Still Trying to Prime LE Parts

Lousy painting weather and other stuff getting in the way of priming my LE parts. My wife managed to locate a set of stainless steel turkey basters, complete with a cleaning brush, thermometer, and injection needle that screws into the threaded end of the tube - all for a reasonable $10.00 price. I should be able to use those repeatedly for measuring out small quantities of primer and catalyst. The only problem is that you cannot see through the metal tube, but since I use pre-marked paint cups from NAPA auto parts to measure all my quantities, that is really not a big deal.

I also found and bought two large syringes at the Walmart aircraft supply store that are supposed to be used for measuring out 2 cycle engine oil. These are plastic, so they will suffer from the same one-time-only use fate as the other plastic turkey basters did, but they will certainly fulfill their purpose.

Also had to focus on getting two teeth crowned in the past couple of weeks. The trailer is on the short list of prep steps now. Airventure is only a few weeks away and I am really excited to attend this year. The only thing I am really worried about is the weather while I am traveling.

I had also waited on priming the other parts because I was trying to decide if I wanted to go ahead and prime the entire subskin before I do any final trimming. I decided to do just that, since I still have to figure out the jigsaw puzzle that I need to put together from the two overlapping access panel openings in the skin. Here is the subskin after a preliminary scuffing of all sides:

This part had a lot of scratches and abrasions from all the trial fittings and repeated assembly and removal steps so far. It was a bear to get some of the deeper scratches out. None of them were really all that deep. they just looked bad against the remaining shiny alclad layer that has now been removed. I still have some final cleaning to do on this part before it will be ready for priming. I think it may actually fit a little better in between the skin and the ribs after removing the alclad layer. I hope to get everything primed before the end of this week.

The rest of this next series of pics is more for my benefit so that I do not lose the markings and measurements and thoughts that I scribbled down on the subskin  before removing them this evening. I may need to reference them when I am ready to start trimming down the subskin to its final form. As I start trimming this part it will start to make more sense.

KPR....

Prepping the Trailer for Airventure 2017 and Finally Formed the Edges of the LE Skin

After a 2 month stint in the shop, I finally got my trailer back. I had delivered it back in April in hopes of beating the Memorial Day rush, only to see that holiday come and go with the trailer still in the shop. What a comedy (hardly) of problems - mostly weather related - but not all of them.

I had a larger than normal laundry list of fixes this year: Re-weld a broken step support, find and fix an air leak in my water supply line from the water pump, Check to see if I have a water tank leak in my spare water tank, fix a leaking gray water dump valve, re-attach and seal the driver side front corner molding that joins the corners of the walls of the trailer, and the annual wheel bearing repack.

Week one started with the shop telling me that 2 techs had quit that week, so they did not even look at it. Weeks 2 and 3 ended up with freezing cold temps that prevented any type of water  repairs. Week 4 was the week of softball sized hail that pretty much decimated the west side of Denver. Luckily they had pulled it into a stall to do the bearing pack by then, so I lucked out big time on that.

Then came the day that they called to tell me that my axles and were on backwards and my brakes were improperly installed and it would take brand new axles to fix it. Now folks, I have owned this trailer since 1998, and in all that time I have serviced the trailer brakes about once every other year for one reason or another. In all that time I have never had a single tech inform me that my brakes were upside down. This includes the previous 2 years where I did have extensive brake work done by the same shop! That led to several arguments, including comments like "what the hell are you doing with my brakes. That was not one of the things on the list of fixes, because they were working fine. You should not be touching my brakes!"

Then came the 2 weeks I had to wait because they found leak in my main sink's P-Trap, so it needed a new P-Trap. This turned into another nightmare because they had to order the right part. The first attempt at this ended up with the supplier sending the wrong part. Then, several days later, they sent the right part, but it was missing one of the required attachment fittings.So on and on it went......

