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I don't recall whether Tracy adjusted his motor mount for his 2.85 and
larger prop or not.
Tracy's RV-4 mount is
straight, with no offset either direction. When I first put the 2.85
drive on the RV-3, while it still had the opposite engine mount thrust angle, it
was an evil uncontrollable beast.
I made one (and only
one) takeoff from the three point stance. If the plane wasn't so
overpowered, it would have been a ground loop for sure. Despite full right
rudder, the plane left the ground just as it departed the left side of the
runway. From that point on, I would ease into the power, until I could get the plane going
fast enough to raise the tail, then I could roll on the rest of the
throttle. On one hand, this would seem to show that the primary problem
was due to P factor, but on the other hand, the rudder is also far more
effective once you reach tail flying speed, so maybe that's the simple
reason it was more controllable.
I was able to shim the
mount back to zero offset, but that was as far as I could reasonably go.
Of course, when you shim the mount on an RV-3, you're also turning the main gear
as well. What I ended up with was the engine pointing forward, and the
main gear pointing a couple degrees to the right. Maybe that helped
too. The difference was simply
amazing, and the plane is a pussy cat compared to having the wrong
thrust.
Cheers,
Rusty (Kolb now has more
wires than any 3 other Kolbs
combined)
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