X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 27 Jun 2008 19:31:06 -0400 Message-ID: X-Original-Return-Path: Received: from elasmtp-kukur.atl.sa.earthlink.net ([209.86.89.65] verified) by logan.com (CommuniGate Pro SMTP 5.2.4) with ESMTP id 2993453 for lml@lancaironline.net; Thu, 26 Jun 2008 23:22:37 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.65; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=Pjp9rq1Nx8kB7JoP6iuZfMJNvspXj4S2VHErr2ap9EXMPkdr1bdmUmsH6cg38oZf; h=Received:Message-ID:From:To:References:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE:X-ELNK-Trace:X-Originating-IP; Received: from [216.57.118.35] (helo=ccaselt3) by elasmtp-kukur.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1KC4XA-0006c5-5j for lml@lancaironline.net; Thu, 26 Jun 2008 23:22:00 -0400 X-Original-Message-ID: <161701c8d804$f6c58df0$6501a8c0@nvidia.com> From: "Colyn Case at earthlink" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Runaway Trim X-Original-Date: Thu, 26 Jun 2008 23:22:00 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_1614_01C8D7E3.6F18E670" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da94035f0b43b5ac13d8d2c1fa7edf14a159d350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 216.57.118.35 This is a multi-part message in MIME format. ------=_NextPart_000_1614_01C8D7E3.6F18E670 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable It may be that an electrical malfunction sort of "runaway trim" = situation is unlikely but I think there is more to the story. Here are = a few disconcerting issues I've found on my airplane: 0) HPAT made me fly with max pitch up trim at speed. I don't think I = would like this at all IMC at 25000 and needing to get down. For that = condition you want lower airspeed which would mean losing = pressurization, prolonged descent time, etc. I didn't try max pitch = down but according to my test pilot report that looks like it would be = even more challenging on approach. 1) I have dual trim control (pilot and copilot) with a disable on the = copilot. I had a condition early on that turning OFF the copilot trim = cause d the auto-pilot to do weird things. It turned out the copilot = auto-pilot disable was stuck ON. since the sorcerer is looking for a = transition (bad idea IMO) it saw the transition to OFF as a toggle. = ...which could mean a/p off, a/p on, or cws depending. I sanded the = parts and decided to live with it. but generally that copilot disable = only moves on the ground. 2) the RAC system wants 12V so I run it from my 12V power converter. = That makes my power converter part of my safety of flight. I don't like = that in the first place. ...but one day the 12V supply CB popped, = killing my trim. It's never done it before or since. I really = don't like the fact that RAC doesn't make a 28V part. I've considered = dual redundant and dedicated power supplies just for the trim. 3) My pitch trim servo installation was customized to use a shorter = lever so as to be aerodynamically cleaner. This results in it having = more travel that it needs. I've purchased parts to reduce travel. 4) RAC relays don't seem to last very long. 5) I have a/p auto-trim on my airplane. Although I haven't experienced = it on this airplane, I have experienced the a/p dialing in a heap of = trim and then disconnecting. This is attention getting in a cessna. = Right now my a/p auto-trim is always on disable. So although there may not be a likely runaway situation with RAC = components alone, there are still lots of ways for the trim to end up = where you don't want it, and possibly without the ability to fix it. = dual redundant 28V trim servos, or manual trim would be nice. ------=_NextPart_000_1614_01C8D7E3.6F18E670 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
It may be that an electrical = malfunction sort of=20 "runaway trim" situation is unlikely but I think there is more to the=20 story.   Here are a few disconcerting issues I've found on my=20 airplane:
 
0) HPAT made me fly with max pitch up = trim at=20 speed.    I don't think I would like this at all IMC at = 25000 and=20 needing to get down.    For that condition you want lower = airspeed which would mean losing pressurization, prolonged descent time, = etc.   I didn't try max pitch down but according to my test = pilot=20 report that looks like it would be even more challenging on=20 approach.
 
1) I have dual trim control (pilot and = copilot)=20 with a disable on the copilot.   I had a condition early on = that=20 turning OFF the copilot trim cause d the auto-pilot to do weird=20 things.   It turned out the copilot auto-pilot disable was = stuck=20 ON.  since the sorcerer is looking for a transition (bad idea IMO) = it saw=20 the transition to OFF as a toggle.   ...which could mean a/p = off, a/p=20 on, or cws depending.      I sanded the parts = and=20 decided to live with it.  but generally that copilot disable only = moves on=20 the ground.
 
2) the RAC system wants 12V so I run it = from my 12V=20 power converter.   That makes my power converter part of my = safety of=20 flight.  I don't like that in the first place.   ...but = one day=20 the 12V supply CB popped, killing my trim.    It's never = done it=20 before or since.    I really don't like the fact that RAC = doesn't=20 make a 28V part.  I've considered dual redundant and dedicated = power=20 supplies just for the trim.
 
3) My pitch trim servo installation was = customized=20 to use a shorter lever so as to be aerodynamically cleaner.  This = results=20 in it having more travel that it needs.   I've purchased parts = to=20 reduce travel.
 
4) RAC relays don't seem to last very=20 long.
 
5) I have a/p auto-trim on my = airplane.  =20 Although I haven't experienced it on this airplane, I have experienced = the a/p=20 dialing in a heap of trim and then disconnecting.   This is = attention=20 getting in a cessna.  Right now my a/p auto-trim is always on=20 disable.
 
So although there may not be a likely = runaway=20 situation with RAC components alone, there are still lots of ways for = the trim=20 to end up where you don't want it, and possibly without the ability to = fix=20 it.   dual redundant 28V trim servos, or manual trim would be=20 nice.
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