Preparing for launch

Hammer the wooden stake into the ground.
Half fill the rocket with water and slide the launcher into the bottle neck. Make sure the tie wrap heads are around the lip of the bottle and slide the locking collar into place. (left picture)
Now turn the whole assembly over and clip it onto the wooden stake base. (right picture)
Push a tent peg into the ground underneath the rocket and tie (or clip) the string to the coathanger wire. Feed the string under the tent peg and pay it out. This allows you to trigger the launch from a safe distance.

I also made an extention tube to the styrup pump with the small bore reinforced water pipe. This means that I can also pressurise the rocket without standing next to it. Another safety must. I have never had a rocket explode, however I don't want to be stood next to one if it does.

The pictures below give a better idea - I hope - of my setup. The extention hose has a valve connector at one end and an old valve from a defunct bicycle tyre at the other.

All set up and ready to launch at a safe distance.

A 2 litre bottle takes about 20 pumps to reach 6 bar.

My pump didn't have a pressure guage (It was a cheap plastic one from Halfords - JJB Sports do a similar priced one). Instead I recovered a guage from a defunct cheapo foot pump and fixed it into the chain of pipes.

Note: if for any reason the rocket fails to launch, you can depressurise it by depressing the valve on the end of the reinforced extention pipe.

Three tenths of a second of a launch...

These really are three consecutive frames from a movie. The movie was taken at 10 frames per second.

1.  All ready to go. The tent peg is arrowed in the first shot.

2.  Pull the string, the collar releases and the rocket begins to move.

3.  There's no stopping it now.