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Steve, The spar, or "beam" as the parts manual calls it, is a part that is primarily made up of the upper spar cap, the lower spar cap, and the spar web. The spar caps are relatively heavy, "T" shaped pieces of aluminum which provide most of the strength of the wing spar. You can see the inboard ends of the upper and lower spar caps by removing the fairing strip that covers the wing attach bolts. The main wing attach fittings or "hinges" are riveted onto the capstrips and spar web by 5/16ths inch rivets. The spar web is made up of aluminum sheet, with two or three layers of the sheet being used on the inboard end of the spar, and a single layer running the entire length of the spar. (The spar caps only go outboard as far as the spar splice which is a located few feet inboard from the wingtip. From the spar splice outboard, the spar consists of either flat or formed aluminum sheet stock, riveted together to form the outboard part of the spar.) The spar web is riveted onto the spar caps, so that the assembly basically looks like a big letter "H" laying on its side (kind of like an I-Beam). You can inspect most of the front and back side of the spar assembly through all of the inspection holes in the bottom of the wing. The corrosion that I have personally seen on spar caps would have been visible through the inspection holes, because it was exfoliation corrosion that was located on the upper (exposed) surface of the horizontal part of the lower capstrip (if you can follow that description). My experience is limited to seeing three examples, so there are certainly more knowledgeable people on the list who have seen a lot more instances than I have. The problem with inspecting the capstrips is that a good portion of the surface of the capstrip is covered by the spar web that is riveted onto it, and an even greater portion of the capstrips is covered by the upper and lower wing skins. If you picture the I-Beam that we were talking about, the top of the upper horizontal on the I-Beam is covered by the upper wing skin, and the bottom of the lower horizontal on the I-Beam is covered by the lower wing skin. Therefore, even if you inspect every square inch of the capstrip that you can physically see, there is still a bunch of area that you can't see without taking the skin off and drilling out rivets (which is a major job). If there was corrosion between the capstrip and the spar web, you may not be able to detect it unless you saw a rivet head or two popped off, or if you saw some other indication of corrosion in the area. One thing that is kind of worrisome is that the junk wing that I have hanging in my garage has extreme exfoliation corrosion on one area of the lower capstrip, and just a few inches away, on the same piece of metal, the capstrip looks brand new - bright and shiny with no sign of any corrosion. There is a web site that has the video inspection tool for sale on it that has some excellent photos of wing spar corrosion on it. I was looking at it the other night, but I don't remember the link. Didn't mean to ramble on.... And as always, all of this is just my opinion, so take it for what it's worth... Wayne __________________________________________________ To unsubscribe from this list please send mailto:[EMAIL PROTECTED] ==^================================================================ EASY UNSUBSCRIBE click here: http://topica.com/u/?aVxiLm.aVzvvT Or send an email To: [EMAIL PROTECTED] This email was sent to: [EMAIL PROTECTED] T O P I C A -- Learn More. Surf Less. Newsletters, Tips and Discussions on Topics You Choose. http://www.topica.com/partner/tag01 ==^================================================================
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