Bicycle Propulsion

[crazyivan]

hi everyone...wonder if it is possible to make a cannon strong enough to propel a bicycle? i am toying with the idea of mounting a cannon on the rear of my bicycle....

rockets are not legal in my country so yea i am wondering if it is possible to generate enough energy to propel a bicycle with a rider forward very quickly.

[shud_b_rite]

Yes it is possible, but it is not very practical. Dont waste your time, get a CO2 fire extinguisher and use that, it will give you about 15 seconds of fun before you have to fill it up.

[crazyivan]

yea i only want that short burst of speed just for fun....any idea what kind of pressures and how should i make it?

so far i have only made 2 pneumatic cannons with ball valves....

[Insomniac]

A better idea woudld be to make a pvc water rocket, with a ball valve as the throttle. If you mounted a large enough tank on each side of the bike you would probably get some decent speed.

[crazyivan]

pardon me being a noob but why water and not air? asking cause my steel bike generally doesnt like water...and i prefer not to get wet.

[jackssmirkingrevenge]

water rockets

Your bike needn't get wet

Water is heavier than air, therefore has a greater momentum when leaving the rocket nozzle

Action and reaction, more power for your bike

[youtube][/youtube]

[crazyivan]

okay so how much water should there be in the chamber? 50% filled? sorry i have 0 experience with water rockets...

is using a fire extinguisher as a chamber a good idea? as i thought it could be pumped up to much higher pressures than pvc? also thanks for your help guys! very helpful

[Insomniac]

Well pvc is lighter than a fe, and can still hold a fair bit of pressure.

How much water you put in is up to you. More water will last longer, but will be heavy and the pressure will drop really quick because of the lack of air. Less water will give you more sustained thrust over a shorter period of time. To stop your bike getting wet you could have the nozzles right near the back of the bike.

Jack, that vid is definatly faked (must be hanging from a cable)
Each of those bottles would provide only a split second of thust, and the way they are placed on his back would just make him do a somersault straight into the water. The way he spirals like that is impossible given the nature of those rockets. When he is only halfway up and still accelerating, the water is barely dribbling out of the rockets. The mythbusters tried it and it just doesn't work.

[mega_swordman]

Jack, that vid is definatly faked (must be hanging from a cable)
Each of those bottles would provide only a split second of thust, and the way they are placed on his back would just make him do a somersault straight into the water. The way he spirals like that is impossible given the nature of those rockets. When he is only halfway up and still accelerating, the water is barely dribbling out of the rockets. The mythbusters tried it and it just doesn't work.

Either way, it's funny to watch it. I'm sure almost everyone who watched understood that something like that can't be done, but its still funny to think about it. It's also funny to think of all the gullible people who think it was real and it could be done.

Here's another funny one from the same group.
[youtube][/youtube]

[crazyivan]

ok so i have made a rough diagram based on the length and width of my bicycle rear rack...i only have space for one of these.

but i dont know what diameter should the ball valve/nozzle be to be strong enough to push a 70kg mass (bike+rider) on wheels. anyone knows how to calculate?

and is the volume strong enough? if not i can stack two of these vertically on top of each other. but that creates another problem should i connect two of these together to a single nozzle(elbows would decrease flow) or separate them and find a way to release them simultaneously.

water would be filled by pouring it thru the ball valve. the water:air ratio i would try to find the best by trial and error.

[Redcoat]

lol that japanes thing is absolutely hilarious.they talk fast. :laughing6:
I wonder if thats real i think it isn't.To my memory they did it on Mythbusters and he just fell over.

http://www.petitiononline.com/hds2468/petition.html

[spudthug]

imp..thats what we jsut established... for ur question ur not going to get fire extinguisher threads u have to weld a nipple on..i would ue a hakf inch ball valve..

[boilingleadbath]

A couple comments:

1) The specific impulse of the water is related to the pressure... in ideal situations, it'd be sqrt(2*P/De) = V

(P)ressure in newtons/cm²
(De)nsity in kilograms/(100 cm³)
(V)elocity in m/s

2) The total speed gain is equal to V*ln((bike + rider + tankage + water)/(bike + rider + tankage))
(typical rocket equation stuff)

Lets say we have a gallon of water (100 psi, ideal situation) and a 150 pound bike-rider-tankage system...
V = 37 m/s
37*ln(158/150) = 1.9
total speed change = 1.9 meters per second

That's like 4 mph.
However, the full-system/empty-system weight is still small, so we gain alot of benifit from more fuel...
2 gallons = 3.8 m/s
3 gallons = 5.5 m/s
4 gallons = 7.2 m/s
5 gallons = 8.7 m/s

5.5 m/s is fairly respectable.

3) Ideal situations don't exist, but high flow to the nozzle can help you aproch them.
a) Don't put your ball valve on the water exaust pipe... you'll decrease the flow a lot. I recommend using the valve only to provide air from an air tank.
b) Don't put your valve somewhere awkward like that. If you want decent acceleration, you want to be able to hold on!

4) Propulsive force is equal to pressure at the nozzle times the effective area of that nozzle.
Note that I said 'effective' - the actual area of the nozzle might be 50% bigger than this (in worst-case scenarios)

We don't want the bike to tip over, so let's keep thrust under 75 pounds - or about what you'd get from a 1" ideal nozzle or a pair of .7" nozzles.
Real life nozzles are probably within 10% of that, and sharp holes in flat disks are still at 60%...

************
Note that I'm not a fluid dynamics person, nor a rocket scientist.

[crazyivan]

about point

3a. if i dont put it at the exhuast where should i put it in order to release the water+air mixture?

b)i m thinking of making a longer wooden lever to reach the valve at the back actually.


and i am going to use class E upvc pipes. its rated to 15bar or 217psi. suppose i use a 1" nozzle.. what kind of mixture should i use? sry boilingleadbath but i was never good in maths and i dont understand the stuff u just posted.. could u do me a huge favour by calculating what kind of water/air mixture i would need with the same dimensions as the one posted above?

[Insomniac]

I think a setup like this would work best: