September 17, 2006

To do the tapering of the main fin spar in the for and aft direction, I used a method described by George Richards, which is a variation on a method mentioned on the Sequoia site. By fixing the spar in an angled orientation, the taper line becomes horizontal and a router with a straight bit cuts along that horizontal line from above (see picture). It was taking me some time to figure out where to get a channel and L-shaped extruded aluminum large enough for this jig. This past week, I went to the EAA Santa Monica chapter meeting and met a bunch of nice folks. It could be good to have some local people to talk to about building and ask some questions every now and then. One of the guys gave me a tip on where to get the aluminum for the tapering jig. So this weekend I gave it a shot and it worked perfectly.

The taper starts about 1/4 way up on the spar, so I set the angle and the router bit to start the taper there. It's slow going, especially when you get to the ends where a lot of material needs to be trimmed, but the finish is perfectly smooth. This taper is actually two different slopes, changing in the middle, so I did the first section, then reset the slope to do the rest of the taper. It's a very minor difference in slope, so you can't really even see it, especially after smoothing out the taper with some hand sanding.

I cleaned up and then started laying out the measurements for the main stabilizer spar. This is the largest spar of the tail. The spar booms are so thick in the middle, that they need to be laminated from two pieces in order to take the necessary bend in the middle of the spar. The booms are also tapered in two directions like the main fin spar booms. Needless to say, this spar is going to take a bit more work. But, I have a proven method for doing each step along the way, so it shouldn't be too tricky.

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