Then, to top it all off, I finally went to pick it up, only to discover a problem with my front trailer brakes locking up under certain circumstances. So this ranks right up there with some of the worst trailer service experiences I have ever had. One thing I will never dispute - tent campers have it SOOOOO much easier than those of us that haul the boxed metal RV's around. Although they have to do without many conveniences and amenities that an RV provides, the reality is that RVs are pretty much an extremely condensed version of a second home, with many of the conveniences that a normal home provides.

Unfortunately they also require even more maintenance than a regular home to keep them operating properly, because of the pounding and vibration that they take while moving on the road. This is not unlike the maintenance requirements of an airplane, due to the vibrations and high stresses that they must endure. So I consider all the RV maintenance I have to perform as a kind of preparation for the airplane maintenance that will be required eventually.

A couple of years ago, while departing Omaha, Nebraska enroute to Oshkosh, I encountered some of the worst road construction I have ever experienced in my life. I literally think that they forgot to leave cones up along a stretch of I-80, and as a result, I literally thought that the entire frame of my trailer was going to be ripped apart,  not to mention my truck.It's things like this that force you to keep maintaining the unit every year. 2000 mile long trips are also not the normal expected trip length for a small travel trailer. So I also need to pay extra attention to making sure that things like the welds for the spring suspension, the axles, and the bearings are all in tact.

Anyway, now that I have my trailer back, it was time to start on my usual list of chores and checks that I always have to perform when I prepare for the 2000 mile round trip to Oshkosh from my home here in Denver. After spending most of the weekend checking everything out, it looks like it should be ready for the next journey to Airventure, assuming my trailer brakes are working properly. I will be conducting more tests on those in the weeks to come, but everything else seems to be in good working order.

Since that took up most of my weekend, not much done on the plane. However, I did finally get up the courage to perform the edge bend on the left wing LE skin edges using my edge forming tool I mentioned in the previous post. I struggled a bit with how I wanted to do this. I was concerned about securing the skin to keep the edge from moving while I ran the tool across it. I did not want to reattach the ribs because this would have contaminated the cleaning job I did several days ago. So I came up with what I thought was a great plan - I would use a ratchet strap and my wood forming blocks shaped like the wing ribs to force the top skin down into its finished shape and hold it tightly in place. This did not work for a number of reasons - the main one being that the wood rib forms stuck out a little too far and would interfere with the tool, which requires about 1.25 inches of clearance to allow the slight bend in the edges to be formed.

So I abandoned that idea for a much more low tech solution as shown in the next pic:

I slid the skin as far out onto the edge of the table as I dared, and placed some weights on the skin. In retrospect I should have clamped the bottom skin down, but I got lazy - and paid the price for it. The first edge to be formed was the top one. I did my best to follow the setup instructions from Cleaveland tools, and then got ready to form the edge. The tool was drawn across the edge after being clamped to the skin. the slight bend, or crease in the skin as I prefer to call it, was formed as expected with no issues:

The last pic that I have shows where things did not go as planned because I did  not flip the skin and re-clamp it tight to the table. Instead, after I finished forming the edge of the upper skin as shown above, I decided to leave everything in place and turn the tool upside down so I could do the other edge without rearranging the skin.Notice the multiple lines in the next pic where the tool slid off the edge because I was not holding it properly. Fortunately this is not seem to deform the edge of the skin at all, so I think I am OK. If I had made the same mistake that many other builders do when they use this tool by tightening the clamping pressure of the tool on the skin too tightly, it could have been a much different story and a very bad outcome.

I basically went back over the bad areas where the tool slipped and reran the tool over them once or twice to make sure then bend was applied in all the right places. The slight line that runs through each rivet hole is the correct indication that the bend has been applied properly to the edge. This should keep the edges from curling up and creating a gap between the skin edge and the wing spar when they are riveted in place. Glad to get that over with. Now I can focus on getting some parts primed and reassembled so that I can keep moving forward.

KPR.

LE Prep Episode 3

Edit 6-9-17 - I revised some of this post to make it more readable, and also to correct a gross oversight on my part.  I previously used the term "kerf" to describe the process of applying a small bend in the edge of each skin so that it provides some spring back when riveted in place to prevent the edge from curling upward and creating a gap between the two surfaces. This was not the correct term to use, as kerfing is an entirely different procedure for a different reason.

