Building the Shrockets Sea Sting (part 2)

The instructions suggest using Spray Mount or similar low-tack adhesive to attach the fin templates to the balsa for cutting. I went to Staples, looked at what they want for a can of Spray Mount, gagged, and bought a repositionable glue stick instead. Later I discovered my wife for purposes of her own had bought a can of Spray Mount a couple weeks before. Oh well. By then I’d used the glue stick and it worked fine. Better, I think, than the Spray Mount would have; at least in the sense of being easier and less smelly to use.

That 15 minutes estimate for cutting out the fins was a little optimistic in my case. I timed it at just under 26 minutes.IMG_3107The balsa seemed to have some hard streaks running through it which slowed down some of the cross-grain cuts.

I laid out the pieces to be joined and marked the edges that would be glued, to one another or to the body tube and scoop.IMG_3109 I missed one on one of the B pieces before taking this picture but noticed it almost immediately after.

I noticed a discrepancy between the instructions and the fin template. Pieces F, G, and H in the former are labeled G, H, and F in the latter. Pretty obvious and not going to cause any confusion.

I rounded most of the un-marked edges. That included about 2/3 of one edge on each A piece; a bit tricky, but doable.IMG_3110 The exception was the strake pieces, fin template letters G and H. Way too thin for me to want to try doing anything of that sort. I plan on rounding the leading edge of the strake once it’s glued together, but the long edges will stay square.

For some reason, either because I misplaced it or because it didn’t make it into the kit in the first place, I didn’t have a tube marking guide. I contacted Shrox who confirmed that the fins are evenly spaced at 90 degrees, so it was easy enough to make my own guide and mark the fin lines. There’s no launch lug line, as we’ll see.

In went the motor mount.IMG_3112Back to the fins; the wing pieces and scoop fin pieces were glued together. Note the straightedge used to check the scoop fin edge. I had to do some sanding on the edges at the joins, particularly on the end of B that mates with A, to get the edges straight.IMG_3114I weighted these down with books for drying, then skipped ahead a bit. I used the aluminum angle as a guide for cutting a split down the scoop tube. In this blatantly posed photo I see I’m holding the hobby knife at an angle to the tube, where in reality I was trying to keep it vertical for the cut.IMG_3116 Getting the scoop to stay in place for gluing to the body tube under the wings is, I expect, going to be a pain. I’m stretching it out on the edge of the desk in preparation for that.IMG_3118I used the Estes fin guide to put the “wings” on. I’ve had some problems with this thing, and I think it’s due to a combination of factors: play in the casings that hold the tube, play and inaccuracy in the slots and tabs, and imperfections in the flatness of the fins themselves all can add up to fins not being parallel to the tube. But used with some care I think it’s better than nothing.

To help line things up, I drew parallel lines on both sides of the fin center lines.IMG_3120Once the wings were on I added fillets with TNRND.IMG_3122This is about as far as I can go before needing to do some priming/sanding/painting on the scoop fin and the inside of the scoop.

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3 thoughts on “Building the Shrockets Sea Sting (part 2)

  1. I just realized the A pieces may be geometrically symmetric, but there’s a right way and a wrong way to orient them due to the grain, and I think I may have gotten both of them wrong. Oh well…

  2. Hi Rich,
    I thought the tail “C” piece was interesting.
    Maybe the leading edge should have gone all the way to the root edge of “B” instead of being cut off at an angle. That would make the “B” piece more of a trapezoid shape.
    I would be concerned the C piece could pop off on a hard landing.

    Still a great design and I’m enjoying the build thread.

  3. Good point, Chris — securing C to the body tube with a good filleted joint; it’d reduce B’s connection to the BT, but B’s not the part taking the brunt of impacts.

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