Sunday, February 22, 2009

Reinforcing couplers

You might recall my concern about the level 3 rocket folding under tremendous stress at the coupler interface between the booster and payload sections.  I was able to easily reach into the 7.5" space and apply 3-4 layers of fiberglass/resin to that region to prevent failure.  Now I'm building Giant Leap's Dynawind version of their Vertical Assault kit and I'd like it to survive any 54mm motor made. Overal the design seems very robust and the coupler doubles as the electronics bay with two all-thread bars running through it.  This seems strong but I wanted to reinforce the 3" coupler anyway and couldn't reach in easily.  I recalled that the Gates Brothers had used balloons to compress the reinforcement to the inside of their couplers for the Porthos design (scroll down to "avionics bays").  I'd forgotten their vertical orientation and water-filled balloons, however.  In any event I was able to do something similar with my air compressor, some resin spread inside the coupler, and two wraps of fiberglass unwound into the interior:
I also wrapped a section of polyethylene bag over the glass/resin before inflating the balloon.  I  failed to take a photo of the interior post-cure but suffice it to say that it's incredibly glossy and uniform!  I think this rocket will now survive a K1275 or 2675L730.

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