Busy Preparing for the Fuel Tanks and Tech Counselor Checks out my LE

My Technical Counselor and former long time EAA Chapter 301 President Jim Elliot has been mentoring me through all this LE mod fiasco. I had to wait a couple of weeks for him to become available to come and visit the "almost" finished LE work, and he was finally able to come out last Saturday and take a look. He is a Mooney aircraft owner and has helped several people build different makes and models of experimental airplanes. He definitely knows his way around an airplane, and with evaluating potential affects of modifications such as mine. More on that in a bit.

Since I knew I had to wait for a bit for him to be able to come over, I started preparing (for about the third time now) to get back to work on the fuel tanks. So although I have not posted in while, I have still been very busy thinking, reviewing, and planning for re-engaging on the fuel tanks to get those behind me as soon as possible. his started with a review of many previous posts where I actually started on the left fuel tank because you needed to match it up with the LE to check alignment and drill some holes in the T-712 mounting brackets for the wing spar and the rear tank baffle. This little journey took me clear back to posts from the Fall of 2017. About the last thing I remember about the tanks was fabricating the tank stiffeners for the bottom of the fuel tank skin, and countersinking skin-to-rear baffle holes per the plans.

After reviewing the stuff from the past, I ended up coming up with a list of new additional questions that required answers from Vans. As a side note, to date I have order at least 2 proseal tubes, a small sized can of proseal, and a full sized quart of proseal - ALL of which have shelf lives that have long since expired, so they will not be used to seal any part of my fuel tanks, and I will need to put in an order for more proseal yet again. Sucks to be me I guess - that's about the only way I can sum that up.

Many of these additional questions are questions that you do not see either asked or answered by others, but I find it quite strange that others are not asking the same questions. Anyway, to make sure that I don't lose the content, I am posting them here for myself and anyone else following my blog that might also appreciate the info:

385b and c SW fuel senders - for left and right - is it correct that the potentiometer scale/meter on c version for the right tank will be reversed (facing forward instead of to the rear, when installed on the side of the tank, or should the scale for both still appear toward the rear of the tank when installed correctly.

Vans says this backwards orientation is normal - important thing is that they both point down when installed either on the end rib or the rear baffle plate.

Am I supposed to scuff the back side of the sender flange of each sender if I am going to proseal it directly to the tank rib (NOT use the rubber gasket or cork as recommended by many who have been there before.)

Vans says not needed.

The left sender seems to have a dead spot at the end of travel of the arm (empty indication) - either no ohms reading at all or much higher (300 ohms or more - much higher than expected 240 ohms per the plans.) The right sender seems to be indicating correctly per the palns info. Ordered both SW senders from Vans on 4-16-18 order # 74191. SW says has a 2 year limited warranty - how do I proceed with a replacement. Go through Vans or direct with SW?

vans - Contact SW directly to replace it

Left tank will be flop tubed, so sender will be in bay #2 in rear of baffle.
1. Did I do a lot of extra unnecessary work by cutting the big hole in the aft of the end rib, when I found out that the sender needed to be placed in the second bay via the baffle in the first place.

Vans   -still good to have access t that bay due to the trap door and the flop tube/anti hangup bracket attachments.

2. With the sender in the secnod bay of the rear baffle, that means that the only way I can service that sender if necessary is to pull the entire tank, correct?

Vans - correct - you will have to pull the tank to service the sender that is mounted this way

3. For tank baffle mounted sender, do I need to cut another big round hole in the second bay AND use a reinforcement ring (T-407) as well, or just the hole big enough for the sender to fit in?

Vans says nope - no reinforcement ring or big hole needed - just a hope big enough for the sender to be inserted/mounted directly onto the rear baffle plate web. No reinforcement ring needed because the baffle plate is thicker/stiffer than the rib web.

4. Do I need to use another reinforcement stiffener ring for the T-411 cover plate on rib T-703 if no sender is being mounted in that hole, or can I just mount the cover plate, with nut plates mounted on the rib web itself instead of the combo of the rib web and the reinforcement ring?

Vans - would still use the stiffener ring here as the rib is not very thick and alot of strngth is removed by cutting that big hole.

5. Depth of tank for SW sender specs to determine what size to cut the rod - what dimension should I use for that (tank depth so I cut the rod to the correct length?

Vans - just clamp the sender in place and measure to determine based on the area where the float will be traveling.

6. Since the left tank sender will go in the rear tank baffle, do the dimensions of the float wire change from original plans for mounting in the rib on the side? Any issues with clearance of the bottom stiffeners when mounting the sending in the rear tank baffle?

