David and I just finished watching the story of Burt Rutan’s ‘Spaceship One’, on Discovery Science. What a great story and what fabulous airframes and aerodynamic technology it all is. We couldn’t help but notice that the rocket was nothing like as impressive as the craft it was powering. The rocket exhaust was disorgainsed, it pulsed and its power output (for its size) was really not that impressive. On the succesful flight, at the end of the burn, the rocket seemed to be coming apart internally with visible hard debris being ejected.
For years now, Nitrous Hybrid rockets (the type of rocket used in 'Spaceship One') have been using a solid plastic or rubber fuel grain. The ‘grain’ is that part of the rocket that burns as fuel in the Nitrous Oxide. When we started out, that’s what we used, as it was a proven material for this application. These fuel grains had their drawbacks. They are dirty and smokey when they burn. They are hard to get lit and they rely on the available surface area of the inside of the tube to provide fuel for the burn. Folk at the drag-strip did not like the mess the rockets left behind.
So we decided to try a cardboard fuel grain as burning paper left much less mess behind. Unfortunately the cardboard absorbed so much moisture from the air that it did not give the needed power and reliability. One day, while taking a shower, I was thinking about how to keep the cardboard dry. It occurred to me that, if we soaked the cardboard in an oil, then it couldn’t take up moisture from the air. It turned out to be a major breakthrough. After a couple of tests, using rapeseed oil, we discovered that we could get more power and a steadier burn using about one third the amount of Nitrous oxide. Later we tried other oils, the most spectacular turning out to be kerosene. One of our six inch external diameter rockets produced over 1,500lbs of thrust, using less than 2lbs of N2O per second of burn. We have shared these results with many people in the rocket world expecting that these results would put an end to the faith in plastic and rubber as fuels.
So why is the oil-soaked cardboard so much better? Simply, the cardboard is now acting as a ‘wick’ allowing oil deep inside to boil out under pressure forcing oil vapour into the heart of the rocket. The result is that the surface are of the cardboard does not so much limit the power of the burn.
To a man (or woman) the rocket folk have ignored it and carry on with their plastic and rubber fuel grains.
The next major development we came up with is the piston accumulator. We use pressurized nitrogen to push the N2O into the rocket. This is always at a higher pressure than the boiling point on N2O on the day. Systems that use the self-pressurisng property of N2O, by allowing it to boil, thereby producing high-pressure vapour, have several inherent problems.
The first is that N2O in the form of gas is very dangerous stuff and can explode without an ignition source. The second is that it rarely boils fast enough to keep the ‘push pressure’ up and the rocket tends to pulse as pressures and back-pressures fluctuate. The Third is that the N2O boils in the feed-lines to the rocket, making the lines full of a compressible liquid/gas mixture, which causes further pulsing and makes even metering of N2O flow impossible.
We discovered that, as a result of horizontal acceleration, with vertical bottles in the car, the liquid N2O would slosh up the side of the bottle. The Nitrogen, would then find its way around the N2O causing the rocket to lose power and splutter. If we sloped the bottles to allow for the acceleration effect, the Nitrogen would find its way around the N2o as soon as we opened the main throttles.
The solution was to place a free-floating piston between the Nitrogen and the N2O. This prevents Nitrogen blow-by and makes the system impervious to acceleration or to the angle at which the bottles are mounted. Another benefit is that all the N2O can be used without any gas mixing as the bottle empties, making the use of the N2O much more efficient. An unexpected side-effect, was a significant increase in power for the same oxidizer/fuel ratios and flows.
Again, one would think that this development would have been eagerly embraced by users of Nitrous Hybrid Technology. No chance. ‘Very interesting, but we’ll keep on doing it the same old way.’
One wonders how it is, in such a supposedly advanced engineering culture as we have in the UK, that such advances can be simply ignored by so-called ‘experts’.
On reflection, this country has never embraced technological advancement easily or readily. We gave away Frank Whittle’s gas turbine to the Americans and the Russians, while cutting Whittle’s funding and ripping him off for an invention we did not value at the time.
We are not making unsupportable claims about an idea that has yet to be proven. We have the video and the hard experimental data. We have the best power-to-weight ratio N2O hybrid around with the most beautiful and steady flame you could wish to see. We have full throttle control. And it's very very low-cost to build and use. I have done something the armchair engineers and modelers haven't done. I've got into the car, and lit the rockets quite a few times, which is no small thing to do.
With all this in mind, and having failed to get any acknowledgement or recognition for these significant advances, we have decided to take our technology to the other side of the planet, where the imagination and sense of adventure is still strong enough for these technologies to be taken seriously and welcomed with open arms.
Your loss, Britain! We tried and you didn’t want to know.
