Restarting yet again - a year and half later

 Hard to figure out exactly where to start this Blog again. Recap - I screwed up the inner and outer skin of my left wing LE Mode in April of 2019. Tech Counselor came out and we discussed using a planishing hammer and dolly to reform the damage to the outer LE skin and inner subskin. I bought the hammer and the dolly, and was about to attempt the task of re-forming the skin, when I had yet another epiphany. 

1. I realized that positioning the dolly had to be done exactly right in a very tight spot inside the LE, and I determined that this would just be next to impossible for me.

2. After having a very honest conversation with myself, I also realized that even if I managed to reform the skins correctly, this mod went wrong almost from the start where I did not create the wood form blocks for the sub skin properly. This meant that curve of the LE of the subskin has NEVER been formed exactly as it should, and leaves a gap between the outer Le skin and the subskin that then causes issues with how the removeable plate would sit when screwed onto the subskin. It also puts additional stress on the rib flanges underneath. IOW, the removable plate will NEVER sit flush the outer skin because of the subskin deformity, and the added stress in the rib might lead to other structural problems later. I should have taken much more care and ensured that the wood form blocks I used to bend the subskin EXACTLY matched from the curvature of the LE Rib so that the radius would have mated with the LE skin correctly.

3. The final straw for me was the realization that, after seeing it all come together, there was a much easier way to approach this whole thing, without the need to use the massive subskin and all the forming, measuring, bending, cutting, laying up, and riveting that was involved. I also realized that I could still attempt this mod AFTER the plane was built per the plans that would take very little time, and could be done using much simpler techniques than my original design.

As a result of this, I decided to abandon the entire mod and order the necessary new parts, including a new left wing LE skin and some ribs to build a stock LE. The only thing I will still do differently is order a left wing LE skin from Vans WITHOUT the cutout for the stall warning vane service access plate. 

It is sad to have spent so much time and effort on this, only to reach the conclusion that I need to abandon it. It is even more sad to come to this decision only after assembling and almost completing it.  However, I am not sad about having made the attempt, as I learned tons about airplane design in the process, and I now have a very deep appreciation for those that undertake the challenge of designing airplanes from scratch. So my only regret is the time I have lost, but nothing else. Basically it was not until seeing entire mod coming together to figure out that there was a much easier, simpler, less invasive and less time-consuming way to do this. I'll keep the details of that to myself for now.

So what happened after all that?

Instead of working on the fuel tank as I previously stated in my last post, I spent the next couple of months working on some mods for my 14 inch RIGID bandsaw.  This saw became notorious for not being very well built to the point that it vibrated so badly that it was difficult to make fine, accurate cuts. With the forming of the forward Fuel tank mounting brackets looming in the distant future that would require the use of my bandsaw, I decided to spend the time to perform several well-documented mods to reduce the vibration and turn it into the tool that it should be. There are numerous You Tube videos on the subject and I watched all of them.  

I needed to purchase some new Neoprene tires for both wheels, some longer mounting bolts for the motor as well as the saw base itself, a custom cut piece of 3/4 inch plywood to fit over the top of the mounting stand, and some new composite saw guides. After much work on this, I ended up with a good saw that passes the "nickel" test, where you place a nickel on the saw table on its skinny edge, then turn the saw on. If the saw is balanced properly, the nickel will stay on its edge without falling over. I was able to achieve this to my satisfaction. 

The end result was that I could now cut the 1/4 inch thick Fuel Tank Angle Mounting brackets with reasonable accuracy on the bandsaw to reduce the amount of forming work to do after the initial cuts. One of the most challenging parts of the saw mod was the need to trim the 1 inch wide neoprene tires down to about 7/8 inches so that they fit in the wheel tracks properly. This required making a special wood frame and using my belt sander to trim the edges accordingly. That, balancing the wheels, and adding the 3/4 inch plywood base and a new composite "link" belt all contributed to solving the vibration problems with the saw. Unfortunately this was yet another delay in the build.

Then, my wife and I needed to take a much needed vacation together, so spent the next couple of months focusing on a multi-faceted trip the New York for the first time. We spent one week in New York City and did all the NYC things a newbie would want to do - Statue of Liberty/Ellis Island, 9-11 Memorial and Museum visit, which I highly recommend to any red-blooded American, went to a Broadway show, Times Square, Stood outside during a Today Show airing, had a real New York Pizza slice, learned how to ride the subway, went to Grand Central Station, Went to Battery Park, the Fashion district, visited the famous toy store FAO Schwartz, and much more.

Then we flew off to Buffalo and took a shuttle to Niagra Falls, Ontario to see the falls for the first time. We had so much fun there, and the falls were so beautiful, that we both want to go back someday. this all happened in early September of 2019. As the whole world now knows, only a few short months later all of New York and the rest of the world would be shut down and fighting for its life due to the COVID pandemic. I have not been back on the build ever since May of 2019 as the the wind just went out my sails after coming to decision about the mod, and too many other things got in the way. After  our vacation, winter and the cold set in yet again, and I still had no heat in my garage. 

Then COVID showed up in the spring of 2020, and the massive wild fires in Colorado soon followed, and it was a struggle to stay alive and to breathe through smoke and ash all at the same time. I almost lost relatives in the Troublesome Fire in Grand County - very scary. So airplane building was not on my list of things to do throughout that entire period.

I endured multiple furloughs and layoffs at work last year, only to find myself working 15 hours days, 7 days a week, for at least a couple of months. So you could say that yes, I kept my job, which was a good thing, but at great personal cost to my overall health and well-being.  Now we are in 2021, where winter is once again upon me, and still with no heat in my garage. What a wildly exhausting time it has been over the past year and a half. 

Is there a plus side to any this? Well, in the interest of counting my blessings, both kids have graduated college, have jobs, and are out of the house and successfully on their own. Several major financial burdens have ended, I have not contracted COVID nor have any of my family members, and COVID vaccinations have begun. Aside from politics and some extremely idiotic people in this world, it seems like the sun may be trying to shine on the world again. So I decided it is also time for me to re-engage with the plane project again. I need to order parts from Vans and finish the wings.

More to come..... Sorry for the long hiatus. Stay safe, respectful, and peaceful everyone. Life is too short. I'll have pics of the bandsaw mod, planishing hammer and dolly, and some other stuff in the next post.

Small Amount of work done on the Leading Edge

Life and weather getting in the way again. After enduring a snow storm yesterday, the weather finally warmed up enough to get out and do something on the airplane. Unfortunately that "something" was pretty minor. I finally decided to redraw the lines on my LE for the rivet line, cut line, and nut plate line.

