Archive for May, 2012

Incredulous Rebuild – Part 2

Last night I completed a four hour post-cure of the booster section to finish the rebuild. I am happy with the way the layup turned out, but a bit disappointed with how the capped leading and trailing edges turned out. I loosely followed Jim Jarvis’ guide (seen here), but ran into some issues while refining the new (for me) process. Next time around I should be able to make it look far more aesthetically pleasing, but for this go around I hope it works better than it looks. Final mass of booster section is 2180 grams, with the nose cone at 1300 grams.

We have a 50,000′ wavier in place at FAR this weekend, looks like I’ll be flying again Saturday.

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Incredulous Rebuild – Part 1

When I first built Incredulous I intended to fly it on longer burn motors to high altitudes at relatively lower velocities. This was a poor plan, so for the rebuild I’m going to be more deliberate about making a high performance rocket that can stand the high temperatures associated with Mach 2+ velocities. The main difference this go around is the epoxy I’m using. I chose Cotronics Duralco 4461 low viscosity resin for the tip-to-tip and Proline 4500 epoxy to coat/cap the leading edges. Both are rated to 500F with a post cure, which shouldnt be a problem with the new curing oven I made.

For the tip-to-tip, I’m using three layers of carbon fiber. Layer one is 4.1oz unidirectional carbon, while layers two and three are 6oz plain weave. The first build used unidirectional for layers one and two, adding a lot of stiffness to the span of the fins, but left the 45 degree orientation a tad too flexible.

I have one more side to bag, then I will treat the edges and clean up the layup. The first two sides have come out great, probably the best layup I’ve done, extremely stiff and looks great. Assuming the fins don’t delaminate again, the next flight is simming to roughly 46k feet at Mach 2.6. More to follow.

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Curing Oven

The past few I weeks I have been working on repairing Incredulous, stripping the remaining carbon fiber off the fin can and sanding like crazy. I took a break and started working on an oven capable of curing some higher temperature epoxy systems. There are still some tweaks to be made, but as of right now the oven is at a steady 240° F without any problems.

The construction of the oven is made from 2″ thick foil-lined polyisocyanurate foam purchased at Home Depot, rated to 250°F. The joints are pinned and then taped using foil tape used for HVAC work. The lid has a wood frame that allows the top foam cover to be recessed inside the oven such that the top of it is flush with rim of the box.

I just happened to stumble across a prefect little fan at the grocery store that is equipped with a metal blade. I took it apart and rigged a shaft extension to route through the wall of the oven so that the fan can circulate the air inside the oven while the motor is mostly thermally isolated.

All this to hopefully build a much more resilient fin can to high Mach numbers and the associated aerodynamic heating.

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