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Michael,
May I be the first to welcome you
and your friend to the Ercoupe fleet. Nose gear and shimmy are
addressed in four Service Memorandums. These memo's range from simple nose
wheel inspections to complete nose landing gear rebuild instructions.
Here are the memo numbers and titles:
-
Ercoupe Memorandum #15 - Vibration - Nose Landing Gear Strut and Wheel
-
Ercoupe Memorandum #34 - Inspection of Nose Landing Gear Wheel - Die Cast
-
Ercoupe Memorandum #41 - Rebuilding of Nose Landing Gear Assembly
-
Ercoupe Memorandum #51 - Installation of the 5.00x5 and 6.00x6 nose wheel
These memos are a good read and will
help you in troubleshooting. Not knowing what model or serial number
Ercoupe you have I've given you all references, some may not even apply to your
airframe.
Your right in your assumption about
the spacer. Reading your description of the situation raised warning flags
to me. Hopefully after careful inspection of the wheel assembly no
other "modifications" or damage was found.
With the single bearing nose
wheel, note that even with a new bearing there will be some internal
play. As these bearings wear through their normal service life, they
will eventually contribute to shimmy. With the wheel halves assembled and
properly torqued the bearing should be firmly held within the wheel. You
shouldn't be able to spin the bearing assembly or wobble it within the wheel
halves. If so, one or both of the wheel halves are worn. Also the
axle nut tightens against the inner race (the part that slides on the axle), not
the sidewall of the bearing (the part the rotates with the wheel). Try
contacting Univair for drawings on the nose wheel assembly for
dimensions.
There isn't any balance
markings per se on the wheel halves other than aligning the balance dot on the
tire to the inflation valve, if that dot hasn't worn off the tire.
The service memorandums cover how to balance the wheel assemblies using
automotive style balance weights. Take note on how old the tire may be, if
it has any abnormal wear pattern. If it's been on quite a few years and
the aircraft was static for some time, the tire could of taken a set in the
carcass ply.
Other things to look at are the
nose gear torque links. Check for play at the upper attach bolt, lower
attach bolt, and center bolt. You can grab the upper and lower link
and apply opposite pressure to trouble shoot that. Replace bushings and or
bolts as required to take out the slop.
Lastly, observe the nose
strut. With the tail weighted down, try to move the extended inner
strut in a circular motion then compress the strut and note any play while
moving the inner strut in a circular motion. Trying to guess over
this e-mail how much play is too much, well, I'll leave that to you. I'd
to the less expensive items first.
I've had much the same problem
with my aircraft last year. A high speed taxi would shake the
fillings out of my teeth. My wheel assembly was good but the torque
links and nose strut were badly in need of a rebuild. The
service memorandums cover how to rebuild. Now the only time I'd get
any shimmy is during landing roll out and rolling across a
pavement repair patch. Even then the nose gear would shimmy
momentarily. If you still have questions, please e-mail
me.
Walt Uebele
1946 415-C
N94113
From: Amundson, Michael [mailto:[EMAIL PROTECTED]
Sent: Tuesday, October 26, 2004 10:36 AM
To: [email protected]
Subject: [COUPERS-TECH] nose wheel vibrations
----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----
hello,
I'm a new comer, but
I have questions already.
A good friend of
mine just recently acquired a coupe, and while changing the inter tube, and
bearing on the nose wheel, several things surfaced which I'm hoping you people
can help shed some light on.
This is on an old
style one leg nose gear...
First of all the
axel nut was not "on" far enough, the threads of the axel didn't even come
all the way through the nut. The new replacement bearing was thinner than
the one that was removed. When the wheel was split to replace the
bearing there was a 3/16 spacer between the wheel halves. My thoughts
were the original bearing spun inside the aluminum wheel and allowed the proper
size bearing to "wobble" and whom ever repaired this problem decided
it would be an acceptable method to use a wider bearing and a shim a
little less than the oversized bearing width that would allow the wheel to
tighten around the outer race of the bearing. Could this be right?
Looked in the parts manual and there was no spacer pictured, it's rather unusual
to have spacers between wheel halves.
We installed the
correct bearing, aired up the tire and did a high speed taxi, " got to about 55
and the vibrations were of such magnitude it would have made a spinster
smile.
so what are our
options?
Purchase a new nose
wheel?
Does anyone have
proper dimensions of the bearing seat of the wheel so we can mike them to see if
our guess was correct?
I looked for wheel
markings " side to side for balance purposes but could not find
any.
I guess I'm hoping
some one can help help us, or at least give some suggestions what to look
for....
thanks
M
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