Episode 63: Air Cylinder Rocket

Air Date: October 18, 2006

A compressed air cylinder can blast itself through a concrete wall.


Once the MythBusters constructed a launch tube and perfected shearing off the cylinder’s valve, the cylinder shot entirely through their constructed cinder block wall and damaged the solid concrete wall behind it. The MythBusters were also aware of recorded instances of such a thing happening.

A compressed air cylinder can power a speedboat.


The two cylinders could only propel the boat 120 feet at a maximum of 5 knots. A second attempt resulted in the boat barely making half the distance, and barely registering any speed at all. It was jokingly said that Jamie could swim faster than the boat and that the speed should be measured in "miles per day" rather than miles per hour.

An engine can run on gunpowder alone.


Even though gunpowder has a greater energy density than gasoline, none of the three historical designs worked for more than one cycle; the team could not find a practical or reliable way to feed the gunpowder into the engines (Most likely because black powder is not a liquid and therefore is not transported as easily). They were also unable to convert a modern lawnmower engine to run on gunpowder.


  1. Martin says:

    Regarding black powder not being a liquid:
    It’s not essential for it to be a liquid for it to flow. It only has to be a fluid.
    Many powders & cereals are transported around factories using pipes & air to transform them into fluids.
    I seem to recall incidents of explosive powders in factories due to the air/powder mix & static (flour/custard/etc). The mix is due to using a gas to transport them.

  2. Gary says:

    Robert H. Goddard, the father of liquid rocketry, found this out and invented liquid rockets in the process.

  3. James Cooper says:

    I agree with Martin on this one. Just because they couldn’t figure out how to do it, doesn’t mean it couldn’t be done.

    I see no reason why the gun powder couldn’t be fed in using forced air. A simple venturi with enough air flow would be enough to pick up gun powder. The tricky part would be doing this while maintaining the right fuel/air mixture.

  4. Ray says:

    Spose, but what about longevity? Wouldn’t the residue build up quite quickly, making a motor ineffective? Sure there is residue with fuel, like petrol, but this is an oil-based, isn’t it? The remnants of the gunpowder would require some form of lubrication, or some super-hot burning engine. Anyway, it isn’t my strength.

  5. James says:

    Ray has it right, the real problem with a gun powder engine is the build up of soot, LOTS of soot. Any combustion chamber you use is going to have to be cleaned continuously as the engine runs. The external combustion engine was probably the best route, and it has it’s own set of problems.

  6. Charles says:

    I liked the air cylinder rocket, but think the ‘busters missed a great opportunity with the speed boat: a hig-pressure bottle-rocket.

    Thrust is governed by momentum change (not something to “thrust against” as suggested by Jamie), so using a liquid of 1000 times the density will dramatically increase the thrust. (Think about a bottlerocket with plain air vs water.)

    I want a revisit!

  7. Michele says:

    you mix the gunpowder with alcol and insert it into the engine

  8. Ali says:

    if u wud add gun powder with air as martin said the engine is highly able to explode because air wud be runnings faster and there low chance of the air/gunpowder mixture to reach every cylinder with proper equal quantity, which cud cause malufuntions in the engine…. it can be done surely but with very low oppturnities and mixing it with alcahol wil cause it to become wet which wud have very very low chance to burn, only the alcahol wud certainly burn but the gunpowder wud slowly start collecting in the engine and block it completely

  9. Eduardo says:

    Well, any machine gun or automatic gun is indeed a gunpowder engine. You already have the slider on the reloading mechanism. If one adds a weil to it, we have a engine in the traditional sense.

  10. Gary Gore says:

    I am a Safety Manager in the indutrial construction industry. I am a huge fan especially the air cylinder rocket thru the wall. However, I noticed on some of your shows, you use a waist belt for fall protection in a lift. Unless Cal. Law is different, you guys should wear full body harness and tie off to the anchor points in the lift. I am stating this so you guys do not get hurt in the case of a fall or tip over. Keep up the good work.

  11. Ellis O'Brien says:

    Reference the air cylinder rocket, I believe you need the release of the compressed air acting on a type of propellor to harness the energy sufficiently enough to generate forward motion. The cylinder would replace the engine on a conventional motor propellor, with the compressed air acting as it’s fuel. All motorised boats use propellors in one form or another, as it is the only effective way to generate forward thrust.

  12. Mark in Chico says:

    By placing the exhaust of the air cylinder rocket underwater, it limited the force with which the air could leave, thus weakening the rocket effect… if revisited, keep the exhaust above the water line and HOLD ON TIGHT!

