Joined: Mon Dec 28, 2009 11:28 am
I use a launcher with a 1 foot launch-tube and a Clark release mech.
The tube is a bit of a bugger. In the UK, the neck of those 2L PET bottles is 21.5mm diameter.
The launch-pad is constructed from copper plumbing and there are only 2 tube sizes : 15mm and 22mm.
So, you would hopefully use the 22mm tube. However, as you know, despite the tiny discrepancy, you just
cannot push a 22mm copper tube inside the bottle.
Wrocketeers use alternatives :
One is to reamer out the bottle neck to fit. I've tried this and it does work, but I find it a real pain.
The second method is to use plastic tube. You can get 22mm plumbing tube in plastic, but the fit problem remains.
However, you can also get plastic pipe used for the over-flow in water-tanks. This really is 21 to 21.5mm and fits perfectly.
Unfortunately, it isnt perfect because it's a bit bendy, and really needs to be made rigid. I've treid various tricks
which havnt worked very well, but I think I've got one now. It's a bit of a performance, but you may think it worth it.
DIY stores sell thin metal tubing meant for making a 'rail' inside a wardrobe to hang clothes. There are 2 sizes: 19mm and 25mm.
The inside diameter of our 21mm plastic launch-tube is 18mm, so initially, I realised, to my intense frustration, that this wouldnt 'fly'.
Then a stroke of luck. Wilkinsons ( a kind of el-cheapo hardware store common in the Midlands ) sell a '19mm' tube, but it is actually an 18mm steel tube with a thin plastic sheath to make it look pretty. Bingo.
I wont go into details, because it really would need a pic, but part of the metal tube( with plastic cover removed ) fits inside the plastic launch-tube and makes it rigid. At one end, the metal tube still has its little plastic sheath. The plastic launch-tube is pushed hard over this
19mm part. This has the effect of making the 21mm launch-tube 'bulge' a little and that makes it a perfect fit for the 22mm copper compression fitting.
This would obviate the need for remembering to reamer out any bottle being usd as a launch bottle and a plastic launch-tube
would probably be better ( more slippery ) than a metal one. Worth a try, IMO.