The Reality of the “Flying Taxi”

Human beings have always been big dreamers. Early Hollywood sci-fi films in particular habitually pushed the 21st Century vision of civilian aerial transport as commonplace.

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The famous DeLorean DMC-12 from Back to the Future

Fast forward to 2018, and we are in actual fact nowhere near that reality. Aircraft for human travel is still largely confined to airports, and the internal combustion engine still rules the roads (though Tesla and co. are hot on their heels). Passenger aircraft for regular commutes are still a long way away.

That said however, some companies are making strides in bringing civilian air travel to the masses. The promise of flying taxis has seen companies like KittyHawk generate significant amounts of interest and funding to develop this technology. Majority of the designers of this technology stick to the simplest, lowest-cost alternative for their builds; electric multirotor aircraft. But just how practical are these flying taxis, especially in a multicopter configuration?

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The Kittyhawk Flyer, an electric multirotor-based aerial vehicle prototype

The first issue to tackle is the gross inefficiency of operation. Regular passenger aircraft have fixed wings that take up the majority of the load during flight, with the engine’s sole purpose being to maintain forward speed to allow the wings to do their job. Multirotors, on the other hand, rely on their engines entirely, for both forward motion as well as lift, in turn requiring much more energy to transport even the lightest of passengers and payloads. A 12-20 minute flight time typical of these multirotor-style aircraft simply wouldn’t be adequate for a reasonable commute.

The second issue is battery technology. Batteries have come a long way over the years, especially with the advent of the lithium-based cells, that have unrivalled power density and performance under load when compared with their lead-acid counterparts. That said, typical batteries contain only a tenth of the energy capacity per kilogram when compared with fossil fuels, allowing petroleum-powered planes to be lighter and cover an extended range. Batteries will need to drastically bring their energy densities up and recharge times down to be seen as viable options for air travel.

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LiPo batteries on multicopter. They typically account for 20-50% of the weight of the aircraft.

So, what exactly can be done to allow multirotor aircraft to be used effectively for human transportation?

The first thing is that designers will need to incorporate some level of hybrid power for aircraft propulsion. This can be done by including a petroleum-powered electric generator within the airframe, enabling the electric propulsion system to run for much longer periods of time, and in turn increasing the usefulness of the aircraft.

SureFly
The SureFly Passenger Drone, which uses electric motors powered by a petroleum generator

Something else that designers would need to consider is a VTOL (Vertical Takeoff and Landing) design. This particular implementation includes vertical thrust rotors for takeoff and landing in limited space such as helipads, and fixed wings to allow more efficient flight over long distances.

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A VTOL aircraft concept by Uber, showing the incorporation of both multirotor and fixed wing design

To sum it up, the future has never been brighter for mainstream, short-haul air travel. That said, however, the technology adopted, including propulsion mechanisms and fuel systems used, would truly need to be optimized for this particular use case, in order to allow safe, practical and affordable entry into the market, and enable us all to reap the benefits of the future of civilian travel.

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