Final Assembly of the Left Wing LE Begins

After evaluating the nutplate situation a bit more I decided that the nut plate is fine for now. I can still replace it later if I want to.

SO the next step was check the instructions again. They basically take you through the entire process to finish the fuel tanks, but because of the mod to the LE I really needed to finish that first. After the tanks are all but finished, the instructions tell you to rivet the LE together with it in the LE cradle. So the reality is that the LE can be assembled while in the cradle at any time. It cannot be riveted to the Wing spar, however, until the fuel tanks are done, because the screw holes in the tank skin that slide over the top of the joiner plate attached to the LE need to be final drilled, deburred, and dimpled for the #8 screws, and the assembly fit-checked with the LE again to make sure everything is AOK. One of the things that also gets in the way of this is excess proseal on the end rib of the fuel tank that may interfere with the joiner plate flange. Sometimes this has to be trimmed away to prevent this interference, which can cause the screw hole alignment to get messed up if this is not resolved. SO this is all interlinked,  but for now I can go ahead and rivet the LE together, shich also means that the subskin is finally going to become a permament part of the LE.

The instructions say to cleco it all together and then "ensure that the rear holes are perfectly aligned with each other, which I guess means the holes on the rear flanges of each LE rib. SO to reverify this I think I clecoed it all to the wing spar one last time to reset all the ribs after tugging and pulling on all that vinyl, then I carefully removed the LE again, making sure that I did not twist or bend it so that the hole alignment would not be disturbed. Then I carefully placed it back in the cradle.

Next, there were some scratches on some of the rear rib flanges and the area of the joiner plate where the tank skin edges dug into the primer and the metal a little bit, so I sanded those areas out to remove the stress risers. Then the instructions say to start with the rear-most rivet hole with a squeezer on the top and bottom of each LE rib to secure them into place. I was able to do this easily with the pneumatic squeezer and a flange yoke. As part of the mod, the two inboard-most LE ribs also have two additional holes that I needed to add to the skin and each rib and the subskin. These "second" to the last rivet holes are relatively close to the rearmost holes, so I thought I could set those rivets with the air squeezer as well. The thing that I forgot was that the #2 inboard rib, which is a modified 408-1 rib, has the shop heads of the AN470 rivets protruding a bit from the rib web, and when I tried to set these with the air squeezer the rivet set hit the edge of those shop heads and caused the set to jump, which resulted in a badly set rivet, which I had to drill out and replace. After drilling out the bad one, I decided that in this situation I needed to use the hand squeezer to maintain positive control of setting the rivet so that I could ensure that both the yoke AND the rivet set would clear the shop heads of those AN470 rivets holding the rear rib flange extensions onto the rib web. I put the 3 inch yoke on the hand sqeezer and got those rivets set as well.

Now that the rear-most rivets were set on the top and bottom sides of each LE rib, it was time to get out the rivet gun and the bucking bar. More decisions to make and prep to do. For example:

I had to decide the pattern I would use to set the rivets on each rib
I had to get towels and place them inside the LE skin to prevent accidental dings in case the bucking bar slips out of my hand
I had to tape up the edges of each rib web to help prevent gouges from the bucking bar if it slides off the rivet shaft
I had to figure out how to clamp down the table/cradle assembly to ensure that NOTHING would move or slip during the riveting process
I had to check the air pressures on the compressor and at the adjustable pressure regulator on the gun with the new slightly heavier rivet set.
I had to determine all the rivet sizes I would need to attach various parts together.

ON the last, the plans call for AN426AD3-3.5 for he main rib flanges, and AN426AD3-4 for the rivets that attach the skin, rib flange, and joiner plate assembly. However, I found that the 3.5s are OK for the main rib flanges on the main ribs, but on the two ribs that are involved with the subskin assembly, I found that the 3-4s were good for the skin-to-subskin rivets with no rib flange involved, but I found that a 3-4.5 was the correct length for the rib flange, subskin, and outer skin assemblies. A 3-4 just is not quite long enough for some reason.

SO the plan was to start on the center ribs and then work outward toward each end rib. I also started on the bottom side of each rib because it is flatter than the top - this is something that many builder advise to do when building the fuel tanks because you can set the tank down on the bottom afterward to make work on the top a bit easier. I worked from the rear-most hole to the front, as stated in the instructions.

