Tuesday, September 8, 2009

Designing a New Rocket Motor (step by step)

I have decided to design, build, test, and fly a new rocket motor. Why not just fly one of my existing rockets with any one of the existing motors that I've already constructed? The reason is simple. I really enjoy going out to Mojave and flying rockets but the really fun part for me is the design and construction. The process is the cool thing, the fact that the culmination of that process is a rocket flight is just the icing on the cake. Plus it's been at least a couple of years since I've designed a new motor and I miss it. The one thing that I plan to do differently than in the past is to document the entire process right here.

The motor that I've been thinking of is an updated version of one of the earliest designs that I made. Large enought to loft a good sized rocket and but not too big to be a chore to prep for flight. Simplicity and ease of use are my goal. The orginal motor was my first step away from the venerable B-200 motor designed by Richard Nakka and was influenced by Richard's Kappa motor development. It was in the same class as the Kappa motor with a similar propellant configuration. I chose to use steel for my motors casing to simplify the design. I also utilized a retention groove in the nozzle and bulkhead which provided a recess for the retention screws which engaged into threaded holes in the casing. This was a holdover from the B-200 design and though simple to implement, in this larger diameter motor didn't prove as hardy as in the smaller diameter motors. While I never experienced a failure, the screw holes would get torqued pretty well and the casings would need to be replace frequently.

Anyway here is a picture of that original motor as well as the nozzle drawing that I did. I love that it has oil splatters on it from hanging behind that lathe while I made the part.

Next step will be to crunch some numbers in SRM and come up with a working design, and some basic dimensions.

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