Water/Air Pressure Bottle Rocket

[Guest kevo214]

I recently received a challenge/project in which I need to shoot a water/air pressure powered bottle rocket into the air and get it to stay in he air for as long as I can while not breaking and egg that has to be somewhere on the rocket. Here are the rules I received.

 

Material: 2- 2 Liter Soda Bottles (minimum)

4 File Folders

Duct Tape

1- Large Egg (App. 70 gr.)

**No Metal

Guidelines: 1- 2 Liter Bottle for Fuselage

No more than 60 PSI of air

Total Length, 9ft or less

Total Weight, 300 grams or less

**No Metal, explosives, or other fuel

Rules: 2 Chances, 1 with each rocket

Add as much or as little water as you want

No more than 60 PSI

Time is measured from launch to the first item that hits the ground

10 - Seconds to remove the egg -stronaut

If egg is broken you get time

If egg survives you get time X 2

 

So from what I gather the materials are not mandatory just suggestions and I can use almost anything. The one thing I am not sure of is if the 300 gr. limit includes the water but I will update later with more info. I wanted to know if anyone can help me with the design and if you can please post or email me at kevo214@si.rr.com Thank you for your time.

[LucidDreamer]

If the challenge is about keeping the rocket in the air for as long as possible why not use a parachute that ejects after it reaches maximum height. It would help protect the egg from breaking as well. Of course your instructor may have thought of this and made a rule against it.

[rbp6]

I recommend trying a velcro strap thingie to hold the egg in the rocket. i.e suspend it somewhere in the center of rocket. like the velcro would be holding it in air. Or at least I think that would be the easiest way to hold it.

[drz]

A plastic bottle can hold alot of psi. I've had a 20 oz bottle up to 60 psi. I was trying to launch something out of the bottle though. It worked pretty good, would launch a paintball further then walmart guns.

 

Anyhow, if you have to launch the bottle itself, you would need some kinda nozzle that would force the flow of the air out through a smaller hole, maybe several holes. You would want the egg to be about dead center in the craft, to high or to low will cause that side to plummet to earth. The velcro idea sounds like a good idea, but remember, duct tape is good enough for Nascar.

[Dave]

Perhaps have the egg located in the nosecone of the rocket for stabilities' sake? Plus that allows for extra padding etc.

[Stusi]

We did an experiment similar to the one your doing minus the egg. What we learned is, nose heavy is best for stability. If it is back heavy it will have a very random flight pattern, and will most likely break the egg. Also, no one ever figured out the exact amount of water, but i did make a smaller "nozzle" out of a form of epoxy so my force on take off was greater. Sadly my rocket was very light (had very little weight in the nose) and it didn't go too high. Also small fins for stabilization are good. No need for anything too big. Hope this helps, and let us know how it turns out!

[swansont]

Also, no one ever figured out the exact amount of water

 

That should be easy to estimate, if you know the pressure. Assuming an isothermal process, PV will be a constant. P must always be greater than atmosphere to eject the water, so you want to make it so that P is 1 ATM when the volume is that of the bottle. If you can pump to 2 ATM, then you want half air, half water. 3 ATM, 1/3 air. Add maybe a 10% safety margin (more air) to make sure you're ejecting all the water with a downward velocity.

[5614]

i once saw a guy do this, but with slightly different rules, he did electrolysis on water and used the hydrogen and oxygen as a fuel, the only thing was that is was soo powerful it melted the bottle, which was plastic, but i dont think that you can do electrolysis and it wont work in a plastic bottle.

 

remember you said you wanted time in air, not height, something which goes up quickly isnt as good as something which goes up slowly, a massive parachute to slow down the descent and save the egg is a good idea.

compact the air as tight as possible [i think there's a limit in the rules]

 

if you are confident that you can do it right, use two different rockets, but if one is likely to fail, use two of the same...

 

remember the rule first thing to hit the ground stops the timer, so you cant have a parachute behind a lid, coz the lid can't fall off as it would hit the ground first.

[Guest Garyr]

I did the water/botle rocket thing a while back. The 60lb. air pressure will be the limiting factor. Real short flite if at all. The nossle will be a challenge, start whith a hole in the bottle cap. Get a lot of bottle caps. This will be where 90% of your work will be, not with the egg. Was easy for me, I have a machine shop to work with.

 

GaryR