Wing Attach Brackets

With the Wings Fastbuild kit, the most significant steps have been completed regarding the Wing Attach Bracket placement. The only steps the builder must perform are described in Chapter 7, Section C. Those tasks include:

Prepare the Fiberglass Surfaces on the Fuel Tank Side of the Spar for Bonding
Mount the Brackets in Place with Appropriate AN Hardware
Torque the Bolts & Nylock Nuts to the Appropriate Inch-Lbs Values
Seal the Wing Attach Bracket Bolt Holes on the Fuel Tank Side

As mentioned earlier, the critical steps for bracket placement have been completed. The slots that the brackets slide into have been completed and the holes have been pre-drilled.

The construction manual has you cut a piece of 1/4” thick high-density foam to build up the surface around the bolts so that the fiberglass that seals the bracket bolts will lay flat. Also, bolt holes must be cut in the foam to accommodate the bolt heads. The finished foam piece for the right wing is pictured below set in place.

1/4" Foam w/ Holes Cut For Wing Attach Bracket Bolt Heads

I cut the high density foam piece that will be used in sealing the Wing Attach Bracket Bolts ( Ch. 7, Pg. 24 ). I first cut a template for the piece out of Brown Builders Paper that I purchased from the paint department at Home Depot. This paper is easier to fold then poster board, but a lot more rigid than newspaper. I first shaped the template by folding it in place against the forward shear web. I then used a straight edge and a utility knife to cut the template to the exact shape. I performed the cutting on a workbench, not in place in the wing. I then put the template in place in the wing, holding it in place with regular scotch tape. I used a small flashlight with a Nite Ize Fiber Optic Adapter to insert in the bolt holes from the opposite side, to show through the builders paper. When I pressed against the paper so that it was firmly against the shear web wall, the light would show me exactly where the hole was through the paper. I then used a Ultra Fine Point Sanford Sharpie Marker to mark the center of each bolt hole. From there I positioned the template on the high density foam core, using the Sharpie to mark the 4 corners on the foam, and to mark the center of the bolt holes by punching the tip of the marker through the paper at each point. Then I used a straight edge and utility knife to cut the foam. When I test fit the piece in place, it fit just fine.

To cut the bolt holes in the foam, I tried a few different things. The thing that worked the best was a 3/4'' Diamond Hole Saw that I had gotten from Harbor Freight. This worked wonderfully. I could cut the holes quickly and easily. When I put the foam back in place in the wing, all of the holes were perfectly placed. A drill press made it a little easier to start each hole, but a hand drill is just fine.

Builder Note:

The Wing Attach Bracket Removal Myth

On page 7-25, in step C5, it states “Mix up a batch of thick epoxy/flox and cover the bolt heads as shown in figure 7:C:4. The idea is to pot the bolt heads in place so the wing attach bracket can be removed without getting the wrench on the bolt heads (you should never have to remove the wing attach bracket!).” There is a problem with this ”idea”. In order to remove the wing attach bracket, you MUST remove the bolts. If you seal the wing attach bracket bolt holes as described in Chapter 7, Section C, you will not be able to remove the bolts. So... unless you modify the way you seal the bolt holes is some way that is designed to permit the wing attach bracket to be removed, you will be permanently installing the wing attach brackets. ES builder Mike Salzman has come up with such a solution.

Bolting the wing attach bracket in place for my right wing is pictured below. The procedure for putting this bracket in place is a pretty simple procedure with the Fastbuild wing kit which includes the following steps:

slide the bracket into the already cut slot at the root of the wing
align the bracket bolt holes with the bolt holes cut in the shear web
put the appropriate AN bolts into place
put the AN washers and AN nylock nuts in place
torque the bolts to the specified inch/lbs
place a spot of red fingernail polish over the seal between the tip of the bolt and the nylock nut to make the bolt "flight ready" (note the red spot on bolt tips below)

There are also 3 bolts that will be on the outside of the wing pictured below. There are 3 different AN bolts used for mounting these brackets, so it is important to carefully follow the manual for properly placing the correct hardware in the correct places.

The picture below shows the seal that I laid up over the wing attach bracket bolt heads and 1/4" thick foam. Later this will be one of the walls of the fuel tank. There are several light colored spots that can be seen under the 2 BID fiberglass in the photo below. Those are not air bubbles. They are epoxy/flox potted bolt heads, and epoxy/ micro patches that used to be bubbles. The first time I laid the 2 BID layer over the high density foam, I did have some air bubbles from 1/8" in diameter to a couple that were 1/2" in diameter. Bubbles are very unacceptable in a composite aircraft. Using a Dremel rotary tool, I ground them out, filled the new holes with epoxy/micro. Then I put a whole new 2 BID layer over the entire repaired area. The job on this seal does not look good, but that is not a problem. It will be first covered over with a shinny gray layer of fuel tank sealer epoxy. Then the wing skin will be bonded over the open side of the wing, which will permanently close the wing. The important things are that:

the seal has no holes that will allow fuel to leak out of the tank
there are no air bubbles trapped underneath the fiberglass layers
the resin that was used in the seal cures to it full hardness capacity (which is dependent on correct resin to hardener ratio, proper mixing, and a few other factors)

Wing Attach Bracket Seal (Right Wing)

The fiberglass in the photo above has a different color than the fiberglass around it. That is because my epoxy hardener had discolored due to a chemical reaction with some of the metal fitting inside the epoxy pump. This discoloration does not jeopardize the hardness or straight of the fiberglass.

To avoid the bubble problem I had with putting this seal in place, I did the left wing slightly differently using the following steps.

With the high density foam on the work table, I put a 2 BID layer over the side of the foam that faces the fuel tank cavity.
Once the resin was cured just to the point that it was no longer tacky, I trimmed the edges of the fiberglass off so that the fiberglass edge was flush with the foam edge.
I also cut the fiberglass covering the bolt holes, which helped prevent trapping bubbles around the bolt heads.
From there, I followed the manuals defined procedure for putting the foam in place. There was one bolt hole that would not be covered by the 2 BID that I put around the edges. I put peel ply over that hole to help contain the epoxy/flox.
Then I put 2" 2 BID strips along the perimeter such that the stops cover the out 1" of the seal surface, and 1" inch of the perpendicular wall surfaces around the seal the same way in which the ribs are glassed into place.

This process was a lot easier to lay up bubble-free. The photo below shows what the seal looks like in my left wing.

Wing Attach Bracket Seal (Left Wing)

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