X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 29 Jun 2008 21:18:15 -0400 Message-ID: X-Original-Return-Path: Received: from mta31.charter.net ([216.33.127.82] verified) by logan.com (CommuniGate Pro SMTP 5.2.4) with ESMTP id 2996602 for lml@lancaironline.net; Sun, 29 Jun 2008 10:48:14 -0400 Received-SPF: pass receiver=logan.com; client-ip=216.33.127.82; envelope-from=troneill@charter.net Received: from aarprv04.charter.net ([10.20.200.74]) by mta31.charter.net (InterMail vM.7.08.03.00 201-2186-126-20070710) with ESMTP id <20080629144729.NIUT2641.mta31.charter.net@aarprv04.charter.net> for ; Sun, 29 Jun 2008 10:47:29 -0400 Received: from axs ([75.132.241.174]) by aarprv04.charter.net with SMTP id <20080629144728.LSXJ4495.aarprv04.charter.net@axs> for ; Sun, 29 Jun 2008 10:47:28 -0400 X-Original-Message-ID: <00b001c8d9f7$0d8971c0$6401a8c0@axs> From: "terrence o'neill" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: runaway trim X-Original-Date: Sun, 29 Jun 2008 09:47:28 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00AD_01C8D9CD.245AC270" 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-Chzlrs: 0 This is a multi-part message in MIME format. ------=_NextPart_000_00AD_01C8D9CD.245AC270 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Fifty years ago I was flying P2V-5s in the Navy, (twin-engine patrol = bomber) and there was a runaway 'Varicom" on takeoff in another squadron = somewhere that caused excessive nose-up both pilots were unable to = overcome... went straight up and came straight down. The Navy and = Lockheed came up with a remedy. Varicam was a trim surface in between the stabilizer and the elevator, = powerful enough to balance the big Fowler flaps. The emergency procedure was to roll the plane into a 45-60 degree bank = and put full flaps down, both of which demanded more 'nose up', of = which there was already a plethora. And the circuit breaker was pulled, = while both pilots pushed forward. Then an enlisted-crewdog struggled = under about 2Gs to find the hand crank, made his way back into the tail, = stuck the hand crank up into the overhead de-energized trim motor and = cranked like hell to lower the Varicam back to neutral. But the point is, full flaps and a steep turn should help if the trim = runs away 'up'. If it goes 'down'? Reflex the flaps and hope you don't = have to roll inverted periodically to maintain altitude until ... = hmmm... any suggestions? fwiw Terrence L235/320 N211AL ----- Original Message -----=20 From: Jeremy Fisher=20 To: lml@lancaironline.net=20 Sent: Saturday, June 28, 2008 11:06 PM Subject: [LML] Re: runaway trim I used to fly Canberras, which had a powerful electric trim motor that = changed the horizontal stab angle of attack. There were several fatal = accidents before it was found that the trim could run away, and the = elevator did not have enough authority to overcome the hardover trim. = We then fitted two microswitches that had to be pressed simultaneously, = which fixed it. As we have heard, it can happen. The obvious thing to check is that you can overcome a runaway trim = motor in flight. If you cannot, then reduce the trim authority, most = easily by reducing the size of the trim tab. Beyond that, I am = installing a circuit breaker near the trim controller so that I can pull = it and cut off all power. Runaway trim frightens the hell out of me. It can be very hard, or = impossible, to manage. We need to make sure that we can deal with it by = checking it out in flight and making it controllable. Just my opinion. Jerry Fisher On Sat, Jun 28, 2008 at 5:42 PM, wrote: Posted for "Abe Gaskins" : In my Legacy I had autotrim installed. I am empirical proof that a = runaway=20 trim condition can happen. Upon attempting to reach Sun-n-Fun this = year I was=20 over flying Chattanooga and I had a progressive runaway trim pitch = up=20 condition. Trim went to the stops. I found the condition managable = though I=20 did have to push forward with heavy input in order to maintain = control. OK in=20 VFR but scary and potentially leathal in IMC on a dicey approach.=20 Abe Gaskins=20 N272AG -- For archives and unsub = http://mail.lancaironline.net:81/lists/lml/List.html No virus found in this outgoing message Checked by PC Tools AntiVirus (4.0.0.26 - 10.072.012). http://www.pctools.com/free-antivirus/ ------=_NextPart_000_00AD_01C8D9CD.245AC270 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Fifty years ago I = was flying=20 P2V-5s in the Navy, (twin-engine patrol bomber) and there was a runaway=20 'Varicom" on takeoff in another squadron somewhere that caused excessive = nose-up=20 both pilots were unable to overcome... went straight up and came = straight=20 down.  The Navy and Lockheed came up with a remedy.
Varicam was a trim = surface in=20 between the stabilizer and the elevator, powerful enough to balance the = big=20 Fowler flaps.
The emergency = procedure was to=20 roll the plane into a 45-60 degree bank and put full flaps down,  = both of=20 which demanded more 'nose up', of which there was already = a plethora. =20 And the circuit breaker was pulled, while both pilots pushed = forward. =20 Then an enlisted-crewdog struggled under about 2Gs to find the hand = crank, made=20 his way back into the tail, stuck the hand crank up into = the=20 overhead de-energized trim motor and cranked like hell to lower the = Varicam back=20 to neutral.
But the point is, = full flaps=20 and a steep turn should help if the trim runs away 'up'.  If it = goes=20 'down'?  Reflex the flaps and hope you don't have to roll inverted=20 periodically to maintain altitude until ... hmmm... any=20 suggestions?
fwiw
Terrence
L235/320 = N211AL
 
----- Original Message -----
From:=20 Jeremy Fisher=20
Sent: Saturday, June 28, 2008 = 11:06=20 PM
Subject: [LML] Re: runaway = trim

I used to fly Canberras, which had a powerful electric trim motor = that=20 changed the horizontal stab angle of attack.  There were several = fatal=20 accidents before it was found that the trim could run away, and the = elevator=20 did not have enough authority to overcome the hardover trim.  We = then=20 fitted two microswitches that had to be pressed simultaneously, which = fixed=20 it.  As we have heard, it can happen.
 
The obvious thing to check is that you can overcome a runaway = trim motor=20 in flight.  If you cannot, then reduce the trim authority, most = easily by=20 reducing the size of the trim tab.  Beyond that, I am installing = a=20 circuit breaker near the trim controller so that I can pull it and cut = off all=20 power.
 
Runaway trim frightens the hell out of me.  It can be very = hard, or=20 impossible, to manage.  We need to make sure that we can deal = with it by=20 checking it out in flight and making it controllable.  Just my=20 opinion.
 
Jerry Fisher

On Sat, Jun 28, 2008 at 5:42 PM, <marv@lancair.net> wrote:

Posted for = "Abe=20 Gaskins" <abe@mail.mgmindustries.com>:


In my = Legacy I=20 had autotrim installed. I am empirical proof that a runaway
trim = condition can happen. Upon attempting to reach Sun-n-Fun this year I = was=20
over flying Chattanooga and I had a progressive runaway trim = pitch up=20
condition. Trim went to the stops. I found the condition = managable=20 though I
did have to push forward with heavy input in order to = maintain=20 control. OK in
VFR but scary and potentially leathal in IMC on a = dicey=20 approach.
Abe Gaskins
N272AG

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