Setting the Final LE rivets, Cont'd.

One of the other things I failed to mention in previous posts is how important good lighting is when riveting these enclosed structures together. This was yet another reason why I wanted to have a portable, moveable work surface that I could position various ways to take advantage of the lighting as necessary. The problem that I encountered, regardless of how positioned the table and LE, was that I have very poor lighting in my garage to begin with. Even after I thought about positioning the table so that my 4 high intensity 150 watt work lights could focus all of their available light on the inside of the LE, I still did not have enough light in there. So what to do.....

Solution was to grab my trusty Ryobi adjustable flash light with a LO battery pack, and one of the bath towels, and lay it on its side with the head of the light poking through the aft lightening hole of a rib on either side of the rib flange whose rivets I was about to set. I placed the towel underneath it s that the vibration from the rivet gun would not cause other damage to the skin or ribs via the flashlight bouncing around. This allowed me to directly focus enough light into the bay while still allowing enough room for me to insert my hand and bucking bar of choice into the bay.

Here are a few pics showing that setup:

As I began working on these forward rivets, I tended to position myself in such a way that the rivet gun was centered directly over the rivet to be set, and then I would bend down to see the positioning of the bucking bar over the rivet shaft underneath the skin. I mostly watched the bucking bar while riveting, relying on the gun to stay in position with the proper amount of force applied. As I have previously reported, sometimes this worked as expected, and other times the gun would slide out of position and I would have to stop and reset everything all over again. I do not like not seeing the bucking bar because that usually leads to improperly set, overdriven, or canted shop heads. For some of these rivets doing it blind by not being able to see the bucking bar was unavoidable. These were mostly the most forward rivets where I had to pay much more attention to the gun position due to the extreme curvature of the LE skin. my biggest concern about this is having the bucking bar slide off of the rivet shank, which leads to all sort of potential damage - damage to the rivet, damage t the skin, or damage to the rib, or sometimes all three. I have seen it all during my short riveting career. So when I can't see the bucking bar and verify its position over the rivet shank it really bothers me.

The pic above showing the light shining against the rib flange and the rivet shank also gives yo an idea of the curvature of these surfaces that you have to deal with. Each rivet is at a slightly different angle than the other rivets, so to set these properly the bucking bar has to be placed t the correct angle for each one. To figure this out, I tend to use the tips of my fingers against the rib flange to gage the angle that I am dealing with, and then use my fingers t adjust the angle of the bucking bar to match what I am feeling. its not very precise, but its the best you can do on these hard to reach rivets f working by yourself. Of course the best solution is to have a riveting buddy, so that each of you can focus on the gun or the bucking bar and not worry so much about it. However, this causes other problems when working with small confined areas where more than one body may also cause its own interference problems that have to be worked out.

Here is another pic showing the positioning exercise of my fat man bucking bar against one of the rivet stems. For the rivets along the rib flanges this was not too difficult, but where I had rivets, nutplates, and additional skin-to-subskin rivets all very close to each other, I had t choose between different bucking bars for different rivets to maintain clearance from and prevent possible damage to the other obstructions.

In fact in the same pic to the left through the lightening hole you can get an idea of all the rivets and nutplate proximity to each other.

As I proceeded with setting the bottom rivets, I had to stop and slide the LE into different positions to allow clearance for the rivet gun. This required removing the long bar clamps holding the 1x4 against the rear rib flanges, sliding the next bay of the LE into position in the cradle, and re-clamping the rear brace back on again. I should also mention that a very important part of this whole assembly is the 1/8th inch thick weather proofing vinyl tape on the cradle supports. This is an absolute MUST for tis assembly, because without that bit of shock absorption between the wood and the outer LE skin, you would be causing pretty severe damage to the LE when you attempt to set each rivet. So I check this stuff every time I reposition the LE in the cradle to make certain that it  is properly placed.

