Return-Path: Received: from [65.33.165.45] (account ) by logan.com (CommuniGate Pro WebUser 4.0b4) with HTTP id 1626737 for ; Fri, 12 Jul 2002 18:32:38 -0400 From: "Marvin Kaye" Subject: Re: [LML] lead weights To: lml X-Mailer: CommuniGate Pro Web Mailer v.4.0b4 Date: Fri, 12 Jul 2002 18:32:38 -0400 Message-ID: In-Reply-To: <00f201c229cc$2502c180$6501a8c0@cp172883-b.arlngt01.va.comcast.net> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Posted for Bob Pastusek : For Dan Newland, Based on the results with shot bag weighting/clamping on our wings, I'd recommend against using vacuum for wing closure. The reason is that the vacuum will cause the skins to deform in the unsupported areas. When we closed our wings, we used angle iron and long wooden slats to help distribute the load over the spars and ribs, and even this caused some distortion that required "body work" to fill and restore the airfoil shape in some areas. One thing is sure: Once the wing skins are bonded and set, your shape is defined--the depressions we made in 1999 during closing were waiting for us to fill in 2002 when we started to prep for painting! I think the vacuum would work well where an even clamping pressure is required over the complete surface area, but this is not the requirement here. You might talk to Mark Mahnke at Lancair about your idea. He's built a very large number of composite planes and likely has some advice about this. BTW, there was a great post to this forum a few years ago that is relevant: Seems a fellow attempted to leak test his wing tanks using a vacuum pump. Not watching the vacuum too closely, he managed to cave in one of the skins. Thinking this a fluke, he proceeded to do the same with the other wing. I'm sure this story has grown a bit with the retelling, but understand the basis to be true. I also recall that Don Goetz, famous Lancair test pilot, had an engine failure at high altitude. During the glide, he noticed that he could see all the ribs and spars outlined on the wing skin. Switched fuel tanks with the selector and restored the engine to life; later determined that the vent line had plugged--even the small vacuum from the fuel pump was apparently enough to deform the wing skins. Lots of second-hand hangar talk here, but my advice would be to stick with the shot bag weights--and some boards/steel to distribute the load where you want it. Bob Pastusek -----Original Message----- Wrom: KYLEJGDGVCJVTLBXF I was wondiering if anyone has tried using a vacuum pump to provide pressure for clamping wing skins on to the spars.