eVTOL taxis: The tight-rope walk of trade-offs to reach commercial success

This is my 4th post covering the exciting world of eVTOL Urban Mobility and its emergence as a viable transport option. Here I cover various trade-offs that must be considered by the 170 or so companies world wide that are currently developing such vehicles…

Evening clouds above

One of the most exciting elements of the emerging eVTOL taxi industry is just how diverse the designs and concepts are showing up to be. The use cases that they are intending to serve have up until very recently been technically unfeasible, and with no successful baselines to refer back to, creativity and experimentation rule the day. You would expect that over time designs will become more and more homogeneous, as has happened with the aerospace and automotive industries. However, until then, we have many years of varying designs to look forward to as many organisations seek to find the magic formula to ensure that they are more effective than their competitors.


Unfortunately, as with everything in life, an optimal design will come from effectively balancing between competing requirements, you can’t have everything. Below I explore some of the more pertinent of these necessary trade-offs.

Take-Off Efficiency Vs Horizontal Flight Efficiency

On the one extreme you have a design similar to a helicopter, with vertical facing rotors, this concept is very efficient at providing vertical lift, and hovering in one position. However, when it comes to flying in a horizontal direction, this design is very inefficient.

On the other extreme you have a fixed wing design, similar to a Harrier Jump Jet, this is very maneuverable and efficient when in forward flight, but takes a lot of skill and energy to enable vertical take-off. Not to mention produces a lot of noise during this process, as shown in the video below:

Although developments in electrical propulsion systems mean that more advanced concepts can be used to power this next generation of vehicles, thus leading to quieter and more energy efficient solutions. The vertical vs horizontal trade-off is unavoidable. Inherently, solutions optimised for vertical lift will be more suited to shorter journeys and more frequent landings, but will tend to be more noisy and slower in horizontal flight. Those designs optimised for horizontal fight will tend to have noisier and more energy intensive take-offs. According to Uber’s elevate white paper: Uber Elevate, an eVTOL vehicle can expect to use the same amount of energy to take-off and land as it would need to travel horizontally for 50 miles.

rotor fixed wing

Performance & Efficiency VS Ease of Maintenance and Certification

One way of countering the vertical vs horizontal trade-off is to design a vehicle with propulsion systems that rotate into optimal positions for both modes of flight (see example above). Several eVTOL developers have opted for variations of this solution. The draw back of this approach is that with significantly more moving parts and mechanisms to control, there are a lot more things that can go wrong. This will mean increased frequency of scheduled maintenance as well as the need for more replacement parts. This also means that the vehicles will be more complex and expensive to pass through certification. Estimates can be taken from the aerospace industry, but judging by the variations in designs it is not yet obvious where the sweet spot is in terms of efficiency of flight operations vs cost of maintenance and certification.


Battery Service Life vs Battery Weight & Logistics

Lithium Ion Batteries are happiest when 50% charged, and least happiest when 100% or 0% charged. In general the more that they are subjected to 100% or 0% charge the quicker they will degrade and need to be replaced. Volocopter estimates that the battery will consist of up to 75% an eVTOL vehicle’s operating costs. Most appliances (including Tesla’s vehicles) get around this by not allowing you to charge up to 100%, or run down to 0%, but this means your battery capacity needs to be bigger than what is actually accessible. As batteries tend to be heavy, this becomes an issue in vehicles that need to escape the Earth’s gravity. Thus battery size and capacity needs to be carefully matched against likely journey times.

There is an added complication in that fast charging these batteries also causes them to degrade more quickly. An option can be to simply swap out batteries at service stations, and then charge the spares at a slower rate. This means that more batteries need to be held in inventory, complex mechanisms and fastenings need to be utilised to enable them to be switched, and inspection and certification requirements will become more complex.

overloaded bus.jpg

Carrying Capacity Vs Noise Pollution

This is a particularly tricky trade off. As seen with traditional commercial airliners, the most economic and cost effective method of transporting people in the air is to build a fairly large aircraft. This improves the mass efficiency, as the increase in the weight of the aircraft is less than the increase in weight carrying capability of passengers and their luggage. Unfortunately however, the power required to create lift increases at a greater rate than the increase in passenger weight. This isn’t so much of a problem when you can take a long take-off, utilising the lift efficiency of a fixed wing, but when you are relying on rotors or turbines to create lift, this large increase in power requirements means noise increases very quickly. This problem is compounded when utilising electric power, as it means more battery power (and therefore battery mass) is also required. Thus there is a direct conflict between carrying capability and the economic benefits of  carrying more passengers in one vehicle, vs the power and noise that is necessary for take-off and landing. Once again, the use case of the vehicle will need to be carefully considered to ensure that an optimal balance is achieved.


Population Density & Demand Vs Certification & Regulation Requirements

Basic logic dictates that demand for transport services that will drastically reduce travel times will be in higher demand in areas where there are higher population densities, where people tend to be more time poor, and where there is congestion problems with incumbent substitute travel options. However, as specified by Volocopter in their recent white paper Volocopter White Paper certification requirements are 100 times more stringent over cities than they are over rural areas. This is without considering that before too long there could be traffic jams in the sky, and thus there will likely be tariffs to cover the cost of directing and managing air traffic in densely populated areas. Another factor to consider is that in densely populated areas you are never far away from people, great for potential customers, but not so great when it comes to noise pollution and regulations that come with it.

