As the designated « Dream killer » (it’s not true - I dream as much as any of you- it’s just that when I build a dream out of cobwebs and moonbeams I look up the albedo of earth’s satellite and the tensile strength of spider silk) I’m taking on aircars. For some reason, personal vehicles swooping through the atmosphere rather than staying sensibly at the bottom of it seem to be one of the standard elements of peoples images of the future - I blame the pulps.
What advantages do getting them off the ground give us ? The end of traffic jams, reduction in road building and maintenance, straight line communications, speed. Serious off road, with reduced ecological impact. Using the roofs of buildings for parking, the reduction in local airline flights.
But holding something off the ground will always be less energy efficient than rolling it across a smooth surface (for a broken surface the equation becomes less simple, and the actual smoothing takes quantities of energy- but for a large percentage of the developed world it’s already done) and energy is going to be in short supply for the immediate future. The only things that could be solar powered would be personalised zepplins, tethered above the office absorbing sunlight as you worked, but useless in even a medium wind and dangerous in a gale (and don’t forget that global warming will increase violent air movements in general. )
So either a breakthrough gives us huge quantities of cheap energy, and some way to transport it efficiently (which isn’t impossible- several thousand different aproaches might give us one or the other, or even both- pocket sized fusion generator, room temperature super conductor loop) or aircars are for the super rich, those who can call up a helicopter to come and pick them up now. This isn’t necessarily a bad thing- in the half century or so while they worked their way down to the hoi polloi, society could work out the laws, regulations and learn the associated disadvantages, plan the driving (piloting) tests, decide how much computer control was compulsory, rule that each flying vehicle transmit at all times it’s position to a central control- in short, add enough red tape to hold the things down.
A relatively conventional design would have wheels, so that it could be driven like a conventional automobile, do wnward facing jets, giving VTOL capability (essential, as you can’t be certain of finding a runway, fore and aft facing jets, for accellerating or braking, a shell designed for predictable lift, and a couple of small steering jets. However, all these jets need to run cool (if you’re taking off from a crowded M25 cooking the surrounding vehicles is a no-no, even if they are motorcycles), reasonably quiet and be very lightweight. Variable angle turbines are preferable to kerosene guzzlers- maybe even MHD. It needs a very high power to weight ratio, which means that its fuel has to be extremely energetic- meaning in turn that in an accident it’s converted into quite an efficient bomb (possibly not in the case of fusion power- as the mechanism to fuse the hydrogen breaks up, al the excess hydrogen can do is burst into flames, a big advantage over the nuclear weapon we’re using to fly the car) Ejector seats, automatic parachutes and air bags- in case of breakdown we can probably save the occupants, but even a lightweight car hitting you from above at 400 odd km/sec is annoying (temporarily)- a demolition charge to spread it all over the landscape ?(very dependant on the fuel/power source)
Magnetic levitation has been proposed- but the Earth’s own magnetic field is totally inadequate for this job. Any magnet that could lift itself on such a feeble net would be devastating to any electronics in the region, and induce hundreds of amps in telephone wires, quite probably disrupting the nervous systems of living creatures, too. So, superconducting roadbeds- but that takes away most of the advantages of getting off the ground. Plus, the energy drops off as the square of the distance, so if floating an inch off the ground took so much energy, floating six feet up would require a thousand three hundred times as much. Plus, vehicles would interact violently, either pushing each other apart or rushing together depending on their relative heights.
Cornering- that friction we’ve been trying to eliminate comes in exceedingly handy when wishing to change direction rapidly. It’s very rare that the force required to change the momentum of a car and its passengers causes the surface of the road to move appreciably. In the air, you have to convert a proportion of your lift into horizontal force, or move a rudder that is several thousand times less effective in air than in water. I suppose you can rotate your craft (or your propulsion method if you’re in a flying saucer) so you are pushed sideways- but all the ex-forward momentum is still there until absorbed by air friction or compensatory drive
Air traffic control would have a lot to say about thousands of extra radar reflections, each a potential hazard to landing aircraft (unless they can fly quite high, in which case they’re a menace to all aircraft) and would probably insist on them being under centralised computer control in flight paths. Indeed, since shooting down every manually controlled car that blundered into a flight path would probably be taken badly by the public, why not insist that every car in flight is computer controlled, with no manual controls but a joystick, in case of system failure. Of course, we’d have to trust the system a lot- a computer crash could become disturbingly literal. (distributed intelligence replacing the present driver’s distributed stupidity- but how much would a terrorist pay a hacker to insert a virus into that system?)
Antigravity- assuming antigravity is possible (and I don’t believe we understand gravity well enough to say one way or the other) then I guarantee the energy needed will be at least as great as that required to lift an equivalent mass out of the Earth’s gravity well- anything else would be magic. Of course, this doesn’t eliminate the possibility that this is a one off expenditure, no energy being expended while it’s flying, and recuperate some or most of the energy when it comes down- I don’t really expect that, it’s against Murphy, but it’s not excluded. And then what ? When the gravity is turned off, assuming you’re not anihilating inertia at the same time, near the equator you’re thrown off the planet at high speed, near the poles you fly off away from the sun. We obviously don’t need anti gravity, but continuous gravity control (cavorite roller blinds ?), leaving some contact with mother earth. We’ll then need some form of propulsion- turbines or jets would seem most likely, but perhaps the controlled gravity could be tilted, to give a forward vector, or we could harness up thousands of pigeons and use a whip. Much electronic feedback to the gravity controller, so that atmospheric lift from the forward motion is compensated by increased weight. A whole new book full of rules for in town piloting- no need for traffic lights exactly, but vertical roundabouts, enter from the left above anybody aproaching from your right, give way to traffic from below- and insurance rates um sky high- still, that’s true of any aircar- increase the reliability as you will, the probability that any accident will be very expensive rises to virtual certainty.
So, I won’t be seeing aircars- and, in all probability, neither will any of you. Not that they’re impossible, or even drastically difficult, just that they don’t fit in the overpopulated, energy poor immediate future- and short of an extreme technological breakthrough (always possible, but probabilities very low- and even lower if you consider governments allowing that much energy in so many unpredictable hands) this is going to continue for several decades. And, in all probability, when they arrive they won’t be the « easy rider » symbols of freedom and independence, but heavily monitored by big brothers.
Takes all the fun out of it, doesn’t it?
What advantages do getting them off the ground give us ? The end of traffic jams, reduction in road building and maintenance, straight line communications, speed. Serious off road, with reduced ecological impact. Using the roofs of buildings for parking, the reduction in local airline flights.
But holding something off the ground will always be less energy efficient than rolling it across a smooth surface (for a broken surface the equation becomes less simple, and the actual smoothing takes quantities of energy- but for a large percentage of the developed world it’s already done) and energy is going to be in short supply for the immediate future. The only things that could be solar powered would be personalised zepplins, tethered above the office absorbing sunlight as you worked, but useless in even a medium wind and dangerous in a gale (and don’t forget that global warming will increase violent air movements in general. )
So either a breakthrough gives us huge quantities of cheap energy, and some way to transport it efficiently (which isn’t impossible- several thousand different aproaches might give us one or the other, or even both- pocket sized fusion generator, room temperature super conductor loop) or aircars are for the super rich, those who can call up a helicopter to come and pick them up now. This isn’t necessarily a bad thing- in the half century or so while they worked their way down to the hoi polloi, society could work out the laws, regulations and learn the associated disadvantages, plan the driving (piloting) tests, decide how much computer control was compulsory, rule that each flying vehicle transmit at all times it’s position to a central control- in short, add enough red tape to hold the things down.