Vans - measure to be sure, but should not be a change or a problem as far as they are aware.

7. Do you know a part number for a more malleable proseal for access plates that is not as hard as normal proseal to remove??

Vans - they do not use it and did not know the part number of hand - said to check Spruce and others.

8. Grounding the sender - how is this grounded to the airframe if you have the tank baffle or rib web, proseal, and the flange of the sender on the thin later of proseal. Are we supposed to run an additional ground wire from one of the sender mounting screw holes to one of the tank attach bolts or something similar?

Vans - Use a lock nut with the cut flanges that bites into the metal on the underside of the screw head and on the sender flange as it gets mashed down during screw tightening to establish contact for a good ground - so additional wire should be needed, even if screws are prosealed. Do it on all screws or just one or something in between?

As far as the tech counselor visit is concerned, Jim took a look at my unfortunate demise on the LE. Said that it is a dent and not a crease, but that it did deform the outer skin and the subskin. Then we had a conversation about acquiring an autobody or planishing hammer and a dolly that may have to be customized to try to pound (actually TAPPED) out to try to reform the skin back to the shape that it was in before. Unfortunately I can see where my unbelieveably STUPID idea t just keep pounding on the skin with the rivet gun when the rivet was not setting properly has indeed flattened it out a bit. So as a result, if I want to continue with the LE mod using what I have done thus far, I now get to learn a new skill that involves removing dents and reshaping metal, and I probably have to custom-make yet another tool = more wasted time.

So I went to local NAPA store, found a planishing hammer with a rounded head (NOT the kit you find at Harbor Freight, that only has flat headed hammers), and a Toe dolly that, when I fitted it up against the curvature of one of my LE ribs that I took with me to the store, looks like it will almost perfectly conform to the curvature of the LE skin/subskin/rib as long as it is held in the correct position. This is probably going to require a helper to hold the dolly in position while I tap the outer skin and hope like hell that I don't just deform everything beyond reasonable repair.

The last part of our visit was spent having a heart to heart about the possible structural impacts of what I am trying to do, and if I should go ahead and contact a DER (Designated Engineering Representative) to come and look at my invention and provide some further experienced insight on what I am doing. I wanted to go ahead and finish this mod regardless of the ultimate decision about its feasibility, just to see what it would take. At the end of the day I am not certain that this is a safe thing to do, and may still decide to abandon it all together. But I'm not throwing in the towel on the mod just yet.

I've got some parts to order from a number o different vendors so I am also putting that list together. I'll have some pics on the next post that show the damage from the F'd up riveting job  more clearly, and the tools I am going to attempt to use to fix it.

Cutting to the Chase

Well, the next logical sequence of this long drawn out process would have been to go through the steps to rivet the top side of the LE ribs together after finishing up the ones on the bottom. However, right now I think its just best to cut to the chase and remind any readers following this blog that deviating from the plans always involves risk.

To cut to the chase, I did unclamp everything and flip over the cradle and reclamp everything back together and begin the process of riveting the top side rivets to the LE skin, subskin, and ribs. In fact, I thought that this had gone just as well as I had thought that the bottom side had gone - perhaps even a bit better, now that I knew what to expect. I felt that way -  right up to the point that I shined the flashlight on the bottom most forward rivets attaching the subskin, outer skin, and ribs. If you have read the last 2 posts or so you will note that at one point I commented that I did have some difficulty with one of those most forward rivets, but at the time I did not know why, and I thought that I had overcome the problem eventually without doing any damage to anything in the process.

Well, when I viewed the shop heads of the forward rivets in that area, it become very apparent what had happened, and it was exactly what I had said all along that I absolutely could NOT do if  were to successfully complete the mod. In short, I discovered a crease on the subskin where the edge of my bucking bar had been digging into the subskin just beyond one of the most forward rivets on one side, so all the energy from the rivet gun was being passed through the bucking bar and into the subskin, which is why that one rivet would not set properly. My continued pounding with the gun only served to tighten the skin and stretch it a bit, which caused the outer skin to stretch a bit as well.

You can almost see it in the very last pic from my previous post by double clicking on it to make it larger and clearer, and look at the forward area next to the cut out in the outerskin along the one side. You can just see that the outer skin des not sit the same way against the subskin that the rest of area is, and that means that the outer skin has been stressed.

Here is a pic that I took, that, without even realizing it, captured the issue.

