compressed air propulsion

[bnhk88]

would it be possible to propel a canoe with compressed air?

the only thing i have thought of so far is to have a 12volt compressor fill air tanks and use an impact gun to power a drive shaft with a propeller.

its just a shot in the dark. i dont know how much air pressure would be needed? would a 12 volt compressor have enough power? could you use a power inverter and use a 110 compressor? would a car battery provide enough power for a couple hours on the river?

just looking for some superior knowledge. im not set on this idea just throwing it around. any suggestions or alternatives would be appreciated.

thanks

bnhk88

[wardd]

sure if you only need 5 mins of power

anything more and the tanks would probably sink the canoe

[Rick Willoughby]

would it be possible to propel a canoe with compressed air?

......

bnhk88

Yes. If well engineered it is comparable with using batteries with electric drive.

There are a few air powered cars in development such as this one:
http://www.popularmechanics.com/automotive/new_cars/4217016.html

If you look around for car information it will give you an idea of what is happening. In a boat the air motor would be used to rotate a prop instead of wheels.

I designed a one-shot air powered rocket for a movie stunt. The motor was a 20ft length of pipe filled with water and pressurised from a small 3000psi air bottle through a valve and flow restrictor. Only good for a single shot but very fast acceleration.

Overall the air system is much less efficient than an electrical system but that it is not really an issue with a canoe. The main requirement is energy density, namely energy stored for weight, and an air system is not too bad in this regard. Initially you would probably be able to refuel at the local service centre for free. At least until they woke up to you coming in every second day with an air cylinder to charge up.

Most systems would use higher pressure than normal shop pressure as it keeps the size of the cylinder down. But weight is more of an issue with a canoe. You would need to look at low weight pressure bottles. A high torque miniature motor connected directly to a prop and a control valve is all that is needed. Probably want to exhaust away from the prop.

Rick W

[pistnbroke]

So That Would Be A Ww2 Torpedo Then

[CDK]

would it be possible to propel a canoe with compressed air?

the only thing i have thought of so far is to have a 12volt compressor fill air tanks and use an impact gun to power a drive shaft with a propeller.

its just a shot in the dark. i dont know how much air pressure would be needed? would a 12 volt compressor have enough power? could you use a power inverter and use a 110 compressor? would a car battery provide enough power for a couple hours on the river?

just looking for some superior knowledge. im not set on this idea just throwing it around. any suggestions or alternatives would be appreciated.

thanks

bnhk88

If you are thinking about a battery, forget the compressor and the impact gun but use an electric motor and a prop instead.
You could however use compressed air as energy storage, but then you need much higher pressure, like a diver's bottle, otherwise you carry only a few minutes worth.
Pneumatic tools are very inefficient, they would waste most of the energy in your bottle. You could experiment with a venturi type pump, like the one divers use to uncover objects in the seabed. It is also inefficient but has no moving parts and could provide an almost noiseless propulsion for a canoe.

[MattZ]

Might want to use an air drill instead of an impact wrench. Quieter, and probably more efficient. That, or a die grinder with like 300:1 gear reduction.

[hoytedow]

You could always try the old vinegar and baking soda routine.

[Jimbo1490]

Air tool motors have really terrible efficiency. All they are is sliding vane eccentric rotors, after all. They make a lot of power in a small package but that is about their best attribute.

My Dynabrade sanders are all rated .5 hp but it takes about 2HP worth of air compressor to drive one of them- and I LIKE air tools!

WWII torpedos (and modern ones, too!) use very efficient axial piston motors to efficiently harness the compressed air. The storage trick would be to store the air in the liquid phase. I have not looked at what pressure you would need at iso std, but I would guess it's 2500 psi or more. But if you stored that way and used efficient piston motors, you could get reasonable duration.

In the end it's just a neat engineering puzzle as it has no hope of competing economically with an ICE.

Jimbo

[MattZ]

You'd have to cryogenically cool the air to liquefy it. No amount of pressure can liquefy air at room temperature.

[portacruise]

The answer to your question is YES, you can propel a canoe with compressed air. But there are simpler, more efficient and less costly ways to do it. The car battery could provide a couple of hours or more depending on speed when used directly with a trolling motor, but a deep cycle battery would last much longer.

Porta

would it be possible to propel a canoe with compressed air?

the only thing i have thought of so far is to have a 12volt compressor fill air tanks and use an impact gun to power a drive shaft with a propeller.

its just a shot in the dark. i dont know how much air pressure would be needed? would a 12 volt compressor have enough power? could you use a power inverter and use a 110 compressor? would a car battery provide enough power for a couple hours on the river?

just looking for some superior knowledge. im not set on this idea just throwing it around. any suggestions or alternatives would be appreciated.

thanks

bnhk88

[Bob E]

If this works out- http://www.popularmechanics.com/automotive/new_cars/4217016.html then other applications are sure to follow.

