OK, so its a bit later than "tomorrow." Been a horribly busy week of work and other stuff this past week, but I have also managed to keep working on the plane, slow-going as that may seem. As promised, moving on with my LE modification - it all started with the piece of 12 inch wide x 3 foot-six inch long x .032 inches thick piece of aluminum sheet. First it had to be cut to size, and then the fun part was bending it to roughly the same shape as the original joiner plate, which wraps around the contour of the W408-1 L and R ribs, and is sandwiched between the rib and the LE skin.
The width stayed the same - 12 inches. This seemed to work well because it was just wide enough to span the entire distance between the first two inboard ribs, while still allowing for just enough excess on either end to allow for the 11/16ths of an inch extension on the inboard side for the nutplates and bolt holes for the fuel tank attach points, and just enough on the other end to overlap the rib flange by a bout 1/4 inch or so. I am glad I did not have to trim the width at all.
Here is the sheet that I began with:
Then came the fun part. I actually ruined the first sheet by not carefully thinking about the cut lines, so before I knew it, I ended up with yet another piece of scrap metal. In a nutshell I had to trim the edges of the length-wise portion of the part to account for some differences in the rivet hole pattern of the LE skin between the most inboard W408 rib and the and what was originally the first inboard W709 rib, now converted to another W408 rib. It turns out that the skin-to-rib flanges are shorter on the W408 rib since it was originally designed to clear the spar bar that lays down across the main wing spar web on both sides. I also discovered that the most rearward rivet hole on the LE skin is also about 1/4 of an inch lower than the same one that attaches to the original W408 rib. This again is due to the difference in the flange lengths of the W709 and W408 ribs.
In short, about half of the width of both ends of the sheet had to have the original 36.5 inch length for the first half of the part, but the second half of this edge had to be about 1/4 inch longer, or 36.75 inches, to account for the different rear-most rivet hole locations on the two rib bays. After correcting my measurement problems from the first attempt to trim the part, here is a series of pics showing the lines, radius holes, and rough cut appearance after it was all cut to size:
I used a #30 drill bit to drill a 1/8 inch hole to create a 1/16th inch radius in the sheet where the dimensions on the ends change. Then I smoothed the edges on the scotch brite wheel.
Then I had a real dilemma to figure out - I needed to try to find a way to ensure that I could bend the sheet into exactly the same shape that the original joiner plate was bent, which follows the contour of the W408 rib. THis also brought to my attention one small detail about the aluminum sheet that ordered from Vans, and that is that I was not sure how the grain of the metal should be oriented. After looking at the original joiner plate strips that I fabricated, I determined that the grain of these strips ran along the long side of the strip (parallel). Of the two sheets that Vans sent tome, I determined that one of them had the grain running across the long edge of the sheet. So I had two sheets, each cut with the grain running in a different direction. My problem was that the sheet that I had mismeasured and cut was the one with the grain running in the same direction as the original part, so I was concerned about this, but I decided to proceed with the other sheet anyway. I figured if I really need to make another one then I will know how to do it quickly. SO I considered this to be a true "experimental" exercise in how to fabricate a part of my own design. IT was more important to get the process down than to worry about which way the grain is running at this point.
This led me back to the original problem - how to form a curve in a piece of aluminum sheet that was originally only 1.5 inches wide, but is now 12 inches wide? The original skinny part was hard enough to form to the correct shape, so I was not looking forward to this wider one. My idea was to create a series of form blocks out of wood that matched the shape of the rib, and stack them together to make a form block that was almost as wide as the 12 inch wide sheet. I already had some cut outs that matched the general curve of the nose of the LE ribs from the parts I cut to make the LE cradle. I decided to head over to HD aircraft supply and pick up a 2x10x 8 foot long piece of wood. I then traced the rib pattern onto the wood and used my jigsaw to cut out each rib form: Here are some pics of that process:
Even though I drew the pattern from the same rib, the nose of each piece of wood did not come out as uniform as I had expected. Cutting with the jigsaw is not always very exact. So I took each one and ran the noses against my rotary sanding wheel to even them up:
With the nose sections of the wood forms mostly uniform, I now had to decide if I wanted to bolt them together to keep them tightly held together, or if could just clamp them into place while forming the aluminum sheet around the part. I decided to try to clamp them together first and see if this would work. I used several bar clamps as shown in the following pics to clamp the forms near the edge of my work table, and then slipped one side of the sheet in between the forms and the par clamps. The only other thing I needed to figure out was where to place the end of the sheet against the rear part of the forms to make sure that the ends of the part would end up in the right position. Once I determined the correct location of the end of the sheet, I clamped it down against the form, and then I started to bend the sheet around the LE of the forms by hand.
As shown from the above, this was good enough to form the initial bend, but due to the spring back it was not quite good enough to form the sheet as far as it needed to be.So I resorted to another method tht could apply a little more force than my feeble hands. I used my ratchet straps to cinch down the skin around the forms and this helped a little more, but again was not quite enough:
Next I unfortunately had to remove the part and begin that wonderful exercise of finishing up the form with my hands. This took quite a while and involved some squeezing, rolling, forming, pulling pushing, swearing, cursing, bleeding, - - you know - - basically all those things involved with trying to form a complex part by hand. Here is a comparison of the "finished" part and the original joiner plate:
Not too bad if I do say so myself. From the above pic you can also see that I clamped the rib down on the table. Once the original form was complete I began using the actual rib to verify that the curvature of the part was at least close enough to form correctly around the rib. The true test, however, came when the part was placed inside the LE skin and mounted on the Main wing spar. More on that in the next post.....
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