When I started, the one thing I forgot to do was check and reset the pressure on the air compressor, which had been tuned down to 75 psi for the air squeezer. Since the pressure on the rivet gun is controlled by  separate regulator attached to the air inlet of the gun, the pressure at the compressor needs to be at 90 psi. Since I forgot to do that, the first several rivets I set seemed to take forever, and the shop head was not being formed as quickly as I was expecting. A quick check and reset of the pressure at the compressor basically fixed that problem.

Time for the pics. Here are some of the new "rubber boot" flush mushroom rivet set showing the before pic, the disassembled pic before trimming down the rubber, and the "after" pic showing the trimmed down rubber on the reassembled tool:

I took the rubber boot and ran it by hand across some aluminum oxide 220 grit sandpaper after marking it with a sharpee line. I did not want to sand too much of it away because it is still supposed to be a little proud of the set to provide some gripping ability on the skin. Then I put the tape on the rivet set - another important little trick to prevent damaging the metal with this pesky tool:

Here are some pics of the tape prep and towel prep to minimize or prevent other possible damage:

And finally some pics of te rivet gun in place and ready to set a rivet, and another pic of the bucking bar, using the angled side of the bar, showing how all this has to be positioned to set each rivet:

And here are some pics showing the progress - basically not more clecoes and a clean looking skin. the reality is that I have several rivets to drill out, mostly because they were overset, but a few are badly set rivets that need to come out. Overall I was pleased with the rivet process, and the rubber mushroom seems to do well at preventing skin damage. But the one thing that it does NOT do is ensure that the set cannot "walk" across the skin. I had numerous events where this set decided to have a mind of its own and start walking up, down, and to either side. Luckily it did not seem to damage the skin at all, thanks to the rubber edges I guess. It is designed to allow it to swivel a small amount so that you can presumably hold the gun not quite perpendicular to the skin and still get a good set. Personally I found that I still had to figure out what angles to use both up and down and side to side and how much pressure to apply to hold the rivet gun in place. 

You will notice that I left the bottom/forward-most rivets for later. These are too low to be bucked - both from a position standpoint of the gun and bucking bar, and a gravity standpoint where the rivet cannot stay in the hole at the curved angles of the these holes - it falls out. SO these will be set with the cradle turned on its side after all other rivets have been set. These forward rivets are the ones I dread the most, because the potential for skin damage due to a slipping rivet gin or bucking bar is extreme, and I already have enough bad experiences with that to prove it. The trick, once again, is securing the work so that it cannot move, and so that you can easily position the gun and the bar to set those rivets. it usually also means that you have to set these "blind", meaning that if you do this solo, you will either be able to view the bucking bar on the rivet, or the rivet gun, but you will not be able to see both at the same time. I hate setting those rivets. Curved surface riveting sucks big time.

Anyway, this was the longest work session I have had on the place for a very long time several hours today. I only have about 3 more ribs and the final forward rivets to go, as well as the swiss cheese rib, subskin, and outer skin assembly for the LE mod, so there are still a large number of rivets to set. Hopefully I will get most, if not all of them done tomorrow.

Pounding rivets again using every method on the planet and lots of tricks you learn along the way - so far so good...….

Subskin prep - Drilled and Dimpled Remaining nut plate rivet attach holes and Reassembled the LE

Today was a busy day at the factory, but for the amount of progress I made today you would probably not believe me. I finished sanding the edges of the cutout section of the LE skin smooth and straight, and used the combination of my pneumatic rivet squeezer and C-Frame tools to dimple all remaining #40 nut plate rivet attach holes on the subskin. I had to switch from my flange yoke to the standard 3 inch yoke to be able to reach all the rivet holes along each side of the subskin, and this worked out nicely. I had to use the C-Frame to reach most of the rear-most rivet holes on both sides of the subskin, and this also worked out well.

Unfortunately I had to use the #30 cleco method to secure the nut plate to the subskin so that I could align and drill the holes for each nutplate on the top side of the subskin, just as I had previously done on the bottom side. Just as before, I had trouble keeping the line of rivet holes in alignment with other straight edges, and some of them got a bit slanted. As I stated before, these holes are just for the rivets that attach each nut plate to the subskin, so the MOST important hole is actually the center hole where the screw will be inserted, and not the rivet holes.

