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Joby air taxi
Image courtesy Joby Aviation


Electric VTOL Aircraft Like Joby & Archer Are Making A Wrong Bet On Battery Energy Density (Part 1)

Simplicity is the silver bullet of electric rotorcraft.

A couple of decades ago, the world went through one of its collective periods of deep irrationality concern value in markets. This happens regularly. While no one personally remembers the Dutch Tulip Bubble, it’s regularly invoked around things like housing, the dot com bubble and by TSLAQ adherents. There’s certainly a deep whiff of tulips about electric vertical take-off and landing (eVTOL) aircraft right now, as the market valuation of the Joby, Archer, Lilium, Ehang, and Blade suggest.

Projecting out aviation fuel shifts for decarbonization through 2100, I began looking at the various early movers in earnest, and looked at the underlying assumptions. As I pointed out in a piece comparing the assumptions of urban, advanced, and regional air mobility paradigms, there are few use cases of any value for urban areas in allowing electric VTOL aircraft, and things like 200 tiny light show drones falling out of sky in China recently make it clear that there is a very long road of proven safety before there will be megadrones carrying passengers (or cargo) over heavily populated areas.

But what strikes me with the electric tilt-wing companies, the ones which are truly overvalued (with one possible caveat), is how they are both betting on and against battery energy density.

They are betting on battery energy density to be able to fly with fully electric systems. They are betting against battery energy density because they are building very complex machines to get adequate range for many use cases which will only appear, if they appear at all, decades in the future.

As discussed in previous articles, rotorcraft have specific use cases that they do well, and outside of the military, there are no hybrid VTOL aircraft that transition to horizontal flight on wings. The Harrier jet and Osprey twin-prop planes and the brand new F35B are about it on the military front too. They cost a lot more than either a rotorcraft or a conventional plane, they cost a lot more to operate, they cost a lot more to maintain, and they have a lot more failure conditions. You really need a very specific use case of extraordinary value before it makes sense to jam both vertical take-off and landing and horizontal flight on wings into the same package.

There are no civilian use cases that need apply. No commercial VTOL aircraft exist. Electric VTOL aircraft are mostly just trying to compete with current helicopters and their ranges using today’s battery energy densities, adding complexities, costs, and failure conditions to do so.

As I discussed with Heart Aerospace CEO Anders Forslund earlier this year, powering anything with batteries is a question of economic constraints, leading to picking batteries that make sense. For cars costing $50,000 or less, you want the cheapest batteries that give you 300-400 km range you can get. But for aircraft costing over a million and with the massive efficiency gains of electricity, the engineering constraints change substantially. Engineers have their pick of high energy density technologies measured in Wh/kg, at a commensurately high cost, and also with a deeply uncertain regulatory path.

Picking one example, a new Bell 505 helicopter capable of holding four passengers or about a ton of cargo, has a base cost of $1.3 million, but usually sells for $1.5 million with popular options. Its maximum range is 565 km. Globalair lists 120 used helicopters for sale right now with an average asking price just under $2 million. The second most expensive one only flew 285 hours in four years. Two of the top five are 50 years old, and averaged 300-400 hours of flying per year for their extensive lifetimes. The most heavily used one, a 1980 Sikorsky S61N used for heavy lifting, managed an average of 700 hours of flying a year for its lifetime. That’s less than two hours a day.

Helicopters Are Expensive, Don’t Fly Often, & Don’t Fly Far

Vancouver’s Helijet takes about 35 minutes to fly 50 km multiple times a day from Vancouver to Victoria and back with a couple of aircraft, and might be one of the heaviest users of helicopters in the world. And it’s a lot more expensive per passenger than the Harbour Air float planes that are a kilometer away in Vancouver, have the same flight duration, and dock much more conveniently in front of the Empress in Victoria. The Nanaimo route runs less often and takes only 20 minutes or so. The float planes are visual flight rules only, so I only took the Helijet when weather or daylight hours ruled out the float planes. They run a dozen helicopters covering the 44 flights a day that they schedule. That’s an average of 670 hours of flight time per bird.

Helijet, by the way, is one of only two companies flying regularly scheduled helicopter services in all of North America, the other being Blade Urban Air Mobility. That’s it. Two companies.

Lance Sherry, who is the Director of Center for Air Transportation Systems Research in the Volgeneau School of Engineering at George Mason University, reached out based on some of my earlier publications in this space. He provided an advance draft of a paper he and a team are co-authoring, “Aero Medical Transportation: Analysis of Rotary Wing Operations in the United States (2020).” While the transportation of doctors, patients and organs in the US is a growing market, there are just under 1,000 helicopters currently working, and they fly an average of only twice a day, with an average individual flight being 60 kilometers and taking less than 50 minutes.

When I spoke recently with the CEO and CFO of Blade Urban Air Mobility, Rob Wiesenthal and Will Heyburn, their projections for the expected use of eVTOL aircraft was a thousand hours a year, considerably above the Helijet apparent average, but they are the sole other operator of scheduled helicopter flights on the continent, so I trust their numbers. Blade’s most heavily traveled route is likely Manhattan to JFK, a roughly 20-kilometer, 8-minute flight. By comparison, many of the eVTOL projections are for 4,000 hours of flight time a year, something that the people investing billions in those companies apparently didn’t do any math on.

This is an expensive and niche market, in other words, and Helijet and Blade frequently buy used aircraft rather than new ones, at price points roughly 20% to 40% of the electric VTOL aircraft.

Simplicity Is The Silver Bullet Of Electric Rotorcraft

Electric drivetrains for rotorcraft have a lot of advantages. The amazing torque at any rotation speed means that rotors can be optimized for reduced noise and a more pleasant pitch. The simplicity means you can have a bunch of rotors for redundancy, instead of just one. The simplicity allows you to run double-rotors, one above and one below the motor to maximize thrust. Moving electricity to motors is trivial compared to running avgas or Jet A to engines. The combination of the flat torque curve and trivial incrementing of power means you have the option of doing away with pitch controls entirely. Multiple rotors means you don’t have to have a tail rotor countering the torque from above that wants to spin the aircraft in circles. Multiple rotors allow quadcopter control systems to move the rotorcraft in any direction trivially just by changing power ratios a bit. Computerized control systems from quadcopters make all of this work.

And electric multi-rotor rotorcraft are trivially easy to fly compared to helicopters. The pithiest version of what it’s like to fly a helicopter I’ve seen is “Flying a helicopter is like riding a unicycle while playing the tuba and masturbating at the same time.” This is a common refrain. It takes weeks for new helicopter pilots to figure out the basics of the collective, the cyclic, and the rudders. The first changes the pitch of the rotors, the second changes the pitch of the rotors differently, and the third changes the pitch on the tail rotor. Hovering in place requires constant, tiny, and careful changes to all three controls. Human brains take a while to figure out this weird combination of skills. Then they take longer to be able to do all of this automatically so that they can actually deal with the radio and thinking about where they are going.

Electric multirotors have scaled up quadcopter control systems. The computer does 99% of the work and the pilot has controls for up-down and left-right. No human being could control everything going on to make a quadcopter fly in real time, but with computerization it’s easy.

That simplicity has great value. Typical helicopters require 4-5 hours of servicing and maintenance for every hour of flying. The dual-pitch controls for the main rotor, the pitch controls for tail rotor, the mechanical linkages from the engine to both the main rotor and to the tail rotor, the fuel systems, and the complex engine itself are amazing feats of engineering, but finicky, subject to failure, and require constant inspection, maintenance, and adjustment. Except for the battery pack itself, the rotorcraft becomes instantly much lighter.

By comparison, electric helicopters are nothingburgers. Six or eight electric motors are the only moving parts. No pitch control. Some wiring. A battery. A computer. That’s an amazing leap forward in hovercraft.

Unless you turn it into something that tries to get range with today’s batteries by adding massive complexity. Unless you try to perform all of the compromises necessary to make a bad helicopter and a bad airplane, one that’s much more expensive than simpler machines fit for actual use cases.

And so, the end of this part of the assessment. In the next article, I’ll talk about why most of the innovators aren’t paying attention to the lessons of The Innovator’s Dilemma, which ones seem to at least be thinking clearly into the future, and why the entire current crop of companies are likely headed into the tulip bulb waste bin of history.


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Written By

is Board Observer and Strategist for Agora Energy Technologies a CO2-based redox flow startup, a member of the Advisory Board of ELECTRON Aviation an electric aviation startup, Chief Strategist at TFIE Strategy and co-founder of distnc technologies. He spends his time projecting scenarios for decarbonization 40-80 years into the future, and assisting executives, Boards and investors to pick wisely today. Whether it's refueling aviation, grid storage, vehicle-to-grid, or hydrogen demand, his work is based on fundamentals of physics, economics and human nature, and informed by the decarbonization requirements and innovations of multiple domains. His leadership positions in North America, Asia and Latin America enhanced his global point of view. He publishes regularly in multiple outlets on innovation, business, technology and policy. He is available for Board, strategy advisor and speaking engagements.


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