PHAK Ch. 5 · MIT 16.687 · study note

Left-turning tendencies

On most U.S. single-engine trainers the propeller turns clockwise as viewed from the pilot’s seat. At high power and high AOA (takeoff / climb), several effects produce left roll and/or left yaw. Right rudder is the usual antidote—not a mystery, a checklist of mechanisms.

Four panels explaining torque, P-factor, spiraling slipstream, and gyroscopic precession — **Figure 1.** Four classic mechanisms. P-factor and slipstream are especially important in the climb; gyroscopic effect depends on pitch change (e.g. tailwheel liftoff).

1. Torque

Newton’s third law: propeller applies a twisting force to the air → air applies equal-and-opposite twist to the airplane. Clockwise prop (from pilot) → airplane tends to roll left. Strongest at high power; felt more at low airspeed when ailerons are less effective.

2. P-factor (asymmetric thrust)

At high AOA, the descending (right) blade has a higher angle of attack / produces more thrust than the ascending (left) blade. Center of thrust moves right → left yaw. Classic knowledge-test: left-turning from P-factor is due to the descending right blade producing more thrust—not torque, not “the prop wash only.”

3. Spiraling slipstream

The prop imparts a corkscrew of air that wraps around the fuselage and often strikes the left side of the vertical stabilizer → left yaw. Strong at high power / low speed (takeoff roll and initial climb).

4. Gyroscopic precession

A spinning prop acts like a gyroscope. A force that tries to tilt the disk shows up as a reaction 90° ahead in the direction of rotation. Whether that makes left yaw depends on the maneuver (classic: tailwheel raising the tail on takeoff). Course/PHAK note: this is not always a left-turning tendency—don’t force every yaw into this box.

When it bites hardest

Phase	Main players
Takeoff roll / rotation	Torque, slipstream; gyro if pitch rate high (tailwheel)
Climb (high power, high AOA)	P-factor + slipstream + torque
Cruise	Much reduced (lower AOA, less power)

Pilot actions

Anticipate right rudder on takeoff and climb (and as needed in slow flight).
Keep the ball centered—uncoordinated + stall is how spins start.
Know your airplane: multi-engine and opposite-rotating props tell a different story.

Sources

FAA PHAK Ch. 5 — propeller effects / left-turning tendencies
MIT 16.687 Lec 2 — four mechanisms list

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