I used the same technique to mark the alignment of the rivet holes on the top as I did  on the bottom, by placing a straight edge along the center line of each #30 screw hole and drawing short lines on either side of each hole that I used to align the rivet holes of the nutplate after it was clecoed to the subskin through the screw hole.

I drew the lines along the sides on the outer side of the skin, and drew the lines for rear nut plate holes on the inside of the skin, just as before. As shown from the pic above, I also came up with a different clamping and prep method of drilling these rivet holes. This time I really did not care so much about trying to rig up something so that I could clecoe the nutplate in plate as shown above, and then ensure that I was drilling each rivet hole into a piece of wood. I reasoned that any slag or burr on the holes would be removed by my deburring tool afterward, and so this time I chose NOT to waste a substantial amount of time coming up with ridiculous ways to ensure I could drill each hole into a piece of lousy wood. This worked out fine, except for the slight shifting of the nutplate because the clecoe just does not apply enough force to keep the drill from moving the nut plate around. SO I much prefer using the nut plate jig which prevents this from happening, but since I was not yet ready to drill the #30 hole to a #19 hole yet, which the jig uses as a pilot hole, I could not use the jig tool.

I used my 4x4 clamping blocks to provide some height to allow the cleco mounted from the underside as shown in the next photos to clear the table and saw horse ends, and the next pic shows how I clecoed the first hole after it was drilled, which keeps the second hole from moving around as well, so that both rivet holes are in alignment with each other.

As each set of rivet holes was drilled I detached the nut plate and moved it to the next hole and re-clecoed it in place, and repositioned and reclamped the subskin as necessary to retain some rigitidy in the subskin near the nut plate locations so the drill would not slip or cause the skin to warp and the hole to become mis-aligned. Here is the series of pics as I continued to drill each set of nut plate holes along the sides:

With the sides done it was time to drill the rear nutplate hole. I had to flip the subskin over and reposition and reclamp it once again. I was able to use the edge of the table to help position the skin so that the clecoe underneath butts up against the edge, keeping the skin nice and stiff while drilling.

The last pic above actually shows the holes after I dimpled them. The mot important thing to call attention to here is that I have NOT yet final drilled the screw holes to the proper size because I need to make a template first so that I can fabricate a properly sized part that will replace the cutout section in the skin. I cannot final drill the screw holes to #19 and dimple them for a #8 screw until the template has been created and at least 1 or 2 .025 removeable LE skin sections have been fabricated and fitted in place. To do that I need the screw holes to remain at #30 for now. 

Next I had a bit more cutting, filing and sanding to do on the subskin. A long time ago I had marked the location where the hole for the tie down ring is located by tracing the hole I had already drilled in the LE skin onto the subskin, which, until today, had been covering up that hole. I used the cut off wheel o n the Dremel tool to carefully cut away the metal in this area, staying just OUTSIDE the drawn lines so that  could ensure that the subskin would have enough clearance to screw in the tie down ring. Here is the pic of that after filing, sanding, and rounding all corners was completed:

With most all of the subskin prep work done, it was time to reassemble the LE for what I hope will be the second-to-the-last time before it goes together permanently. the subskin was attached first using all the rivet holes that are not part of a rib flange hole. This gets the subskin in the proper position for the ribs. Then the two inboard-most ribs are clecoed to the subskin and outer LE skin. This process always takes some work because the ribs are a very right fit in this area due to the thickness of the subskin. Again, the goal of all this was to reassemble the LE with the newly cutout section in the skin that exposes the subskin that will be used to attach the removeable LE section.

Here is a series of pics I took to show the fit of the LE and subskin after remounting it all back on the wing spar again. Overall I was pleased, but the problem that I feared and mentioned in a previous post is exactly what I encountered. The outboard are of the cutout section of the LE skin shows a bit of a gap between the subskin and the outer LE skin, whereas the inboard section seems to be draped over the subskin fairly well. This will make fitting the removeable part a bit of  a challenge, but we'll see how that goes. I am not overly concerned about the gap because I think the rib in that area combined with the subskin provides more than enough support to keep the LE from deforming in any way as a result of this gap. In other aircraft designs, such as the Sonex for example, I know that their ribs do not even wrap around the contour of the LE skin. Instead, they stop well short of the very front of the skin so that NONE of the ribs have any rounded contour that wraps around the LE at all, leaving a void between the rib and the very front part of the LE skin.