The other problem with this is that in previous posts from long ago when working on my rudder I may have also referred to this process as "rollling" the leading edge, which is also an entirely different procedure for a different purpose. The problem is with the way the edge forming tools is contructed. It is basically a set of modified locking pliers with a set of custom-positioned rollers welded on to the ends of the pliers at a pre-determined angle. The "rollers" on this edge forming tool can be confused with the term "edge rolling," and thus the confusion.

SO let me stand corrected - the official name of the tool that I am about to use is an EDGE FORMING TOOL. It uses a set of rollers to force a small bend in the edge of the skin. This process has NOTHING to do with kerfing, which is a procedure that awaits me whenever I get back to working on the main wing skins. There, now I feel better..... ----------End edit.

No pics tonight. One other thing I almost forgot about was the outer edges of the LE skin. So I went out last night and ran my finger across the edges, and it took less than a second for me to discover the same small bumps about 3 inches apart from each other along the edges. These are the separation points where the skin is still attached to the metal blank that is placed into the CNC machine to perform the initial cutout of the LE skin. Vans does not remove these seemingly minor bumps from the skins. They can, however, act as stress concentration points, and could cause metal fatigue and cracking if they are not smoothed out.

So, like everything else with this kit, all these little bumps along the edge need to be filed and smoothed. I used my flat jewelers file and a piece of 320 aluminum oxide sand paper glued to a 1/2 inch wood dowel to file and smooth all of the bumps. I also had to residual scratches that needed a bit more work to smooth those out before priming everything.

A call to Vans also revealed two more things. I need to slightly round the corners to get rid of the sharp corners - another potential stress concentration point on the skin. They also confirmed that I will want to slightly bend the edges of the LE skin where they attach to the wing spar flange. So now I have to find my edge bending tool, practice with it on some scrap metal, and hope like heck that I don't screw up the edges on the LE skin. I think I will need to clear off a large area on my work bench so I can clamp down each skin edge so I can use both hands to draw the edge bending tool along the skin edges.

As I recall, one problem many builders were having with applying this small bend to the edge of the skin was that they were using the tool incorrectly. They close the pliers too tightly so it is extremely hard to run the rollers across the skin to achieve the small bend. Then, when they start to apply the bend the rollers slip off the edge, messing up the edge of the skin along the way. Only slight pressure is needed on the skin while the tool is drawn toward you to create a very small and barely noticeable bend on the edge of the skin.Cleaveland Tools now has a video on their website that demonstrates how to set this tool up and use it properly.

Tomorrow I will probably scuff and clean the subskin, apply the bend to the edges, and on Thursday I should be ready to prime a bunch of metal again. Then more assembly, measuring, disassembly, cutting, deburring, etc., etc.

And to think I was going to have my fuel tanks done by the end of this summer - yeah right!

KPR.

LE rib and skin prep for primer - part 2

Had some family obligations this weekend, so not a lot of time spent on the plane, but I am inching ever closer to spraying more of that expensive epoxy primer on my remaining LE parts. Here is pic that I love showing to folks so they can see the difference between brand new "tools" and what it looks like after you use them during the build. On the left is a brand new, as yet unused medium grade (maroon) scotch brite pad. On the right is the one that I started using when I prepped the first two LE ribs and a couple of other parts. Since then I have prepped the 4 remaining LE ribs, and the interior LE skin.

When prepping my main wing ribs for primer a long time ago, I decided to follow a practice that Steve Riffe used to clean his parts prior to priming them. I took two orange HD buckets, filled both with warm water, and put Dawn dish soap (original formula) in one of them. I have found that the subsequent cleaning with acetone goes much faster if the most of the grime and residue has first been removed by washing the parts with Dawn first. It does not take long for the soapy water to turn pitch black, and I am always amazed at how filthy the parts actually are. Anyway, I set up a wash/rinse routine for the 4 remaining ribs, using a scrubbing sponge with the green scuff pad attached to one side.

