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No familiar with the SA-16, Bob, but are both props turning same direction
or opposite - would make a significant difference in whether there is a swirl
(my spell checker says OK {:>)) effect or not. If in opposite
directions then I would agree, if both props rotating in same direction then
harder to say.
For a long time I thought that Torque was the major cause, however, I
remain convinced (at this point) that the low rolling and large yaw force is
primarily caused by swirl. Having encountered prop swirl on take off roll too
close behind Finn's RV3 there is no question in my mind that prop swirl is a
powerful force. But, regardless whether torque or swirl (or
combination), the 2.85 gear box and larger prop makes a considerable
change.
I don't recall whether Tracy adjusted his motor mount for his 2.85 and
larger prop or not.
Ed A
----- Original Message -----
Sent: Monday, December 12, 2005 10:01
AM
Subject: [FlyRotary] Re: "P" factor? Re:
Static Engine RPM
As I understand it, the P factor only comes in when the
prop is advancing in a direction different than it's axis. Like a tail
wheeld airplane with it's tail still on the ground or any airplane at a high
angle of attack. That is not a factor on a tri geared aircraft on
innitial role.
An engine properly trimed for a counter-clockwise prop (1
or 2 degrees left thrust) would have a large effect when changing to a
standard (American direction) prop. A lot of left turning reaction
tendencies plus left thrust would require lots of right rudder. A
major force is torque. More HP, more torgue. The swerl effect is mild
in comparison.
As an example, the SA-16 (large twin amphibion) drivers
start their max take-off run from the left side of the runway, pointed about
45 toward the center line. Said that there was no way, when
quickly adding full power that they could keep it from turning-so they just
planned for the turn. No swerl effect here.
FWIW
Bob Darrah
(I know, but my spell checker said it was ok)
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