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I agree, Bill. Any time the plane of the prop is not perpendicular to the relative wind you have "P" factor. However, at the start of the take off roll, the tail dragger has its prop at an angle to the wind (until the tail lifts) whereas the tri gear does not. Anytime the relative wind is not perpendicular to the prop you have a "P" component whether caused by aircraft attitude on take off or - turbulent air over mountain passes {:>).
I agree that the much larger prop is undoubtedly causing a bigger swirl of air than my older prop, this is what I believe is the dominate factor in my case - but, clearly just my opinion.
Ed
----- Original Message ----- From: "BillDube@killacycle.com" <billdube@killacycle.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, December 12, 2005 1:19 AM
Subject: [FlyRotary] Re: "P" factor? Re: Static Engine RPM
P factor is caused by the angle of attack of the prop blades relative to the motion of the prop through the air. No P factor when the plane is not moving. Lots of P factor at high power low speed.
Tricycle gear airplanes do indeed experience P factor. Go over a high mountain pass at the service ceiling and you will experience P factor in spades. After a day of mountain flying, I get cramps in my right leg from pushing the rudder pedal.
If the propeller is tilted upward relative to the oncoming air, as the blades travel downward, they have a large angle of attack. As they travel upward on the other side, they have a small angle of attack. They pull hard on the down stroke, and much less on the up stroke. The "swirling" you may observe is the result of a lot more air being pushed though one side of the prop circle compared to the other.
Cocking the thrustline slightly helps reduce the rudder pressure at slow airspeeds.
Bill D.
Perhaps you all know this already, but it didn't seem like everyone had it 100% correct from what I read in some of the previous posts.
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