Air Cylinder Rocket/Black (Gun) Powder Engine

Mythbusters Episode #63

Original Air Date: October 18, 2006 

Air Cylinder Rocket

The Myth:
Can breaking a safety valve on a high-pressure air tank cause it to take off like a rocket?

The Experts:
George Raterman - Raterman Manufacturing

Joe Hughes - Mythbusters Fan

Memorable/Quotable Moments:

"These tanks are actually filled with geese...and they're complaining!" - Jamie

"We need to go with hydrogen next time...and light it!"

"*That's* for another show." - Adam & Jamie

The Action/Results:
As Adam shows the ruptured scuba tank from "Jaws Myths", a cut to a scene from that episode demonstrates that merely puncturing an air tank will cause it to "chase the rat"...that is, rocket  wildly around (in the Jaws Myths case, inside a confined space, causing dents in the walls.) The myth further states that a T Cylinder can shoot through a wall.

So, the guys hash out a way to test the myth safely. First, they need to build an 'aiming rig' just large enough to hold a T Cylinder. Next, they need to devise a sort of guillotine to break the valve off the tank.

Next, Terry and Tyler build a target wall of cinder blocks and mortar inside one of the abandoned bunkers. Adam takes the opportunity to do some leg work and check with air tank expert George Raterman on T Cylinders to see what sort of damage they could expect to see. George explains that yes, any compressed air tank has the potential to become a deadly missile, should the valve be catastrophically damaged. He also warns that an incomplete break (that is, one where the valve doesn't break cleanly off the tank), could be just as deadly.

While Adam is talking shop with George, Jamie builds the aiming rig and guillotine, then, as Adam returns, they load up the rigs and several T Cylinders into the Seagate truck for the trip to Alameda NAS.

When Adam & Jamie arrive, Adam can't seem to wait to put a tank through their target wall. They discuss their setup, then set up their tank-aiming rig. Mythtern Jess has the unenviable task of greasing the launch rail with lard. Next, the guys set up the valve-breaking guillotine, which they test it first on a spare cinder block. The block shatters instantly, triggering one of Adam's maniacal giggling fits. The guys then set a tank on the aiming rig, arm the guillotine, and drop the weight.

Instantly, the worst-case scenario that George warned Adam about happens. The 40-lb. weight isn't enough to break the valve completely off the tank, so they essentially have a time bomb. The escaping air takes 45 minutes to completely empty.  Once the tank is empty, they try again, this time making a few changes. They grease *everything* with more lard, increase the weight in the guillotine to 80 pounds, set up a second tank with the valve rotated to where the weight can shear it off more cleanly, and try again.

Success! The tank shoots off the rig at 40 MPH, punches a neat hole in the target wall, and, as Rob observes a few moments later, puts a dent in the opposite wall six feet further over.

Well, with that myth confirmed, Adam & Jamie decide to try a few experiments. Jamie jokingly suggests putting a saddle on a tank, but Adam comes up with a better alternative. He suggests powering a boat with compressed air. Jamie needs to secure a boat, so he finds Joe Hughes, who's willing to sell them just what they need. Then, it's back to M5 for some 'special modifications'.

Jamie states that "it always brightens my mood when we get to break out the sledgehammer," as they modify the stern of the boat to accept the tanks and rigging they need to hold them in place.

Adam builds a throttle that will release the air in both tanks simultaneously, while Jamie builds a platform to hold them. Then, the whole team pitches in to mount the platform, the throttle linkage, and the seat.

With the boat properly modifed, it's time to get it wet. Since the boat had never been in the water prior to Jamie's purchasing it, there's some trepidation as they ease it into the water.

"Mythtanic V" floats!

With Adam shouting encouragement to Jamie as they tow the boat out into open water, they cast off the 'rocket boat' to the cheers of an impromptu 'cheering section' as Jamie gingerly opens the throttle. The boat takes off at 5 knots, but quickly runs out of air.

Jamie decides the boat needs further modification, thinking the nozzles need to be narrower (and underwater!), to propel the boat faster. They refill the tanks and give it another go. Jamie decides to throw caution to the wind and gooses the throttle. Submerging the nozzles turned out to be the wrong thing to do, as is quickly discovered, when the boat doesn't go nearly as fast, or as far as the first time.

Dockside with Mythtanic V, Adam and Jamie decide:

Air Cylinder Rocket: CONFIRMED

Air Cylinder Rocket-powered Boat: PLAUSIBLE (but not practical)

=====

The Myth:
Can an engine be built that runs solely on black (gun) powder?

