What is P-Factor? | A Deep Dive into its Impact on Flight

Have you ever experienced a situation where your airplane operates at a high angle of attack which causes the center of thrust of the propeller to shift off-center? This phenomenon is known as P-factor, the asymmetric disc or blade effect. This is an aerodynamic occurrence that is linked to the rotation of an aircraft propeller. 

P-factor occurs due to varying loads experienced by the propeller blades, resulting in a non-uniform lift or thrust distribution. The displacement induces a subtle yawing moment that causes the airplane to yaw to the left. From our guide, you will get to know the causes of P-factor, its effects, and how to compensate for it. In addition, you will learn about the forces acting on the aircraft.

What are the Causes of P-Factor?

You will often see P-factor in propeller aircraft. P-factor is caused by the blade performance differences during different flight conditions. In P-factor scenario, the propeller disc tilts at lower speed and high altitude which affects the blades airflow.

The tilt has two main effects on the aircraft. The first effect is the down-going blade experiences increased forward speed, which in a result causes a higher thrust. At the same time, the up-going blade experiences reduced forward speed and generates lower thrust. It creates an imbalance in the distribution of thrust across the propeller disc. 

Second, the tilt increases the angle of attack of the down-going blade and decreases the angle of attack of the up-going blade. P-factor is most noticeable during takeoff or slow flight scenarios, especially in the case of high angles of attack and high power.

Effects of P-Factor on Propeller Aircraft

P-factor can affect both single-engine and multi-engine propeller aircraft. These effects significantly affect the aircraft's behavior, especially during takeoff and flight. In the case of single-engine propeller airplanes with clockwise-turning propellers, a yaw tendency to the left occurs during climb and descent. To counteract this yaw, pilots must apply opposite rudder inputs. 

In multi-engine propeller aircraft with counter-rotating propellers, P-factor of both engines is likely to cancel out each other. If both engines rotate in the same direction or one fails, P-factor will induce the yaw.  This determines the critical engine. 

The critical engine failure requires more significant rudder deflection to maintain straight flight. The left engine in many aircraft is considered necessary with clockwise rotating propellers. The pilot’s awareness and ability to take corrective actions on time is essential to dealing with P-factor during various phases of the flight, especially in high-power and high angle of attack situations, like taking off.

How to Compensate for P-Factor?

Compensation for P-factor varies in different types of airplanes. In single-engine aircraft, pilots master the fundamentals of compensating for P-factor by using precise control inputs. 

Pilots do that primarily through rudder adjustments. This skill is essential for pilots during power changes and alterations in pitch angle, where timely compensation and anticipation help maintain stable and controlled flight.

The critical engine rotates in the same direction and is determined by the proximity of the downward-moving blade to the fuselage. 

The negative impact of P-factor is neutralized in the event of an engine failure. Suppose both engines in an aircraft are essential due to opposing rotations. In that case, an engine failure scenario can be complicated by additional yaw induced by P-factor. 

What are the Forces Acting on the Aircraft?

Aside from P-factor, there are other forces that are acting on the aircraft. Pilots must know how these forces affect the plane to keep it in the air. Let’s learn about each force and see how they work together.

Thrust - The Forward Propulsion:

The powerplant or rotor of the aircraft generates thrust or forward propulsion force. The thrust force opposes the drag force, propelling the airplane forward along its longitudinal axis and this is aligned parallel to the axis. The thrust force is important for overcoming the resistive drag force. It's essential to note that thrust force sometimes may only act solely in the forward direction.

Drag - The Retarding Force:

Drag, or the retarding force, is caused by the disruption of airflow around the airplane and its components, including the rotor, wing, fuselage, and other protruding components. As we have mentioned before, the drag force acts opposite to the thrust force. It is essential to reduce the drag force for effective flight, and reducing this force is achieved through streamlined design and aerodynamic considerations. 

Lift - The Force of Ascension:

The lift force, also known as the force of ascension, is caused by the dynamic effect of air acting on the airfoil. The force of ascension acts perpendicular to the flight path through the center of the lift and also perpendicular to the aircraft’s lateral axis. In level flight, this force opposes the downward force of weight. It’s essential for pilots to understand the dynamics of lift force to control altitude and ensure a safe and stable flight.

Weight - The Downward Force:

Weight force or the downward force acts vertically downward due to gravity. This downward force is the combined load of the aircraft crew, fuel, and cargo. The sum of all forces, including weight and lift is zero during steady-level flight. Weight force is essential to maintain equilibrium and stability during flight operations.

Angle of Attack (AOA):

The most overlooked but essential concept in aviation is the angle of attack (AOA). This is an acute angle between the relative wind’s direction and the airfoil’s chord line. The angle of attack plays an important role in the aircraft performance, stability and control. Pilots adjust the AOA to make sure that lift is equal to the weight force mainly during low speed flight operations. 

Induced Drag and Downwash:

Induced drag is the inherent consequence of lift production. When the airfoil generates lift, vortices and downwash are created at the wingtips, which induces additional drag. This downwash affects the angle of attack and overall efficiency of the aircraft. It's essential for pilots to know how to manage the induced drag and optimize the airplane’s performance.

Conclusion

To conclude, P-factor is an important concept that pilots need to understand. P-factor arises from the asymmetric blade effect in propeller-driven aircraft. This problem is usually triggered by variations in blade performance during different flight conditions, which as a result introduces yaw tendencies that require skilled pilot intervention. 

The effects of P-factor are common in single-engine and multi-engine propeller aircraft. These effects impact the climb, descent, and engine failure scenarios. Pilots must know the fundamentals of forces that act on the airplane and know how to manage those forces.

There are certain things pilots can do to control these effects. First, they should understand how to use the rudder correctly and know what’s happening around them. Learning how to compensate for P-factor is a vital skill for pilots. 

You can use these skills during high power and angle of attack situations to ensure a stable and controlled flight throughout the journey. In addition to that, you also have to master counteracting other left tendencies like torque, gyroscopic precession and spiraling slipstream.