Tech requirements for viable flying car.

[Sky Captain]

In sci fi it is common to have flying cars offering convenient door to door transport often using some sort of exotic propulsion system. I'm wondering what kind of tech advances would be required to build similar vehicle in reality. Basically a vehicle that you could VTOL on any flat surface, has range similar to a normal car, can drive short distances, can carry 5 people and some luggage, is not much bigger than large SUV or delivery van and would be affordable to those who can afford a premium car.

What comes to mind is something with 4 pivoting ducted fans providing VTOL capability and retractable or foldable wings to assist in horizontal flight. However it would probably be very expensive to buy and maintain since there are 4 engines. Also if one engine fails during VTOL phase of flight the whole thing comes crashing down.
Collison safety also would be big issue because with thousands of those things in the air collisions would be likely and in the air every minor fender bender would end with falling to death and possibly also on someones head. Maybe a parachute and fully computer cotrolled flight control could solve some of those problems.

[StandingInFire]

A fan style system would probably be needed without fancy magic tech.

You want as few fancy moving parts as possible, so retractable wings + multiple pivoting fans pretty much guarantees it wouldn't become commercially viable and has to many failure points. Now ignoring all the liability concerns for flight (which would pretty much force any such system to be computer not human controlled). You also don't want exposed rotors that people can easily injure themselves with.

So probably your best bet is something that has 2 Large fixed (or minor tilting ability) fans (think in the hood and trunk area so harder to get to accidentally) that suck in air from the top for lift, and has flaps/ducts on the bottom to direct the air at angle for movement. To further assist flight & provide safety you could add light gas bladders on the sides, that could also serve as a form of bumper (compartmentalized so it would fail in small sections) and reduce fall speeds in case of fan failures. Would have to be chemically fulled because batteries are to heavy & likely wouldn't be faster than cars without significant cost increases.

But regardless it will never be as cheap/efficient as land based transportation as the only advantage of flight is to be able to ignore terrain, which in cities doesn't help much because of tall buildings.

[Broomstick]

In sci fi it is common to have flying cars offering convenient door to door transport often using some sort of exotic propulsion system. I'm wondering what kind of tech advances would be required to build similar vehicle in reality. Basically a vehicle that you could VTOL on any flat surface, has range similar to a normal car, can drive short distances, can carry 5 people and some luggage, is not much bigger than large SUV or delivery van and would be affordable to those who can afford a premium car.

Errr.... good luck with that....

What comes to mind is something with 4 pivoting ducted fans providing VTOL capability and retractable or foldable wings to assist in horizontal flight.

Wow, that's a shit load of moving and mechanical parts to go wrong/jam/break. What sort of redundancy in systems are you thinking about?

Also - keep in mind flying vehicles (even those that weigh tons) need to be relatively lightweight for their size. Using very strong, very light materials is probably a good thing. Carbon fiber has gotten popular in recent years, along with the perennial favorite aluminum.

However it would probably be very expensive to buy and maintain since there are 4 engines. Also if one engine fails during VTOL phase of flight the whole thing comes crashing down.

Yes, that is a downside of rotorcraft... but do look up something called "autorotation".

With an extremely sophisticated and reliable on-board computer you could have the thing compensate for one lost engine. Even if it can't increase or maintain altitude if you can reduce the descent rate to a relatively slow speed you'll have something survivable. I don't think the average person is going to be willing to undergo the training to learn how to reliably handle such an emergency on his/her own so automation is very important in your design.

Collison safety also would be big issue because with thousands of those things in the air collisions would be likely and in the air every minor fender bender would end with falling to death and possibly also on someones head.

Untrue. Even today mid-air collisions have a 50% survival rate on average, with the odds favoring craft in about the size range you're talking about due to simple physics. They're small enough/slow enough not to build up enough energy to make airframe failure certain or occupant death inevitable, but large enough to provide some protection to occupants.

The survival rates for mid-airs is actually higher than 50% if you just consider immediate survival of the collision, as it's frequently the long fall with the sudden stop at the end that is the fatal part, but more on that in a moment.

Mind you, the best tactic would be avoidance of collisions of any sort.

Maybe a parachute and fully computer cotrolled flight control could solve some of those problems.

