I mentioned to an engineer fried the problem some of us are having with cracked motor mounts. His response was interesting to say the least.
Mark S.
(I wrote)
On another subject, some of the Lancair ES's have developed cracks in
their motor mounts. I may need to remove my mount and send it back for
magna-fluxing and repair. There have been a number of severe shimmy
incidents, one resulted in nose gear collapse. They're still trying to
figure out why that's happening. I have not experienced any shimmy in
six landings, but they usually begin later on, after 100 or so
landings. Personally, I believe that the mounts are cracking which
weakens the mount and allows the shimmy to occur. The cracks are on the
cross-over tube right at the nose strut attachment. I'll be
inspecting mine for cracks this weekend. Hopefully, I won't have to
ground it for mount/strut repairs.
Other than that, it flies great!
Mark S.
Sorry about messing up the margins. ;-(
From just looking at these pictures of the MM
it does not look like it has any positive damping in rotation other
than the friction in the cylinder seals. Once the seals wear a bit
the friction is probably reduced. A scissor link and a circular
disk damper could be retrofitted. I'll do a 3D for you.
The structural design is not great either. It needs an FEA done
as there are tubes in bending and torsion. I take it you are using the
stock Continental bed mount. I have never been a fan of that mount.
Also some of the bays are not triangulated. CC copied it unfortunately.
I take it you steer with the brakes?
Has Tom Parke's had any nose gear problems. Tom?
Paul Lamar ...No rotor no motor.
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Paul,
I figured some sort of bending/twisting was happening to cause those cracks. As for the strut, it does have an internal damping mechanism. Some of those have blown the o-ring which resulted in severe shimmy, or maybe it is the other way around (severe shimmy caused it to blow the o-ring). There's a mod to those to add a second o-ring. So far, mine is doing fine. I feel that the shimmy is caused by the weakened motor mount. The strut mounts in the area where the cracks are forming.
Would you mind if I forward your analysis of the Lancair motor mount to the Lancair group? They are headed down the path of adding gussets. I don't feel they are addressing the real problem (as you described).
Thanks,
Mark
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