In a prior post when I did this the first time, I noted that when I performed my trick to extend the cut line from one side of the Le to the other using a file folder as a flexible straight edge, I was not happy with how the lines were close, but not quite lining up with each other correctly. SO I vowed to correct this problem at a later time. Well, that time was now. At that time I commented that I had made my marks by referencing both sides of my best guess as to a centerline based on the centers of the rivet holes on both sides of the skin. I reasoned that I might not have accurately measured the lines on the top and bottom of the skin, and that may have been the reason the lines were slightly off when I tried to join them together with the file folder trick. So I surmized that the next time I would use measurements from a single reference point - that being the inboard edge of the LE skin. ALL measurements for both sides of the skin would be taken using the inboard edge of the wing skin as the reference point.

I had to take some isopropyl alcohol to remove the previous permament Sharpee lines. Works great for removing the so-called "permanent" marker. After that was done I set out to recreate the lines using the inboard edge of the LE skin this time. I started with the bottom side of the LE. I removed the necessary clecoes ad then suddenly realized why my line measurements s might have been slightly off. The very first rivet holes closest to the Actual LE of the airplane are in a very slightly different location than the line of the remaining rivet holes. this is because this very first hole goes through a single tab flange in the forward-most part of the rib. This tab is not as wide as the rest of the main part of the rib flange because this nose area of the rib is gradually reduced as it forms the very tip of the rib, and then it begins to widen again as it wraps around the the other side of the rib. I believe that this occurs as a result of the rib forming process at the factory, where slots are cut into the rib flange area BEFORE the flanges are bent, and they must also be cut at an angle to each other to avoid interfering with each other as the flanges are bent around the semi-circular form of the curve of the LE. Each successive rib flange TAB gets a little smaller than the previous one, until the curve is completed and the flanges can resume a more normal, flatter shape.

As a result of this reduction in flange surface area, the rivet hole of that very first hole ends up being about 1/16th of an inch offset from the other rivet holes. So I think I may have made an incorrect measurement by measuring the distance from the very first set of rivet holes, which obviously would have forced the line from the other rivet holes to be adjusted by that 1/16th of an inch offset, which is why my lines did not match up to each other very well. So the lesson learned from that experience was NOT to use the forward-most rivet holes as a basis for measuring any lines that originate from the other rivet holes further back along the rib.

With that now understood, I proceeded to re-measure the lines again. the numbers, starting with the edge of the LE skin near the second rivet hole (not the first), was about 1 and 1/16 inches from the edge of the skin. This still left a 3/4 inch distance between the rivet hole and the first line known as the rivet line. the second measurement taken from the inboard edge of the LE skin was 9 and 9/16th of an inch. This marks the rivet line on the more outboard line as measured from the inboard edge of the skin, instead of from the rivet hole from the rib line on that outer section of the LE skin. This also results in s 3/4 inch spacing of the rivet line and the rivet holes of the second rib, which matches the spacing on the inboard rib flange. So far so good.

With both rivet lines drawn correctly this time, I was able to measure the same 5/16 inch spacing for the remaining inboard and outboard cut lines and nut plate lines on the inboard and outboard side of the LE skin. Just need to make another file folder flexible straight edge and confirm that the lines on the top and bottom of the LE skin on the inboard and outboard sides now line up as expected. This has to be the case before I finish this exercise by marking and drilling the initial holes for the new rivets and the nutplates that will need to be added.

Lots more work coming up on the fuel tanks, and some orders to place at Vans and a few other places for some parts and supplies that I need, including some special 90 degree corner nut plates for a #8 screw. More later.

KPR

Dimpled the Cover Plate for the Fuel Tank rib

Well I suppose that's a long enough break since my last post. Time for some updates. In my previous post I was trying to decide what side of the tank rib to place the cover plate over the hole in the web about half way up the width of the web. After mulling that over a bit, I decided to put it on the outboard side of the rib web instead of the rib web. My reasoning for this was that MOST of the time the wings should be level, and there is a slight dihedral angle in the wing where the tip will be just a bit higher than the root.

This, combined with a slightly positive angle of incidence of the wing while it is in sustained level flight, lead me to believe that pressure from the fuel inside the tank will be greater on the outboard sides of each rib most of the time, while the small holes at the bottom rear of each rib will allow fuel to slowly escape to the next inboard bay. Since the fuel pressure should be greater on the outboard sides of each rib due to the reasons I mentioned previously, I decided to put the cover plate on the outboard side of the hole in the rib web, so that any pressure from the fuel against that rib and the patch plate would tend to push the patch plate tighter against the rib web, keeping the fuel from entering that hole, and forcing it to go through the trap door instead, as intended.

Having finally decided where to put the plate, the next step was to dimple the holes for the rivets. This turned out to be yet another exercise in "imaginative problem solving." If you haven't guessed by now, I am documenting this entire tank rib trap door fabrication process because almost nobody documents this to the level of detail that satisfies me, and as it turns out, the steps required to complete this little side assembly are a little more involved than you might think.

First problem - decide which side to put the dimples for the 4 AN426AD3-3.5 rivets. I decided to use flush rivets for this since that should be sufficient for holing this small plate in place, and flush rivets take up less space inside the tank than an AN 470 rivet. Remember, I am trying to stuff as much fuel as possible in these tanks, so every little bit helps, even if that does seem a bit anal.

I decided to put the manufactured head of the rivet on the outboard side of the rib web. Again, this is because fuel pressure will tend to push the rivet head against the rib head, instead of pushing it away.

So I put the dimple dies in my hand squeezer and set the dimples in the over plate:

Next problem -I would need to use my C-Frame tool and table to set the dimples on the rib web. None of my yokes were long enough to reach the holes in the rib web. Then another problem cropped up. The trap door was getting in the way. In hindsight, all I had to do was remove the hinge, but stupid me likes to do everything the hard way. The rib sits awkwardly on the table because of the trap door.Another problem was that my C-Frame table had been setup with the male dimple die on the bottom and the female die on the top. With this application they would need to be reversed so that the male die is on the top and the female die is on the bottom. Why is this a problem - the female die is longer than the male die, so my table no longer sits "flush" with the dimple dies in this reversed state.

So the combination of the trap door interference and the reversed setup of the dimple dies on my C-Frame table presented some challenges:

Here you can see the female die sitting very proud of the table

And it looked like this sitting on the table as a result of the trap door interference:

So how do I get the rib to set level on the dimple dies so I can pound these dimples properly: I was not concerned about the proud dimple die situation, but I did not want the dimples to be improperly set at an angle, so leveling the rib web was a concern. My solution was to place a couple of the fuel tank access plates on the other side of the rib to level it out just enough for me to set the dimples properly.

And here are the pics with all the dimples set in both parts:

I will have to use the rivet gun and a bucking bar to set these rivets. this will be the first time I have picked up the gun in a very, very long time. I will have to do some practice rivets on some scrap first, to make sure my air pressures are set properly, and I get my timing back. I want to set all of these rivets perfectly so I can move on with other much more important tasks. This little adventure has certainly resulted way too much of a time suck on the build.




