Propeller left-turning tendencies

Single tractor propeller turning clockwise (seen from cockpit): four left-turning tendencies.

• All worst at high power and low speed.
• Hold right rudder on take-off and climb.

1. Torque reaction (TP 1102)

• Equal-and-opposite reaction to spinning prop rolls aircraft left. Correct with aileron.
• Torque does not yaw directly. Roll causes the yaw.
• Take-off roll: high power puts more weight and friction on left wheel, adding to yaw left. Correct with rudder.
• Some aircraft offset torque, set for cruising speed (PHAK ch.5):
  • Extra left-wing incidence (TP 1102).
  • Offset engine (PHAK ch.5).
• Torque yawing moment depends on (PHAK ch.5):
  • Engine size and horsepower
  • Propeller size and rpm
  • Aircraft size
  • Ground surface condition

2. Spiralling slipstream (TP 1102)

• Corkscrewing airflow strikes left side of fin, yaws nose left.
• Also rolls aircraft right, partly cancelling torque's left roll (PHAK ch.5).
• Any power change yaws nose:

• Offset fin balances this at cruise power only.
• Slipstream velocity exceeds aircraft's speed through air: parts inside it (fin, rudder) see faster airflow than parts outside (TP 1102 ch.1).

3. Gyroscopic precession

• Pitch or yaw input to spinning prop is felt as tail comes up on a taildragger (TP 1102).
• Reverse: yaw input produces pitching moment. Correct with elevator and rudder together (PHAK ch.5).

4. Asymmetric thrust (P-factor)

• High nose-up attitude: descending right blade meets air at greater angle of attack, bigger bite, yaws left (TP 1102).
• Zero in level cruise (propeller shaft horizontal) (PHAK ch.5).
• Strongest at high angle of attack, e.g. climb or slow flight (PHAK ch.5).

Nosewheel aircraft: exempt from gyroscopic precession and P-factor on take-off roll, since thrust line stays parallel to ground until rotation. Exception: soft-field, nose-up takeoff (TP 1102).

Trap: forgetting the fix is right rudder, and that effects peak at high power and low speed, exactly on take-off.

Practice