You've got two axis of movement at 60mph. Stray a couple feet left or right and you die in fiery inferno. Stop too fast or too slow, same deal. Maybe appropriate for highly-trained specialists, not for every-man's garage.
My point is not that "cars are death machines no one should own," although there are certainly those who hold that opinion. Rather that inherently dangerous things can be made relatively safe with enough systems around them: roads, signs, traffic laws, licenses, seatbelts, and so on.
Actually, the high level question in here is quite interesting (and has even been discussed in some sci-fi).
Humans evolutionarily think about movement with a 2 dimensional mindset because for much of our history we only needed to think about 2d movement. It's why even modern flight is centered around the idea of stacking multiple 2d environments (via elevation / flight levels) and then just ignoring that 3rd dimension for the most part.
This is why something like a car is operationally intuitive -- humans don't need training to quickly pick up the interface for one, even a kid could operate a 2d vehicle. The systems around them mainly manage the risk around _conflict_ introduced by having multiple actors.
This is also where a plane (or submarine, or jetpack) is fundamentally different. The systems around those need to manage not only conflict but also our sensory deficiencies. It's very easy to get disoriented in 3d movement (it's very easy to lose the ability to tell up from down) and there have been plenty of plane crashes due to this. That's why pilots need to infer their orientation from instruments rather than just their senses. That's also why flying cars and jetpacks are not widely available -- the amount of training just to operate such devices _alone_ is already very high, let alone having to manage conflict in addition to that.
Cars are mostly 1d vehicles in practice, unless they are bumper cars. We try really hard to minimize 2d interactions between cars by stacking multiple 1d environments (lanes) and ignoring the 2nd dimension for the most part. Where we cannot ignore it we try to make it safe by adding turn lanes, roundabouts, traffic lights or building interchanges.
>It's why even modern flight is centered around the idea of stacking multiple 2d environments (via elevation / flight levels) and then just ignoring that 3rd dimension for the most part.
Generally you want to fly at a constant altitude because climbing and descending require energy transfers. Humans have little trouble coping with the concept of 3-dimensional flight, indicated by the enduring popularity of combat flight simulators, but aircraft that aren't built for combat physically struggle (and even in those that are, such flight demands careful energy management).
The answer here is what we have in drones. Drones can stay perfectly still in the air now. A flying car or personal "jet pack" would be the same. The usable system would provide all the stabilization of a drone and your controls would be just that of a car, with a separate setting for altitude.
And just like cars, you wouldn't be flying it randomly, we'd have to build "lanes" at different heights, etc. You don't drive your car randomly through buildings. In fact, connecting to a network and having it fly for you would be the most likely scenario.
Not to say that there wouldn't be "free flight" parks around.
> It's why even modern flight is centered around the idea of stacking multiple 2d environments
That's for sharing the space. It's not only a set of stacked 2D environments, those are also divided in road-like spaces, with a limited number of junctions.
You raise some interesting points here that I had not previously considered with respect to flight/submarines vs. land vehicles/boats. That third dimension must introduce a lot of cognitive load, even before conflict of other vessels/aircraft enter the scene.
There's some sci-fi (that I cannot remember off the top of my head) that actually uses this as a plot point.
I may be misremembering, but the idea is there's a special race of humans who have continued to evolve living in low gravity (space) environment, and the terrestrial human (those living on planets) governments would hire them as space mercenaries because they're at a huge advantage when it comes to 3d combat compared to training some terrestrial guy.
I had always thought of that line as metaphorical (“two dimensional thinking”), but that’s a very interesting idea, and fits well with the final battle that immediately follows it.
> Humans evolutionarily think about movement with a 2 dimensional mindset because for much of our history we only needed to think about 2d movement.
That might depend on whether the aquatic ape hypothesis is true ;)
More seriously, in addition to diving and climbing, humans have been using throwing weapons for hundreds of thousands of years -- not the same as navigating one's body through 3 dimensions, but it still requires a 3 dimensional mindset because you need to work out where the trajectories will intersect with something traveling in a different plane of movement. So I'd be curious how much hard evidence there actually is for human deficiencies in 3 dimensional thinking compared to say dolphins or parrots.
It _is_ special but we cannot perceive it correctly. We do not have an absolute sense of "down" (and our absolute sense of "forward" and "backward" are based on a assuming fixed "down").
