Quote:
Originally Posted by AeroMcAeroFace
In the Tahoe hybrid thread the car would only ever get 60mpg(US) due to rolling resistance, in the insight thread half of the drag was rolling resistance.
Theoretically rolling resistance is proportional to force applied, so a lighter car would have lower rolling resistance.
A car that generates significant lift has lower rolling resistance at higher speed.
Low drag shapes in ground effect often have high lift coefficients.
I am imagining a car, a bit like an ekranoplan, but never leaves the ground so the wheels always drive the car. Steering angle sensors, wheel slip sensors and brake pedal sensors cause the lift to stop and spoilers to create downforce pop up. Turning at speed can be assisted by aerodynamic aids.
As long as it is aerodynamically stable, in all directions, can dump lift as necessary I see no reason why this wouldn't reduce rolling resistance.
Obviously this is really complex but looking at cars like the huayra, certainly possible. Is it the case though that by the time significant rolling resistance reduction occurs, the speed is so high that rolling resistance is a tiny fraction of total drag?
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It's only friction with the ground that provides ALL of a car's propulsive, braking and cornering forces. You can easily experience what a car that is only just in contact with the ground would be like by driving on a surface with almost no friction (like on ice, or aquaplaning with all four wheels on water). Basically, impossible to control.
Alternatively, if you wish the car to be like an ekranoplan, you then need to devise different propulsive, braking and cornering systems to those used in cars. For example, propellers or jet engines for propulsion. With ekranoplan-style braking and turning systems, no normal roads would be suitable, and no normal vehicle spacing would be possible either.
Finally, if you wish a car to be able to change from being just in contact with the ground (or not at all in contact with the ground) to being a conventional car when friction with the ground is required to turn, brake or accelerate the car, then cars will need to be enormously complex (because they will need to be two different types of vehicles) and roads will need to be huge and traffic spacing equally huge (because of the finite time it would take to change from one mode to the other).
Sounds like a really bad idea to me.