Bamboo cannons... Backyard ballistics... How to!
First you need to select and cut your bamboo, at least 2 weeks in advance. Preferably cut on a moonless night (dark night, sap rises and falls in plant life with the lunar cycle).
*(Editor: Don't scoff, we once cut bamboo in the "wrong moon" to make an awning, and it rotted and fell apart in weeks. Our Gardner at the time, Seukraj, said he hoped we had learned our lesson and built us a new one in the "right" moon. It lasted for ever.)*
The bamboo must be at least 4 inches outside diameter, with a bore at least big enough to get a tennis ball in, the walls must be fairly thick, half an inch is minimum. An experienced harvester can determine this by knocking the bamboo in the grove with the back of his machete. The tonal quality is the proof!
You then cut the bamboo to include four to five whole joints in the length, depending on the actual joint length..so that you have at least four sealed chambers (bamboo, if you didn't know, grows in jointed sections, each naturally hermetically sealed at the nodes by a robust internodal wall) (That's why bamboo explodes with such a crash during a bush fire). You now need to borrow a length of metal pipe about six feet long and about one inch diameter, you're gonna use this to carefully "rod out" the internodal walls except for the last one (this will be the back of the cannon, the wider end). Some people reinforce this back-end node with clay.
Once you've broken and cleaned out the internodes, lay the bamboo down flat on the ground. You must now make a small hole, about the size of a quarter (3/4 inch diameter) in the wall of the bamboo, about 3 inches forward of the back nodal wall of the cannon... this is your firing/lighting hole.
You now need to get a gallon or so of kerosene (pitch oil), some to make a Flambeaux (flame torch or lantern) by filling a beer bottle up with kerosene and stuffing some cotton fabric into the mouth of the bottle et voila! Your very own Molotov Coctail. And you need a good dry stick about a foot long....this is gonna be your lighter or firing stick. Also keep handy a small tin pan with raw kerosene in it as well. This is your lighter fluid!
Now lay the cannon down on the front lawn, and prop up the open end using a brick or something similar. The mouth needs to be about a foot or so off the ground. Fill the cannon thru the firing hole at the back with about two cups of kerosene, roll it from side to side to wet the walls of the combustion chamber with kero, then wedge the bamboo with some rocks to prevent un-commanded rolling and medical issues!
Light up your flambeaux, dip your firing stick into the tin of kerosene or simply wet the stick with kerosene by poking it into the firing hole.
Now light up your firing stick using your handy flambeaux, carefully pass the firing stick over the firing hole..... Nothing happens, good! The kerosene in the bamboo needs to burn for about ten minutes to heat up the walls of the cannon and the kerosene itself until it begins to vaporise into a thick white smoke.
When this happens, cover the firing hole with a good thick (slightly damp) rag to put out the fire. Carefully blow into the firing hole (to introduce fresh oxygen). About two short puffs should get the air/fuel mixture just right, now re-light your firing stick..... Exciting part coming up........ Keeping your face and upper body clear of the combustion chamber, pass the lit end of the lighter stick over the firing hole.....
Now quick, make sure there's no fire in the hole.... Puff puff lit stick...
Thanks, Seanos! Mommies, stand by and try not to jump and say "eeep!" with every explosion. This is definitely a Dad thing! Presently you will hear answering explosions from the other boys in the neighbourhood, and no-one will get any sleep until Divali is over.
Usually, some minor burns will happen. Boys go to school all week with eyebrows missing, from trying to blow oxygen into a firing hole that is on fire! Make SURE there is no fire in the hole before you blow!
This year Chas burned all of the hair off one of his arms, but somehow everyone's head hair is intact. Max jumped and said "Ow!" and sucked his fingers for a while, but he SAYS he wasn't burned. (I was born yesterday!) There were no blisters.
I have never heard of serious burns happening, but small boys? Kerosene? Fire? Explosions? It could happen. BUT, you would have to be careless. So BE CAREFUL! And have fun!