I have not yet done this for the main wing skins, and I had not used this method for any of the other larger skins yet. But since I needed to prime a larger-than-normal part of the interior LE skin due to my subskin that will be in contact with the interior of the first bay of the LE, I decided that I would also try the same washing method I used for the ribs. Obviously due to the size of the LE skin I could not dunk it into the buckets like I did for the ribs, but I did use the sponge to wash the interior as best I could, and then wiped it dry with a micro fiber cloth. It seems to have worked well.

Prior to this I realized that I had not yet deburred any of the edges of the access panel holes or the outer edges of the LE skin itself. So I took my edge deburring tool and took care of that. this also raised a question that I will need to get answered from Vans or from someone on VAF. I am not certain if I am supposed to kerf the edges of the skin where they will attach to the main wing spar flanges. I think that I still need to do this, but I need to make certain.

I only question this because these skins are supposed to butt up very closely to the main wing skins and the fuel tank skins. I don't know if kerfing the LE skin will introduce a larger than desired gap between the main skins ant the LE, or if this is still necessary regardless, so that the edges of the skin will lay flat against the wing spar flanges when riveted in place. If I find out that I need to do this, I will need to find my edge kerfing tool from Cleaveland Tools, that I haven't used since I put all the tail feathers together.

Next is a pic of the 4 ribs all scuffed, cleaned, and final cleaned with acetone and a microfiber cloth. when you do multiple parts like this, especially those that need to be assembled in a very specific order, you have to devise a method to keep each part organized, since all prior identifying markings will be removed during the cleaning process. In this case, I kept the ribs organized by keeping them stacked in a very specific order each time I scuffed or cleaned them. I lined them up on the table after cleaning them so that they were in the same position that they will be installed in the LE from left to right. The end rib flanges face a different direction than the rest, so that one is easy to spot. But the others are exactly the same rib, with the same rivet holes and flanges all facing the same direction. Keeping them in order is very important, since even small variations in the match drilling process can make a difference in the final fit of the parts when they are riveted together. After they are primed I will put some tape on them and mark the rib position on the tape.

And finally a pic of the wing skin all washed and ready for primer. After the suds bath all scuffed metal was final-cleaned with acetone and a microfiber cloth (my carcinogen of choice for cleaning metal). I used chemical-resistant rubber gloves to keep it off my hands. These are the long green ones at the bottom of the pic. Also shown are a large number of microfiber towels that need to go in the washing machine so I can try to reuse them. Suggestion: do NOT put these in with any other clothes. Best to keep the airplane building/chemically-laiden materials away from other things, just in case.

Since I will most likely need to use a bit more primer to cover these parts than I did for the last batch, I will plan to use my HF HVLP spray gun, since it has a 20 ounce cup and larger spray area, compared to my touch up sprayer than only has a 7 ounce cup.I think that one full cup-load of primer from the HVLP gun will cover the interior skins and the 4 remaining ribs.

I will probably scuff and prime the entire subskin as well, since I have not yet determined the final form of this part, and I can't really do that until I have this access panel mess taken care of once and for all. One nice thing about living in Denver is that I don't have to worry about surface corrosion very much. So I can leave the scuffed parts till tomorrow, when I have more time to set up the sprayer and everything else that has to be setup for priming.


Till then,

KPR...

Deburring holes and edges, scuffing ribs and LE skin for primer

 First things first - a shout out to fellow RV-8 builder and friend Steve Riffe, now living/flying in the Dallas area. We started our tail kits at about the same time in 2009, and he just received his airworthiness certificate for his finished airplane. N ow he can take his first flight and continue with phase 1 flight testing. See post on VAF here , and his builders log is at this location 

Its really great to see another soon-to-be-flying RV-8 make it to the finish line. Way to go Steve!!!!

