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BBC's Water Rocket-Vehicle Contest 120

jmichaelg writes: "The BBC is running a rocket contest to see who can build the fastest 2 liter water bottle propelled vehicle. The idea is you use a bicycle pump to pressurize the bottle to drive the vehicle. There are pressure limits (no more than 70 psi) so dry ice is out of the question. Gotta use a bike pump. Fastest car to go 20 meters is the winner. If you're going to play, you had better get going ... contest ends on Nov 6." Bonus points if you're riding it at the time.
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BBC's Water Rocket-Vehicle Contest

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  • this is how they're going to attack the taliban?

    time to go back to the drawing boards ;(
  • Boyscouts (Score:3, Funny)

    by MxTxL ( 307166 ) <> on Friday October 26, 2001 @09:45PM (#2486288)
    And you thought you escaped racing little model cars when you got out of boyscouts.
    • This is better, this time the engineer fathers
      will actually be the ones who can take credit
      for their creations. No little son to get in the
      way of all that glory.
  • by Omerna ( 241397 ) <> on Friday October 26, 2001 @09:47PM (#2486291) Homepage
    Since the vehicle can have a moving start, just give it a good kick. This will easily move it 20 meters. (Well, maybe not easily, so get a little propulsion from the bottle too).
  • Water? Nah. (Score:2, Funny)

    by SEWilco ( 27983 )
    The rules don't require water. They happened to use water in their example.


    Cleanup is left as an exercise for the experimenter.

    • No, no.

      Clearly you want something that will combust when exposed to air.
      After all they called it a "rocket" contest.
      • Not only would this be the fastest car to cross the finish line, it would be the fastest car to melt into a puddle at the end too!
      • Oh. Liquid hydrogen or kerosene at 70PSI? Have to mix it with air...a jet or turboprop would probably take too long to build (even if you can start with an automotive turbocharger) -- a ramjet is simple enough though.

        It probably would be the noisiest entry. Particularly loud if the liquid hydrogen version shatters the plastic bottle while the glowplug is hot.

    • Optimum density for the reaction mass is around 0.3 - mercury would be *way* slower than water. Remember you have to accelerate some of it. Try it at except the server is down (being fixed) at the mo.
  • With a very high proof... Once atomized by the high pressure air and ignited - it should make for a nice flame effect even if it doesn't do anything for increased propulsion. Flying two litre bottles of doom!!! Sounds like it would also make a good weapon for the next version of Quake...
  • =) (Score:3, Funny)

    by Myuu ( 529245 ) <> on Friday October 26, 2001 @09:54PM (#2486312) Homepage
    Finally, something to use those old school NASA programs on!
  • OK, it's clearly not what was intended :-) But use the same bicycle pump pressure mechanism to push the jet fuel / gasoline / whatever out to the nozzle and let it burn there.
    • the problem with this theory is that the fuel would have to be pushed out faster then the burn rate, not to mention I don't think the plastic would withstand the heat longer then a second or two, make for a nice explosion thoe
      • Jet-A doesn't burn all that well in liquid form, it is kinda hard to get started. It is kerosine after all. Once you do get it started it burns nice and hot with lots of black smoke, it won't explode unless you atomize it. Gasoline is much more explosive than Jet Fuel in liquid form.
      • Okay, so some fraction of my vehicle (or less) goes to the 20-meter-finishline in record time. In fact, I suspect that the whole vehicle (or pieces thereof) would go 20 meters in *all* directions, save for the ground, which we could measure concretely (no pun intended) by the depth of the remaining crater.

        Just so that what I'm saying doesn't sound like crazytalk, ask yourself this: what spacefaring rocket *doesn't* expend most of its mass to get some vehicle to its destination?
  • Suppose you could generate a lower E.T. by driving wheels with the power instead of using strictly the push of the jet? 20 meters on pavement seems like its a long enough distance that you'd be coasting by the end under jet power. Perhaps you could harness more of the energy by driving wheels.
    Or not. What do I know. Guess I'll have to try it and see. Incidentally, why do they limit charging it to a bicycle pump? 70 psi is 70 psi if it came from a pigs lips or an air compressor.
  • by Anton Anatopopov ( 529711 ) on Friday October 26, 2001 @10:09PM (#2486337)
    I would like to enter this, I have a keen interest in amateur hydraulics, and I think I have a chance.

    My vehicle would probably be a three-wheeler made primarily from balsa-wood, with ceramic skateboard bearings (coated with a thin film of latex for wheels. I figure if I can minimise the weight of this thing, and keep the rolling resistance down then I am in with a good chance of winning

    I just hope they let American Residents enter the comp. I cannot wait to get going on this.

  • by Anonymous Coward
    Since the rules allow a rolling start, here's my plan:
    Take a pop bottle. Pressurize it to 70psi if you feel like it. Hook it onto the catapult on an aircraft carrier. Start timing once the bottle's airborne. :)
    • Just make sure you fill it with somthing heavy, water would probably do.

