Aksrockets
Now with 8% more aluminum
- Joined
- Apr 1, 2011
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This is going to be a down and dirty experiment of an idea I've had for a while.
In the next few months I'm going to be building a rocket that should reach speeds in the upper M3s. This means I need to step up my fincan game, starting with fillets. Regular epoxy fillets are great for 99% of most hobby applications, but this is the point where I need to start looking elsewhere.
Neat epoxy actually has a very poor tensile strength (8000 psi for Aeropoxy Es6209). Compare that to the ultimate tensile strength of a 0° carbon fiber laminate with a 50% fiber content at over 200,000 psi (source) .
The bridge between those two materials seems to be a chopped CF, KEV or FG / Epoxy paste, which seems to work fairly well. However, these still underpreform regular laminates because of their short fiber length, low fiber content and random fiber orientation.
What I'm calling "Fillets 2.0" consists of many layers of carbon fiber, kevlar or fiberglass cloth and Aeropoxy PR2032, staggered to create a concave fillet shape. They will be laid up much like layers of T2T, but just at the root of the fin/tube joint. For the experiment, I'll be making 2 T joints, one with my "Fillets 2.0" idea and one with neat Aeropoxy ES6209. These will then be tested until failure.
I'll be using 5.7k 90/0 cloth for this, but since the 0° direction is optimal, it's likely that I'll use uni CF when I'm actually building.
For this test I'll be testing so the fillets will be under tension, not compression. I may do compression tests later.
Alex
In the next few months I'm going to be building a rocket that should reach speeds in the upper M3s. This means I need to step up my fincan game, starting with fillets. Regular epoxy fillets are great for 99% of most hobby applications, but this is the point where I need to start looking elsewhere.
Neat epoxy actually has a very poor tensile strength (8000 psi for Aeropoxy Es6209). Compare that to the ultimate tensile strength of a 0° carbon fiber laminate with a 50% fiber content at over 200,000 psi (source) .
The bridge between those two materials seems to be a chopped CF, KEV or FG / Epoxy paste, which seems to work fairly well. However, these still underpreform regular laminates because of their short fiber length, low fiber content and random fiber orientation.
What I'm calling "Fillets 2.0" consists of many layers of carbon fiber, kevlar or fiberglass cloth and Aeropoxy PR2032, staggered to create a concave fillet shape. They will be laid up much like layers of T2T, but just at the root of the fin/tube joint. For the experiment, I'll be making 2 T joints, one with my "Fillets 2.0" idea and one with neat Aeropoxy ES6209. These will then be tested until failure.
I'll be using 5.7k 90/0 cloth for this, but since the 0° direction is optimal, it's likely that I'll use uni CF when I'm actually building.
For this test I'll be testing so the fillets will be under tension, not compression. I may do compression tests later.
Alex
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