×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

The Air Car

The Air Car

The Air Car

(OP)
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?

RE: The Air Car

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

RE: The Air Car

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

RE: The Air Car

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: The Air Car

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?

RE: The Air Car

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources