Bjorn’s Corner: Sustainable Air Transport. Part 51. eVTOL wrap.

By Bjorn Fehrm

December 23, 2022, ©. Leeham News: After 25 articles about the eVTOL, it’s time for a wrap. We have looked at most aspects of this new form of air transportation, including how sustainable it is.

Today we summarize what we found before we go on to the next subject in Sustainable Air Transport.

Figure 1. The series started with a picture of the eVTOL that leads the trend, Joby Aviation’s S4. Source: Joby Aviation.

What we learned

In the 25 articles, we looked at several aspects of eVTOLs. First, we discussed how they work and classified them into different types based on the flying principle ( we had multicopters like Volocopter, vectored thrust ones like Joby S4, and lift and cruise like Embraer EVE).

Then we looked at the weak area for the eVTOLs, the batteries. We then found the lack of standardization of how you fly an eVTOL affects pilot training and safety, and how the increased air traffic shall be managed is not solved. Finally, we discussed operating costs, production costs, and production volumes.

Here are the principal takeaways from the series:

eVTOL Utility and Economics

eVTOLs have one major advantage and several disadvantages:

  • eVTOLs have advantages in operation where sound is a problem, as the noisy gas turbine-driven helicopter main rotor is replaced with electric motors driving low-tip-speed rotors. It’s a major advantage, but it’s perhaps the only one when one dissects the category closer.
  • Proponents also say the eVTOL is cheaper to operate. They forget that the eVTOL is about 40% larger than a comparable helicopter, the four-passenger R66 (Figure 2), thus occupies more heliport space and is two to three times heavier. It also has four times higher acquisition costs. (The comparisons in the Investor pitch decks can take ridiculous proportions: Joby compares the S4 operating costs to a 13-seater Sikorsky S-76 with five times the endurance “based on similar cruise speeds.” It takes the prize when it comes to Apples and Oranges to prove a point!).

Figure 2. The pilot plus four-passenger Robinson R66 helicopter. Source: Robinson Helicopters Company.

  • The results of the larger dimensions, higher weights, and higher net prices are higher landing and underway fees and higher insurance and capital costs. The landing fees are also increased as new charging infrastructure is needed on all landing spots.
  • The high maintenance costs of the helicopter are not so much higher when you add the battery cost for the eVTOL, and pilot costs are similar.
  • The bottom line is the operating costs will be similar to equal-capacity helicopters. But the helicopter flies twice as far, thus having more utility when noise isn’t a problem.
  • The problem area for the eVTOLs is the batteries. We went pretty deep into batteries and their management, but if you want to understand the subject even deeper, follow this reader’s tip: Batteries are not Fuel.
  • The peculiar characteristics of batteries influence the utility of the eVTOL in a major way. If you use more than the middle 1/3 of the battery capacity for your flights, the battery costs explode. So the OEMs, in their business cases, assume you charge the battery to 2/3 capacity and then drain it to 1/3 capacity. Go beyond, and the battery costs go up. In total, you have a 30 to 40 minutes flight endurance, but if you want to keep the charging times within 10 to 15 minutes and extend your battery life, you shall not operate longer than 20-minute flights.
  • Theoretically, 20 minutes gives you a 20-mile range, but in practice, ATM procedures mean you have to stay in the air longer than 20 minutes to cover a 20-mile spacing of landing spots. It’s a VFR operation, so you are weather dependent, and it many times forces detours around rain showers. An eVTOL does not have energy reserves for IFR operations or de-icing equipment.
  • The eVTOL uses electricity from the grid and could thus be classified as green when our grids have green electrons. But we will probably have SAF to fuel helicopters by the time the grid electrons are green, so this advantage is questionable.

The category will be heavily scrutinized regarding safety. We found three areas that cause concern;

  • There is no standardization on how a pilot flies an eVTOL. We found five different control metaphors in the top six eVTOLs. It will be difficult for a pilot coming from helicopters or fixed-winged aircraft to relearn the muscle memory to react correctly in a crisis where the brain is no longer in the loop.
  • If a propulsion battery catches fire, it can’t be extinguished. The regulators impose stringent qualification criteria to mitigate this catastrophic hazard. We will only know if these measures are good enough after years of eVTOL operation.
  • The Air Traffic Management (ATM) of an increasing fleet of eVTOLs cannot be done with today’s ATM. Yet the evolution of the ATM to something more efficient is the slowest of all areas of air traffic. How many incidents will happen before we have meaningful air traffic management for drones and eVTOLs?
Will the eVTOLs be everywhere?

Most eVTOL OEMs are investor financed. As such, they must present business plans showing a huge market filled with thousands of eVTOL a few years after certification and healthy operating margins.

We looked at these facts and found:

  • No one knows how large this market is. The used “Tera dollar market projections” have little substance, and those who don’t need 3rd party investments are honest about it: “We don’t know the size of this market and how fast it will develop. We happen to be those with the most market knowledge, and we don’t know.”
  • The thousands of eVTOLs in production after three years are equally hard to underpin. Aeronautical production typically ramps 30% to 50% per year after the first year of production. There is no support in the aeronautical world for the production of a thousand eVTOLs three or four years after certification.
  • The high business margins will have to find ways around the purchase cost of around $4m per eVTOL with a steep obsolescence curve. The resulting high capital and insurance costs, paired with small helicopter-level operating costs, will push operators into the red. The OEM’s Investor deck cost projections are far from reality.
Will the category survive and carve out a niche?

Yes, it will. The noise level and the use of electrical energy (which can be turned green) are positive factors. These will carve a niche for the eVTOLs. But the limited utility and the high costs will throttle many plans for eVTOL use, and the probable deployment ramp is shallow.

Batteries, the weak link in an eVTOL, will improve, but not at a pace to save the business plans. It will be the turn of the decade before solid electrolyte battery cells bring improvement.

At this time, we will look back at the crazy years of eVTOLs, where these should fly like grasshoppers in our skies, and ask: How could we be so naive after the personal jet bubble and all other bubbles we’ve experienced?

7 Comments on “Bjorn’s Corner: Sustainable Air Transport. Part 51. eVTOL wrap.

  1. Perfect wrap-up to a great series! You mention the higher initial cost of aquisition. With the trend towards higher interest rates, this will add one more headwind to the adoption of eVTOLs.

  2. I remember when there were thousands of orders for the Eclipse and similar size aircraft and that was the ‘future’. That never happened and it will probably be the same fate for these eVtol ideas

  3. “f a propulsion battery catches fire, it’s non-stopple.” Non-stopple? =Uncontainable?

    An excellent series, keeps me coming back to LN, even tho I can’t afford a subscription

  4. There migh be a separate power for anti-ice besides batteri charging befors flight and a limit on flight time at icing conditions

  5. The eVTOL taxi market is the path many players have taken. The Hopper VTOL aircraft has a water recreational use.
    The Hopper will use a hybrid power system to extend flight time. The Hopper design is pretty badass with no exterior rotor blades, this makes the Hopper Safe, Quiet, and efficient.

    There are new batteries being developed that do not catch fire, but this technology can be 10 to 15 years to get to mass production rate.

    If you want to learn more contact Tom through the website, Thanks

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