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2 Answers

Using Left Rudder on a Descent. Is it Negative P-Factor?

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Aerodynamics, Commercial Pilot, Flight Instructor, General Aviation, Private Pilot, Student Pilot

I know that my P-factor is greatest at high power and high angle of attack. To overcome that we use the right rudder, but my question is that does the P-factor changes in a descent? Because when I fly a 172, during a descent I experienced that left rudder is needed to keep the ball centered and my instructor says that it is due to change in the direction of P-factor but when I went over internet everybody says there’s no change in the direction of P-factor it’s effect just decreases while on descent. 

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2 Answers



  1. KDS on Mar 20, 2020

    Here is a reference from FAA-H-8083-3B Airplane Flying Handbook. It is found under the subject of Glides in Chapter 3:

    Certain considerations must be given to gliding flight. These considerations are caused by the absence of the propeller slipstream, compensation for p-factor in the airplane’s design, and the effectiveness of airplane control surfaces at slow speeds. With the absent propeller effects and the subsequent compensation for these effects, which is designed into many airplanes, it is likely that, during glides, slight left rudder pressure is required to maintain coordinated flight.

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  2. Craig Johnston on Mar 21, 2020

    The need for slight left rudder pressure is evident in at least these two places.
    The first is at top of descent when power is reduced from cruise. As the throttle is reduced, slight left rudder is typically needed to maintain coordinated flight. Otherwise, the airplane will be in a slight slip to the right.
    The second is when power is reduced in the traffic pattern when reducing power abeam the numbers. Slight left rudder is typically needed to maintain coordinated flight. Otherwise, the airplane will be in a slight slip to the right.

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