Here you can see the wooden support, complete with decorations, for holding the launch tube. It also has the bottle locking mechanism (the 4 x meccano strips and two tent pegs).
The tent pegs slip over the lip just above the thread on a soft drink bottle and prevent the bottle taking off until you tug on the string (on the left, in its cunning cable tidy) and pull the tent pegs out. the two pegs are held together with a bit of coat-hanger wire on the left hand end and the string is attached to this to ensure that both pegs come out together and the rocket launches smoothly.
The launcher is really basic, made from one old shelf. I cut the two ends off and screwed them in to make the uprights. Two pipe clips hold the tubing in place, and crucially allow you to take it out to fit to your rocket. Fitting is done off the launcher so that you hold the rocket upside down, insert the tubing and make the seal, then carefully turn it right way up so that the water doesn’t go into the tubing but stays in the bottle.
The two holes in the board at the right for are putting two more tent pegs through to anchor the launcher to the ground, so that it doesn’t move when you tug on the launch string.
That is essentially it. All in all it took two days-ish to make, but that’s only because the bloody glue takes so long to dry.
*the yellow circle bit on the left is an off-cut from the new design and should be in the bin.