Wing Tie Down Assembly

The kit comes with a threaded tie down assemblies for each wing. Each assembly is made up of two parts. The first is stainless steel tie down anchor that is mounted inside the wing. The tubular part of the bracket with a threaded hole extends to the outside skin surface of the bottom side of each wing. This anchor is pictured below already fully mounted in place. Instructions for mounting this anchor is covered starting in Chap. 7, Page 79. The second part is a tie down ring with a threaded post that screws into the threaded hole in the tie down anchor pictured below. This allows the tie down rings to be removed for flight to reduce drag. If the steel anchor is positioned correctly, the outer surface of the threaded hole will be flush with the outer wing skin.

As pictured above, part of the anchor extends above the capstrip. The anchor actually has to pass through the capstrip, so a hole must be drilled in the capstrip to accommodate this. After I drilled the hole through the capstrip, I positioned the anchor in place. I also measured the height of the part that extended above the capstrip to insure that it would be flush with the wing skin when it was in place. I made these measurements with the depth measurement end of a caliper. When I had the anchor positioned so that the top would extend through the wing skin far enough to be flush with the outer surface, I discovered it could not be pressed flat against the shear web it would be ultimately bonded to. I decided to build up a spacer pad that would hold the anchor in just the right position. The picture below shows the pad after it was created.

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I made this pad out of a mixture of epoxy resin and flox. The next problem would be to hold the anchor in place while the epoxy/flox mixture cured. I considered several options. None of the options seemed like they would hold the anchor in just the right place without a lot of careful effort in positioning the anchor. It occurred to me that I could use a carriage bolt, and a few scrap pieces of MDF to create a custom clamp that would automatically hold the anchor in the exactly correct position. The hole that the carriage bolt goes through in the MDF block at the top should be drilled in a drill press at 90 degrees. If other builders use this technique, it is critical to note that you must only finger tighten the nut, or the capstrip will be damaged. The blocks of MDF are laying flat on the capstrip. They hold the carriage bolt in place at a 90 degree angle from the surface of the capstrip, which holds the anchor right where it needs to be.

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The epoxy/flox mixture will bond to the anchor unless you rig a release. I have placed a layer of duct tape on the anchor as a spacer to factor in the layer of Hysol adhesive that will be used to bond the part in place. ( Shown on the right anchor pictured below ). I then placed clear packing tape over the duct tape and most of the rest of the anchor to make sure the resin would not bond to the anchor while I was forming the spacer pad. You may be able to see the clear packing tape on the left anchor pictured below if you look carefully.

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Once I completed the spacer pad on the shear web, I needed to permenently bond the anchor to the pad using Hysol structural adhesive, and build epoxy/flox fillets around the anchor to insure that the glass will conform to the shape of the anchor without forming small air pockets.

Builder Note:

Wing Tie Downs

When closing the wings, it can be very easy to get resin into the threaded hole. Before the resin set us during wing closing, check to make sure that no resin has gotten into the threaded hole. One trick I learned from Jim Nordin, you can pour enough melted paraffin in the hole to fill just the end of the hole. If you do this, when you are closing the wing, you don't have to worry about not getting resin in the hole. Later you will be able to punch the wax out of the hole.

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