Wing access panel botch

[grog]

Was working too late at night drilling the access panels and somehow (yawn) skipped double-checking before drilling. My rivet holes in the wing got drilled too close to the edge (on two edges, no less!) Grrrrr.

My repair plan is to nibble the access panel hole (left and bottom edges, below) oversize and create suitably oversize doubler and a new access panel. Any other suggestions are appreciated.

Eric

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[Mark Goldberg]

The holes do look too close to the edge of the material especially on that side to the left in the picture. The "frame" that gets riveted inside there for the inspection door doubles up the material. So I doubt there is structural issue. But I will ask Bob next time we speak and post his answer. Mark

[svyolo]

A week or two I was going to post something about drilling the access panels because the instructions I read had it backwards. Everything on a BH kit is taken to the limit, that is how you make a light airframe. Edge distances are usually at the minimum.

I think the access panels should be drilled by marking and drilling each individual hole in the wing, first. Then transfer those to the access panels, not the other way around. If you drill the panel frames first, you can mis-drill the wing skin.

It is a lot easier to make a new access panel frame, than fix a mis-drilled wing skin that is already installed.

I tried to take a shortcut, and did. Luckily I did not transfer that shortcut to the wing skins. I did get to make a half a dozen new access panel frames. :<)

[Mark Goldberg]

I spoke with Bob about the holes in the wing skin close to the edge of the material. He agreed with my guess that it would be OK because of the .032 backing frame basically more than doubling up the material there. He said it was possible you might get some cracking but unlikely. And it is not like the wing would fall off if it happened. You should keep an eye on them as you fly the plane. But most likely it will be OK. Mark

[Bcone1381]

Here is another data point. The inspection cover is match drilled to the frame first, and the rivet holes that will secure the frame to the skin are drilled before doing any task on the wing skin.

A strip of steel about 1 inch wide and held in place across the access hole with magnets. The cover is balanced on the steel strip and held with couple more magnets. (The magnets are the super strong variety.) I center the inspection cover in the access hole and can see everything clearly. I then carefully place the frame on top of inspection cover and cleco them together. Now I am ready to drill my first hole. Masking tape might also come in handy to hold things

When the holes are drilled I can take it all apart and install the frame inside the opening and attach the cover to it.

I like to obtain a 1/16th" clearance between the edge of the cover and the wing skin's hole. This clearance will provide a margin to accommodate paint and will prevent paint from chipping which occurs if the margin is too thin. So keep that in mind when you are planning the screw hole edge margins in the cover.
IMG_6757.jpg

[Bcone1381]

One more thing......A builder who can show an error here on the forum is resilient. Good job. Resilient builders learn to continue in spite of errors. I have so many educational events and sessions I cant believe it. I redo things regularly. (example, it took me 4 months to fabricate shock strut fairings. It was my first composite part.)

You are not alone. I can't let myself get angry, which I am prone to do. Anger will destroy a build. Errors will not. EVERY error is a very inexpensive educational session. Thats how I look at it after putting 4 boys through college...Thats BIG bucks.

[svyolo]

Brooks I did the same as you. But before I drilled the skins, I marked them to make sure they had adequate edge distance. Some didn't. I ended up making some new frames.

[BTAZ]

20140824_132930.jpg20140824_133659.jpg20140824_134724.jpg20140824_133714.jpg20140824_133830.jpg20140824_134454.jpg20140824_134103.jpg Perhaps the quick build is different but I did the following on my scratch built.

I positioned the frame and cover where I wanted it on the wing. Note the cover and frame were only drilled to 3/32(I.E. don't drill out the holes that will ultimately have screws to their final size, leave them at 3/32)

Drill both the frame rivet holes and the cover screw holes into the wing

Then you can cleco just the cover in place and trace around it for your cutout.

The photos loaded out of order with regards to the operation, not sure how to fix it.

[grog]

Thanks all for the ideas and Brooks, the encouraging words. It was a real 'doh' moment after I drilled and pulled the doubler off - especially when all the previous ones I'd marked with a pen and double-checked before coming back and drilling. Educational, indeed! Measure twice, cut once, like the man says...

Mark, I appreciate you getting the word from Bob as well. I'll see what happens and keep my eyes peeled for any weirdness.

Thanks again,
Eric

[James]

My brother used to work in a marine heavy maintenance facility.
On the wall of the shop was their motto: "Do it right, do it three times." :-)

[svyolo]

Mistakes?

Maybe part of every builders' Log should be a time lapse video of their scrap pile, or box, of material/parts, growing over time.

Brings new meaning to words "mine is bigger."

[rv8bldr]

If you are REALLY worried about it, put a second set of rivets in BETWEEN each of the existing ones but with proper edge distance. Probably overkill but it would ease your mind....

[James]

Hi Grog,

yep when I inherited my kit with the wings started, one of the access panels had rivet edge distances like yours. I classed that entire part of the skin as "damage" - i.e. I traced outside the rivet holes, and that line became the new "edge" of my inspection panel. I went up to a 40 thou backing plate, with a second line of rivets, staggered in between the first line. The backing plate ended up about 1.5 inches thick. Then I "plugged" in the old holes with CSK rivets as per a standard damage repair.

One big thing I didn't think about is there is a world of difference between the structural loads inboard of the lift strut, and outboard of the lift strut. Smart move asking Bob to double-check your work.

I remade every single inspection panel, and nearly all the backing plates, because the edge distances for the nutplates weren't right. If I were starting from fresh again, I would make round inspection holes, and also make up an MDF template so I could use a router. So much quicker and more accurate.

I also went up to #8 screws on the backing plates, because I was worried about chewing out the #6 ones during annual inspections
Big weight penalty, but then my wife's got me on a diet, so I'll be ahead in the long run :-)

James

[grog]

Hi James,
Thanks; I'm curious what the "standard damage repair" is - I looked in AC43.13 and couldn't find a way to plug the holes that are so close to the edge that the countersink will likely cause a tear-out. That's why I was considering nibbling out the old holes and re-fabricating a new cover to fit.

And yes, I'm wondering about stripping the screws as well, but probably more concerned with stripping the Philips heads. Something like an Allen head or Torx would be more durable, I suspect.

Eric

[James]

Yeah Eric, well I'm not a specialist sheetmetal worker, but whenever we have a previous rivet hole that is later covered by a repair or is structurally redundant, we fill it in - we often countersink both sides of the hole, put in a short countersunk rivet, and then drive the tail end flush as well. Then sandwich each side with the repair patches.

In my inspection panel above, the existing rivets were way too close to the edge of the top skin to be structurally sound, but then I didn't want to cut them out and make the inspection panel opening an inch wider. So I remade the backing plate thicker for a second row of rivets, picked up the existing holes in the top skin, and drilled them into the backing plate, and put CSK rivets in. You end up with the same sized opening, but with a thicker backing plate, and two rows of rivets through the backing plate. If they are so close they'll tear out, then you might have to cut them out.

Other guys on this forum put me on to NAS514 screws - they are a special screw designed for repeated removal on access panels. I think they'll do the job.

James