I also finally called my tech counselor Jim Elliot ad he came out for another visit to help me finalize plans for the mod to the Leading Edge. I think I now have all the info that need to be brave enough to drill the final rivet and nut plate holes in the skin and the subskin, so that I can take it off the wing spar and make that all important cutout. More on that visit and the next steps for that tomorrow.

KPR

Drilled the Screw Holes in the Joiner Plate to Final Size and checked the Clearance

After a lot more stressing over the fit of the edges of the fuel tank and LE skins and presence of any gaps, I finally got tired of trying to make this "perfect" and decided that it was time to do the best I could to ensure that the skin edges were as "perfect" as I could make them, and then drill the attach holes for the #8 screws to their final size with a #19 drill bit. Here was the outcome:

While it's a little hard to see in the above pic, the black colored clecoes in the middle are where the attach holes have been final drilled.

Just prior to doing that I was trying to get a pic of the gap between the LE and Fuel tank rib to verify that I had about a 1/16th inch gap between the end of the joiner plate and the fuel tank rib. even I am able to see the inside of the gap through the new access plate opening in the LE, it was difficult to get a good picture of this. I am still trying to figure out why i seems as though I have a correct gap on the top side of the LE and Fuel tank ribs, but the gap on the bottom side seemed to be quite a bit smaller. In fact, this gap is so small that the edge of the joiner plate appears as though it almost touches the flange of the fuel tank rib. None of that makes much sense to me.

The only way to view this gap is with a mirror. It is possible that I am dealing with an optical illusion, but I don't think so.

Trying to hold the mirror in one hand and the camera in the other, and insert it into the access panel hole is a bit of a challenge. Anyway, you get the idea. There is a diagram in the plans that shows this gap between the joiner plate flange and the fuel tank rib flanges, and it should be about the same on the top and bottom sides.

After the holes were drilled, I removed all the clecoes securing the fuel tank and removed it from the wing frame. I then deburred all the holes.

I was a little concerned about the edge distance of these holes once they were final drilled into the joiner plate, because I was not able to maintain the 11/16th of an inch measurement all the way around the LE. In some spots it does meet that measurement, but in others it is about 1/16th of an inch shorter, which leave less space for the nut plate and dimple for the #8 screw that will occupy these holes. After trial fitting a nut plate in several locations I don't think I have anything to worry about. the dimples and nut plates should have plenty of room.

I called Vans today to ask about the forward-most hole, after realizing that there is a bit of a curve in the flange of the joiner plate that causes the nut plate for this hole not to sit flush with it. Vans told me that you could either slightly bend the flanges of the nut plate, or clamp the joiner plate down as flat as possible and drill the rivet attach holes. they have seen builders do it both ways and I was told that it does not seem to make much difference whichever method is used.

Next steps are to get with my Tech counselor to review the plans for the cut in the LE skin. Then once that is finalized, it's time to drill the rivet holes and screw holes for the planned nut platesin the subskin, and then remove the LE and disassemble the subskin so I can make the cuts in the outer LE skin. Then I will need to smooth out the edges of the cutout in the outer skin, and fabricate a new .025 inch thick skin. This will become the "removable" LE that will fit exactly in the new cutout area.

Then I will need to and mark and drill the holes in the new removable skin by starting at the bottom and wrapping it around to the top, drilling and clecoing as I go, to make sure that it sits tightly around the subskin, and that all the edges line up perfectly with the edges of the outer skin. How to mark the holes in the fabricated replacement skin is something else that I also need to think through.

I still can't believe that the time for this near-final phase of the mod is actually almost here.

Preparing to Cut the Outer LE skin

I'll start this section with a huge disclaimer. I am not, nor have I ever been - a certified aeronautical engineer or aviation mechanic. Any changes that I am applying to my aircraft are entirely of my own design. I do try my best to research all aspects of making substantial design changes to an aircraft, and evaluate and address all safety concerns. I try to apply recommended procedures to any modification that I make that may differ from the original kit designer's plans.

If anyone decides to utilize any part of the information I provide in this blog to apply similar changes to their aircraft, they do so at their own risk. Each builder must evaluate their own research, skills, abilities, and experience, and must reach their own decisions as to the safety and applicability of any change applied to a tried and tested aircraft design.

I am embarking on a modification that, if it should go wrong while in flight, can have serious consequences. Having said that, I have done my best to ensure that all safety precautions are being taken, and that standard or recommended procedures are being followed for all modifications I am making. So, now you have been warned!

With the LE and fuel tank skins finally butting up to each other properly, it is now time to figure out once and for all just exactly where the new rivet holes, screw holes, and holes for the nut plates will be located for the removable LE. While most other builders would simply view what I am about to do as something very similar to installing a Duckworks support bracket assembly through a small opening in the LE skin for installing a landing light, they would only be partially correct.

There are some key differences in what I am about to do and the duckworks landing light bracket assembly:

1. For the duckworks installation, this takes place in the last or next-to-last bay in the leading edge, closest to the wing tip. For my installation I am using the opposite or most inboard bay of the LE. Higher loads are experienced in this inboard area of the LE than those that occur out at the wingtip.

2. The opening in the outer LE skin for the duckworks installation for the landing light is not as wide as the entire bay, whereas my removable LE assembly will span almost the entire width of the bay - somewhere in the neighborhood of 7 or 8 inches in a bay that spans 10 inches from one rib rivet hole to another rib rivet hole.

3. I don't think that the duckworks mod cuts the skin back as far as I am going to cut mine. Again the key difference here is that I will have a large section of LE skin that will be completely removable. All you are doing with the duckworks mod is cutting a hole that is big enough for the landing light support, mounting bracket, and the light itself to fit through.

4. The only "subskin" that the duckworks mod utilizes is the flanges of the support spar that rest against each rib web. I don't even think that the top or bottom flanges of the support bracket even touch the LE skin at all. My subskin rests against both the top and bottom of the LE skin and inserts between the ribs and the outer LE skin.

So while there are some similarities to the duckworks LE/Landing light mod and what I am doing, there are still some significant differences.

Here are some pics from tonight that show the joints between the LE, Fuel tank, and top main wing skins where they all butt up to each other. The seam between the LE and fuel tank skins is barely visible running vertically in the center of the pics, and the top wing skin seam is on the bottom.

The first several pics above are of the top side, and the last one on the bottom. Apparently I did not take any pics of the gap issues I mentioned in my previous posts, but lets just say it was extremely noticeable. In the above pics, it simply does not exist - exactly the way it is supposed to be.

For my final "before cut" measurements, I think I may have hashed at least some of this out in a previous post from several months ago, but doing it again here to make sure I have captured all the latest detail. Here is what I am dealing with:

Each 408 rib has a top and bottom flange where the LE skin is attached to the LE rib.

Those rib flanges are about 5/8 of an inch wide, or 10/16th of an inch

The rivet holes in each rib are pretty much centered in the rib flange, at about 5/16ths of an inch.

This leaves the remaining rib flange edge width of 5/16ths of an inch that I must  account for in my removable skin measurements.

