P-Factor.......

[GremlinX]

Ok... so appearantly there are 4 things that make an airplane pull to the left...
1-Torque reaction from engine and prop
2-Corkscrew from slipstream effect from the prop wash hitting the vertical stab/rudder from the left.
3-Gyroscopic Procession from the prop
4-P-Factor- or the air hitting the "disk" on an asymmetrical fashion.


I understand most of this, but I don't quite differentiate P-Factor from 1&2.

[3D-Seth]

I've always understood p-factor as air off of the prop corkscrewing around the plane and hitting the bottom of the elevator/stab and the rudder/vertical fin from the left, basically your #2.

I'm pretty sure this is what it is, but I'm not completely certain about it.

Seth

[nordqk]

The p-factor is caused by the difference in angle of attack between the ascending and descending blades of a rotating propeller blade. Specifically, in a "nose-up" situation where the propeller disk is inclined to the flight path, the descending blade has a higher angle of attack relative to the ascending blade. The propeller blade with the higher angle of attack will provide more force, in this case, measured as thrust. With the descending blade providing more thrust than the ascending blade, the center of thrust is moved away from the center of the propeller disk and out towards a parallel point somewhere along the descending blade.

Number 4.

That's why a twin engine airplane that has both engines rotating in the same direction has, what is called, a critical engine and it is the one on the left. The right engine creates a much larger yaw moment due the outboard thrust asymmetry (P-factor) and requires significantly more rudder correction if the left engine goes out. Planes with counter-rotating props do not have this phenomena (P-factor on the inboard side of both props) and therefore neither engine is critical.

[FixedWing172]

Torque from motor/propeller is your basic "for every action there is an opposite reaction". As the propeller spins clockwise as viewed from the cockpit the aircraft wants to "roll" to the left.

Corkscrew or slipstream is a result from the prop wash. It is most pronounced during high rpm and low airspeed i.e. during takeoff. As you correctly stated as the air corkscrews around the fuselage it pushes on the left side of the vertical fin which causes the nose to push to the left.

Gyroscopic precession is the tendency of a spinning object to move on it's axis. In this case the motor and propeller are acting like a giant gyroscope. This effect, although present, is minimal in aircraft.

P-Factor. During a high angle of attack such as the takeoff, the descending propeller blades on the right side produce more thrust than the ascending blades which cause the airplane to yaw to the left. This will only occur when the propeller is not meeting the relative wind head on. And P-Factor does not have as much affect as prop wash. Hope this clears things up for you.
Stan

[N726AC]

Too much coffee before take-off !!

Actually nordqk nailed it.

[nesikachad]

So, in an airplane like the Kelly F-1 would prop wash affect it as much since the tail's shape is a bit "unconventional" in comparison to most aircraft?

[N726AC]

	Quote: Originally Posted by nesikachad
	So, in an airplane like the Kelly F-1 would prop wash affect it as much since the tail's shape is a bit "unconventional" in comparison to most aircraft?

P-factor is not prop wash affecting the tail,,,

[Danny Baker]

P-Factor is best explained if you hold a spare prop in your hand, face the prop foward so you are looking at the flat side rear of the prop (you are now in the "engine" position) and tilt it up about 15 degrees as if in a climb or take off. Hold prop parallel to the ground. If your plane is flying forward but your prop is tilted up 15 degrees (like in taxi position on a taildrager) you'll see that you just de-pitched the left blade and added 15 degrees of pitch to the right blade. There will be little thrust from the entire left side of the prop arc, and tons from the right side. Now turn the prop 180 degrees clockwise, the left side of the prop is still de-pitch and there is still tons of pitch on the right side. All this thrust coming from the right side is sending the nose left on take off. Just that simple, try it.

[GremlinX]

	Quote: Originally Posted by Danny Baker
	P-Factor is best explained if you hold a spare prop in your hand, face the prop foward so you are looking at the flat side rear of the prop (you are now in the "engine" position) and tilt it up about 15 degrees as if in a climb or take off. Hold prop parallel to the ground. If your plane is flying forward but your prop is tilted up 15 degrees (like in taxi position on a taildrager) you'll see that you just de-pitched the left blade and added 15 degrees of pitch to the right blade. There will be little thrust from the entire left side of the prop arc, and tons from the right side. Now turn the prop 180 degrees clockwise, the left side of the prop is still de-pitch and there is still tons of pitch on the right side. All this thrust coming from the right side is sending the nose left on take off. Just that simple, try it.

