Jim,
I would like to put my 2 cents in on your
shimmy. Most of my experience has
been with Glasairs but the causes of shimmy are usually
pretty much the same. I have test
flown 3 ES’s and experienced a shimmy with the
second one. That airplane was cured
by going to a thicker more viscose strut oil. The nose gear has a controlled leak from
one side to the other side of a divider that restricts movement. Using a heavier
oil sometimes will fix it. Vern
advised me of this years ago and I simply went to a
motorcycle shop and purchased 30 wt strut oil.
Your problem sound more like it is coming
from the main gear. I experienced
this same type shimmy in a new Glasair SIIS-RG a
couple of years ago. It drove me up
the wall. I tried everything. I tightened the friction clamp on the
nose gear until I could hardly taxi it.
I tried more air pressure and less air pressure. I tried forward and aft C/G solutions,
etc. It always happened when I got
on the brakes and stopped when I got off. Finally I had a good friend taxi the
airplane up to about 60 knots and get on the brakes while I stood on the side
of the runway with a camera. I didn’t
need the camera. Shortly after the
brakes were applied the right main gear started jumping up and down like it had
a 10 pound weight tied to one side of the wheel. I couldn’t believe it. This was the first Glasair
we had ever worked on that came from the factory with new Grove Brakes. I called Grove and told him what had
happened. He immediately said the
brakes were too small. He sent me
the proper brakes and the problem went away forever. Turns out Glasair
has sent brakes for the Glastar by mistake. Another possibility is extreme heat caused
by the closely fit wheel pants. This
would explain the warping of the disc.
I noticed the newer ES kits come with a recessed area on the inboard
side of the pant for venting.
Hope this helps.
Lanny
-----Original Message-----
From: Lancair Mailing List
[mailto:lml@lancaironline.net] On Behalf Of Jim
Scales
Sent: Saturday, August 25, 2007
4:36 PM
To: lml@lancaironline.net
Subject: [LML] Re: ES Strut issues
I
checked the alignment on the strut when I reinstalled it during the
annual. It is set right at 1.5 front to rear, 0 side to side. I
agree with you that there is something in the ES that is prone to produce this
shake. Finding it is the difficult part. I believe that whatever it
is the flaw is present in most of the ES models that are
flying. There are too many reports of this problem for it to be
coincidence.
-----
Original Message -----
Sent: Saturday, August 25,
2007 9:07 AM
Subject: [LML]
Re: ES Strut issues
Jim,
Since
you have done all the logical things without effect, I'm wondering if there
isn't something "built-in" that is causing the problem, like
geometry. The only geometry issue I can think of is the strut rake
angle. The correct angle was the subject of some debate a while
back. All I know is that I set mine at +1.5 degrees (lower end forward)
and I have never had a trace of shimmy. The previous discussion, as I
recall didn't result in a definitive answer, but 0 to +1.5 or so seemed to be
the "correct" rake angle. I have the rebuilt strut since new
and have a different engine mount (for a Lycoming) and either of those might
make a difference, although I'm pretty sure my engine mount is not more rigid
than the standard one. While my strut is not held laterally any better it
is probably more rigid in the fore-and-aft direction because of the different
drag link design.