What is the imaginary line passing through the center of the propeller hub, perpendicular to the plane of rotation called?

• A. Time And Speed Table
• B. Thrust Line
• C. Thrust
• D. Torquemeter

Answer: (B)

The main idea is the thrust line—the imaginary line along which the propeller’s thrust acts, passing through the center of the propeller hub and perpendicular to the plane of rotation. This line represents the path of the propulsive force on the airplane. Its position relative to the aircraft’s center of gravity matters because if the thrust line does not go through the CG, thrust changes create a pitching moment, causing the nose to rise or lower depending on whether the line is above or below the CG. Designers seek to align the thrust line with the CG to minimize unwanted pitch changes with throttle adjustments and to predict how increasing or decreasing thrust will affect attitude. The other terms refer to different things: thrust is the force produced, torquemeter measures torque, and a time-and-speed table is unrelated.