Flying cars are impossible
Jul. 3rd, 2025 02:43 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
glaurungFlying cars have been a staple of science fiction since the dawn of SF. Along with jetpacks and moonbases, saying "where's my flying car" has become a shorthand for how the promises of a certain kind of future - made by admen, futurists, and SF writers in the heyday of techno optimism - have have failed to materialize.
The other day, I learned that back in 2000, Larry Niven, who despite being a right wing shithead, writes well researched hard SF, once said in response to an interview question at space com about what things he and other SF authors got wrong, "the wealth (as in flying cars) predicted by Heinlein and his followers (including myself) was another matter. It all went to welfare programs."
Niven's presumption seems to be that the only thing keeping flying cars from becoming reality was sufficient middle class wealth, which did not come to pass due to government policies which diverted that wealth into welfare programs (as a right wing poophead, Niven is fundamentally incapable of admitting that the wealth was in fact siphoned off to the billionaires, who proceeded to buy themselves learjets and yachts and sixth homes and generally act like complete sociopaths).
It so happens that I have been thinking about flying cars off and on for a while. Niven being an ass inspired me to actually write something down. So, have a post.
Looking through the scenes involving cars in Heinlein's "Puppet Masters" (an example of "flying cars are the future" SF from the 50's that I own and have read), we can make up a set of specifications for a flying car:
- It flies, very quickly - there's dialogue saying that someone's house 200 miles away can be reached in only half an hour (aka flying over 400 mph is routine).
- It drives on legacy surface roads like a regular car (the novel includes municipalities with restrictions on overflying where the narrator must drive the vehicle on the ground)
- It can do vertical take off and landing, no runway needed, using "launching units" which behave like rockets (set them all off at once and the car goes up very fast at high g).
- It seats 4-6 people, with one vehicle early on being like a stretch limo with two facing rows of back seats in a "lounge". I assume 4 seat versions are more common. In front, there are two side by side pilot's seats with twin controls. It has a trunk for luggage, again like a regular car.
- No one ever mentions needing to refuel it, so I think it's supposed to be atomic powered (in a much later Heinlein with flying cars, "The Number of the Beast," the cars are explicitly nuclear powered).
Not alluded to in the novel, but clearly necessary:
- it has a form factor like a regular 1950s car, so it can drive down legacy streets without damage to the car/infrastructure, and so it can fit in legacy parking. (there's a paragraph that talks about how new buildings are distributed unevenly through the city, with some neighbourhoods built in the ruins after World War III being all new, and other neighbourhoods being essentially unchanged from the mid-20th century).
- The novel never mentions what keeps the cars in the air, but at the speeds described, the only real-world solution is wings with jet engines for power. "The Number of the Beast," does mention the car having wings, and makes them variable geometry, capable of extending for lift or retracting out of the way. And those wings *will* be in the way, if extended with the car on the ground:
ID: overhead schematic of various real world aircraft and automobiles, with everything sized to be at the same scale (1cm = 1 pixel at original resolution). The plane at the top is a CMC Leopard (seats 4 and exists only in prototype because the manufacturer went belly up before they could start making them to sell), the plane at the bottom is a Morane-Saulnier MS.760 Paris (a 4 seat business jet and military liaison plane). The helicopter is a Hughes OH-6 (built for the military, seats 4). The cars, from top to bottom, are a 1961 Lincoln Continental (one of the largest cars of its era), a 1970 VW Beetle (the opposite end of the size spectrum from the Lincoln), and a 2023 Toyota Prius (a normal sized modern car). (nb: a liaison plane is an unarmed craft for ferrying officers or other military personnel around to meetings and such).
In short, a flying car needs to cram the following into the form factor of a traditional ground vehicle: four to six seats and a trunk, wheels (and motors to turn them, brakes to stop them), a jet engine, a power source (fuel or a nuclear reactor), retractable wings, and VTOL jets/rockets. Which is a lot. Take a harrier jet (vtol), mash it up with an F-14 (variable wings), give the wheels motors to make it road-ready, shrink it to the size of a regular car but make the cockpit much bigger with room for several people, and you're looking at something *at least* as complicated and labour-intensive to build as a fighter jet, if not more, with a commensurate price tag.
