Aeronautical Terms Defined
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P-factor, also known
as asymmetric propeller torque, is a significant factor that affects the performance
and stability of single-engine aircraft. It occurs when the lift and drag generated
by the two blades of a propeller are unequal, creating a yawing moment that can
cause the aircraft to roll or yaw in the direction of the descending blade. Here
is provide an overview of the physics behind P-factor, its effects on aircraft performance
and stability, and the mitigation strategies used to counteract its impact.
When an aircraft is flying straight and level, the lift and drag generated by
both blades of the propeller are equal and balanced. However, when the aircraft
is climbing or descending at a high angle of attack, the lift and drag generated
by the blades become unequal. The blade on the descending side of the aircraft generates
more lift and drag, while the blade on the ascending side generates less lift and
drag.
This difference in lift and drag creates a yawing moment that can cause the aircraft
to roll or yaw in the direction of the descending blade. This is known as P-factor,
and it is most noticeable during takeoff and landing when the aircraft is at a high
angle of attack.
Physics of P-Factor
The physics behind P-factor can be explained by the difference in lift and drag
generated by the two blades of a propeller as they rotate. The blade on the descending
side of the aircraft generates more lift and drag, while the blade on the ascending
side generates less lift and drag. This difference in lift and drag creates a yawing
moment that can cause the aircraft to roll or yaw in the direction of the descending
blade.
Effects of P-Factor
P-factor has a significant impact on aircraft performance and stability, particularly
during takeoff and landing. The yawing moment created by P-factor can cause the
aircraft to roll or yaw, affecting its ability to fly straight and level. Uncontrolled
P-factor can also result in instability and reduced control during flight, compromising
safety.
Mitigation Strategies
To mitigate the effects of P-factor, pilots must be aware of the phenomenon and
make compensating inputs to the rudder to keep the aircraft flying straight and
level. In some aircraft, the propeller pitch can be adjusted to counteract the effects
of P-factor, while in others, the pilot must rely on their training and experience
to make the necessary inputs.
References
J.D. Anderson Jr., "Introduction to Flight", McGraw-Hill Education, 2007 R. W.
Phillips, "Aerodynamics, Aeronautics and Flight Mechanics", Wiley, 2015 J.C. Heinrich,
Posted February 4, 2023
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