Incredulous is another 98mm minimum diameter rocket designed to fly on 42″ of propellant and hopefully hit 40,000′. The design is a fairly simple 3FNC rocket, using one 60″ length of profusion fiberglass tubing with the altimeter and two trackers (RF and GPS) in the 6:1 Von Kármán nosecone.

The three fins are .093″ fiberglass with two layers of unidirectional carbon fiber and one layer of plain weave bagged tip-to-tip. Like my other recent builds it uses dual deploy via a line cutter and no drogue at apogee. Everything minus the motor comes in at 9 pounds. I might actually paint this rocket!

  1. #1 by Phil Babcock on February 23, 2012 - 7:36 am

    Another awesome looking rocket! For the line cutter, how are you making sure the wires leading to the line cutter do not get disconnected after apogee? And do you use dual redundancy for it?

  2. #2 by James on February 23, 2012 - 10:54 pm

    I run the wires through a nomex sock that covers the shock cord, and allow a slight amount of “relief” inside to keep any tension from transmitting through the wires. Doing this protects the wires and keeps them from getting snagged and pulled through the bulkhead. The only loads the wire sees is from the inevitable twisting on the descent. It’s hard to describe, the way I package the whole thing takes some time and thought to ensure it won’t get snagged/damaged. So far it has been working flawlessly. The next time I configure it I will take pictures for sure.

    I have not been using a redundant system for the line cutter, although I will for the next project being a 6″ O/P motor vehicle. There we be two cutters on the same ziptie that restrain the main.

  3. #3 by Phil Babcock on February 24, 2012 - 10:44 am

    Thanks! I look forward to the pictures and seeing your build of the 6″ rocket. What altitude are you expecting from that one?

  4. #4 by James on February 25, 2012 - 11:18 am

    Not sure yet, I haven’t done much with the design. I just have a 6″x60″ motor casing waiting for a ride.

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