The Urbanski-Colburn Valve for Hybrid Motors

"The Urbanski-Colburn Valve for Hybrid Motors"
by Bill Colburn

At Balls in 1995, I was present with a hot idea. By using the Korey-Pooley idea of filling through the nozzle of a Hybrid Motor, substituting a thermoplastic tube for a metal one, and then using the simplest device possible (the PrestoLoc (TM) Fitting or a facsimile thereof) a valve was created which did the following:

1. Filled the tank with Nitrous Oxide.
2. Acted as a safety valve (bursting at 1000 to 1200 psi at 65 F).
3. Acted as a start valve by failing under pressure and heat at the injector face during ignition.
4. Act as an orifice when selecting it and/or drilling it slightly to match the motor flow rate needs.

Since the tank then would be open and could not be filled outside of a launch, it need not be DOT certified (though hydrotesting would still be a requirement). Another fallout was that odd numbers of injectors could be used, the even ones connected by tubing loops and the odd one used to fill through the nozzle.

Well, this hot idea was being deployed for the first time and exclusively at the Balls Experimental Rocket Launch in 1995. Or so I thought! As I proudly described my new invention to interested rocketeers dropping by my tent, one chirped up with "Hey, that's just like John's method!" 

"Wait a second!" I chirped back. "Who is this John?"

"He's the guy in that blue striped tent on the second row over there," he said, pointing to the west. 

I dropped everything and scurried over to discover what was going on.

At the blue striped tent I saw a beautifully machined Hybrid motor and vehicle. And there is a PrestoLock (TM) fitting on the head end!

I said, "Wow! I guess we had the same idea at the same time!"

John Urbanski and I chatted for a bit, compared Hybrid notes, and he later dropped by some nylon tubing for me to try; I had brought kel-f tubing, which I thought would be more compatible with the N2O.

The first Aerocon "M" Hybrid was launched with John's tubing and ignited perfectly, but suffered a burn-through; a transducer hole for static testing was not plugged correctly. 

We came out in September to MudRoc and successfully flew it with the rest of John's tubing. All the Aerocon Motors use this method and Dave Griffith employs it in the H-70 and I-70 motors he is making (very cute little things, 29mm diameter). 

The method is in the public domain, but John and I please request that if you use the idea to please refer to it by name. I humbly submit, the "Urbanski-Colburn Valve". Hey, call it the UC-Valve, for short. 

billc_ original H motor

Bill Colburn's Original H motor

billc_original I motor

Bill Colburn's Original I motor


Bill Colburn with L Hybrid Black Rock 1994

bill colburn L Launch

Bill Colburn with L Hybrid Launch Black Rock 1994

billc_M 1995

Bill Colburn M Hybrid Black Rock 1995


Bill Colburn, Bill Lewis, and Walt Horscht loading M Hybrid BR 1995




Launch! Black Rock 1995, M Hybrid


Recovery - A bent tail fin


Recovery - A Motor Head End Burn Through


Recovery Analysis - Nitrous Tank snapped off due to lateral acceleration forces at burn-through

Black Rock 1995