      The balistic coefficent of an empty (or 70psi air filled) 2 liter soda bottle is reasonably poor.
  • Pop bottles and bike pumps can be dangerous. Last time those two came together I ended up with quite a lump on noggin. Just thankfull that the lead nosecone wasn't on at the time :)
  • I guess now I know why the British have never been to the moon.
  • The Rules
    *Use a 2 litre pop bottle
    *The pressure must not exceed 5bar, 70psi, this is about the amount of pressure you can get from a cheap bike pump.
    *The car can have a rolling start or fixed start - it's up to you.
    *The car that completes the straight 20-metre tarmac/concrete course the fastest wins!
    *Anything else goes!

    Anything? MAAAAAAN that leaves SOOOOO many things to try.. TNT.. JetFuel.. Beer.. a Catapult.. and whatever else is posted here :)

    • Wait a minute now... wouldn't the pressure generated by burning jet fuel in a 2 liter greatly exceed the pressure generated by a bike pump?

      This would make it seem that all these fun things are out of the question.
  • ... so what about a bit of JET A and a little jet motor? You use the pop bottle for the fuel.

    Where does it say you can use water? Oh, anything goes. So, if the Jet A idea doesn't pass, what about using good old coca-cola instead of water? That should give it an extra kick (without exceeding the pressure limits, you should get a bit of extra pressure over time once the soda starts bouncing around... Pump it up to, oh, 60 psi. Let it rip. The CO2 released from the soda as the car bounces around should keep the pressure up there for longer than just air and water alone....)

  • by SClitheroe ( 132403 ) on Friday October 26, 2001 @11:02PM (#2486419) Homepage
    Chassis - The car that wins is going to have very carefully measured and constructed alignment. Getting the vehicle to run 20 meters straight, and with the thrust exactly aligned (in whichever direction the particular design calls for) is key. You can't afford to waste any of those thrust newtons on trying to drive the car sideways, or having the car trade forward velocity for lateral movement.

    Water/Air ratio - if you run out of air too quickly, you are hauling excess water all the way down the track. Similarly, if you design the vehicle such that air can escape freely once the water level falls below a certain point, you are wasting power.

    "Gearing" - one has to wonder if a direct-drive design (air pushing water out the back) is the most efficient. If you used hydraulic principles, you could in effect "gear down" the high pressure, resulting in high-torque that could drive over-size wheels, similar to the way that a hydraulic lift works. The winning design is going to have to find a tradeoff between quick accelleration/coasting and continued power for the duration of the track. Could the careful design of a nozzle accomplish the same thing? (/me thinks back to the model rocket days)

    Multiple pressure vessels - this is just fanciful thinking, but one of the techniques steam locomotives used was to use the high pressure air in one set of cylinders, and then re-use the resulting lower pressure to drive a second set of cylinders. Extrapolating from this, I wonder if having two pressure vessels, totalling the legal limit, and firing at different times (ie. one for acceleration, one for maintaining speed) might be feasible.

    I guess, though, in the end, the simplest, lightest design will win. Having a good chassis is still key though.
  • Tank up with heavy water.
    • Deuterium Oxide is less than 10% heavier than standard water. Think deuterium contains 1 proton and one neutron. This is only 1 atomic weight heavier than Hydrogen. The Oxygen however has 6(?) protons and 6 neutrons giving it an atomic wieght of 12. A standard water molecule would thus have an atomic weight of 14. A heavy water molecule has an atomic weight of 18. Not much difference really.

  • This brings back memories of playing with water bottle rockets as a kid. You'd take a 2-liter bottle, fill it half way with water, mount it on a thingamajigger, and pump it up. If it didn't explode, you could launch it fifty feet in the air. Hours of fun for the whole family.

    I ended up drawing a picture of it and using it for the science fair. It's amazing how low your standards go when you've put it off until 10:30 the night before it's due.

    Ideally, the design for this vehicle would keep the water relatively high, for added pressure, and keep the nozzle fairly small, to increase the velocity at which the water leaves. Balsa wood might also be involved.

    Finally, this post was actually a clever ploy to hype my new sig. Try it. It's pretty cool.

  • I remember playing with bottle rockets a while ago. I don't remember the pressure, but we were using a bike pump I think. Unlike what they're showing, our nozzled was actually just the end of the bottle. When we'd let it go, it emptied almost instantly while the bottle would rise above 10 meters faster than we could track it.

    Wonder what it would look like when fired horizontally. I bet you'd do the 20 meters in about one second. I'm not sure you could make it stay on the ground though. And, well there might be safety issues...
    • Staying on the ground is the trick to this contest. It is easy (and a lot of fun) to make any 2-liter bottle shoot up in the air with water and an air compressor. The engineering challenge of this contest is to get all the water to shoot sideways with out letting the propellant (air) to escape unused.

      BTW if you have never made a 2L rocket I highly recommend it. But...I DO NOT RECOMMEND THIS! []

  • by cr@ckwhore ( 165454 ) on Saturday October 27, 2001 @12:11AM (#2486534) Homepage
    We did something similar in my high school chemistry class several years ago. We were allowed to use chemical reactions as a source for the propulsion. We had a 2 lane "water drag track", and were given 1 soda bottle, and some basic supplies, like rubber bands, balloons, soda straws, etc.

