Isaac Newton Says You Can't Have a Flying Car

Isaac Newton Says You Can't Have a Flying Car
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It has been the lifelong dream of many a young scientist, engineer, and science-fiction fan, and I myself have often used it as a gauge of whether we're really in the "the future" or not—so it is with great personal sadness that I have to break the news to you that you can't really have a flying car. None of us can.

And worse: the reason is not a mere technological complication or economic limitation that can be overcome with more investment and research. The problem is the basic physics of the thing. The person telling you that you can't have a flying car is Isaac Newton.

To understand why, let's first define what we're talking about when we talk about a "flying car." We're talking about the kind of vehicle we've seen over and over again in science fiction: a car that can drive along just like normal, then at a moment's notice take off vertically and move through the air. Like the flying cars in Blade Runner.

Or in Back to the Future.

Now let me explain why this definition is not just arbitrary or setting an unrealistically high bar (aside from the fact that the time period in which these examples were supposed to happen is already upon us—two years ago for Back to the Future, two years from now for Blade Runner). The point of this kind of flying car is that it offers the prospect of true point-to-point air travel, of picking up from any random spot on the surface of the globe and going to any other random spot without touching down on any intervening earth. The reason this is so exciting is that it solves so many problems of traffic flow. Stuck on the freeway? Everyone can just go airborne. Route some of the traffic at 500 feet, some at 1000 feet, some at 1500, and pretty soon the volume becomes totally manageable and everybody gets to work much faster.

Roads? Where we're going, we don't need roads. This, after all, is the main reason why we would elect to travel in the air rather than sticking to the much easier technology of surface transportation.

Compare that, however, to what we actually get with the "flying cars" currently being developed. Some of them, like the sleek-looking AeroMobil, are basically just small airplanes with folding wings.

Not only are these a distinct compromise as a car—bulky and hard to maneuver, but with little interior space or luggage capacity—but they also require a runway to lift off and to land.

The PAL-V is a little more like a cross between a motorcycle and gyrocopter, though even it requires a short runway.

Other concepts have been proposed that are more like a true vertical-takeoff-and-landing craft, which requires no more than a helipad. But note that this is still a significant commitment of real estate. A regulation helipad—and oh boy, are there regulations—"can vary from an open area of 64′ x 64′ for a small two-seat helicopter to 109′ x 109′ for a medium twin-engine helicopter." That, plus "approach slope requirements for at least one approach and departure route," which can require hundreds of feet of clear space. If you've ever seen the powerful prop wash generated by a helicopter as it lands, you understand the reason for these requirements.

It's clear why this doesn't achieve what the flying cars of fiction are supposed to achieve. You can't take off and land from anywhere, only from large, specially prepared landing sites. This means that instead of being stuck in traffic on the freeway, your "flying car" is going to be stuck in the line for the nearest runway or helipad.

It's the prop wash that is the problem, and that brings us back to Professor Newton, who tells us why this can't be avoided. Isaac Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. What that means for the problem of human flight is this: if you want to push a vehicle up off the ground, you need to push something else down. With current technology, that means pushing air molecules down—a lot of air molecules, very fast. It means creating a substantial prop wash or jet wash underneath the vehicle that is taking off. (The third solution, rocket propulsion, is even more violent and correspondingly less likely to become part of your morning commute.)

If you want to see this visualized, check out a video of a jetpack demonstration in London. This is just a jetpack, lifting only its pilot and the pack itself—we can estimate it's probably a little north of 250 pounds total. Notice the spread of the jet wash on the water of the Thames, particularly at about the five-minute mark.

For a larger vehicle, look at this test of the Cormorant, which is about the size of a small car. Notice at about the one-minute mark when it is flying at what looks to be 30 feet above a field of grass, and the vehicle is followed by a significant bow wave made by the air holding it up.

Now compare this to our fictional examples, or maybe to the Millennium Falcon blasting out of Mos Eisley spaceport. Using known technology, lifting such a large vehicle even a few feet, much less into orbit, would require a jet blast on the order of a rocket. And if you add in the additional weight of the fuel required for that kind of propulsion, you would actually have a rocket on the order of the Saturn V.

Science fiction can gloss over this issue by assuming some future technology that allows vehicles simply to float off the surface of the planet, without the need for pushing down a massive volume of air. But the point is that this assumes radically new science that has yet to be discovered. We can imagine it, but we can offer nothing more than wild speculation about how it would actually work. It's definitely not going to happen with anything like our existing science and technology.

What we have instead, in the foreseeable future, are various ideas for building fleets of air taxis using some kind of incremental development on the helicopter, but presumably cheaper and probably autonomous. Which is good, it's great, it's an expanded transportation option. I have no doubt it will be a fun doodad to show off in Dubai or maybe a high-tech way for Google executives to get to their campus.

But it's not really a "flying car." It's certainly not what we keep imagining in science fiction, and it's not likely to have any impact on the average person's commute.

Rob Tracinski is the editor of RealClearFuture.

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