# Shooting down aircars



## chrispenycate (Nov 28, 2005)

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?


----------



## ras'matroi (Nov 28, 2005)

wow 
that is really detailed.

The only way to overcome gravity I can see is:
Built something like a hoovercraft.
I think it would need way too much energy to be a realistic idea.

If one of this future-cars would be about 1200kg there would be energy of 161 MegaJoule needed just to get it 10 meters up in the air. That are about 4 liters of gasoline.
Cars with new developed engines can go over 100km with that (and there is no doubt that the engines of the future will be more efficient).
And after the car is in the air it needs to be accelerated upwards the wole time by 9.81 m/s² to keep it up. For our car that be a konstant force of 11770N.
And then there would still energy be needed to move the car where you want to go.
hope I got that all right   

But there is still hope. Scientists believe that there is an elementary particle called graviton. It is still a wild theory...but if there is one and if we could learn how to manipulate it..........


----------



## Jaxom_Ruatha (Nov 29, 2005)

I've heard, most likely it's simpy an urban myth, that they did develop hoverboards (Alternatives for skateboards), but they didn't put them into production because they were potentially dangerous and could easily bring the riders to harm.


----------



## chrispenycate (Nov 29, 2005)

I rejected ground effect vehicles (air cushion hovercraft) as they didn't get high enough to fulfill my definition of "aircar" (and they can't fly over each other, so you can't stack traffic patterns vertically, and you still need traffic lights and roundabouts, so where's the fun?)
I have an engineer freind who's built his own hoverbike- where I learnt several of the useful facts about stopping and turning for this thread- it looks like a cross between a motor scooter and a flying saucer (and goes slower than either) Won't climb slopes, needs a huge turning circle, its principal advantage is that it can take a shortcut over the lake, severely annoying the windsurfers.
I can't see any real advantages to a hover board-  it's bigger, heavier and more fragile than a standard board, you can't do figures, if you go of the edge of the curb you lose your lift and scrape along the bottom and it needs fuelling.
I suppose being to cross water (with no big waves and no major wind) is worth something.


----------



## Pyan (Nov 29, 2005)

chrispenycate said:
			
		

> I can't see any real advantages to a hover board


 
Tell that to Marty McFly!


----------



## ZLBilley (Dec 11, 2005)

There is one flaw in your argument.

Aircars are friggin' cool.

People don't necessarily make decisions based entirely on efficiency here, especially if energy were very cheap. Why do you think people buy SUVs today when you can get a car that gets 60 miles per gallon?

And an aircar is probably going to be much lighter than 1200kg, no sense in making it a hunk of solid steel if you want it to fly.


----------



## Neal Asher (Dec 12, 2005)

With the new materials we're making an aircar could be very light. It could be made out of forms of aerogel (maybe expanded with helium) and carbon fibre.


----------



## Cyril (Dec 12, 2005)

If we want aircars as common as cars are today, we must make technological revolutions... find an engine powerful enough to raise the mass of the aircar plus its passengers and additionnal cargo weight. An air control system able to manage a thousand more massive traffic with enough security. But, the main issue is how to manage the breakdowns. When I was student I had an old car which regularly broke down. What if the engine stops at 2,000 meters of altitude?


----------



## Neal Asher (Dec 12, 2005)

For the traffic control and the possibility of breakdown the answer is simple: computers computers computers. The engine, however, is a different matter, or rather is is a question of energy supply. To that I submit that fifty years ago the sheer power of the batteries we put in our digital cameras now was undreamed of.


----------



## cornelius (Dec 12, 2005)

well, the nearest personal air transport means will be more like small copters, I think. maybe with a gattling or two...


----------



## Cyril (Dec 13, 2005)

Neal Asher said:
			
		

> For the traffic control and the possibility of breakdown the answer is simple: computers computers computers.


 
I agree for traffic control, good computers with small AIs or expert softwares to manage them should be sufficient.

But for breakdowns, I desagree. If your aircar stops with a main system blackout (due to an essential little piece failure) in altitude, you must have a way to save the passengers and avoiding this aircar to fall on pedestrians. Computers won't do that. You can't only stay on the roadside with aircars.


----------



## dreamwalker (Dec 14, 2005)

hmmmm

Its more a social and economic issuse to be perfectly honest.
On the whole people wanna get around as chaply as possible.
Could they do that in a hover bus if normal buses still existed? No

The social issuse comes into play when you consider jet engines, or helicopters, they are pretty much our hover/aircars but when John Travolta gets one, the entire neighbourhood goes into uproar because of the fact that these things produce noise and damaged there quality of life.

I've never really liked the idea of a flying car, always thought it was stupid, and a little regresive, and I don't actually think we'd see them until sub-orbital and interplanetary travel becomes regular (due to orbital space stations etc) and even then, it wouldn't be personalised unless you where extremely rich, it'd be more like catching a train or a plane - 

But then again there a millions of computer's throughout the world...


----------



## Neal Asher (Dec 15, 2005)

Or course the kind of arguments you apply here are very similar to those applied to the car itself when it first appeared: too noisy, and too expensive so only the province of the extremely rich. Then along came Henry Ford.


----------



## chrispenycate (Dec 15, 2005)

Neal Asher said:
			
		

> Or course the kind of arguments you apply here are very similar to those applied to the car itself when it first appeared: too noisy, and too expensive so only the province of the extremely rich. Then along came Henry Ford.


And early Fords weren't noisy?
We could build an aircar now, cheaper than the military aircraft most of the technology would be stolen from. Running on available fuels its range would be pathetic, and its fuel consumption horrendous. What is more, it'd be very, very noisy, and the blast on takeoff and landing would blow dust, pebbles, pets and small children intu the eyes of onlookers. Even then, the sight of the pont de Mont Blanc at 8.30 am, completely stationary all lanes in both directions could convince you that driving across the lake was worth the inconveniences, particularly if there were enough demand to bring the price down.

But, without getting the thing licenced, you'll be behind bars and the vehicle confiscated within hours- and what do you licence it as? An aircraft? I doubt whether it would fulfill half of the requirements, An ultraligh? Ignoring for the moment the access limits put on flying lawnmowers, it doesn't qualify there, either. No, it would need its own classification, issued by burocrats and politicians- who would be lobbied by greens, home owners and safety freaks at every turn not to.

And truthfully, they shouldn't licence them until the laws concerning obligatory computer control in built up areas and flight paths, rights of way, headlights and at what windspeed they must drive along the ground et cetera, et cetera, ad nauseum. At a european level. And a permanent beacon so the traffic control system knows where you are at all times to prevent you smuggling undesirables across now permiable frontiers. I did observe that I wouldn't live to see them, didn't I?

Else we could start with ultralights, with all the limitations, and try and increase the capacity, speed, safety, number of places they're allowed to fly, ditto for land, reduce noise levels and annoyance factor, introduce a new driving test and mass produce them. Perhaps have a man with a red flag walking in front- sort of a bicycle solution, slow, cold, not much load bearing capacity- not something to load the kids into for a trip to the supermarket, but just possibly opening the door to improved models down the line.


----------

