REFLECTOR: Take Off Shimmy

[Terry Miles]

If it helps your strain of consciousness, think of the wheel and tire
assembly as a gyroscope.  Mayve see if you can increase it or decrease
shimmy based on turns after takeoff while the wheel still has higher rpm.
Just like a toy gyroscope in your hands: Tip it one way and it wants to
rotate 90 degrees in the opposite plane.  When the USAF C-5 first got into
the field the main trucks had something like 26 relatively small tires and
the gyroscopic action was causing mayhem.   The gear retraction was an
arcing movement (forward and inboard) from full down to full up with no
wheel speed snubbers.  The crews were required to leave the gear down for
the 1st 15 mins of flight.  Just thought I'd toss this into the mix.  Good
luck with it.

 

Terry

 

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Andy Millin
Sent: Wednesday, October 15, 2008 12:46 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Take Off Shimmy

 

Bill,

 

It sounds like you are pointing in the right direction.  My first
inclination was to check the balance on the nose tire.   That seems where
you are headed.

 

Andy

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of tstockmn at aol.com
Sent: Tuesday, October 14, 2008 10:20 PM
To: reflector at tvbf.org
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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