We sense "down" based on assuming that 1G of acceleration is the "down" position. This is fine if you're stationary. This is fine if you're moving in 2d. But accelerate in 3d and all of a sudden you can get completely disoriented because the "down" you're latching on to could be any acceleration vector.
We _can_ manage this, but it is an acquired skill and we need instruments to help us. Pilots (and especially fighter pilots or astronauts who truly experience a lot of 3d acceleration) need to train for years to acquire this skill.
Can you imagine training an average person years just to _use_ a jetpack? That's why we have jetpacks and yet most people don't care.
Most of the astronaut and pilot training on this, btw, is to completely ignore what our internal intuition is and use instruments and direct math - for the reason you’re talking about, but also because especially at the astronaut level ALL intuition related to speed, direction, etc. is generally wrong. for pilots it’s often only mostly wrong, but using intuition and flying IFR is not going to work for long.
For an astronaut in orbit, going ‘up’ means accelerating. Going ‘down’ means slowing down. Going sideways (in the way we typically think of it) involves changing velocity in least 2 vectors twice, etc.
They have the pointy bits forward AND treat down as a problem as well. Gravity applies equally to Roombas and Cessnas and Soyuz, but only one of those is built on planar symmetry rather than radial symmetry. Don't you agree with that and isn't that interesting, that humans seems to have something about having a forward facing Cartesian plane.
> Humans evolutionarily think about movement with a 2 dimensional mindset because for much of our history we only needed to think about 2d movement.
Citation required? If you hang out with a child you quickly discover that their world is quite three dimensional. Heck, climbing is a fast growing sport. Again, three dimensional. We're made to run, jump, and climb. Three dimensional.
"When there is no visual input as is common in many flight situations, we rely more heavily on our vestibular sense for this information. However, in flight and in space, our vestibular system, _which is designed to work on the ground in a 1g environment_, often provides us with erroneous or disorienting information."
We have a system to somewhat understand and orient ourselves in 3d obviously, but it has quirks because evolution tuned it to work best on the ground + assuming 1G of gravity as "down".
Orienting in 3d is not intuitive for us. We can do it but we need a _lot_ of help to do it safely.
Kids don't act in true 3-D, they act in Doom-like 2-D. It gives the appearance of 3-D, but the Z-axis is barely off zero. Climbing swaps X and Z, but is still 2-D.
If it helps, think of what everybody else is calling "3-D" as "no obvious primary axis."
1) People, especially kids, jump between and across structures all the time.
2) Humans are great at throwing and catching objects, even with complex, changing trajectories--bouncing off walls, etc.
3) We have two innate senses that are clearly adapted to 3 dimensions: stereoscopic vision and proprioception.
What makes those behaviors relatively intuitive is constant acceleration. In a sense constant acceleration makes everything 2D. (Or 2.5D?) When humans need to track objects which independently accelerate along 3 axes, then there's a much stronger case for an environment alien to humans. (Counter point: hunting birds, though I believe hunters prefer to take their shot when birds are beginning or ending their flight. But notably the most salient characteristic there is acceleration, not merely relative movement in 3D space.)
Yeah, the more that I think about it, you get much more predictive power by emphasizing acceleration, not spatial dimensionality. And I don't think that's being pedantic; the distinction matters. When you look at studies of how the brain processes motion, constant acceleration (at least along 2 of 3 axes, unless/until hitting another object) is often one of the key assumptions that seems to be built into our cognition.
For example, tracking many objects moving independently in 3D space is pretty darned difficult for humans.[citation needed] But that probably has more to do with relative motion (and thus relative acceleration) than with the number of dimensions as a human can track two such objects surprisingly well, especially if they have a third, fixed reference independent from themselves.
Would be curious to compare & contrast studies of spatial cognition between marine animals and terrestrial animals, though.
The third axis adds the risk of a gravity impact to every accident. Maybe it's solvable with some kind of failproof parachute system, I dunno. I wouldn't invest in it.
Showing that cars are scary doesn't disprove that flying cars are more scary
Jetpacks don't have brakes. Once you start moving, coming to a stop is very difficult or very harmful. You have to be a highly trained specialist to operate a jetpack at all, while you can gently learn to operate a car.
Flight in general is unforgiving this way. There's only so much practicing you can do under 20 ft and 20 mph.
Airplanes you can at least use simulators and flight instructors who can take control when you mess up; jetpacks you lose any opportunity for a co-pilot, so you probably need good flight simulators you can log hundreds of hours in before strapping in.
