X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 30 Jun 2008 21:04:22 -0400 Message-ID: X-Original-Return-Path: Received: from smtp-ext-03.mx.pitdc1.expedient.net ([206.210.69.143] verified) by logan.com (CommuniGate Pro SMTP 5.2.4) with ESMTPS id 2997798 for lml@lancaironline.net; Mon, 30 Jun 2008 10:49:09 -0400 Received-SPF: none receiver=logan.com; client-ip=206.210.69.143; envelope-from=rpastusek@htii.com Received: from dlhtpax009 (static-71-178-198-10.washdc.fios.verizon.net [71.178.198.10]) by smtp-ext-03.mx.pitdc1.expedient.net (Postfix) with ESMTPA id 30DE338093 for ; Mon, 30 Jun 2008 10:48:31 -0400 (EDT) Reply-To: From: "Robert Pastusek" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: RE: [LML] Re: Runaway Trim X-Original-Date: Mon, 30 Jun 2008 10:48:27 -0400 Organization: Holmes-Tucker International, Inc. X-Original-Message-ID: <013901c8dac0$5b6152e0$1223f8a0$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_013A_01C8DA9E.D44FB2E0" X-Mailer: Microsoft Office Outlook 12.0 thread-index: AcjZnZ0rSzz13GdbSQaL7hVNIXfiUgBHtPpw Content-Language: en-us This is a multipart message in MIME format. ------=_NextPart_000_013A_01C8DA9E.D44FB2E0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Given the recent discussion on this, and the fact that I am now in flight test with N437RP (Lancair IV-P), I conducted a runaway trim test yesterday. As background, I have set the trim travel to provide a moderate amount of pitch down trim, but substantial up trim .as would be required for landing. I also installed a locking toggle switch in the center of the panel, just below the radio stack, that switches the trim from left to right stick control. This switch has a center OFF position that completely removes power from the trim system. I started the in-flight trim test at 120 KIAS. Full down trim was controllable with moderate stick back pressure. I judged this to be manageable for a reasonable period of time given the forces involved-estimated at 10 pounds or so, but not measured. The full up trim, however, required significantly more force to maintain level flight. I would estimate 25 pounds. The force was great enough that I could hold it with my left hand, but could not operate the coolie hat trim switch with my thumb and maintain the pressure at the same time. I rolled into a 70+ degree left bank to ease the forward stick pressure, and even though I applied significant power almost immediately, the airspeed dropped to 110-100 before I could control it. This was a real attention getter; enough so that I trimmed it back to normal and came home to think it over on the ground! A runaway up trim in my airplane will require immediate and positive action to retain control of the airplane. I want to also see if I can/should limit the trim travel in this direction. I don't think I am using all of the available nose up trim during normal landings, but have not explored the full CG range yet. If possible, I will limit the travel to the max required for "normal" landing, and try this test again. Bob From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Gary Casey Sent: Sunday, June 29, 2008 12:07 AM To: lml@lancaironline.net Subject: [LML] Re: Runaway Trim If the trim motor fails it will certainly just stop moving - can't move without power. But moving back upstream, if one of the relays fail closed there is a runaway condition, and a relay can stick either open or closed. Further, the stick switch can fail open or closed. Granted, it is more likely for one of these components to fail open than closed, but the severity of the failure is far, far worse if closed than open. In my case, if a stick switch fails closed I have to recognize this and switch to the other stick immediately. If the relay fails closed I have to find and pull the breaker. It would be nice to have a "master" trim on-off switch. In my case there are coolie-hat switches and I worry that something could fall under one of the switches, jamming it in position. On my list of things to modify are, in order of priority: 1. Reduce the travel of at least the elevator trim tab so that it will produce only the minimum-required down trim. Full up-trim is probably manageable, but full down-trim might not. 2. Eliminate the relay array by wiring the two sticks in parallel. The only disadvantage of this is that if the two pilots trim in opposite direction simultaneously the breaker will pop (at least settling the disagreement :-). 3. Going to a two-switch arrangement as mentioned below by Robert. The certificated planes i have flown have this arrangement for exactly this reason: If one switch sticks closed power will be interrupted by the other switch when released. If the opposite trim direction is then selected the breaker will blow. Intuitive and fail-safe. 4 And I've also thought about putting 4 switches on the stick. Instead of a pair of SPDT momentary-contact switches use 4 SPST momentary-contact switches. The two on the front of the stick are to trim down and the up-trim switches are on the back. My coolie hat is on the back and I've had a couple of times when doing a go-around that I was unable to simultaneously push hard enough and operate the trim switch so I had to operate the trim switch with the other hand. The theory is that when pushing forward the index finger is free and when pulling back the thumb is free to move the appropriate switch. Gary Casey From: Dennis Johnson [mailto:pinetownd@volcano.net] Sent: Thursday, June 26, 2008 9:51 PM To: lml@lancaironline.net Subject: Runaway Trim My understanding from talking with the RAC guys, who make the trim components I installed in my Legacy, is that stuck (runaway) trim is unlikely. (Actually, they said it was impossible, but I find it hard to use that word.) _____ A runaway trim seems unlikely to me too. There was one GlaStar incident a few years back that was attributed to such a failure while in the pattern. That incident resulted in two fatalities, and a design change to the GlaStar trim authority. Remembering that accident and having experienced the muscle required to overcome the mis-trim on my ES-P even when slowed to 90 kt, I figured I could either install a mechanical backup (not practical) or try an electrical approach. To eliminate runaway some installations have two buttons that must be pressed simultaneously to activate either direction. That eliminates runaway but not single-direction failure. In my failure mode it was not a runaway failure: I was able to trim nose-up but not nose-down. This new controller should allow me to reverse the previous direction bypassing the control stick buttons. So if after climb out I again could not trim nose-down I would be able to press the reverse button and reduce stick pressure. At least - that's the theory. Robert M. Simon ES-P N301ES ------=_NextPart_000_013A_01C8DA9E.D44FB2E0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Given the recent discussion on this, and the fact that I = am now in flight test with N437RP (Lancair IV-P), I conducted a runaway trim = test yesterday.