Look at the left side, just past the most forward nut plate on the bottom, and you will see what appears to be a whitish line. This is the crease that was hammered into the subskin. Remember to double click on the pic to make it larger. If the sides of my bucking bar had not been covered by duct tape I most certainly would have plowed the obviously incorrectly placed bucking bar right through the subskin and continued to pound into the outer skin. 

Finding this just about made me sick to my stomach, because this was precisely the thing that I feared the most that I knew I absolutely could not do. I now fear that the only way to correct this issue would be to completely remove all rivets, and remove and refabricate a new custom subskin. This is something that I absolutely will NOT do. I hate the fricking forward rivets just about more than anything I have ever hated in my whole life, and I will absolutely NOT start over to remanufacture a new custom subskin.

Right now I am waiting for a tech counselor visit to thoroughly inspect this damage and determine what to do next. Even if I am told to remove the subskin to effect a repair I don't think I will even do this. Instead, I am now prepared to order a new LE skin and perhaps new ribs to go with it, and rebuild the stock LE and completely abandon this idea so that I can hopefully have a flying airplane sometime before I leave this earth.

For anyone out there following - and I have said this before - if you are thinking about building then I strongly urge you to get the quick build wings and then you can decide if you want to do the quickbuild or slow build fuselage. The quickbuild wings will already have the LEs and fuel tanks completed by the factory - so you wont have to mess with ANY of those fricking forward-facing rivets. 

So I am pretty disgusted right now - but I still have fuel tanks to finish, so until I get a chance to talk with the TC about my latest blunder I will shift my focus to the fuel tanks once again. I  have discovered through this process of building a metal airplane that I absolutely hate riveting - so this will most definitely be the first and last time that I endeavor to build one. There is just too much aggravation involved for me. YMMV.

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...….

Prep for Final Assembly and Riveting of the LEFt wing LE

As mentioned previously, the next step was to remove the vinyl inside the LE skin that I have left on all this time to protect the metal. I do not prime the entire interior surface to try to save some weight. The epoxy primer overspray and cold temps have left this remaining blue vinyl in a state that is very difficult to remove. Here is one of the problem sections that I needed to remove:

I was not able to take my finger nail and lift up the edge to peel it away like I normally can. The primer hardened onto the metal next to the vinyl making this difficult. So what to do? I still need to remove this protective vinyl because if left on it can cause corrosion to occur by trapping moisture and debris between the vinyl and the metal. Unfortunately the vinyl only chips away and it won't peel off as one piece. 

After pondering this for a bit I remembered that I have a heat gun around here somewhere. I thought that maybe I can use that to heat up the glue on the back of the vinyl to at least soften it up a bit and see if that would allow it to separate from the metal easier. So I got this bad boy out and gave it a whirl:

After mucking with the setting son the gun and experimenting with how hot things could get, I finally came up with a procedure that involved holding the gun at a safe enough distance and heating up the entire surface of the vinyl as well as the edges until the vinyl softened up enough for me to peel it away. What I found out real quick is just how fast and how hot that heat gun can heat of the vinyl AND the metal. SO after figuring out how not to burn myself too much, this actually started to work pretty well:

Here is the sheet removed from the inside of the LE skin:

And here are some shots of what happens to some of the remnant primer 

It separates from the vinyl and rolls up into little flakes that have either a positive or negative charge that causes them to stick to the LE skin. After I got all the vinyl sections in between the ribs removed I had to use a shop vac to remove all the primer flakes.

The next task was to remove the red ink with the metal specification information. Normally isopropyl alcohol removes this very easily, but it has been baked on for so long that t was no longer doing a very good job, so I switched to using acetone, which worked very well. I was not too worried about wiping the acetone on some of the epoxy primer because that stuff, once hardened, is almost impervious to anything, and is very hard to remove with anything but acetone rubbed very deep and hard into the primer to soften it. What little acetone did come into contact with the primer evaporated away before it did any harm to the primer. I used paper towels and small dab of acetone to remove the red ink on the metal. Why remove this? Well some say it can lead to corrosion over time as well, but others say it doesn't harm anything. UP to now I have always removed it from the metal as part of the final assembly prep, so I did it here as well.

Once this was all done, it was time to final assemble the LE for what I hope will be the last time. the subskin and two inboard ribs were re-clecoed to the LE skin again, and the entire LE was placed back on the wing spar due to one thing I read in the instructions about making absolutely sure that the rear edges of each LE rib were exactly straight. The only way I knew how to ensure that was to re-cleco the LE back onto the wing spar again so that all the rear rib flanges were in alignment with the spar web, and then I can remove it again and start riveting the entore LE together. 

