This article originally appeared on LinkedIn, authored by Mehmet Emre YAZICI. * The word “shape” is freely used to describe the external configuration of the aircraft. Why Airframe Shape is Important? For the first time in known history, humankind is this close to make the “flying-car” a reality. Today, 70+ manufacturers worldwide, (including; Airbus, Bell, Boeing, Embraer, Rolls-Royce, Toyota, Volvo, etc.) are seriously involved...
This article originally appeared on LinkedIn, authored by Mehmet Emre YAZICI.
* The word “shape” is freely used to describe the external configuration of the aircraft.
Why Airframe Shape is Important?
For the first time in known history, humankind is this close to make the “flying-car” a reality. Today, 70+ manufacturers worldwide, (including; Airbus, Bell, Boeing, Embraer, Rolls-Royce, Toyota, Volvo, etc.) are seriously involved in developing some form of an electric vertical take-off and landing (eVTOL) vehicle. As of September 2018, total global investment volume has exceeded $1 billion. According to The Electric VTOL News™, since 2011 some 140 different eVTOL projects based on four basic configurations, have been announced. While wingless multi-copterconfiguration is the most favored (45%), electric helicopters are not-so-popular (3%).
There obviously are major difficulties ahead. Although, the prioritization differs from person to person, I believe that the top three are; regulatory issues, environmental effects (mostly noise) and public acceptance (due to security and privacy concerns). So, configuration of the aircraft is not among the top three challenges that UAM (Urban Air Mobility) pioneers are facing today. Why do I bring it forward, then?
Simply because, throughout the life-cycle of the aircraft, major changes on the airframe are avoided, not only due to cost or performance concerns, but also because of huge re-certification efforts required. Some minor modifications, however, such as adding winglets or external domes for sensors which are covered under supplementary type certificates (STC) are more common. Beyond that, you can easily change or upgrade almost any other component (avionics, engines, furnishing, etc.) that comes on the aircraft. So, the airframe shape or form (housing all the other components) becomes single fundamental element that will affect all; regulatory, environmental or public concerns.
Who is Doing What?
According to polls, the public tends to favor eVTOL products by well-known manufacturers vs the start-ups. So, it will be worthwhile to see which configuration the aerospace and automotive giants are preferring:
- Airbus: A³ Vahana and CityAirbus
Back in 2015, Airbus had been the first (among the traditional aerospace companies) to announce its plans to secure a place in the commercial eVTOL market. “A-cubed Vahana” is a tilt-wing (i.e. vectored thrust) aircraft project being handled by an Airbus subsidiary in the Silicon Valley. Whereas, CityAirbus is a four passenger, autonomous wingless multi-copter program ran by the Airbus Helicopters.
- Bell: Nexus and APT
Nexus is a six-passenger vectored thrust aircraft announced in 2017 Uber Elevate Summit. On the other hand, APT (Autonomous Pod Transport) is 20 to 32 kg payload tail-sitter that we can classify as a vectored thrust vehicle.
- Boeing/ Aurora: PAV and CAV
Creatively named as the Passenger Air Vehicle (PAV) developed together with Aurora Flight Sciences is part of the Boeing NeXt urban air mobility project. It is a two-seat lift+push design which made its maiden flight in January 2019. Also a part of Boing NeXt, CAV (Cargo Air Vehicle) is a 225 kg payload wingless multi-copter.
- Embrarer: DreamMaker
Also announced during the 2017 Uber Elevate Summit, the DreamMaker is a piloted four passenger lift+push aircraft.
- Rolls-Royce: EVTOL
During 2018 Farnborough Airshow, Rolls-Royce announced the EVTOL concept. Rolls-Royce’s aircraft is a hybrid tilt-wing (i.e. vectored thrust) carrying 4-5 passengers.
- Lockheed Martin/ Sikorsky: VERT and ARES (with Piasecki)
Lockheed Martin and its new subsidiary Sikorsky are working on both military and commercial VTOL concepts. While Lockheed Martin is indulged in development of a vectored thrust configuration for military use together with AVX and Piasecki, Sikorsky is working on a project named VERT. And that is all we know, for the time being…
- Toyota: Cartivator SkyDrive and Joby S4 (co-investor)
In 2017 Toyota agreed to invest in Cartivator -a Japanese start-up, to develop the world’s smallest flying car. SkyDrive concept is a single-seater wingless multi-copter. Additionally, Toyota is among the investors in the Joby Aviation’s S4 program. S4 is a four-seat vectored thrust aircraft.