I think this comment is reasonable and the replies to this comment are filled with bad takes.
Currently designed Jetpacks don't have brakes, or any safety features really, but that's just a lack of development.
You could easily think of hundreds of safety features that would make Jetpacks in a distant future seem pretty safe, from auto pilot/recovery features, automated object detection and avoidance, body suits with built in airbags, better designed packs that give things like 100x better articulation control, built in parachutes, the list could go on forever really.
Meanwhile cars actually have additional dangerous properties: being stuck in very confined tracks where any other user errors affect you, limited visibility, and a massive amount of heavy metal surrounding you.
I don't see why Jetpacks couldn't be as safe as a cars given they had an equal amount of investment into safety as we see modern cars. And to answer the article as to why they aren't popular, it's pretty easy to see that they just kind of suck as they are now, they need improvements in nearly every dimension.
I think there are a couple of key differences that you’re underplaying.
First, for usage of cars in society, there’s a nice gradual curve where an early slow unreliable car is still somewhat useful, and a faster car is a bit more useful, etc, and that’s what allowed them to get off the ground (as it were). There’s a vastly higher threshold before jetpacks start being usable and useful.
Second, cars are relatively fail-safe in that if you take your foot off the accelerator the car will coast to a halt. Lots of cars can easily come to a safe stop together -- traffic jams are bad but not immediately life-threatening.
Jetpacks aren’t nearly as failsafe because if you stop flying you need to land (or more likely, crash-land).
Planes have the same two advantages over jetpacks, because even a slow or unreliable plane is useful because it can carry cargo; and most planes can glide a bit which helps reduce the risk of crash landings.
Apart from anything else, the minimum viable car was pretty much as safe as modern cars (probably actually harder to kill yourself in the original car with its 10mph top speed), and just as intuitive to operate safely. The safety advances came later to deal mostly with problems which arose later (speed and other cars and boredom from long distance low effort driving)
The reason they are not popular is that we don't have a practical power source. Flight times are measured in minutes. And practical ones that could be used by anyone would be much larger (think VTOL hang glider, not Bobba Fett).
Even with a practical power source, you know have an immense amount of energy stored right next to your body. You need to be able to direct said energy in a safe way. Good luck.
There's only so much airbags can do. Imagine where you would locate those airbags. Cant be pressed against the body either (airbags can cause horrible injuries). Parachutes won't help close to the ground.
yes but the way to make cars safe is to - seriously constrain their movements (all cars here move in this direction, you can get off here, you can get on here etc. ), have different types of licenses for different kinds of cars, and limit their speeds based on location.
Jetpacks, and the flying car, have more possible ways to move.
The Jetsons used to show the flying car working the way the normal car did - highways in the sky - that's basically the way it would have to work to be made safe, as long as there are any sizable amount of users of the jetpack or flying car.
The jetpack has of course other hazards associated with it such as the engine being really close to the human operating it with significantly less shielding than one has on the car.
on edit: I think there might have been problems with the car in some Jetsons and George had to parachute to safety, arms crossed and a seriously miffed expression on his face.
So all that said - what would be required of the flying car for it to work well enough to supplant the car? (not the jetpack, that will at best be the skateboard of the sky)
1. It would have to be significantly faster, able to go longer (makes sense this would be the case because obviously you can fly quicker than you can drive so I assume this benefit will be a gimme, but it has to be significant for people to care. If you can make the flight to grandma's house in 3 hours instead of 8 there would be interest)
2. It would have to not cost very much more to own or to run.
3. It would have to not be any less safe for drivers than it currently is to drive - at the beginning this might be the case because less drivers means more safe maybe.
4. there would probably have to be significant safety features built in to keep flying cars from causing catastrophic damage if they failed - this seems to right there make it impossible because it has to not cost much more than a normal car.
5. There would probably have to increase in automation of cars to be able to detect when something wrong, when someone breaking flight rules etc.
6. no internal combustion engine flying cars, because a falling car with internal combustion engine is also a potential bomb.
so what are the benefits - we've already mentioned 1 but are there others?
Conceivably with a mass movement to flying cars instead of cars the infrastructure of cars would no longer be needed or need to be maintained. A utopian vision would then be that all that land that is currently big packed freeways get converted to parks etc. although a cynical vision would say oh nobody would want to pay for that and they turn into dystopian hellholes and kids go there to get eaten by coyotes.
