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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.

Test 1

The valve was only partially severed, so the MythBusters had to wait 45 minutes while the cylinder slowly drained of air.

Test 2

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.

Gunpowder Engine

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.



The Cayley gunpowder engine will work if they do three things:

1) have an expansion chamber rather than direct drive piston

2) use a feed mechanism like the original

3) use slower burning, old fashion gunpowder

The original engine worked, but had very little endurance

All the Best!


What about the most common gunpowder engine. A gas powered automatic or semi-automatic rifle. All many of them do is use the expanding gas from the round to drive a return rod that re-cocks and reloads the chamber by moving the breach block. If you decrease the stiffness of the return spring and use some of that energy to drive mechanical system then you have an easy to build gunpowdered engine.

I missed this episode but really wish I could have caught it. When I was told about it I realised that the boys might be onto something here considering the high energy and renewability of black powder.

But their fuel system was doomed to fail. From the sound of it they had no way to control the actual feed in a concrete way. If the fuel could be reliably and consistantly fed, it WOULD work.

I also don't understand how exactly they were having issues with powder mixing with the oil unless it was getting past the piston rings or it was a two stroke motor.

i think they should have looked into some type of rotary fuel delivery system. If a valve was used like in the "coates" head design they could run an engine based air compressor that would provide the pressure to force the powder in and essentiall the valve would "scoop" the powder in.

I don't think it's very wise to be using glow plugs though. With glow plugs you'll risk damaging a lot more parts as you're not truly controlling the ignition timing and as soon as fuel is entered it ignites. In the rotary valve design this would create issues with inevitably blowing up your fuel supply.

So what they'd need is a more industrial type of spark plug running higher than OEM voltage with a wide gap. As long as the majority of the fuel gets burned it shouldn't foul the plug.

The big ticket theory here though is that they need a system that's directly tied into the timing of the motor, that's driven by the crankshaft, and the car needs to be started by a starter, not a combustion. A gasoline engine doesn't start because from one cylinder firing, it starts from several in conjuntion getting the engine up to speed and creating a rhythm. They really should take a cue on this and figure out how to do it right in order to bust the idea completely.

All in all, it's got me thinking enough to want to buy a junkyard motor to run some tests on.

Mark and Nathan have the correct idea.
The engines failed due to the delivery system used for the gun powder.
The gupowder must be belivered by a rotating disk that allows gunpowder to drop into slot or hole in a disk that has had time to cool. The disk turns to a point that allows the powder to drop or be sucked into the engine, much like a gun, but without cartridges. The engine also needs a starter of some sort to get it into motion, only electric motors and rocket motors start from static.

it would seem that there is a perfect working gunpowder engine in mass use all over the world, its called a machine gun, it is self maintianing, has an effective feed system for the powder.