- Volvo/ Lotus: Terrafugia TF-2
Chinese company Zhejiang Geely, which owns the Volvo and Lotus car brands, has acquired Terrafugia in 2017. In its current form, TF-2 is rather a modal transportation “system” than a simple “air vehicle”. The flying component of the well thought-out design is a lift+push solution.
Out of the 12 (excluding Sikorsky’s VERT) vehicles above, 50% have preferred vectored thrust, while lift+push and wingless multi-copter have 25% preferences each. The choice of giants are not in-line with the alternatives preferred in the eVTOL community. So, we can easily say that the best configuration is yet to be agreed.
Basic Disadvantages of Popular Configurations
The wingless (multi-copter) designs (preferred by 45% of the whole community and 25% of aerospace and automotive giants), although very popular and made the “drone revolution” possible, are doomed due to their slow top speeds. For commercial eVTOLs, the economics of the vehicle would dictate to perform as many cycles as possible in a given time. In addition to that, large un-protected propellers placed close to the ground is a major safety concern for passengers and crew alike. Therefore, although simple and well understood, multi-copter designs will unlikely be the choice for a successful flying-car design. (Best illustrative example: EHang 184/ 216)
Despite the simplicity and weight advantages offered by lift+cruise designs (preferred by 12% of the whole community and 25% of aerospace and automotive giants), they inherently possess serious safety challenges. Un-protected (i.e. un-ducted) horizontal propellers, operating very close to ground (usually due to the size limitations of small vehicles) constitute a safety risk just like the multi-copters. Therefore, I see a bleak future for the designs utilizing unprotected props located close to ground. (Best illustrative example: Boeing/ Aurora PAV)
Vectored thrust designs (preferred by 40% of the whole community and 50% of aerospace and automotive giants), provide the best compromise between versatility and speed. But, when utilize un-protected propellers (tilt-wings mostly), they have the same disadvantages of lift+cruise designs (Best illustrative example: Airbus A³ Vahana). On the other hand, ducts employed to eliminate risks associated with props, bring in weight disadvantages and some additional drag during the cruise (Best illustrative example: Bell Nexus).
So, what is the solution? Which design will prevail? Frankly speaking, I don’t know! But, I believe that the applications employing Distributed Electric Propulsion (DEP) concept through small units and in large quantities are closer to an optimum solution. Such configurations give way to enclose unnecessary units during cruise in other components (i.e. wings) to reduce drag. Additionally, large amount of redundancy in propulsion system relaxes safety margins. Aurora Flight Science’s VTOL X-Plane Program XV-24A LightningStrike and Lilium’s Electric Jet are best available examples of this concept, both of which have successfully demonstrated the feasibility of the concept.
The LightningStrike program had aimed to develop a vertical take-off and landing 12,000 lb (5.4 t) demonstrator aircraft with 18 motors in the wings and 6 motors in canards, that will achieve a top sustained flight speed of 300-400 kt (555-740 km/h). A 20%-scale demonstrator aircraft weighing 325 lb (147 kg) with a flight model of the full-scale demonstrator was flown in March 2016. Surprisingly, in April 2018 it was decided that the subscale model demonstrated the program’s major objectives and DARPA cancelled the project.
Lilium’s two-seat “Eagle” prototype completed a series of unmanned test flights in April 2017. It had a total of 36 electric fans: 12 on the upper surface of each wing with tilting flaps and two rows of three fans on each side of the canard, which was designed to be retracted in cruise flight.
Until someone comes up with anti-gravity technology, I believe this is the best shape for flying-cars of urban air mobility initiative…
From 19 December to 21 December 2018, hundreds of flights were cancelled at Gatwick Airport near London, England, following 67 reports of drone sightings close to the runway. The incident negatively impacted about 140,000 passengers and disrupted over 1,000 flights during peak holiday travel. Reactions by UK police, military, and government officials exposed a lack of preparation in responding to...
From 19 December to 21 December 2018, hundreds of flights were cancelled at Gatwick Airport near London, England, following 67 reports of drone sightings close to the runway.
The incident negatively impacted about 140,000 passengers and disrupted over 1,000 flights during peak holiday travel. Reactions by UK police, military, and government officials exposed a lack of preparation in responding to unlawful drone incursions.