While discussing this with my tech counselor, he agreed that I will need to leave a certain amount of LE just past each rib flange on both ends, and I will then need to add new rivets on this additional portion of the skin that will hold down the edges of the outer LE skin very close to the cut line for the removable section of the skin.AC 43.13 is almost no help with the details of how to apply rivets in this situation, however I learned from my tech counselor that the overall objective of a mode like this is to try to ensure that any loads imposed on the structure are allowed to pass through the structure in a similar manner that they would have if the repair or mod was not needed or applied. So you can't build up a set of rivets that will cause load paths to shift to other weaker areas of the structure, so this requires some careful planning and understanding how these loads were originally designed to be handled by the kit manufacturer.

After toiling over all this stuff again, I decided to follow a particular paragraph in AC 43.13 on page 4-26, paragraph 4-58, SubPart e, that describes how "repairs" to "damaged" skin should be made, which states that
" The repair seams are to lie along stiffening members, bulkheads, etc.; and each seam must be made exactly the same in regard to rivet size, splicing, and rivet pattern as the manufactured seams at the edges of the original sheet."

Then it references figure 4-16, which shows several examples of skin patches and repairs and how the rivets are to be applied.

Since I am actually the "manufacturer" of this plane, and Vans is actually the "designer" of the kit, this loosely translates to ensuring that any major skin "repair" matches the original designer's rivet layout as much as possible. To that end, I now know that I will add another row of rivets  in parallel with all the rivets already attaching the skin to each LE ribs. The details of this are:

Top side:
The first 3 rivets in top flange of each LE rib are 1 inch a part. Then all remaining holes are 1.25 inches apart.

The outer LE skin starts to truly flatten out (not as curved) after about the 8th rivet hole from the front of the LE. This is almost 2/3 of the total distance from the front to the rear of the LE skin. This is a lot further back than I was planning to go to make the cut line for the top side of the removable LE. So I need to ponder this a bit more.

Bottom side:
Only the first 2 rivets in each rib are 1 inch apart.This is because the bottom of the LE is obviously flatter than the top and is not quite as stressed as the curvature on the top part of the LE is. The remaining rivets after this point are once again spaced about 1.25 inches apart.

The LE bottom skin starts to flatten out after the 4th rivet.

SO I will be creating a parallel set if new rivet holes that will mirror the existing rivet holes in each rib. As far as where how far back to cut the LE skin is concerned, I have to decide if I will stagger this so that the span-wise cut line will be the same on both top and bottom (5th rivet hole from the tip) or go to the 5th rivet hole on the top and the 4th rivet hole on the bottom. I'll have to eyeball this a bit more.

This post is more than long enough, so I'll pick up where I left off tomorrow.

KPR

Scarfing the wing skins - more info

Wow. It's been a week and a half since my last post. In that time there has been a winter storm, large tree branches falling off the trees that threaten the roof of the house, severe winds, cold temps, and a lot of other things that I had to get done to meet other obligations that had nothing to do with work or with building the plane. I was way too over-extended last week, and I finally got a chance to recover a bit on Sunday. I was pretty much running on empty all last week.

I had to finish editing a video that I produced for my EAA chapter with footage that I shot at Oshkosh when B-29s FIFI and DOC flew together, making this the first time in 50 years that more than one flying B-29 flew in formation with other B-29s. Turned out pretty good - but as always video editing-doing it properly anyway - is an awful lot of work.

Then I promised to do a presentation for the meeting as well - so I had a double whammy for last Friday.

I finally had some time this evening to get back to the scarf joint. In between the last post and this one, I did some more research on VAF about this whole scarfing process. Turns out that, as usual, I should have done the research BEFORE I started the process when I mistakenly thought I had it all figured out.

NEWS FLASH for builders trying to scarf this joint with power tools. DON'T DO IT! I found a 3 page post on VAF with folks basically asking the same questions that I was. The basic advice was NOT to use power tools, as there is a risk of a sanding disc grabbing the skin and sliding away from the desired work area. TOO LATE FOR ME! I already did this on the outer surface of my inboard wing skin, you know - the part that everybody looks at on the top of the wing when your airplane sits on the ground. I took off too much metal over too wide an area. Now I am going to have to have an ugly primer patch on that section of the inboard skin. So, it's not too big of a deal since I plan to paint the plane anyway. But had I wanted to polish my airplane, this skin would probably need to be replaced.

So once again I have proven that for every step that I take where I do something that I have never done before, I manage to screw something up at least once. So my advice to anyone following this blog is frankly to follow somebody else's (Venting). Anyway, following the advice on this VAF post that I found, I drew lines on the inner and outer section of the skin where the joints overlap so that I would know what the borders are supposed to be. Then I took some electrical tape and placed it along side the marks to provide a sort of protective barrier for the next step.

Then you take a standard tooth vixen file and start tapering the skins using the hand held file - and NOT a power tool. Here is pretty good shot of what things looked like before I started to remove more material with the file:

While this is hard to see, the fuel tank skin is on top, and the inner and outer top wing skins are on the bottom half of this pic. There is no longer a large triangular gap where the outer skin rides over the top of the inner skin, so that is progress. However, there is just enough of a ridge sticking up a bit higher than the fuel tanks skin edge, so it still needs more work. I was quite discouraged to read that some builders had managed to complete this whole task in about 15 minutes. Sucks to be me I guess.

Here is shot that shows the damage that a runaway sanding disk can do, as well as the sharpee line that I drew on one side of the skin. So I am overextended with my skin removal by about another 1.25 inches or so. I drew another line from the bottom side of the wing on bottom of the outer skin so that this line would also be present on the other skin when I separated them again.

And here is the tape applied along each line on both skins

Then you take the file and start systematically taking even amounts of metal off by running it across the area of the scarf joint on both skins

You need to keep slightly angling the file so that it takes more material off at the upper corner of each skin, and thickens up the further away from the corner that you are. My original plan included using a small scotch brite wheel on my drill, but I used it for the wrong purpose. My plan was to use it to remove fine amounts of material, just like it does when you use it to debur the edges on various sheet metal parts. However, for this task, it does not do so well, because the wheel gets gunked up with aluminum as you run it over the flat skin. It is not meant for removing large quantities of aluminum across large flat surfaces. So after I tried this on both skins, I could see where it left some peaks and valleys in the surface of each skin.

Using the straight file allows you to remove an exact amount of material much more controlled and precise than sanding by hand or using a power tool, and you can do it a little at a time and repeatedly check your work as often as you wish. In my case, using the file allowed me to knock down the peaks and even the valleys out so that the skins would lay flat against each other when clecoed together. Here is shot after I filed some more material away on both skins:

So this was looking better, but there was still a pretty good ridge between the tank skin edge and the wing skins that you can feel when your finger nail runs down along the tank skin toward the edges of the top wing skins. At this point I was satisfied with the fit from using the file. But now it was time to start smoothing out the scratches, and doing some final material removal by switching to smaller grit aluminum oxide sand paper. The sanding disk that I used was 180 grit (quite coarse). Next I used some 220 grit sandpaper to take out the larger scratches from the disk and the file. I also had to smooth out the areas where the disk ran away from me a little. These are the areas where primer will unfortunately be visible on the upper surface of the wing, but it has to be done.

