Building the (scratch) Big Blinka (part 2)

So I was nearly finished with the upper section when I decided to rip it apart.

Here it is before that moment, along with the lower section with its Baby Bertha fins glued on. (Just three of them. Got plenty of stability.)IMG_6104

There were too many little things I could have done better (like the dent visible above, created by stupid handling on my part), and since I had three more foam batons untouched, as well as what I could salvage from the first upper section, I decided to try again. Among my reasons for dissatisfaction was not the glue joints, but as I soon discovered, that was perhaps the best reason to start over. The epoxy really didn’t stick to the foam very well.

So I started googling “pool noodles glue”. At least one site said epoxy should work well. Right.

Some sites recommended hot glue. Some said don’t use hot glue, it’ll melt the foam. Some said you could use it to glue cardboard to foam if you applied it to the cardboard and then stuck it to the foam. I verified (using scrap pieces) that indeed hot glue directly on the foam melts it, and as for hot glue on cardboard on foam, it didn’t work for me. Perhaps I did it wrong.

Someone on a forum said “Hot glue won’t stick, I use Gorilla Glue.” I tried Gorilla Glue. It wouldn’t stick.

Another site suggested Elmer’s Glue-All for cardboard on pool noodles. This may surprise you. It may surprise you less if you know the site in question was elmers.com. What the heck, I tried it. Didn’t work.

While rummaging in my adhesives stash I found a tube of Liquid Nails, so I gave that a test. Which it failed.

Another forum poster mentioned Goop. Specifically Marine Goop, but plain Goop was all I found locally. While shopping I also picked up some J-B Weld ClearWeld.IMG_6149These both certainly worked better than the Gorilla Glue, hot glue, and Elmer’s, and maybe better than the Bob Smith epoxy — not significantly worse at least, and the ClearWeld a little better than the Goop. Also, I noticed the epoxy seemed to have worked better on the cut end of the foam baton — where there are open voids — than on the smooth sides, so I tried comparing these with and without some holes poked into the sides of the foam with a hobby knife. The holes did seem to improve the adhesion some.

All right then. I decided the ClearWeld would work well enough.

So onward. I tied two slip knots in a piece of Kevlar

IMG_6127 and tightened the loops around the LED unit in the baton, between the foam and the lip:IMG_6128 To keep epoxy off the Kevlar loop I covered it (and the push button and battery cover) with blue tape. I did not cover the Kevlar ends; I wanted them in the epoxy.IMG_6133-001 I cut three pieces of BT-60: 1″, 2″, and 2.5″. The middle piece I sliced a narrow strip from, to make it a slip fit inside the 1″ piece.IMG_6112 I glued the former into the latter, then epoxied that to one end of the baton, and the 2.5″ piece to the other end. The Kevlar ends were captured between the baton and the coupler.IMG_6152

All this seemed pretty good until I realized I’m relying on the LED unit to stay put when the shock cord pulls on it. Well, sort of; if the LED unit pulls out, the Kevlar ends are still glued down, so the top and bottom sections should stay connected, but the LED unit could get lost. I’m not happy about this but I haven’t thought of a fix that I like. I may just have to fly it and hope.

Anyway, the CG is somewhere along the length of the baton, and understandably I was not particularly attracted to the idea of gluing a launch lug to the foam, so instead I glued some small pieces of balsa to the top and bottom BT-60 pieces and then launch lugs onto the balsa. (The foam is slightly larger in diameter than the BT-60, so the balsa pieces were needed to provide an offset.)IMG_6158That pretty much completes assembly. I’ll see how much painting I can do this week, but hey, night flight rocket, doesn’t need to be pretty in daylight, right? Even if it’s only in primer I plan to fly it Saturday.
IMG_6167

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