This weekend, my eldest son and I did some serious academic research into thermodynamics, general physics and the science of ballistics. In other words, we were testing out this year’s science fair project: the potato gun.
Those who know our past experiences with science fair projects, such as rocket-powered helicopters, were a little leery about the idea of Kevin (and I) doing anything that had to do with combustion. (With the helicopter–a twin-rotor job built from scratch–there was the small matter of not having enough amperage/too much resistance to ignite the engines on all four rocket motors, and having to get a little too close to harm’s way to attempt to get ignition.) But we figured that if we followed standard safety procedures, there was little chance of either one of us catching on fire.
Last week, using directions off of SpudTech.com, we assembled a fearsome-looking spud bazooka out of pressure-rated PVC pipe. The whole apparatus is just about 4 feet long (3 feet of barrel, and the rest being combustion chamber). The firing mechanism was the most expensive component: a $15 replacement piezoelectric gas grill igniter.
Yesterday, Paula retrieved our ammunition for us (four good-sized Idaho russets and two cans of Suave deodorant) before taking ZoÃ« out for a few hours. I grabbed an old sock, and told Kevin to accompany me to the backyard, where we performed our first test-firing–with the sock as the projectile. The shot sounded more like a wind instrument than a firearm; the sock flew about 30 feet, scaring a stray dachshund out of the alley.
Then we headed out to a nearby field behind a large city school, where we had a clear half-mile of range to work with. And the spud-hurling commenced.
It was way more fun than it should have been.
We, er, needed to check many different firing angles and propellant loads to establish what we would need to do to properly prepare for the actual data collection phase of the experiment, so we ended up shooting for almost an hour and a half–first just with potatoes, and then with a mix of projectiles. A few field-notes:
- The butane in aerosol deodorant is certainly an adequate propellant, but the deodorant itself quickly fouls the electrodes and prevents spark unless you clean them between shots. I’d try propane, but I fear it might be a bit too efficient a propellant for the task of measuring ballistics. (In other words, we might not be able to find the projectiles afterward.)
- You can easily convert the spudthrower to other, found ammunition by using a cloth or sock as wadding. Golf balls found at the scene were excellent projectiles. In fact, one was perhaps too good a projectile, as it never was observed actually landing.
- Any crowd that gathers to see what you’re up to can easily be assuaged if you’ve got a teenager with you and you simply say, “Science project.”