Amateur Hybrid Rocket Motor

After debating for a while about buying a RATT Works hybrid rocket engine, I decided it would be more interesting, and that I would learn more, by building my own. As I understand it, this is legal here in the UK, whereas building your own solid rocket engines is definitely not.

To outline the project, I am constructing a small hybrid rocket motor, which will use nitrous oxide for the oxidiser and initially PVC for the fuel, but later I hope to experiment with various other fuels and additives.

The motor casing is a length of aluminium pipe, 37mm OD and 31mm ID, given to me by Andy's father who runs a scrapyard. Thus, I have no idea on which aluminium alloy it is exactly. However, the 3mm wall thickness should give a fairly large safety margin. All the parts are made from aluminium, with the exception of the nozzle, which is made from graphite purchased from Bob Fortune at Aerocon Systems. I am also having a steel nozzle made up for static testing of the motor, as I'm not sure how long the graphite one is going to last.

The motor will be filled via a length of 1/8" nylon hose, also bought from Aerocon. The hose will be attached to the motor using a Swagelok compression fitting (part number B-200-1-2RP with gasket CU-2-RP-2). Ignition will be by the Urbanski-Colburn (U-C) method, almost exactly the same as the RATT Works motors, hopefully utilising wire wool ignited by passing an electric current through it, for a totally non-pyro gnition system (for an explanation of the U-C ignition method, see here). Also, rather than venting the nitrous oxide out of the motor like the RATT Works motors do, mine will vent straight into the combustion chamber, an idea I got from Paul Kelly's website. This should help to get the motor started quicker.

Here are a couple of pictures of the parts of the motor: Picture 1 and Picture 2. As you can see, the engine itself is finished, all I have to do now is get hold of some nitrous oxide to perform some static tests of the motor (easier said than done, it seems!)

Update. 3rd October 2001

I've just uploaded the technical drawings of the individual parts of the hybrid rocket motor. They aren't great, as I've never done this sort of thing before, but the guys at Rolls Royce had no trouble making the bits. Note the greasy fingerprints from the machine shop on some of them!

Technical Drawings

Note that all measurements are in millimeters.

Also, I just managed to get my nitrous oxide tank filled this weekend at HighPower Systems in Doncaster, so static testing will begin very soon. Results will be posted here when I have them.

Update. March 2001

The casing has now been hydrostatically tested, and holds up to 750 psi fine. Unfortunately I am still waiting on my steel nozzle for static firing :-(


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