[paul.fr]

You can make a homemade rocket with a soda bottle and pump, but what other ways could you build a rocket in your back garden...?

[Karen W.]

Did you post how to do that in the kitchen science or did I miss it??

[paul.fr]

Did you post how to do that in the kitchen science or did I miss it??

no, i have not posted it. I think dave may have in the main section of the website, if he hasn't i will post one tomorrow.

[daveshorts]

I haven't put it on the main site, but I have written one here in the past:
http://www.chaosscience.org.uk/pub/public_html//article.php?story=20050605135858118

If you can get hold of a rubber bung it works better.

if you make the hole smaller - by epoxing a smaller diameter pipe through a hole in the lid it will go a lot better, especially if you run it purely on air without the water.

[DoctorBeaver]

Stick some mustard on a cat's bottom & watch it go!  []

[paul.fr]

I haven't put it on the main site, but I have written one here in the past:
http://www.chaosscience.org.uk/pub/public_html//article.php?story=20050605135858118

If you can get hold of a rubber bung it works better.

if you make the hole smaller - by epoxing a smaller diameter pipe through a hole in the lid it will go a lot better, especially if you run it purely on air without the water.

cheers, Dave.

I was thinking of doing a similar one, but replacing the bottle with a section of hollowed out foam as the rocket.

[daveshorts]

I think that a bottle will work far better. Lemonade bottles will hold huge pressures for their weight, I think they are designed not to fail at 5 atmospheres, and generally don't fail until 8-9. unless you are using some pretty fancy foam you won't be able to hold much pressure at all, and because the energy stored in compressed air goes as the square of the pressure, it won't go ver well.

[paul.fr]

I think that a bottle will work far better. Lemonade bottles will hold huge pressures for their weight, I think they are designed not to fail at 5 atmospheres, and generally don't fail until 8-9. unless you are using some pretty fancy foam you won't be able to hold much pressure at all, and because the energy stored in compressed air goes as the square of the pressure, it won't go ver well.

I was thinking of this type of launching device:

a section of hose or similar material, at one end a sort of sack, like a bagpipe that is full of air. On the other end you have your launcher / rocket and all you basically do is jump hard on the sack to expell the air down the hose which launches the rocket.

Does anyone else have any rocket designs?

[felixtheferret]

Hi Paul. 
   I built a water rocket for my little boy last year; don't believe these posts that say they don't go very well!  They can go several hundred meters quite easily.  You will need a WIDE open space to test it, not just a big park.  I live near Greenham Common and this is ideal for water rockets.  It is literally just a lemonade bottle with a male hoselock attachment glued on.  The best way I find is to make the thread of the lemonade bottle soft with a blow-torch, and then screw the male hoselock thing on (the threads are not the same, so this squishes the plastic and the threads end up the same.  Let it dry and unscrew, then glue it permanently with Evo-Stik 'serious stuff' - it's the best large-tube glue I've tried.  The female end is more difficult as you have to glue a bit of copper pipe inside a short bit of hozepipe, stick it in the socket and tighten up as hard as possible - make sure you use the better connectors with a jubilee clip on.  the copper pipe is then brazed onto a 90 degree joint, and thento a long (say a meter) copper pipe with a reducer brazed on the end.  Inside the reducer is an old bike inner tube valve.  Oddly enough they fit perfectly into a small standard reducer.  The rocket sits on a raised bit of wood, and a bit of string is tied to the female hose-lock , round 90 degrees on a pulley and then onto a very long bit of string!  Some net designs show the string going round a big nail, but I found this just didn't work - too much friction.  Get a cheap pulley and it will work.  I find about 150 pumps will send ot several hundred metres.  1/4 fill of water and the rocket is stable, goes up and straight back down , however with say 1/2 full of water the rocket is unstable and veers off in a huge arc - this is when it can travel a long way!  caveat emptor !!!

[Batroost]

Much simpler... but a bit messy!

 [ Invalid Attachment ]

My son made this rocket out of a plastic lemonade bottle with a cardboard nose-cone and fins. We 'fuelled' it with a litre of water and vinegar, to which a few large spoons of bicarbonate of soda were added with a cork inserted and the rocket upended very quickly!

It had three flights on Sunday afternoon - the first I didn't see because I was standing underneath the jet of water/vinegar at the time. Once you smell that bad you stop caring so...

Flight two - very fast but sideways across the lawn!

Flight three (the one in the picture at lift-off) with the rocket rapidly rising vertically to about twenty feet.

Rocket now retired and myself thoroughly showered...

 

[paul.fr]

Ver nice felix and Batroost.

Batroost, i too have had the "pleasure" of being soaked in vinegar and bicarb from flying rockets, much to the amusement of my watching daughter. That'll teach me not to keep going up to the rocket when it fails to lift off on time.

do you notice that the reaction is quicker in warm sunny weather?

[Batroost]

Yes - and giving the bottle a quick shake to mix things up makes a big difference as well.

[lyner]

Daveshorts

it will go a lot better, especially if you run it purely on air without the water.

This is not correct - to make a rocket work, you have to give the propellant momentum - so the rocket gains corresponding momentum in the forward direction.
Using the low velocities available from a 'pumped up' device, you just  have to expell something with significant mass - i.e. water.

Jet engines use exhaust gases and air with success, but the velocities are thousands of m/s.
Ion drives use a very small mass ejected at near the speed of light but only produce a tiny thrust.

There is an optimum amount to fill the bottle; how much propellant (water) against how much energy stored (compressed gas). The details depend on the weight of the payload, strength of container and the nozzle design.