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.....