Been a while since I last posted. Snowblower repairs, bad weather, and a wonderful cold have kept me at bay for a while on the project. Finishing the scarf joint turned out to be royal pain in the butt. I thought I had finished the joint, had a pretty good fit between the wing skin edges and the fuel tank skin edge, and then I final sanded everything with 320 grit aluminum oxide sand paper to remove the deep scratches. Then I took both wing skins off of the frame set all the remaining dimples with my squeezer, masked off the sanded areas of the wing skins where I formed the scarf joint, and primed them all with NAPA 7220 self etching primer.
Then I reapplied both wing skins to the frame to check the fit, since this was the first time that the dimples were added to that entire area. To my utter disappointment, the skins looked like they had not even been touched. The edges stuck out like sore thumb. My friend Mike had warned me about this a while back, but I thought that was because of the skin edges not being slightly bent, which I had already addressed. However, it became apparent real fast that the newly dimpled skins and the added primer were both causing the skins not to ft very well against the wing spar flange.
SO I called Vans about this. they said that you really can't judge how they will go together until you actually rivet them to the spar, and not to worry about it too much. Well, I decided to try to alleviate at least some of this ill-fitting issue, so I took off the inner skin, noticed that the edges of the skin were quite thin, but that the rest of the metal moving away from the edges still seemed to be a bit thick - indicating that I had not removed enough metal on the inner portions of the wing skin. So out came the file one more time. This time I focused ONLY on the inner portion of the skin, staying away from the edges as much as possible.
Then I re-sanded the deep scratches from the file and re-primed the small 1 inch square area that I was working on. Then I rechecked the fit and decided that enough was enough, and it was time to move on. I think I pretty much realized at that point that it was the dimples and how they were fitting into the countersunk hole of the spar flange, that as causing the fit problem, even though the hole has been countersunk a little bit more than flush per Van's instructions.
When this areas gets riveted to the spar that metal will be forced into the spar flange hole and hopefully will smash down a bit more with the force from the rivet gun. If I don't like the fit after that, I can drill the rivets out and figure something else out. OH - but wait - by the time you get to this joint in the wing for riveting, you have already done the rest of the holes in the skin, because per the plans you save this lovely area for last. So I'll be damned if I am going to rivet everything else just to find that this area is still not seating properly. Others don't seem to have problems with any of this, so why the hell am I?
Time to move on. The scarf joint is as done as it is going to get. I am pretty certain that all that I will get for my efforts on this is a cracking wing skin in this very area once I start flying. If I do, you can bet that I will be asking myself why I even bothered with this stupid scarf joint - which some builders have also decided not to do, since it is "only cosmetic" per Vans.
I re-inspected the state of the leading edge assembly after my near disastrous and stupid attempt to force it off of the wing spar with the fuel tank mounted next to it. (See my Stupidity label to find the post). I tweaked the rear flange of the inboard 408 rib a bit more with the handseamer, and I checked for cracks or fatigue, and did not see any evidence of that. I removed the fuel tank assembly from the wing spar and remounted the LE assembly, all the while having flashbacks to my stupidity from before. I re-secured the LE assembly to the wing spar with clecoes and then added the fuel tank assembly. That's when I got my next head scratching moment - when the edge of the fuel tank skin and the LE skin did not line up correctly.
Initially I had a situation where there was no gap at the very tip of the LE and the fuel tank skins, but as you went further aft, this turned into at least a 3/64s inch gap. WOW! I thought I had everything here all matched up nice and neat - so once again I foud myself asking what the ^&*O&%$^! Obviously this was some sort of angular issue between the wing frame and the LE and Fuel tank assemblies, which I had verified long ago were butting up to each other with no gap whatsoever - so I knew that something just "wasn't right."
So I'll cut to the chase. There were two things that found that I needed to do. The first is a long standing problem that I have had ever since I put the frames on the wing stands. I used a hydraulic jack to support the center of the wing frame, which does sag under the weight of the wing assembly when mounted on the stands at both ends. I thought that this would be a great method - but found out long ago that these jacks do NOT hold their pressure forever, and they start to slip. As a result, I have had to continuously reapply pressure to the jack to lift the center section to keep everything aligned.
This time I wanted to be sure to recheck the "level" state of the frame by using a fish line strung across the rivet holes of the spar flange and held in place by two clecoes - one at each end. Then you apply the pressure from the jack until the fish line cuts through all the rivet holes evenly. Works great, and I found that I needed to apply more pressure once again to level everything out. The only problem with this is that to do it correctly you need to remove the wing skins from the frame. I did all this in warm weather, before the cold snap hit over the past couple of days. Seemed to level everything out again.
