Mike,
In the last sentence in your message below, did you intend to type,
REL-2 rather than REL-1 as shown?
Rod
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf Of mikeeasley
Sent: Sunday, May 30, 2010 6:54 AM
To: lml@lancaironline.net
Subject: [LML] Re: Legacy Trim Tab Servo Speed Control
I
know this started out as a Legacy trim speed question, so I apologize for the
digression.
The
ES has heavier control forces than a Legacy and the CG range is larger so the
elevator trim has to be more powerful. The standard ES elevator trim is
set up with a 1.0" travel RAC trim motor. The travel is divided
evenly between up and down. ES's need all the up trim, sometimes even a little
more with the TSIO or far forward CGs. But after flying my plane for a
while I noticed that the LED trim indicator never got much past the middle
position in cruise. So that left a bunch of down trim that was never
used. A couple ES guys experimented with trying to fly the plane with the
trim full down and never got there. So the solution was to eliminate any
unused trim. I replaced the 1.0" travel trim motor with the
.7". I adjusted the travel to keep all the up trim and remove most
of the extra down trim. Now in cruise I'm one LED from the end of the
range, perfect.
You
can imagine Steve's runaway trim situation in an ES with fast and powerful
trim. Pulling the CB might not be enough to keep the plane
controllable. Slowing the trim speed down is not only a convenience, but
a safety issue in a runaway trim scenario.
Back
to the stuck switch. My Mooneys had a double switch on the yoke for
elevator trim. It ends up that's a safety related design. The two
switches are in series so if one gets stuck or shorted, you still have control
over the trim. Of course if one switch fails open, you lose the electric
trim. But Mooneys have a manual trim wheel. I tried to locate those
switches but was unsuccessful.
A
couple posts ago, Steve mentioned the history of the failing RAC relays.
Those are the REL-1s. The new REL-2 is better. Another Lancair
owner at my airport has had two REL-1 failures in 5 years. After the
second failure, he replaced all his REL-1s with REL-2s. I believe the
REL-1 failure mode is no trim, not runaway trim.