Pneumatic Water Rocket (first one)

[Thursto]

Well this is my first post on this forum. I have been a member of a spudding forum for a while now. i Known alot about pressure PVC ABS DWV etc etc.

But i have put this topic on spudfiles.com and after some googling i found this website, which was more suited for this, and i need some advice and help.

I know it will more then likely stumble in flight, because of the 2 engins etc and un even balance. well thats what i have been told.

This is for my school semester project, its a pneumatic water rocket. it has 2 "rocket engines" the main body and fins.

it will be mounted on a base, with quick release brass hose fittings.
It will be actuated by a pull motion of a cord with a handle, which pull a plank down on rods (to keep it straight etc) on the plank the brass female couplings will be fixed so when you pull it should pull both at the same time. i might even rig up a spring actuated piece to do it.

Well enough chit chat here is some specs:

"engines" x2

Length: 40cm
Width: 2"
Material: Pressure rated PVC
Nozzle port: Li'l bigger then 1/4"

Main body:

length: 70cm
Width: unknown at this point

nose cone:

length: 30cm
Width: same as main body (but coned shaped, so main body thick at base)

Launch pad:

Dimensions unknown.

Release mech:

Brass hose fittings (see pics for details)
Pull actuated (possibly spring, not sure yet)

Fuel:

100psi
have to work out water ratios.

enough crap heres some pics...









Note that 2" PVC is just for reference not actualy length

same with the PVC in this one









What i am wondering is will it propell into the air?

Do you think it would work?

It will have stabalizing fins

what should i do for a parachute technique???

And what should i change or what do you think will fail?

any modifications i should make?

Thanks heaps in advanced

[october sky]

First off nice setup.

I have seen PVC rockets fly, not as high as bottle rockets but they will fly.

first the two rocket thing bad idea. if you have to use it then you mite want to stick two foam shuttles to both sides or stick three fins onto the each rocket in total 6.

also the board thing good, but rather then have two strings on the out sides, how about one in the middle of the broad.

you mite want to check the psi rating on the PVC pipes before you decide that the max psi will be 100, mostly because this thing is heavy, so the more psi you have the higher it will go. these things have like a rating of I think about 150-200psi, so just 10 below it and you should be safe.
also how are you are you going to put air into it???? a bike pump would work fine but you have two boosters and two tubes, that means you have to have two pumps. I would combine then into one.
As for the parachute, you’ll need one, A pop bottle you don't really need one for this type rocket but PVC is hard and will shatter if you let it fall. So I would go with then simple releaser. You make it so the nose cone can fall off easily when inverted, then you put weight in the nose cone(clay or something like that) and pack the chute IN the nose cone, then when the main part of the rocket slows down the nose cone will continue on(since it is heavier) and pull out the chute, then the chute will deploy, also you will need a 0.5-1m chute for this type of rocket.

And one more thing, get some pics or video of this we would love to see how this things flies.

Enjoy October Sky

[october sky]

First off nice setup.

I have seen PVC rockets fly, not as high as bottle rockets but they will fly.

first the two rocket thing bad idea. if you have to use it then you mite want to stick two foam shuttles to both sides or stick three fins onto the each rocket in total 6.

also the board thing good, but rather then have two strings on the out sides, how about one in the middle of the broad.

you mite want to check the psi rating on the PVC pipes before you decide that the max psi will be 100, mostly because this thing is heavy, so the more psi you have the higher it will go. these things have like a rating of I think about 150-200psi, so just 10 below it and you should be safe.
also how are you are you going to put air into it???? a bike pump would work fine but you have two boosters and two tubes, that means you have to have two pumps. I would combine then into one.
As for the parachute, you’ll need one, A pop bottle you don't really need one for this type rocket but PVC is hard and will shatter if you let it fall. So I would go with then simple releaser. You make it so the nose cone can fall off easily when inverted, then you put weight in the nose cone(clay or something like that) and pack the chute IN the nose cone, then when the main part of the rocket slows down the nose cone will continue on(since it is heavier) and pull out the chute, then the chute will deploy, also you will need a 0.5-1m chute for this type of rocket.

