There is a good rule of thumb that whenever a headline is phrased as a question the answer is, “No.” This headline is no exception. You might not think this from reading a recent AP article titled: “A commuter’s dream: Entrepreneurs race to develop flying car.”

I am old enough now where I can say that I have been reading such headlines for literally decades. Since I was a nerdy teenage technophile I have been reading about, and dreaming about, flying cars. They are undeniably cool – one of the holy grails of future technology.  I still sometimes imagine myself rising above the congested roads during particularly bad traffic and flying to my destination unhindered.

The AP article, however, is an excellent example of the overhyped future technology trope. Often a dramatic new technology, like flying cars, requires that several different component technologies all work sufficiently so that the application is feasible. Skyscrapers could not be built until the elevator was invented. It didn’t matter if engineers had perfected ways of supporting really tall buildings if no one could get to the upper floors.

I have discussed this idea with batteries many times. A useful battery has to simultaneously have multiple properties: good energy density and capacity, stability, sufficiently rapid charge and discharge rates, many charge-discharge cycles, and be made of material that is not too expensive, heavy, rare, or toxic. There also has to be a way to economically mass produce them. Missing even one property can be a deal-killer.

After reading score of news items on battery technology, there is a very common theme. The articles will discuss a new battery “breakthrough” in breathless terms, because one of the necessary features was significantly improved – a battery that can last for millions of cycles, or that can be recharged in seconds. They gloss over, however, the fact that one or more of the other features are deadly – oh, but they have to be made out of platinum, or their capacity is tiny. This is usually coupled with the notion that all the researchers have to do now is fix the fatal flaw, and we will soon have these wonderful batteries. That, of course, is always the rub, and we never hear about these technologies again.

For this reason I am usually more excited about incremental advances to existing working technologies. I would take a 10% increase in existing lithium-ion batteries over the possibility of a battery with 10 times the capacity but a fatal flaw that scientists are sure to work out in 5-10 years (because they probably won’t).

What About Flying Cars?

Flying cars are a compelling idea because they would be massively useful (and fun). Just like we were never going to have skyscrapers without elevators, there is at least one dependent technology we need before flying cars will be feasible – a high energy-density fuel or battery.

In the last decade engineers have cracked the problem of making flying vehicles safe and stable – sufficiently safe for an average person to fly like driving a car. Computers are powerful enough and software programs robust enough to stabilize a vehicle with multiple small rotors. This is why drones are now ubiquitous.

Many of the articles I have read in the last decade or so are about this kind of breakthrough, engineering a flying car that is safe and stable. But that was never the main problem preventing a viable flying car, it has always been the energy source.

Material science is also important, constructing a very sturdy but light-frame vehicle. That, however, is related to the deeper problem of energy, a light vehicle requires less energy to lift. Incremental advances over the decades in terms of construction material has certainly helped, but will not solve the problem on its own. Cars still need to lift people.

The big problem is that the flying car needs to lift its own fuel. This gets into the rocket problem – the more fuel you carry to extend your range, the more fuel you have to carry to carry the extra fuel, and so on. This has always placed a severe range limit on such vehicles. (The same, by the way, is true of jet packs, that other promise of future technology.)

The AP article acknowledges (but glosses over) this problem:

Key for many of the designs will be the development of longer-lasting lightweight batteries. Currently available batteries could probably keep an air taxi aloft about 15 to 30 minutes before it would have to land, experts said. Depending on how fast the aircraft flies, that probably isn’t quite enough to transport passengers between nearby cities or across metropolitan areas, experts said.

All we need is that massive battery technology breakthrough we have also been promised. In fact, for a flying car the requirements are even more stringent, as weight is a critical factor.

There are other options instead of batteries, such as supercapacitors. They currently do not have the storage capacity to be useful, however. Some kind of fuel cell might work, but again we do not yet have a sufficient working technology.

Essentially flying cars exist, but have a very short range, and so are not useful. We don’t really need any further flying car breakthroughs, and there is nothing an engineer can do to solve the fundamental underlying problem. What we need is advanced mobile energy technology.

Therefore, if you are waiting for your flying car, you should pay more attention to battery, supercapacitor, or fuel cell technology news. I certainly hope we do have a breakthrough in this area, but I have also learned not to hold my breath. We probably won’t win the lottery, but we are making solid investments that are paying off incremental dividends.

Battery technology will slowly improve. Maybe in 40-50 years we will be at the point that we have an energy source that is light and dense enough to make a flying vehicle practical. By that time, however, the same battery technology will make electric cars very practical, with impressive ranges, and easy recharge. Self-driving cars may also solve the traffic problem. There simply may never be a window where a flying car is a practical solution for the average commuter.

Still, I can see flying cars having a niche as a sport or luxury vehicle. There may also be locations where roads are not practical that would benefit from flying cars. There may also be military and other niche applications.

It is simply too much more energy efficient to roll around than to fly for flying cars to ever compete with conventional cars for most applications.