View Full Version : Ideas / Tips for Building a Fin Ring?

9th June 2010, 01:58 AM
Our club has decided to do a group HPR build, which will involve a 4" wide 18" diameter ring fin.

Anyone here have experience building a large HPR bird that used a ring?

If so, how did you make it and what problems did you have?

Any ideas, experience, etc. appreciated!

9th June 2010, 02:41 AM
I haven't built one, but i would probably try the following:
1) cut some 18" diameter wood discs
2) assemble them, centered, on a tube of some size (like you are building a motor mount). top and bottom discs should be a little less than 4" apart
3) cut some 1/64" ply 4" wide
4) wrap the 4" wide 1/64" thick ply and wrap around the discs
5) fiberglass the ply.
6) remove the disc assembly
7) fiberglass the inside of the ply ring.

9th June 2010, 03:49 AM
The Lusty Cornmaiden had a 16" diameter ring that was 4" tall -- very close to what you're after.

I bought a length of 16" Sonotube. The ring was approximately 1/4" thick. The ring supports were 3 pieces of 1/2" baltic birch plywood, each of which was 1/4" shorter on the top half than the bottom half. The ring had corresponding notches to accept the longer portion on the bottom of each support.

After the ring was installed, I applied a layer of 9oz fiberglass over the outside of the ring, as well as to the interior of the ring at the ring/support joints.

This resulted in an extremely sturdy ring which survived a hard landing from a stripped main.