"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:
Since the tank then would be open and could not be fille 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
|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.
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.