IT SEEMS FLYING TAXIS
The flying car is something we’ve been anticipating for a very long time now. Around the world there are plenty of active flying car projects, many of them with actual flight- tested hardware. If a practical flying car can ever be built, it would naturally offer the possibility of airborne taxis, often envisaged as something you might find in the smart cities of the future.
An air taxi is a more realistic idea to begin with than a personal flying car; a taxi operator is able to finance an expensive vehicle and get it to pay its way more easily than an individual owner. That’s why, when the first motor vehicles appeared on city streets over a hundred years ago, they were typically cabs rather than private conveyances. Until after World War II, the only way a normal person would ever ride in a motor car was in a taxi (or maybe for military service). Personal cars were rare for many decades after cars took over from horses in taxi service, and it would seem that history may say the same of the flying car.
BIG BUSINESS
Certainly big money is now backing the idea of air taxis, rather than privately-owned flying cars. Billions have been ploughed into the new wave of air-taxi startups. In March, German air-taxi firm Lilium announced a special purpose acquisition company (SPAC) flotation plan that values it at $3.3bn. Others besides Lilium are heading for stock market listings via SPACs. One of them, Joby Aviation, has been valued at nearly $7bn. Another, Archer, is worth almost $4bn. Morgan Stanley has estimated that the market for aerial taxi rides could be worth $674bn by 2040.
But a flood of investment doesn’t necessarily mean the dreams will come true. In truth there are several serious technical obstacles ahead of the flying-cab dream.
First, an air taxi should be able to pick people up and drop them off in the heart of a city. This means that it can’t make use of a runway: it has to be able to take off and land vertically. The main type of aircraft in widespread use today which can take off vertically carrying a useful load is the helicopter. Way back in the 1940s people expected that the helicopter might become the flying car of today. Helicopters did catch on to some degree, but the fact is that they aren’t suitable for pick- ing people up or dropping them off in city centres.
MULTICOPTERS
One answer offered by the new wave of air taxi firms is basically an electric helicopter, often called a “multicopter”. Such designs, rather than a single large set of rotors, usually have many small sets of rotors attached to a frame above the fuse- lage, each powered by its own electric motor (though China’s eHang attaches the rotor frame to the bottom of the cab).
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One prominent electric tiltrotor design is that of Joby Aviation, set to list on the NYSE through the SPAC Reinvent Technology Partners at a projected valuation of $6.6bn. Joby’s current aircraft, the Joby 2.0, is a five-seater design with six tilting propellers, four on the wings and two on its V-shaped tail. It has actually flown, though mostly unmanned so far, and its maker claims 250km range and
JULY 2021
Perhaps the best known multicopter design comes from Volocopter, a German company which has been working on its aircraft for ten years now. Its latest fourth generation machine, is called the VoloCity. A multicopter’s many rotors give it almost as large a thrust disc area as a normal helicopter, so if it can muster as much power and carry as much energy as a normal helicopter it will offer similar performance.
The VoloCity is similar size and weight to a normal light helicopter. Volocopter says it can lift two average men with a small margin left over, and as such will be suitable for piloted taxi operations with one passenger. However, the VoloCity won’t be able to stay up for long before its batteries go flat, but the company says it can make useful short trips.
TILTROTORS
Electric multicopters are seriously limited in endurance, range and speed. Volocopter claims that the VoloCity can make 35km trips. The reality, as with any battery-powered machine, is likely to fall short of the manufacturer’s spec, especially once the batteries have been through a significant number of charge-discharge cycles.
This range problem is why most air taxi startups favour something other than a simple multicopter. There are many variations out there, but all involve landing and taking off vertically under propeller thrust and transitioning to aero- plane-style flight once moving horizontally. Using lift from wings requires much less power than vertical thrust, and allows aircraft to achieve a much greater speed and range.
Tiltrotors point their propellers up in helicopter mode to make vertical landings or takeoffs and swivel them to point forward when flying in aeroplane mode which allows them to fly further and faster than a normal helicopter can. They are a popular idea in the air taxi world as it’s comparatively easy, with electric drive, to use lots of propellers bringing safety and reliability benefits as the machine can keep flying even if it should lose a motor or a prop (or even two).
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