Back to work - Tech Counselor Visit and Access Panel Progress

Technical counselor Jim Elliot come out to the house to check on my project and answer some burning questions about my current dilemma. Jim has built or helped build many experimental aircraft and has a great deal of avionics, electrical, and mechanical expertise in all types of aircraft. So it was a great relief just to have someone with that kind of experience help sort through these issues.

The wallowed out holes on the tips of the first two ribs are still going to be a challenge, but  thanks to Jim I now have a plan of action to try to address that problem, and several possible solutions depending on what happens. He also answered several questions about rivet and nut plate placement and effect on loads being applied in certain areas as it relates to the mod that I am working on. I'll detail that more later.

For tonight, I'll just focus on the question about how many rivets I need to put in the plate that simply covers up the old hole. I was glad to hear Jim tell me that I do NOT have to turn that plate into a piece of Swiss cheese by drilling a million rivet holes into it. I only need to place enough rivets around the perimeter of the plate. The reason I am able to do this, however, is not immediately obvious, and all the books that I read to try to find an answer to this question did not really address it much.

The reason why I only need perimeter rivets is that the loads for the majority of each bay of the LE are carried by the rivets that attach the skin to each rib flange. The mounting brackets for an access panel act as I stiffener to help replace some of the strength that is lost when the hole us cut out. The last part of this has to do with the objective to ensure that the loads being applied to the LE while standing still and while flying are allowed to transfer across the structure as designed, without being concentrated too much in one area. For this reason only a minimum number of rivets should be used in areas other than the primary area where loads are designed to be transferred across the part, i.e. the ribs.

So Jim told me to use the width of the nut plate rivets that otherwise would have been used to attach the nutplates for the mounting screws as a guide, and to try to apply rivets around the perimeter of the plate using that spacing. the #8 K1100 nut plates have a rivet spacing of 22/32 of an inch, or 11/16ths. Tonight I started measuring out the rivet line around the perimeter and pre-punched a few of them. Here is pic. I am using 1/4 inch spacing around the edges and will fill in the remaining gaps using the nut plate rivet spacing as much as possible.

Ona final note, yesterday was the first time I had removed the entire LE assembly from the wing since I fabricated the new access panel hole in the subskin and created the patch plate for the old hole. I was also very happy to find that the holes I had drilled through my fabricated rear rib flange additions to the second rib appear to have worked out fine as far as edge distance is concerned. SO no more worries about that.

A lot of stuff about a stupid patch plate, but at least I have a plan to move forward.

KPR

One last bit of metal work before heading for Oshkosh 2017

Yes this post is coming well after Oshkosh. I got slammed with way too much stuff to do after I returned on August 2, so I have been a bit busy with other things, like:

Online course from King Schools to renew my CFI certificate - Completed after 2 weeks
Medical renewal due by the end of August - In Progress
Niece's Wedding on August 18
Preparation for upcoming hunting trip on the Labor Day weekend
And so on

More about the medical and the Oshkosh trip later on. Best way to sum it all up is "BEST AIRVENTURE EVER!!!!!"

Anyway, back to building airplanes. I was able to do a little bit more fine tuning of the fit of the metal access plates after completing the rough cut of the new access panel hole. This next pic appears to be a fitting of both panel plates. Also note that I have the SafeAir mounting bracket installed over the new panel cover and the filler plate. I think this was prep for drilling out the screw holes with a #21 drill bit per instructions to prepare for the dimpled #8 screw hole. I also think I was trying to visualize the layout of the mounting bracket compared to the filler plate.

The next one shows the different files I used to smooth out the edges and the corners of cutout area for the new panel:

Next is a close up showing the fit between the two plates after drilling all the holes using the mounting bracket as the template:

And another shot after doing some serious filing and sanding of the filler plate edges, especially the radius where it fits up against the lower right corner of the new access plate:

This next one is a bit hard to see, but the gold #30 clecoes have been replaced by the larger black 5/32" clecoes after enlarging the #30 screw holes to #19:

And the next one with the cover plate intalled again to recheck the fit after the larger screw holes were drilled:

And the next with most of the clecoes removed to show the larger holes now drilled into the cover plate AND the subskin:

And finally the subskin/mounting flange with the access plate removed showing the clearance of the new larger screw holes and the mounting area of the subskin.

