The difference is that in cars most of the weight is in engines and transmission, while in airplanes most of the weight is in the body. I think carmakers have already gotten most of the weight out of cars they can.

The engine needn't be metal.

The trick will be to get the engineers to make the leap back to the external combustion engine.

Come on, dudes, the real reason OJ wants cars made out of composites is that they are too expensive for people to buy, forcing them on to public transportation.

OJ -

A non-metallic combustion chamber is not something on the horizon for jet engines. There is quite a difference between the exhaust temperature from an automobile piston engine and a high-powered jet engine burning kerosene.

Making mechanical parts out of composites -- 'tain't easy. Before buying I'd recommend letting the environmentalists drive the first composite-engine cars for a decade or so. Also, make sure you get the AAA plan that covers engine replacement.

Now, trains -- there's something that could be usefully made out of composites. Lighter trains would stop faster, saving ten improperly stopped automobiles per year.

PJ: "Now, trains..."

SHHHHHhhhhhhh!!! Don't encourage him, man!

How come the future is always being planned in Europe, but landing in America?

The 1973 Chevy Vega with the aluminum block engine still haunts the collective minds of General Motors.

Well, here is a car with technology adapted from the aeronautical industry, just not the one you are referring to. The best of both worlds.

If it were easy the French would do it, instead we will.

IIRC, Ford was experimenting with a ceramic engine 25 years ago. One advantage was that the ceramics dissipated heat so effectively that it didn't need a cooling system. Don't remember why it didn't go beyond the experimental stage.

Mike - Wikipedia has a good discussion (http://en.wikipedia.org/wiki/Ceramic):

In the early 1980s, Toyota researched production of an adiabatic ceramic engine which can run at a temperature of over 6000 °F (3300 °C). Ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. Fuel efficiency of the engine is also higher at high temperature. In a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts.

Despite all of these desirable properties, such engines are not in production because the manufacturing of ceramic parts in the requisite precision and durability is difficult. Imperfection in the ceramic leads to cracks, which can lead to potentially dangerous equipment failure. Such engines are possible in laboratory settings, but mass-production is unfeasible with current technology.

The fuel savings for cars will be rather modest, mostly because you don't have to lift your car to 35,000 feet of altitude before you go someplace with it. And the material most likely to replace steel will be good old-fashioned aluminum. Still worth it, but don't expect miracles. By the way, aluminum engines are becoming more and more common even in light trucks. My Trailblazer has one, very nice motor.

My Chevy Beretta (circa 1985) had aluminum heads. One day the Temp light came on, and I promptly pulled over. The heads were irreparably warped, even though the light was on for probably less than a minute.