Wish you had a way to fire projectiles in your backyard but lack a firearm and/or the proper permit? Not a problem! With $40 in plumbing supplies and an hour of your time, you too can launch Russets with extreme prejudice.
You should do this if:
You enjoy controlled explosions and fast-moving tubers.
Moment of Satisfaction:
Getting medieval on a sack of potatoes.
Biggest Pain in the Ass:
Ensuring an airtight seal between the combustion chamber and the igniter.
Materials and Tools Required:
- Flint igniter, such as the Coleman Lantern Spark Igniter.
- 4-inch PVC end cap.
- 4-inch PVC fitting adapter.
- 4-inch PVC coupling pipe.
- 4-inch x 24-inch PVC pipe. This is the combustion chamber.
- 4-inch to 2-inch PVC reducer.
- 2-inch x 48-inch PVC pipe. This is the barrel.
- PVC cleaner and cement.
- PVC primer (the purple liquid).
- Fiberglas filament tape.
- Hairspray-Aquanet is best, White Rain also works. Carburetor cleaner is also an excellent fuel.
- Drill with a bit sized to cut a hole for the igniter.
Image: Dangerously Fun
Difficulty and Cost:
5 out of 10. It costs about $40, and takes an hour to build.
1. Make a Series of Tubes: Cut the 2-inch and 4-inch pieces of pipe into 4-foot and 2-foot lengths, respectively. Don't get this backwards—the wider pipe is the shorter pipe. Smooth down the cut edges using the file. Sharpen the muzzle end of the 2-inch-diameter barrel pipe so it can shear off excess potato and create a supertight, thrust-enhancing seal when loading.
2. Assemble the Gun: Screw the end cap on to the 4-inch fitting adapter. Do not glue it into place; this part is meant to be removed. Fit, prime, and glue the 4-inch fitting adapter to the 4-inch coupling pipe. Fit, prime, and glue the coupling pipe to the 4-inch x 2-foot pipe. Fit, prime, and glue the 4-inch to 2-inch reducer to the other end of the combustion pipe. Once all that has dried, then fit, prime, and glue the 2-inch diameter barrel into the 2-inch end of the reducer pipe. Let the whole assembly dry and cure per your PVC cement's instructions.
A word on how to "fit, prime, and glue": You absolutely need to make sure that every joint is completely air tight, otherwise you run the risk of gas escaping and reducing the gun's efficacy and safety. So, when assembling it, thoroughly swab the PVC primer before brushing PVC cement to the inner and outer faces of the two pieces being joined. Then run a bead of cement along the joint after the two pieces have been pressed together. You'll also do well to wrap the combustion chamber a few times with the filament tape, just to be safe.
3. Add an Igniter: About a third of the way up the combustion chamber (measured from the back, where the end cap is), drill a hole for the igniter. Drill a hole just large enough so the sparker's head, cylinder, and smaller hex nut fit securely inside. Press the metal tab (between the nuts on the Coleman) against the body of the gun and affix it with a screw. Then, seal around both the screw and the igniter port with PVC cement. The Coleman striker uses a flint and steel to generate a spark. The mechanism can get gummed up, so do not spray hairspray directly on the sparking hardware.
4. Load the Spud: First things first. Find somewhere safe to responsibly fire this thing. You'll need at least 200 yards of distance with 25 yards on either side of your projected flight path to account for cross-winds. Also, obviously, don't point this gun toward anything with a pulse, any private property, or anything fragile. Obey local laws. Operate only under adult supervision. Attempt at your own risk. Don't be stupid. Disclaimer disclaimer disclaimer.
That said, choose a potato just barely too large for the barrel's diameter, so that the sharpened end shears the spud skin for a tight fit. Wear a glove when loading the spud. Jam a potato about halfway down the barrel of the gun using a broom handle as a ramrod.
5. Fuel and Fire: Unscrew the end cap. Spray one-second's worth of Aqua Net (or carb cleaner) into the combustion chamber and quickly screw the cap back on. Aim the gun skyward, toward a safe target, and announce that you're ready to fire. When all is clear, with one hand firmly gripping the gun, use the other hand to twist the sparker's ignition wheel.
If you successfully launch the potato, congratulations! Try spraying more or less aerosol into the combustion chamber to measure launch distance and time aloft with varying oxygen and fuel ratios. Do not ignite hairspray outside of the sealed combustion chamber. And do not waste too many potatoes in the pursuit of science.
[Instructables - Dangerously Fun - Image: Matt / Instructables]