I took a couple more shots after sanding, but they came out really blurry, so I'll have to take some more tomorrow. The end result after sanding was encouraging. The rise in the skin is almost gone. I got tired of re-clecoeing every single bay of the wing skins each time I wanted to check the fit, so as I got closer to the finished edge that I wanted, I ran clecoes along each bay, closest to the overlap joint, to secure the wing skin edges against the wing spar flange. Then I clecoed the overlapping skins together, and checked the fit.This seemed to work pretty well without having to re-cleco ALL of the ribs and skin holes on the more outer and inner sections of each skin.

The current state of the joint is that it is almost flush with the tank skin. I still have about 2 more stages of sanding to do. Most builders recommend final sanding of the scarf joint area with 600 Alum Oxide sand paper.I am going to start with 320 sand paper first, then clean with acetone very thoroughly, and then finish with 600 grit paper, and finally some primer.

Here is a parting pic of my hands full of aluminum dust after sanding the skins with 220 grit paper:

I decided that I am going to leave a small ridge on the skins for now. When the time comes for paint, There will be a lot of additional prep that will involve sanding, filling, priming, and sealing. This finishing process should being the edges flush with each other, so I am happy with where the joint is at right now.  I also do not want to remove any more metal, because I pretty much messed up the whole "scarfing" process, and managed to remove a hell of a lot more skin than I should have. So now I get to worry about the skin being too thin in this area, and being prone to cracking later on as the wing flexes in this area during flight. FANTASTIC!

Anyway, the joint looks a heck of a lot better than when I started. When I do the right wing skins and the bottom skins on the left wing I will exclusively use the file from now on, and I will pay close attention to keeping the scarf joint within the confines of the overlapped section of each skin.

I do still like the decision I made to make the joint with the skins and the fuel tank still attached to the frame, since Vans implies that you do this step with the skins off the wing, and they certainly do not have you check the fit with the fuel tank in their crappy instructions.  As I said before I started this step, how in the hell are you supposed to verify that the fit is correct if you don't check it against the fuel tank skin? But I digress - again.

All for now.

KPR

Scarfing the Adjoining Corner of the Top WIng Skins, and More....

There was a slight change to the sequence of tasks that I had defined previously after I ran into a small issue arose. I started today with the thought that I would scarf the overlapping joint of the forward-most part of the wing skins where they butt up against the fuel tank skin. This reason this needs to be done is pretty simple to understand when you see it on the wing, but a bit more complicated to explain in writing.

I then realized that in order to scarf the joint properly, I would really need the skins to be secured as closely as possible to the way that the would be riveted to the wing spar and the ribs, so that I would know exactly how much the skins would need to be tapered (scarfed) to remove the .025 ridge that sits higher than the fuel tank skin when the wing skins overlap each other. They overlap each other by about 1.25 inches or so, with the side by side rivet holes about 7/8 of an inch apart from each other, and each outer-most rivet hole in each skin is set at about 5/16ths of an inch from edge of each skin.

As I thought through this, I realized that although I had countersunk the holes for the inner wing skin rivet that attach it to the wing spar flange, I had NOT yet re-countersunk the rivet holes in the wing spar flange for the outer wing skin. I needed to do this BEFORE scarfing the joint, to ensure that the wing skins were seated properly in the slightly over-countersunk holes, so that the skin edges are sitting flush against the wing spar flange.You cant set a scarf joint very well on two skins that are pillowing where they attach to the spar, so this had to be done beforehand.

SO I grabbed the drill and the MS countersink bit that was still set for the slightly deeper countersunk hole, and started re-doing all the holes for the outer wing skin attach points on the main wing spar flange on the top side. I started from the outboard (wingtip) end and worked my way back toward the fuel tank, which was still mounted on  the wing spar. And that's where I ran into my issue. the wing skins overlap each other at a point that extends beyond the outboard end of the fuel tank skin. Therefore there are a small number of additional holes that lie directly under the fuel tank skin that also must be re-countersunk. The problem is that with the tank skin in the way, you can't set the microstop countersink bit flush up against the spar flange to ensure an evenly drilled hole. SO the fuel tank has to come of the wing AGAIN in order to finish countersinking. (UGHHHH)!

I removed the tank attached to the baffle plate this time, and then I realized something else that I also needed to do. This was the first time since I drilled all the tank baffle plate - to - Z bracket holes that they would all be exposed so that I could check the spacing and edge distance of the new holes in each Z bracket. I think they turned out exactly as expected. Here are some pics:

With the top sides of these holes exposed I was able to debur them. Then I realized that I needed to debur the matching holes on both sides of the fuel tank baffle plate as well. So I removed the the baffle from the fuel tank assembly that was now sitting on the work bench, and deburred both sides of the drilled baffle plate holes, and I also deburred the aft side of the inboard and outboard tank ribs where they rested on the Z brackets. Then I realized that I would also need to reattach the baffle plate to the tank assembly and eventually remount the tank before I could scarf the wing skin joint. So I reattached the baffle plate, but left it off the wing spar so I could finally finish countersinking the remaining holes in the wing spar flange. It just never ends.

Next is a really blurry pic of the holes that lie under the nut plate holes for the fuel tank attach screws. You can still see the rivet I put in the hole to show that is has the proper amount of over-countersunk depth as specified by Vans in the latest section 5 revision of their manual.

After all the top holes were re-countersunk, it was time to remount the fuel tank and the outer wing skin to the wing spar in preparation for the scarfing task. Before I remounted the fuel tank, I attached the outer wing skin. these next pics attempt to show the gap between the wing spar flange and the inner and outer top wing skins where they overlap. In this pic I am looking down over the edge of the main wing spar flange where the skins attach to it. The rivets on the right are the doubler rivets on the top and bottom of the main wing spar web. IOW, pretend you are fuel tank skin that is about to butt up to the edges of the skins shown in the middle of the pic.

The skins need to be tapered in this corner so that the gap between the outer skin and the wing spar flange no longer appears, and the two overlapping skins join together flush with each other, and the edges are also flush with the edge of the tank skin.

After these pics I reattached the fuel tank to the spar and put a #30 cleco through the holes for the screws in the fuel tank skin so that the tank skins on the top and bottom are flush against the top of the wing spar flange, and butted up snugly against the top edges of the wing skins.Then I had to determine how many bays of clecoes I was going to remove from the wing skins so that I could bend each of them out of the way of the wing spar without creasing or kinking them so I could begin the scarfing process.

