P-factor is the left yaw a propeller produces when the airplane flies at a high angle of attack. With a propeller that turns clockwise as seen from the cockpit, as in most airplanes, the descending blade on the right side of the disc takes a bigger bite of air than the ascending blade on the left, so the center of thrust moves right and the nose yaws left. P-factor is one of four left-turning tendencies the FAA groups under “torque,” along with torque reaction, the spiraling slipstream and gyroscopic precession, and together they are why you hold right rudder on the takeoff roll, in climbs, in slow flight and in go-arounds.
Part of our How Airplanes Work guide. For how the blades make thrust in the first place, start with how a propeller works.
The four left-turning tendencies at a glance
The FAA’s Pilot’s Handbook of Aeronautical Knowledge (PHAK) says that to the pilot, “torque” is made up of four elements. They act on different axes and peak at different moments, which is why the rudder you need keeps changing. Most U.S.-built engines turn the propeller clockwise as seen from the pilot’s seat, and everything below assumes that.
| Tendency | What it does | Strongest when |
|---|---|---|
| P-factor | Shifts thrust to the right, yaws left | High power at high angle of attack |
| Torque reaction | Rolls the airplane left; on the ground, loads the left tire and yaws left | High power; most evident as the wheels leave the runway |
| Spiraling slipstream | Hits the left side of the fin, yaws left | High power, low airspeed |
| Gyroscopic precession | Turns pitch changes into yaw | Pitch changes, such as raising a tailwheel airplane’s tail |
P-factor (asymmetric loading)
When the propeller shaft points straight into the relative wind, both blades meet the air the same way. Raise the nose to a high angle of attack and the disc meets the oncoming air at an angle. The descending blade on the right now has a higher resultant velocity and angle of attack than the ascending blade on the left, so it makes more thrust. The center of thrust moves right of the hub and the nose yaws left. The PHAK notes the imbalance shrinks as the shaft lines up with the relative wind and disappears when it is aligned. Its glossary adds that P-factor would be to the right with a counterclockwise-turning propeller.
Torque reaction
This is Newton’s third law: as the engine turns the propeller one way, the airplane tries to rotate the other way. In the air that is a rolling tendency to the left around the longitudinal axis. The PHAK says designers counter it with engine offset, or on some older airplanes with rigging that gives the down-going wing a little more lift, usually set for cruise, with aileron trim tabs on some airplanes for other speeds. On the takeoff roll, torque reaction presses the left main tire harder into the runway, and the extra friction yaws the nose left. How much depends on engine power, propeller size and rpm, airplane size and the runway surface.
Spiraling slipstream
The propeller throws its slipstream back in a corkscrew around the fuselage. The Airplane Flying Handbook (AFH) says it strikes the left side of the vertical fin, yawing the nose left, and that designers sometimes offset the vertical stabilizer to counter it. The PHAK says the spiral is tight and strong at high propeller speed and low forward speed, such as takeoff and the approach to a power-on stall, and stretches out and weakens as airspeed builds.
Gyroscopic precession
A spinning propeller is a gyroscope. Push on the rim of its disc and the result appears 90 degrees later in the direction of rotation. Raising the tail of a tailwheel airplane on the takeoff roll pitches the nose down, which the PHAK says has the same effect as pushing on the top of the propeller disc; the resultant force acts 90 degrees ahead and yaws the nose left. The AFH’s tailwheel chapter says the force depends on how fast the propeller axis is tilted, so raise the tail smoothly and be ready with rudder. Any pitch change produces some yaw and any yaw some pitch, but the PHAK notes the effect has always been considered more prominent in tailwheel airplanes. Our tailwheel endorsement guide covers that training.
When you will feel them, phase by phase
- Takeoff roll. Advance the throttle smoothly; the AFH warns that abrupt power can yaw the airplane sharply left, especially with a high-horsepower engine. At low speed torque and P-factor pull the nose left, so use whatever rudder it takes to track the centerline, and less as the rudder gains authority. Keep the balls of your feet on the rudder pedals, not the brakes.
