A simple (but effective) water rocket

After launching a few pop bottles you will realise that they are not very aerodynamic.
Here is a simple but very effective design for a rocket. It will go at least twice as high as a bottle on its own.
Don't forget, what goes up, must come down. Make sure that when it does come down it won't cause any damage, especially to people.

You need...

Two bottles, scissors and some Duct tape. It is probably a good idea to have a Stanley knife as well, to make the initial cut into the bottle, then finish the cutting with the scissors.

Here's how its done...

One bottle is the rocket motor. This remains in tact.
The second bottle needs to be cut in two places...

First cut off the top of the bottle, I used the ridges in the bottle as a guide, however not all bottles have these, the actual measurement isn't critical. This section will be the nose cone of the rocket. I haven't here but you might want to cut the top (where the screw cap goes) off the nose cone as well, this should make the descent a little slower.

Secondly, cut off the bottom of the bottle so that you are left with a cylinder of PET. This will be the tail fin of the rocket.

Tail fin...

Cut some square holes in the cylinder of PET. I cut three holes. Use the picture as a guide. This makes the cylindrical tail fin.
You can experiment here, but the shorter the tail fin the slower and more erratic the decent.
A short tail fin coupled with the screw top cut off the nose cone would lead to a less dramatic landing, you might even get it to "side glide" back down.

Assemble the parts...

Slide the nose cone over the bottom of the first bottle and the fin over the neck of the same bottle.
Make sure they are straight...

...And tape it up with the DUCT tape.

And there you have it, a water rocket.
Half fill with water and put it onto your launcher ready for launch.
If you want it to go really high, put a small amount of water into the nose cone (don't fill it and don't cap it). It might be a good idea to pump the bottle up to 1 bar (no more) before you do this, as this will stop any leaks.
Pump up the rocket and let it fly! As the rocket climbs it will loose water out of the nose cone, but not before it has gone very high. Looks cool in bright sunshine. It goes up heavy and comes down light... ideal!

Click here for an example of a launch with a rocket like this. Requires the DIVX codec to run (www.divx.com).

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