That last pic above also shows how much smoother the edges of the cutout are. I spent  significant amount of time filing and sanding the edges down. I am not quite finished with them but they are very close.

Now for the dire news......
I spent a very large amount of time reviewing AC43.13 and another source book for airplane builders trying to answer sme very straight forward questions:

1. With my current situation on the bottom part of the leading, how many rivets do I use to permanently attach the cover plate to the old access hole?
2. What do I have to do with the subskin to ensure that this mod has not:
a. Added more strength than required or desired to the area than originally designed?
b.  ensure that the correct amount of support has been added to the entire area to compensate for the loss of strength in the area due to the extra hole in the bottom of the skin.

If you think you can take any of this lightly you are sadly mistaken. You cannot build this structure too strong or too weak, or the results may be disastrous. AC 43.13 contains information about accepted methods to repair metal (Chapter 4). Unfortunately they only discuss applying a "patch" to a torn or damaged area of the skin.This is not really a tear or damage, but a previously fabricated area of the skin that was cutout. It has more than adequate support to attach it to the subskin, If I apply certain formulas that the book provides to determine the number of rivets, it would require a very large number of rivets. So I am now involved in yet another issue of trying to figure out the accepted method to attach the filler plate. I may even need to seek the advice of a DAR that is knowlegable in metal and structural repair to get proper advice on how to address this. What a mess I have created.

I haven't even got to the best part yet. With all the drilling and re-drilling of rivet holes into the LE skin, I have managed to wallow out several holes in critical areas near the extreme LE of the first Rib. These may even be too large for me to attempt to use an "oops" rivet. While at Airventure I got some input from Mike at Cleaveland Tools after explaining my problem, and he said that if the holes are larger than #36 or so then I may not be able to use the #40 dimple die to set the dimple in the hole. Many of the holes appear to be larger than that. The problem is that the dimple will enlarge the hole a little bit, so if it is already too large, well, you get the idea.

So because of that alone, I may have to abandon this whole mess and buy a new LE skin and ribs. This is the part that you dread when you attempt to do a mod. You think you have it all figured out, but you find out very quickly that metal is not as forgiving as other materials. I think I will seek out a technical counselor at this point and see what they think. Personally I am about ready to abandon this whole idea so I can build the thing and get it flying. Months and months of wasted time and energy.....

New Access Panel Hole Created

With some careful planning and delicate surgery with a Dremel cutoff wheel, I was able to drill 4 individual 1/4 inch pilot holes on all 4 corners of the subskin where the new hole for the new access panel needs to go, and then I set out to cut out the new access panel hole. I had to remove different sections of clecos to allow 2-handed access with my flex shaft and cutoff wheel assembly as shown in the photo:

I mounted the actual Dremel tool on a bar clamp that I mounted on the work bench near the location on the wing where the cutting work needed to take place. You have to allow enough clearance for the bend radius of the flex shaft tool, so proper positioning of the tool was important.this setup allowed me to keep 2 hands on the flex shaft handle while carefully cutting along the previously drawn cut lines on the subskin.

It is very easy to watch these cutoff wheels suddenly develop a mind of their own and completely ruin in a split second whatever you are so painstakingly working on. So when accuracy is required, the key to maintain solid control of the tool with both hands to to go very slowly, and ensure that the tool is positioned comfortably and correctly to make the cutting as easy as possible. My other trick is to use a plunge cutting method instead of trying to cut the entire edge like a saw. This way you are cutting small sections of metal with the wheel, overlapping the previously cut section as you go. It only jumped on me once, and it did not jump very far since I had both hands on the tool and I was ready for it to do that, so I consider myself lucky once again.

Here is the result after cutting all 4 sides with the wheel. I would remove all interfering clecoes, test fit the tool and do a non-powered dry run to ensure the cut would go as planned, and then turn it on and cut one side, Then I would shut it off, re-position the clecoes, and do the next side, I did the left, bottom, right, and finally the top side. I cut just inside the drawn line to ensure that I did not cut any metal outside the lines, since space is tight as you can see, and the resulting cut line is very close to mounting surface for the nut plates.

And a close up of the part now "removed."

I guess I should also mention that to drill the 1/4 inch holes accurately on all 4 corners, I measured 1/8 inch from both sides of each corner, drew intersecting lines, and then used my hole punch to mark the 1/8 inch radius spot for the drill bit. Then I started each hole by manually turning the drill chuck to ensure that the bit was positioned correctly, and then I pulled the trigger on the air drill and finished drilling each hole.

