THINGS THAT GO BOOM

Last Updated on June 20, 2000

What's new: killed some links 6/20. Emergency notice: The makers of Glade have apparently changed formulas, and it is no longer explosive. (9/15): The first part of a planned treatise by Mr Science on the technical aspects of fuel-air explosive guns is available on the Technical Page.

In light of some recent e-mail, Mr Science would like to note that he is a peaceful and generally harmless person, who wishes for the enlightenment of sentient beings everywhere. Mr Science cautions those who experiment with homemade cannons not to shoot sharp pointy things, not to shoot bouncy things in an enclosed space (e.g., a basement) because something like a golf ball retains nearly all its kinetic energy after collisions with walls, and to be careful with compressed air and PVC; he recommends hydrostatic testing for guns operating near the rated pressures. Also, wear eye protection.

THE WATERMELON CANNON
First, we made a potato gun. We did the usual experiments; measuring the chamber pressure, muzzle velocity, things like that. Then, one day, Scott was struck by a flash of inspiration: We could make a really big cannon out of a 12" sail tube! On it's first firing attempt, the cannon lost the last 4 or 5 feet of barrel in a spectacular fashion, throwing PVC shrapnel, albeit at low velocity. Thus, a new word was added to the Kanganerd vocabulary: Safety. After this, we hid behind large fixed objects when firing the cannon. I was concerned that the muzzle blast would blow the windows out of Scott's basement, but not nearly concerned enough to refrain from firing it.



Technical Details
The cannon is made out of really thin PVC sail tube, with a 12" pipe cap on one end with the igniter, a fireplace lighter. We close off the muzzle end with a sabot made of blue foam,with tape wrapped around it to seal the barrel. The preferred propellant is cinammon Glade, which smells much better than burnt hair spray. Okay, we've never really shot a watermelon out of it, it doesn't really have enough energy for that. We have shot popcorn from it, about two bags full, through the hatch in Mr. Sciences roof late one night during a party.
MR SCIENCE'S CATAPULT
Inspired by the book "Catapult: Harry and I Build a Siege Weapon", by Jim Paul, and fondly remembering his college days when he and his friends bombarded fraternity parties with water balloons using hand held surgical tubing funnelators, Mr. Science decided to build a catapult for throwing water balloons. Mr. Science's spouse was not happy to discover that he had bought $100 worth of surgical tubing from a medical supply house, not even when Mr. Science suggested that it could be used for kinky sexual purposes as well as a ballistic aid.

Several months later, Mr. Science emerged from the garage, blinking in the sunlight, with the odd and menacing looking object shown in the photograph. (moved to separate page to save space). It required about a 400 lb pull, supplied by a comealong, to crank the basket back. In the photo we are still using the "cut rope with knife" release method, as in ancient times. The performance of this device was relatively disappointing, lobbing balloons for 300 ft or so, mainly because I kept it short enough to fit in my car. Catapult Pictures

THE TOMATO GUN
One day before a party, Mr. Science decided to make a larger and more energetic, but still portable, sort of gun. Using a 6-ft piece of 4" PVC pipe, he rapidly constructed the tomato gun, which soon exceeded his hopes. The tomato gun shot a tomato (reinforced with tape) through both sides of a cardboard box intended to catch the remains, through the (closed) wooden garage door, and through the garage to adhere to the back wall. According to a simulation using numerical integration on my SGI workstation, the tomato gun should be good for 300 fps with small fruit such as a lime.











THE CHICKEN GUN
For industrial strength object lobbing, it's hard to beat the chicken guns used by most of the major aircraft manufacturers to test windshields and other airplane parts which must stand up to bird strikes. The gun used by Cessna is a steel tube about 6" in diameter and 40 ft long, powered by a large tank of relatively low pressure compressed air. It can propel 4 or 8 lb of chicken parts at up to 300 kt. (506 fps). The parts are surrounded by a foam and fiberglass sabot, which is cut away by splitter knives at the muzzle. I witnessed a test shot recently against a 1" thick aluminum plate. The plate rang like a bell when struck by the chicken, and chicken parts shot 50-80 ft into the air. I sidestepped some which descended near my location. Rumor has it that another aircraft manufacturer (you know who you are) once missed the test article completely with the chicken and sent it sailing through a lumberyard.

OTHER THINGS THAT GO BOOM

OTHER THINGS THAT JUST BURN QUIETLY INSTEAD

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