Episode 63: Air Cylinder Rocket, Gunpowder Engine
Episode 63: Air Cylinder Rocket, Gunpowder Engine
- An air cylinder break through a cinder block wall: confirmed
- You can run an engine using only gunpowder: busted
The air cylinder myth was an easy myth for Adam and Jamie to test, which leads me to believe that it was really just an excuse for them to build an air-cylinder-powered speed boat, which took up the rest of the segment. The results were far from spectacular, but they had their fun.
The gunpowder engine myth was a tour through history as the build team tried out several historical designs for gunpowder engines. It culminated with a test of a modern combustion engine hooked up to gunpowder fired through a mini-sandblaster, but they couldn't get it turning. In most cases, the gunpowder was too powerful and easily overwhelmed the reloading mechanisms necessary for sustained power.
Air Cylinder of Death
Myth: An air cylinder break through a cinder block wall
See also: Jaws Special
Setup: * Air cylinder position 20' from cinder-block wall * Sever valve with a large 40lb weight dropped from a tall height * Guide rail to keep air cylinder moving towards wall
They talked to George Ratermann of Ratermann Manufacturing, Inc about the myth. Ratermann supplies valves and cylinders but has never heard a first-hand account to verify the story, though he has heard the myth. Ratermann expressed some concern that their rig would only get a partial break on the valve, which would prevent the cylinder from flying straight.
The valve was only partially severed, so the MythBusters had to wait 45 minutes while the cylinder slowly drained of air.
They worked on the severing mechanism to ensure a clean break. They increased the weight, lubricated the drop system, and repositioned the valve so that the weight would hit more on the tip.
The cylinder flew straight towards the wall and straight through the wall. It also shifted the entire wall by half an inch and punctured the cinder block wall of the building behind it.
Air cylinder speed boat
With their myth confirmed, Adam and Jamie decided to attach air cylinders to a boat to harness the power they witnessed. They picked up a 16' hull that was missing engine, dashboard, and steering. Two air cylinders were quickly set into the hull, with Adam replacing the valves on the air cylinders with ball valves that could be released simultaneously.
They took their rig down to the marina at Seaport Blvd in Redwood City. Their first run went 120' with lots of water spray. They decided to do one more run with a change to the valve design -- instead of keeping the valves above water, they refitted it to shoot underwater. The second run only went half the distance of the first run.
Myth: You can run an engine using only gunpowder
The build team first tested some past experiments in gunpowder engines to see what they could learn. They tested designs by Christiaan Huygens, George Cayley and Thomas Payne.
Tory: "Finally we get to learn from someone else's mistakes."
Experiment 1: Gunpowder vs. Gasoline
Grant built a large piston to test the strength of gunpowder against gasoline. The top of the piston was set to hit a large magnet on a scale. The test wasn't even close: the gas-powered piston hit the magnet a modest amount; the gun-powder-powered piston shot the magnet off the scale.
Experiment 2: Huygens Engine
Christiaan Huygens designed a blueprint for a gunpowder-powered piston in a cylinder 300 years ago. In Huygens' design, blackpowder ignites inside the chamber and forces air out one-way valves. The resulting vacuum sucks the piston down. The design was never actually realized by Huygens.
Despite upping the amount of powder from 15 to 20 grains, they weren't able to generate vacuum power. Their seal and one-way valves weren't tight enough -- the design was a bust. It seemed unlikely to the MythBusters that the Huygens design could have been built in Huygens' time.
Experiment 3: George Cayley
George Cayley's engine design used gunpowder ignition to push a piston up. A bowstring then forced the piston back down. More gunpowder is dropped into the cylinder as the piston drops back down. In order to verify the engine design, they were shooting for two cycles from the piston.
On the first run they loaded it with 5 grains of black powder. The piston fired, but their hopper with the black powder reload got knocked over into the propane flame. This prevented any reloading for a second cycle. They remedied this for the next run by putting aluminum foil over the hopper.
The second run couldn't get two cycles in either: the reload mechanism was too slow for how quickly the piston fired.
Experiment 4: Thomas Payne
After two internal combustion engine designs failed, they decided to go with an external combustion engine design from Thomas Payne. The design is essentially a waterwheel, where you replace the water with gunpowder force. Tory welded a bunch of metal cups to a wooden wheel. A small protrusion on the wheel triggered a reload mechanism for the gunpowder on every turn.
Grant: "Dude, it's like an 1860's circular saw"
Their first test run used 15 grains of black powder per cycle. There was no turning. They went up to 70 grains, but still no turning. Tory replaced the gunpowder chamber with a smaller tube to improve the compression. The compression was too much for the design -- the gunpowder ignition blew back into the hopper and ignited the remaining store of gunpowder.
Experiment 5: Modern internal combustion engine
They used a miniature sandblaster to fire a constant stream of gunpowder into a modern internal combustion engine. Their first test run was a failure due to the oil in the engine: the oil and blackpowder mixed into a slurry that couldn't ignite.
They drained the oil from the engine and replaced the spark plug with a 'glow plug' that gave a constant ignition source (instead of the spark plug's intermittent spark). They still couldn't get the engine to turn over.
On a final test run, they put 5 grains of gunpowder directly into the engine. They got the 5 grains to ignite, but they couldn't keep the reaction going.