this is an instructable working with rockets. water rockets in particular . this launcher can send 2 liter bottles over 500 ft. in the air .use at your own risk. it is from http://sciencetoymaker.org/waterRocket/index.htm
so i give all the credit to them
Step 1: materials
1 10 foot piece of 1/2 inch, schedule 40, PVC (plastic) pipe. You might be able to find this in the plumbing section of a building center/hardware store, or in the form of conduit in the electrical area. Usually the conduit pipe is gray in color instead of white.The pipe size is printed on the pipe. If you actually measured the pipe, you would find the outside is about 21mm (almost 7/8"), and even the inside is 15mm (9/16"). Choose by what is printed on the pipe, not by actual measurements. The "schedule 40" refers to the thickness of the pipe, and rest assured that schedule 40 is the most common, easiest to find kind. See picture below.
1 piece of PVC 1 1/2" (one and one half inch), schedule 40 pipe. You only need 2 inches of it, but some building centers only sell it in 10 foot lengths (even a 10' long piece is only a few dollars). You might be able to find a sympathetic plumber or home handyman who can give you a couple of inches. 2 PVC 90 degree elbows for the 1/2" pipe.
1 end cap for the 1/2" pipe above.
1 small can of PVC pipe cement (or borrow some).
1 package of 8" (or close to it) general purpose ties (also called cable ties). These will be in the electrical wiring area of the building center.
1 hose clamp. The size is important. I get hose clamps with a range from 11mm to 23 mm (a little less than 1/2" to a little less than an inch). The hose clamp must be a little bigger than the pipe because that's what holds the all purpose ties securely to the pipe. Better to have the hose clamp a little too big than a little too small.
1 tire stem. This is the one thing you are not likely to find at a building center or hardware store. However, it is easy to find at any automotive parts store. Tire repair shops often throw them away. The inner core of the tire stem does not have to work, or even be there. If you tell the person at the tire repair shop they might give you some free.
A half inch (1/2", 13mm) diameter drill bit, a quarter inch (6 or 7mm) diameter drill bit, and drill. There are only two holes to drill, so if you don't have a drill find a neighbor who does. You will only take a minute of their time. A drill press is even better.