Possible benefit #3 - to make safe have to have much routes for everything but given that we have all the sky conceivably there could be more routes, including emergency routes that would be left to emergency services or people registered for a possible quick route (quick routes to hospital for birth etc.) All of this of course implies flying cars with effective computer surveillance of drivers.
So I see these benefits to flying car - 1. quicker longer trips enabled. 2. No longer need driving car infrastructure 3. possible solutions to congestion are still available with flying car.
But does that mean it is doable.
I think the needed functionality points basically cancels out it ever working but maybe I am pessimistic, although I do think that now we are actually getting to the point where the necessary prerequisites for flying cars are starting to be built - specifically good electric cars and driving automation and services (but way early for that, flying cars in 100 years at this rate)
Drivable aircraft would need to be more convenient than cars.
Does anyone do a pre-drive walk-around and engine test of their car, or do they just turn it on and go? If you're in a city do you request permission to begin a trip from a DMV controller via local frequencies, or just go wherever? Does every home have a runway or just a driveway?
These aren't insurmountable challenges but there are chasms on the way from possible to safe to convenient.
(Also to your point 6, I'd add to the Kzinti lesson: any energy storage device is a weapon effective in proportion to its stored power—gas tank, flywheel, Li+ battery, dammed hydro, you name it.)
That's a big part of my reasoning, there are some fundamental impracticalities to personal aviation that limit it to particularly niche use cases. Those don't really change just because it's a flying car or jetpack.
I can of course picture a world where there are automated skyways, and electric AVs guide themeselves from abode to shopping mall airport, I'm not without imagination. But I'm not hopeful.
I think maybe the problems are: 1) the extra axis of movement means more operating complexity, and 2) there is no equivalent of "5 mph in a parking lot" on a jetpack, either you're flying or you're not.
> inherently dangerous things can be made relatively safe with enough systems around them: roads, signs, traffic laws, licenses, seatbelts, and so on.
While this is true, the issue is that what is required for "enough" can vary very widely. In particular, what would be "enough" for jetpacks (and flying machines more generally) is a lot more than what experience has shown to be "enough" for cars. Some indications of why that is are the frequency of airplane accidents involving experienced pilots, who have had a lot more training on how to fly a plane than anyone gets on how to drive a car, and also the amount of time and effort and the level of continuing human supervision required to keep commercial air travel as safe as it is, even though that also involves experienced pilots and has the support of many complex systems.
It's not really a "new frontier being misunderstood" though, it's very clear what it's value proposition is, and it's also clear from our history with aviation so far, what the challenges are. As I said in another comment, we don't even trust people to fly small drones without certification and FAA regulation, there's good reason for that, being in the air is nothing like being on a road.
To answer your question-- people in the past were expecting what has happened with small drones. Namely, that there'd be a metric fuckton of them, and that regulators would have to scramble to keep order before angry townsfolk began firing their rifles up at in the sky at them.
> we don't even trust people to fly small drones without certification and FAA regulation, there's good reason for that, being in the air is nothing like being on a road.
We don't trust people to operate cars on a road without DMV certification, FMVSS regulations, and a substantial amount of liability insurance.
Do parachutes help when you lose control 50ft off the ground? Deploy time is probably too short. Also lateral speed may be fatal enough with a jetpack.
Still needs a certain minimum height to be effective, >= 400 ft in straight and level flight, 920 ft in a spin [1]. Don't think it would be much use in a jetpack (apart from the fact that the article states that they haven't found a way yet to attach both a jetpack and a parachute, let alone a ballistic one).
Yes, that will work. It's how Spirit and Opportunity landed on Mars. Many people will die in airbag deployment failures before it works reliably, some of whom would have survived without the airbags, and they will be prohibited in the sort of repressive jurisdictions that prohibit bulletproof vests and gas masks.
> Yes, that will work. It's how Spirit and Opportunity landed on Mars.
What do you know that makes you say "that will work"? A planned and controlled landing for a rover (engineered from metal and stuff) on a planet with a gravity 38% that of earth is rather different from this hypothetical emergency system for fragile humans on earth.
Ok, let's do the math. The result is easy: When you fall from h meters (accelerating), and then decelerate over s meters cushion, your deceleration is (if it is nice and uniform) h/s. So, when you want to decelerate with at most 5g, your cushion needs to be 1/5th of the free fall distance.
For example: Velocity from a 100 metre (300 ft) free fall is v = sqrt(2gh) = 44 m/s = 160 km/h = 100 mph.
