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2 Answers

P-factor

Asked by: 3096 views Aerodynamics

Hello,

The explanations for the effect of p-factor seem to make sense, i.e. one half of the path of propeller rotation "bites" more air than the other half relative to the oncoming angled airstream.   However, what is not clear is why is the stronger pull occur over the downward half as opposed to the lower half?  Shouldn't the strongest point of pull be at the nadir or lowermost point of rotation where the propeller angle of attack is greatest?   For a propeller angled uppward relative to the airstream why is there not an upward force as opposed to a leftward force?  Any help in understanding this concept would be appreciated.

 

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2 Answers



  1. Koehn on May 13, 2016

    Imagine the plane is configured for level slow flight. The nose is pointed up above the horizon, but the plane isn’t actually climbing. Even though the plane is moving through the air level, the propeller is tilted up, say 10°. Air molecules striking the bottom of the aircraft as it is dragged through the air. Because the propeller isn’t aligned with the direction the plane is moving, on the downstroke the blade is actually moving through more air than it does on the upstroke: it’s moving forward 10° when it goes down, and backward 10° when it goes up.

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  2. spikeone on May 16, 2016

    Great explanation. I was considering what was happening from the wrong position of the propeller: ie. the horizontal axis is actually the position of maximal differential thrust or bite between the right and left blade, not vertical. I appreciate your thoughts. Thank you for answering the question!

    Not to be confusing, but wonder if there is a downward “P-factor” effect with a yaw or sideslip to the left, or an upward effect with a sideslip to the right. . . . . . . . .?

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