Compressed Air Rockets

When I was at the Bay Area Maker Faire earlier this year I saw a display that had a compressed air paper rocket launcher. Kids would make their own paper rockets, load them onto a launching tube and fire them into the sky. I thought it was pretty cool, but wanted something more dangerous different.
So, how do you make compressed air rockets better? By making exploding compressed air paper rockets!!

Using simple Chinatown fireworks, combined with an elastic deployment system to eject a small toy parachute action figure, I designed a rocket which jettisons the parachute man from altitude. I made 3 test rockets which were designed to test and calibrate the compressed air launcher and 6 live rockets which were intended to test the theory and intent of my design. Unfortunately, it didn't quite turn out the way it was supposed to. All 6 live rockets exploded, melted or malfunctioned and no parachute men were successfully deployed.

So, instead of this being a how-to it's more of a how-not-to. Check out the video where all the spectacular failures are captured:

Obviously working with fireworks, compressed air, power tools and rockets is dangerous business. Use common sense and work within your ability.

Enough talk, let's explode some rockets!

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tools hacksaw wood saw drill + bits (various sizes, wood bits) scissors hobby knife PVC glue lighter masking tape bicycle pump

materials pvc pipe 1 x 2" diameter pipe (roughly 24" long) 1 x 2" cap 1 x 2" diam to 1.5" diam. bushing 2 x 1" threaded coupler 1 x 1" diameter pipe (roughly 24" long) launch platform scrap wood uprights scrap 1/4" plywood base scrap 2x4" for blocking scrap 2x4" for launcher stabilizer sprinkler valve (1" ingress/egress) compressed air-gun trigger Schrader valve (inner tube valve) paper cardboard / cardstock elastic bands threaded rod + wingnut cable ties

All compressed air rocket launchers work under the principle of rapidly displacing air to launch a projectile. Air can be pressurized in a chamber and then deployed by means of a trigger or stored in a bladder and squeezed to be released, these are active and passive systems.

Active, or pressurized assemblies are capable of producing some spectacular results due to the high pressure able to be stored in the chamber. Passive systems like stomp rockets reply on the pressure created when the air bladder is squeezed. This project focuses on the former.

The setup of this pressurized air launcher is simple:

• air is supplied through a bicycle pump attached to the intake nipple
• air is held in the pressure chamber until released by trigger
• trigger is attached to a modified sprinkler valve (pilot valve)
• when trigger is activated air is released through the exhaust

^{Keen observers of Instructables.com may recognize this canon as Fungus Amungus' Christmas canon.
This is the same canon but adapted to fit on a launching pad. And this version shoots exploding rockets, not confetti.}

Chamber:
This canon was made with about 28" of 2" PVC pipe as the chamber. Cut your 2" pipe to length and glue on the 2" cap to one of the ends.
On the other end, glue on the 2" to 1" bushing. Then, cut a 4-6" length of 1" PVC and glue that into the bushing.
Finally, glue the 1" threaded coupler onto the 1" pipe attached to the bushing.
Set chamber assembly aside for 24 hours until glue has cured.
One set, drill an opening in the cap for the schrader valve. Tap the opening and wrap the valve in teflon tape and screw into opening.

Sprinkler Valve:
I did not perform the modifications to this valve. It appears that the valve has had the electronic solenoid removed and replaced with the handle and trigger for a compressed air nozzle. The trigger is threaded and fits directly into the place where the solenoid trigger was. Replacing the electronic portion with a simple mechanical action.
The valve is 1" female threaded on both ends.

Exhaust:
Cut a length of 12-14" of 1" PCV pipe, then glue the threaded couple to one end. Set aside to dry.

Time to make our rockets!
Take an A4 (8.5x11") sheet of paper and roll it lengthwise, using a 1" PCV pipe as our frame. When the paper has been completely rolled tape the length with masking tape.

Next, cover the top of the paper with a cardboard or cardstock circle roughly the same size as the pipe (1" diameter). Then secure it in place using several layers of masking tape. The masking tape allows the rocket to withstand the pressure when the PVC pipe is filled with air, and the cardstock provides a rigid flat base for the rest of the payload to be build upon.

The payload is the most tricky part of the assembly, and errors here are probably what brought my project to failure.

lower assembly (charge):
After the fuselage has been completed a short cylinder of cardstock was installed on top of the bottom deck previously installed. The cylinder was secured with plenty of masking tape, and a firework was installed inside.
Notches were made in two places on the top portion of the cylinder after it's been installed; one at the location where the firework will explode/emit flame and another off to the side which will allow the fuse to pass through and be lit once the assembly is closed.
With the firework installed, another circle of cardstock was covered in aluminum foil and installed over the cylinder opening. More masking tape was used to secure the charge in place, ensuring that the notched openings created earlier weren't covered.

upper assembly (parachute man):
Another longer cardstock cylinder was made and attached to the lower assembly in just one small area using masking tape, making the top cylinder a hinged. This hinge will allow the payload to open when ignited and the brave parachute soldier will be deployed. Well, that was the idea. The top of the upper assembly was capped with another circle of cardstock, then a parachute soldier was inserted into the assembly. Close the upper assembly and use a single strip of masking tape over the notch made earlier for the firework explosion point.
A cone of paper was added to the top after the payload was finished assembly.

elastic mechanism:
To allow the upper assembly to flap open when the masking tape strap was severed an elastic was used. Cut a rubber band and fix one end to the upper assembly, pull taught and fix the other end to the base of the fuselage. I used masking tape to secure the elastic in place.

Since I was going to be filming, lighting fireworks and pulling the compressed air trigger I needed a platform to hold the launcher.

I made this launch platform in less than a hour with scrap wood hanging around the shop. This platform is made from a 12"x12"x1/2" sheet of plywood, a drawer face which measured 6"x48"x1/2", and some 2"x4" off-cuts of various lengths.

A threaded rod was installed near the top and through a 2"x4" which allows the launcher to be directed at an angle. you know, in case I wanted to launch exploding rockets at the neighbours and not just straight up.

Holes were drilled into the top movable platform which the launcher will be strapped to with cable ties.

My measure of success for this project was successful deployment of the parachute soldier at altitude. To that end, this project did not work as intended. However it was loads of fun to make and any project I can walk away from with all my fingers should be seen as a positive learning experience.

Here's the video of testing the different variations of the firework I used. The first iteration was a control with each variant after modified the firework slightly so it would behave differently.

A special thanks to kazmataz who was my diligent launch Commander, took amazing photos and was great support.
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Did you make your own version of compressed air rockets? Place a picture of your version of this project in the comments below.

That's it, get outside and fire off some rockets.
Be safe and have fun!