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How to make the Best (Water) Bottle Rocket? Answered

My teacher, as an end-of-the-year "fun" project, partnered us up and wants us to build water bottle rockets using two liter bottles. The only rules are that the rockets must not be propelled by anything else that uses fire, for obvious reasons, and that we must have a parachute or other recovery system. That leaves my options wide open. I've never built a rocket like this, so I'm looking to y'all for some advice. The contest is for the longest hangtime and highest altitude. I really want to win. I've considered heating a 2-liter and extending the bottom into a rounded-point nose. If I use a parachute, I want to make it as big as possible to cause as much air resistance as it can. I've thought about using wings instead of a chute, but the idea seems a bit complex. I have no idea how to calculate anything, like the ratio of chute size to descent time or even terminal velocity, as it's never been covered in our curriculum. If any body has ever made anything like this or has any sensible ideas, please, please let me know! We launch next week, so time is pretty short! Thanks, Bran.

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Kiteman (author)rocketgirl122012-06-06

Were you replying to a specific comment?

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aholt3 (author)2011-10-05

what would you say about cutting the edges off the fins to make them more
aerodynamic

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Crafty123 (author)2010-05-06

My school is also doing this project of testing air rockets. We are supposed to somehow design a rocket in a contest where it is measured on the amount of time that it stays in an air. We are allowed to create a parachute, but I have no idea how to make it and store it into the 2 liter bottle. I am unsure on how to put the parachute on without reducing its aerodynamics. Any ideas??

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maximus276 (author)Crafty1232011-05-05

thirty second answer: you take a garbage bag put a big circle on it and cut it out then, when attatching use string and poke some holes then, PUT IT IN THE TRANSITION AREANOF YOUR ROCKET THAT ADDS LENGHTH MAKING IT MORE AERODYNAIMIC AND ROLL IT UP AND SHOVE IT IN (make sure it is lose and attatched to your nose cone as well

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science project1 (author)2009-09-14

hey killer......how should a make the best water rocket for my science project?....we have a maximum psi.

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killerjackalope (author)2008-05-07

Well you'll want to be pushing as much water as you can out to get the rocket higher, that means more pressure... Umm aerodynamically a simple set of fins and a cone on top goes a long way... I keep meaning to do an 'ible on my take on bottle rockets, ours tend to fly far and go fast, the best one ever was launched at 95psi and nearly full of water, near exploding point... It took off like nobody's business... A good release system is also helpful, which is where the work comes in

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westfw (author)killerjackalope2008-05-08

Amount of water vs amount of air is a relatively complex question. Too much water makes the rocket heavy, and water isn't a particularly good propellant (not compressible, you know.) OMSI had an interesting exhibit where you could control the amount of water and pressure independently and fire a bottle at the ceiling (on rails), but it didn't let you use high enough pressures to be relevant to contests... IIRC, the altitude records for this type of rocket (pressure rockets) were set using fluorescent tube covers pressurized with air only (using water at the pressures involved resulted in high initial accelerations that buckled the airframes.) The record these days is well over 1000 feet, BTW, which is a pretty respectable number even by (pyrotechnic) model rocket standards.

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killerjackalope (author)westfw2008-05-08

Hmm true but int he case of one's built around bottles it tends to be water powered for the first part, air expansion plays a very small role... Any the pattern I saw when doing this alot tended to be at much higher pressures you could afford to have more water to give a higher powered launch, at 2/3 full of water you get a nice general pattern for above 30psi, however with reinforcement, usually in the form of taping you can add much more pressure to a bottle and get a more impressive thing to fly, allowing you to start working with either alot more water or negating it all together and using a more controlled release of air, well a smaller nozzle which even with water makes a difference as it lowers initial thrust but prolongs the thrusting... I suppose it depends on aerodynamic possibilities, if you can make a nice flying one then go for as close to go flight path with fins etc. and blast it skyward with as much water and air as you can, once yu start in to better aerodynamics and lower weight you have a lot more play in the system...

