Freedom 7 Build Part 21 Fins

The fins are cut out using templates from the wrap sheet.

I didn't use the supplied kit balsa, it seemed soft and wouldn't hold the sharp tapered, leading edge.

I cut the fins from some harder 1/16" balsa. Double check the grain direction on the steering vane pieces.

Here I'm checking the 90 degree corner angles of the fins using a 2" machine square. You can see the fins are pinned together for uniform sanding.

People have asked how I get a defined sanded edge on fins. I'll do my best to explain.

The taper is marked on the fins with pencil.



You must use a sanding block. The sandpaper grit is chosen based on the density of the balsa. This is a harder balsa so 220 grit was used for the initial shaping.

Don't just sand back and forth and expect good results.

Set your block on the edge and visualize the angle of the taper. Change the angle of the block to match the final angle. Sand only on that angle "plane". Go straight - back and forth, don't rock the sanding block.

Make just a couple of passes and check your work under a strong light. Be sure what has been sanded is the same depth and consistent on both sides. If not, adjust pressure on your block to take a little off the high side.

Now that some of the taper has been taken off, set your block back on the fin. Set the block flat on the area already sanded matching the angle of the block "attack". Make a few more passes, each time being sure the block is sitting squarely on the area already sanded off.

A quick review:

1. Mark the edge with a pencil reference line.
2. Always use a sanding block
3. Set the block on the leading edge, angle the block to the desired angle
4. Make a few passes then check your work under a strong light. Adjust the angle of the block to correct the sanded angle
5. Before making sanding passes, always set the block on the sanded taper making sure it sits flat on the already worked area. Make a few more passes, check it again under the light

I don't sand the leading edges to a knife edge. On the finished fin there is a narrow, squared off leading edge. If you can see light through the balsa you've sanded down too much.