HUGE ROCKET TO BE FIRED AT SCHOOL OPENING DAY

When: Thursday 21st October 2010 7:30pm

Where: Ormiston Victory Academy, Norwich

The Laffin-gas Rocket Car team will be firing the biggest rocket ever to fired at a School.

Last Tuesday, we conducted a site inspection at the Ormiston Victory Academy to make preparation for the first public static firing of one of our Hybrid Rockets.

The Ormiston Victory Academy is an amazing new institution rising from the ‘ashes’ of Costessey High School in Norwich. We were greeted at the door by the Deputy Head and Rod Stevenson (a teacher at the school who is also a well-known person in the world of Rocketry). We were then treated to a quick tour of their engineering and technology facilities. At last: A school with lathes, milling machines, band saws, two forges, CNC equipment, a laser-cutter and so on! These tools weren’t sitting idly as ‘not safe enough to use’ but actually working, teaching and producing product!!

We met a few staff members and caught the infectious ambition and enthusiasm they all project. Is English Technical Education finally turning the corner and starting to produce the ‘hands-on’ engineers we so badly need? If this school is anything to judge by, the answer has to be a definite ‘YES’.

In an example of a spirit of ‘Education-Over-Caution’, the school approached us and not only asked us to bring our ‘Laffin-Gas’ Xperimental Hybrid Rocket Car to their Grand Opening Day, they also asked if we could FIRE one of our rockets for them. After agreeing on safety arrangements, and conducting a site visit to test the ground and ensure this can be done with a reasonable degree of safety, we have decided to go ahead.

At over 1,000lbs Thrust, this Nitrous Oxide and Bio-Diesel rocket will be far-and-away the largest rocket ever fired at a school, probably anywhere on the planet.

We’ve long been advocates of this kind of approach to technical education and we are delighted to have the honour of being part of this celebration of a truly ground breaking new school.


Contact: carolynnecampbell@gmail.com 01933 313816 (Rocket)
G.Howe@ormistonvictoryacademy.co.uk 01603 742310 x3438 (School)

OFF GOES THE TECHNOLOGY

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.

STILL PLOUGHING ON

Long time no write!

Firstly, our website is down. We’ve had a dispute with our Hosting Service.

We are now making new hosting arrangements and will be re-designing our website, taking into account all the developments that have occurred over the last couple of years on the internet.

In the meantime, we are still here and still working!

David has manufactured a new prototype valve that goes inside the input end of the rocket in an attempt to prevent backfires on start-up. We’ve had a couple of incidents on hot days where back-shock from the idling rocket has destroyed a throttle valve. We are installing this in one rocket and we’ll be conducting a test to see if it has the desired effect. We have also developed a new purging procedure that should prevent any recurrences of the problem.

Attempts to co-operate with a couple of Universities have come to nought. We had been warned that this may well turn out to be a waste of time, and so it has been. All kinds of positive emails and undertakings were received, but when it came time to ‘DO’ we have been met with deafening silence.

We are not yet ready to give up on working with educational institutions and we are trying again with another college. Actual research and development of challenging engineering seems to be something these institutions can’t actually do. If we are ever to get youngsters interested in engineering and science, in the numbers needed by our economy, something has to change in education.

We know that youngsters love the car and the rockets and they rapidly engage in learning the moment they get near the car. Unfortunately the teachers don’t seem to want to be bothered.

We will be at Sywell Aerodrome in a couple of weeks to take part in their superb ‘Youth in Aviation’ event. We expect to be overwhelmed by bright young people who can’t get enough of this kind of stuff. We spent the event last year utterly bombarded all day.

BANG!!

On Sunday 25th July, at the ‘Ladies That Launch’ event at Shakespeare County Raceway, ‘Laffin-Gas’ suffered its first start-line incident.

We were there in support of the very first event dedicated to the women who take part in Drag Racing. We were also using the weekend as an opportunity to train our newest team member, John London, who comes from the world of rocketry and was having his first experience of the world of Drag Racing. As training had gone well on Saturday, we decided to go for a two-rocket run on Sunday, which turned out to be a lot hotter than forecast.