And if it's conventionally powered we have to find room in there for a BIG fuel tank (jet engines use a LOT more fuel per mile travelled than a car), if nuclear powered we need room in the weight budget for heavy shielding. And the passenger compartment has to be low enough when on the ground to get in and out of it as easily and quickly as with a real-world car (there are scenes in Puppet Masters and Number of the Beast where people are getting in/out of the car in a rush). And the jet engine powering it needs to be as reliable, low-maintenance, and safe as a car's internal combustion engine, and, and, and.
You don't need a degree in engineering to realize how impossible this is. The motors for ground driving are just so much dead weight when it's in the air. Enabling VTOL adds even more weight, as does variable geometry. Everything the car is expected to do makes it bigger and heavier, which has a negative impact on performance. But it's also supposed to be high performance.
The wings need to be near the front of the vehicle in order to keep them from sticking out the back absurdly far when retracted. They have to retract to somewhere without squishing the passengers, so they have to be either above or below the cockpit/passenger compartment. Below is already full of wheels, motors, and VTOL jets. So we're adding height to the vehicle on both ends - VTOL stuff on the bottom and retractable wings on the top (with the jet engine nestled down the middle, either above or below the passenger compartment). This is starting to sound less like a sedan and more like a tall SUV in terms of scale. And yet in the spy novel Puppet Masters, there are scenes where the characters are outside of their car, looking around for enemies. But there's never any mention of the car being tall enough to obscure your vision of what lies beyond it, as is the case with today's SUVs. Heinlein just assumed that everything would fit in a sedan-sized package. It can't.
Oh, and this already impossibly overloaded vehicle is (in the books) supposed to be nuclear-powered. In the 50's, it was possible for Ford to dream that you would soon be able to shrink a nuclear reactor into something small and light enough to fit in a car, shield it well enough to not irradiate the passengers, and have it output enough electrical power to drive the car. It never happened. Shielded reactors can be made quite small, but miniature steam turbines to convert the reactor's heat into enough electricity, and mini radiators to dissipate the waste heat adequately? That was the stumbling block (google "Inside the Impossible Dream of the Nuclear-Powered 1958 Ford Nucleon"). In a nutshell: for a target power output, the more you shrink and simplify the generator design to reduce weight, the less efficient it becomes at making electricity, requiring a hotter reactor, which requires more and heavier cooling equipment. The only out is to use water as a coolant (allowing it to boil off as in a steam engine), but then you're range limited by the supply of water in the coolant tank, which kind of defeats the purpose of putting a nuclear reactor in the car in the first place.
Dreams of atomic powered aircraft dispensed with the whole "make electricity to power the vehicle" step and assumed that heat from the reactor would replace burning fuel in a jet engine. Jet engines are basically a long shaft with compressors at one end and turbines at the other. In the middle is a combustion chamber. Outside air gets drawn in and compressed, then burning fuel heats it very hot, making it even more compressed. The only exit for the air is through the turbine blades, which spin the shaft, powering the compressor and incidentally making some electricity to run the airplane's systems. Finally the hot air exits the engine at high speed, producing thrust. An atomic powered airplane would stick a nuclear reactor in there and use its heat instead of burning fuel to make the compressed air hot.
Plus side: no fuel needed! Down side: you need shielding (heavy), and you lose the benefit of adding combustion gases to the air in the engine, so you have heat the air even hotter than in a regular jet to get the same power. But not too hot, or stuff in the engine (or worse, the reactor) will start to melt. Sadly nuclear reactors produce heat even after you've turned them off (the fission products keep making heat as they decay). That's no good - the reactor might be fine, but that heat is going to go somewhere, and if you don't want the inside of the airplane getting dangerously hot for humans, once again, you're going to need to budget for the weight of a cooling system.
