Asymmetric Loading ( P-Factor) Diagram

lhornaday

lhornaday

Well-Known Member
Can anyone explain P-Factor using the differences in AOAs? I don't think I have ever seen an accurate drawing.

The FAA knowledge book says "To prove this explanation is complex". So complex they don't even try. They just a bunch of thick arrows and thin arrows on the different blades. "See, look it is right!"

Using the resultant velocity thery makes more sense to me. But we can't blaspheme FAA definitions, less we be flogged and thrown outside.
 
lhornaday said:
Can anyone explain P-Factor using the differences in AOAs [and velocity]?
Click to expand...


pfactor.png
 
Go out to the airplane with your instructor and another person. Have the other person push the tail of the airplane down. You and your instructor go from the left side of the prop to the right and note the difference, it's quite obvious and this is a pretty practical experiment.
 
Thanks for the diagram TG. Some discussions I have seen (and as I was taught all through my years) din't mention forward velocity as a factor in the AOA of the blade changing. I am certain now it is a requirement for the plane to be moving forward otherwise the AOA wouldn't change.


JordanD said:
I don't have anything to add other than hats off on the Milton avatar.
Click to expand...

And I said, I don't care if they lay me off either, because I told, I told scheduling that if they extend me one more time, then, then I'm, I'm quitting, I'm going to quit. And, and I told the Union too, and I used to be an FO, and I could have weekends off, and they were marry, but then, they switched from the Saab to the CRJ, but I kept my briefcase stickers, and it's not okay because if they change my schedule then I'll set the airline on fire.
 
lhornaday said:
And I said, I don't care if they lay me off either, because I told, I told scheduling that if they extend me one more time, then, then I'm, I'm quitting, I'm going to quit. And, and I told the Union too, and I used to be an FO, and I could have weekends off, and they were marry, but then, they switched from the Saab to the CRJ, but I kept my briefcase stickers, and it's not okay because if they change my schedule then I'll set the airline on fire.
Click to expand...

Out...freakin...standing post....literally rolling on the floor here!
 
go grab a 152. turn the prop horizontal. pull the tail to the ground. think of which angle the relative wind would be hitting the plane. then look at the angle of the decending vs accending blade. There ya go p-factor at its easiest
 
mtnflyer said:
go grab a 152. turn the prop horizontal. pull the tail to the ground. think of which angle the relative wind would be hitting the plane. then look at the angle of the decending vs accending blade. There ya go p-factor at its easiest
Click to expand...

Still trying to figure this out fully myself, but it isn't all about pitch attitude. If I did that to the extreme wouldn't it be a helicopter? I can't see any reason to say that a helicopter experiences p-factor while on the ground or hovering. Forward motion would have to take place before we get into the whole retreating blade stall stuff.
 
lhornaday said:
Forward motion would have to take place before we get into the whole retreating blade stall stuff.
Click to expand...

Agreed. Otherwise, the relative wind seen by the propeller blade is due solely to the rotation of the blade, and the AoA will merely be the blade angle setting.
 
The 152 tail on the ground is a good visual example for students. It would roughly be sitting at a 40 degree angle in relation to the ground. P-factor is most prevelent in a powered climb. The realative wind would be parrallel to the ground. This simulates the AOA that is easier for students to understand if they are more visually learners. So you will see the decending blade hits the relative wind at a different angle than the accending. And that is p-factor
 
I knew what i was saying in my head, but reread what i typed. And parrallel to direction of flight. prob should proof read.
my bad
 
That is a good demonstration. I would clarify that the relative wind in relation to the propeller is not parallel to the ground or even opposite the flight path. You have to consider the propeller's rotation which is very fast.

Also P-factor is most prevalent while at high a AOA regardless of a climb or straight-and-level flight.

Sitting still on the ground there is no p-factor even if the airplane where pitched up to a high AOA (relative wind is the same on both blades). In straight-and-level flight at cruise speed there is also no P-factor (relative wind is still the same on both blades). Speed and blade AOA both contribute.

Worst case scenario would be at faster speeds and much higher AOA on down-swinging blade.
 
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