And one more thing, get some pics or video of this we would love to see how this things flies.

Enjoy October Sky

[WRA2]

Well this is my first post on this forum. I have been a member of a spudding forum for a while now. i Known alot about pressure PVC ABS DWV etc etc.

But i have put this topic on spudfiles.com and after some googling i found this website, which was more suited for this, and i need some advice and help.

I know it will more then likely stumble in flight, because of the 2 engins etc and un even balance. well thats what i have been told.


And what should i change or what do you think will fail?

any modifications i should make?

Thanks heaps in advanced

A few suggestions.

1. Consider using 3 engines instead of two. Three will counter any thrust imbalances better then two. With two you will have more of a chance that the rocket will fly in an unpredictable direction of the pressures and water levels are not perfectly matched.

2. Consider replacing the metal "quick connects" that you are using with non-metallic ones. Metal on a pressure vessel is a safety hazard and also adds extra weight. A metal part can be extremely dangerous should the rocket fail when pressurized and explode. The use of metal for the construction of the pressure vessel is not allowed in most water rocket competitions including the ones we hold. Should you become interested in competing you would have to change to non-metallic.

3. Make sure that when using PVC for your rocket construction that you keep a distance from it when it is pressurized. PVC tends to shatter when failing under pressure creating a shrapnel hazard. UV also weakens PVC so protect it from the sun. A coat of UV resistant paint will help.

[Aquafire]

I am curious to learn how two nozzles in this manner will work on a water rocket. Octobersky is smart to point out to use one pump because if you use 2 then pressure is going to be never the same in each side. This must be the same to fly correctly.

[Thursto]

Ha-ha thanks, yeah I know PVC is heavy, but I didn’t want to use a plastic coke bottle because it’s for a school project and it would look to basic.

I thought the metal would be better then plastic nozzles because it’s less prone to break/shatter, higher stress rating.

Yes I know this PVC can go very high. But I'm limited to 150PSI because that’s the max output on my pump.

On the design, the green tubes, each of them have a tire valve in the end of them, so u lock the rocket in with chambers with the water, pump to say 120, disconnect pump, redo for the other side.

I think it will work better with the strings on the outside, coming into 1 string because it will be more even (if I do good measurements).

Ahhh my plan was to sit right beside the rocket, that’s what the foot pedals are for, and it will have a seat attach to the launch base. BUT all the pressure section and the rocket, will be behind ½” thick clear PVC (acrylic)

The nose cone will be machined by a foam machinists, it will be heavy duty strong foam, almost like rubber, but light weight. It will be 30cm and the same width as the main body, which I’m yet to work out I was thinking 65-80mm DWV PVC.

My idea for the parachute was you wrap it around the nose cone, (strings attached) and when it takes of the wind resistance will be pushing against it, but when it starts to fall back down air will catch under it and pull it of the cone and deploy.

Yeah I know I will need a large parachute, what sort of material do you all recommend?

I would say 3 engines are out of the question sadly  to much money :S and I can’t think of how to make the launch pad to pull 3 down at a triangle sort of thing.

And yes I know all about PVC shattering, and ABS splitting and all that crap, and I know how to pressure glue them all together correctly with primer. That’s not new to me. But yes I do also known UV rays and sunlight damage it.

[Bellarossa]

Ha-ha thanks, yeah I know PVC is heavy, but I didn’t want to use a plastic coke bottle because it’s for a school project and it would look to basic.

I thought the metal would be better then plastic nozzles because it’s less prone to break/shatter, higher stress rating.

Yes I know this PVC can go very high. But I'm limited to 150PSI because that’s the max output on my pump.

On the design, the green tubes, each of them have a tire valve in the end of them, so u lock the rocket in with chambers with the water, pump to say 120, disconnect pump, redo for the other side.

I think it will work better with the strings on the outside, coming into 1 string because it will be more even (if I do good measurements).

Ahhh my plan was to sit right beside the rocket, that’s what the foot pedals are for, and it will have a seat attach to the launch base. BUT all the pressure section and the rocket, will be behind ½” thick clear PVC (acrylic)

The nose cone will be machined by a foam machinists, it will be heavy duty strong foam, almost like rubber, but light weight. It will be 30cm and the same width as the main body, which I’m yet to work out I was thinking 65-80mm DWV PVC.