The last pic for the evening shows clecoes now occupying the holes around the perimeter of what would have been the mounting flange of the pre-cut access panel hole that Van's created at the factory. (The one that I now have to fill back in since I am using the new one.). I decided to go ahead and drill and rivet these holes just to allow the subskin to support the LE outer skin in that area, since so much material has now been removed. I am still a little concerned about strength in this area, but I think the subskin provides more than adequate stiffening of the area, especially since the edges of the subskin rest over the tops of two LE ribs.

Next steps are to get the files out and do some more critical surgery to smooth out the edges of the new hole, and also to trim and final-form the odd shaped piece of metal that I had to cut to fill in the space from Van's old hole. Sure will be glad when this stuff is all done. The time suck for just this little thing has been enormous. I can only imagine what putting nut plates and screw holes in all the floor panels of the fuselage is going to be like when the times comes.

I also had a revelation today while at work. For some reason I had been thinking that I still had over one and one half weeks left before I would be leaving for Oshkosh. Then I looked at a calendar and realized that one week from today I will once again be on the road for the greatest aviation show on the planet. Very cool........

That's all for tonight.

KPR

Drilled the Rear Rib Flange Holes and Created Template for Covering the Old Hole

I managed to get up enough nerve to try to drill the two holes in my custom rear rib flanges of the second 408 rib. I used my 12 inch extension #30 drill bit and tried to apply enough force toward the inner part of each flange go ensure that my edge distance would be maintained. After drilling the holes, I checked the result using my hand-held mirror and a flashlight. The results looked promising.

I could not take off the LE assembly yet because I still have some custom work to do to fill the void created by the old access pane hole that Van's pre-cut into the skin. To begin, I took rough measurements of the major part of the hole, which was a square measuring 4 7/8 inches on all sides. I then grabbed an old file folder and applied those measurements to it:

Then I cut it out, being careful to apply a little extra material but cutting just outside the lines.

Then I removed some of the clecoes holding the new access panel cover plate on the bottom, and slid the paper template up and underneath the panel cover while aligning the other edges with the edges of the LE skin:

Then I traced around the edge of the bottom right side of the new panel cover to transfer the contour of that portion of the panel onto the paper template. Then I removed the template and cut out the area taken up by the new panel cover. This left the rough dimension of the area that needs to be filled after the new panel cover is completely installed.

The next step involved carefully checking the thickness of the new cover plate and trying to find some scrap material of the same thickness. Frankly I am a bit confused, because I think the outer skin is .028 inches thick, and it would stand to reason that if you are filling a hole surrounded by a .028 inch thick skin that you would want to use a piece of metal that was also .028 inches thick. However, when I checked the thickness of the new SafeAir cover plate, it is only .025 inches thick. So I do not understand the mismatch in thicknesses, but it could also be that I am mistaken, and the outer LE skin is also .025 inches thick.

I searched everywhere for some .028 inch scrap aluminum but could not find any. I finally settled on using some .025 inch thick 2024-T3 aluminum from my trim bundle kits for the empennage and wing kits. I taped the template to the metal and drew the outline. This is where I called it a night.

Next steps are to cut out the part from the scrap metal, debur the edges, and start final fitting and trimming it to the old hole. I then need to determine a rivet pattern to use to permanently attach this part to the subskin.Then I need to drill the holes needed for that.

Then comes the all important critical decision of how to cutout the section of the LE skin and trim the remaining portion of the subskin to its final form.Only then will I be ready to dimple all the holes and rivet the whole thing back onto the wing. So still some significant work to do, but its getting done - one day at a time.

KPR...

Transferred all Holes in the Access Panel Mounting Flange to the Subskin

If you have not quite figured out what I am doing in this series of posts (join the club!), I am basically eliminating the need for a separate access panel mounting flange by creating one out my existing subskin. I originally was not planning on doing this until I realized that the subskin was already going to be there, and would serve as an access panel mounting flange just as well as the other one.

