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Old 02-11-2005, 05:52 PM
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Dust Dust is offline
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Location: Troy, Michigan
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Default Braking shimmy - Solved

Marc Z had a heck of a time solving his main landing gear vibration problems and went to allot of effort to detail all possible problems and solutions, in his search for the problem, he found that ALLOT of planes, not just canards or any specific canard has landing gear vibration problems - SOOOOOO without further ado


Great Vibration Hunt Part 3 - Conclusion:

So, after a few weeks of beating on this vibration stuff, I've got a list
of things that folks with main gear vibration should/could work on to try
to eliminate their problem. Most of them were suggested by others, but
I've never seen them ALL collected in one place before. I feel that if
someone methodically corrects all these possible problems, there is an
excellent chance that they will eliminate the forcing function causing the
main gear resonance.


Here's the list (in MY estimated order of importance, but not necessarily
always the case - you can get stung by any one or more of these things in
combination):

1) Wobble of brake disc rotors due to mounting point misalignment

2) Runout/warping of brake disc rotor

3) Combination of (1) and (2) - dial indicate rotor ON wheel - ensure
less than 0.003" total indicator runout - the lower the better

4) Free movement of caliper in "float" bushings

5) Gear leg attachment points tight - NO movement

6) Wheels/tires balanced - 1/2 oz max.

7) Tires round

8) Wheel pants balanced - test with and without pants

9) Tire pressure between 45-50 psi, minimum

10) Toe-in per plans - no toe-out

11) Camber per plans


If fixing all of these things does NOT fix the vibration problem, then
possibly addressing the resonant frequency of the gear legs themselves by
changing gear leg material to carbon (NOT recommended by Mike at
Featherlite), adding extra torsional wraps of UNI (suggested by many,
including Mike at Featherlite), or other, more complex fixes may become
worth investigating (if you haven't gone nuts from chasing the first 11
things).

DONE! Thanks again to everyone who wrote, helped out, and made it clear to
me that this was NOT an isolated instance - there is apparently a large
minority of folks that have this problem (and not just in canards,
either). At least in MY case, it seems to have been mostly due to poor
quality control in the manufacture of the wheel/brake assembly (sorry,
MATCO - but apparently this happens with Clevelands as well, so you're not
alone).


I've copied MATCO on these messages so that they'll have more reference
info the next time someone calls them with this question, and hopefully
will modify their MFG practices so that they machine the rotor mounting
points with the wheel assembled on an axle.

--
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dust

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