Skylight fasteners

[svyolo]

I was wondering if anybody had a more elegant solution for nuts on the bottom of the fuselage formers for the skylight. I am using 1/2" sq tube for the inner formers, same as the kit wing formers. I am using #8 screws on about 4 inch centers, and would like to use blind nuts. Right not the best thing I can come up with is just nut plates, and then paint the formers and nut plates so they match. Rivet nuts?

[jaredyates]

How about all-aluminum rivets instead of screws? Or tap threads into the steel?

[svyolo]

I think I remember a couple of posts about threading the square tube. I am not sure how it works out. The tubing is pretty thin walled. Steel rivet nuts or nutcerts would be my first choice, but so far the steel ones I can find are too long before you seat them.

I know that there are lots of dissimllar metals all over aircraft built like ours, including mine. But aluminum fasteners in the steel fuselage is a bridge too far for me. The other way around is fine. There are rivet nuts in aluminum that would fit, but haven't found steel ones yet.

[Archer39J]

I’m still debating how I’d like to handle attaching my skylight, for now it’s just standard steel hardware bolted through the formers. My concern is water ingress so I’m thinking about installing the hardware wet (with primer). I considered filling the holes with RTV on install but I’m worried about trapping water. I have rubber-backed washers to use on the exterior, but they stick up a bit so I’m also unsure if I’ll use those either.

[whee]

The square tube we used was too thin to thread. We used steel rivnuts but had to shop around to find ones shallow enough to fit. Unfortuanly I haven't a clue where we bought them from. It was likely Spruce or Tacoma Screw.

[svyolo]

It looks like these would work. .42 inches long.

[Archer39J]

Rivnuts in tension? It is just the skylight, not much up force there especially spread out. Honestly for the ability to see water ingress in that tube I'd recommend sticking to through bolts and nuts, else you'd have to disassemble your skylight before you'd see any corrosion. At least that's my thinking.

[whee]

Those look like the rivnuts we used...I think.

Rivnuts are used in tension all the time, Cessna belly pods are an example. I'm not too concerned about water getting in since my plane in hangared but I did silicone the screws when I installed them. If your concerned about water getting in the tube maybe a drain hole is appropriate.

My Luscombe had through bolts and nuts that held the skylight on. I hit my head on them enough times that there is no way I'd use them if I had another option.

[AZBearhawk272]

I have used binding post fasteners, Chicago Screws,
SEX Bolts, got them from McMaster Carr.
They seal great with a bit of RTV on the interior flange face.

KD 272

[Bcone1381]

Dennis Reynold's Patrol skylight doesn't leak too much water. I forget how he secured the side edges of his skylight. I'm thinking the mechanical fasteners are hidden under the wing root fairing.....his ingenious, nearly screw less wing root fairing.

But I do recall the center of the skylight is secured to a center structure with (I think) a 3M VHB adhesive tape product. They attach windows in sky scrapers with that stuff. Maybe Dennis will chime in again.
IMG_5821.jpgIMG_5818.jpg

[Bcone1381]

Please give me permission to add a couple more photos of Dennis' Patrol, and a couple of that use a different method that might spur some ideas.

The first three are close ups of Dennis' aircraft.
IMG_3659.jpgIMG_3660.jpgIMG_3661.jpg

Below first is a cut/paste of the Patrol Plans followed with two photos of Bob's Patrol. On the inside Bob used a flanged .050 aluminum structure that is contoured to match the Riblett airfoil. The Lexan is sandwiched between the interior and an exterior cap that is 1/2" wide and 1/8" thick. #6 screws hold the sandwich together. (This might not help you with your square tubes.)

The center white piece is a cap strip. The Patrol Plans call out .060 Lexan for the skylight material. The second shot is a poor interior photo that shows the interior support and the acorn nuts that receive the #6 screws. I can see a cork gasket fitting under the cap strip to keep the water out.
Screen Shot 2019-10-23 at 1.21.18 PM.png

IMG_3638.jpgIMG_3642.jpg