As long as the shape of the front of the LE skin remains consistent across its entire span I do not see a problem with this. I think this will occur because the rest of the LE outer skin is stressed, so it retains most of its shape due to the tension of the bend that is force-ably wrapped around the top and bottom flanges of each LE rib.

First pic is the top side of the LE with the subskin now showing through:

Next are the inboard and outboard curves of the front of the LE skin showing the gap I mentioned between the LE skin and the subskin  on the outboard section. Both pics are takne from the top side of the LE:

 

The next set of pics is the same series taken from the bottom side of the LE

And finally 2 pics that show the clearance of the tie down ring hole through both the outer LE skin and the subsin after trimming it away from the subskin. Looks pretty good to me, but I may decide to wien both of the holes a bit to make certain that stresses placed on the ring from high winds etc. will not start contacting the edges of the LE sin in this area. The ring can be screwed in and out with ease.

So this was a day that was very long in the making. I had to wait 2 weeks for it to warm up enough in the garage to get to this point. took about 3 hours or so to do everything described in this post. Next steps are to make the file folder template and fit it to the cutout section of the LE, mark and drill the #30 screw hole locations in the paper template with the LE firmly mounted back on the wing spar, remove the template and use it to trace the new removable section of the LE onto a piece of .025 aluminum. I may decide to go buy some Home Depot grade stuff to practice on until I am certain that I have the outline of the part measured, cut, and formed correctly. My concern now will be what I need to do to make the curved front end of the removeable section match the curvature of the inboard and outboard outer LE skin. Not sure if I will need to apply some shims due to the gap, or if I will be able to pre-stress the removeable section similar to the outer LE skin so that it will retain its shape with the rest of the LE skin. Time will tell on that one.  Hopefully I will be able to get to that point this week since the weather is finally supposed to be warmer.

Finished Dimpling the Remaining Perimeter Skin to Subskin #40 Rivet Holes

Last night I finished dimpling the remaining #40 rivet holes that will attach the outer LE skin to the subskin around the edge perimeter of the removable skin section.  There were some holes in the LE skin and the subskin that I could not reach with the pneumatic squeezer, so those would need to be completed with the C-Frame tool. First I completed all the #40 holes in the subskin, and then I completed the remaining holes in the LE skin.

To do the LE skin, I have to move even more stuff on the workbench out of the way, because all of these remaining rivet holes are on the inboard edge of the skin. This means that the rest of the skin will be hanging off the edge of the table to some extent, and so I had to ensure that there was clearance for that. It was also a trick to get the LE skin from the cradle over to the dimpling table. I needed to remove all clecoes from the LE ribs, mark them for their position I sequence so I don't screw up the location like I have done once before. After the ribs were removed I removed the skin from the cradle and careful moved it over to the dimpling table. Then I ponded out the remaining #40 holes in the top and bottom of the LE skin and placed it back in the cradle. DONE with that step!

Then I had to put some thought into how and when to locate and drill the #40 rivet holes for the nutplates. I was having some difficulty trying to remember if I should use the screw inserted method or the nut plate jig method to drill these holes in the subskin. to avoid the confusion, I had to separate how I was thinking about the Fuel Tank attach holes on the inboard edge of the subskin, from the nutplate holes for the removable section of the LE. The tank attach holes have already been drilled to #19 and are ready for the drilling of the #40 holes for those K1100-8 nut plates. The other nut plate locations for securing the removable section are still only drilled to #30.

For the tank attach nut plates, my dilemma was trying to determine if I should dimple the # 19 screw hole first, and then position the nut plate over the dimpled hole to drill out the #40 nut plate rivet attach holes, or if I should NOT dimple that hole and apply a different technique to locate and drill the #40 holes first, BEFORE I dimple the screw hole.

For the other nut plate holes the decision was a bit easier, because those screw holes have not been enlarged yet, and so I can't dimple those at all just yet for reasons stated in previous posts. A review of my Sept 2017 posts when I did the nutplates for the access panel in the subskin revealed that the #40 rivet holes should be drilled BEFORE the screw hole is dimpled. So my plan for both sets of nut plates is this

Tank Attach nut plates: Use my nutplate jig for K1100-8 nut plates to locate and drill the #40 rivet holes for each of those nut plates.

