Rocket Vehicles (The half meter long, 12Newton boat, and the JETCAR)
Since the ancient times Man has marveled at jet propulsion. The Chinese, probable inventors of gunpowder, were making them for displays and, later on, weapons as early as 1400BC, and Hero had a steam turbine running in ancient Greece at about the same time. As jet propulsion developed it has come closer to us, as fireworks, space flight, and, closer still, jet aircraft. But, contrary to what people think, developing a rocket is not as difficult as the term “rocket scientist” would lead you to believe. With enough skill and ingenuity rockets can be built on any basically equipped laboratory with minimal resources. This page starts off with my hobby making model rockets (sorry, no high power stuff, they don’t sell it in Holland), and goes on to show how I made use of that experience to produce my first rocket powered vehicles. Than, finally, it presents some ingenious rocket projects of my own, and gives the reader a glimpse into what is to come in the future of POWERLABS’ rocket research.
To your right you can see a picture of my small rocket collection. All of these, with exception of the largest one, are powered by ESTES class “A” through “C” rocket engines: Those are the pressed sulphur-rich black powder type, 75% KNO3, 10%S, 15%C with an Isp (specific impulse) of 80seconds. The smaller engines produce thrust between 2.5 and10Newtons for 0.5 to 2seconds+. The largest rocket uses “D” engines capable of up to 20Newtons thrust for 2 seconds. They can fly up to several hundred meters high, and can reach velocities of several hundred kilometers per hour. The ultimate challenge for me in rocketry is to break the sound barrier. Even with a reasonably small rocket this will require a very high power motor utilizing a high performance propellant (not black power of course). My research with high performance propellants has yielded some very good results, but due to lack of space I have never been able to make a full scale rocket with one such motor.
Here is a fun picture: Just after I finished my big rocket I went out in the field with a friend to test fire it, and the engine exploded! This catastrophic failure was probably caused by a propellant crack inside the case, either by manufacturing defect, or due to rough handling. Either way, when such cracks exist they increase the surface area of the single grain propellant, and the increased burning rate takes the chamber pressure to far higher levels than what the engine was designed to handle, so it explodes… The base of the rocket was shredded, and the lunch pad was ruined. And as the fireball traveled through the inside of the rocket, it melted the parachute (see that smoking fireball leaving the rocket? That was the parachute:). Also notice the nosecone shooting out like a bullet: I found it over 50 meters from where the rocket blew up. Fortunately, both the engine cases and the rocket bodies themselves are made from cardboard (and only a few parts are plastic or balsa wood). Hence, no shrapnel is produced and any fragments slow down quickly enough so as not to hurt the operator (which in this picture would be me, standing to the back of the picture, with the 10M range remote control:).
Another picture of my rockets… And a few interesting bits of info: The largest rocket stands over a meter high, and the smallest is less than 20cm long. The yellow rocket with a black nosecone has a camera integrated on it’s nose (I still haven’t developed the film yet… It takes 36 photos, one per flight). The thin, long rocket which is shown in the first picture but not in this one was a two-stage rocket. During it’s test flight it flew so high that it parachuted into a nearby city and disappeared with its small payload: A small plastic toy figure (hey, I couldn’t find anything better!)
It was my first attempt at using a rocket engine for more than making fireworks or launching rockets. As I remember it, it was a dragster-like balsa wood car measuring 30cm (1″) in length, 10cm (4″) width, and some 5cm high. It was powered by a C class engine producing 6newtons of thrust, and had a parachute to stop it 3 seconds after the engine had burnt out. On its first test run it left the ground a meter from where the engine was ignited, flew a semi-circle approximately 2 meters above the ground, and crash-landed some 15 meters from where it had been launched, being completely destroyed in the process. The fact that it had air spoilers and stabilizers, and was carefully balanced for maximum stability did not seem to help counter the other fact: That its engine was producing 2.3 times the car’s weight in thrust! This project was scrapped and a new one was started:
Now, anyone can build a rocket… But this rocket powered boat (the red flame, I called it) is not your average rocket! It is made from 2.5mm thick premium grade balsa wood, varnished with pore filler inside and out for higher structural integrity, and covered with red Monokoteï¿½ plastic wrap for extra low drag. It was fully waterproof to the point that it could be immersed in water up to a meter deep and nothing would get in. The boat maintains its shape due to 6 internal sections, each shaped progressively larger so as to form it’s slim pointed shape and large square back. Overall, it is 50cm long, 14.5cm wide, and 8cm tall (not counting air spoiler, rudders, and side wings). The whole boat weights 500 grams, and contains lead on it’s nose, so as to center the gravity right ahead of the side wings. This prevents it from either sinking down or flipping over as it accelerates. The engine was a C-8-3 inside an aluminum tube, so that the engine case would be ejected from the boat once the engine was finished. Later it was upgraded to a D-12-5. With 1200 grams of thrust, the boat would move through the water at such a speed that it came off the surface, flew a meter or so a few inches from the water, landed and immediately bounced back up into the air. After it’s second test run, a side wind threw it against the side of the water canal… Since it was moving so fast, it smashed itself against the wooden plank that held back the water and became a floating mess of balsa wood.
A glorious end to an awesome boat… I don’t think I’ll build a new one though… Way too much trouble… From drawing the plans to cutting each individual balsa wood piece and varnishing it, it took me almost a week to get it done (note: It was all done from scratch: The plans were drawn by hand using purely arbitrary values, the wood, plastic wrap and glue were leftover from my planes, the rocket engines came from my rockets, and the red paint was leftover from the big rocket (yeah, I know it’s *too* red…)… As with all my other projects, this was done alone, without any outside help.
