The Air Car

[SBBlue]

Someone on another thread mentioned the "Air Car" and gave a URL, which is:

http://www.theaircar.com

I couldn't really figure how the air engine was supposed to work, so I did a google search and found this reference, appropriately enough at a website called "How stuff Works":

http://auto.howstuffworks.com/air-car1.htm

Now I'm not absolutely sure that what is discussed in URL #2 is the same as what is presented in URL #1, but the pictures of the cars sure look the same. I think they are the same device -- in spite of being referred to by different names.

Website #2 (How Stuff Works) gives the following information on the car, which runs on compressed gas;

Compressed air tank: 4351 psi pressure, 300 liters volume

Vehicle weight: 1543 pounds

Vehicle top speed: 60 mph

Vehicle range: 124 miles.

Doing some calculations with the standard air tables, it appears to me that the mass of air in the compressed air tank is 253.4 lbs, which means that if it is all used up over two hours, the average air mass flow rate will be about 2.1 lbs/min.

Making a couple of assumptions -- 1) the compressed air tank uses a big spring so the pressure stays at 4351 psi until the last ounce of air is used, and 2) we have a handy, dandy, 100% efficient compressed five stage air engine, and 3) we also have a heat exchanger so we can reheat the air as it expands from one stage to the next, the horsepower that the engine will develop is. . . . .

8.96 hp.

Maybe my calculations are wrong, but it appears to me that a 1500 pound vehicle might not be powered real well by a nine horsepower engine. Of course, once realistic efficiencies are considered it won't be nine horsepower -- it will be something more like 7 horsepower.

I did find one other URL that somewhat interesting:

http://www.wired.com/news/autotech/0,2554,60427,00.html

It appears that the company has only three prototypes built so far, and the best range they have got with a full tank of air is. . . . .4.5 miles.

Anybody else heard of the air car?

Anybody have any comments?

 

[IRstuff]

run away as fast as you can.

Their licensing model makes no sense. They're talking about selling 400 production line licenses worldwide.

http://www.theaircar.com/licences.html

GM, which sells 6 million cars and trucks every year has about 60 assembly plants worldwide:

http://www.gm.com/company/investor_information/docs/sales_prod/assembly_facilities.xls

TTFN

 

[GregLocock]

It is worth digging around on the aircar site, they have a table demonstrating how the range of a prototype of 4 miles can be extended to >100 by known technology (figures from memory).

A quite breathtaking piece of extrapolation!

I don't entirely agree about the licensing, there is some advantage in having more than 1 assembly plant in big countries, we spend a lot of money shipping fragile boxes of air around.

Cheers

Greg Locock

 

[IRstuff]

GM does about 70% of its business in the North America with only 31 plants producing about 6 million cars and trucks. The remainder of the plants are outside of the US, but produce only around 3 million vehicles. I miscounted earlier, GM makes about 9 million vehicles worldwide.

MDI is proposing to license 50 plants in the US, which would require completely supplanting GM and FORD combined.

That's a completely unrealistic expectation. Most automobile factories are highly automated, thus incurring essentially a large fixed cost that is amortized over the number of vehicles produced. If they expect to produce fewer cars per facility, the expectation of decent return on investment would become unrealistic.

TTFN

 

[patprimmer]

Just a point on power to weight.

A 1959 VW beetle weighed in the region of 1500 to 1600 lbs.

It had an engine SAE rated at 36hp, but normally dynoed with 25 real hp at the flywheel in as installed std tune and std accesories.

This would give a very old Beetle 3 to 4 times the power to weight that you calculate for this car. 36 hp Beetles were not exactly inspiring performance.

Regards
pat

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[maniacle]

Nope, 36 hp wouldnt thrill anybody now days. The site does say the piston remains at TDC for 70% of the crankshaft rotation though. While it may not developing the punchy hp people enjoy today, would it not develop substantially more torque?

 

[patprimmer]

maniacle, maybe I missed something, but how does time at TDC influence torque.

Also power is what determines performance. Power and torque times speed are directly related, so if you have the same power but twice the torque, you have only half the speed, so you need a 2:1 step up on gear ratios, which gives about the same net torque, power and speed at the wheels. There are slight variations due to variations in friction etc at the different speeds and loads.

Regards
pat

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