Quote:
Originally Posted by JulianEdgar
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.
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Good post Julian.
I am a long time hovercraft enthusiast, and probably the only one in the forum that has attempted to operate their hovercraft on an asphalt road with a crown and attempt to drive straight and turn a curve (about 23 years ago).
The goal of the experiment goal was to get a feel for what some casters and or wheels might add to the control at low parking lot speeds, and wanted to establish a baseline stating point.
I made sure their were no parked cars to hit, and no traffic, and that was a wise decision as I had my hands full to say the least.
If you have ever hit black ice in your car and spun out while changing lanes or sliding off the crown of the road you just might be able to relate to the hovercraft experiment I did.
In a word, "Lateral Stability" or Longitudinal Control" become factors long before braking and cornering when the forces of momentum caused by mass rear their ugly heads.
You have heard the expression that the only thing between you ad the road are your tires, well it's true.
In short, I was sliding all over the place with only my ability to lean my body weight around to counter the forces of a friction-less platform.
If there is a magic ratio of
friction to mass/weight which is in-between that of a 400 lb hovercraft + 175 lb operator, and an automobile I personally have no faith in finding it if safety and control are at all considerations.
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I also did an experiment on my Porsche 911 about 15 years ago that may be of interest.
I was storing my car in the summer in my neighbors garage that was bigger and more dry than my own garage. However, the single wide narrow concrete drive had a steep incline with a double step in it because of a public sidewalk.
The scraping pads on the front suspension points would scrape terribly no matter the speed and approach taken, it as an acoustic wreck and worthy of a horror film soundtrack for strange noises like nails on a chalkboard 10X.
As a temporary solution/experiment for that single summer I fitted a row of a half dozen or so fixed angle casters, the supporting flanges of which were weak enough to fail long before damaging the front underbelly pan of the car.
In short, the casters fixed the scraping problem, however when I hit the sidewalk (
slowly at snails pace) they would lift the car just enough as to lose steering despite the front wheels still making some contact.
The car would ease down the drive with little steering control, it was scary as the approach angle had to be perfectly straight.
Another person in the Pelican Parts forum (
JMPro as I recall) placed long hard neoprene rollers/ cylinders attached to the front suspension points. On a lowered 911 the front end would dive down just enough as to contact the rollers to the ground and thereby raise the front wheels off the ground just a little, more like take a little weight off them as with my car, and again they lost some braking and steering as the car lifted. The project development did not continue after that experiment as it was deemed an unsafe concept.
As for my casters, the next summer I used my own drive and a temporary fabric and steel tube carport. I left the casters on as they were not hurting anything. That is until I went down a wavy brick road near a stone church in Ann Arbor, a large swell followed by the raise in the road bottomed out my car. I felt the car lift for a moment and then drop.
Later an inspection revealed that some of the casters did make contact at speed about 20 mph verses the 1/2 mph they were intended for and were bent and or sheered off completely, presumably left at the gutter in front of the church.
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Conclusion: Anything that lifts weight off the car be it at 1/2 mph, 20 mph or 200 mph leads to compromised vehicle control.