We have whole-aircraft parachute either at the size range you're talking about, or just under it and research continues, Such parachutes have saved lives post-collision or during airframe failures although they aren't guarantees of survival in all circumstances. Absolutely, such a parachute is a wise addition to the aircraft.

There have also been airbags developed for aircraft. In the case of aircraft they're in the seat harness and not in the "steering wheel", but the basic concept of deploying them during an impact is the same. Definitely include those.

Likewise, automation of systems is very much a good idea. I've flown some quite primitive airplanes and while they're enjoyable for every day transportation modern systems, even on the low level I was using, are much more practical.

So, OK, you want something about the size of an SUV or mini-van, right? But you'll need to build it out of lightweight (but strong) materials. This does mean it will be at a disadvantage vs. a ground vehicle in a collision, because ground based vehicles are almost always built heavier.

You might also want to automate the pre-flight checks as much as possible. General aviation aircraft are starting to incorporate sensors (I flew an airplane once that had embedded temperature sensors in the carbon fiber main spar to make sure it was within proper temperature range prior to take off - too warm and the spar would get, um, sort of floppy which would be very bad). You probably should, too. The on board computer should perform a check of as many systems as possible prior to take off and alert the human occupants to any faults.

[Sky Captain]

Well, here is something similar to what I have in mind although it seems the development has stopped some time ago. Not sure is it because some inherent physics problems with the concept or because company ran out of money.

Wow, that's a shit load of moving and mechanical parts to go wrong/jam/break. What sort of redundancy in systems are you thinking about?

Yeah, four pivoting engines bring a lot of complexity into the design. Howewer going single engine with transmission shafts to four ducted fans may be even more complex and with even less redundancy. A helicopter has problem with large exposed rotor that would be a major hazard especially since the thing would often land and take off close to buildings and other obstacles. Also rotor hitting something and shattering would send a hail of splinters flying that would be dangerous to bystanders. Ducted fans are definately safer and could survive if the thing bumped a bit into something although they are less energy efficent than large rotor.

Yes, that is a downside of rotorcraft... but do look up something called "autorotation".

Is it possible also with small ducted fans? I was under impression only helicopters with their large rotors can land using autorotation.

With an extremely sophisticated and reliable on-board computer you could have the thing compensate for one lost engine. Even if it can't increase or maintain altitude if you can reduce the descent rate to a relatively slow speed you'll have something survivable. I don't think the average person is going to be willing to undergo the training to learn how to reliably handle such an emergency on his/her own so automation is very important in your design.

A fully automated flight control with pilot only selecting destination and route definately is a must because if this kind of vehicle is to become videspread it must be easy to use. Few people would want to undergo training required to manually fly the thing especially in the crowded airspace and to manually handle various possible emergency situations.

There have also been airbags developed for aircraft. In the case of aircraft they're in the seat harness and not in the "steering wheel", but the basic concept of deploying them during an impact is the same. Definitely include those.

Maybe also some sort of external airbag to cushion the impact would be good idea, something like those used to land Mars rovers.

So, OK, you want something about the size of an SUV or mini-van, right? But you'll need to build it out of lightweight (but strong) materials. This does mean it will be at a disadvantage vs. a ground vehicle in a collision, because ground based vehicles are almost always built heavier.

That's one problem although since this thing would be mostly an aircraft driving only short distance to get to nearby VTOL pad statistically it would be less likely to get involved in high speed collision with heavy ground vehicle.

[Dass.Kapital]

While I know this is not exactly what the Original Poster was on about and is also a complete work of fiction, the images none the less evoke a little of what the original Poster was talking about.

http://cutangus.deviantart.com/art/Blac ... -315724872

Very much cheers to all.

[Broomstick]

Well, here is something similar to what I have in mind although it seems the development has stopped some time ago. Not sure is it because some inherent physics problems with the concept or because company ran out of money.

Moller is no longer considered a player in the field and has been sued for fraud. Here is a link to an earlier thread that mentions the Skycar, with links to other discussions on another message board for further discussion if you're really interested in everything I and some other pilots have had to say on the subject.

Yeah, four pivoting engines bring a lot of complexity into the design. Howewer going single engine with transmission shafts to four ducted fans may be even more complex and with even less redundancy.

It seems that in aviation builders have opted for multiple engines over multiple transmission shafts nearly unanimously. When the aviation world is "near unanimous" and those that dissented pretty much aren't successful it might be a wise idea to go with the herd.

