Comments on: Episode 63: Air Cylinder Rocket

By: garyB

garyB — Thu, 03 Jun 2010 00:37:32 +0000

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.

By: Hays

Hays — Thu, 03 Jun 2010 00:21:22 +0000

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

By: Ernest

Ernest — Thu, 03 Jun 2010 00:00:30 +0000

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.

By: leonard kjellberg

leonard kjellberg — Tue, 06 Apr 2010 00:36:15 +0000

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

By: Tetsu Uma

Tetsu Uma — Mon, 18 Jan 2010 20:41:53 +0000

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.

By: Jan

Jan — Mon, 04 Jan 2010 03:47:37 +0000

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?

By: cliff

cliff — Mon, 28 Dec 2009 06:17:06 +0000

would smokeless powder be any different from black powder?

By: Bob

Bob — Sat, 26 Dec 2009 21:01:29 +0000

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

By: Me

Me — Sat, 05 Dec 2009 23:00:46 +0000

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

By: Kirk

Kirk — Tue, 10 Nov 2009 20:14:49 +0000

What about mixing gunpowder and gasoline together?