Picking up where I left off yesterday, the next step was to match drill the #30 pre-drilled holes in the other mounting flange, through the predrilled holes in the access panel cover plate, and finally into the subskin at the proper locations. By placing the mounting flange over the LE skin, there is a gap between the subskin and the mounting flange that is filled by - you guessed it, the thickness of the access panel itself. it is pretty much the same process that I had to follow to cut the hole in the outer skin. Everything gets mounted in reverse order. The access panel goes under the mounting flange and over the LE skin as shown below:

My first step in transferring all the holes to the subskin was to match drill the predrilled #30 holes. to start this, I first clecoed all the #40 holes around the perimeter of the LE skin. I then had to line up the access panel cover with the predrilled holes in the mounting flange by hand, because remember, the #30 holes do not exist yet in the subskin, so there is no clearance for them yet. I think I started with the upper middle hole and worked my way around, drilling the hole through all 3 layers of metal, clecoing it, and moving to the next hole. The pic above shows what it looked like after drilling adn clecoing everything. The next pic shows the resulting holes after removing the assembly:

Now I needed to match drill the #40 holes on either side of the #30 holes. These are the rivet holes for the nut plates that will ultimately be installed under the subskin. The #30 holes will eventually be drilled to a larger size to accept the mounting screws for the panel cover.

After having a hard enough time with trying to line up the holes of the subskin, ribs, and leading edge skin, I wanted to make sure that all of these holes were as spot-on the mark as possible. The problem now is that I cannot drill the #40 holes through the access panel cover. Those holes only exist in the mounting flange, or in my case, the subskin. If I don;t use something underneath the mounting flange to fill the small gap between the subskin and the mounting flange, the holes might become misaligned during the drilling process.

So I came up with a plan - I decided to sacrifice the panel cover that Vans provided to supposedly fill their pre-drilled access hole in the LE skin. I used it as a "filler" to fill the void between the subskin and the mounting flange so I had solid layers of metal to drill through.

I started with the lower right corner area by placing the Vans-supplied cover panel over their precut opening as follows:

This allowed me to be able to drill most of the $40 holes in that quadrant into the subskin.Here is the post-drilling pic for that section:

Then I relocated the panel cover to the upper right section and drilled as many of those holes that I could:

Every time I finished a section I had to uncleco everything and reposition the access panel to the next section.Took a little time to do this but wasn't that bad. Next was the upper left quadrant:

And then finally down to the lower right quadrant:

I was able to get all the holes from the mounting flange drilled except for one, which unfortunately is located on the left side just below the middle, right where the Vans hole and my new hole merge together. If I were to drill match drill this hole it would just hit the corner of the outer LE skin. So I have to put some thought in to this hole, which I will probably re-position slightly AFTER I figure out how I am going to fill the remaining area of the original Van's hole.

Anyway, after all this was done, I removed the entire panel assembly again to check my handy work and verify if I successfully transferred all the holes to the subskin. I think it came out pretty darn well:

As further proof, I placed the new access panel cover in its position and, now that all the holes have been drilled in the subskin, I was able to cleco it into position to check the fit:

The inner and outer edges of the panel cover are right up against the edge of the outer LE skin, so I may have to do some trimming to account for vibration and airflow pressures causing the two edges to rub and wear against each other. Vans panel cover was WAY undersized for the hole that they made, and I still can't understand why it was cut so undersized. Anyway, he fit of this new, slightly larger acess panel is pretty darn good, and I am pretty happy with these results.

The last pic is of my now machine gun holed Vans access panel cover. It turned out to be a really good back plate for the drilling that I needed to do. I was OK with doing this because, as you can tell from the above pic, I will need to fabricate a rather odd looking piece of metal to cover up the remaining portions of the old hole. Hopefully the pics make this a bit clearer now.

Next step is to drill the two holes in my custom flanges of my custom rib. I am really dreading this for reasons that I mentioned in my last post. Once these last holes are drilled, I need to fabricate that weirdly-shaped piece of metal to fill the remaining void from the Vans pre-cut hole, and come up with a rivet pattern to attach it permanently to the subskin. I will probably treat it like a patch again to ensure that sufficient strength is added back to that area that has been substantially cut away now.

Then I follow the remaining SafeAir instructions to mount the nut plates and drill the screw holes to the required size. Then I still need to decide how much of the subskin to leave in tact, and how much to remove around this entire area.Luckily I managed to check the right wing LE, and was relieved to find out that there is NO Vans precut hole on that side. I don't think I could go through this fiasco again!

