| Author | Message | ||
     wayne norris |
I wondered about those spacer blocks coming loose, good idea to bolt them. That is why I didn't "drive" mine in, use all thead and pull them in. All the more reason to make sure the blocks are well fit and mill fiber to take up any airspace. I hope to never see mine again. Blame the post on Lew, he started it here. | ||
| Sean Crooks New member Username: Sean_crooks Post Number: 3 Registered: 11-2003 |
Hey guys, I am about to start on the wing of my express 90 and it appears the wing spar is twisted just a few degrees. Any experience with this problem. The outward most rib does not match with contour(in the jig). It points nose up away from the skin while being held flat against the spar. I think the spar had the other wing sitting on it for years in hot florida. I am thinking the heat/weight made it twist. It does not require much force to bend it back into place. Any ideas.....sean | ||
| Jerry Sjostrand New member Username: Jerry Post Number: 43 Registered: 08-1999 |
Sean, After setting up the wing jigs perfectly level and placing the upper wing skin in the fixture, I put pressure on the skin at several points by using adjustable tubes (3/4 inch electrical conduit with 1/2 nuts welded on and then lengths of 1/2 all-thread for adjustment) placed between my ceiling and the wing skin. In my case, I have a shop with wood trusses into which I screwed the tube (having welded a screw on the end) and placed the adjustable end over a piece of 2x4 or? I left these in place while I assembled the wing thereby eliminating any twist (or removing it in your case) and maintaining the correct airfoil. If you have a typical garage sheetrocked ceiling, screw some 2x4s or?, at appropriate points to accomplish the proper pressure points. I built my lower fuselage the same way. If you feel the twist is a result of "heat" then I would place some quartz/halogen lights in place to heat the skin while in the fixture. Do not heat above 155 degrees. When cool, the skin should hold it's shape after the ribs and glassing is done. Let me know if you have any other questions. Jerry | ||
| wayne Unregistered guest |
Good idea to do something. I didn't on my first wing(the ribs were already bonded in) but the second was so far off the curature of the cradles I had to do something, I layed weights in the bays between the ribs. This could be why one wing flies heavy as both root and tip AoAs are the same. | ||
| Brian McKinney New member Username: Bmckinney Post Number: 52 Registered: 05-2000 |
Wayne, Well no wonder you have a heavy wing! You should have removed those weights before closing...  Brian | ||
| Jeff Dingbaum New member Username: Aviators Post Number: 15 Registered: 12-2000 |
I would second Jerry's advice. Mine is a 1990 kit, one wing with the ribs in the other not started. When I put the 2nd wing in the jigs the leading and trailing edges made contact with the jig, but the skin under the spar was about 1/2" away from the jig. After much debate I finally tacked a 2x4 to the ceiling of my garage and then cut another 2x4 so that it forced the spar down the distance. It fit in the cradles perfectly then. I glassed in the ribs and it has kept its intended form. One other item. If I recall, you had to set the first and last saddle and then put the wing in and then fit the last two. Since my wing was "off" I took a string line down the leading edge and one down the trailing edge. Also down the spar line. That way I lined up the jigs. When I put the wing into the jigs and pressed the spar down it fit perfectly. Jeff | ||
| Jim Oyler New member Username: Midniteoyl Post Number: 73 Registered: 07-2003 |
With Sean's 'twist', the way he explained it, the root is fine, but the tip twists so even if he forced it down on the jig, wouldn't the spar twist back once the ribs are in? The way I read your responses it seems you guys are explaining how to get the skin to curve correctly and the ribs/spar would hold that after bonding, but what if the spar itself is the problem? I can see a twisted tip after closing... or am I being blind to something? Jim | ||
| Sven-Ake Eriksson New member Username: Sven Post Number: 19 Registered: 11-1999 |
I made two sets of sawhorses and templates and built both wings at the same time. Reason: I was then able to make both wings match almost exactly. I also aligned the templates with a leveling instrument and found that I needed to weight the spar/skin to make a good contact with the templates. When closing the wings You need to weigh everything down again. When doing so my wings stayed very straight and have kept so since. I initially found one of my spars to be off about the same as described above (slightly twisted in one direction). I did not use more weight than neccessary to just keep the wing skin /spar tight against the templates. Without doing this one of my wings would not have come out straight. The method to align root and tip template and then fit the other two against the rest of the skin/spar is no good method as you have absolutely no guarantee your wings will be straight. Sven | ||
| Jeff Dingbaum New member Username: Aviators Post Number: 16 Registered: 12-2000 |
Sven, You do need to level and plumb the first and last jigs. Then the directions call for putting to wing in and fitting the next jigs. I agree that step doesn't work too well with wings that aren't straight. That was the step that I modified. I used the string lines basically for the height of the jig. They are still level and plumb as specified in the manual. Maybe that is my point. My wing didn't really want to fit into the jigs as described in the manual (and it seems that many others have had this problem, I've heard about it before too). Jim, About the twist. There are some ribs on the back side that may help prevent it from twisting back. Not too many, though. My problem was a little different than Sean's, but I thought that if he had an old kit he may run into that problem as well. Not only that, but sometimes a solution to one problem might spark an idea on another. I hate to admit it, but I had my wing sitting in the jig for a month or two, just thinking about how to solve the problem that I had. Jeff | ||
| Sven-Ake Eriksson New member Username: Sven Post Number: 20 Registered: 11-1999 |
Actually what I did was to plumb all four (x2) templates to the floor line(s) and approximately make them level. As the wings are a linear taper from root to tip, I then used the leveling instrument to set the heights of all templates to conform to straight lines from root to tip. When putting the wing skins into this jig it was easy to find any misfit. Actually one wing was a real good fit almost without weights but the other one was both twisted and slightly curved in the up/down direction. When closing the wings you get a closed box from aft spar up to the main spar. As the leading edge is open (no seam laminates at this point) you do not get full torsional stiffness fwd of main spar. Nevertheless the torsional stiffnes of the "aft box" is more than adequate to keep the wing(spar) from distorting the wing again. Just weigh the wing down into your jig at close out time and it will be ok when cured. Sven |