A helicopter has problem with large exposed rotor that would be a major hazard especially since the thing would often land and take off close to buildings and other obstacles.

There has also been a long-standing problem with large rotors lopping bits off of people. For that matter, propellers have a similar problem. It seems to be one of the inherent risks of aircraft, except for jets, which have other hazards when you're near the engines like being sucked into one or the exhaust setting things/people on fire if they get too close.

Yes, that is a downside of rotorcraft... but do look up something called "autorotation".

Is it possible also with small ducted fans? I was under impression only helicopters with their large rotors can land using autorotation.

I honestly don't know for sure. Autorotation relies on airflow through the rotor to happen, so it would seem that it would work on a ducted fan, but it may not produced enough lift to have much effectiveness in slowing a fall. Airplane propellers don't "autorotate", they "windmill" but it's similar thing in a different plane. It can have enough effect that some multi-engine aircraft allow the pilot to stop a rotating prop in the event of engine failure (that's a grossly simplified statement, I'll leave it to an actual multi-engine pilot to more accurately discuss that issue if necessary).

There have also been airbags developed for aircraft. In the case of aircraft they're in the seat harness and not in the "steering wheel", but the basic concept of deploying them during an impact is the same. Definitely include those.

Maybe also some sort of external airbag to cushion the impact would be good idea, something like those used to land Mars rovers.

If you could make it work, sure.

[Korto]

You know, I'm looking at this "Flying Car" from the other side, as a car, because to me if it's meant to be a flying car, it also has to function as a decent car, on the road. If it's just meant to fly, get a plane.
Fuck, this Moller thing looks shit.
Are those poncy things meant to be wheels? What's going to happen the first time you hit a good, old-fashioned Australian pothole? Forget that, just a damned speedbump?
And three wheels? We tried that concept for cars, and we no longer use it. With good reason. Admittedly, the engines sticking out there may stop the entire vehicle rolling over like the old Reliant Robin would (and I've only seen this on Top Gear, where the car was extensively modified for filming), but they don't look like things you'll want crashing into and scraping along the tar to me. Particularly since, as something to go into the air, it'll be made low-weight, so very expensive materials and very optimized directions of strength.
Is it supposed to be propelled along the road by those turbines? Sucking up dirt and rocks and blasting them back into whichever poor bastard's behind? No. I don't think so.

As for a "common person's" car, common people expect boot space, and the ability to load their shit in any which how without worrying about how balanced the load is.

[Broomstick]

That whole "weight and balance" thing is another obstacle to a flying car because you're right, most people don't want to bother with that shit. Hell, every year a certain number of actual pilots get into trouble over weight and balance.

I dunno, maybe you can somehow incorporate weight and balance sensors into the interior areas and automate some of that, too, but if so that would definitely be new and cutting edge stuff. Useful, though, if you could make it work. You could probably wind up selling the concept to actual aircraft manufacturers as well, and probably marine folks too.

[Sky Captain]

Moller is no longer considered a player in the field and has been sued for fraud. Here is a link to an earlier thread that mentions the Skycar, with links to other discussions on another message board for further discussion if you're really interested in everything I and some other pilots have had to say on the subject.

Thanks, that was lot of interesting info. It seems the problem is if you want fuel efficient flight you need large wings or large rotors which are hindrance when operating in confined airspace and on the ground and in case of large rotor also danger to nearby people. So a ducted fan approach to personal VTOL craft seems the way to go. Tradeoff would be higher fuel consumption because high RPM ducted fans at slow speeds are not very efficient. Maybe a lifting body design with small wings could generate some lift so at least when at cruise speed ducted fans could only provide forward thrust and if engines fail the thing could glide to survivable crash landing.
At least on RC scale ducted fan VTOL craft work fairly well

Maybe something like that could be scaled up to carry a person.
If only there were batteries with at least 1/3 energy density of fossil fuels. Then the whole thing could be made electric powered without sacrificing range solving a lot of complexity and maintenance issues arising from multiple internal combustion engines.

As for a "common person's" car, common people expect boot space, and the ability to load their shit in any which how without worrying about how balanced the load is.