Removable LE skin nutplates: Us the #30 clecos as I did in the previous post to position the nutplate onto the subskin, and then match drill the #40 rivet holes through the holes in each nut plate.

SO I will be using two different methods to locate and drill the #40 rivet holes for these nut plates, due to the differences in the sizes of the screw holes in each of these sections of the subskin. No pics tonight - I'll do this work tomorrow when I am fresh and awake. This is no time to screw things up now. I'll repeat that same statement when I am finally ready to cut out the section of the LE skin. Still plenty of opportunity to completely mess this up if I am not careful.

Marked and Drilled Corner Rivet Holes, Removed and Disassembled the LE and Deburred the Holes

I was really stressing over the position of the nut plate screw holes, and then, after all the measuring, marking, research, and second guessing everything, I suddenly realized something. The removable section of the skin is not really going to be all that "stressed" when compared to the rest of the outer skin. the subskin underneath is what is designed to handle the loads imposed over that portion of the LE. The removable section is just going to be a curved piece of aluminum that basically form fits over the subskin. There will still be some loads imposed by tension and compression due to aerodynamic forces of the air flowing over that section of the LE, and these loads will fluctuate based on the G-loading that is placed on the wing curing certain maneuvers, but again, the subskin is what is going to absorb the vast majority of these loads.

Because of this, I really do not need to fret so much over the location of the screw holes. That said, I had settled on 3 along each side and 4 along the rear edge to ensure that everything is held down firmly so that the removable section still aligns with the rest of the LE skin when it is screwed in place.

From my previous post, I also knew that I had to reposition the rear corner screw hole so that it was not placed directly in each corner, but placed on either side of the corner. One other thing that was causing me pain was that I was trying to prevent additional stress points by maintaining the existing rivet pattern as much as possible. As such, I was trying to maintain a line of screw holes along each side that would align the screw holes I had already drilled for the nutplates that will attach the fuel tank skin to the LE skin when the two sections are joined together. While this would hve almost worked well for the bottom side of the LE, this was not going to work all that well on the tops side of the LE, since the screw hole patterns differ just a bit on the top and bottom sides of the LE.So I decided to use the most-forward screw hole of the joiner plate area to align the most forward nut plates of the removable section as a starting point, and I chose to move the rear-most nutplate center hole 3/8 of an inch forward from the corners where the nutplate lines from the sides and the rear intersect each other. Then I decided to move the rear-most corner screw hole locations inboard about 3/4 of an inch from that same intersecting corner. This created the desired effect of offsetting the rear and side nut plates in each corner so that the screw holes would be on either side of the actual corner, but close enough that they should lock down the corners of the removable section with no problem.

Here is a close up one of the corners after measuring and drawing the approximate location of the nutplate by positioning it over the mark for the hole and tracing the outline of the nut plate so you can see what I am rambling about.

As you can see this provides plenty of clearance between each nut plate. Do  not get confused by the drawing of the side nut plate where the end appears to be right over the corner again. You have to remember that the nut plates will actually be installed on the inside of the subskin to accept the screws from the outer skin. They are drawn here so that I know how they will be oriented on the subskin when I install them.

The next thing to resolve was the spacing between each of the nutplates along each side  and the rear of the removable section on both top and bottom of the LE. As I previously mentioned, for the sides I chose the location for the most forward and most rearward nut plates, and then I more or less decided to split the difference of the distance between each of those locations for the location of the nutplate in the middle.