    The easiest rig to build, and the most common, was simply the soda bottle with a rubber stopper in the opening. The rubber stopper had a hole in it, which would function as an outlet... the bottle would then be filled with the infamous vinegar and baking soda mix. This provided enough fuel for long lasting propulsion, while being simple. One of the biggest problems with this design however, is the outlet on the bottle was usually above water. To acheive optimal propulsion with this method, the best thing is to make sure the jet is below the water line.

    Another method (and the winning method) was to completely seal the bottle with a full rubber stopper. The bottle was filled with the infamous (and bad smelling) baking soda & vinegar mix, and promptly plugged with the stopper. After about 2 minutes of building pressure, the stopper would fire out of the bottle, propelling it forward with great velocity. There were some minor problems keeping the boat in the water, but that was the winning design.

    Fancy designs don't work... some over-acheivers were inclined to build more complex designs, incorporating a lot of internal parts, etc. Go for the K.I.S.S theory! (Keep It Simple Stupid).

    • One of the biggest problems with this design however, is the outlet on the bottle was usually above water. To acheive optimal propulsion with this method, the best thing is to make sure the jet is below the water line.

      Wrong. The velocity of the exhaust is the key. After all F=ma, right? It is of no consequense what the exhaust is "pushing" against.
  • First off, minor correction:

    *The pressure must not exceed 5bar, 70psi, this is about the amount of pressure you can get from a cheap bike pump.

    so they weren't saying you gotta use a bike pump, just that thats the best you can get w/ a bike pump. You can fill it up any way you want (so long as the pressure dosen't exceed 75psi).

    Second, they didn't say the 2 letre had to be the main part of the body, so how about taping one to the inside of, say, a farrari. I bet that'd take 1st place vs anything else they could throw at it ^_^
    • Actually, over the distance of 20 meters, I think a thoroughbred race horse has better acceleration than most types of motor vehicle. At least, I seem to remember that from some documentary comparing a race horse to a sports car.
  • This was actually an event in a High School science competion called Science Olympiad. I participated in it about six years ago, and I'm not sure if they are still doing doing that event (called Bottle Rocketry). The object of the game was to keep the 2 liter bottle aloft for as long as possible. People used streamers or parachutes, all sorts of stuff. The hardest part was to get the parachute to deploy correctly. My designs would always accidentally deploy the parachute while the rocket was still on it's way up... So we scrapped the whole chute idea and just decided to go for altitude. After experimenting with a few designs, it was found that attaching a funnel for a nose-cone and using triangular fins that encircled the body of the bottle worked best. Simple and light, shot off like a bat out of hell, and would stay aloft for around 8 seconds before lawn-darting in the field we launched it from. It rocked. Next year we got a bit fancier. A friend of mine came up with this really cool way to keep the chute from deploying until the rocket was at it's apex. It's actually a lot harder than you think...

  • Hee Hee! (Score:3, Interesting)

    by gnovos ( 447128 ) <`ten.deppihc' `ta' `sovong'> on Saturday October 27, 2001 @02:35AM (#2486766) Homepage Journal
    As it doesn't mention *water* anywhere, just for kicks I would fill the bottle up with a liquid right on the verge of vaporizing at room temperature when kept at a pressure less than 70psi. As long as the car is kept cool and pressurised, it will stay in liquid form, but as soon as it starts slushing around and depressurising, the liquid will begin to vaporize and ramp up the pressure. Additionally, since you don't actually have to have the liquid escaping (as long as the liquid remains, you will have a very hefty supply of gas), only the gas, you will be under acceleration for the entire trip!
  • What are the rules concerning weight and kinetic energy? Can I make a pressurized bottle trigger a trip mechanism to a heavy weight attached to a gear?
  • 1. Get horse and chariot hooked up.

    2. Fill 2 liter bottle full of cayenne pepper solution.

    3. Attach bicycle pump to bottle.

    4. Attach hose from bottle into horse's ass.

    5. Pay up life insurance, make out will and start pumping.
  • fill a 2 liter bottle with liguid nitrogen, cap it and throw it in water. Although the explosion is relatively non-destructive, it makes quite a boom.
  • It would be great to have a follow-up contest to see who can make a bottle travel the furthest distance, not necessarily fastest. The key here would of course be steering. I imagine you could figure out some pretty creative ways to keep a 2-liter bottle going for a mile or so on a flat road.
  • In high school, we had a competation to launch a bottle the higest through the same methods. We found this out:

    1) Bottles with the big ridges (bumps) on the bottom actually went farther and stratighter then just round bottoms.

    2) The bottle would need to be filled no more then a 1/3 with water to get the most thrust.

    If you are worried about it going straight, just add a few fins. E-mail me if you have any questions.
  • Links about Water Rockets: je lly.htm zzle.gif ll/pad_fil l.htm grosse/ h2oRocketIndex.htm ket/index.htm

    There are probably more links than these. I am not karma whoring, it just didn't seem like anyone posted links to the "sport" of water-rocket building. It is too bad that they limit the size, etc - some water rocket builder/enthusiasts have built 2 and 3 stage rockets, added cameras and other payload packages - sent thier rockets up super high (higher than you would think)...

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