All right. Why are cars still made of heavy metal, then?
The lighter a car is, the better acceleration, braking, and most importantly mileage it can boast of. Any automaker would love to be able to wave around stats like that. They do, in fact, do their best to make cars as light as possible without compromising safety or structural integrity.
It’s certainly within the bounds of physics to make a safe and ultralight car, but it seems to me that it’s not practical with current technology, or someone would have done it.
Or that people aren’t willing to spend the money to have a safe and ultralight car.
The bigger point though is a social one. Until everyone drives lightweight cars, the energies the cars have to absorb is potentially much higher so greater weight is needed for safety features. So we’re stuck with our ludicrous situation.
I suspect that when people are largely removed from driving cars in favour of self-driving cars, the safety concerns will be dramatically reduced and skewed very much in favour of the unpredictable aspects of roads - kids running out, cyclists swerving etc (i.e. not very massive things).
Self driving cars are going to be cool (for so many other reasons besides).
To paraphrase a very interesting book I once read by a lunatic/engineer:
Anything that gets you further from the Earth is an anti-gravity system. Planes and helicopters are anti-gravity devices. A step ladder is an anti-gravity device.
Ah flying - really simple until you realize how insanely complicated it is.
Formula one cars are insanely light. On at least one occasion this resulted in one actually taking off and flying into nearby trees. There are practical advantages to being heavier as well (although, admittedly, these don’t necessarily kick in until well below the weights of typical cars).
Follow the money. Carbon fiber is stronger and lighter than steel, and it’s much more expensive per unit of strength. Solar cars and ultra high milage cars are built this way, but you couldn’t charge enough money make it worth building for the mass market.
All I can think of, is that people who like the flying car idea have only ever flown in commercial jets. Those feel enough like a bus , they can’t imagine why a small car couldn’t fly just as well. Anyone who’s flown in a single engine prop plane can intuit the problems with trying to drive that plane on the road,. No matter how hard you try, physics are against you.
Might as well have a drivable submarine while you’re at it!
With more thinking, maybe it could get gyroscope-stabilized, though. Or some sort of fast-reacting computer stabilization, with some sort (infrasound tomography?) of imaging of the air currents in the vicinity of the craft. Would not solve the cases when the whole airplane drops, but would alleviate the twisting and tumbling.
Instead of a plane-like flying car, what about a helicopter-like flying car? An Israeli company is developing an “AirMule” with internal rotors so it has a car-like length and width, and could land in city streets to function as a flying ambulance. See the article here and video of a test flight below. Put some regular tires on it like the proposed vehicle here and it seems like you’d have something pretty close to the sci-fi vision of a flying car.
Now that one doesn’t send all my alarm bells ringing the way fixed wing hybrids do. But now I’m thinking of ground effect: a car that was also a hovercraft… That could make short hops, even… There are definitely some useful applications for that one out there!
I could be wrong on this, but I’d want to see some safety research before using carbon fiber in car frames. It’s strong and light, but when it does fail, it fails catastrophically where metal would merely crumple.
Carbon fiber is popular for racing bicycle wheels and frames, for exactly the reasons you mentioned; but a lot of racers have eaten pavement at high speeds because stress and wear that would bend steel or aluminum makes carbon fiber shatter without warning.
Metals when repeatedly loaded above their bearing capacity will form fatigue cracks. (Presence of preexisting stresses, e.g. from welding, especially combined with corrosive environment, will make it worse.) These can grow for years to decades until they get to critical length and then crack. Alexander L. Kielland rig can tell you a nice story, and there are many more. They can be detected by ultrasound or xray or fluorescent dye penetration or so.
At loads beyond the yield strength, the material deforms inelastically, often visibly to naked eye, which shows up at inspection. Or should. Fatigue cracks are below this limit so are rather treacherous.
Composites are often based on ceramics (carbon, glass fibers…) and the ductile yield at overload won’t happen. One of their risks. Then there’s the fragility of some fibers (hi, carbon!) that could lead to catastrophic failures. There’s delamination, an especially nasty failure mode; though that can be discovered by ultrasound or so during inspections. And so on and on and on… And a strong impact can break enough fibers to make the structure incapable to bear projected loads anymore, without it being visible. My guess is that that’s behind the acquired road rashes of the mentioned cyclists.
That said, carbon-resin composites aren’t good as deformation zones. They shatter in a bad way. Maybe some foam composites? Integral metallic-foam panels can be pretty lightweight while pretty strong and stiff…
