All rockets are powered by explosions. All explosions are rapidly expanding gases. Usually they’re expanding because they’re burning, but not always. In the PVC rocket launcher the propellant is burning hairspray.
The Science Behind the PVC Rocket
In the rocket we built, the hair spray inside the tube is set on fire. Hairspray is tiny particles suspended in the air, it is in aerosol form. This means each little particle is mixed with lots of air. And each little particle is also very inflammable, it will burn with the slightest provocation. When the hairspray burns the chemicals in the hairspray, which usually includes some form of alcohol, mixes with oxygen and forms carbon dioxide gas. The carbon dioxide gas formed is in much greater concentration than that of the surrounding air. That means the pressure inside the launching tube is much greater than the pressure outside. The easiest way for this pressure to escape in the PVC rocket is by popping the foam rocket off the launcher, so that’s what it does. The force is enough to send the rocket 40, 50, or 60 feet into the air.
How to Build the PVC Rocket
First the base
- You need an 18″ long piece of 3″ diameter PVC pipe, a 3″ end cap, and PVC primer and cement, plus a BBQ igniter and a couple of 1 1/4″ self taping screws.
- Glue the end cap on to the PVC pipe.
- Use a power drill to put the self taping screws through the PVC pipe about an inch from the bottom of the pipe (the end with the cap). When you’re finished you want the tips of the screws to be about 1/2 inch apart inside the PVC tube so you get a good arc between them. Just before you finish tightening the screws down, insert the naked wire ends of the BBQ igniter under the screws so they have good contact with the screws.
Now the rocket
- Cut a piece of foam from a sleeping pad, like the kind you go camping with, so that it fits around the launcher tube and has just a bit of extra space. When the body is finished it needs to be snug, but able to slide on and off the rocket launcher.
- Tape the seam with duct tape then strap duct tape around the body to make it strong.
- Cut a 2 liter pop bottle in half and slide the top half (the half with the cap) onto one end of the foam rocket body. Secure it with more duct tape. This makes the nose of the rocket.
- Next cut fins from more of the foam pad. The exact size and shape isn’t important and they don’t have to exactly match each other. Just eyeball a 45 deg cut ending in a square end. Secure the fins to the rocket body with hot glue. Make the fins angle around the rocket body in a gyre shape so when the rocket is launched it will spin. This makes it fly straighter.
How To Launch the PVC Rocket
- Do it outside.
- Spray hairspray, the cheapo kinds work best, into the launch tube for about 2 seconds.
- Slide the rocket over the tube.
- Have everyone stand back a bit.
- Click the BBQ igniter.
The BBQ igniter makes a spark inside the hairspray filled tube and BOOM! the rocket takes off.