Here I started building my first engines. This is a picture of my final jet car prototype. It is a lot more than it looks… The body itself is made from 3mm thick balsa wood, treated with pore filler, varnished and painted for maximum stiffness. The front bumper is 5mm thick plywood (after smashing so many other balsa bumpers..), the wheels are 2″ high density foam airplane wheels and the axles are 5mm dia steel bars. Both the front and the back wheels have interdependent suspension, provided by the fact that the axle sits on a high density foam cushion. Suspension travel on both sides is nearly an inch, which prevents the car from bouncing off the road when it is going fast. The body is held together with epoxy glue and balsa triangles, and the bottle in the middle is PET 1.5litres (with a *TESTED* bursting pressure of over 250PSI!). It can also hold the larger, 2litre cola bottles. This car can be operated in several ways. One is to inject a fuel into the bottle and ignite it, rocket style. I normally use 75cc of butane (though I have also used 250cc of hydrogen, with rather spectacular results). As the fuel burns it produces pressure (up to 90PSI for Hydrogen) which escapes out of the 6.5mm dia exhaust with a nice high pitched “WOOSH” and pushes the car forward, at a moderately high speed (estimated 30km/h). It goes about 50 meters far like that.
The other way would be to simply pump air into the car and than remove the adaptor, so that the jet of escaping air propels the car forward. This allows much greater velocities as air can be pumped into the bottle to pressures much higher than combustion alone would allow (since the volume and original pressure is fixed, and using an oxidizer such as oxygen in the combustion chamber results in the bottle melting). Using this method, at up to 200PSI, the car literally takes off.
But than there is an even better method: Partially filling the bottle with warm water and than putting 30 – 50ml of Liquid Nitrogen, sealing the chamber, causing the pressure rises as the LN2 vaporizes. Than, when the seal is removed, the gas starts to escape, much like the above (with compressed air). Except that as it does so it lowers the boiling temperature for the LN2 inside the bottle. So more LN2 vaporizes and this keeps the pressure in the chamber more or less constant throughout the drive. With this method I have seen the car travel a couple hundred meters at easily over 60km/h. In the picture above a chunk of ice from a pervious run got stuck in the exhaust, which is why there is so little smoke and the smoke is going downwards. Normally the exhaust travels straight back from the car and forms a smoke trail some 5 meters long (and no, the blur in the picture is not a Photoshop filter or any camera trick, it simply due to camera movement, trying to keep up with the car).
Well, rocket powered vehicles are always on my mind, so it shouldn’t be too long before I pull off that stunt again, and this time it will be with rockets of my own making (Chemlabs has conducted extensive research on the field of solid fuel production, with impressive results)… Also, my research with solid rocket fuels has reached the point where I would now be able to produce my own high performance rocket with a fair degree of certainty that it would work. Hence, that too should be featured here sometime soon.
But look to your right: There is the real challenge! I shall use this 40-gram CO2 stainless steel cylinder measuring 15 X 3 cm (6 X 1.25″; 54cc) and weighting 150 grams (It’s walls are 3mm thick!) on a different kind of engine; In normal duty this cylinder stores liquid carbon dioxide (critical pressure: 900PSI at room temperature), and is required to maintain a large safety margin at up to 50C. Therefore, it is built with such a geometry so as to eliminate any possible weak spots, and it is made tough enough to (in theory) burst at nearly 10 000PSI. Considering that a hydrogen/oxygen mixture combusts at 500PSI under normal confinement conditions (Ok, 20 times that if it DDT’s (Deflagration to Detonation Transition), but that shouldn’t happen)… Yup, you can see where I am going… I shall build a steel De Laval’s nozzle for it and thread it so it screws on to the end of the cylinder (there is no way a weld would hold), and than pressure-fit a fuel line and an oxidizer line to it, and make a high powered liquid fuelled rocket engine out of this. This is actually my second liquid fuelled rocket engine project… My first one used a similar, but smaller combustion chamber (a 12 gram CO2 cartridge) and was fuelled by a liquid propane/butane (60/40) mix stoichiometrically mixed with nitrous oxide in the combustion chamber… There were 4 fuel lines, arranged like a square at the back of the cylinder and connected to 4 individual gas tanks (each tank had a capacity for 20cc). All fuel lines pointed inwards at an angle. In the middle there was the oxidizer line. To start the engine the fuel valves were opened gradually until a foot long yellow flame shot out of the rocket. Than the oxidizer line was opened gradually, and the yellow flame gradually grew brighter and shorter (but more intense) until it was about 10cm long. Than it entered the combustion chamber with an explosion and the rocket was started. It made a beautiful rocket flame and an awful lot of noise, but when I really throttled it up the pressure inside the combustion chamber became so high that it pumped the fuel back along the fuel line and the engine started running roughly… So this time a pressurized (use nothing but nitrogen!) fuel tank will be on order. Or maybe I’ll just use hydrogen / oxygen. I haven’t ruled out the possibility of having them both gaseous (the problem with that would be the fuel consumption… My first engine *REALLY* drank its NO2/hydrocarbon mix!!!), but depending on what sort of equipment becomes available to me, I may well use cryogenic oxygen with some other liquid hydrocarbon fuel (cryomethane is high on my list).
Check back later for a complete design theory (HEAVY on math) on this engine, as well as some graphics of what it should look like. I shall build this when I gain access to a machine shop.
Note: POWERLABS assumes no responsibility for any accidents resulting from misuse of this page. Rocket engines operate at very high pressures and can cause great damage if they are to explode. Experiment with care.
Also make sure to check back later for information on building your own solid fuelled rockets.