March 15, 2014

I finished up with the trim tab tube for now. I flared the end and then mixed up some 2216 epoxy. The section of the tube enveloped in the stabilizer spar is epoxied in there. Then I added cotton flox to the epoxy to thicken it up. It took a surprisingly small amount of flox to thicken. I used a cheap plastic syringe to spread the mixture around the tube pass through's. It was pretty sticky stuff so it wasn't entirely clean. When I came back a little later it was still formable but less sticky so it was a little easier to get a smoother fillet then. The middle one was still a bit messy. That tube, is never coming out...

Also, I just got a new batch of Aerolite so I made another test block. I found access to this beast of a machine so I had some fun and measured the force required to break something.

I glued up the block as normal, waited the required 2 weeks for full cure and loaded it into the machine. I usually just take a big hammer and smash the raised block until something fails but this was interesting to try.

The verdict: Nothing at all happened until it got up to 9,550 lb where it yielded a little and started to compress a lot more. It kept climbing until there was a big yield at about 10,350 lb. The block was still together (on the outside) so we kept going, even though the force was much lower now due to the yield. At this point, the broken middle block was probably pushing out so it wasn't getting a pure shear force and the block finally started coming apart.

So somewhere around 10,000 lb is where the wood failed, about where the published shear strength of maple is. Yay, physics, the world can continue turning, and I can keep building.

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