REFLECTOR: Take Off Shimmy

[Ann DaSilva]

+Your wheel is out of Balance

-----Original Message-----
 Subject: REFLECTOR: Take Off Shimmy

Velocitites

For those of you flying fixed gear birds, I've got a question.   I recently
replaced the rubber shock mount on my front gear strut with the "new" rubber
mount due to suffering three failures of the factory mount.     So far no
shimmy on landing or on the take-off roll.    However . . . . . . I've
notice that as a I climb out the first 500 feet or so, I experience a
"shimmy" that starts about five to ten seconds into flight and then
dissipates after 5-10 seconds.  You feel it in the fuselage, but no in the
stick or rudder pedals.    It only happens on takeoff and I can't reproduce
it in flight while simulating takeoff or anything else.    Nothing else has
been done to the plane (600+ hrs TTAF) recently other than the gear mod.  I
checked all the flying surfaces and not indication of flutter.   Prop tight,
motor mounts good.   I even put the brakes to see if it wa! s the main
wheels turning causing the shutter.    My rule of thumb is that the most
likely cause of a problem is normally the last thing you "fixed."    I
suspect it is either due to the front wheel spinning down and being slightly
off balance or some other transitory vibration coupled with the spinning
wheel.     My guess is that the previous nose gear installation was loose
enough that it didn't transfer any shimmy or vibration once the wheel left
the ground.    Now with the new rubber shock mount, the nose gear is solidly
pressed against the fuselage (though the bumper and capture plate) and it
amplifies any transient vibration.

Any suggestions or anyone have a similar problem.


Bill  Stockman    173FGE   N12WS

"no good repair goes unpunished"

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