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Old Sep 28, 2012, 02:49 PM
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Firecracker!
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San Francisco & Santa Cruz
Joined Oct 2004
2,408 Posts
Exhaust duct in blue foam

Hi guys, some news from the world's slowest build! I realized that the exhaust duct design wasn't right before I started building it, so it was back to Sketchup. I am finally starting to get the hang of it after many days of practice.

The new design starts with a conical section with the shroud diameter at one end and 100% FSA at the other, long enough to clear the motor fairing. I totally left out that piece on the first design for unknown reasons. Then it splits into 2 half-circles, each with area 50% FSA (for a total of 100%). Each of those transitions to a full circle of the same area. This is the start of the nozzle, which ends with a 90% FSA circle. That's a lot of transitions in a very short distance.

I had to move the fan forward about an inch because the motor fairing is longer than the one on the Detrum unit. Anyway, it's kind of cool to see the part in reality after seeing it for so long on the computer.

The plan is to make the duct from two layers of 1.7 oz Kevlar using the lost foam process.
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