I think some of you are very correct... I just could not quite understand it... for example, if you hold out a 10' board going 100 mph lets say, and you continue to go straight with the board, but you just rotate it a little, both side of the board on each side of the axis still see 100mph. That's what I could not understand about folks saying the right side is generating more force... how? In my little pee brain, the "disk" is seeing 100 mph... who does it know if it is climbing or going straight down at 100mph? I think if you are going up at 15* at 100 mph, the entire prop is seeing 100 mph. If the left side is seeing less, you are in trouble... Is it really just the pitch is greater at a higher angle of attack that creats P-Factor? Summed up is that correct? I know you guys are right, I just want to make sure I am understanding it correctly. Thanks for the info guys.

[Barn-E-Stormer]

	Quote:
	The p-factor is caused by the difference in angle of attack between the ascending and descending blades of a rotating propeller blade. Specifically, in a "nose-up" situation where the propeller disk is inclined to the flight path, the descending blade has a higher angle of attack relative to the ascending blade. The propeller blade with the higher angle of attack will provide more force, in this case, measured as thrust. With the descending blade providing more thrust than the ascending blade, the center of thrust is moved away from the center of the propeller disk and out towards a parallel point somewhere along the descending blade

Absolutely right.

P-Factor is defined as asymetrical (uneven) loading of the propeller disk.

Think of it this way: In straight level flight the spinning propeller creates a disk that has equal forward thrust all over the the surface of the disk, pulling the plane foreward. When the nose is high, relative to the air flow, now the right side is "biting"into the wind harder, creating more thrust on the right side of the disk, which pushes the nose to the left.

The slip stream coming off the propeller is actually called "spiral slip stream". The air is not blowing straight back, it is moving in a spiral, hitting the wings and tail, turning the plane to the left.

[Danny Baker]

Is it really just the pitch is greater at a higher angle of attack that creats P-Factor? Summed up is that correct?

Correct. The pitch is greater on the right side of prop at high angles of attack. Causing more thrust from the right side of the prop arc. The entire disc "sees" the same amount of air from in front of the prop, but the pitch of the prop at high angles of attack is different on the right (more) than the left (less). Those of us that are versed in doing a harrier circle know that the circling clockwise and circling counter-clockwise are very different in stick commands. You are adjusting for P-factor.

[FENWAYFLYER]

The angle of the dangle + the mass of the a$$ = the heat of the meat...Hope this was clear enough.

[GremlinX]

I understand it now.... thanks guys.... Lots of people including myself were incorrect about P-Factor... I thought P-F was the spiral slip stream. Thanks for clearing it all up.

[N726AC]

Right rudder for upright harriers, Left rudder for inverted harriers.

[haste232]

Hi Dudes
As far as I understand
Torque does not act in the yaw axis, only in the roll axis. It acts to rotate the plane in the oppossite direction of the prop rotation.
Slipstream is the spiral airflow along the fuse. Due to the direction of rotation there is more air hitting the left side of the rudder and fuse so it causes the plane to yaw to the right.
P factor as the other guys explained is due to the different angle of attack of left versus right side of the prop. It will yaw the plane to the left when you pitch up, but it will cause a yaw to the right if you pitch down.
The gyroscopic procession is the force that acts 90 degree in the direction of the prop rotation to a applied pitch or yaw. If you pitch it will cause a yaw, if you yaw it causes a pitch.
Now the tough part is that theses forces act differently depending on the attitude, attack angle, speed, and size or weight of prop. Sometimes they will cancel each other out or they may act together to cause an unwanted yaw or pitch. You can program it out in a simple case like knife edge flight, but it is impossible to do so in all different flight conditions. And that my friends is what separates a top flyer from a regular hacker like me, the ability to maintain precise and balance flight in all speeds, attitudes and wind conditions through anticipating and correcting for these forces.
As Wayne Gretzky said, I skate to where the puck is going to be not where it is.