flyrotary@lancaironline.net Mailing List Archive

Can't really say, George

However, don't forget we are swinging a much larger diameter prop with the 2.85 than we were with the 2.17. So I expect we are getting a much larger swirl of air. No doubt the torque at the prop is also up but not certain enough to account for this much change. If it were just torque I would expect to find more of a "rolling" force whereas it seems to have little roll component but a lot of yaw component.

----- Original Message -----

From: george lendich

To: Rotary motors in aircraft

Sent: Sunday, December 11, 2005 10:17 PM

Subject: [FlyRotary] Re: "P" factor? Re: Static Engine RPM

Ed,

What you are saying reflects what I've read also - however Tracy's experience with the difference between the 2.17 and the 2.85 suggests that there is also the centrifugal forces of prop + rotor direction to contend with, as Tracy required full R rudder to maintain directional control with the 2.85, whereas with the 2.17, it wasn't anywhere near as difficult - so I'm led to believe.

If it were just the wind from the prop corkscrewing around the fuselage until it hit the rudder, the L and R turning props would give a similar response in intensity. This wasn't the case, it would seem.

George ( down under)

Hi Georges,

The "P" direction factor only changed when I changed from the 2.17 to the 2.85 (with the opposite propeller rotation) . The shortening of the prop slight reduced the "P" factor but did not change its direction.

One thing I think I should mention. I used to think the force was caused by the "P" factor, but after reading an article about the effects of Torque, "P" factor and Airstream whirl, I came away with a different understanding. Apparently "P" factor is a factor primarily with tail draggers as it is caused by the effect of the relative wind and the prop blades not being perpendicular to the relative wind (until the tail comes up). With a nose gear, the blades are perpendicular (at least until lift off) and therefore the "P" factor is minimal.

Apparently the real cause of the rather powerful force that wants to push the nose to the left or right is the swirling air caused by the spinning prop. Think of a cork screw. With my prop now spinning CCW (from pilot's perspective) the corkscrew of air is swirling CCW as well. It appears the distance from prop to vertical stabilizer is such that the air corkscrews around so that more of it hits the left side of the fuselage and vertical stab than the right. This air forces the tail toward the right and the nose to the left, thereby requiring right rudder to counteract the force.

Sounded reasonable to me. Not to say there is not torque or "P" factor but given the magnitude of the turning force I would say the air swirl probably is the major factor.

Ed A

Ed A

----- Original Message -----

From: Echo Lake Fishing Resort (Georges Boucher)

To: Rotary motors in aircraft

Sent: Sunday, December 11, 2005 8:53 PM

Subject: [FlyRotary] Re: Static Engine RPM

Hi! Ed

I guess I missed something, how can the P-factor be in the"opposite" direction after shortening the prop 2"?

Georges B.

-------Original Message-------

From: Ed Anderson

Date: 12/10/05 14:54:00

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: Static Engine RPM

Hi Bernie,

Good point, Yes, you are correct the engine mount is still the same. However, since it only causes 1/2 ball deflection in cruise, I not certain that the mount is that far offset in the wrong direction. Guess I should add a few washers and find out - just kidding. One of my numerous projects is to fabricate some new engine mounting brackets (keeping the same mounting frame) with the offset to the opposite side.

Besides, its really the increased ROC that really tells the story. I consistently get over 1500 fpm and even get up into the 1700 fpm range on cold days lightly loaded. Previously it was in the 1000-1200 fpm range.

Ok on the prop, Bernie.

I'm planning at this time to fly out to Bill Eslick flyin in Feb weather permitting - make a nice long flight for your 9.

Ed A

===========================================

Hi Ed,

Don't forget to add that the P-factor is now in the opposite direction and I believe you did not change angle of engine mount to offset this. I'm not questioning that you get more thrust with this set up, just questioning if your criteria of lack of rudder is a good indicator.

Took your prop and the sensenich to plant city and left both with them. Will probably be able to pick them up on the way home from Memphis after Christmas.

Cheers and Merry Christmas in NC,

Bernie