The Fins

7/6/04

I framed up the fins yesterday and today. Total time spent was 10 hours and that includes building a jig and cutting the parts. It's too late now but it would be much easier to just sheet some 1/2" Styrofoam or even just fiberglass over foam. I was tempted several times during the building of Fin #1 to stop and go get some styofoam but decided each time to press on figuring I got this far, I might as well continue but man what a pain! Lots of little parts and parts that have to fit into other parts before other parts go on. That first fin was a learning experience and the second fin went much faster. (I am still battling the urge to make a Fin from Foam even though I don't need it anymore) The two Fins are identical except for the "T" connectors.


The parts cut by the kit cutter were the same lousy quality so I decided to make my own. I made two sets of everything. I made a jig from some scrap 3/8" MDF to hold the 1/2" and 3/8" x 1/32" ply bands and put some scrap 1/16 balsa under the outside band. I wet the plywood strips a bit to make the curve and pinned them in. I cut the twenty FR1's (they go in between the two bands) from a strip of 1/16 x 1/2" balsa and sanded them to shape after the frame was finished. I took it off the jig and pinned it down over the plan.


I put down a 3/32 spar and then all five ribs FR6A onto that. The rest of the ribs FR2 - FR10 went in and then the rear spar and the hinge rib RHB3 on the spar. The top and bottom hinge ribs RHB1 & 4 were carefully aligned and glued in. The 1/8 x 1/4 spline went in and then eight FR6B's to finish it up. On Fin #2 I changed the sequence a bit and it was better. It went, 3/32 spar, FR6A's THEN the rear spar with hinge rib RHB3 and then the top and bottom hinge ribs RH1 & RH4 THEN the spline and the other ribs. I used a small alignment block and made sure the hinge holes all lined up before gluing. If I were to do it again, and I hope I don't have to, I would leave the end of the hinge ribs squared off to make alignment easier, and then sand the curved shape in after they are glued in. I then sanded the slot for the "T" connector and making sure I made a right Fin and a left Fin, glued them in.

As soon as the glue was dry I tried to fit the Fin onto the Stab but couldn't. The Stab spars spacing shown on the Fin & Stab plan do not match, which means the inner 1/32 ply band ended up smack dab in the middle of the forward spars. And that means I'll have to slot the spar.
At this stage each Fin weighs only 1 oz. and is very sturdy. After sheeting and fiberglassing they should be indestructible.

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Updated July 14, 2009