- Crosswinds. The AFH points out that the left yaw from takeoff power can help against a crosswind from the right, which tries to weathervane the nose right, and adds to one from the left.
- Liftoff and climb. Torque’s rolling force is most evident as the wheels leave the surface. In the climb, P-factor yaws and torque rolls the airplane left, so the AFH calls for right rudder and aileron pressure. Its common errors include a sideslip in the initial climb from too little correction for torque and P-factor.
- Slow flight and power-on stalls. High power at a high angle of attack is P-factor’s home turf. The AFH says the closer you are to the stall, the more right rudder you need. See slow flight and power-on and power-off stalls.
- Go-arounds. Adding full power with the airplane trimmed for the approach raises the nose and yaws it left. The AFH says to expect considerable forward pressure and enough right rudder to counteract torque and P-factor.
- Cruise. The PHAK says the built-in compensation is set for cruise, where you spend the most time, so little rudder is needed.
- Power-off glides. The propeller effects fade but the compensation remains, so the AFH says slight left rudder pressure will likely be needed to stay coordinated.
Plan the rudder before you add the power. On every takeoff, go-around and power-on stall entry, have your right foot ready as the throttle comes forward, and look outside at a point straight ahead: if the nose drifts left against the horizon, you need more right rudder.
How to tell you need more right rudder
Outside, the nose should hold a point on the horizon in a straight climb instead of creeping left. Inside, the ball tells you: the PHAK’s rule is “step on the ball,” so if it sits right of center, press the right rudder. The AFH notes that not all light airplanes have rudder trim; where it exists, trim the rudder only after airspeed and pitch attitude are stable, because the built-in compensation for left-turning tendencies makes trimming at varying airspeeds impractical. Until then you simply hold the pressure, and with practice, the AFH says, the correction becomes instinctive.
Left-turning tendencies on the checkride
Left-turning tendencies are a named knowledge element in the private pilot ACS soft-field takeoff and climb task (PA.IV.C.K6), and yaw effects appear in the knowledge elements for slow flight, power-off stalls, power-on stalls and spin awareness (PA.VII.A.K1 through PA.VII.D.K1). On the oral exam, be ready to name all four, say which axis each acts on, explain when each is strongest, and explain why a glide can need left rudder. The related adverse yaw and ground effect guides cover the other low-and-slow aerodynamics examiners like to ask about.
What you'll need
The FAA handbooks that explain the left-turning tendencies, plus an oral exam guide to rehearse your answers, from PilotMall.com.
Frequently asked questions
What is P-factor in simple terms?
P-factor is uneven propeller thrust at a high angle of attack. With a propeller that turns clockwise as seen from the cockpit, the descending blade on the right takes a bigger bite of air than the ascending blade on the left, so thrust shifts right and the nose yaws left. You correct it with right rudder.
What are the four left-turning tendencies?
Torque reaction, the spiraling or corkscrew slipstream, gyroscopic precession, and asymmetric loading of the propeller, better known as P-factor. The PHAK groups all four under what pilots loosely call torque.
Is P-factor the same as torque?
No. Torque reaction is the airplane’s tendency to roll opposite the propeller’s rotation, Newton’s third law at work. P-factor is a yaw caused by uneven thrust across the propeller disc. Pilots often use the word torque for all four left-turning tendencies together.
Why do I need right rudder on takeoff?
At high power and low airspeed the slipstream pushes on the left side of the tail, torque reaction loads the left tire, and P-factor grows as you rotate to a higher angle of attack. All of them pull the nose left, so right rudder keeps you on the centerline and coordinated in the climb.
Why might I need left rudder in a glide?
Airplanes are designed to compensate for propeller effects in powered flight. In a power-off glide those effects fade but the built-in compensation remains, so the AFH says slight left rudder pressure will likely be needed to stay coordinated.