  13. Erik B says:

    The piston style black powder engine may be plausable. I believe the reason it didnt work was because the reloader was to fast to allow the powder to fall in to the firing chamber and residual pressure in the cylinder blew the powder up and out.
    Just a suggestion: try a valve (similar to a ball valve) that rotates/ratchets one direction half a rotation per engine cycle. But the ball part of the valve, where it would normally be open and straight through, you would have to block it right in the center creating two small cavities(ONE POWDER SIDE ONE CYLINDER SIDE) for the powder to fill one at a time when the cylinder is firing. Near the BOTTOM of the stroke, the on the way down the valve would be rotated half a turn(through the one way ratchet and simple mechanical action of the cylinder)alowing a specified quantity of powder to fall on the igniter at its leasure. NO BLOW BY INTO THE POWDER RESIVOIR AND NO ISSUES WITH THE GRAVITY TYPE VALVE THAT YOU USED OPENING AND CLOSING TO QUICKLY. If you have questions about timing or the valve in general Ill be glad to draw it up for you.

  14. DonnyH says:

    Gunpowder cannot be used instead of gasoline, but can it be used instead of a spark plug?
    Would the gunpowder be used, in reasonable quntities, to create enough heat to ignite gasoline?

  15. Eric says:

    The compressed air cylinders were tried both underwater and above water, but they were not sure which would work better — in fact, the mass flow rate of the cylinders are a functions of the differential between the tan’s internal pressure and the atmospheric pressure. As expected, when the exhaust is underwater, the exit velocity of the air is lower, which means less thrust is exerted.

  16. Colecoman1982 says:

    One of the reasons the gunpowder engine didn’t work, and one of the reasons many of their inventions don’t work, is that they don’t devote the time (in many cases years) needed to develop the idea to a workable prototype. The schedule of TV production limits how much effort they can put in. They may have been using existing designs, but those designs had already been proven as failures. One idea I stumbled across online, which may have allowed them to succeed, was to make use of the gunpowder engine that already exists (a.k.a. a machinegun). Firing a machinegun with blanks and attaching the end of the barrel to a tank which would even out the pressure and then pass it on a steady pressure flow to a turbine.

  17. Jacob Perrotta says:

    Colecoman1982 has it right. The Automatic machinegun IS a gunpowder engine. Connect to pneumatic-type engine. I don’t see why mechanical reloaders couldn’t be modified to recycle onboard shells and the piezoelectric effect could be used along with existing mechanical actions within the “gun” to ignite the powder.

  18. kenny says:

    Where can you fine the blueprints for the gunpowder engines?

  19. Stan says:

    Mix the black powder with the air before it enters the combustion chamber. Use a small gear type feeders, similar to that used on agricultural seeders, and it should work.

  20. James Garner says:

    Regarding the Gun-Powder engine…
    On the show you cited demonstrated the abiity to use air to shoot the powder (as suggested above) in a stream or fluid type manner.

    I believe a turbine engine (jet engine) would be more suited to black powder than a piston engine.

    In a jet engine, the fuel is sprayed into the combuistion area, and mixed with compressed air. It is ignited, (in the center) and all exhasut and expanding air used to generate thrust. Soot goes out wiht the heated air. A continuous flow of fuel (blackpowder) and air, would provide a continuous burn.

  21. Kirk says:

    What about mixing gunpowder and gasoline together?

  22. Me says:

    about the gun powder engine, if you threw a fire-cracker in it would ignite.

  23. Bob says:

    The gunpowder engine could have worked. The first Diesel engine used powdered coal.

  24. cliff says:

    would smokeless powder be any different from black powder?

  25. Jan says:

    On New Year’s Eve a deadly accident happened in Holland, because of an exploding gas cylinder, see http://www.telegraaf.nl/binnenland/5699592/__Man_dood_na_explosie_bij_vuurkorf__.html
    Ir says that a man used a butane gas cylinder that had been filled with oxygen, to fan a bonfire. The cylinder exploded as a result, killing the man
    Why would the cylinder explode under these circumstances? Mechanical failure, as demonstrated in this myth? Or perhaps some butane remained behind in the cylinder when the cylinder was filled with oxygen, thus creating an explosive gas mixture?

  26. Tetsu Uma says:

    Regarding the gunpowder engine. Rudolf Diesel originally intended his engine to run on powdered coal. For the gunpowder engine, combine the previous suggestions of having finely ground gunpowder in suspension in the air as fuel and use compression to fire it rather than using a sparkplug. Also the M1895 “Potato Digger” machine gun had an activating level that cycled back and forth. That mechanical action could easily be harnessed.