A production car with a range of 125 miles on compressed air means that other people are thinking of compressed air as a possible solution too.

Bob

[srimes]

The highest energy storage density that would be practical would be a CO2 tank as that is stored in liquid form. That could work great but would be expensive to refill. Liquid N2 would be great too but where would you get it?

If you want to recharge it yourself then regular compressed air is the easiest, either 125psi shop pressure or 2000 psi diver's tank.

The plus side of shop pressure tanks is they provide good flotation too.

[srimes]

oh and you would want a much more efficient motor than an air tool motor. It'd be basically the same as a steam engine, just operating at much cooler temps. I'd try building one with an air cylinder, small diameter long stroke, with a large expansion ratio. It would look and sound (and feel!) cool anyway.

[hoytedow]

Steam would be cheaper, because it can run on garbage, scrap lumber or un-recycleable types of plastic and paper waste, saving landfills. It takes energy to compress the gas in the first place, much of which is thermal, and wind turbine energy kills more birds than the Exxon Valdez and solar takes up too much land area for the amount of energy derived, so why not use steam in the first place? The water that comes out as steam is cleaner than it went in, and you could even partially clean "gray" water in the process.

[hoytedow]

As the h2o supply dwindles, flotation increases as well.

[portacruise]

This air car concept has been promoted for well over 10 years with nothing to show, even the pictured one was due last year! Read some of the comments below the article written by engineers to get an idea why this is so inefficient and why it is being promoted. Not even the liquid nitrogen cars which are way more efficient than compressed air are close to being COST effective. Liquid nitrogen is available in most large cities at prices considerably above petrol. Or you extract liquid nitrogen from the air with a cryogenic refrigerator using electricity at home. But again, why not just power an electric motor directly with a recharged battery which is more efficient and cheaper?

That's just the way I see it, anyway.

Porta



If this works out- http://www.popularmechanics.com/automotive/new_cars/4217016.html then other applications are sure to follow.

A production car with a range of 125 miles on compressed air means that other people are thinking of compressed air as a possible solution too.

Bob

[hoytedow]

Isn't regular compressed air already about 70% nitrogen?

[Submarine Tom]

Closer to 80 % nitrogen. Why?

[hoytedow]

Submarine Tom,
I ask because some auto service advertise nitrogen for filling tires, on the claim that the N2 molecules are larger than the O2 molecules. While I do not dispute this, I figure that if as the tire loses pressure due to O2 sized micro leaks, the remaining gas in the tire will have a higher N2 percentage, anyway, so why pay a higher premium on inflation? This LOGIC? would also be applicable to the pressure tanks for propulsion, no?

[wardd]

we're running out of oil now they want to use up all the air too

[portacruise]

Nitrogen molecules (formula weight 28) are smaller than oxygen molecules (formula weight 32). I think the reason for using nitrogen in tires has more to do with the fact that nitrogen does not significantly react with rubber, whereas oxygen (20% of air) would cause some degree of oxidation with rubber over time and possible leaks. I am not convinced that the DIFFERENCE is particularly significant unless 100% oxygen were being used in tires- without documented lab proof. On the surface, this just appears a case of marketing taking command over scientific illiteracy, IMHO.

Nitrogen is fairly inert and not reacted or converted to another compound in most applications including the filling of air in tires. Some amounts are consumed in making fertilizer and explosives and by plant life in nitrogen fixation. But there's enough around and it gets regenerated enough to have remained at 80% as long as man has been around. The bigger threat to air would appear to be pollution from human activity added to whatever already occurs from natural processes.

Porta

we're running out of oil now they want to use up all the air too

[mark775]

I think that one advantage to nitrogen in tires is because some race cars might do it for the lower expansion, therefore greater control of pure nitrogen. Although gasses all expand at, I think, 33% per 100C, the deal is, you get pure nitrogen without water vapor which would change pressure much more as it converts to steam in a race tire. You also get a green valve-stem cap which screams "my wrung-out Corolla would be more capable than your rapped-out Civic at speeds we couldn't possibly achieve."
See also: Folgers can exhaust for stimulating visual effect...
35213

And: ricer wing conversation pieces ("Just think how much that stupid shit spent on that!")
35214

[hoytedow]

Thanks for the enlightening.

[Submarine Tom]

I was tempted to put argon in my car tires at one point.

It's readily available at dive shops now but figured it wasn't worth it.

I know at one time ~100% nitrogen was being used in commercial aircraft tire inflation.

[Submarine Tom]

Compressed CO2 would be the way to go for propulsion. Phase change and expansion characteristics are impressive.

Perhaps that's already been covered on this thread I can't recall and don't have time to review.

Tom

[apex1]

would it be possible to propel a canoe with compressed air?


Lets make it short.........
yes, but who would be soo stupid?