April 16, 2021 by Biljana Ognenova
Convenience is an important aspect of urban air mobility. If we consider safety, security, speed, and affordability as minor components of the umbrella term ‘convenience’, engineers have an arduous ahead road to make eVTOL (electric vertical take-off and landing) technology convenient...
Following Emmanuel Ikimi’s Electronics Point article on why commercial vertical take-off and landing aircraft may be more viable than they sound, this article by Biljana Ognenova suggests that we still shouldn’t be expecting commercial access to urban air mobility any time soon...
Advances made in electric propulsion, including motors, batteries, sensors, and controllers, have introduced the electric car concept into urban air mobility. Progressive sustainability goals and autonomous vehicle engineering are accounting for a major share of future vehicular design. With that in mind, we should all be welcoming eVTOL with open hands.
However, the regulatory and technological fusion of cars and planes is quite the mouthful from an engineering and manufacturing perspective.
From a consumer’s perspective, the convenience of eVTOL aircraft ranges from luxury (the idea of having a personal vehicle you can fly from your office to an important meeting across town) to essential serviceability (package drone delivery).
Today’s eVTOL developments are somewhere in-between: struggling to design sufficiently lightweight and durable batteries that can be placed on an aircraft that carries four passengers and flies at least several hundred miles before having to land for charging.
For now, road mobility remains the more viable urban transport option, particularly when you compare it cost-wise to urban air mobility (UAM).
A Joby air taxi demonstration prototype
Image credit: Joby Aviation via CNBC
The exemplary commercial eVTOL manifestation is an urban air taxi that will ideally become the new Uber in the aerospace realm: an all-electric plane-car that will transport people and cargo at low cost. The main problem is the UAM infrastructure that is essentially non-existent and expensive.
Take Joby Aviation, for example, whose acquisition of Uber Elevate aims to offer urban air taxi rides by 2024. The aircraft that can carry four passengers and a pilot up to 150 miles at a top speed of 200 mph is still in the testing phase, having completed 1,000 test rides. The price of this hailing ride service is not yet known, so it is a big question of how many people will be able to afford this copter ride.
The Transition roadable aircraft by Terrafugia is a two-seat hybrid car plane that received only a limited airworthiness certificate by the U.S. FAA (Federal Aviation Administration), as it did not quite meet the FAA full production standards. This aircraft is on the high end of the price range, available at $275,000 (and an additional insurance cost of $60,000 a year). The main problem is that this automobile-aircraft is not an actual eVTOL: it is powered by a 100-hp Rotax 912iS Sport fuel-injected engine that runs on either premium gasoline or 100LL (low lead) aeroplane fuel.
A digital mock-up of the electric-powered Volocopter landing on a UAM (urban air mobility) airport
Image credit: Volocopter
Aside from Terrafugia’s Transition, there is also the eVTOL giant Volocopter, which may have a greater probability of fast-tracking its way into commercial waters. Volocopter is a Europe-based developer of the electrical copter aircraft with publicly demonstrated flight operations and a design organisation approval from EASA (the European Union Aviation Safety Agency).
The odds of seeing numerous electric VTOL aircraft in the immediate future are better for cargo-laden drones, whether they’re manned or unmanned; and small piloted air taxis (the UK‘s electric aircraft airport has helped to lay the foundation for the latter).
Who will pilot larger, commercially deployed eVTOL aircraft? Piloting is expensive as a skill and as an occupation. The solution lies in developing self-flying aircraft that will require minimum training for human pilots who will handle emergencies and monitoring while the aircraft does most of the flying autonomously—another task standing at the doorstep of engineers and manufacturers.
If we are to be serious about commercial, personal aircraft of any kind, we also have to think about storing aircraft when they are not in motion.
City parking is expensive in dense urban areas, and not many buildings have roof space available for helipads. If we compare the minimum landing requirements for civilian helicopters (which needs to be a 100-by-100-foot area ideally covered by grass), we lack the spaciousness required to safely manoeuvre commercial aircraft, especially those that carry enough passengers to be environmentally friendly.
Current eVTOL models resemble planes and helicopters more than cars, but they also come with all the added demands—particularly compliance—that come with automotive engineering and manufacturing (especially for EV designers).
A synergistic approach between automotive and aviation is necessary, and the field of electronics gives a secure foothold t create the synergy to redesign the UAM concept into a brand new means of transportation that will be neither a car nor a plane—but an aircraft with a new class rating.
To be airborne, drones need to be as light as possible: the battery size needs to be adjusted to the drone size. The same principle applies to any aircraft that needs to remain in the air without adding excessive weight to the airframe. Electric batteries for EVs weigh between 300 and 600 kilograms, whereas larger battery packs usually have a better lifetime but can slow down the vehicle and require longer charging times.
A digital mock-up of CityHawk (viewed from above), the fan-based aircraft powered by hydrogen cells
Image credit: Urban Aeronautics
Nanodot batteries, as well as lighter lithium-ion battery alternatives (such as lithium nickel manganese cobalt oxide and lithium-sulfur), are considered as lighter alternatives. The same goes for hydrogen cells, as in the case of the above-pictured CityHawk: a fan-based aircraft (or ‘fancraft’ as its manufacturer, Metro Skyways, calls it) that’s designed by the Israel-based Urban Aeronautics for taxi transport (of up to six occupants), emergency services, and corporate limousine transport.
The weather sensitivity of vertical takeoff and landing aircraft is directly proportional to how small their size is; however, this is fortunately a challenge that can, and must, be addressed by microscale weather prediction.
Most eVTOL flights are supposed to take place in urban environments, after all, and it’s due to the involvement of built-up areas that such micro-scale weather model reporting is so vital. This is because microscale meteorology forecasts can cover both small (within a 1-kilometre radius) and short-lived (up to 1 hour) atmospheric phenomena. So far, the HRRR (high-resolution rapid refresh) atmospheric model has proved the more successful option in predicting weather at the mesoscale—namely on spatial scales of 10 to 1,000 kilometres.
Nevertheless, another question that arises, which further challenges the potential for the quick adoption of VTOLs, relates to the pitfalls of human error and poor decision making: how prepared will the pilot will even be to make their own snap decisions based on such real-time weather forecast technologies?
Electric vertical takeoff and landing aircraft are complex technologies, dependent on multiple sources of funding. Such a (potential) new generation of urban transport combines aviation, automotive, and urban transport and logistics.
The commercialisation of eVTOL technology is an urban planning challenge for future cities. Design, compliance, and battery requirements for eVTOL cars make them a life-cycle engineering challenge with questions of environmental sustainability that are not easy to quantify. As a transportation breakthrough, they are far from the required level of technological maturity before a comprehensive air control and management system takes place.
Indeed, we may have to wait at least several decades for that.
