My Balls 2005 project idea came together rather quickly. I wanted to do something different than just load up Sponge Bob with several solid motors which was my original idea. You know a central white motor and air starting two 54mm red motors and two 54mm blue motors. Spectacular as that may seem, I am going to save that for a local launch. I needed something that I would need the higher waiver for. Our local waiver at 20,000 is pretty respectable but I have always wanted to go higher.
A few of the local CEG guys got into building their own hybrid this year and I liked what I saw. I also liked Jeff Jakob's projects (Rockethigh.com) he always brings to Balls so I called him up and we start talking rockets. He already makes a very nice 4 inch vehicle which is also quite expensive. Plus I wanted more thrust to go higher. We talked some more and came up with a plan. Before I settled on the plan, I called up Bill Colburn to discuss the project with him as well to see if it could be done the way I wanted it. Bill gave me the ok and some software to start working on simulations. Ok, so I also bought his book "A Manual for Hybrid Propulsion System Design" which came with a CD full of information from his SORAC project. I started learning about hybrids and doing research. Since I like the 4 inch range of rockets, this was the size I was going to go with.
My specs for a flight that was over 35,000 on a "N" engine and of course have a good burn time of about 7 seconds. With several simulations and Jeff and Bills experience we came up with the design I have. A 4-inch rocket using the tank and combustion chamber as the rocket body. The current rocket simulation is just under 40,000 feet at 2800 feet per second (I think they will both be less). The engine simulation is between 650 to 675 lbs of thrust for 6.98 seconds using 19.5 lbs of nitrous and 4.5 lbs of HTPB rubber with a total of 20320 Ns...just 160 Ns short of a complete "N". So we designed what I wanted and now I had to build it. The rocket itself is just a tad over 13 feet long. This is because I needed a 5 foot tank to hold all the nitrous to get the thrust and burn time. This with the 2 foot combustion chamber, 4 foot upper body and 2 foot nose cone comes to 13 feet.
I had a lot of work to do including machining several parts like the tank closure/couplers, make my own fin can and cut my own nozzle. Jeff sent me the combustion chamber and threaded boat tail from a left over project so I at least did not have to make these parts (thanks Jeff). Here is what I have so far:
