What are torque and P-factor, and how do they affect propeller aircraft handling?
Learn what torque and P-factor are, when each is strongest, why propeller aircraft pull left, and how pilots correct the resulting yaw and roll.
Torque is the aircraft’s rolling reaction to the engine turning the propeller; P-factor is asymmetric thrust across the propeller disc when its axis is inclined to the airflow. In many conventional single-engine aircraft, both contribute to a left-turning tendency at high power and low airspeed, requiring coordinated rudder and aileron corrections.
In our Aviation & Real-World Flying coverage, the useful distinction is that torque primarily causes roll, while P-factor primarily causes yaw. Pilots often call every take-off swing “torque”, although spiralling slipstream, gyroscopic precession and even crosswind may be contributing at the same time.
What is the difference between torque and P-factor?
Torque is reaction roll; P-factor is uneven propeller thrust that moves the effective thrust line away from the aircraft’s centreline.
| Effect | Cause | Primary handling result | Most noticeable |
|---|---|---|---|
| Torque | The airframe reacts in the opposite direction to engine and propeller rotation | Roll, sometimes with secondary yaw on the ground | High engine torque with limited control authority |
| P-factor | The descending and ascending blades produce unequal thrust when the propeller disc is inclined to the airflow | Yaw towards the side producing less thrust | High power, high angle of attack and low airspeed |
Torque follows Newton’s third law. If the engine turns the propeller clockwise as seen from the cockpit, the reaction tends to roll the airframe anticlockwise. This is not the same effect as propeller slipstream.
With the same common rotation direction, the right-hand blade is descending. At a positive angle of attack it normally produces more thrust than the ascending blade, moving the centre of thrust to the right of the propeller disc and yawing the nose left. Our explanation of the blade-angle and thrust principles behind a propeller covers the underlying mechanics.
These directions are not universal. An engine with the opposite propeller rotation reverses the associated roll and yaw, while counter-rotating installations are designed to balance some of these effects.
When are torque and P-factor strongest?
They are most apparent when power is high, airspeed is low and the aircraft is pitched nose-up, but each condition affects them differently.
- Start of the take-off roll: engine torque and spiralling slipstream are already present, while P-factor may be modest if the propeller axis is nearly aligned with the airflow.
- Rotation and initial climb: the increased angle between the propeller axis and relative airflow strengthens P-factor, while low airspeed leaves the rudder and ailerons less effective.
- Slow flight or a go-around: high power combined with high angle of attack can produce a rapid yaw and roll if the pilot does not anticipate it.
- Cruise: higher airspeed, lower angle of attack and greater control authority usually make both effects less conspicuous.
- Low-power descent: both effects are normally weaker, but they return quickly when substantial power is applied.
Low airspeed does not itself create more engine torque. It makes the resulting motion harder to oppose because the flight controls have less aerodynamic authority. RPM alone is not a reliable measure either: a constant-speed propeller can absorb considerable engine torque while holding its selected RPM.
Why does a propeller aircraft pull left on take-off?
A typical left swing on take-off is the combined result of several propeller effects rather than P-factor or torque acting alone.
- Torque reaction tends to roll the aircraft left and can place more load on the left main tyre, adding a ground-handling tendency.
- P-factor shifts thrust towards the descending right-hand blade and yaws the nose left.
- Spiralling slipstream can strike the left side of the fin, pushing the tail right and the nose left.
- Gyroscopic precession produces a yawing response when the propeller disc is pitched. Its direction depends on propeller rotation and the direction of the pitch change.
Gyroscopic precession is especially relevant in tailwheel aircraft when the tail is raised or lowered. Our guidance on controlling taildraggers during take-off and landing explains how these effects combine with ground-loop risk.
How should pilots correct torque and P-factor?
Pilots use rudder to control the yaw, aileron to manage the roll, and smooth power changes to avoid demanding more control authority than the aircraft can provide.
- Apply power smoothly: anticipate the expected swing rather than waiting for a large deviation to develop.
- Hold the runway centreline with rudder: many conventional single-engine aircraft need right rudder at high power, but the required direction and amount depend on propeller rotation and aircraft design.
- Control bank with aileron: use enough input to maintain the required wing attitude without trying to correct a yaw solely by banking.
- Coordinate after lift-off: keep the slip indicator centred with rudder while using aileron for the intended bank. The explanation of how rudder and ailerons divide yaw and roll control provides the relevant control-surface detail.
- Reduce the correction as conditions change: increasing airspeed, reducing power or lowering the nose usually changes the required rudder pressure. Rudder trim may unload steady pressure once the climb is established, where the aircraft’s procedure permits it.
A fixed amount of right rudder is a common mistake. It may be insufficient during rotation, excessive as speed builds, and completely wrong in an aircraft whose propeller turns the other way. In a real aircraft, type-specific handbook procedures and instruction take precedence over a general rule.
Why does P-factor matter in a twin-engine aircraft?
P-factor can make the failure of one engine more difficult to control than failure of the other, creating what pilots call the critical engine.
On a conventional twin whose propellers both rotate clockwise from the cockpit, the operating right engine’s displaced thrust acts farther from the aircraft centreline than the left engine’s thrust. Losing the left engine therefore leaves the more adverse yawing moment, so the left engine is normally critical. Other aerodynamic effects also contribute; P-factor is not the sole reason.
Many counter-rotating twins arrange their descending blades towards the fuselage. This makes the thrust moments more symmetrical and can remove the conventional critical-engine distinction.
Why might these effects feel wrong in a flight simulator?
If propeller effects seem absent, excessive or constant in a simulator, check assistance settings, control assignments, weather and the individual aircraft model before blaming P-factor.
- Auto-rudder or take-off assistance can conceal the expected yaw.
- Large rudder dead zones can delay correction, while duplicate pedal, joystick-twist or keyboard assignments can create a permanent input.
- A crosswind, asymmetric brake input or nosewheel-steering problem can resemble a propeller-induced swing.
- Different simulated aircraft use different propeller directions, power levels, landing-gear geometry and flight-model tuning.
A useful diagnostic is whether the tendency changes predictably with power, airspeed and pitch attitude. A constant pull with the engine stopped is not torque or P-factor; it points instead to wind, trim, controller calibration or an asymmetric aircraft configuration.