Here are some shots taken from both sides after finishing the initial rivet setting exercise for the bottom side rivets. Most of them seem to set pretty well, but I did have issues with the curved surface of the forward, just as I had expected I would.

Setting the Final Rivets of the Left Wing Leading Edge

With the vast majority of the leading edge rivets set while in the cradle in the upright position, I could note get the rivet gun in the correct position to set the remaining 4 rivets on the top, and the last 3 rivets on the bottom of the LE (the most-forward rivets for each rib).

Part of this issue was due to the design of my cradle, and the other reason was because I refused to try to set these rivets on the most extremely curved surface of the LE working solo, due to the extreme likelihood of completely screwing up the entire LE assembly. the LE is a little deeper than 1.5 feet tall. To successfully buck these remaining rivets, you have to have be able to reach from the back side of the LE all the way to the forward section where the remaining holes are located. This is next to insane as far as bucking rivets goes, since the main idea is to keep the rivet gun and the bucking bar as close to your body as possible. The other serious complication is the need to hold the bucking bar at the correct angle with one hand, while holding the rivet gun also at the correct angle for the same rivet.

I knew from past experience with all the other skin riveting episodes of the tail surfaces that taking what amounts to a small vibrating hunk of polished metal (the rivet set), and sticking it in a gun whose sole purpose is to deliver rapid and very precise vibrating pulses that transfer to the rivet set, and holding another piece of polished metal (the bucking bar) on the other end the rivet, and trying to do all of this on curved surface, is a recipe for disaster when trying to do this alone.

I also learned from that experience that what makes a huge difference in the ability to set rivets like these successfully if you are working solo is that at the very least you MUST ensure that the entire work piece to be riveted is positively secured at all times  and accounts for all possible directions and positions from which riveting will take place. Since the most forward rivets on the LE have to be bucked, and they are located on the most forward curvature, the tendency will be for the rivet gun to push the entire LE assembly backward. SO this has to be prevented at all costs.

the other decision was to ensure that I could bucker the rivets so that gravity is helping to force the rivet gun  as straight downward as possible. The gun is rather heavy, and trying to hold the gun upward against the skin would become very tiring very quickly. So the best method/setup for this IMHO is to set the work up so the gun works with gravity and as straight up and down as possible. The pros probably have rotisseries that can lock an entire work piece into the just the right position as described above, or, they also probably have other hands from other people to help them rivet things together.

SO without additional help and without a professional rotisserie two work with, I cam up with the best solution that I could. It starts with unclamping the cradle and table top from the saw horses. The next step was also very important, and it was only after seeing something on the saw horses that it dawned on me what I needed to do. I realized that my saw horse assemblies came with metal frames from HD aviation supply, and that these saw horse frames had adjustable metal legs. Normally my garage work benches are high enough to allow the work pieces to be at a comfortable working height, but my problem with these benches are that they located up against the rear wall of my garage, and so I have limited ability to move around the benches to get best position on the work piece. It was for this reason that I set up the mini table on the saw horses in the first place - so that I had the ability to move around in any direction and put the table in any location to take advantage of additional lighting etc.

With that, I removed the cradle and table top and then adjusted the legs on each saw horse to add about another 8 inches of height. They were fine in their default "lowest" setting while setting the rivets with the LE in the vertical position, but to set the forward rivets of the LE I would need to turn the cradle on its side. T put the LE at the proper working height, I needed to add about 8 inches to the saw horse height. Turns out that this was pretty optimal.

After raising the saw horse height, the next trick was to figure out how to secure the work with the cradle turned sideways. After a lot of thought, I finally came up with a solution that worked so well that I almost thought about patenting it. It ended up taking no less that 10 bar clamps, and some of the them had to be changed out for different sized ones when I flipped it over to rivet the bottom and top sides of the LE. More on that later.