I also needed to put it back on the wing spar because I wanted to screw down the new removeable section using those new nutplates I just riveted to the subskin, so that I could check the actual "installed" fit of everything. As with everything else, I found out that after I screwed down the removeable section, all of ONE of my screws sat nice and flush to the skin exactly as planned. One of the screws was not laying flat on once end, suggesting that either my screw dimple or the hole or the nut plate was not properly oriented for the screw. It is not so bad that I feel that absolutely must fix it, but it may end up bugging me enough to the point where I am going to fix it anyway. This means removal of the subskin again to reset another nut plate, and of course it is one of the corner nut plate that are difficult to set.

I may actually try to set the new plate with everything mounted on the wing, but I am still debating that with my self. Here is the string of pics showing the part as originally envisioned, planned, and realized:

And finally, the same non-matching fit that I have been dealing with shows up once again after the part is screwed down onto the subskin, but the inboard side is quite flush and looks really good. I think I can still flush out the other side with the LE by applying a little fiberglass magic later on. 

Overall I am happy that it seems to have gone together pretty much how I envisioned it. Here are some final shots of the screws through the nutplates on the inside of the subskin:

More Nutplate Hell and Creative Clamping

After several days I was finally able to finish riveting all 20 nutplates to the subskin. Man did that turn into a royal pain in the ass. As of the previous post I had made it to the last side and had messed up the rivets on the last, most-forward nutplate along the edge. This is where the skin starts to curve at the very front, which makes trying to set straight rivets with a rivet squeezer a bit of a challenge. I think I managed to finally get it after drilling bad rivets out a couple of times.

With the side nutplates installed, it was now time to tackle the hard part - the remaining rear-most nutplates on the top and bottom sides of the subskin. I could not use a rivet squeezer on these because they are too deep into the center section of the subskin for any of my squeezer yokes to reach. SO that meant that it was time get out the rivet gun and the bucking bar - something that I have not done for a very, very long time.

I decided I did not think I needed to practice on anything, because I was able to get the air pressure setting correct for the rivet gun. Looking back I wish I would have been more experienced about that when I riveted the horizontal stabilizer skins onto the frame. It hangs up on the wall in my garage so that every time I walk in I have to look at it, and I cringe every time that I do. That is because I literally beat the shit out those skins because my pressure was too high, and almost every rivet attaching the skin to the forward spars has this large skin dimple from over hammering the rivet gun on the skin. By the time I got to the elevators I had pretty much figured that out, but I literally pounded the HS skins almost to death..

Anyway, with the air pressure set on the gun, the next step was to figure out how to clamp everything down tight. I ended up deciding that using my bench vise should allow me to set everything up to use both hands to buck these rivets without needing to worry about securing or holding the part. Here are some pics if what I came up with. IT involved the bench vise, a small 2x4 for the smooth front side of the skin, and a custom sized much smaller piece of 3/4 inch plywood for the back side. All of this had to be positioned very carefully to ensure that there was enough space for the rivet gun and bucking bar, and to allow everything to be clamped tightly down without deforming any dimples in the skin. With so many dimpled rivet holes in this custom part, this became a challenge at times.

The top part of the skin was easier because there were not as many holes to dodge while clamping it all down:

I used a bar clamp to provide stiffness and resistance on the top part of the skin. This was the difficult part of trying to use the bench vise for this large piece of aluminum. The vise only provides a small amount of depth, so the top part of the skin remains very flimsy unless it reinforced with something such as the wood that I used.

On the front side I had to make sure there was enough room for the rivet gun:

And here is shot of the back showing how I had to be careful about the size of he wood  used and how it was positioned to avoid smashing or deforming any existing dimples. The other concern was of course making sure that I had enough room to use the bucking bar. This did not prove to be much of a problem until I got to the corners where the first side nutplate is located relatively close to the rear-edge nut plate in the corner. 

And here is yet another creative clamping method where I was able to use the access plate hole on the bottom side to insert another bar clamp for added stiffness. 

The stiffness is needed because, regardless of who you may talk to or what you may read in a book, you HAVE TO apply some pressure on the rivet gun and the skin to ensure that it will NOT bounce when the rivet gun is activated. This is what directly causes badly set manufactured rivet heads where they sit noticeably proud of the dimple because the underlying skin was allowed to flex and bend each time the rivet set was pounding against the skin. The part needs to be clamped in such a way that any movement of the part is severely restricted. This is the only way that you are able to buck good quality rivets. Sometimes the temptation is such that you do not take the necessary steps to ensure that everything is properly clamped. Then you basically pay the price for the mistake, and you have to drill out bad rivets and try again.

