X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 27 Aug 2007 05:42:58 -0400 Message-ID: X-Original-Return-Path: Received: from BAY0-OMC3-S10.bay0.hotmail.com ([65.54.246.210] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2286559 for lml@lancaironline.net; Mon, 27 Aug 2007 01:09:09 -0400 Received-SPF: pass receiver=logan.com; client-ip=65.54.246.210; envelope-from=joscales98@hotmail.com Received: from hotmail.com ([65.55.135.15]) by BAY0-OMC3-S10.bay0.hotmail.com with Microsoft SMTPSVC(6.0.3790.2668); Sun, 26 Aug 2007 22:08:30 -0700 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Sun, 26 Aug 2007 22:08:30 -0700 X-Original-Message-ID: Received: from 75.81.226.134 by BAY130-DAV5.phx.gbl with DAV; Mon, 27 Aug 2007 05:08:28 +0000 X-Originating-IP: [75.81.226.134] X-Originating-Email: [joscales98@hotmail.com] X-Sender: joscales98@hotmail.com From: "Jim Scales" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: ES Strut issues X-Original-Date: Mon, 27 Aug 2007 00:08:28 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0091_01C7E83E.64E93550" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.50.0039.1900 Seal-Send-Time: Mon, 27 Aug 2007 00:08:28 -0500 X-OriginalArrivalTime: 27 Aug 2007 05:08:30.0149 (UTC) FILETIME=[4EE91750:01C7E868] X-Original-Return-Path: joscales98@hotmail.com This is a multi-part message in MIME format. ------=_NextPart_000_0091_01C7E83E.64E93550 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thanks for your input. Just to get the information up to date about my = taxi tests of the shake, it should be noted that the taxi tests were = done without the main gear wheel pants installed. Jim ----- Original Message -----=20 From: Kyrilian Dyer=20 To: lml@lancaironline.net=20 Sent: Monday, August 27, 2007 12:03 AM Subject: [LML] Re: ES Strut issues What I take from the points below leads me to focus on the main gear = more than the nose. As Fred so well described, resonance occurs when = the modal frequency of a system coincides with the frequency of a = vibration source. If there is little damping, then the source can be = very small but still result in potentially catastrophic motion/damage. = Perhaps I'm misunderstanding, but it seems that: 1. Vibration has been observed with various nose strut designs 2. Braking (on the mains) has an influence on the vibration Though I'm not arguing that the nose strut does not have exhibit = resonance itself, I wonder if the mains act as an amplifier, that if = removed would relegate a nose strut vibration mode to an infrequent or = non-existent issue. I proffer that a small imbalance (due to the wheel or rotor CG not = being precisely on the rotational axis), or uneven brake application = (due to a slightly warped brake rotor) may excite a longitudinal mode of = the strut/wheel/pant. The energy of one or both wheels/struts/pants = moving longitudinally may cause a yawing motion of the fuselage that = either simply loads the nose strut laterally, or also causes the nose = strut to shimmy (energetic nose wheel yaw to strut roll interaction). A = modal impact (rap) test could be used to determine the natural frequency = of the strut and damping of the structure (which I'm guessing is very = low), and a simple calculation would show at what wheel speed an = imbalance would coincide with this. Removal of the wheel pants will = reduce the mass, thus driving the natural frequency up, and potentially = out of range of normal landing speeds. I have no personal experience with this, and offer the above solely as = conjecture. If someone is willing to provide the bird, I may be able to = assist with said rap test. It would have to be in south FL, after = October. Cheers, - Kyrilian Skip Slater wrote:=20 I don't have a taxi speed that I avoid, though I can get a = shaking if I try to brake lightly at low taxi speeds. I don't get any = shimmy at all when taxiing with the brakes off. -------------------------------------------------------------------------= ----- Shape Yahoo! in your own image. Join our Network Research Panel = today! ------=_NextPart_000_0091_01C7E83E.64E93550 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thanks for your input.  Just to get the information up to date = about=20 my taxi tests of the shake, it should be noted that the taxi tests were = done=20 without the main gear wheel pants installed.
 
Jim
----- Original Message -----
From: Kyrilian Dyer
Sent: Monday, August 27, 2007 = 12:03=20 AM
Subject: [LML] Re: ES Strut = issues

What I take from the points below leads me to focus on = the main=20 gear more than the nose.  As Fred so well described, resonance = occurs=20 when the modal frequency of a system coincides with the frequency of a = vibration source.  If there is little damping, then the source = can be=20 very small but still result in potentially catastrophic = motion/damage. =20 Perhaps I'm misunderstanding, but it seems that:
1.  Vibration = has=20 been observed with various nose strut designs
2.  Braking (on = the=20 mains) has an influence on the vibration

Though I'm not arguing = that=20 the nose strut does not have exhibit resonance itself, I wonder if the = mains=20 act as an amplifier, that if removed would relegate a nose strut = vibration=20 mode to an infrequent or non-existent issue.

I proffer that a = small=20 imbalance (due to the wheel or rotor CG not being precisely on the = rotational=20 axis), or uneven brake application (due to a slightly warped brake = rotor) may=20 excite a longitudinal mode of the strut/wheel/pant.  The energy = of one or=20 both wheels/struts/pants moving longitudinally may cause a yawing = motion of=20 the fuselage that either simply loads the nose strut laterally, or = also causes=20 the nose strut to shimmy (energetic nose wheel yaw to strut roll=20 interaction).  A modal impact (rap) test could be used to = determine the=20 natural frequency of the strut and damping of the structure (which I'm = guessing is very low), and a simple calculation would show at what = wheel speed=20 an imbalance would coincide with this.  Removal of the wheel = pants will=20 reduce the mass, thus driving the natural frequency up, and = potentially out of=20 range of normal landing speeds.

I have no personal experience = with=20 this, and offer the above solely as conjecture.  If someone is = willing to=20 provide the bird, I may be able to assist with said rap test.  It = would=20 have to be in south FL, after October.

 Cheers,
-=20 Kyrilian

Skip Slater = <skipslater@verizon.net>=20 wrote:=20
<snip>

   I don't have a taxi = speed that I=20 avoid, though I can get a shaking if I try to brake lightly at low = taxi=20 speeds.  I don't get any shimmy at all when taxiing with the = brakes=20 off.

<snip>

Shape Yahoo! in your own image. Join=20 our Network Research Panel today! =
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