Now let's say we might survive 5g to 50g (Astronauts pull 5g routinely, Lady Di in her car crash had about 70g).
So, to brake a fall from 100m somewhat comfortably, you need a 20m cushion. To brake it such that you have a small chance of survival, you need at least a 2m cushion. This scales linearly with height you fall from, until you approach terminal velocity.
Interestingly, terminal velocity is around 200 to 300 km/h (depending on position), or 125 to 185 mph, or 54 to 80 m/s, requiring a 3m to 30m cushion.
A 30m airbag in a jetpack strikes me as unlikely. A 2m airbag in a jetpack that achieves constant deceleration may be feasible, though not soon, and certainly not something I want to experience.
For reference, these Fall-Pac units at 1.2 metres cushion promise fall protection up to 3-5 metres.
https://en.wikipedia.org/wiki/John_Stapp#Work_on_effects_of_... shows that 50 gees is survivable, at which speed you need 120 ms and 3.6 m to decelerate from 60 m/s. Not pleasant but still safer than a car crash. If the airbags inflate before you hit the ground your terminal velocity is much lower, decreasing roughly in inverse proportion to your hydraulic diameter (√(2mg/ρ/A/Cd)), so a 1.5-meter-radius cocoon of airbags around you will cut your terminal velocity to about 20 m/s, at which point you need 40 ms and 400 mm to stop safely. For this you need something like 4-12 1.5-meter-diameter airbags, 7 m² of surface each; at 20-μm thickness that's 140 cc, and if it's mostly something like gel-spun UHMWPE fiber or polyimide film, it's also about 140 g each, so 0.5-1.7 kg total bag weight --- plus conventionally 2 kg of nitrogen per airbag in the form of 3 kg of sodium azide, which is another excellent reason to perform the inflation well before you hit the ground, so you can use atmospheric air instead.
Suppose you weigh 100 kg. To stop you at a safe 20 gees max when you hit, the bag needs to exert 2000 kg max force or 20 kN, so the pressure in a bag acting over something like 1 m² of your body needs to peak at 20 kPa, about 0.2 atmospheres or 2.8 psi. Approximating hoop stress as ½Pr/t we get a bit under 400 MPa stress in the bag, too much for unaided polyimide but an order of magnitude lower than what UHMWPE fiber can handle. So you can make the bag thinner than that, lowering the weight further, perhaps to 40 g per airbag. There are whiplash shock loading problems conventionally handled in automotive airbags by generous safety factors that can be reduced by origami design and judicious addition of thicker compliant material like nylon.
A 30m airbag would need to be 20x thicker and would have 400x as much area, so it would weigh 8000x as much, 320 kg. This would indeed be unwieldy for a backpack.
You can closely approximate constant deceleration by connecting the airbag under you with other, more voluminous airbags on the other side of you, just as a car tire closely approximates constant pressure when traveling over bumps in the road. But it's not necessary; what's necessary is acceptable peak deceleration and, probably, minimal jerk. It's true that constant deceleration is the best case of minimal distance and time for a given peak deceleration, but even linearly increasing deceleration, like from a Hookean spring, only doubles the time needed to stop when holding the peak deceleration constant, thus multiplying the distance by √2.
So, you see, all the materials and mechanisms necessary are already available, though only in the last few decades. There's no technical risk. It's "just" a question of engineering the thing to not kill people all the time when it fails, based on experience with what the deadly failure modes are. It'll require a lot of work and many deaths, but if people put in the work, it will definitely work.
Let me know if I got any of the calculations wrong!
If only that invention wasn't supposed to be strapped to the same part of the person's anatomy as the jetpack, with the result being that no practically working implementation combining the two exists...
It's also not the solved problem your snark implied. I mean, someone's been working on it for decades and his solution is fly over water as much as possible!
(As other posters have alluded to, parachutes won't save you at low altitudes. In the mean time, it's further weight on your back on a device which is already difficult to control, and not really optimal for releasing next to jets of hot kerosene either)
Tens of person-years of work is not as much investment as you are implying in the context of manned heavier-than-air flight. Boeing spends ten person-years on developing flight every 40 minutes on average. Since you wrote your comment 4 hours ago Boeing has spent about 60 person-years on developing flight.
I think it was a mistake to allow just about anyone behind the wheel of a car. It results in upwards of 1 million deaths per year, that's more than malaria. And that's not including deaths attributed to air pollution.