Over the past several days I have been taking care of several small jobs. The first involved more trimming of the Left wing LE skin edges for the new access panel. I discovered that one of the edges was decidedly not aligned with the corners and was not straight. So I took a straight edge ruler and marked "straight" with the sharpee, and then carefully took the file and trimmed down the metal, being careful not to dig any more ridges into the skin. This next pic shows the result:

If you click on the above pic and view it in a larger resolution and look at the left and right edges you can see the problem. What happened is I filed away a little too much metal on the skin edges. leaving a small gap between the access panel cover and the edge of the LE skin.This happened because I forgot to stop filing after reaching the INSIDE edge of my sharpee line. Instead I kept on filing until the sharpee line was almost gone. Even the ultra fine sharpee can leave at least a 1/32 or 3/64 inch wide line, so you have to remember where to stop removing the metal.

Here is a close up that shows the gap better:

The funny thing is that this gap is much smaller than the Vans access panel and cutout for the original access panel LE skin. I think I have seen posts from other builders where they actually fabricate a new panel cover so that it fits better. Perhaps I will do the same, but for now I will leave it. I still have a lot of surgery to do to figure out how to close up the original hole, and right now that is just a bit more important.

Next is a pic showing the vinyl that I removed from the tip of the LE and the outer races for the rivet holes for each LE rib.

As I mentioned before, I am pretty certain that leaving the interior and exterior vinyl on the pre-bent edges of any skins applies a bit of extra force away from the wing ribs, making them just a little bit harder to bend into position when assembling the ribs. If you remove the vinyl from this area it reduces that stress a bit. Works for me. YMMV.

With the LE ribs completely disassembled I starting scuffing them in preparation for primer. I still need to clean them, but at least the hard part is done:

A couple of important notes about this for other builders. even though I took the time 2 years ago to use a small jewelers flat file to remove the bumps that result from the factory bending of the tip sections of each rib, I found that all of the ribs still needed to be filed a bit more. You can see the file I used in the middle of the above pic.

I made sure I rechecked all of these on each rib, because I was surfing the web one day and found a PDF file link to what I presume to the the new Section 5 of the Vans manual for the RV-14, which is much more informative and contains a lot more tips and tricks than my older Section 5 contains. One of the sections specifically called attention to making sure you do whatever is necessary to remove ALL bumps on the front of all leading edge and fuel tank ribs to prevent bumps from appearing in the skin when you start riveting everything together. they even had pictures and diagrams of how this should look.

My litmus test for this is a little bit visual, but mostly by feel. I ran my fingers over the tops and bent sides of each cutout on each rib, and if my finger gets stopped by a ridge, I went to town on it with the file until is felt reasonably smooth. I was surprised by how much more I had to dress these edges out until I was satisfied that they were smooth enough. It will shock you just ho much you need to thin down the edges of some of these sections. don't be bashful about this trimming if you don't want bumps in your LE wing skins after riveting.

I should have mentioned that prior to scuffing everything I deburred all the rivet holes in each LE rib. I honestly do NOT think I had ever deburred any of these holes in the remaining ribs, while i definitely deburred everything involved in the area of the mod that I am doing, I don't think the LE holes had ever been disassembled beyond that. I was amazed at how much some of the holes needed to be deburred.

One of the hardest things I had to do was deburring the inside of all the rivet holes that attach the top and bottom of the LE skin to the wing spar. The outer holes were easy because they are right in front of you, but I must admit I was not prepared for the need to do all of the inner holes. These were a pain for several reasons:

- They are hidden under the wing spar flanges so you have to bend and contort your body in weird ways to get to them all.

- With one side of the main wing skins clecoed in place, I was not able to get my electric drill with my deburring bit into position to debur one side of the holes. The other side was easy because the wing skin was removed. While I suppose I could have removed the mounted wing skins, I did not want to do this because they do help maintain the structure and placement of the frame. So I took the deburring bit out of my drill as I have done before, and twirled it between my fingers, while contorting myself even more while trying to blindly fit the tip of the bit into each inside hole. Easier to demonstrate than explain, but lets just say it was a major pain in the butt, and it leaves my fingers in a rather raw state after doing this for about 100 holes or so. Anyway, the wing spar holes are now deburred as well, so mission accomplished.