There was a very loud bang, and a lot of gas was released from the car. We exploded one of the four main-throttle valves on opening the main throttle. The debris from the exploding valve was caught by the ballistic protection we had built in around the throttle assembly. While the bang was loud and, therefore, very energetic, the damage was limited to the valve itself and the hoses immediately upstream. No damage was caused either to the rocket or the pressure-vessel. The burst-disc protecting the pressure-vessel was not ruptured, indicating that the energy was dissipated further downstream. No-one, (including myself) was at serious physical risk from this event, but it does require an explanation.

It was the same sort of thing that occasionally happens in any big Nitrous burning car, often resulting in bits of carb and manifold being ejected through the air-scoop on the bonnet. In fact it was nothing like that big! When our car is on the line, everything is so quiet- the bang really stands out. In other cars it gets masked by the roar of the engine.

When we returned to the pits, we invited Paul Satchel (Senior Scrutineer and member of the MSA Drag Racing Committee) to inspect the car. Paul was happy that the safety systems had done their job and that we had acted responsibly.

The explosion was a result of something called ‘Compression Shock’, which happened when very warm gas (it was a hot day), which had built up in the very small space between the safety shut-off and the throttle valve, was exposed to back-pressure from the idling rocket just as the throttle was opened. We were firing two rockets. The one with a safety valve that was tightly sealed, did not have this problem. The volume of gas that did explode was less than 20cc. That is a tiny volume for such a big concussion!

We have built chillers into our race transporter to ensure our gasses and liquids are cold when we fuel up. We use insulating blankets to keep things cold after fueling. We pre-pressurise with Nitrogen Gas to ensure that Nitrous in the vessels and lines is always in its liquid state. But Sunday was a hot day, and a very small amount of N2O in a small section of the system, turned to gas, and was not purged (as the rest of the system is) when the start-up valves were opened.

We have now devised a new protocol to ensure that this section of the system is purged immediately prior to launch. We will also employ a cooling method directly on the throttles in future.

Photo courtesy of Missb Fotos

Something for the Techies

We're looking for testing partners who have nitrous oxide bikes and cars to help to develop a new application of our Accumulator technology. Below is a short paper on the subject.

NITROUS OXIDE AND ITS USE IN ROCKETRY AND HIGH-PERFORMANCE PISTON ENGINES

Nitrous oxide has long been employed both as an oxidizer in various forms of rocket propulsion, and as a performance enhancer for internal combustion engines. Many internet sites and published documents represent N2O as a harmless substance that can be handled safely with a minimum of expertise. As such it is very popular with amateur rocket enthusiasts, drag racers and others interested in getting more horsepower out of engines.

Nitrous oxide is, in fact, quite a unique substance with its own special physical and chemical properties, Properties that should be fully understood by anyone handling and using it in rockets or engines. Under certain circumstances, nitrous Oxide can explode in a very violent manner without any apparent source of ignition or oxidant to fuel such an explosion. These circumstances can easily occur during transfer and actual use and can occur in apparently normal conditions.

The attraction of N2O is that it is a good source of free oxygen, and that it is relatively easy and safe to handle and store. At lower temperatures it is a stable compound that is not very reactive, if a little corrosive. As it gets warmer it becomes less stable and predictable. High temperatures are needed to ‘split’ N2O into its two component elements, Nitrogen and Oxygen. Once split, a gas mixture of two parts Nitrogen to one part Oxygen is formed. One can see that this mixture is much richer in oxygen than is air. In air just under 80% of the mixture is Nitrogen and just over 20% Oxygen, four parts Nitrogen to one part Oxygen. It’s that extra oxygen in N2O that makes rockets burn so well and gives the horsepower boost to piston engines.

