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Date: Fri, 07 Sep 2007 17:48:25 -0400
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From: "Jim Scales" <joscales98@hotmail.com>
Subject: [LML] ES shake (apparently not strut related)
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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
>
>