X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 25 Jan 2010 21:42:39 -0500 Message-ID: X-Original-Return-Path: Received: from web57508.mail.re1.yahoo.com ([66.196.100.75] verified) by logan.com (CommuniGate Pro SMTP 5.3.1) with SMTP id 4094896 for lml@lancaironline.net; Mon, 25 Jan 2010 07:29:21 -0500 Received-SPF: none receiver=logan.com; client-ip=66.196.100.75; envelope-from=casey.gary@yahoo.com Received: (qmail 26407 invoked by uid 60001); 25 Jan 2010 12:28:44 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=VVZjzXR5UJf+q97Umqq1mfXsp9uA21rUxg2Kxg6T1Wcz2f3QMSjFuPO3uh4ez49GfuscxS+Iaj+6fdHYpLLZbXXUNql8FPQNfsgWJuY9tDxCo173wzABB1cA+0+3sVATCU+VsDtguBEqjPGxoCf3TmrbZNiKVW3OJRqghmnPquo=; X-Original-Message-ID: <629883.25622.qm@web57508.mail.re1.yahoo.com> X-YMail-OSG: KXn6z_AVM1lX0Cecb4fw3mwg7jem6fFN8vI00fTkmLtF0OZbYURHO02jP3xiS69zaPoBJcwRM8n2B.Gadb2SY38TB0S44qRl92UewnJXlQ.VbwYdhZLQ6Yn.Q_s6DVdhDv.8Et1gOqUnlti7Fk_8pnqtTziiDeukDVb6yvSMgdPAMCujeg8Z0IT_Srac8rmN3dvCzS65Gn46c_Cx9Ew35l.TZsaHFoyAR0gjYivupIoSv9JJAStthggQwhcnvEwG2PfysSvvNqijv8hmtawn8_X5dGF6D1fz2HxcmMOz8xW1uTeKluEGFqnRvsg8nQA89e3044ecpBLd23g6CAQA9G4- Received: from [97.122.177.200] by web57508.mail.re1.yahoo.com via HTTP; Mon, 25 Jan 2010 04:28:44 PST X-Mailer: YahooMailRC/272.7 YahooMailWebService/0.8.100.260964 References: X-Original-Date: Mon, 25 Jan 2010 04:28:44 -0800 (PST) From: Gary Casey Subject: Re: L-IV Alignment X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1300123261-1264422524=:25622" --0-1300123261-1264422524=:25622 Content-Type: text/plain; charset=us-ascii Good point, Matthew. But I think the question is whether or not the gear is able to "normalize" just rolling back and forth under weight or if the wheels need to be placed on greased plates to normalize. Certainly you can't just lower the plane down without moving it and expect the alignment to be anything close to correct. Do the tires develop enough side force to stress the gear legs just by rolling? I suppose it is possible, but I doubt it. One sign of that would be if you pushed (or pulled) the plane, let go, and it responded by rolling back the other way. If it is true, then I would measure the toe-in by pulling the plane forward and then block the nose wheel to keep it from rolling back and then measure the toe-in in the "stressed" condition. Cessna has built thousands of each version of tubular gear (swept forward and straight out) and I don't know of any special technique they use or recommend to measure alignment. They do sell shims that can be used to adjust both toe-in and camber, as I recall. Both my Cessnas exhibited positive camber angles in the air, but only slightly positive camber on the ground, which I ignored. The tires always wore on the outside and I attributed that to the scuff spinning the tire up on landing, not normal taxiing. Another thought related to oscillation while braking. The "correct" geometry of the gear leg would be to have the tube pointed at the center of the tire contact patch. That eliminates the potential torsional load on the tube while braking. Any twist of the leg will significantly change the toe-in and I would think that would be bad. I admit I haven't looked to see if it is close the correct geometry, but I think on the ES it is close enough. The IV is a different story because of the shape of the tube - but it isn't different that any of the Cessna retractables, so what does that say? I don't know. I don't know if there is a truly correct way to measure toe-in, but the way I do it is to place blocks the approximate height of the axle ahead and behind the wheel. Then I put a straight edge against the tire sidewall, resting on the blocks. I measure from the ends of the straight edge to the aircraft center line to get the toe-in measurement. I aim for zero, but should there be a slight toe-in so that brake drag will bring it back closer to zero? I don't think so, if only from the tire wear perspective. Gary ________________________________ Re: [LML] Re: L-IV Alignment January 24, 2010 4:07:52 PM MST From: "Matthew Collier" To: "" Gary, I made the assumption that we were discussing the Lancair IV. The ES does not have the same issue since the angle of the leg is nearly straight down when viewed from the side. When viewing the IV from the side the legs go forward quite a ways from their attach point in the gearbox. This causes the toe and camber to change with load. The ES will almost only change in camber with changes in load. Toe being off by a degree or two (in opposite directions) will show excessive tire wear very quickly, while camber being off takes much longer and may never seem to be a problem. Matthew Collier Fibercraft Inc. --0-1300123261-1264422524=:25622 Content-Type: text/html; charset=us-ascii
Good point, Matthew.  But I think the question is whether or not the gear is able to "normalize" just rolling back and forth under weight or if the wheels need to be placed on greased plates to normalize.  Certainly you can't just lower the plane down without moving it and expect the alignment to be anything close to correct.  Do the tires develop enough side force to stress the gear legs just by rolling?  I suppose it is possible, but I doubt it.  One sign of that would be if you pushed (or pulled) the plane, let go, and it responded by rolling back the other way.  If it is true, then I would measure the toe-in by pulling the plane forward and then block the nose wheel to keep it from rolling back and then measure the toe-in in the "stressed" condition.  Cessna has built thousands of each version of tubular gear (swept forward and straight out) and I don't know of any special technique they use or recommend to measure alignment.  They do sell shims that can be used to adjust both toe-in and camber, as I recall.  Both my Cessnas exhibited positive camber angles in the air, but only slightly positive camber on the ground, which I ignored.  The tires always wore on the outside and I attributed that to the scuff spinning the tire up on landing, not normal taxiing.

Another thought related to oscillation while braking.  The "correct" geometry of the gear leg would be to have the tube pointed at the center of the tire contact patch.  That eliminates the potential torsional load on the tube while braking.  Any twist of the leg will significantly change the toe-in and I would think that would be bad.  I admit I haven't looked to see if it is close the correct geometry, but I think on the ES it is close enough.  The IV is a different story because of the shape of the tube - but it isn't different that any of the Cessna retractables, so what does that say?  I don't know.

I don't know if there is a truly correct way to measure toe-in, but the way I do it is to place blocks the approximate height of the axle ahead and behind the wheel.  Then I put a straight edge against the tire sidewall, resting on the blocks.  I measure from the ends of the straight edge to the aircraft center line to get the toe-in measurement.  I aim for zero, but should there be a slight toe-in so that brake drag will bring it back closer to zero?  I don't think so, if only from the tire wear perspective.
Gary

Re: [LML] Re: L-IV Alignment

January 24, 2010 4:07:52 PM MST
From:
"Matthew Collier" <ivdiggs@gmail.com>
To:
"" <lml@lancaironline.net>
Gary,
I made the assumption that we were discussing the Lancair IV. The ES does not have the same issue since the angle of the leg is nearly straight down when viewed from the side. When viewing the IV from the side the legs go forward quite a ways from their attach point in the gearbox. This causes the toe and camber to change with load. The ES will almost only change in camber with changes in load. Toe being off by a degree or two (in opposite directions) will show excessive tire wear very quickly, while camber being off takes much longer and may never seem to be a problem.

Matthew Collier
Fibercraft Inc.

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