Today is the first day since I got sick that I have been able to go out and check on things in the garage. What I found this time was even more shocking. This time the gap between the LE and fuel tank skins was consistent from top to bottom, and was quite large on both sides. So once again I am asking what the ^&%^%#%$!. I rechecked the jack, but after leveling the center again I still had this huge gap.
The Le had been firmly reattached to the wing spar several days ago, so it was not moving. That meant that something was up with the fuel tank for some reason. When I put both assemblies back on the wing spar, the fuel tank was butted up against the LE skin and then I clecoed the inboard-most holes in the baffle and Z bracket on that end. Then I put #30 clecoes back in each screw hole through the nut plates, just as I had done many times before. None of the other fuel tank ribs, including the outboard-most rib, were clecoed, because at the time I did not think I had access to those holes since the LE an fuel tank are now butted up against each other.
So while scratching my head about this latest quandary, I came up with a plan, based on the only thing I could think of that was causing this gap problem - the clecoes I used to attach the fuel tank assembly to the spar were not allowing the skins to line up correctly for some weird reason. So I came up with a brilliant idea - make absolutely sure that the center of the wing frame was level (again), remove all the fuel tank attach clecoes, slide the fuel tank assembly over till the skins are snugged up against each other, and re-clecoe the fuel tank to the spar again. Then check the fit and go from there. I was skeptical about this whole thing, because I thought that the rib to Z bracket holes would now be out of alignment after sliding the skins together to "make" them fit. I found myself asking - "did I really mess up the whole fitting process and drilled the wrong holes in the wrong places, and that is what is causing all this?" Could I really be that stupid - again?
However, much to my surprise, after I re-clecoed the inboard rib to the inboard Z bracket, and then started carefully applying #30 clecoes to the screw holes through the nut plates again, the skins magically all lined up like they were supposed to, and they stayed that way as I added each cleco. Thank goodness for that is all I can say. Then I saw that I could still apply the clecoes to the outboard fuel tank rib and Z bracket through the access panel opening of the LE. And the skins stayed flush together after I did that. How bazaar is that!
The only thing that I can conclude from this is that I think there was some misalignment of the inboard and outboard ribs when the rest of the fuel tank assembly was removed to match drill the baffle to Z bracket holes for the remaining fuel tank ribs. It could also be that the sagging center section of the frame, combined with some slight shifting of the screw hole clecoes, may have caused the misalignment occur. Putting #30 clecoes in the holes intended for the screws in the fuel tank skin, which have yet to be dimpled, is a bit out of the ordinary. Normally you put clecoes through matching holes in two or more pieces of metal.
However, in this case, until the fuel tank skin holes are final drilled to size for a #8 screw, and dimpled, you are inserting a clecoe into a hole in a flat skin, and then in turn the rest of the cleco must extend further than normal, all the way into the end of the nut plate on the inside of the spar flange. This results in a clecoe that is under higher spring tension than usual, since it has to be extended more than usual, and the flat skins are then being pulled slightly into the large countersunk hole in the wing spar flange, causing some uneven tension on the fuel tanks skin. When you combine all this with an unsupported center section of the wing frame, it is not hard to see how things might not line up correctly.
The lesson learned from this is to make sure that parts that you know are supposed to fit together are actually mated that way first, and THEN you cleco everything in place - NOT the other way around - i.e. clecoe everything and then check the fit. Clecoes that are inserted into places where they may be allowed to shift or distort the assembly a little (flat skin screw holes into countersunk holes nut plates for example), can cause such a mis-alignment of closely fitting parts like skins. The second lesson learned here is that I need to replace the STUPID hydraulic jacks with a 3/8 inch threaded shaft with a small wood support on one end, and a large washer and nut assembly on the other end, inserted into a solid wood base with a hole slightly larger than 3/8 inches for the rod to freely insert into, and adjusted so that the center section of the frame remains level ALL THE TIME! Don't use stupid hydraulic jacks unless you want to feel my pain.
So I already have one screw jack assembly from another builder, which I obviously never used, and I'll need to fabricate another one for the other wing stand. That is my mission for tomorrow. SO in short I have been on a bit of wild ride ever since the time came to remove the LE from the frame to start working on the fuel tank assembly on the wing spar. It's been one wild thing after another ever since.
The last thing for tonight is that I finally have the LE back on the wing frame, which is the point that I was trying to get back to ever since this latest round of madness began. I needed to get the LE back on the frame one last time for it is final-assembled so that I can get down to business and make those final decisions about cut lines and new rivet holes and locations for nut plate and screw holes, all in preparation for the big "cut your LE to pieces" exercise. I worked out some final measurements tonight and will elaborate more on all that in my next post. I am very close to being ready to make the cut in the LE skin once these measurements are finalized.
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