Here is a pic that kind of shows the area that needed to be deburred. I only focused on the top row of rivet holes for now, since those are the holes for the LE skin. I will have to do the bottom row of holes when  am ready to finish prepping the main wing skins, but that can wait.

And then finally, after a bit more precise vinyl removal on the inside of the LE skin, I started scuffing the inside of the LE skin. What follows is a series of pics that shows the overall scuff job of one side, and what appear to be rather deep scratches from all the mod work and fitting, installing and removing parts multiple times, and how those scratches seemed to scuff out pretty well with the scotch brite pad, indicating that the scratches were probably only as deep as the alclad coating of the metal.

And finally, since I will be priming another small batch of parts in the near future, I needed to get two more turkey basters to measure out both parts of the primer, just as I did a few weeks ago. Here is the uncontaminated "new" turkey baster that I got from King Soopers.

Next steps are to finish scuffing the other side of the LE skin, then wash and clean the ribs and skin, then prime them. Once that is done I will reassemble the LE and attach it on the wing spar so I can mark up the subskin for the new access panel opening and start trimming that lovely piece of metal to its final form, whatever that may be!

KPR!

Deburring Holes and removing More Blue Vinyl.

No pics tonight - just a quick update on the LE progress. I reviewed the work I did on the new access panel opening. I still have a bit of edge trimming, smoothing, and deburring to do, but other than that the panel opening is pretty much done. I am now mired in thought about how to manage the panel attach brackets for both holes. This is perplexing for me because I really want to trim away as much of the subskin as possible to lighten it up, but still leave the proper amount of material to serve as the mounting platform that I need.

After thinking about it, instead of jumping in a reassembling everything so I could put the LE back on the wing spar, I realized I needed to do some serious deburring of all the holes in the LE skin. I finished deburring all the new holes I drilled the other day for attaching the access panel attach bracket to the LE skin. But then I realized that most of the blue vinyl has remained on the LE skin since I received it many years ago. Even though I had match drilled all the rib holes and the wing spar attach holes, I have never fully deburred these holes, and so this was long overdue.

Before I could start deburring those holes, I needed to remove some vinyl using the tried and true soldering iron method and a straight edge. One thing about this that I ahve contended all along, is that this vinyl is a real problem with pre-bent surfaces such as the LE and tank skins, and the skins for the HS and the VS tail sections. The reason is that none of these skins is form fitting to the underlying rib structure. The skins are only pre-bent so far, and must be forced into their final positions over the substructure. This is how stressed-skins are designed, so that the skin ends up providing a certain amount of support to the total structure. The vinyl around the outer edges of these skins acts as a deterent to bending the skin to its final shape, especially the outer vinyl that goes around the outer leading edge of the skin.

I made a point to remove the vinyl in this area when building the HS, but somehow forgot to do this on the LE skins. So tonight I finally removed the small section of vinyl across the outer and inner edges of the front the LE skin. I also removed the vinyl along the rear spar attach holes and along the outside rib holes  I had managed to remove the vinyl a long time ago where the rib flanges meet the inner skin, to ensure that the rib-to-skin fit was as form-fitting as possible. But that was the only vinyl that I had removed after all this time.

Anyway, I got all the vinyl removed, saw how badly I have botched the rib flange rivet holes for those first two ribs that I have been working on for so long by having to re-drill through them way too many times, and did my best to debur those holes as much as possible. I am now fearing that those holes are much too big for a standard AN426 AD3 rivet, and I my be heading for ordering a new LE skin. But its a bit too early to throw in the towel, and I really won't know how bad this is until I dimple everything and prime it and start riveting.

Every time you have a pre-bent skin, there are 4 sides that have to be deburred - 2 on the outside and two on the inside. I managed to debur the holes on one of the outer sides tonight, so I have 3 more sides to do. I had almost forgotten how much "fun" it is to debur a million holes in a complex piece of aluminum. There sure was a lot of metal shavings on the ground after getting rid of all the burs that were in the holes on the skin - makes me a bit nervous since this skin is only .025 inches thick.

After I get all the skin holes deburred I think I will go ahead and debur and re-straighten the rib flanges, then scuff, clean, and prime the inside of the skin and the remaining ribs.I don't think I will dimple everything until I reassemble the LE again on the wing spar and get the panel attach bracket and subskin plans figured out, and the rear rib flanges drilled out. Once that goes well I will probably try to dimple the LE skin and ribs and the subpanel and see what happens. Lots of work to do yet, and I'm still not quite sure how it will turn out.

KPR.

Cut the New Access Panel Hole in the Left Wing LE Skin

As I hinted in my last post, the new access panel from SafeAir ends up overlapping the access hole that Vans had already cut in the bottom of the Left Wing LE skin. So the mission became cutting the opening for the new access panel and figuring out how to seal up the existing one. Where this becomes a bit complicated is trying to account for the space of the underlying support/attach brackets for both panels, because these also overlap each other on the underside of the wing, and are larger than the removable panel since they have to permanently attach to the wing skin while also providing enough metal to serve as the mounting flange for the panel.

The last piece of complexity for this whole mess is a decision that I have to make about the subskin I am fabricating. In a previous post titled "Getting Ready For The Big Cut" I mentioned that I was getting ready to trim away a lot of the subskin structure as it would not be needed. the only reason I had not done that already is because I needed the full skin in tact so that I could accurately match drill rivet holes in the skin, the subskin, and the two rib flanges, and I also was not certain where I was actually going to trim the subskin for its intended purpose - to serve as the mounting platform for my detachable leading edges I plan to fabricate.

After reading the instructions that came with the SafeAir access panel kit, I decided to start with cutting the new opening for the new access panel. they give two measurements that I think I have already mentioned - 6 inches and 2.25 inches, to locate the new panel.I measured and then drew the outline on the Le skin.then I had to determine what radius was used to create the new panel, because it was obvious from looking at it that it was not the usual 1/8 or 1/4 inch radius, and was much bigger. After some creative measuring with a plastic hole template that I bought from a school supply aisle at the store a long time ago, I determined that the radius was 1/2 inch.

This then meant that I needed to buy a new unibit (step drill) from HF aircraft supply that had a 1 inch diameter step, as none of the ones that I currently owned were that large. Before I could drill the 1 inch holes in the Le skin I had to measure the radius of .5 inches by measuring that distance along the straight edge on either side of each corner. Where the lines cross is .5 inches. then I decided to place the pilot hole just a bit outside of that mark, because you need to leave some excess material and file your way down the final fit to ensure that the access panel fits nicely into the opening. This next pic shows the .5 inch marks and the #40 pilot holes I drilled:

The next reality was that in order to drill the necessary 1 inch holes with the new unibit, I would have to be able to raise up the skin by just over 1.5 inches to allow enough clearance for the drill bit. So I took some 2x8 pieces of wood that I use to level my trailer tires when I camp, and some spare wood that I still had from when I cut the LE rib templates for bending the subskin, and I placed them on my work table. Then I tool a 3/4 inch thick and very long drill board that I had not used in a very long time, and placed it on top of the 2x's, giving me plenty of clearance for the drill bit. I also needed to make sure that the wood was placed directly under the wood to keep the unibit from severely marring the metal.

I mounted the bottom of the LE skin on the drill boards and clamped everything down. Here was the first hole, all drilled using my cordless electric drill. I went slowly and took time to clear debris from the hole to allow the drill bit to continue cutting. In the next pic you can see how much excess material I left between the edge of he hole and the traced panel line around the corner (about 1/16th of an inch or slightly more). Having gone through the entire procedure now, in hindsight I would have left less material to remove around the edges, because it took a lot of filing, sanding, and smoothing to get the fit just right for the panel. But at least you can definitely verify that this was definitely using a .5 inch radius:

Here is the clamping arrangement of the table and drill boards:

I had to adjust the LE skin a bit for the third hole due to the width of the 2x8 not being quite wide enough to drill all three holes. After that was done, I ended up with three pretty uniform holes:

Then came the cutting of the rest of the metal. I used my Dremel tool with a flex shaft extention and an EZ lock cutoff wheel. These have seemed to serve me pretty well in the past, and this time as no different. This is always nerve racking, however, because it is very easy for these 30,000 RPM cutting wheels to decide to grab the metal and completely destroy whatever you are trying to cut in a matter of split seconds. SO I mounted the actual Dremel tool on the shaft of one of my clamps that I intentionally mounted independently on the work table, so I could use both hands to control the flex shaft and the cutting wheel. this actually went fairly well.

