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Rick,
Thanks for your input and comments. I'll try to answer as much as I know.
Early on I observed that the gear legs were sloppy in the mount and the spindle brackets were sloppy on the gear legs. I had the legs knurled and ground to fit both ends and that worked fairly well. They are still not what you would call tight but the movement is greatly reduced from what it was pre-modification.
The motion appears to be front to rear with some lateral movement of the wheel pant as the spindle essentially moves on its radius from the main gear leg mount.
I use the standard style pad in metallic compound. I have had good results with the pad and have not noticed abnormal wear.
I don't have air vents in my wheel pants. I don't think it would make a difference in my case. I have done some taxi testing without wheel pants and the problem seemed to be the same.
The comments about the damping of the gear legs being a good idea is something that my head engineer has suggested. He talked about the natural frequency of the gear leg/wheel assembly and what the excitation input might be. Obviously, it is brake related but what is the bad thing that is already present at the time the brakes are applied that is magnified by the brakes? Ahah..........I don't know yet.
The video is analog and I have transferred it to my computer but the quality is not as good as the tape. I'm still working on it.
Thanks again for trying to help. If we ever figure this out I believe a lot of people will benefit.
Jim
From: "rtitsworth" <rtitsworth@mindspring.com>
To: "'Jim Scales'" <joscales98@hotmail.com>
Subject: RE: [Lancair_ES] FW: [LML] ES shake (apparently not strut related)
Date: Fri, 7 Sep 2007 13:36:03 -0400
Jim,
I don't have nearly the experience may of you on the list do (approx 20hrs
total ES time, all in other builder's ES's). However, I thought your post
was VERY insightful!
I've always had a feeling the main gear legs were shaking due in part to
prior observations of my C172 legs and to witnessing Tim Ong shimming Kirk
Hammersmith's ES gear legs into the weldments with thin SS shim stock in
Redmond when I was there for builder assist in Oct 05. It looked to be a
nasty job (especially since Kirk only had small access holes), and thus the
only way that Tim was going to be doing it himself was if it was of
particular interest to him and/or important. I'm not sure the C172 gear is
a good surrogate for an ES, but the overall setup (and apparently the
braking shimmy effect) is similar.
That insight is what lead me to have my ES gear leg weldments and legs
re-machined to fit tight (ref: my prior ES-list posts). I'm not sure if my
approach will matter much, but I discussed it with Tim and it seemed like
the right thing to do. I was told that Lancair is now machining (honing)
the ES gear leg weldments to get a tighter, more consistent fit on the more
recent kits (unverified).
At one time I thought that "perhaps" the wheel/gear motion was rotational in
nature (or at least had a rotational component) versus being purely
fore/aft. This may still be the case. However, if it is, the tightness of
the gear legs to the weldments is then perhaps unrelated, since the leg
attach bolt tends to hold the leg tight in rotation (even if it is free to
move/shake a fore/aft a bit).
My understanding is that the Cleveland high energy brakes (metallic) use the
same brake disks as the std brakes. I'm 99% sure of this, as I upgraded
when I bought my kit and the rotors came with it, but the calipers and pads
were backordered. So, there is nothing to be gained by looking at that -
perhaps except for the fact that the metallic pads tend to wear the disks
faster. That could be a good or bad thing. Good in that they may wear the
disks into submission. Bad in that the disks may wear faster and thus be
more prone to warping and/or non-uniform wear. Which style brake pads do
you have?
Do you have air vents in your wheel pants? The ES kits currently come with
air vents molded into the rear inside surface of the pants. It seems excess
heat would be a bad thing for the disks in all cases.
FYI, 20+ years ago I was a Tire Engineer (right out of college). An
interesting characteristics of a car tire is it Uniformity. In addition, to
balancing it from a weight/mass standpoint, the ride quality is also
influenced by any relatively stiff spots in the tire itself
(circumferentially). Thus, in a radial tire, some care is given to be sure
the various ply splices are not all stacked on top of each other during
manufacturing. This is typically less of a concern in a bias ply tire.
Also, I don't think it's all that relevant for our ES situation since the
effect seems to be largely braking related.
It might be interesting to share your video with some engineers at Cleveland
to get their insight. Seems they might have some experience with similar
phenomenon in all their testing.
The other post about the stiffness of the wheel pants and mountings, also
seems like an interesting thing to examine.
Otherwise, I'm not sure there is much we can do if it is just a by-product
of the ES gear leg design. Perhaps some sort of rubber coating around (or
inside) the gear leg to help dampen the leg itself.
Would love to see a couple clips of the video if you can figure that out.
How did you take the video? What media is it stored on?
Also your posts on the LML get broad exposure (a good thing). Are you aware
there is also an ES focused list? You can get detailed sign-up
instructions at http://www.n727rt.com/ref-yahoo.htm or jump to the group
page at http://groups.yahoo.com/group/Lancair_ES.
Rick
Call if you'd like to talk Cell: 313-506-5604
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