 

As background, I have set the trim travel to provide a = moderate amount of pitch down trim, but substantial up trim …as would be required = for landing. I also installed a locking toggle switch in the center of the = panel, just below the radio stack, that switches the trim from left to right = stick control. This switch has a center OFF position that completely removes = power from the trim system.

 

I started the in-flight trim test at 120 KIAS. Full down = trim was controllable with moderate stick back pressure. I judged this to be = manageable for a reasonable period of time given the forces = involved—estimated at 10 pounds or so, but not measured.

 

The full up trim, however, required significantly more = force to maintain level flight. I would estimate 25 pounds. The force was great = enough that I could hold it with my left hand, but could not operate the coolie hat = trim switch with my thumb and maintain the pressure at the same time. I = rolled into a 70+ degree left bank to ease the forward stick pressure, and even = though I applied significant power almost immediately, the airspeed dropped to = 110-100 before I could control it.  This was a real attention getter; = enough so that I trimmed it back to normal and came home to think it over on the = ground! A runaway up trim in my airplane will require immediate and positive = action to retain control of the airplane. I want to also see if I can/should limit = the trim travel in this direction. I don’t think I am using all of the available nose up trim during normal landings, but have not explored the = full CG range yet. If possible, I will limit the travel to the max required = for “normal” landing, and try this test again.

 

Bob

 

From:= Lancair = Mailing List [mailto:lml@lancaironline.net] On Behalf Of Gary Casey
Sent: Sunday, June 29, 2008 12:07 AM
To: lml@lancaironline.net
Subject: [LML] Re: Runaway Trim

 

If the trim motor fails it will certainly just stop = moving - can't move without power.  But moving back upstream, if one of the = relays fail closed there is a runaway condition, and a relay can stick either = open or closed.  Further, the stick switch can fail open or closed. =  Granted, it is more likely for one of these components to fail open than closed, = but the severity of the failure is far, far worse if closed than open.  In = my case, if a stick switch fails closed I have to recognize this and switch = to the other stick immediately.  If the relay fails closed I have to find = and pull the breaker.  It would be nice to have a "master" = trim on-off switch.  In my case there are coolie-hat switches and I = worry that something could fall under one of the switches, jamming it in position.  On my list of things to modify are, in order of = priority:

1.  Reduce the travel of at least the elevator = trim tab so that it will produce only the minimum-required down trim.  Full = up-trim is probably manageable, but full down-trim might not.

2.  Eliminate the relay array by wiring the = two sticks in parallel.  The only disadvantage of this is that if the two = pilots trim in opposite direction simultaneously the breaker will pop (at least = settling the disagreement :-).

3.  Going to a two-switch arrangement as = mentioned below by Robert.  The certificated planes i have flown have this arrangement for exactly this reason:  If one switch sticks closed = power will be interrupted by the other switch when released.  If the = opposite trim direction is then selected the breaker will blow.  Intuitive = and fail-safe.

4  And I've also thought about putting 4 = switches on the stick.  Instead of a pair of SPDT momentary-contact switches = use 4 SPST momentary-contact switches.  The two on the front of the stick = are to trim down and the up-trim switches are on the back.  My coolie hat = is on the back and I've had a couple of times when doing a go-around that I = was unable to simultaneously push hard enough and operate the trim switch so = I had to operate the trim switch with the other hand.  The theory is that = when pushing forward the index finger is free and when pulling back the thumb = is free to move the appropriate switch.

Gary Casey

 

 

From:= Dennis = Johnson [mailto:pinetownd@volcano.net] =
Sent: Thursday, June 26, 2008 9:51 PM
To: lml@lancaironline.net
Subject: Runaway Trim
My understanding from talking with the RAC guys, who make the = trim components I installed in my Legacy, is that stuck (runaway) trim is unlikely.  (Actually, they said it was impossible, but I find it = hard to use that word.) 

 

A runaway trim seems unlikely to me too.  There was one GlaStar incident a few years back that was attributed to such a failure while in the pattern.  That incident resulted in two fatalities, and a design change to the GlaStar trim authority.  =  Re= membering that accident and having experienced the muscle required to overcome the mis-trim on my ES-P even when slowed to 90 kt, I figured I could either = install a mechanical backup (not practical) or try an electrical approach.  =

 

To eliminate runaway some installations have two buttons = that must be pressed simultaneously to activate either direction. That eliminates runaway but not single-direction failure.  In my failure mode it was not a runaway failure: I was = able to trim nose-up but not nose-down.  This new controller should allow = me to reverse the previous direction bypassing the control stick = buttons.  So if after climb out I again could not trim nose-down I would be able to = press the reverse button and reduce stick pressure.  At least - that's = the theory.

 

Robert M. Simon

ES-P N301ES

 

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