All in all, a spokesperson for Gatwick Airport estimates the total cost to the airport and airlines at £20 million in lost revenue. As of writing this article, the perpetrator, or perpetrators remain at large, and another suspected drone sighting affected Heathrow Airport on 8 January.
Unfortunately, many airports, air navigation service providers (ANSPs), civil aviation authorities (CAAs) and governments around the world are not yet prepared to respond to drone incursions and are understandably worried that they could be affected by similar incidents.
Many early reactions have called for counter-UAS (unmanned aerial system) technology as the most effective solution for prevention. Of course, there is a key role for these systems in airport safety, but they are a last resort against criminals. Without the ability to remotely identify good actors from bad ones, these counter systems will be constrained as drone operations scale.
Thankfully, a lot can be done today to reduce the risks of drone incursions to a manageable level that only requires basic regulation and technology. Here are three concrete steps that airports and aviation authorities can take to keep airports safe from unwanted and/or criminal drone activity.
Step 1: Implement a registration mandate with easy-to-use technology
Airspace authorities should establish clear regulations that require all drone operators to register themselves and their aircraft along with a simple, streamlined process for doing so.
Implementing a digital registration system is relatively easy – drone operators can enter name, contact, and aircraft details on an internet-enabled device, which populates a secured registration server, that also attest identities and authenticate users. Access to registration data is managed by authorized personnel, with appropriate personally identifiable information (PII) protections in place.
Mandatory registration can also require that a drone operator self identify in order to get authorized access to fly in controlled airspace near airports. Registered operators are responsible actors who have demonstrated intent to operate in compliance with regulations.
Step 2: Enforce civil aviation regulations with a UAS Traffic Management (UTM) system
Popular drone manufacturers already implement geofencing options, and firmware updates to meet national airspace regulations. In practice, geofencing prevents a drone from flying in restricted, controlled and other unsafe airspace, which helps ward against illegal drone operations by careless and clueless operators.
Geofencing can be “unlocked” for authorized drone operators, such as airport maintenance staff or law enforcement operators, by connecting to an Unmanned Traffic Management (UTM) system with services and procedures designed to support safe, efficient and secure access to airspace for drones. These services include registration, flight planning, geofencing, airspace authorization, conformance monitoring, telemetry, deconfliction, and remote identification, among others.
The right UTM system analyzes operator details, flight path information, real-time air traffic positions, and more, to enable airspace authorities to grant permission-based access to drone operators in controlled airspace, either manually or programmatically as already implemented by the Federal Aviation Administration Low Altitude Authorization and Notification Capability (FAA LAANC) programme. The result is enablement of safe drone operations while controlling against non-compliant or illegal activity.
With all “good actors” participating in the UTM system, aviation authorities can visualize, monitor, and track real-time manned and unmanned aircraft telemetry for deconfliction. Participating drone operators can be remotely identified by their aircraft, flight path, and/or registration details and can be contacted directly for risk mitigation.
Step 3: Combine UTM with counter-UAS system for a complete picture of an airspace operating environment
Intentional bad actors that are not registered are not included in the UTM system and do not follow the appropriate authorization procedures to access controlled airspace. These illegal operators may also hack their drones, unlocking geofencing, or spoofing their location.
In these instances, the integration of counter-UAS (C-UAS) technology into the UTM system provides the ability to identify all aircraft movements within the controlled airspace. Information related to any aircraft detected by C-UAS is exchanged with the UTM system and remotely identified as either collaborative (registered) or non-collaborative, requiring intervention.
Much of the reaction to the Gatwick incident has centered on counter-UAS technology as the answer to all illegal drone operations. But as drone operations near airports scale with enterprise demand, C-UAS alone will not be sufficient in determining whether a drone operation requires intervention because not all drone operations at airports are unlawful. Detection must be coupled with UTM intelligence to adequately inform, and ensure the safety and smooth operations of all airports.
Written by Ben Marcus, Chairman and co-founder of AirMap.
This story first appeared on the World Economic Forum Agenda Blog.
The transportation industry has been at a crossroads between convention and innovation for the last 10 years. In the next 10, we’ll complete the next biggest thing since the advent of the jet engine following World War II. Transportation, medicine, finance, and real estate: all industries that at one point or another undergo a transformation. While some of these periods...
The transportation industry has been at a crossroads between convention and innovation for the last 10 years. In the next 10, we’ll complete the next biggest thing since the advent of the jet engine following World War II.
Transportation, medicine, finance, and real estate: all industries that at one point or another undergo a transformation. While some of these periods of “redefinition” are slow, others are step function inputs of technological progress, scientific research, or novel approaches to best business practices. Fortunately, the key indicators for large changes (while uncommon in specific mechanism) share commonality among the environments which spark the cycle of rapid development.
For aviation, there were two such sparks, arguably three: the Wright Brothers (powered flight), the jet engine (World War II), and spaceflight (The Cold War). Two of these three periods of innovation were bred from necessity, and the first from (arguably) desire for adventure and pursuit of overcoming adversity. While it may be easy to retroactively claim that two brothers yearned to fly in a powered machine, or that the fastest aircraft would win battles in war, or even that the first country in space could possibly end up controlling the world, it’s harder to pinpoint realtime the complex psychology of a herd mentality that has shifted far enough, for long enough, to initiative substantive change.
One common thread today is the initiative for responsible development and management of the earth’s resources, while another is the idea of providing larger breadth in access to the benefits of transportation to the world. A third, and arguably most powerful motive, is the idea that we’ve spent long enough being complacent with increasingly smaller “advances” to our technology to such a point where an actual leap must be made. It was over 50 years ago that man landed on the moon using a computer with 2048 words of RAM. A normal laptop computer could have provided the necessary computing resources for 100’s of thousands of Apollo missions concurrently, and yet we haven’t returned.
While the moon isn’t necessarily a good benchmark (there are other political and environmental factors at play) the idea that we haven’t accomplished something of the same magnitude in so long is reason enough to raise the question – when will we?
The answer is simple: we’ve been doing so for the last 10 years.
It could be argued that Urban Aviation started in the early 1950’s with the advent of New York Airways, shuttling passengers to and from Manhattan regularly. Unfortunately, a crash in 1977 ended that airline, and widespread urban commercial aviation operations haven’t returned since. However, since 2009, a number of Urban Air Mobility companies have been working tirelessly to make the industry a reality. A lot has been learned since 1977, to the point where Morgan Stanley claims that by 2040, UAM will be a $1.5 trillion dollar industry. We’re much closer to 2040 than 1977, and the level of investment in the industry (over $1 billion USD in 2018 alone) is providing the resources for rapid growth.
A $1.5 Trillion Dollar valuation is massive, but considering the magnitude of technological advancement that’s being baked into this industry, more attainable than the sticker shock implies. Here are some of the key watch items for Urban Air Mobility in 2019 that will continue the progress toward a track of commercial application in 2023 and that $1 Trillion + valuation in 2040:
- Distributed Hybrid Electric Propulsion – By taking advantage of distributed hybrid electric propulsion, the UAM industry can leverage gas turbine strengths while also realizing the benefits of reduced energy requirements during the cruise and descent phases of flight.
- Smart Avionics – While there’s a large push for complete autonomous operation of urban aircraft (and in many cases the technology will be installed on urban aircraft to support complete autonomous operations) the initial commercial operation of UAM will not be autonomous. Public sentiment and regulatory requirements mean that autonomous operations aren’t necessarily ready today – not for the sake of technological readiness, but rather for societal readiness.
- Flight Testing & Certification Processes – for a number of OEM’s, the flight testing and certification process is already well underway. The dialogues that occur during 2019, and the resulting certification paths forward from these relationships between OEMs and regulatory agencies will define future, steady state interactions for the current group of earlier-stage urban aviation OEM’s.
- Composite Manufacturing – Composite manufacturing is difficult at small-scale, and even harder at large scale. Innovative techniques for manufacturing composites at scale will prove to be some of the highest value-add propositions that the UAM industry may lend to the rest of industrials.
- Low-Altitude Airspace Management – UTM technology is another watch item for 2019. The application of UTM technology in the US and globally is spreading quickly. Hear Ben Marcus, Chairman and Co-Founder of AirMap, the world’s leading low-altitude airspace management platform, explain how.
- Battery Technology – Why wouldn’t a Tesla battery work for an air taxi? TransportUP explained why in this article. (The TL;DR version is that we haven’t achieved the necessary energy densities required for revenue-generating commercial operations yet, and the rate of progress is pretty slow). If the “secret sauce” of increased battery energy is discovered, expect things to pick up, very rapidly.
Why it’s important: The common thread – innovative application of existing technologies. Besides brand new battery technology, most of the watch items listed for 2019 have existed for some time – but what hasn’t is the combination of all of them on the same system. A number of moving parts must perfectly sync for UAM to realize commercial usage in 2023, but we made the moon in ’69 with that 2048 word RAM guidance computer. The odds look good for UAM.
Want to learn more about urban aviation? Subscribe to our Urban Aviation Newsletter and our urban aviation podcast on iTunes to learn about how the leaders in the UAM industry are developing their technology in 2019.
NASA and Booz’s Executive Brief in Detail NASA and consulting firm Booz Allen Hamilton released a joint study on November 12 that outlined future projections of the urban aviation industry. The original executive briefing was presented on October 5th to NASA’s Aeronautics Research Directorate. Before we go into the details of the study, here are some of the key takeaways:...
NASA and Booz’s Executive Brief in Detail
NASA and consulting firm Booz Allen Hamilton released a joint study on November 12 that outlined future projections of the urban aviation industry. The original executive briefing was presented on October 5th to NASA’s Aeronautics Research Directorate. Before we go into the details of the study, here are some of the key takeaways:
- Airport Shuttle and Air Taxi markets have a total addressable market of over $500 Billion
- Air Ambulance services are not practical due to technology constraints – but hybrid aircraft may provide feasible alternatives
- Legal, regulatory, weather, public perception, and infrastructure hurdles exist
- 0.5% of the TAM, or $2.5 Billion, could be captured in the near term
- Constraints may be eased by government partnerships, industry collaboration, industry commitment, and existing legal and regulatory enablers
That’s the Summary. Here are the details.
A Strategic Advisory Group, or SAG, was assembled from prominent figures in the UAM, transportation, government regulations, infrastructures, public policy, and insurance disciplines – the SAG serves as an invaluable resource that enabled the information and advice of experts in their respective disciplines to offer their work and research toward answering some of the most pressing issues in the path towards wide spread UAM application. The study analyzed the following key components, each of which will be detailed below:
- Market Selection
- Legal and Regulatory
- Societal Barriers
- Weather Analysis
- Market Analysis
The study focused on a consortium of 10 cities across the United States to represent the larger industry.
Of potential interest in the selection of these 10 cities (and one city that has not been considered as heavily in the past) was that of Denver. Other cities that were selected, such as Los Angeles and Miami, have already been under consideration by real estate development companies and technology firm UAM development plans. However, the selection of Denver in this study is important – Denver has the potential for the lowest portion of air taxi shuttle trips within the FAA’s National Airspace System (NAS), which balances the perspective of a mostly urban-dominated, completely NAS-immersed UAM operating environment.
Legal and Regulatory
The largest legal and regulatory challenges that have the potential to slow urban aviation are regulations that already exist. In general, the framework for certifying aircraft already exists, but there are numerous legal barriers and gaps in the path to certification for some aircraft that may be classified as rotorcraft/mixed propulsion. Similarly, determining which regulations apply to what component(s) of air taxis is another challenge that has not yet been answered. Finally, system redundancy and failure management are critical safety considerations that will not be amended whatsoever for the sake of introducing a new type of aircraft such as an air taxi.
Fortunately, there are answers on the horizon to these challenges; for instance, ballistic parachute recovery systems are being developed for UAM systems. Additionally, the summary also cited that voluntary self-regulation (or even proposal of standards) may help to advance the regulatory process faster than relying solely on federal and state governments.
The largest concerns from the audience surveyed in this study (both younger persons aged 18-29 and older persons aged over 50) focused on credibility of pilots and the manufacturers of the aircraft. In general, those pilots/companies who were older attained a higher level of perceived experience, but gender and racial bias also played a role in affecting a passenger’s comfort with boarding a given flight. Passengers preferred intra-city hops instead of inter-city trips, and surprisingly, accepted a “hybrid flight deck” configuration where one pilot was onboard and the other “pilot” was automated.
Interestingly, the study also analyzed the position of weather in effecting UAM operations, and how in some locales the weather has enough of an adverse effect on air taxi services that their application could be placed in jeopardy. In general, cities in the Western United States had favorably weather, with the exception of impacts due to potential low visibility, high temperatures, and strong surface winds during summer thunderstorms. Cities like San Francisco suffer during the summer mornings when low-lying fog banks generate IFR conditions.
In the Eastern United States, storms and low visibility are the primary limiting factors, especially during summer afternoons. In areas such as Texas, low level wind shear, high temperatures, and storms have large impact potential to UAM operations, storms in the summer, and low visibility in the winter. While the summary did not expound further, expect more details in the full report – and also an overview of just how much the TAM may be reduced by seasonal weather shifts.
