Re: [COUPERS-FLYIN] Wing Bolt Torque

[Hartmut Beil]

----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- Friends. Here is what I found while investigating the bolt torque issue. When I removed the wings on 3330H I found the wing bolts not very strong tightened. These wings were at least ten years that way on my plane and after removing , I could not find any wear on bolts or fittings. I think the bolts act pins, designed to withstand shearing action. They fit snug and the nuts are there to keep them in place. The surface of the fittings (plates) seems not big enough to take up the force of the moving wing, even when clamped together with some 1000lb. If the bolts are clamped that strong, they will stretch and get slightly thinner. Now you'll have what we are trying to avoid - room for play. Now the attachments and bolts have a chance to wear. What's more is that the preloaded bolt might break away when shearing forces are applied, because it is taking already some 1000lb  as stretching force inside. Of course the bolts should be tight enough to avoid movement of themselves.That could lead to wear as well. The proper procedure for tightening the bolts is described in the latest SERVICE BULLETIN NO. 31 from Univair. http://www.univair.com/bulletin_add/sb31/sb31.pdf For those who don't have Adobe Reader, here an excerpt. "Reinstall outer wing panels, if removed per Method 3, in reverse sequence of removal, making sure that mounting bolts are properly fitted and safetied. NOTE: The recommended method for tightening the nuts on the wing attach bolts is to draw nuts down tight and continue tightening as required to line up the nearest slot and cotterpin hole provided you do not exceed 100 ft-lb dry torque on the front bolts and 10 ft-lbs dry torque on the rear bolts. Safety wing attach bolts with NEW cotter pins: AN380-4-4 (MS24665-353) for front and AN380-2-2 (MS24665-132) for rear fittings. DO NOT reuse old cotter pins." There are a lot of joints in an airplane which are not meant to be clamped together, usually in the controls and on landing gear etc. The use of clevis bolts is a sure sign that the bolt in the joint acts as an axle in way. I see the wing bolts as some form filling pins, which allow the parts being stuck together with no play in the joints. This is my opinion on that matter. Of course anybody might have his own. I am in no way authorized to tell anyone what to do. I also do not want to proof anybody wrong or right. I just gathered information and added my thoughts. Have a good evening my fellow Coupers.   Hartmut N3330H San Francisco   ----- Original Message ----- From: [EMAIL PROTECTED] To: flyin@ercoupers.com Sent: Saturday, May 10, 2003 3:48 PM Subject: [COUPERS-FLYIN] Wing Bolt Torque ----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- Fellow Coupers, Here is a link to an excellent discussion about the hows and whys of bolt torque. www.avweb.com/news/maint/182851-1.html Please read this article before you decide that "pretty tight" is a good way to tighten the wing attach bolts.  Pay particular attention to the section titled "The Need to Preload a Bolt". The friction between the wing attach fittings, not the bolt itself, is what is supposed to keep the wing from moving in relation to the center section.  The bolts must be tightened properly to apply enough pressure on the "plates" of the wing attach fittings (the joint) to develop the required friction.  If the bolts are too loose, then the load will be "felt" by the bolt as a shear load and the bolts and the holes in the wing attach fittings will wear.  As I understand it, after discussing it with a mechanical engineer, if the bolts are torqued properly, the bolts will only "feel" a tension load caused by the torque applied to the nut.  If the bolt is too loose, the joint will move, and the bolt will "feel" a shear loading. Below is a copy of an e-mail that Stefan Fanselow posted to the group some time ago concerning wing bolt torque.  Regards, Wayne Alon N5618F Subj: Re: [COUPERS]  wing bolt torques again Date: 6/29/00 10:14:16 PM Eastern Daylight Time From: [EMAIL PROTECTED] (Stefan Fanselow) Reply-to: [EMAIL PROTECTED] To: [EMAIL PROTECTED], [EMAIL PROTECTED] Here is a copy of the message I put onto the Coupers forum some time back: QUOTE As the one who initiated the discussion on the correct torque value for the wing bolts, I feel compelled to share with the group the final results of the discussion here on the forum and of my direct communication with Univair: 1.) The wing bolts need to be torqued properly, just "tightening them really well" is not sufficient. 2.) There are no recommended values by the manufacturer, so  AC 43.13-16 is the appropriate source 3.) The large and the small bolts used for the main wing attachment are indeed shear bolts. The nuts are, however, tension type nuts. This had led to some confusion during the discussion about whether to use shear- or tension values. 4.) The proper torque values are 1100-1300 inch lbs for the large bolts/nuts at the leading edge and 100-140 inch lbs for the smaller bolts/nuts at the trailing edge. Both values are indeed shear values. I have (for obvious reasons) only confirmend these numbers for the Mooney M-10. I am assuming that they are the same for Ercoupes / Aircoupes, but I urge everybody referring to this information for their own assembly to check for themselves in case the type of airplane is different. Safe flying, and have fun. Stefan in Tokyo Mooney M-10 Cadet N9547V ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers/ ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers/