wingtip nav light mount

[Bcone1381]

How should a nav light be mounted to a wing tip? The Whelen light has a base plate that will be screwed into a sheet metal aluminum mount with nut plates to receive the mount plates screws.

I have very little composites experience, but have some supplies. I have some foam, epoxy, micro balloons, flocked cotton, and 8.8 oz bidirectional fiberglass cloth and some 3 oz cloth.

What is the industry best practice for attaching the lights base plate?

I am thinking
-attach some sand paper to the wing tip and shape a block of wood or foam so it conforms to the tip, then
-attach the sheet metal mount with nut plates to the block using epoxy, then
-attach the mount/block assembly to the wing tip with two layers of cloth/epoxy (is two layers enough)
-Drill a hole thru the mount/block assembly and feed the wing tip lights pig tail thru it.

But I am sure this is not industry best practices and curious how its done.

Brooks
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[N942VT]

Good plan, plywood and fiberglass to make a wing mount

[geraldmorrissey]

I'm not much of a fan of wood in an all metal airplane. I would establish a plane where the light would mount to. This plane could be made of anything, sheet metal, wood etc. Put some clear packing tape on the inboard side of the plane to act as a mold release. Some paste wax on the tape wouldn't hurt if you have any. The plane could be rigged in place with a piece of 1/4" all thread through a hole in the wing tip and the plane to maintain an off set from the wing tip. Use nuts on the inside and outside of the wing tip and plane to hold it securely in place. Then I would fill the space between the plane and wing tip with 2 part pour in place foam. You will have to rig up some containment dams out of paper and tape to hold the foam liquid in place until it expands and cures. The initial shape of the cured foam is not inportment as you will sand away most of it to get a pleasing faired shape. Remove the plane. Cover the shaped foam with glass/epoxy. Add a flange of glass at the plane area for attachment of the light. Dremel out the foam to remove the all thread.
Lots of ways to do it, this is my way.
Gerry
Patrol #30 Tandem

[S Lathrop]

If you want a really good looking finished wing tip, I would get some clay and model exactly the shape you want. There is a type of clay that has to be warmed to work into a shape. The clay can be worked to a very fine finish. The clay makes a plug to then make a "skin mold". The mold covers the mounting for the light and several inches of the wing tip.

Next you cut out the portion of the wing tip that is under the clay form you made. Then use the skin mold to layup that shape on the wing tip. Yes this seems like a lengthy process but the finished part will be exactly what you wanted the wing tip to have in the first place.

The clay I used was what was commonly used to make mock-ups of cars in Detroit. I did it to make molds for race car bodies. The clay works very well when making a complex fairing or cover. I found that I can reuse the clay after I clean of any parting agent or way. I plan to use clay for all the fairings or scoops I need.

[Bcone1381]

Next you cut out the portion of the wing tip that is under the clay form you made. Then use the skin mold to layup that shape on the wing tip. Yes this seems like a lengthy process but the finished part will be exactly what you wanted the wing tip to have in the first place.

I am having trouble visualizing this step.

[S Lathrop]

I am having trouble visualizing this step.

Sorry that I did not better explain what I am doing. The end product is a mounting for the light that is an integral part of the wing tip and from the outside looks like it was molded in the wing tip originally. The skin mold not only has the shape of the light mounting but has several inches of the wing tip that surround the mounting. You would cut the wing tip out where the mold and the wing tip are not the same. You would taper the edges of the cutout so that where the mounting starts, The hole in the wing tip is exactly the shape mount and where the mount blends into the wing tip. From the inside you have a hole in the wing tip that you skin mold covers.

There is almost nothing to prevent you having a smooth and edge free transition from the original wing tip and the mount. You would then do the composite layup of the mount from inside the wing tip, thus bonding the 2 parts together.

Using the clay to form the mount and the surfaces to blend it into the wing tip is relatively easy. Making the mold allows you to use the mold and the wing tip to form and bond the mounting to the wing tip in one operation and the joint is so small that you can treat it like a scratch when you paint the wing tip.

[Bdflies]

Some good suggestions! I'll throw in my 2 cents too.
Its times like this that make me wish I'd taken more pictures. But I didn't, so lets see if I can verbally paint the picture. I cut a piece of .025" aluminum that exactly matched the base of the light. I drilled holes in this plate that matched the attach holes and wire pass through of the light. I positioned this plate in the desired location on the wingtip. Drill the wingtip, using the plate as a template. I masked the tip, about 1/4" beyond the plate and then scuffed the wingtip. I applied a little paste wax to the side of the plate that would be adjacent to the wingtip. I mixed some catalyzed resin with microballoons to the consistency of toothpaste. (You could substitute lightweight body filler). I globbed a scoop of the mixture onto the tip and massaged it a bit, to be sure of contact with the tip. Then, I screwed the plate onto the tip, through the previously drilled matching holes. Tighten the plate till it's snug against the tip. With a glove on your hand, using a finger, wipe away the excess resin filler, leaving a smooth tapered transition from the tip to the plate. This is actually very easy and leaves a nice surface. When the filler is cured, remove the masking tape (leave the aluminum plate in place!) and sand the transition smooth. I left the plate on, until I was ready to shoot the top coats. Because the plate was waxed, it popped right off when the screws were removed.
It came out nice and the transition is quite small.

Bill

[geraldmorrissey]

After seeing Bills pictures, I would have to say his idea is better then mine. Anything you can do to reduce the wing span and surface area is good. His tiny fillet with the light tight against the wingtip is elegant. And his construction simple. Might mean the difference of getting it into a hanger or not.
Gerry
Patrol #30 Tandem

[Bcone1381]

I want to learn S Lathrop's method. My vision for this mount is exactly matches Bills photo and complexity. So, from here lets focus this thread on Bills method. When it comes to fabricating scoops or sing strut fillets I'll try to apply the Clay Mold method.

Back to Bill's method. Bill, you
1) Used the base plant to Match drilled a .025 piece of AL then
2) Match drilled the wingtip to these two.
3) Masked the wing tip 1/4" beyond the plate and scuffed it up
4) Waxed the side of the base plate to act as a mold release
5) Slopped on Micro mixture to the wing tip
6) Screwed the two pieces together (that is the base plate and the match drilled .025 piece.) to make a sadwhich with the micro acting as the egg salad and the two pieces acting as the bread. We need enough Micro to squeeze out the sides of the bread.
7) remove the excess Micro around the base plate with our finger to form a nice fillet.
8) Let the Micro cure.
9) Remove the masking tape and sand smooth.

I assume that
1) The match drilled .025 piece has nut plates installed to receive the screws from the base plate.
2) The piece is placed inside of the wing tip, and the screw heads are screwed from teh base plate, thru the wing tip and are received by the .025 piece on the inside of the wing.
3) do you secure (attach) the .025 piece on the inside of the wing tip with Micro too?

[Bdflies]

No nutplates. No internal piece. Just screws through the lights, with washers and nuts inside the tip.

Bill

[S Lathrop]

I think that Bills solution to this problem is the winner. The bump out is just not worth the effort that my suggestion would take.