A Monte Carlo analysis was performed under a range of constraints to determine max usabilities – constraints involving customer’s willingness to pay, infrastructure limited, time of day limited, weather limited, and unconstrained scenarios. After performing these analyses, it was determined that only ~0.5% of unconstrained trips were captured after all other constraints were applied. This figure translates the $500 Billion as mentioned originally to the $2.5 Billion TAM. While the UAM market itself provides a lucrative magnitude of TAM, it is not without competitors – such as autonomous cars.
Additionally, analyses were conducted to determine the cost of air ambulance transports. After 10,000 iterations of this analysis, the estimated cost for an average trip was $9,000 for an eVTOL, and $9,800 for a hybrid – compared to $10,000 for that of a conventional helicopter transport. While there is a potential cost savings and practical benefit to eVTOLS as air ambulances (potential lives saved) the operational proficiency for eVTOLs will require time to establish – time that helicopters have had to demonstrate their applicability in situations that require extreme consistency. Another important consideration is the return time for an eVTOL, which is much higher than helicopters. While helicopters can be fueled with Jet-A in a matter of minutes, the charging technology for eVTOL’s is still not completely matured.
The best case scenario for air shuttle and air ambulance services includes a TAM of $500 Billion. In the near term, 5-seat eVTOL’s will cost ~$6.25 per passenger mile to operate. The high cost of infrastructure (and the current availability of infrastructure) are both large hurdles to overcome. Legal and regulatory analysis found that the air taxi, air ambulance, and air shuttle markets all face similar barriers. Additionally, psychological analysis and market surveys have proven that the general public is much more likely to board a piloted aircraft than an autonomous one. Finally, weather is a larger influencer in the applicability of air shuttle services than the industry has previously considered.
Why it’s Important: The joint Executive Summary between NASA and Booz Allen Hamilton has underscored many of the points made by numerous other consulting studies – but it also includes new considerations that will be important for the future development of the UAM industry, including the effects of return time for air ambulance operations and the effects of weather on all three markets. Stay tuned for the release of the full study and increased details on each of the topics addressed in the executive summary. The study emphasizes that a market of $2.5 billion may be reached in the short term (even after all the constraints are applied to market modeling) which is a large enough magnitude to continue to sustain the level of interest and dedication toward making this industry commercially operational in about five years.
They’re Great for Cars, But Not so Much Urban Aviation Over the last 20 years, batteries have been one of the slowest developed hardware components in the world. Solar power, advanced materials, and next generation manufacturing processes have all sparked new business and provided the technological momentum to create new industries. All but the battery. In order for the Urban...
They’re Great for Cars, But Not so Much Urban Aviation
Over the last 20 years, batteries have been one of the slowest developed hardware components in the world. Solar power, advanced materials, and next generation manufacturing processes have all sparked new business and provided the technological momentum to create new industries. All but the battery. In order for the Urban Air Mobility industry to accomplish the major tenet of environmental sustainability, battery tech needs to catch up. So why the lag? And how have companies like Tesla and Faraday Future been able to bring their products to market despite the challenges that battery technology provides?
The Current State of Battery Technology
To understand why the Urban Air Mobility industry is still 10 years from being completely electric, the current state of battery technology should be understood. The key metric for any battery is energy density – the amount of energy that can be stored in a given volume. The higher the density, the smaller the battery required for a certain amount of energy, or the more energy that can be stored in the same amount of space. To “optimize” battery tech, energy density must be maximized. However, unlike Moore’s law (in which processor power, or components per function, increases exponentially with time) battery energy density has seen a meager 3% increase in energy density year over year.
Just 3% in Energy Density Increase Per Year.
There are a couple types of batteries that have widespread application – Lithium Ion and Alkaline. While Alkaline is used in virtually all household batteries, its energy density is much lower than that of the Lithium Ion batteries (by about 200x) – but Alkaline batteries are much safer than Li-Ion batteries, which have a nasty habit of being impossible to extinguish should they combust. Most electric transportation applications require a large amount of energy, and so virtually all use Li-Ion batteries to take advantage of the greater energy density while accepting the safety risk. But, Li-Ion energy density is still too low; the required density for flying transportation modes is much higher than driving applications because weight is at a premium.
Surely the world can do better – so why haven’t we?