Then the whole LE comes back off the wing and gets disassembled yet again (sigh), so that the subskin and other holes can be deburred, and then the dimples will be applied to every hole that needs one. Never thought I would be using the word "dimple" this soon. I wonder if I even remember how to do that?

Progress.........

KPR....

Primed Some LE parts and Reassembled and Mounted it to the Wing - FINALLY - PROGRESS!

It's been a long time comin', but I finally made some progress today. I put aside all house crap and other interruptions that have plagued me in recent weeks, and with weather also in my corner I managed to get some airplane building done today. Nothing earth-shattering mind you, but for me it was substantial.

Here is the left wing LE skin, ribs, and subskin all primed:

I used the same Akzo-Nobel 2-part epoxy primer as I did before, using the same trick I previously wrote about by using a plastic turkey baster to meter out the 20 ounce mixture from the larger paint cans. I knew I needed a bit more primer than my touch up gun could hold, but I wasn't sure exactly how much would be needed. For this job I used my $15.00 HF HVLP spray gun as shown below. It has a 20 ounce cup, so in addition to delivering the primer a bit better than the touch up gun, it also holds more. I mixed the full 20 ounces, mixing 10 ounces each of the primer base and the hardener. Waited the required 30 minutes after it was mixed and in the cup, and then did the deed.

I used my large paint box, but I did not put everything on the box at once. I did the ribs and the subskin first, and then removed those parts and did the LE skin. Why? because  I only wanted to prime the inside of the LE skin, and did not want to get any primer on the outside of the skin. Although it would also fit on the larger paint box, with everything else, there was a risk of over spray getting on the outside of the skin, so I primed it separately. I ended up only using about 17-18 ounces of primer, so at least I now have a marker for how much material a full load of primer will cover when  using the HVLP gun.

I really do like the HVLP gun. This next pic is what I will call a "self" portrait. What a great likeness, don't you think?

Actually this was my test sheet from the post-it poster sheets I have used in the past. The HVLP gun has a larger spray pattern that is perfect for larger parts. At the bottom you can see what happens if you don't keep moving the gin across the surface to be painted. I also liked that the fact that I did not need to make any of the fine tuning adjustments that this gun has for air pressure, paint flow, and paint pattern.

The next task was to reassemble the ribs and LE and remount it to the wing. This was a bear to do, especially when I had to re-cleco the two inboard ribs that lay underneath the subskin and the outer skin.It took me quite a while to get the LE reassembled and remounted, but I managed to do it.

This next series of pics shows one of the things that needed to do next - redraw the patterns for the new access hole and mounting flange on the now-primed subskin.

The first pic is after I matched drilled the holes for the mounting flange of the new access panel from the outer skin to the subskin, and then I clecoed the mounting flange to the outside so I could trace the necessary patterns onto the subskin.

I then drew the inner and outer outlines of the new mounting flange onto the subskin and removed the mounting flange. I now know where I have to remove material for the new access panel opening.

And a couple of notes added about radiuses and where to remove metal after the next dissasembly.

Hopefully this now starts to make some sense when I tried to describe this process in several previous posts. Pics are always better. From the above pics you can see the area that that new access panel mounting flange is supposed to occupy, as well as the remaining area from the old access panel opening that I still need to figure out how to close up. The challenge is how to blend the lower right corner where the new mounting flange goes with the old hole with the odd shape that now has to be closed up in the proper places.

So I've got some more math and measurements to make to continue this work, and, sadly-yes, I will need to remove and disassemble this all over again for the 80th time to debur the new holes and cut lines, so I'm not quite out of the woods on this just yet, but it will get done. We'll see just how much I get done before leaving for Oshkosh in 2 weeks.

Not shown in the above pics is the fact that I can now also match drill the 2 rear rib flange holes in the outer rib flanges that were added to the custom 408 rib from long ago. I'm a little worried about edge distance being correct on that one because I think I trimmed too much material from the flange that sits on the wing spar, but there is only one way to find out. Since these are the outer flange holes I will also probably have to dig out my 12 inch long #30 drill bit. If I do it right, the holes should have just enough edge distance. If not.......Well, let's just not go there yet.

Felt good to do some work on the bird again. These LE mods are kicking my ass, but as long as I still have some ass to kick, I'll keep going.

KPR.

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....