For the rear-most nutplates, after setting the two corner ones 3/4 of an inch inward from the intersection of the two nut plate lines, I then used a distance of 2 inches from each rear corner nutplate hole to position the next two inboard rear nut plates, and that left whatever distance in the middle, which was about 1 5/8 inches or so between those two nut plates. These distances are within the same distances where other similar nutplates are installed on the plane, so I feel pretty comfortable with the locations that I came up with. 

here is the pic that shows how I aligned the forward-most nut plate holes with the existing holes in the joiner plate:

And here is a shot of the spacing between the rear-most nut plates, flipped 90 degrees the wrong way for some stupid reason:

Next is a shot of how the perimeter rivet holes for the skin and the nutplate screw hole locations looked after they were drilled with a #40 drill bit for starters . I once again used a center punch to mark each hole, and manually turned the #40 drill bit to start each hole before finishing it with the drill under its own power:

After all the perimeter and nut plate holes were drilled to #40, I then switched to a #30 drill bit to enlarge the holes for the nut plates, since the screw holes ultimately need to be drilled to #19 to accept the #8 screw. Here is a shot showing the clecoes in each of the enlarged holes for each nut plate. Unfortunately it came out blurry for some reason and I could not correct it.

Tonight I had made my decision about the gap in the corner for the outer perimeter rivets. I decided to do exactly as I stated in my previous post where I would add one more rivet to each corner but back it up just a bit so that the edge distance was consistent with each rivet on either side. SO I drew a line to bisect the 5/16 x 5/16 square that includes the rear-most corner, and then I took a ruler and measured along that line, and used the edge of the curved corner of the removable section that intersects with that line to measure another 5/16ths of an inch from that point outward, and marked that location for the rivet hole. The net affect of this is that it provides a rivet line with the same rounded contour of the removable skin, which is something I have also seen done in other areas of the build.

Here is the pic after the new corner holes were drilled to fill the gap:

And here is the entre bottom section with all the holes drilled and clecoed. From this you can start to get a better idea of what I am trying to do:

And another blurry one of the top side of the LE

With those holes done I was ALMOST ready to go ahead and enlarge the nutplate screw holes to their final size using a #19 drill bit. It was a good thing that I decided not to do that just yet. Just as has happened to me about a million times in the past, I started to think about the next steps after this was all done, and that major next step is to disassemble the LE and subskin and finally cut out the LE skin along the cut line marks and clean up the edges so they will accept the .025 removable skin that I would still need to fabricate. As  I thought through this process it dawned on me that I would still need to figure out how to mark and drill the same screw holes in the new part. Unfortunately it looked like I was going to need to try to do this from the inside of the subskin, because the new removable skin would have to be fabricated from a new piece of aluminum, since the skin on the LE would be cut away and not really viable any longer - or so I thought. 

Then, after thinking about it today, I realized that I can resort to a trick I have used before, by taking a file folder and cutting it to size to match the dimensions of the cutout section of the LE after I finish trimming it away. Then I can also use either the cut out section of the outer LE skin, or even the subskin holes to locate and drill the nutplate hole locations in the new file folder template. Then I can drill them out on the template and use it to outline the new removable section on a piece of .025 2024-T3 aluminum, match drill at least the first set of nut plate holes on the bottom side to start, and begin the process of form fitting the new part to the LE by attaching the bottom and wrapping it around the front of the LE to ensure that it is tight against the subskin, attaching the screws as I go.

SO, I can use the file folder template to ensure that I put the holes in the correct location on the new part that I must fabricate. I may have mentioned before that this part of the process is very similar to what one does when they place a landing light in the outboard section of the front of the LE. The only real difference is that the templates from most landing light kits for RVs are already created and so you just have to use the marks on the template that is provided. IN my case I am te one that has to create the entire template - just oodles and oodles of fun.

So the hole point of this ramble is that I should NOT enlarge the nutplate holes any further until the LE skin section is removed, and new part is fabricated so that I can match drill the removeable section and the subskin at the same time when I am finally ready to do that. SO those holes will remain sized to #30.

SO the next steps were to remove the LE assembly from the wing, remove the clecoes attaching the subskin, and debur all the new holes, and then dimple the outer perimeter rivet holes in the subskin and the outer LE skin. Then I will be ready to cut out the section that is to be replaced by the removable skin. Frankly, after all this time, I cannot believe that I am even talking about this. Of course the sad part is that I have all of this same thing to do on the right wing, and the thought of that is a bit daunting right now, knowing how long  it has taken me to do this on the left wing. 

Anyway, some pics after the LE was removed and the holes were deburred:

And finally the bottom and top side of the subskin after it was removed from the LE and the new holes were deburred. At least the hole placement for everything seems to have come out pretty nice. Now I just have to hope that I do not screw up cutting the section out of the LE skin!