Both superpowers experimented with atomic powered jet engines in the 50's, with an eye to making a bomber with unlimited range that would never need to refuel. They built test reactors and used them to power engines on the ground, but no working aircraft were ever built (the incentive to perfect such a bomber went away once ICBMs made it possible to deliver bombs without airplanes, and the programs lost funding). The reactors and engines tested in the 50's would need to be shrunk down drastically to fit in a car-sized craft, with all the obstacles that entails - you need just as much shielding for a little reactor as a big one; no matter how small the plane, you're going to need to heat the air in the jet engine just as hot; shrink down a part designed for high pressure/temperature and it will fail at lower pressures and temperatures, and so on.
Given the safety issues and the contamination danger presented by a crashed atomic powered aircraft, I doubt anyone will ever build one even if all the necessary design work had been done in the 50's, which it was not.
Flying cars remain a staple of SF movies, but invariably, they are just car-shaped things that fly by magic (ie, antigravity or the like), no wings, no noisy jet engines. The real thing? Is impossible.
All that said: We have personal flying vehicles today - small aircraft and helicopters, like those in the image. Rich people can afford them. And they have availed themselves of private jets (which are much larger than car sized, and limited to airports) and of personal helicopters with pilots on staff to ferry them from place to place.
There was a time in the 19th century when automobiles were the toys of the rich. It didn't last, because everyone, regardless of income, could see that automobiles had many advantages over horse-powered transport. Car makers gradually lowered their prices to make cars available to a wider swath of the well-off, until Ford tried making cars that anyone could afford, and discovered the virtues of selling to the masses.
Personal flying vehicles don't have the same obvious benefits. Aircraft are just plain less pleasant than cars. They're far, far noisier, both for people riding them and people on the ground. There's turbulence up there. Airplanes operate far above the human landscape - you can't see the city as you pass over it, there's no way to notice new shops opening or someone having a yard sale, and no ability to stop on an impulse to pick up the thing you forgot about getting.
In short: car based transport was an upgrade from horses. Air-based commuting is a downgrade. Newspapers have been reporting on the existence of wealthy executives who commute to work by helicopter for decades, but all of those reports are based on it being uncommon.
To return to Niven's brainless bullshit. Cost and affordability aside: flying cars are impossible, and nobody without a staff of servants wants to use personal flying vehicles (much bigger than a car) for getting around day to day. Flying sucks. We put up with it because it takes us across long distances quickly. For day to day travel over short distances? The benefits aren't there, for reasons that have nothing to do with the absence of supporting infrastructure, the limits of regulations, or the many safety issues involved.
The other day, I learned that back in 2000, Larry Niven, who despite being a right wing shithead, writes well researched hard SF, once said in response to an interview question at space com about what things he and other SF authors got wrong, "the wealth (as in flying cars) predicted by Heinlein and his followers (including myself) was another matter. It all went to welfare programs."
Niven's presumption seems to be that the only thing keeping flying cars from becoming reality was sufficient middle class wealth, which did not come to pass due to government policies which diverted that wealth into welfare programs (as a right wing poophead, Niven is fundamentally incapable of admitting that the wealth was in fact siphoned off to the billionaires, who proceeded to buy themselves learjets and yachts and sixth homes and generally act like complete sociopaths).
It so happens that I have been thinking about flying cars off and on for a while. Niven being an ass inspired me to actually write something down. So, have a post.
Looking through the scenes involving cars in Heinlein's "Puppet Masters" (an example of "flying cars are the future" SF from the 50's that I own and have read), we can make up a set of specifications for a flying car:
- It flies, very quickly - there's dialogue saying that someone's house 200 miles away can be reached in only half an hour (aka flying over 400 mph is routine).
- It drives on legacy surface roads like a regular car (the novel includes municipalities with restrictions on overflying where the narrator must drive the vehicle on the ground)
- It can do vertical take off and landing, no runway needed, using "launching units" which behave like rockets (set them all off at once and the car goes up very fast at high g).
- It seats 4-6 people, with one vehicle early on being like a stretch limo with two facing rows of back seats in a "lounge". I assume 4 seat versions are more common. In front, there are two side by side pilot's seats with twin controls. It has a trunk for luggage, again like a regular car.
- No one ever mentions needing to refuel it, so I think it's supposed to be atomic powered (in a much later Heinlein with flying cars, "The Number of the Beast," the cars are explicitly nuclear powered).