Next decision which side to address first - the top or the bottom. Recalling a post from someone while building their fuel tanks, I decided to set the rivets on the bottom side first, because the bottom is flatter, and less curved at the front than the top of the LE, and once you have set the bottom rivets the LE can set down on a flat surface without rolling around too much. For my solution the le stayed horizontally mounted in the cradle at all times, but doing the bottom side rivets sounded easier than the top so I opted for that.

SO the cradle was turned sideways, and the clamping innovation began. Once the cradle was solidly clamped to the saw horses and the make-shift mini-table, I was able to insert the LE into the cradle, but then it became apparent that I would need to figure out a way to clamp down the back side of the LE along each of the rear rib flanges to keep it from flying or falling out of the cradle. A search of my scrap wood supply revealed the solution. Here are the pics showing the setup that I used. These pics show the LE in the cradle with the bottom of the LE on top:

I had a 1x4 piece of wood tat was long enough to lay across most of the rear rib flanges, and then I needed some additional 2x pieces of wood to extend beyond the rear-most outer LE skin edges so that the clamps would not destroy them. This setup allows me to get my arm and hand with the bucking bar inside the assembly while holding the rivet gun on the top side with the other. A couple of 36 or 48 inch bar clamps to squeeze everything up against the forward part of the cradle. This is how the LE is prevented from slipping out of the cradle during riveting. The extra pieces of 2x that I used were remnant from the form blocks that I created long ago after using one of the LE ribs as a template. The only thing that I needed to be careful about was applying too much pressure on these clamps that might cause the forward sections of the LE to crus or deform against the cradle supports.

Here is s shot from the other side, and more shots that show the rest of the clamping arrangement, sing various pieces of wood to make it all happen.

It took 10 clamps to make it all work, but it worked great once I figured it all out. I had to use some additional 2x4 pieces as blocks to allow me to secure the cradle to the table and the saw horses.

The next decision was to decide which part of the LE rivets to work on first. Since I had more rivets to set to finish securing the sections of the outer skin to the subskin on the inboard portion of the LE, I chose to work on those first. I started out by setting the skin-to subskin rivets that secure the outer skin where it is cut out to receive the removeable section. These were the easiest to set because they were also the most rearward rivets to be set, so reaching them was easy, and setting them was easy too because they were also still on a flatter part of the bottom of the LE. 

For some reason I only have a shot of the bottom side shop heads of these rivets after I bucked them. They are the span-wise rivets in between the nutplates at the top and center f this pic:

Then it was time to start setting those pesky forward facing rivets. I had to use combinations of the Fat Man and Little boy tungsten bucking bars to fit then in between the nutplates, rib webs, and other rivets. The process to set these 6 or 8 rivets along the strap portion of the outer LE skin took me well over an hour to complete. As expected, trying to hold the rivet gun on the most curved part of the LE at the front was NOT fun, and I had to contort my arms, hands and body in very unnatural ways to get everything to fit correctly before pulling the trigger on the rivet gun. None of this process was what I would call "fun," but when I was able to set all of these rivets, I felt pretty god about what I had done. I should also point out that even though I was using the mushroom rivet set with the rubber cup around it, on several occasions the rivet gun decided to have a mind of its own and would slide off the rivet head, causing me to reposition it and try again, and in some cases I had to replace a rivet because the head was so badly damaged from this that it was unusable. Fortunately the rivet gun air pressure must have been perfect because I never dinged up the outer skin at all. I was completely amazed by this after looking at the less that good job I did riveting the skins on my HS. 

This next pic shows that I also had to determine the sequence of which rivets to set first, seconds, etc. For the area around the modified skin of the LE, I decided to set all "outer" rivets first, followed by the corresponding inner rivet, working from the rear-most rivets to the most forward, which is in line with Vans instructions. SO all rib flange rivets were set first, followed by the inner skin to subskin rivets along side. Thise process seemed to work well, and the outer skin was riveted to the ribs and subskin quite well. Also amazing was that I was able to use the AN426AD3-3.5 rivets as called out in the plans for the majority f this remaining riveting, except in the area surrounding the mod, where the 4.5 rivets were the correct size to account for the extra thicknessof those ribs and the subskin.