The other attraction of N2O arises from its quirky physical properties. Normally stored under pressure as a liquid, it has a very high vapour-pressure that is commonly used to push the N2O out of its containing vessel either into a rocket or into an engine. This ‘self propelling’ characteristic removes the need for pumps or other devices to move large volumes of liquid very quickly. At 20 deg C, the vapour-pressure is 58.5 bar or 850 psi (pounds per square inch). Nitrous oxide is very temperature sensitive. The higher the temperature, the higher the vapour-pressure, and the opposite applies to lower temperatures. A chart is included that shows the relationship of temperature and pressure. At 36.4 deg C, N2O reaches its CRITICAL POINT, when it starts behaving strangely. At and above this temperature all the N2O in a vessel becomes gas. It also becomes much more reactive as it approaches this temperature and can be made to explode by the application of a compression force. By ’explode’ one means an exothermic chemical reaction that is a true chemical explosion- not just simply a sudden release of high pressure gas. This stuff can go off like Semtex when it is too warm.

The boiling point of a liquid is determined by the gas pressure it is subjected to. If you go up Everest and want to make a cup of tea, the tea won’t be very hot, because, at that altitude, the air pressure is so low the water boils before it gets hot enough to make a decent cup of tea. Nitrous oxide behaves the same way. The lower the pressure, the lower its boiling point will be and vice-versa. At 20 deg C, the gas pressure needed to prevent boiling is 58.5 bar (850 psi). The instant that pressure is dropped, the nitrous oxide boils. The gas pressure that has this effect is, in this case, not air, but gaseous N2O, this gas is the nitrous version of the steam given off by water.

When a valve is opened to allow a rapid discharge of liquid N2O the gas pressure in the container will drop suddenly. As soon as this occurs the liquid N2O boils. Just as with water, the boiling will produce N2O gas and that gas will help to slow the pressure reduction. The gas can only be produced at a rate that is governed by the surface area of the liquid and the scale of the pressure drop. Once a valve is opened to release liquid, the pressure in the container will lower. This pressure is unlikely to be steady as all the N2O in the system is now boiling. Pockets of gas are forming randomly throughout the entire volume of the liquid, making the liquid itself compressible and, therefore, ‘springy’.
This applies even to the liquid in the line leading to the engine it’s supplying. This makes the rate of delivery to the engine much less predictable. It also means that gas bubbles are shot into the engine.

In the ideal set-up, for either a rocket or a conventional petrol motor, we want to deliver liquid N2O at a controllable rate. This makes the engine much easier to tune and to get a smooth performance. One often sees nitrous-aided cars venting the nitrous system to remove gas that may have formed in the lines. Initially this will deliver gasless liquid, but only for an instant as the liquid begins to boil.

Rocket motors that employ the ‘boil-off’ method to propel the N2O into the rocket always seem to ‘pulse’. The exit flame is never steady. One suspects that the same effect will occur in a petrol engine. In a rocket this effect is exacerbated by the resulting rapid changes of pressure in the combustion chamber. The back –pressure on the incoming line will cause the boiling point to fluctuate rapidly, making the pulsing effect worse.
In petrol engines employing a valve ‘overlap’ the same will apply. It’s quite common for my friend, Steve Woods, (who refills nitrous bottles at the track for his customers) to find that the bottle is so pumped full of air (with a little petrol thrown in, no doubt) that he has to let the air out before he can pump in the N2O. Racers beware – a pressurized container with air, petrol and N2O inside is a pretty unstable and dangerous bit of kit. The warmer it is, the more bomb-like it becomes.

For an engine tuner, or a rocket engineer, predictability is the key to ultimate performance. The ideal N2O supply system would never boil. It would deliver a predictable stream of non-compressible liquid, just like a petrol injector. This makes calculation of mixes and power output much easier and far more reliable. From both a safety and performance point of view, it would also be ideal to keep the N2O cold. Fluid densities go up and instability goes down. In a boil-off system, racers often employ bottle heaters to raise temperature in order to increase the delivery of N2O. The same effect could more safely be obtained by making the plumbing allow more N2O through.

