2-Liter Plastic Pop Bottle Rocket Launcher
Variation of demonstration at Philmont Training Center, 1992
This design by Stan Pope, a Volunteer Scouter for W.D. Boyce Council, Peoria, IL
|A, B, C||5 ft. (total)||3/4" CPVC Pipe|
|D||8 in.||1/2" CPVC Pipe - Outside diameter 5/8"!!!|
|E, F||2||3/4" CPVC Caps|
|H||1||3/4" X 3/4" X 1/2" CPVC Tee|
|J||1||Auto Tire Valve Stem|
|K||2.5 in.||5/8" I.D. Clear Plastic tubing - Use thick wall variety.|
|--||1||7/8" to 1" hose clamp|
|--||1||board - 4" x 8" x 3/4"|
|M||2||Pipe clamps for 3/4" pipe|
|N||4||3/4" X #6 flat head wood screws|
|--||1||0.005" X 1.5"X 5" brass shim (if needed)|
|--||4 - 8||2-Liter Plastic Soft Drink bottles|
According to my engineer friends, CPVC is the correct designation for these pipes and fittings. To be on the safe side, shop with a tape measure and the top from a 2-liter bottle in hand.
Drill a 1/2" hole in the center of one end cap (F); insert valve stem and pull it firmly through the hole. Clean and cement all PVC parts together according to the above diagram.
Taper the 2.5" section of clear plastic tubing (K) to about 1/16" wall thickness. Push it down around the 1/2" pipe, small end up. (The tapering can be done by turning the tube on a 5/8" mandrel and cutting with a sharp tool such as a "surfform". I made my mandrel from a 5" X 1/2" rod and 3" piece of 1/2" CPVC pipe.) When shopping for the tubing, take a 2-liter bottle neck with you so that you can verify tubing outside diameter size... if it slides into the bottle neck, it isn't thick enough! (However, see next paragraph.)
If the tapered clear plastic tubing (K) is not thick enough to produce a tight seal with the inside of the bottle neck, it can be increased to necessary diameter by wrapping two layers of brass shim stock around the base of the launch tube and pushing the tubing down over and around it. The inside of the bottle neck is about 0.84" diameter and the outside of the plastic tubing needs to be about 0.86" at the large end to produce a good seal. Secure the tapered clear plastic tubing in place using the hose clamp.
Assemble to board using clamps and screws.
Wrap plastic electrical the tape around 1/2" Pipe at junction with Tee. (Diameter of wrap should be slightly less than diameter of Tee.) Wrap more tape overlapping first wrap and Tee. Note that the tape wears quickly.
Pour about 3 inches of water into the 2-liter bottle. Invert the bottle and place over 1/2" PVC until firmly seated. Press and twist gently (in same direction as wrap, if taped) until a tight seal is obtained. Use 1" (inside diameter) bicycle tire pump attached to the valve stem to pump air into the bottle. (Launch is at 30 to 45 psi is typical for tape; 40 to 100 psi for clear plastic tubing.)
When internal air pressure overcomes the friction of the seal the rocket will shoot into the air trailing a brief stream of water. Altitudes of 50 to 80 feet are typical. If the seal friction is too great, the 2-liter plastic bottle may rupture and spew water. (Ours have survived 120 psi, but they are tested, I am told, at only 80 psi.)
If the bottle reaches a pressure that the Scout can no longer pump air into it, jiggle the "pump end" of the launcher an inch sideways. This usually loosens the rocket and allows a "launch".