My idea for the parachute was you wrap it around the nose cone, (strings attached) and when it takes of the wind resistance will be pushing against it, but when it starts to fall back down air will catch under it and pull it of the cone and deploy.

Yeah I know I will need a large parachute, what sort of material do you all recommend?

I would say 3 engines are out of the question sadly  to much money :S and I can’t think of how to make the launch pad to pull 3 down at a triangle sort of thing.

And yes I know all about PVC shattering, and ABS splitting and all that crap, and I know how to pressure glue them all together correctly with primer. That’s not new to me. But yes I do also known UV rays and sunlight damage it.

I have found that nylon cloth makes the best parachute for rockets which are heavy. I believe that your deploy method may work in ways when you do not expect. So it could deploy when you are still going up. You need a strong material for this because thin plastic like rubbish bags will just rip open when stressed such as this way. You can get nylon for parachutes from model rocketry shops.

[october sky]

um... i have tried the "put the chute on the nose cone" thing, yea my nice nylon chute riped in half, there goes about 10 bucks, unless you can get it on the cone in the DEAD center your screwed. and if you think that pop bottles can look basic check out these guys

Air command rockets

[Tim Chen]

It must be strange to live in a land where 1/2" clear acrylic shield is less expensive than PVC pipes and hose fittings!

Maybe you could trade some of that shield for the extra motor parts with someone here?

I think you'll be a lot happier and a lot safer with 3 motors.

[Thursto]

It must be strange to live in a land where 1/2" clear acrylic shield is less expensive than PVC pipes and hose fittings!

Maybe you could trade some of that shield for the extra motor parts with someone here?

I think you'll be a lot happier and a lot safer with 3 motors.

hahaha nah at my local hardware store its like $70 AUD for a 1m by 1m sheet of clear acrilic BUT my father runs a buiesness in electrical engeniring so he has a job coming up which they need some of that stuff, so he said he'll order "too much" n purpose and i get all the ofcuts and extras :P

Haha nah i think i have a good set up and i have some ideas for fins. I will have 8 in total. 4 large ones at the bottem, and 4 smallish ones near the top.

Thanks heaps, Thursto.

[Tim Chen]

I'd love to get my hands on some of that clear acryilic or some polycarbonate that thick. You're very fortunate!

One thing I am confused with you just said you are putting fins on the top of the rocket. I think this may not be necessary and may make the rocket unstable. You should check the center of pressure if your design and see if it will work.

[Thursto]

I'd love to get my hands on some of that clear acryilic or some polycarbonate that thick. You're very fortunate!

One thing I am confused with you just said you are putting fins on the top of the rocket. I think this may not be necessary and may make the rocket unstable. You should check the center of pressure if your design and see if it will work.

Haha im going to get extra for my other projects and what not. yes i am actually.

Haha its hard to explian ill draw up a diagram if i can be bothered later.

how do i figure out the centre of pressure?

and whats the best water to air ratio?

thanks.

[october sky]

in order to find the centre of pressuret you would tie a some string on it then swing it around your head, if it doesn't tumble everywhere then that is your CP(centre of pressuret) if it does tumble then you move the string up and down the rocket untill it doesn't. and the best water to air is 3:1.

[october sky]

in order to find the centre of pressuret you would tie a some string on it then swing it around your head, if it doesn't tumble everywhere then that is your CP(centre of pressuret) if it does tumble then you move the string up and down the rocket untill it doesn't. and the best water to air is 3:1.

[Tim Chen]

in order to find the centre of pressuret you would tie a some string on it then swing it around your head, if it doesn't tumble everywhere then that is your CP(centre of pressuret) if it does tumble then you move the string up and down the rocket untill it doesn't. and the best water to air is 3:1.

You also need to know where the center of gravity is if you want to know if the rocket will fly stable. That's easy because all you need to do for the center of gravity is to tie the string around the rocket and move the string along the length of the rocket until you can hang it by the string and it balances perfectly.