Chapter 24 - Section 10

Wing and Center Spar Seal

The gap between my wings and the center section spar is about 3/16" wide, except at the wing bolt locations. In addition, I have some 1/4" gaps between the outboard edge of the spar and the wings. I have these gaps because I used the Feather Lite leading edge and the building sequence made it a bit difficult to get a perfect fit between the spar and the wings. Regardless, I have to fill these gaps at the same time.

My first trial in fitting foam to fill the gap was not successful. I cut the foam in a wedge shape and tried to force it to fill the gap. All I got was a bunch of foam dust and broken pieces. My second trial was much better as follows...

Shaping the Foam

I divided the foam shaping into 2 separate sections - the section over the bolts and the normal gap areas. For the normal gap areas, I found trimming a strip of foam (with a band saw) to slightly over 3/16" thick worked best. I drew a line along the length of the foam strip, approximately 1" from the bottom edge - this is the submerge mark. Then I rounded off the bottom edge slightly and slipped the foam strip in the gap (up to the submerge mark) - some sanding was needed of course! Now all my foam strips should have the same depth into the gap. It makes the following glassing step a bit easier. The extra height of the foam above the gap is not important at this time because they will be sanded off in the next step.

The foam over the bolts are similar, except it needs a bit more sanding and shaping. I also have to sand the bottom edge of the foam to accommodate the bolts as well. Separating these foam sections from the normal strips allows me to work with smaller strips and in the event I mess up, I can just scrap a small section only.

Notice the foam strip between the outboard of the strake and wing?

Here's a picture of the foam after it has been sanded down. I used a hack saw blade to cut a thin slot between the foam and the center section spar. The thickness of the hack saw blade is about 1/32", which is about 50% of the thickness called out per Plan. I just wanted to leave a bit of 'meat' in the foam just in case I bump the foam while removing the wing, thus giving me a bit of foam for recovery.

Note the 1" depth of foam into the slot and the thinner foam at the bolt location.

Here's what the foam looks like after I remove the wings.

To prepare the foam for glassing, I made a small wood block / fixture for the occasion. This allows me to get a more uniform foam strip. Most importantly, it keeps me from sanding too much foam off, thus losing the 1/16" gap between the wing and the center section spar (as instructed per Plan).

Note both the bottom and upper face of the block keeps me from removing too much foam. At the same time, it gives me a evenly rounded edge for the glass to lay down nicely.

I roughed up the neighboring glass for the 1 layer BID per Plan. Then I microed the foam strips with wet micro. I also filled the voids and gaps with thick micro. I applied 1 layer BID over the foam with 1" overlap along its sides and peel-plied.

After the glass cured, I removed the peel-ply, trimmed and sanded down the rough surfaces. Susann and Cassandra helped me to put the wings back on. The moment of truth...I did not lose the 1/16" gap between the wing and the spar. Actually, it looked a bit tight at the wing bolt locations. I may have to sand it down a tiny bit. Generally, its good enough for finishing.

[Hindsight] Note the slight jog I have to cut out of the seal to accommodate the hard points?

[HINDSIGHT] Knowing what I know now, I would not have made the wing / center section spar seal per Plan (above). The Plan does not point out the slight jog you have to cut out from this foam seal. This jog prevents me from cutting a straight line seam between the wing and the center section spar! I ended up cutting this foam and glass back out of the wings and redid the seam. (Refer to Chapter 25 - Section 7 Mismatch Treatment)

Here's another look at the seam between the wing and spar...Its less than 1/16" as instructed per Plan, more like 1/32". I believe the width will be fine when I get to the sanding chapter.

Tie Down

Since I was working in this spar / wing interface area, I decided to make the tie down set as well. I have yet to clean it up and eventually anodize the parts.