I was able to get all of the nutplates riveted in place, except of course for the very last one, which was a corner nut plate on the bottom side of the subskin. This one proved to be so difficult that I think I drilled the rivets at least 4 times and replaced the nutplate once because it was deformed beyond acceptable limits on one side or the other. I think I must have drilled out no less than a dozen rivets and replaced 3 nutplates during this whole exercise. The top side ones went pretty well, but the bottom side was another story. In fact, I had screwed up the rivets on the last nut plate so many times that the shape and condition of the dimples in the subskin. it was so bad that I was now unable to secure the nutplate in place with a cleco so that the flange on the nutplate would sit flush against the skin. I had to start using tape to hold it in place. When this did not even work, I had to take out my other arsenal of tools. Luckily I was able to use my 4 inch no hole yoke on the bad nutplate on the bottom of the skin. I mounted it on the hand squeezer because I was not having any luck with the gun and bucking bar, and the pneumatic squeezer was too bulky to fit as well. 

So my only choice was to use the hand squeezer so that I could position it and take my time to set the first rivet to make certain I did it correctly. I was able to set the first rivet on one flange just enough to hold it in place where I could then finish it up with the gun and bucking bar. The manufactured head of the rivet ended up sitting just proud of the skin on one side, but I had a plan for addressing that. Part of the plan was to try to use the rivet gun to move it a bit more flush to the skin - this only partially worked.

With the first rivet set as well as could be expected, I then was able to properly set the second rivet with the rivet gun and bucking bar. The corner rivets only allowed just enough room to insert my small tungsten bar in between the two nutplate flanges on the corner. One slip and the rivet, skin, and nutplate would be history. In fact, he bar did slip one time and slightly creased the skin, but I deemed it as OK since it was a dull crease with no apparent stress risers, which means I just barely stopped the rivet gun in time. Had I not done so this entire subskin and the planned project would have come to a screeching halt.

Here re the pics of the finished nutplate rivets on the ear side of the skin. First the nicely set ones on the top side:

And then the less-nicely set ones on the bottom side. Some of the primer was knocked away from all the repeated pounding from multiple attempts to set the rivets, and if you double click on the pic you can see it in more detail and tell very easily which rivets caused me the most trouble. 

And here is the back side of the nutplates all riveted together.

Now, remember that slightly proud rivet I mentioned earlier? Well, here was my solution for that. A long time ago I was at Harbor Freight, an I just happened to stumble on this next little gem - a watchmakers hammer. I used the round headed side of this hammer to lightly tap on the edge of the rivet that was sitting proud, and I was able to get it to sit much more flush after just a few taps with this hammer. This hammer was critical for this because the small size and weight of the ball end of this hammer was just about perfect for ensuring that it only contacts the surface of the rivet head and not the surrounding skin. If it was too large it would dent the surrounding skin, but I found this little hammer to work exactly as I thought it would:

And finally, here is just a small sampling of all the tools  ended up using to accomplish this seemingly small task. As I said before, most of this was pleasant to work on, but those few times when things got difficult, they got VERY difficult. I could not risk damaging or screwing up the subskin because it has required so much customization that there was no way at all that I would be able to take the time to try to fabricate a new one, nor would I even want to. If that part were to be compromised beyond use or repair, I would abandon the entire modification and return to a stock LE without even looking back. Too much time and too many delays with this to even think about starting it all over again.

And here is he pile of drilled out rivets and damaged nut plates that I had to drill out and replace, sometimes repeatedly:

So yeah, I got really good at drilling out AN426 rivets again, too. Anyway, I was able to pound some rivets again, so that is always good. And, more importantly, that step is now complete, which allows me to move on to the next step. 

So next up s to remove all the remaining internal sections of vinyl covering on the inside of the LE skin that I have left in place all this time. Unfortunately this is proving to be difficult, because some of he overspray from the epoxy primer that I used has hardened the vinyl in those areas, and as a result is very difficult to pry up a corner of the vinyl and keep it going so that I can remove the entire thing without it breaking apart. That vinyl has also been stuck to the skin since 2010 when I ordered the wing kit, and I already know that the longer it stays on the glue makes it harder to remove as it gets older.

After that vinyl gets removed it is finally time to rivet the left wing LE together. Great  - more curved surfaces t deal with. I can hardly wait...….

KPR