If the craft has 3 or 4 ducted fans then flight computer could compensate for uneven load by throttling the engines and if the load is too unbalanced refuse to take off. Even then loading the thing would require much more care than just throwing shit in the trunk.

[Dass.Kapital]

A quick internet search has failed me but,

There was a Vought experimental design which flew that used the exhaust from a turbine to drive ducted fans.

The tech demonstrator showed that the fans could actually produce more thrust than the jet engine powering them.

Shall try more searches on some other forums where I've seen the concept designs extended further.

Hopefully the information above will help others narrow down the searching, if such is wanted.

Very much cheers to all.

[Dass.Kapital]

No wonder I couldn't find the thing. Was looking under the wrong manufacturing name.

Here's the link to a site with a wonderful amount of information. http://www.secretprojects.co.uk/forum/i ... pic=1938.0

Very much cheers to all.

[Simon_Jester]

The balance issue is a killer. This flying car will probably weigh as little as possible, so we're talking about, oh, a 1000-1500 pound chassis, maybe?

Now put a 200 pound man in the pilot's seat, in the usual position for the driver of a car... suddenly the car is unbalanced when it takes the air, because there's no 200-pound counterweight sitting on the other side!

[Broomstick]

Put the engine in the back. Or something heavy in the back. Problem solved.

It's no different than when I flew ultralights that were basically flying poles - engine in the back, pilot in the front. Occasionally, we'd throw a 5 or 10 pound sandbag on board in the right spot to balance everything. Solving the weight and balance is pretty straightforward, the big problem is that giving you an option of 1-2-3-4-whatever people will mean different W&B configurations for different numbers of passengers.

[Arthur_Tuxedo]

Instead of flying or a traffic jam, couldn't cars mount movable electro-magnets on vehicles to hoist and stack them like a cheerleader pyramid? If possible with near-future technology, this would seem to be a more efficient solution to the same problem of unused vertical space in traffic.

[Broomstick]

In the interests of providing solid information, with a WARNING that the link is a 97 page PDF and may take some time to download for slower systems, I present the FAA's 2007 version of the Weight and Balance Handbook. This covers the basic information needed by mechanics, repairmen, pilots, and designers to determine center of gravity/weight and balance, use of ballast to balance and airframe, and how to calculate load variables (i.e. effect of passengers and cargo). There are more intensive references out there, but this is a good introduction to the topic and I certainly found it useful in my flying.

[Korto]

Instead of flying or a traffic jam, couldn't cars mount movable electro-magnets on vehicles to hoist and stack them like a cheerleader pyramid? If possible with near-future technology, this would seem to be a more efficient solution to the same problem of unused vertical space in traffic.

I'm not sure I get you...

Weight and balance with the driver's side / passenger side (and luggage) isn't a real problem if this is looked at as a rich-boy's toy (which is, to be honest, the only way this is conceivable in the near-term). There's been cars made where the driver sits in the centre and the single passenger behind, and the only luggage would be some golf clubs.
The Jetsons (i.e. a family flying car, doing all the same tasks as a present day family car) is still pure SF, though.

[Arthur_Tuxedo]

Instead of flying over a traffic jam, couldn't cars mount movable electro-magnets on vehicles to hoist and stack them like a cheerleader pyramid? If possible with near-future technology, this would seem to be a more efficient solution to the same problem of unused vertical space in traffic.

I'm not sure I get you...

Corrected the typo in my quote.

Imagine that self-driving cars have replaced human operators, and that these cars can talk to each other to form optimal traffic patterns. These technologies are also pre-requisites for any flying car that would not require a pilot's license. In this network of cooperative self-driving cars, you would want magnets so that all of the cars on the highway would touch each other, eliminating wasted space and creating a slipstream effect to greatly reduce wind resistance. If a car needed to exit within a few miles, the other cars would gradually pass it into the right-hand lanes like a foosball. However, assuming the power requirements or mechanical strain would not be prohibitive, you could also have movable magnets that would hoist and stack the cars on top of each other to make the best use of the available highway space. The left-hand lane, consisting of cars that do not need to exit anytime soon, could be stacked three or four high, limited only by the height of tunnels and overpasses. This would allow traffic to achieve high speeds at high energy efficiency with no traffic jams, even with significant population increase and no investment in additional highway capacity. This would seem to be a lot more efficient and practical than a flying car that used aerodynamic lift to soar over traffic.

