CCR75 – Tip to Tip reinforcement

The next and most difficult step is the tip-to-tip reinforcement. I’m using Aeropoxy PR2032/PH3660 ¬†with 2 layers of 5.7oz Bidirectional plain weave Carbon Fiber purchased from Aircraft Spruce.

I created a paper pattern using a printout of the fin and a lot of math. I made 3 copies of each pattern, and taped them to the cloth.

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The first layer is half the size of the second layer, which creates a flutter resistant reinforcement.

All 6 pieces were then cut out of the cloth.

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We encountered some problems here, since the original idea was to cut around the cloth and leave a bit of tape to prevent fraying. However, we soon discovered that trying to take the tape off resulted in more fraying than would have happened if we had just cut on the inside of the line. The next 5 pieces were carefully cut about 1/32″ inside the paper pattern.

 

Here’s what the top pattern looks like when all is said and done.

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The first step was to clean the airframe and fin surfaces with IPA. After this point, the airframe was not touched with bare hands until the process was complete.

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The next step was to mix up some Aeropoxy ES6209 for fillets. I made a 1 and a half gram batch, which ended up being almost perfect for what I needed.

 

After waiting about 2 hours for the Aeropoxy to start to cure, or “go green”, we started the layup.

I painted some PR2032/PH3660 on the surface and then laid the cloth.

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I then painted enough epoxy to wet out the first layer, and then laid the second layer.

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After the entire 12.7 gram batch had been used up, I laid some 0.0005″ mylar over the surface. Mylar is a great peel-ply material because it doesn’t stick to epoxy when the epoxy is cured, but it sticks down when the epoxy is wet. It also leaves an incredible shiny surface which looks great and requires minimal finishing.

We put about 33lbs of lead weights onto the mylar to compress the layup. This technique is essentially the best way to do a layup without having to use a vacuum bag.

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After waiting the ~6 hour cure time, I peeled back the mylar.

The resulting finish is pretty good. It’s¬†certainly not the best I’ve ever seen, but it’s extremely strong and that’s what’s important for this project.

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Now, repeat all of that twice more, and the most tedious step can begin – SANDING!

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