Others will perform the task with the skins removed from the spar completely, but since the object of this task is to carefully trim down the skin so that it forms a smooth, flush joint with the wing spar flange and the fuel tank skin, the only real way to do this is to start removing small amounts of skin and then check the fit. The only way I could figure to do this efficiently was to keep the skins partially clecoed to the wing frame on the most inner and most outer ribs, leaving the center section completely unattached from the spar, so I could lightly bend each skin back without creasing or kinking it while I grind away the metal a little at a time.

Now for the tools to do the job. Here is a pic of the choices I had. I had the pneumatic die grinder with a 3 inch attachment that holds a screw on attachment for a scotch brite pad or a sanding disk. The scotch brite pads seemed a little uneven to me for this application, so I opted for the 180 grit sanding disk. I also opted for the cordless drill instead of the air grinder so I could have a little better control. I also decided to use the 2 inch attachment instead of the 3 inch attachment, again for better control and to keep the area being removed as small as possible to avoid removing too much material from too large an area on each wing skin.

The math for this operation is pretty straight forward. The inner skin is .032 inches thick. The outer skin is .025 inches thick. The tank skin is .032 inches thick. The 1.25 inch area where the inner and outer skins overlap creates a combined thickness of .057 inches. Or put another way, the overlapped section is thicker than the .032 inch thick fuel tank skin by the thickness of the outer wing skin. SO you have to figure out how to reduce this overlapped thickness by .025 inches, taking a certain amount away from each skin. Obviously you cannot remove the entire .025 inch thickness of the outer wing skin. However, I am aware of some builders who have actually done this. In fact, this very thing is already done at the factory where the skins overlap at the trailing edge as part of the fitment process for the ailerons and flaps. SO this technique can be used, but I chose to scarf the joint instead per Vans instructions.

So this means that you have to remove a certain amount of skin thickness from the corners of both skins to arrive at the combined removal of .025 inches.The "formula" I came up with was to remove .0200 inches from the thicker inboard wing skin, and .0120 inches from the thinner outer wing skin. Now this sounds fine "on paper," but in practice I found it rather impossible to get an accurate reading from a digital caliper while trying to periodically check thickness in between sanding sessions to see of the correct depth has been reached. The other complication about this is that the skins are supposed to be tapered (scarfed), so if done correctly, the skin changes thickness constantly. So I gave up the caliper approach, and resorted to visual checks of the fit by pushing the skins together and checking for flush against the fuel tank skin.

SO you might ask, why go to all this trouble for a lousy skin joint. Well, the problem is that the overlapping wing skins cause a rise in the skin that sticks up higher than the fuel tank skin, which also serves as the inboard leading edge of the wing. If this skin edge is not made to be flush with the fuel tank skin, it sticks up into the airflow, disrupting it, causing drag and unstable airflow over that portion of the wing. So to prevent all the ill-effects of this, you need to blend the skin joint so that everything is smoothly joined together.

The other thing to note about this process is that you need to leave the flatness of the inner wing skin against the wing spar flange, so that means you only remove material from the top side of that skin, and the bottom side of the outer skin. EDIT - I later determined that I needed to remove it from the other side as well, so I removed material from both sides o the inner wing skin. You also try to keep the scarf joint a couple of inches or so in size, focusing only on removing enough material for the joint in this corner of the skin to be flush with the tank skin. It should not be a large scarf joint.

I'll add more pics of that tomorrow, but for now here is the joint after I worked on both skins a little tonight. I bent out each skin just enough to separate it from the wing spar and allow clearance for the drill and the attachment. I held the skin in my left hand, applying pressure against the sanding attachment applied to the other side of the skin, and started removing small amounts of material at various intervals, checking my progress as I went. When I felt like I might have enough material removed, I checked the fit. When I thought I had it pretty close, I re-clecoed all the skins to the frame. I've still got a little more work to do tomorrow, but I think I am on the right track.

When I re-clecoed the skins, the fuel tank skin and top edges of the inner and outer wing skins were slightly interfering with each other. I think this may have happened as a result of deburring the tank ribs, baffle plate, and Z brackets, where the tank assembly, and therefore the tanks skins, are sitting just a bit lower than before. The interference is such that a little more edge deburring by lightly sanding each skin will take care of this minor interference. So I am close, but still have a little more material to remove. Hopefully I can finish this process tomorrow.

Countersunk the Inboard Top Wing Skin Spar Flange Holes

Tonight I countersunk the holes on the wing spar flange for the inboard top wing skin. Before I did this, I called Van's builder support line to ask two questions:

1. What Pop rivets can I use to rivet the rear rib flanges of the Leading Edge assembly to the Wing Spar Web, instead of bucking the AN470AD-4 rivets called for in the plans.

2. Do I have to deepen my countersink tool a bit more that normal to set the holes properly to receive the dimpled wing skins? If so, how deep do they need to be?

The answer to question 1 was that I can use LP-4  pop rivets instead of the AN470 rivets to make it a bit easier to set the LE rib flanges against the wing spar web. these are structural rivets that hold the ribs of the leading edge firmly against the wing spar, so setting these properly is very important.

The answer to question 2 was to check the updated Section 5 of the Van's instruction Manual which is available on Vans website in the revisions section. Section 5.5 states that for dimpled skins that must fit into countersunk holes, it is best to deepen the countersink by .007 more than when the rivet just sits flush with the skin or spar flange.

To figure out how to do this, I had to do some more research about my micro-stop countersink tool.  It has a series of "teeth in a spring loaded cage that allow the depth to be changed in very small increments. In fact, each tooth space is the same as a .001 adjustment in depth, so it is very precise. So in a nutshell, that means that I need to adjust the tool and then countersink a few holes in a test piece until the rivet head sits nice and flush against the skin or flange. Then I need to deepen the countersink by 7 more clicks of the teeth in the proper direction to deepen the hole by that much per Vans recommendation. If you do this and then set the rivet in the hole you end up seeing that the head of the rivet is about 1/64th of an inch deeper than flush. Then you take the rivet out and set a test piece with the dimple inside the countersunk hole, and check to make sure that the test piece sits flush against the skin or flange.

I tried to do all this before I countersunk all the outer wing skin holes, and I though that they were sitting OK with my test piece until I clecoed the skin back onto the spar and found out that those dimples were NOT sitting in  those holes very well as my last post or two explains. Here is the triangular teeth of the countersink tool, all meshed together:

The locking ring on the top unscrews and allows you slide the spring loaded half of the tool back to clear the teeth of the other part of the cage, and then you rotate it the requisite number of teeth to achieve the desired depth. All very nice if you know what depth you are trying to achieve, which, until Vans finally updated their manual to provide this very important information, was a mystery that most builders tried to figure out by trial and error.

Here is the test piece that I used - same as before with some new holes drilled and deburred so I could test several of them to make sure I had the tool set exactly the way that it needs to be.
Note the rivet in each hole, first the one that is flush with top of the metal, and then the one that was set just a bit deeper per Vans suggestion:

You can just see how the second hole is just a little deeper than the first, and the rivet head is no longer flush with the rest of the metal. remember to double click on the pics in the blog to enlarge them a bit more to show better detail.