This analogy doesn't really work because car are inherently much much safer than jetpacks just by the virtue of the fact that an error or failure or accident is almost not fatal. 0.7 percent of car accidents are fatal. In serious plane accidents, what laypersons would call crashes, the fatality rate is about 55%. Which is actually not bad considering, but not imagine if a plane was instead not this highly regulated bus-like thing that makes set routes and piloted by only experts, but something anyone can buy and fly like a hypothetical consumer jetpack. How many jetpack accidents are something that don't result in dismemberment or death? It must be a low number.
From a safety perspective, you're going to be in a little bit of trouble because this hypothetical industry will have profiteers and customers that simply won't let you regular them much. Cars are a special case because nearly everyone rides in them so safety concerns (thank you Ralph Nader) are politically easy and the capital owning class have a hard time pushing back on stories of dead families in terrible accidents. The capital owning class finds it easy to push back against regulations on motorcycles, thus maximizing their profit, because even people into motorcycles don't want crumple-zones, roll-cages, big flashing lights, bumpers, etc because it hurts the aesthetic and experience they buy motorcycles for. Lets remember it took 60-70 years of motorcycle popularity before helmet laws got popular. That's a very slow regulatory burn.
So the jetpack is a lot more like a motorcycle. Even on well regulated roads full of safety devices they're still death traps because any vehicle without a "cage" is simply dangerous and impossible to be made safe. The NHTSA: For every mile traveled, motorcyclists have a risk of a fatal accident that is 35 times higher than a car driver.
So no, you probably can't car-ize a jetpack because a jetpack isn't a car. Its own unique mode of transportation and one without a cage and something inherently unstable. I imagine your best case scenario is many times the risk of motorcycles. This is why investors, the living arm of capitalism, refuse to mass-fund these deathtraps, but they'll fund any gimmicky crypto or social media thing. I don't think a successful jetpack company wouldn't want to car-ize it anyway. It would take away the appeal and the profit incentive would demand they continue to make them as sexily dangerous and performative as they can get away with to increase that appeal, thus sales.
You also have the larger regulatory and public safety issues drones have. They can't stay aloft without power and come crashing down without wings or autogyration to helps them down. So in populated areas it would be irresponsible to have these flying over the heads of people.
If you have free time, go ahead and visit /r/weirdwings or /r/weirdwheels. There's no shortage of "innovative" death-traps out there that failed to penetrate the market because they're just too dangerous.
Last but not least, single-person transportation tends to be the kiss of death anyway from both a practicality and cost perspective. People are social, have significant others, children, elderly to take care of, etc so the single-person vehicle has to be something you own ON TOP of owning a car or two. It doesn't replace cars, so a prospective buyer is someone who has to make car payments as well as jetpack payments. What percent of Americans can afford this vs people who can afford cars and the occasional airline ticket? Currently, an affordable jetpack is $200,000. If through the miracle of mass production you get that down to 1/2 or 1/3rd that, its still the cost of an expensive luxury car. What market are you appealing to even if you iron out some of the safety issues? Who is this unicorn who can afford this and would want it, especially considering the wealthy tend to be old men unfit to pilot something like this safely and with comfort, the same way the average Corvette driver isn't hot 20 something guys like in the movies, but older men close to retirement.
Google says the average age of a corvette owner is 61. Do you really want 61 year olds flying over your head in Iron Man cosplay that actually flies? Knowing full well if their arm muscles give out then their vector radically changes and more or less turns them into 70+mph human missiles aiming for the ground?
In a country that has traded efficient public transportation like intra-city light rail, trollies, and fast regional links for car culture, well, you're kinda stuck making car payments then. Not enough people can spend $100,000 on a jetpack the same way we all don't have a Cessna waiting for us as the local regional airport. The money ain't here even if you can fix safety and the absurdly low flight time of just a few minutes. The sci-fi fantasy of flying alone above a city is not only technically difficult, ridiculously dangerous, but economically impossible for all put the wealthiest.
You've got two axis of movement at 60mph. Stray a couple feet left or right and you die in fiery inferno. Stop too fast or too slow, same deal. Maybe appropriate for highly-trained specialists, not for every-man's garage.
My point is not that "cars are death machines no one should own," although there are certainly those who hold that opinion. Rather that inherently dangerous things can be made relatively safe with enough systems around them: roads, signs, traffic laws, licenses, seatbelts, and so on.