SE Vehicles

Will the electric car 'really take off' this time? Part 2

Aug 06, 2017

The best way to predict the future is to invent it. Four developments are quintessential to the eVTOL: -1- the progress in the development of durable, lightweight, stress-resistant materials, -2- battery and electric motor technology that is rapidly advancing; there's already talk about 10 kW (13.4 hp) yield per 1 kg own weight, -3- the possibility of guided transit that will 'denecessitate' the need for a driver or pilot (license), and -4- the trend toward what I call seamless '2D and 3D' transit, probably run by a TNC, a Transportation Network Company.

CLICK HERE to read "Will the electric car really take off this time? Part 1"

Disk loading co-determines if it’s feasible to VTOL on battery power. There is a reason why helicopters use rotors that sweep a large surface area, it's called efficiency. The smaller the thrusters an eVTOL is using, the more difficult it is to use batteries as they add considerable weight. Integrate thrusters into an airframe to have them vector their thrust, and you lose the electric rotor’s advantage of basic simplicity (fixed-pitch blades, minimum of moving parts). Costs go up. Reliability goes down. For instance, the multi-million dollar funded and ESA-supported (!) Lilium eVTOL 'jet' project is based on the deployment of 36 ducted fans with an estimated diameter of 15 cm (600 kg max TO weight, 320 kW output). This means that Lilium's disk loading is 14 times that of the notorious Boeing Osprey! No wonder that Volocopter is furthest in developing a viable eVTOL: structural lightness and 18 individual rotors that sweep over a large disk area.

Click here to see all eVTOL projects

eVTOLS may appeal to the aircraft industry as well as to the automotive branche. In fact, Chinese car maker Geely took over Terrafugia, Toyota (that says it will use solid-state batteries in EVs by 2020) just started its SkyDrive Cartivator project, and Mercedes decided to invest in Volocopter that will bring a production-ready flying two-seater in 2018. eVTOLS are hot because of the prospect of cheaper flight than is offered by using helicopters. More practical. Cleaner. And brought closer to your point of departure and arrival. Even safer.

CLICK to see a comparison with Volocopter VC200 and the smallest mass-produced helicopter, the Robinson R22, that depend on their rotors to keep them up in the air. That's the challenge, have an airfoil take care of that. To give an indication, the Cessna 180 airplane (max TO weight of 2800 lb, that's 1270 kg) has a wing area of 16.2 m2. And while you're at it, replace the fuselage for a lightweight, low-drag road vehicle that can carry three persons. The Technical University of Munich (TUM), for instance, already came up with an electric car, called Visio.M, that can weigh as little as 535 kg, including the batteries. Here's an interesting comparison Visio.M vs iSetta.

HOLD ON! Not so quick. Doesn't a 'system' of separate eVTOLs and cars offer more flexibility to the customer? After all, you are not obliged to continue your journey in the vehicle that you boarded. Well, the thing is that authorities will most likely allow eVTOLs to land and takeoff from designated sites, heliports to begin with. In any major city this means that more traffic can be expected than the incidental eVTOL. Better take in account considerations such as space efficiency, economy of scale and standardize recharging and servicing then.

eVTOL traffic? How big a market are we talking?
To give an impression of how much eVTOL traffic might take place between designated sites, UBER says it needs 500-1000 air taxis in every major city. Worldwide there are more than 500 cities with over 1 million inhabitants. That’s between a quarter and half a million eVTOLs. Over 10 to 20 times more than the number of helicopters sold each year (22,000) globally. And that's just the start. What happens if eVTOLs spread out to smaller urban and rural areas (takeoff and land on your own backyard), and to the rental, lease and personal ownership markets? Like I stated in my previous blog, the eVTOL theoretically (for now) holds the promise of safer, more reliable and more practical 'short to medium' distance air travel. But what about the costs?

eVTOL vs Helicopter - economics
An eVTOL has the potential to do to the (small) helicopter -way quicker- than what the electric car is doing to the fossil-fueled car: replace it when 'shorter' distances need to be traveled. Electric and conventional cars are more evenly matched. That the balance tips in favor of the eVTOL, has a lot to do with the fact that a helicopter is a complicated and therefore expensive piece of machinery that requires costly maintenance, burns fuel at the rate of at least 1 liter per 5 km traveled and requires a trained pilot. The cheapest mass-produced helicopter is the Robinson R22. This two-seater costs approx. $300,000; its variable costs per hour (excl. pilot, what an eVTOL will not need) are around $350.

Disruptive?
So, if eVTOL builders really want a fast track to breaking the (small) helicopter market wide open, they better make sure that the numbers add up, firstly by making sure that their eVTOLS are not overly complicated. What you see with the arrival of the eVTOL, is a phenomenon that you often witness in engineering: simplicity comes after complexity. IMO, at least on paper, the eVTOL beats the helicopter. For instance, if 'properly spaced', the eVTOL does not have the downwash on the fuselage the chopper typically has (aka vertical drag), nor does it need a tail rotor. Both eat away as much as 20 percent of the energy.

Ralph Panhuyzen, sevehicle@gmail.com

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