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12/03/2008
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Tom Shelley reports on an intriguing and uniquely British slice of leading-edge technology
A rocket-propelled car, powered by a mixture of liquid nitrous oxide and chicken fat, delivers 4000 to 8000 lb (18 to 36kN) of thrust, has a power to weight ratio that is four to five times that of a Formula 1 racing car, yet is designed to be reliable and re-used over and over again.
Typically British in the way it has been designed and built by qualified engineers working with minimal funding and facilities, it has evolved as a demonstrator for technologies that open up some exciting opportunities in aerospace.
The Laffin-Gas rocket dragster is the brainchild of David Knight and Carolynne Campbell, who are confident that the technology could equally be applied to rocket-assisted take-off of aircraft and UAVs. For civilian use, the low fuel costs and re-usability could offer big advantages over military developed systems.
At the recent Southern Manufacturing and Electronics Exhibition, chief engineer Knight – who comes from a race engineering background – explained that the four rocket tubes are lined with thick cardboard, soaked in chicken fat.
“That’s biofuel,” he points out. “It’s lit by a firework. The V2 was lit by a firework too.”
The nitrous oxide is held in four high-pressure cylinders, one for each throttle valve and motor. The valves are solenoid operated and open against the flow of the liquid. Any interruption of electrical power causes them to shut instantly. The throttle pedal is replaced by a dead man’s pedal, which cuts flow if the foot is lifted off. Flow is also cut if an inclinometer detects that the nose of the car has lifted too far off the ground. The nitrous oxide is pumped into the rocket motors by weight, so as to equalise the running time and pressure profile of each tube. Pumping pressure is supplied by having nitrogen in two further cylinders under 35 bar pressure. Liquid oxygen would provide more oxidant per unit weight, but is much more difficult to handle and constantly has to be allowed to boil off, so it cannot be stored on a small scale for long periods. The 1.4m long, 6in (150mm dia) rocket tubes are half hard aluminium, secured by titanium tie rods and have graphite nozzles. The tubes are mounted in a purchased chrome molybdenum steel dragster chassis. The pyrotechnic charges that start ignition are set off by glow plugs.
How did Knight come up with the idea? “We live close to Santa Pod,” he explains. “We thought we could do a better job than what we saw. We are looking for 300mph at the end of a quarter mile in 5s.”
Campbell, who is the driver, adds: “We also wanted to be able to do it regularly and as a reliable performance. We got the idea about four years ago, when we saw a tiny rocket car at a track. It made lots of noise, but it wasn’t very quick.”
As for their own dragster, she describes it as backyard built.
“We built the lot ourselves and it works,” she said. “Nobody else is running these kinds of rockets.”
Pointers
* Rockets are completely re-usable and run on nitrous oxide and cardboard, soaked in chicken fat
* The whole approach is to come up with something that is reliable and low cost, yet gives maximum performance
* The technology could also be applied to rocket-assisted take-off of aircraft and UAVs, for either civilian or military applications
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Author
Tom Shelley
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