FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightHard
A CFI explains to a client that on most single-engine airplanes with a clockwise-rotating propeller, the tendency for the airplane to roll to the left at the moment full power is applied is a direct result of:
- Athe increased angle of attack of the descending propeller blade
- BNewton's third law, as the propeller exerts a clockwise force on the air and an equal, opposite reaction rolls the airframe counterclockwise
- Cthe corkscrew flow of the propeller slipstream striking the left side of the vertical stabilizer
- Dthe gyroscopic precession of the spinning propeller disc
Show answer & explanationAnswer & explanation
Correct answer: B. Newton's third law, as the propeller exerts a clockwise force on the air and an equal, opposite reaction rolls the airframe counterclockwise
Torque reaction is a direct application of Newton's third law: as the engine and propeller rotate clockwise (viewed from the cockpit), an equal and opposite reactive force rotates the airframe counterclockwise, producing a left-rolling tendency, particularly noticeable at high power and low airspeed such as during takeoff.
Why the other options are wrong
- A. This describes P-factor, which causes yaw, not roll.
- C. This describes spiraling slipstream, which causes yaw by striking the tail, not roll of the airframe.
- D. Gyroscopic precession causes yawing/pitching effects from pitch changes, not a constant roll from applying power.
Torque Reaction
The tendency of the airplane to roll opposite to the direction of propeller rotation, resulting from Newton's third law (equal and opposite reaction to the propeller's rotational force).
- Most noticeable at high power/low airspeed, e.g., takeoff
- Clockwise-rotating props (viewed from cockpit) cause left roll tendency
- Corrected with aileron input
- Distinct from P-factor, precession, and spiraling slipstream, which cause yaw
Memory trick: 'Torque = twist back' — Newton pushes the plane opposite the prop