller functioning. For instance, while the angle of attack does influence lift and performance, it is not synonymous with blade angle itself, which specifically measures the blade's orientation relative to its rotation.