And here is a pic of all the tools I had to use just to setup the test piece to make this critical tool adjustment.

Once I had the tool properly setup, I removed the fule tank assembly  temporarily to expose the holes in the spar flange, and then I proceeded to countersink the holes for the inboard wing skin.Then I experienced my next error. Some of these holes coincide with a main rib flange that sits up under the wing spar flange. Each side of each main rib (top and bottom of the rib) has two of these holes. Without thinking, I just assumed that both of these holes would get the same countersunk hole, just as I had done for the outer skins.However, there is no attach point for the fuel tank skins in this area, since they are dimpled and inserted into the countersunk for the #8 screws. These holes are already drilled, and the fuel tank skin is screwed to the flange - NOT riveted, since it is designed to be removable for periodic servicing. Since there is no skin dimple being inserted into these holes, the countersink for the top most rivet hole needs to be flush with the spar flange again. I drilled two of these upper flange holes before I stopped and realized what was going on. So hopefully I will be able to set a rivet with a squeezer in those two holes and make it come out flush with the spar flange. We'll see.

Here is a pic of the countersunk holes in the spar:

You can see a couple of the ribs where there is an extra hole in between countersunk holes in the top edge of the spar flange where the screws for the fuel tank will go. Those are the rivet holes that need to be flush with the flange and not set too deeply, since no skin dimple will be inserted into these holes.

And finally, two pics that show the test piece with the dimple in it laying on top of the angle with the countersunk holes. the first is with the dimple sitting in the properly countersunk, slightly deeper hole:

And in contrast, here is the same dimpled test piece sitting in the hole where the rivet was sitting flush with the metal (not countersunk enough for the dimpled skin). You can see how it is not sitting flush on the angle. SO this tells me that the info from Vans is correct - dimples that sit in countersunk holes need to be countersunk just a bit deeper for the skins and flanges to fit together properly.

The reason for all this, of course, is that dimples are round, and countersunk holes have straight edges. SO you have to compensate for the radius of the rounded dimple sitting against the straight edge of the countersunk hole. Kind of like fitting a square peg in a round hole, or vice versa - sort of.

Next steps:

Remove the fuel tank assembly again

Remove the inner clecoes for the rib flange holes that attached the rear baffle plate to the wing spar Z brackets

Replace the tank skin assembly back on the baffle plate

Re-cleco the inner and outer tank ribs to the fuel tank skin again, remove the clecos for the inner and outer rib flanges attaching the ribs to the baffle plate and the Z brackets

Remove the entire tank assembly from the wing

 Dimple the inboard main rib rivet holes - top and bottom - with the squeezer

Cleco the top inner wing skin and wing walk doubler back on the wing frame, removing clecoes holding the outer skin in place where the two skins overlap, placing the outer skin over the top of the inner skin edge.

Remove the outer skin

Re-countersink ALL those remaining holes that need to go just a bit deeper that are currently not quite deep enough - YES, I have to go back and drill all those holes I already did once more time.

Reset the countersink for the flush setting and finish countersinking those holes

Debur the top sides of the Z brackets and the rear holes of the Tank baffle plate

Reattach the outer wing skin, and firmly remount the fuel tank by clecoing the inner and outer ribs to the Z brackets again and securing the tank skins with #30 clecoes into the screw holes and nut plates,  and check the skin fit along the spar flange.

Then I can FINALLY put the LE back on the wing and secure it so that I can mark and measure for the cut out.

And then we go on from there. Lots of little steps, all done in the proper order. At some point everything comes back off again so I can scuff, clean and prime the inside of the top wing skins. Once that is done and the leading edge assembly is done, they will be ready for permanent riveting to the wing frame.

The Theme for Today was.....More Dimpling of WIng Skins and Ribs

Yesterday I had managed to go as far as I could with the top outer left wing skin panel as far as dimpling is concerned. As previously posted (I think) I missed match drilling two holes. I could have taken an easier path by just independently drilling the hole in the skin and rib/rear spar, but as any of you following my blog have already surmised, doing things the easy way is not my forte. SO I needed to match drill these two holes, which meant putting the outer skin panel back on the frame, match drilling the missing holes, and then removing the skin again to debur the holes properly and dimple them.

SO I did just that today. Since this was the first time I mounted the skin to the ribs and the spar with the dimples and countersunk holes in place, I was able to check the fit as I reclecoed the holes. At first there was some misalignment of all holes on the inboard edge for some reason, but using a graduated approach to clecoing the holes, and they managed to align themselves pretty well.

Once this was done, I we to check the fit of the skins to the ribs and the spar with the dimples. I was pretty happy with the dimple-to-dimple fit of the skins to the rib flanges, but the ft of the dimples to the countersunk holes in the spar is another story. I don't seem to be able to use a "test" dimple on some short piece of aluminum very well. I just can't tell if it actually fits. The problem is that trying to verify the fit of something on the wing spar flange is difficult for me because the flange is bent, and there is only a small portion of the test piece that rests on the small flat part of the spar flange I cannot tell if the test dimple and the metal surrounding it are actually fitting correctly, because if I apply a little pressure to it it seems to end up flush with the spar.

Other folks with videos of this always show some test dimple and a another "test" piece of aluminum, but they never show the test piece up against the actual part, such as a wing spar flange. I find this to be troublesome. Are you supposed to have a little spring back with the dimple in the countersunk hole, or none. I do know that if the countersunk hole is too deep, you risk denting the skin as you rivet it, which causes other major problems. SO you definitely do not want to end up doing that.

Anyway, the edge of the skin where the dimple fits into the countersunk holes of my wing spar appear to be "pillowing" just a bit when clecoed. this is a sign that the countersunk hole may not be deep enough for the dimples.  This will become even more pronounced once you try to rivet these holes. MY problem is that the pillowing seems to be evident in between clecoes as shown the next pics:

However, if I put clecoes in every hole, they seem to tighten up. I watched some videos of other builders today who demonstrated that if you are placing a dimple in a countersunk hole you have to enlarge the countersunk hole quite a bit to allow the dimple to rest in the hole properly. In fact, from the examples I saw, it looked like it took 1/32 of an inch more depth to make it fit properly for a dimple, as measured by the exposed metal at the top of the hole if you put an AN426AN- 3 rivet  in the hole.

Then you can take a caliper and measure the width of the dimple and the hole and compare them to see if the edges of the dimple should fit inside the the countersunk hole. The last time I had to deal with this, and frankly I am about to find out if I did it right back then, was when I was countersinking the holes for the #8 nutplates and screws in the wing spar for the fuel tank. That was a long time ago, and it was not for any 3/32 holes that would be receiving a dimpled skin. SO this feels like some new territory.