Prepping for the cut. It tool several episodes of clamping, cutting, repositioning, and reclamping to put the metal in just the right spot to cut each of the 3 sides. Sometimes you just have to get creative and use whatever is around:

After cut number 1:

The goal is always to cut away from the line a bit to ensure you don't mess up the cut. IN this case the task was to remain inside the lines of the panel.

Repositioning and reclamping for the next cut:

And after the second cut:

And after the third and final cut. Normally there would have been 4 cuts, but since the existing hole was already there, only 3 cuts were needed:

Next came the task of slowly filing away the remaining material up to the lines drawn around the panel. I used a normal, fine tooth, straight flat file, and even my cut off wheel in a rather unique fashion that I have never tried before, to trim the corners and the straight edges as much as possible. Then I resorted to a 1/4 inch sanding drum with the Dremel tool to perfect the corner areas, and to blend them with the straight edges. A word to the wise - be very careful using the straight file, as it is very easy to create a ridge of metal or to cut too deeply if you are not paying attention. this is always an exercise in patience and in removing very small amounts of material and constantly checking the result to make sure you do not over-do it. I almost made that mistake with the cutoff wheel in one of the corners, but I think I averted the problem after smoothing the corner with the sanding drum. This next pic shows I am getting close but not quite there yet.

After finally getting the fit to be acceptable to me, It was time to fit the mounting flange for the panel by clecoing the panel to the flange in an upside down manner and using the panel to center the flange so that the flange mounting holes can be drilled into the skin. I have not had to deal with this sort of thing ever since I made my first flange in the Sport Air sheet metal class that I attended many years ago.  So everything was an adventure into the unknown. As long as you do a good job cutting out the access panel opening in the skin, the flange should line up exactly like it is supposed to. Mine was not totally perfectly aligned, but it was close enough for me.

I had to readjust my table setup again to allow a gap between the edges of the skin and the new access panel opening to allow room for clecoes to be inserted without interference from the wood underneath. Here is how I setup for that:

Once the panel is centered in the new access hole, I used a couple of cleco clamps to hold the flange in place and then started to drill the #40 rivet holes through the flange and the LE skin. Only the outer holes are drilled as these are the mounting holes that attach the flange to the skin. the other holes are for the nut plates that the panel will screw into. The larger holes are predrilled in both the panel and the flange to #30, and the panel is attached by some #30 clecoes to the flange.

I could not drill 5 of the holes as these are the ones that overlap the existing hole that I will need to fill in after this lovely task is completed. Here are the clecoes in the holes that I WAS able to match drill:

And finally, from the back side of the LE skin, it is a bit hard to tell from the pic, but I think that the fit of the panel looks even better than I thought it did. When this is finished, the flange will be mounted on this side, and the panel will be on the other side (reverse of what is shown now).

My next steps are to mount the LE back onto the wing spar for the 10 millionth time and reattach the subskin. I still have to decide if I want to trim the subskin away in these areas for the panels, or if I want to use the subskin as the mounting flange.for the panels. This would be relatively easy enough to do now that the flange mounting holes have been drilled into the LE skin. All I have to do is match drill them again into the subskin once it is mounted in place to the LE.

I have to figure all this out to determine how to trim the subskin to its final form. I also need to drill the rear rib flange to wing spar holes in the newly modified 408 rib. Then I will have to remove it yet again to debur the holes. This process just seems like it will never end, but at least I am making progress, regardless of how slow it might be.