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Wing-attach depressions (Cozy ch19,p4)


jpolenek

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Here is a technique I used for my wing attach depressions. Not sure if other builders are already doing this or if I'm the first, but it made sense to do it this way, as I couldn't figure out how to avoid making a big mess of it following the plans' method. So this was my process:

 

1. Make a plug from Styrofoam. This way, it's very easy to get perfect radii using a router, sander, etc.

2. Prep the foam with medium-dry micro slurry to fill the cells, then do the 2-ply BID layup over the foam. Peel ply where possible.

3. Use jig and router to cut a depression at the required location in the wing that will fit the insert.

4. After cure, remove peel ply, scratch sand the insert and micro it into the depression. (Use generous amounts of micro to fill all the voids, thick enough so it doesn't run out but runny enough to enable the excess to squeeze out and allow the insert to sit at the bottom of the depression.)

5. After cure, trim the insert flush with the surrounding surface of the wing. (This is one of the many times when a Fein tool is REALLY handy.)

6. Remove foam from inside the insert and scrape the sides down to the glass. If you remembered to micro-prep the foam before glassing, and it was fairly dry micro, then it will scrape off nicely right to the glass. A 4" screw with Vice Grips for a handle works beautifully as a rasp. A bend in the screw enables it to get into the corners easily.

7. Use a small strip of coarse-grit sanding belt (e.g. 1"x4") and sand the inside of the depressions to smoothness.

 

The method takes a little more work than the plans' way, but the final result is well worth it if this type of detail is important to you.

 

Joe Polenek

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Joe

Cozy Mk IV #1550

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6. Remove foam from inside the insert and scrape the sides down to the glass. If you remembered to micro-prep the foam before glassing, and it was fairly dry micro, then it will scrape off nicely right to the glass.

 

-----> Or, in Step 2, apply peel ply or black electrical tape to the plug before applying the layup. This provides for future mold release in Step 6.

Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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Or, in Step 2, apply peel ply or black electrical tape to the plug before applying the layup. This provides for future mold release in Step 6.

I started this way by building a wood mould, but couldn’t get packing tape to wrap around the corners (compound curves) without rippling. Electrical tape probably would have worked nicely because it is stretchy. Just as well, though, because there are a couple of advantages to using a foam core for the insert, which I didn't realize at the time:

 

1) It is easier to fabricate the plugs out of foam than wood, especially when you're making six of them at once. (The number of set-ups and overall fabrication time is reduced by processing them as a batch of six, rather than making them one-by-one.)

 

2) The other big advantage of a foam core is that it provides rigidity to the fiberglass when bonding it into position. I needed clamps to squeeze all the micro out of the way and get the insert to bottom out in the depression. The two layers of BID alone are pretty flimsy and would likely bend and distort when doing this. If you used a removable mould and waited to remove it after the fiberglass was bonded in place, the lack of flexibility might make the de-mould difficult.

 

Joe Polenek

Joe

Cozy Mk IV #1550

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I started this way by building a wood mould, but couldn’t get packing tape to wrap around the corners (compound curves) without rippling. Electrical tape probably would have worked nicely because it is stretchy. Just as well, though, because there are a couple of advantages to using a foam core for the insert, which I didn't realize at the time:

 

 

 

Joe Polenek

I cover my molds with heat shrink model airplane covering as a release tape.

also cut the depressions with a piece of hot wire bent to the shape of the cut out and mounted to a piece of plywood. hot wire router takes ten minutes to build.

Evolultion Eze RG -a two place side by side-200 Knots on 200 HP. A&P / pilot for over 30 years

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