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Rod,
I don't have any personal knowledge of an REL-2 failure. But I've heard of several REL-1 failures. I believe the failure mode of the REL-1 is loss of trim, not runaway trim. Likely, that's the same thing that would happen with an REL-2 failure, but I don't know for sure. The REL-2 housing is much larger, so maybe it has more robust components that contribute to its increase reliability.
I think I got all my 1s and 2s correct in my previous post.
Mike
In a message dated 05/31/10 07:45:57 Mountain Daylight Time, rpharis@verizon.net writes:
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 e
nd 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.
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