I also had to remove both clecoes in order to be able to position the rivet set on the gun in the right place. trying to keep tha damn thing from sliding around on the outer skin was a real pain in the ass.Trying to reach in and hold the bucking bar in the correct position at the correct angle, and hold the rivet gun the right spot on those curved surfaces was even m ore of a pain in the ass. I had to take my time with every single one of these final rivets, and I also had to recognize when I was getting tired and when to take a break. This happened often as I did NOT want to have to reset any of these rivets or risk damaging the LE because I was too stupid and too tired to know when to quit. 

Much more to come on this later. The good news is that I think I got it all done. No more clecoes are holding this baby together. 

KPR

 

Slamming LE rivets, Cont'd.

Pounded a crap load of rivets on the LE over the past two days. Felt good after getting the hang of it again, but I get real sore from all the strange body positions required to accomplish that. I'm not quite done yet, but I only have a few forward-most holes on the top and bottom side of each rib, and the holes surrounding the area where the outer skin that surrounds the perimeter of the removeable section must be riveted to the subskin. Then I figure I need to drill out and replace about 20% of them, mostly due to over setting them (Shop heads bucked a little too far). Here is a shot at the end of yesterday's session with most of the rib flange rivets in place:

Unfortunately after finishing the rib flanges I decided to get "started" on the business end of the mod - the inboard section that I affectionately call the swiss cheese section, since it has so many rivet holes and cut outs in it. What I forgot t take into account was how much flex exists in that area between the two ribs. you don't realize how much stiffness is provided by each rib until you try to buck a couple of rivets in the middle of the skin between them. What follows is the result - yet another rivet that needs to be drilled out and replaced. So I hung it up for the day to regroup, rest, and attack it again today.

To address this, I came up with an idea. I needed to somehow add some stiffness to that area just as I have had to do at other times. I remembered that I still have several of the form blocks that I used to shape the subskin so many years ago. SO I took one of them and a bar clamp, set it down inside the LE where I thought it would provide sufficient stiffness, and clamped it down just enough to hold it in place. With all the nutplates and shop heads of other rivets it did not sit down inside the skin totally flush, but it was good enough to provide the required stiffness in the areas where I needed to rivet the outer skin to the subskin.

This worked out REALLY well. Even if the outer skin was pressed into the wood a bit awkward due to nutplates being in the way, it was good enough to hold it there temporarily without distorting or bending anything out of whack while I set the rivets. Yet another tip for future builders. 

Here is shot after I was able to use the form block by moving it as necessary to allow room to hold the bucking bar while I set the perimeter rivets around each access hole. These would be the rivets that would normally secure the mounting or backing plate that allows a flange to mount the cover plate onto it with screws. In my case the subskin serves as that mounting plate, but I used the same rivet pattern as called for in each actual mounting plate:

Once these perimeter rivets were set it was time to mount the original cover plate from Vans permanently to the subskin. Here it is clecoed into position for the final time:

And here it is after all the rivets were set:

It still fit just like a glove. I was really pleased with how that went together. I was concerned about some of the edges curling up, but that never happened. It fit just like it was supposed to - to cover up the old Vans hole so I could use the SafeAir access panel hole instead. 

And finally the back side with all the shop heads after this was all done:

Like I said - Swiss Cheese.

 But slowly all the holes are getting filled.  Next steps are to set the cradle on its side and secure the back side of the LE so I can push on the forward tip rivets to set them. The problem is that I still need to be able to reach deep inside with the bucking bar to set those most forward rivets - and these are the most critical to do correctly the first time. I can't afford to have to drill any of those out. So the next session will be spent doing a lot of prep and ensuring that everything is exactly right so that setting these last rivets is as easy s possible.

KPR

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...….