Similar Industries: Tesla & Trucks
Tesla (and more recently Faraday Future) have been able to market electric vehicles effectively because they’ve capitalized on Lithium Ion batteries with energy densities reported to be around 900Wh/L, or 250 Wh/kg.  For reference, an Alkaline AA battery holds about 4 Wh of energy  with a corresponding energy density of 700Wh/L. While this comparison illustrates how much higher the energy density of Li-Ion batteries is compared to that of Alkaline batteries, the quantity of energy required for an electric vehicle is still staggering. A Tesla Model S boasts fast acceleration and performance, but what many fail to realize is that the vehicle itself weighs almost 1,000 lbs more than any similar sedan with an internal combustion engine (mostly due to battery weight). 900 Wh/L is “good enough” for road applications because higher weights are acceptable. However, an electric vehicle in flight demands the minimum weight possible. How much farther must energy density be increased for batteries to become a practical source of aerial energy? The answer is simple: a comparable power to a Tesla Model S is required, but at 80% of the current weight of the Tesla battery packs (which is about 1,200lbs) – more on how we arrived at that figure later. For comparison, the Volocopter weighs 996 lbs – less than the total weight of the Tesla battery packs. Fortunately, the Volocopter (and other UAM solutions) require less than 1,200 lbs, or 85kWh, of power, but weight is still at an absolute premium.
Before we address this ultimate goal of the feasibility of battery power in the urban aviation industry, we’ll turn to a different industry that’s familiar to many: consumer drones.
The Drone Industry
One hybrid industry that provides a bridge between aviation and electric transportation is the recreational drone industry. Drones are little more than battery packs with any number of brushless electric motors powering small propellers at each corner of the device; oftentimes four are used to aid in stability. UAM solutions are much larger and more complex – but the physics of the energy required to stay aloft remain the same in both cases. For instance, the DJI Mavic Pro weighs 734g and can stay aloft for 31 minutes using a 46Wh battery, which is a typical capacity for a small drone. To condense these statistics into one comparable unit, like kg/Wh, we get 0.03. This number doesn’t mean much on its own, but if the weight of the aircraft is multiplied by the time aloft desired, a rough estimate of the total energy required may be obtained.
An important note – using different propeller sizes and energy conservation assumptions will yield different quantities of energy required; this is just a simplified first principles approach.
The UAM Industry
So how much power would a vehicle like the Volocopter require to fly for one hour? Using the kg/Wh factor of 0.03 to solve for this figure the Volocopter would conservatively need 14kWh of power. Remember back to the Tesla example – the Model S batteries have a capacity of 85kWh (6 times greater than that of the Volocopter) but at a weight of 1,200lbs. So if the Model S batteries were removed and 1/6th of the cores were installed on a UAM, they would represent a 200lb weight – which is more than 20% of the weight of the entire aircraft.
This 20% figure doesn’t sound high, but when you compare the energy in that 200lbs of weight (14kWh or 50.3 Megajoules) to the energy stored in 200lbs of Jet-A (4126 Megajoules) it quickly becomes apparent that Jet-A has prevailed for so many years because of its extremely high energy content.
But this doesn’t mean that it’s not possible for batteries to be “good enough”. Fortunately, aerodynamic innovations mean that matching the energy density of Jet-A is not required; batteries can do good enough with their own lower energy density, and with the added benefit of zero emissions, which is a huge win over Jet-A fuel. The magical 80% figure mentioned in the first comparison of Tesla batteries’ applicability to the UAM industry is critical because, in general, a 20% weight reduction of the battery pack alone would free up enough weight for additional energy storage, baggage capacity, or avionics and flight hardware. This would reduce the 200lb Volocopter battery to 160lbs (or just 16% of the total weight of the aircraft) and would allow energy density to scale to the third power since the reduction in volume for a reduction of weight is not linearly proportional. The 20% reduction, or 80% capacity rule is a benchmark to chase.
How realistic would it be to achieve this reduction in weight; this increase in energy density? At the current rate of battery technology advancement, about 7 years. Is this soon enough? Many would say yes, but the bigger concern is not being addressed: how long will it take battery technology to achieve 30% and 40% reductions, or progress to the point where the energy capacity of Jet-A is challenged? The next 7 years will be a true barometer of success, and small scale demonstrations of battery technology in people-carrying Urban Air Mobility situations will help increase the general awareness of the advantages of electric aerial transportation. Eventually the time will come for more than 3% per year, but only once a larger audience realizes the potential benefit.