[Broomstick]

You'd have to make the structure of the cars a lot more robust than at present. Current cars are not designed to carry their own weight on their roofs. This would add weight to the cars to an extent that would negatively impact fuel efficiency due to the need to haul around all that extra structure and weight. Weight isn't as critical for ground vehicles as airborne ones, but it does have an effect.

That's assuming self-stacking cars are possible, or even practical from an engineering standpoint.

[Simon_Jester]

Another big problem with self-stacking cars, or cars that assemble themselves, is that it becomes extremely unsafe to drive around in a vehicle which isn't part of the big self-stacking car hivemind. The transitional period would be a logistics nightmare, at least for the foreseeable future.

The real problem with current highways and traffic jams that might be solved by self-steering cars, IMO, is the issue of freeway on-ramps. As it stands, these are often the catalysts for a major jam, because of idiot numbnuts drivers who go at 60 mph in the right hand lane literally until a merging car pulls right out in front of them, at which point they slam on the brakes. Pretty soon there's a buildup of crawling, stop-and-go vehicles backing up behind the onramp, and choking up the onramp, and forcing drivers immediately behind them to move into the left-hand lanes and causing the same problem over there.

If self-driving cars could be programmed to say "oh, I know there is an on-ramp coming up, let me automatically either slow to 30 mph in the right hand lane or move to the left hand lane," before it becomes a major backlog that backs up traffic, that backlog would take longer to appear, and jams would be less likely to form.

Actually, that reminds me of one big advance that might make self-driving cars salable, as opposed to being an interesting toy. They need to consult the driver about what might be called 'strategic' decisions. Sometimes you're in a hurry, sometimes you're not; the self-driving car should be programmed to ask you "do we take the faster route and change lanes a lot, or the slower route and change lanes less often," and other such decisions.

Otherwise, no one with any sense would buy the car, because they'll have to disable the autopilot anyway any time they have to think about where they're going and under what conditions they're going there. People often rethink their destination in mid-trip with a car, or impulsively stop for things, or make tradeoffs to get where they're going faster or less stressfully.

It's a more complicated problem than building autopilots for, say, civilian aircraft, where you have a well defined "take off from ABC, fly in a straight line at H altitude for T hours, then land at XYZ."

[Broomstick]

Well, that's the theory of aircraft autopilots and instrument flight plans. You can change your mind en route and autopilots can be reprogrammed during flight, but flying has some fundamental differences from driving such that exact comparisons aren't always practical.

[Arthur_Tuxedo]

Another big problem with self-stacking cars, or cars that assemble themselves, is that it becomes extremely unsafe to drive around in a vehicle which isn't part of the big self-stacking car hivemind. The transitional period would be a logistics nightmare, at least for the foreseeable future.

The transition would be gradual, and limited by politics. At first, self-driving cars will still require a steering wheel, pedals, and a sober, alert driver ready to take over. After a decade or two, the statistics will be clear that virtually 100% of all accidents involve one or more human drivers crashing into objects or each other, and the "safety" mandate will disappear. Since a vehicle with no need for any linkages between the cabin and the engine or controls would be much cheaper, only driving enthusiasts will be willing to fork out the extra money. Self-driving cars will know how to work together efficiently, but will be unable to take much advantage because of the human drivers gumming up the works. Eventually, human-driven cars will not be allowed in the left-most lane, then the two left-most lanes, and after many decades, will be forced to share the right-hand lane with amish horse buggies, where they would be angrily honked at were it not for the fact that occupants of self-driven cars would be too distracted by whatever movie, concert, or porn they are enjoying from a reclined position to notice the imbecile with the silly pedal-and-wheel contraption.

[Borgholio]

Great article from Wired about self-driving cars. Looks at it from an ethical / philosophical point of view.

http://www.wired.com/opinion/2013/07/th ... obot-cars/

[Starglider]

You'd have to make the structure of the cars a lot more robust than at present. Current cars are not designed to carry their own weight on their roofs.