A relatively conventional design would have wheels, so that it could be driven like a conventional automobile, do wnward facing jets, giving VTOL capability (essential, as you can’t be certain of finding a runway, fore and aft facing jets, for accellerating or braking, a shell designed for predictable lift, and a couple of small steering jets. However, all these jets need to run cool (if you’re taking off from a crowded M25 cooking the surrounding vehicles is a no-no, even if they are motorcycles), reasonably quiet and be very lightweight. Variable angle turbines are preferable to kerosene guzzlers- maybe even MHD. It needs a very high power to weight ratio, which means that its fuel has to be extremely energetic- meaning in turn that in an accident it’s converted into quite an efficient bomb (possibly not in the case of fusion power- as the mechanism to fuse the hydrogen breaks up, al the excess hydrogen can do is burst into flames, a big advantage over the nuclear weapon we’re using to fly the car) Ejector seats, automatic parachutes and air bags- in case of breakdown we can probably save the occupants, but even a lightweight car hitting you from above at 400 odd km/sec is annoying (temporarily)- a demolition charge to spread it all over the landscape ?(very dependant on the fuel/power source)
Magnetic levitation has been proposed- but the Earth’s own magnetic field is totally inadequate for this job. Any magnet that could lift itself on such a feeble net would be devastating to any electronics in the region, and induce hundreds of amps in telephone wires, quite probably disrupting the nervous systems of living creatures, too. So, superconducting roadbeds- but that takes away most of the advantages of getting off the ground. Plus, the energy drops off as the square of the distance, so if floating an inch off the ground took so much energy, floating six feet up would require a thousand three hundred times as much. Plus, vehicles would interact violently, either pushing each other apart or rushing together depending on their relative heights.
Cornering- that friction we’ve been trying to eliminate comes in exceedingly handy when wishing to change direction rapidly. It’s very rare that the force required to change the momentum of a car and its passengers causes the surface of the road to move appreciably. In the air, you have to convert a proportion of your lift into horizontal force, or move a rudder that is several thousand times less effective in air than in water. I suppose you can rotate your craft (or your propulsion method if you’re in a flying saucer) so you are pushed sideways- but all the ex-forward momentum is still there until absorbed by air friction or compensatory drive
Air traffic control would have a lot to say about thousands of extra radar reflections, each a potential hazard to landing aircraft (unless they can fly quite high, in which case they’re a menace to all aircraft) and would probably insist on them being under centralised computer control in flight paths. Indeed, since shooting down every manually controlled car that blundered into a flight path would probably be taken badly by the public, why not insist that every car in flight is computer controlled, with no manual controls but a joystick, in case of system failure. Of course, we’d have to trust the system a lot- a computer crash could become disturbingly literal. (distributed intelligence replacing the present driver’s distributed stupidity- but how much would a terrorist pay a hacker to insert a virus into that system?)
Antigravity- assuming antigravity is possible (and I don’t believe we understand gravity well enough to say one way or the other) then I guarantee the energy needed will be at least as great as that required to lift an equivalent mass out of the Earth’s gravity well- anything else would be magic. Of course, this doesn’t eliminate the possibility that this is a one off expenditure, no energy being expended while it’s flying, and recuperate some or most of the energy when it comes down- I don’t really expect that, it’s against Murphy, but it’s not excluded. And then what ? When the gravity is turned off, assuming you’re not anihilating inertia at the same time, near the equator you’re thrown off the planet at high speed, near the poles you fly off away from the sun. We obviously don’t need anti gravity, but continuous gravity control (cavorite roller blinds ?), leaving some contact with mother earth. We’ll then need some form of propulsion- turbines or jets would seem most likely, but perhaps the controlled gravity could be tilted, to give a forward vector, or we could harness up thousands of pigeons and use a whip. Much electronic feedback to the gravity controller, so that atmospheric lift from the forward motion is compensated by increased weight. A whole new book full of rules for in town piloting- no need for traffic lights exactly, but vertical roundabouts, enter from the left above anybody aproaching from your right, give way to traffic from below- and insurance rates um sky high- still, that’s true of any aircar- increase the reliability as you will, the probability that any accident will be very expensive rises to virtual certainty.
So, I won’t be seeing aircars- and, in all probability, neither will any of you. Not that they’re impossible, or even drastically difficult, just that they don’t fit in the overpopulated, energy poor immediate future- and short of an extreme technological breakthrough (always possible, but probabilities very low- and even lower if you consider governments allowing that much energy in so many unpredictable hands) this is going to continue for several decades. And, in all probability, when they arrive they won’t be the « easy rider » symbols of freedom and independence, but heavily monitored by big brothers.
Takes all the fun out of it, doesn’t it?