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very knowledgable and clever very thankyou

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No problems... For the record most bottles are OK up to 70psi...

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westfw (author)killerjackalope2008-05-08

I dunno. A pop bottle with no water at all flies pretty well.

Of course, from a SCIENCE class perspective, one of the most important pieces of advice is to EXPERIMENT before the contest. Amount of water is the easiest variable to control...

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killerjackalope (author)westfw2008-05-08

Yeah, along with nozzles, since you can make a bunch using the caps as a screw on mechanism...

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westfw (author)killerjackalope2008-05-08

Hmm. The launchers I'm familiar with all stick a PVC pipe up the inside throat of the bottle, and are therefore incompatible with cap-based nozzles (or any nozzle at all, as far as I can see.) Do you know of a different type of launcher? (note that if your major propellant is water, then the 3-d shape of your nozzle doesn't matter very much; just its diameter. If your propellant is air or other gas, then you can start to worry about convergent/divergent shapes expansion ratios, supersonic throat velocities, and all that good "rocket science.")

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starwing123 (author)westfw2008-12-27

There are launchers using gardena quick disconnect and launchers using copper to latch on to the outside of of the bottle

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killerjackalope (author)westfw2008-05-08

Oh forgot to say there, I have three different designs from that and have never seen any with a pipe up the middle, I'll do my personal one soon enough, it's pretty good.

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killerjackalope (author)westfw2008-05-08

I was talking more about playing with diameter, even with gases it doesn't play a big role to make a specific design, except on the very best of the rockets...

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starwing123 (author)westfw2008-12-27

1000 for bottled rockets over 2000ft for FTC

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msim249193 (author)2008-05-30

what about this one? 2 - 2 liter pop bottles, water, and one raw egg. We need to build one that will fly with a raw egg and land with out it breaking, ideas any one????

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yasmina 123 (author)msim2491932009-07-07

did not understand a thing

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bicky 51 (author)msim2491932008-12-12

cardboard "capsule" use lid & put 2 rubber bands round to hold lid on then attach small parachute

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yasmina 123 (author)bicky 512009-07-07

dont think that is a good idea

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11010010110 (author)bicky 512008-12-13

put the egg in a container and pack with paper / nylon / polystyrene etc put the container on a spring assembly in a long empty part of the rocket. when it hits it dumps its energy into the spring. make sure it cant hit the sides of the rocket from inside too strong

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yasmina 123 (author)110100101102009-07-07

thankyou really helped me, i am in year 8 and we did that project

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yasmina 123 (author)110100101102009-07-07

thankyou that is exactly what we were doing at school

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bicky 51 (author)110100101102008-12-15

use bands to attach parachute to dampen initial parachute lug

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starwing123 (author)2008-12-22

As you climb in PSI or BARs, you'll realize that aerodynamics matter more than pressure. Also, if you do some research, You'll find out there are 3 main types of launchers that water rocket people use. Copper, cable tie, and Gardena quick disconnect. I'll send you my two stage design if you want it.

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ry25920 (author)2008-05-08

DUDE!!!!! I did that too, it's due tomorrow and a tip. NEVER leave it unatended, someone tore apart mine 2 days ago and now I can't rebuild in time. We have to do it on a "budget". I'll tell you whose worked and why. Launch day is tomorrow

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Kiteman (author)2008-05-08

Annual National Physics Laboratory Water Rocket contest

Includes a water rocket simulator, and a detailed how to pdf for building water rockets.

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westfw (author)2008-05-07

A 2-liter bottle? What exactly are the rules? 1L bottles tend to go higher. Hardcore water rocket folk have been known to glue several together... My bookmarks are on my other computer...

One hint is to use fins to make sure your rocket is stable throughout its upward flight (requires experimentation.) The difference in altitude achieved between a rocket that flies straight up and one that wobbles like a soda bottle is substantial. Also, ensure that your parachute deployment scheme allows plenty of coast time...

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