Actually in a significant sense they are; all modern cars are designed to withstand rollover forces considerably greater than the static weight of the car. This is illustrated by stacks of cars in junkyards waiting to be crushed; the pillars and main roof structure remain intact. However most current vehicles don't have mounting points rated for that kind of weight on the top of the vehicle (roof rails are only rated for a couple of hundred kg), so you'd get superficial deformation / denting / scratching. The cost of hardpoints would be trivial compared to the crazy magnets / robotics / etc being proposed. It sounds completely impractical to me in any case due to safey issues; any sort of fast maneuver (e.g. swerve to avoid pedestrian) is likely to cause a crash and a group of linked cars crashing will impose higher peak forces on both the vehicles and whatever they hit (i.e. cause more damage).

[Simon_Jester]

Well, that's the theory of aircraft autopilots and instrument flight plans. You can change your mind en route and autopilots can be reprogrammed during flight, but flying has some fundamental differences from driving such that exact comparisons aren't always practical.

The essential point is that any given trip in the air can be described as "linear route from point A to point B, with deviations as mandated by weather or flight control." It is relatively rare for a pilot to impulsively decide to land at a different airport, or that is my impression, though it can certainly happen.

Drivers' autopilots deal with a more complicated situation. In the air, there's very little for you to crash into, except of course the ground. On the ground, your interaction with terrain and other vehicles can have a huge effect on what you do, tactically and moment-to-moment, as a driver.

The transition would be gradual, and limited by politics. At first, self-driving cars will still require a steering wheel, pedals, and a sober, alert driver ready to take over. After a decade or two, the statistics will be clear that virtually 100% of all accidents involve one or more human drivers crashing into objects or each other, and the "safety" mandate will disappear.

I am honestly unsure whether we will ever reach this point, unless computer and sensor technology both become arbitrarily good and cheap in the future. Which is possible but not certain.

The main problem is that for a long time, we're going to see cases where driver A cluelessly lets the autopilot do something stupid, like toodle along at fifty miles an hour in the middle lane of the interstate- where the accident is clearly driver B's fault as far as insurance is concerned, but where driver A's abuse of the autopilot contributed to the problem.

Hopefully, the programmers will catch all the obvious failure modes, but this is far from certain to happen fast, and our experiences during that transitional period will color the way we adopt the technology. Especially if there's trouble coordinating the smart cars with the information they need to drive themselves- such as situational changes in the speed limit of a road.

If a couple of construction workers get run down by automated cars speeding through a work zone which wasn't there the last time the car's onboard GPS uploaded a route update, it'll set back implementation rather badly. Likewise if people start dying because an ambulance was delayed by a gaggle of robot cars not smart enough to get out of the way.

[Broomstick]

Well, that's the theory of aircraft autopilots and instrument flight plans. You can change your mind en route and autopilots can be reprogrammed during flight, but flying has some fundamental differences from driving such that exact comparisons aren't always practical.

The essential point is that any given trip in the air can be described as "linear route from point A to point B, with deviations as mandated by weather or flight control." It is relatively rare for a pilot to impulsively decide to land at a different airport, or that is my impression, though it can certainly happen.

Depends on what sort of aviation you're talking about. Commerical airlines, both passenger and cargo, very seldom deviate from preplanned routes. General aviation - my level of flying - is often a different matter. General aviation pilots of the single-engine, small and simple airplane variety don't always follow direct routes, in the US they often don't need to consult air traffic control, and can deviate willy-nilly.

I'd say the general aviation crowd are more like the average driver in important respects for this comparison. Certainly, the average citizen in their flying car will want the freedom to start and stop as they desire, much like in their rolling cars.

This does not present an insurmountable problem although the more traffic you have the more regimented you need to be. Flying does have the advantage that you can separate traffic vertically as well as horizontally which might cut down on some types of collisions.

Drivers' autopilots deal with a more complicated situation. In the air, there's very little for you to crash into, except of course the ground.

Hmm... well there is certainly less to run into in the air, and it's less densely packed, there certainly are things to collide with other than the scenery (and controlled flight into terrain, as it is called, is unfortunately a recurrent form of aerial death every year). Off the top of my head, there's other aircraft, birds, bats (I know a pilot who had thousands of dollars of damage done to his Cessna Cardinal by a plane vs. bat collision), and bugs. Oh, and hail, not that anyone should be flying in those conditions but it can and does happen.

On the ground, your interaction with terrain and other vehicles can have a huge effect on what you do, tactically and moment-to-moment, as a driver.

True, those are more significant on the ground. In the air it's the weather that will have the huge and frequent effects.