In a boil-off system, as the bottle empties, gas will actually start to push the liquid aside and go directly down the line. If you watch water leaving your kitchen sink, as it empties a hole appears in the centre of the draining water as the liquid spins (coriolis effect). The same will happen inside a pressurized N2O container, with a resulting huge drop-off in performance. The emptier the container gets – the bigger the hole for gas to go down. Many racers counteract this by having more liquid than they need for the run, ensuring that the levels never get too low.

There is another complication with boil off-systems that is known as ‘Slosh’. In horizontal motion, the liquid will slosh towards the rear of the vehicle, climbing up the side of the container, again allowing gas to bypass the liquid.

In larger rocket motors, some of the downsides of the boil-off method are overcome by filling the gas-space with Nitrogen gas at a much higher pressure than the vapour pressure of the N2O. This prevents boiling. Often an external reservoir of Nitrogen is attached to lower the rate of pressure-drop as the container empties its liquid. This does combat many of the downsides of the boil-off system, but by no means all. Slosh can still happen as can gas blow-by. Back pressure can still make the system pulse quite heavily and the higher pressures mean that even more N2O must be left behind to minimise the blow-by as the levels get low.

So pushing with Nitrogen solves some of the problem but not all. The system is still somewhat unpredictable and the performance curve will be all over the place.
The ideal would be to keep the gas away from the liquid but still exerting enough pressure to prevent boiling. This is known as positive displacement. Gas/liquid shock-absorbers employ this technique. Either a bladder or a piston is used to keep the two separated. The gas acts as a spring damper, smoothing out pulses but the liquid remains free of bubbles and acts in a predictable manner. These shock- absorbers are more properly called ‘Accumulators’. We’ve tried bladders in our rocket-motor tanks, but they just weren’t up to the rigours of the high pressures. It is possible to buy ready-made bladder accumulators, but they cost a fortune, have materials compatibility problems and they are much too heavy for racing and rocketry.

So we tried putting free-floating pistons inside cylindrical vessels, Nitrous on one side, Nitrogen on the other. Now there can be no slosh, and no blow-by. The piston/gas arrangement also acts as a damper, minimizing the effect of back-pressure coming up the line. If the Nitrogen pressure is kept high enough there will be no boiling. The result was a very smooth and predictable rocket performance. We can stay well away from the Critical Point, vastly improving the safety aspects of the operation. In fact, the colder it is, the better it works.

Piston accumulators work very well for Rockets and we see no reason why the same shouldn’t turn out to be true for piston engines. All a tuner needs is predictability – then the rest is much easier.

Rained Off!!

Saturday didn't happen. Rain in the morning and a lousy forecast meant that we called off the trip to Bruntingthorpe. Just can't run in the wet!

Pending clearance from the track, we'll try again at Shakespeare County Raceway in two weeks' time. 12th & 13th June.

The Next Few Weeks

This coming Saturday, 29th May, we're puuting the car on display as part of the Rushden Power Fest, organised by Santa Pod Raceway. We're taking the opportunity to show our neighbours in the town waht has been built and engineered right here. Should be interesting...

On the 29th, we're off to Bruntingthorpe, a large active airstrip in Leicestershire, for a four-rocket running test. The runway is two miles long and very very wide, so it's a relatively safe environment for checking out handling and stopping. We'll be running bio-fuel rockets, not kerosene, as we really don't want all of that power for this test.

We have a few new team members, our fuelling supremo, David Rose can't make it, so we'll be going slow and steady to avoid any possible errors. The chillers are up and runnning. So, if it's a hot day, we should be able to keep the temperatures in the car well down into the safety zone.

Dave Burditt, from Datron Technology, is comiing up middle of next week, to install GPS and other data recording equipment. For the first time we'll be able to collect hard data on exactly what the car and rockets are doing in the real world.

Nerves are already starting to jangle... so slow and steady is the order of the day.