Fin Materials

Last updated 07/09/2008

Fin Cans

These are the "Fin Can Kits" I sent out. There were 6 total kits. The materials were donated by Jerry Irvine. Each kit had two birch ply centering rings, two 1/8 " plywood fins with a 3" root edge, a 4" long 29mm engine tube and a 4.5" long, 2.6 Dia glassine body tube. The instructions were to assemble the can using a provided diagram. The construction consisted of through the wall fin mounting and internal fillets. Three were done with wood glue and 3 with epoxy. Each person building a fin can voted on how to test them.

All parts were donated by US Rockets and Jerry Irvine.

Carbon Fiber / Nomex Honeycomb Comparison Test

This test was set up to contrast the strength of a carbon fiber covered Nomex honey comb material from ACP Composites. The test was performed using 1.5" x 5" samples in my small 3-point bend fixture. The test is the same as below, but the span (the distance between the rollers) is 3", vs the 2" in the test below.

The data shows that the laminate material is not as strong as the aircraft plywood in 3-point bending. You will notice that it continued to bend rather than snap, or break. This is evidenced buy looking at the graphs and also suggests that the laminate material is "tough". Another factor in choosing this material is the obvious weight reduction. I hope to receive more CF/Honeycomb samples in the future.

Giant Leap Honeycomb Comparison Test

This test is of three each, 1/8" and 1/4" thick by 1.5" x 5" Giant Leap Honeycomb fin material. The samples were the same dimensions tested in the "Carbon Fiber / Nomex Honeycomb Comparison Test" above with the same span being 3.0". Remarkably, the 1/8" samples weighed virtually the same as the 1/4" samples. Samples provided by Brianc.

Fin Material 3 Point Bend Test

These are strips of fin materials provided by Greg Deputy. There were three groups of three materials. The three materials were 1/8" balsa wood, 4 ply 3/16 plywood, and 1/8" G10. Each of these were divided into three groups: Bare, fiberglassed, and carbon fiber laminate. As a comparison, the remaining samples of John Coker's materials were also tested. The distance between the two lower rollers or "span" was 2.00". Strain rate was 0.500 in/min. Click here to see the bend test before the break and here for after the break.

The largest standard deviation was with the laminated balsa. This was due to delaminating of the overlay. The tests with the lower results delaminated sooner during the test than did the tests with the higher results.

John's Fin/Glue Tensile Samples Recycled

I took several of John's samples and re-glued them on the opposite side. The samples were flipped over lightly sanded and glued. The specimens have the same amount of area glued but were done a little differently. John glued whole sheets then cut them where I glued the already cut pieces. The different construction methods explain the wider sample to sample variation seen in the recycled samples over John's samples. The CY was applied to both pieces before assembly. The CY actually delaminated the fiberglass when broke. (photos)

Robert DeHate's Fin Material Test

The test samples were 3" x 5". They were made from 1/4" aircraft plywood. Three baseline samples were tested with no modifications. The three other samples were tested had a 1" x 3" section cut out of the middle. The section removed was then filled with expanding foam. The entire surfaces were then laminated with carbon fiber cloth. The test was conducted on a three-point bend fixture. The span, or distance between the two lower rollers, was 4.5"