  27. leonard kjellberg says:

    The Mythbusters have totally got it wrong about successfuly powering aboat with two air cylinders.
    It is a matter of understanding jet power properly. Look at what happens with a garden hose. Get something like a 50ft garden hose with no fittings on it except a means of connecting it to the external tap on a house. Turn the water on full and you will notice the water is not comming out at any great pace and is producing hardly no thrust from the other end (which is open ended). This is very similar to what the mythbusters did, by adding pipe work to the end of their cylinders. Now add a hose jet on the end of the hose tun the water on and restrict the water only at the end of jet ,making sure almost 100% of the thrust is directed in one direction. Now you will have something that produces allot of thrust and supprizingly alot less water is being used. Apply the same principle to the pipe work on the boat by blanking off the exit pipe and drill a smooth quater inch hole on the end of the blank to alow the air to only exit from this hole direct it in one direction away from the end of the boat. This should produce an ear percing thrust of about 1000lbs with 4000lbs tank pressure, and 100lbs thrust with 400lbs tank pressure . Remember the way the Mythbusters originaly did it ,most of the energy would have been waisted in the open ended pipe work over a very short time. NOTE: A car called the MDI Air Car invented in France runs only on compressed air

  28. Ernest says:

    For the rocket boat experiment i feel that this expeiment should not have been busted. If they would have connected the two highpressure tanks to some boat propellers and build thrust under water that way. I think that will give the boat ahigher speed.

  29. Hays says:

    i did not see the whole episode but what if it was a john boat instead of the wide rocket boat so it would hopefully be lighter and skinner although with it being so long it would make so big difference

  30. garyB says:

    How did they get the relative energy densities of gasoline (petrol) and black powder so wrong. I’m pretty sure even wikipedia got this right: gasoline = 44.4 megajoules/kilogram, blackpowder = 3 megajoules/kilograms.

    Worst than not being able to demonstrate a blackpowder engine (see comment on coal dust engine above), they could not show how much more powerful gasoline is than blackpowder. Gasoline does not have its own oxidant, so it needs to be ignited in the right mixture with air. I suspect their method for mixing and igniting the gasoline/air mixture in the test cylinder was flawed.

    I have seen on an older TV show a cannon (mortar really) fire with a tablespoon of blackpowder and then a tablespoon of gasoline. The blackpowder barely got the projectile out of the barrel. The gasoline launched the projectile across a large lake. Then they blew the exhaust gases out of the tube and fired again from the same tablespoon of gasoline, same result. I believe they used a spark plug to ignite the mixture. The key is probably to leave a correct size air space between the liquid gasoline and the bottom of the projectile.

    I hope they re-visit this myth that they created.

  31. PaulR says:

    GaryB is right. The guys got the energy density way wrong. Gasoline has FIFTEEN TIMES the energy density of black powder. This is for two reasons: 1) black powder contains its own oxidizer, so only a fraction of its mass is actually fuel; 2) only half of the mass of black powder gets converted to gas; the rest gets left behind as a tenacious and corrosive soot (which would cause bigger problems in an engine than it did in guns).

    The experiment they used to determine energy density was fundamentally flawed.

  32. travis lewis says:

    I feel like you should be very aware of all the dangers of the stuff around you so you don’t harm yourself and others on the job cause that can cause you to hurt people and lose your job

  33. Blake Baker says:

    I don’t know if one of the other comments said it already, (I was to lazy to read threw them all) But In response to the water boat, Air in it’s self wouldn’t have enough push to move the boat forward, You proved that. But could you have had a Turbin, kind of like a car turbo, wich on one end the air is turning the blades one way, and the other is sucking up and pushing out water on the impeller side?

    Reason I ask is because, Im working on a project much like the “Seabreacher” But I am looking to take it about 5 steps foward, and Im looking for a way to give it a quick hard hitting boost to breach and get as much lift as possible,

  34. Greg says:

    Older combustion engines used large flywheels and spread the combustion cycles out further. They would have one combustion for multiple revolutions then would ignite the other cycle. I am not an expert on these engines but have seen them run. I encourage the mythbusters to look into these old time engines and that could work out for a proof of concept. Though I doubt the efficiency of modern engines would be achieved.

  35. Adam says:

    While a super size bottle rocket would be more effective, maybe water can be entrained in the divergent section of a convergent-divergent duct. As it should actually move more water, it could be more effective. Also ram “pressure” (does that apply to incompressible fluid?) may help the directionality of the flow once it’s going.

  36. Dan says:

    While I don’t dispute the destructive capabilities of an air cylinder through a wall, I don’t feel like they tested it to the fullest. Most cinder block walls have some sort of rebar reinforcement inside of it. The wall they used had none. Adding rebar to the wall would strengthen it exponentially and may provide an element that prevents the wall from being fully punctured.

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