Not alluded to in the novel, but clearly necessary:
- it has a form factor like a regular 1950s car, so it can drive down legacy streets without damage to the car/infrastructure, and so it can fit in legacy parking. (there's a paragraph that talks about how new buildings are distributed unevenly through the city, with some neighbourhoods built in the ruins after World War III being all new, and other neighbourhoods being essentially unchanged from the mid-20th century).
- The novel never mentions what keeps the cars in the air, but at the speeds described, the only real-world solution is wings with jet engines for power. "The Number of the Beast," does mention the car having wings, and makes them variable geometry, capable of extending for lift or retracting out of the way. And those wings *will* be in the way, if extended with the car on the ground:
ID: overhead schematic of various real world aircraft and automobiles, with everything sized to be at the same scale (1cm = 1 pixel at original resolution). The plane at the top is a CMC Leopard (seats 4 and exists only in prototype because the manufacturer went belly up before they could start making them to sell), the plane at the bottom is a Morane-Saulnier MS.760 Paris (a 4 seat business jet and military liaison plane). The helicopter is a Hughes OH-6 (built for the military, seats 4). The cars, from top to bottom, are a 1961 Lincoln Continental (one of the largest cars of its era), a 1970 VW Beetle (the opposite end of the size spectrum from the Lincoln), and a 2023 Toyota Prius (a normal sized modern car). (nb: a liaison plane is an unarmed craft for ferrying officers or other military personnel around to meetings and such).
In short, a flying car needs to cram the following into the form factor of a traditional ground vehicle: four to six seats and a trunk, wheels (and motors to turn them, brakes to stop them), a jet engine, a power source (fuel or a nuclear reactor), retractable wings, and VTOL jets/rockets. Which is a lot. Take a harrier jet (vtol), mash it up with an F-14 (variable wings), give the wheels motors to make it road-ready, shrink it to the size of a regular car but make the cockpit much bigger with room for several people, and you're looking at something *at least* as complicated and labour-intensive to build as a fighter jet, if not more, with a commensurate price tag.
And if it's conventionally powered we have to find room in there for a BIG fuel tank (jet engines use a LOT more fuel per mile travelled than a car), if nuclear powered we need room in the weight budget for heavy shielding. And the passenger compartment has to be low enough when on the ground to get in and out of it as easily and quickly as with a real-world car (there are scenes in Puppet Masters and Number of the Beast where people are getting in/out of the car in a rush). And the jet engine powering it needs to be as reliable, low-maintenance, and safe as a car's internal combustion engine, and, and, and.
You don't need a degree in engineering to realize how impossible this is. The motors for ground driving are just so much dead weight when it's in the air. Enabling VTOL adds even more weight, as does variable geometry. Everything the car is expected to do makes it bigger and heavier, which has a negative impact on performance. But it's also supposed to be high performance.
The wings need to be near the front of the vehicle in order to keep them from sticking out the back absurdly far when retracted. They have to retract to somewhere without squishing the passengers, so they have to be either above or below the cockpit/passenger compartment. Below is already full of wheels, motors, and VTOL jets. So we're adding height to the vehicle on both ends - VTOL stuff on the bottom and retractable wings on the top (with the jet engine nestled down the middle, either above or below the passenger compartment). This is starting to sound less like a sedan and more like a tall SUV in terms of scale. And yet in the spy novel Puppet Masters, there are scenes where the characters are outside of their car, looking around for enemies. But there's never any mention of the car being tall enough to obscure your vision of what lies beyond it, as is the case with today's SUVs. Heinlein just assumed that everything would fit in a sedan-sized package. It can't.
Oh, and this already impossibly overloaded vehicle is (in the books) supposed to be nuclear-powered. In the 50's, it was possible for Ford to dream that you would soon be able to shrink a nuclear reactor into something small and light enough to fit in a car, shield it well enough to not irradiate the passengers, and have it output enough electrical power to drive the car. It never happened. Shielded reactors can be made quite small, but miniature steam turbines to convert the reactor's heat into enough electricity, and mini radiators to dissipate the waste heat adequately? That was the stumbling block (google "Inside the Impossible Dream of the Nuclear-Powered 1958 Ford Nucleon"). In a nutshell: for a target power output, the more you shrink and simplify the generator design to reduce weight, the less efficient it becomes at making electricity, requiring a hotter reactor, which requires more and heavier cooling equipment. The only out is to use water as a coolant (allowing it to boil off as in a steam engine), but then you're range limited by the supply of water in the coolant tank, which kind of defeats the purpose of putting a nuclear reactor in the car in the first place.