Sounds like I have some more tests to run to see if I need to enlarge my countersunk holes a bit more or not. Anyway, with that first fit completed, it was time to remove the inboard wing skin and debur and dimple it AND the wing walk doubler, which I have not laid my eyes on for a very long time. I removed that skin and proceeded with checking the holes again and deburring them again as necessary, and filed those bumps on the edges, then deburred the edges, rounded off the corners, formed the small bend in the skin edges, and dimpled as many holes as I could reach with the pneumatic squeezer.

I also did some math to try to figure out how much material in each wing skin I need to remove to scarf the joint that sits next to the fuel tank skin where the inner and outer wing skin panels overlap. I need to get some attachments for some sanding disks for my die grinder tomorrow at Harbor Freight so I can complete that little fabrications exercise.

Here is the inner skin on the dimpling table. Since this skin section is smaller than the outer one, it was much easier to maneuver and flip this skin panel on the work bench. I also took a pic of the partially dimpled wing walk doubler.

Tomorrow I finish dimpling the holes I could not reach with the squeezer, scarfing the corner of the inner and outer wing skins, and then it will be time for final edge prep, then scuffing, cleaning and priming all the interior portions of the skins and the wing walk doubler.

Mainly I wanted to get to a point where I can remount both dimpled wing skins to the frame and then mount the LE again to layout the pattern for the cuts in the outer skin. That was the original part of the plan several days ago.

Winter arrives tomorrow night and into Monday, but it looks like things recover for the rest of the week.I'm getting closer to some major assembly steps and actually slamming some rivets.

Dimpled the Top Outer Main WIng Skin Tonight

With just about all of wing spar flange holes for the fuel tank, LE, and main wing skins countersunk, the next logical step was to dimple the main wing skins, starting with the top ones, since they will be riveted to the wing first, when the time comes.

I was a little apprehensive about this at first, for the following reasons:

1. These are the longest and probably the widest skins of the entire airplane, so keeping them clear of obstructions or things that could put a ding in them is a challenge
2. The C-Frame is only so deep, and it is not deep enough to dimple all the rib holes in the skin without turning the skin around, but it does get most of them in one pass.
3. I needed to make sure that the skin would not get caught on my bench vise. I used the blankets to prevent this from happening.
4. Ever since I decided where to place the wing stands, I was concerned about the amount of space between the wings and the work bench, specifically for this situation where I would have to dimple the wing skins. It turns out that there is "just enough" space here to be able to work with the skin by turning it slightly in one direction or the other as you dimple the holes furthest to the rear. This brings the front end of the skin outward toward the wing frame. SO you have get creative, but not near as creative as I had to get with the pre-bent LE skin.
5. You have to have almost double the length of the skin available as room on a bench or a table to allow the sliding of the skin from one end to the other as you dimple all of the holes.

As it turned out, everything worked out fine. Unfortunately, I missed match drilling a couple of holes out of hundred or so that are drilled, so that wasn't too bad. I'll get those taken care of just as I did for the ones I missed on the LE skin after I cleco it back on the wing frame. ow you determine that, as I said before, is you pay very careful attention to how the male dimple die fits into the hole. If it does not freely adn easily insert itself into the hole, then most likely it has not been match drilled. Whatever you do, do NOT try to dimple a hole like that, or you will end up with a ding that will need to flattened, or worse yet, a badly formed hole in the skin that needs to be addressed.

I also used the pneumatic squeezer to dimple as many holes as possible around the perimeter of the wing skin, so that I did not have bang as many of them with the C-Frame. You also need to be careful  not to try ot dimple two sets of holes in this skin yet. the first set are the farthest holes in the outer portion of the skin. These are the attach holes for the wing tip, and you do not address these until the wing is essentially finished. The other set of holes that you do not touch yet are the holes for the aileron gap seal and the flap support bracket. These are both on the trailing edge of the wing and are mounted after the row of holes that attach the skin to the rear wing spar flange.

I turned the skin over before I started dimpling to debur the edges on the other side of the skin, and to apply the small bend in the top of the skin edge where it attaches to the wing spar flange, to prevent it from curling up when riveted. I used the edge forming tool for that, and it went rather well once I got the  depth adjusted correctly. I still need to round the corners just a bit and get the back side of this skin by filing those bumps and deburring that edge.

I guess that I should also mention that I temporarily took the fuel tank assembly and put it back on the wing spar. I needed the space on the second work bench for clearance to dimple the skin, and with the LE in the cradle, The only spot for the fuel tank is back on the spar.

Here is a pic of the skin on the dimpling table

Next is the blanket over the bench vise

Next is the skin with some of the holes dimpled

Next is pic of the lack of space you have as the skin comes outward. At its worst points, I had to turn the corners of the skin so I could get close enough to the ram while the male dimple die was held in the hole on the table. IN another case when the ends of the skin start to interfere with objects near the work bench, such as refrigerator, you can curve the skin up against those surfaces while the rest of the skin stays flat on the table, this works just fine.

The last pic shows several holes on the inboard upper corner of the wing skin that I did not dimple yet. The reason for this is that you are supposed to leave an area of about 3-4 inches in this corner to form the scarf joint where the inner an outer wing skins overlap. All that simply means that you need to taper the thickness of the corners of both the inner and outer wing skins on both the top and bottom of each wing so that they flow into and match the thickness of the .032 fuel tank skin. This requires grinding, filing, or sanding the skins in this area to reduce the thickness of each one. So there is no point in dimpling these holes yet until that joint is scarfed.

This skin now needs to be clecoed back on the wing frame after removing the top inner wing skin to counterskink the remaining wing spar flange holes adn dimple the holes in that skin, as well as the wing walk doubler, which frankly I have not seen for a very, very long time since both of them were clecoed to each wing frame. I do know that I never primed that doubler, and the inside of each wing skin also need to get scuffed, cleaned and primed, so there will be some more painting in  the near future,

After I dimpled all the holes in the skin, I turned over the skin to check the top side to see how well the dimples were formed. I have to say I was very happy with these, because they are very crisp and clean and appear to be very well formed. I recently saw a fellow builders RV-7A and was looking at his wing skins, and his rivets and dimples looked very nice as well. This means that the height of my dimpling table is set just right, where the male dimple die is in the set holder and it sits just proud of the rest of the carpeted table, so that the dimple dies are contacting the metal skin when the dies are hammered together.

After I get the top skins dimpled, it will be time to address the remaining work on the LE mod. I also came up with a plan for making a mock up of it using some old aluminum angle and some 1/16th inch aluminum from HD to fab the wing spar web, and I can attach some additional angle to use as a clamping platform. Then I can rivet the two ribs to the mocked up wing spar, fab another subskin and outer skin, and make the cutout, just like I am doing on the real part.

I think I will still need to do this when I finally start fabbing the gun nacelles for the lights that I plan to use. I do need to make sure that the gun ports are strongly attached, and also blend into the front of the LE very well. That will involve some foam and fiberglass experimentation with making a mold for the light mounts. I can do all that on the mock up until I know that I have all the kinks worked out of that process.


KPR