Experts:
Christiaan Huygens, Sir George Cayley, Thomas Payne - designers of the black powder engines.

Memorable/Quotable Moments:
"Finally! We get to learn from somebody else's mistakes!" - Tory

"AAAH! Lemme down! Lemme down! Lemme down!" - Kari

"Dude...it looks like an 1860's circular saw" - Grant (commenting on Tory's wheel)

The Action/Results:
Grant, Kari, and Tory discuss the possibilities of powering an engine using gunpowder (also known as black powder). Kari seems to think it's as easy as dumping it into an engine, but Grant has a different idea. He suggests using some designs that were already drawn up in the past to see if those might work. Tory comments that they "...get to learn from somebody else's mistakes", so the team gets right to it.

First, the team decides on the three most-plausible engine designs, then they set about building a test rig to compare the relative energies of gasoline and black powder. They build a supersized piston to measure the strengths of the fuels, but as a test (to see if the thing even works), Kari sits on the top as Grant charges the piston with air. The piston works, pushing Kari up a few feet.

Next, they haul the cylinder into the bunker and fill it with gasoline. Igniting the gas pushes the piston up in a few seconds. They measure the top of the stroke with a magnet and Sharpie marker, then reset the rig...this time with black powder. They quickly discover that black powder is far more energetic than gasoline, as evidenced by their measuring magnet lying on the floor.

Another discussion proves that black powder is plausible as an energy source, but to actually harness that energy will prove to be difficult, at best. The team sets about building their three black powder engine models to see if they even work.

First up is Christiaan Huygens' 300 year old design of a black powder engine. The team manages to cobble together a pipe-and-pulley sort of contraption that, when fueled by black powder, was supposed to operate by pulling a slight vacuum onto pull down on a weighted rope. Grant immediately notices that the design is flawed...the hole for the fuse won't allow the engine to maintain a vacuum. Tory seems to think otherwise, so they decide to continue.

Grant is certain that Huygens' engine won't work, but concedes that testing is the only way to know...and sure enough, the engine fires, but fails to pull the weight down as far as the design specifies. Tory explains, among other things, that the one-way valves in the engine's design don't work like they're supposed to...in fact, even with an increase in black powder, the entire engine doesn't work as specified.

Huygens' Engine - BUSTED.

Next up, another design...this time, drawn up by Sir George Cayley. It seems to be a rather elaborate concept, complete with a bow to return the piston to zero, and a black powder-reloading mechanism. The team builds the engine fairly quickly, then takes it into the bunker for testing. The concept does prove viable, as they get a full stroke out of the piston, but there's a problem with the reload mechanism. Apparently, there was a backfire that ignited the black powder in the funnel, so the team decides to enclose the funnel with a piece of aluminum foil, and they try again. Once again, the engine fires, but the reload mechanism fails.

Sir George Cayley's Engine - BUSTED

And finally, the last engine, designed by Thomas Payne. His design is probably the most simple, using a wheel with air scoops to catch the exploding force of the black powder. Tory sets about building the wheel, as Kari and Grant decide that they should try to adapt an existing engine to use black powder. They decide to use a lawnmower engine, but first, a simple test to see if the spark plug can ignite a small measure of black powder...and, of course, the magneto in the engine gives them enough spark to ignite the black powder.

Tory finishes building the wheel. A compressed air test proves it to be a good concept, but the real test comes when then the team sets up the contraption in the bunker. They try increasingly larger amounts of black powder, but, try as they might, "Payne's Wheel Of Steel...just ain't spinnin'", as Rob says.

Tory tries a small modification by narrowing the output of the blast chamber, but that proves to be a bad thing. The hopper explodes...and the wheel does bupkus.

Thomas Payne's Engine - BUSTED.

So, with the three black powder-specific engines busted, it's time to test the modified lawnmower engine. Grant uses an airbrush to inject black powder into the engine, and a drill to kick-start it, but there's a problem. Upon cracking open the crankcase, it seems that the oil in the motor isn't letting the black powder ignite. So, the team drains the oil and tries one last time to get the mower engine to fire before it seizes up from the lack of oil. Tory modifies the spark plus into a glow plug to increase the chance of the engine running like they hope.

But, all is for naught, as the engine fails to perform. Out of desperation, they put a bit of black powder directly into the combustion chamber and give it one last shot. The lawnmower engine, like the three busted designs, only fires once, and that's it.

Black Powder-fueled Lawnmower Engine - BUSTED.

As the team recaps their trials, they conclude that black powder is a viable fuel source, but actually implementing it is the hard part.