Dreams of atomic powered aircraft dispensed with the whole "make electricity to power the vehicle" step and assumed that heat from the reactor would replace burning fuel in a jet engine. Jet engines are basically a long shaft with compressors at one end and turbines at the other. In the middle is a combustion chamber. Outside air gets drawn in and compressed, then burning fuel heats it very hot, making it even more compressed. The only exit for the air is through the turbine blades, which spin the shaft, powering the compressor and incidentally making some electricity to run the airplane's systems. Finally the hot air exits the engine at high speed, producing thrust. An atomic powered airplane would stick a nuclear reactor in there and use its heat instead of burning fuel to make the compressed air hot.
Plus side: no fuel needed! Down side: you need shielding (heavy), and you lose the benefit of adding combustion gases to the air in the engine, so you have heat the air even hotter than in a regular jet to get the same power. But not too hot, or stuff in the engine (or worse, the reactor) will start to melt. Sadly nuclear reactors produce heat even after you've turned them off (the fission products keep making heat as they decay). That's no good - the reactor might be fine, but that heat is going to go somewhere, and if you don't want the inside of the airplane getting dangerously hot for humans, once again, you're going to need to budget for the weight of a cooling system.
Both superpowers experimented with atomic powered jet engines in the 50's, with an eye to making a bomber with unlimited range that would never need to refuel. They built test reactors and used them to power engines on the ground, but no working aircraft were ever built (the incentive to perfect such a bomber went away once ICBMs made it possible to deliver bombs without airplanes, and the programs lost funding). The reactors and engines tested in the 50's would need to be shrunk down drastically to fit in a car-sized craft, with all the obstacles that entails - you need just as much shielding for a little reactor as a big one; no matter how small the plane, you're going to need to heat the air in the jet engine just as hot; shrink down a part designed for high pressure/temperature and it will fail at lower pressures and temperatures, and so on.
Given the safety issues and the contamination danger presented by a crashed atomic powered aircraft, I doubt anyone will ever build one even if all the necessary design work had been done in the 50's, which it was not.
Flying cars remain a staple of SF movies, but invariably, they are just car-shaped things that fly by magic (ie, antigravity or the like), no wings, no noisy jet engines. The real thing? Is impossible.
All that said: We have personal flying vehicles today - small aircraft and helicopters, like those in the image. Rich people can afford them. And they have availed themselves of private jets (which are much larger than car sized, and limited to airports) and of personal helicopters with pilots on staff to ferry them from place to place.
There was a time in the 19th century when automobiles were the toys of the rich. It didn't last, because everyone, regardless of income, could see that automobiles had many advantages over horse-powered transport. Car makers gradually lowered their prices to make cars available to a wider swath of the well-off, until Ford tried making cars that anyone could afford, and discovered the virtues of selling to the masses.
Personal flying vehicles don't have the same obvious benefits. Aircraft are just plain less pleasant than cars. They're far, far noisier, both for people riding them and people on the ground. There's turbulence up there. Airplanes operate far above the human landscape - you can't see the city as you pass over it, there's no way to notice new shops opening or someone having a yard sale, and no ability to stop on an impulse to pick up the thing you forgot about getting.
In short: car based transport was an upgrade from horses. Air-based commuting is a downgrade. Newspapers have been reporting on the existence of wealthy executives who commute to work by helicopter for decades, but all of those reports are based on it being uncommon.
To return to Niven's brainless bullshit. Cost and affordability aside: flying cars are impossible, and nobody without a staff of servants wants to use personal flying vehicles (much bigger than a car) for getting around day to day. Flying sucks. We put up with it because it takes us across long distances quickly. For day to day travel over short distances? The benefits aren't there, for reasons that have nothing to do with the absence of supporting infrastructure, the limits of regulations, or the many safety issues involved.