Considering this, it is understandable to see small businesses such as Esprit Aeronautics covered in my previous blog artical: eVTOL, interview: Simon Scott. Founder and Owner of Esprit Aeronautics choose to operate away from cities in under-served rural areas. However, the main players in this sector are developing much more expensive vehicles that will need to be utilised more productively than serving rural areas will likely allow. Thus a strategy to overcome the barriers of operating above cities will be necessary.


Market Segment vs Public Acceptance

The above mentioned Uber Elevate paper estimates that initial flight costs will be approximately $150 for a 50 mile journey. In energy and maintenance terms, it is likely that half of that cost will be just for take-off and landing. Thus there will be an initial $75 levy needed to break even before the journey duration is even considered. Over time Uber expect the cost to fall significantly to just $25 for a 50 mile journey, but in the near time it is clear that the service offering will need to be pitched at wealthy clients willing to choose a more expensive alternative to existing services in order to save journey time.

The problem here is that geographical locations where high net-worth individuals live tend to also to be areas with the least noise pollution, while also being the most aesthetically pleasing. Thus it will be harder to gain acceptance for services that bring easily noticeable noise pollution as well as potentially become a blot on an otherwise beautiful landscape. Further to this, if only 5% of the population can afford to use such a service, then the other 95% of the population are likely to be unhappy to be disturbed to enable the ‘privileged few’ to live a life of increased convenience. In nations where  introducing legislation tends to be a democratic process, introducing eVTOL services under the above circumstances may prove to be a challenge.


First Mover Advantage Vs The Curse of the First Mover

First mover advantage will enable an organisation to work with certification agencies, which will in turn mean that legislation will naturally lean to cover their specific products. It will give you a head start in building a portfolio of qualified materials, processes and operating criteria, so you can tailor these to your business’s strengths. Pilots will be trained on your products and get used to flying them. You will get first option on licencing of areas (assuming air traffic control will be restricted by licencing areas and capping amount of traffic). You will also get a chance to establish your brand while there is less competition.

However, especially considering all of the uncertainties and trade-offs above, committing to capital investments when the industry is young means you are also committed to a strategy that carries a higher risk of failure than for a more mature market. Organisations that come late to the party can gain valuable insight from the first movers’ lessons learned, they can wait to see what concepts and business models become the most successful, and then simply target to beat these early leaders in order to gain market share. The first movers may find it hard to react to these late entrants as they have already spent their capital to develop a market which will likely be unprofitable during its early years.

The same can be said for infrastructure, early investment gives you a likely cost advantage as competition is low, and a head start in setting up key hubs. However, there is risk that as the sector develops, customer’s needs will also develop, and the original locations and architectural designs become quickly overlooked by newer options.

This is not to say that the early movers are destined to fail, but history doesn’t favour their chances. They will need to maintain agility to ensure that they adapt with the fast moving market and it’s regulations.


In my next article I will look at a couple of the first movers in this emergent market, assess the strategic decisions they have made with regards to the above trade-offs, and evaluate what I feel are their strengths and weaknesses…


eVTOL Interview: Damian Kysely; Infrastructure manager at SkyPorts, and co-founder of The Aviary Project

See below for my interview with Damian Kysely; a subect matter expert on eVTOL and Urban Air Mobility (UAM). Damian is Infrastructure manager at SkyPorts skyports.net, a new business focused on developing the infrastructure required to support UAM. Damian is also co-founder of The Aviary Project medium.com/aviaryproject which was set up to facilitate collaboration in the emerging UAM and eVTOL sectors.


Nick: Hi Damian, Many thanks for taking the time for me to tap into your knowledge!

First off, I have read that Skyports have partnered up with Volocopter, this strikes me as a partnership with huge potential for you guys. Volocopter are one of the more ambitious players in the market to date, and they are even working with the innovation arm of the CAA (Civil Aviation Authority) in order to define the new regulations required for UAM.

Further to this, Volocopter have published some very eye-catching ideas of how they see UAM transport hubs of the future. They look like giant ski lift stations that can handle several hundreds of people.

Are you guys at Skyports actively involved with the conceptual architectural work that Volocopter has done to create this promotional material?

Damian: Skyports have worked with Volocopter to design and develop the first prototype ‘Volo-Port’ which will be built up in Singapore. This is effectively a qualification model that will test that we can meet many of the requirements for an eVTOL vertiport. Including managing the flow of passengers, getting them checked-in, and also the recharging of the vehicle itself, in this case battery swap.

We were not involved in the initial conceptualisation of the VoloHub, but of course we look to incorporate some of the high-throughput components into our future work with Volocopter. Skyports’ goal is to be the preferred infrastructure provider to Volocopter and other vehicle manufacturers and operators as the industry scales up.

Nick: Thanks for clarifying. With regards to Volocopter’s grand plans for their transport hubs, these look like they will need to be made on top of purpose-built buildings. Are Skyports currently in negotiations with companies so that they can incorporate new features into buildings that they are yet to start?

Damian: Skyports have secured several sites on top of existing buildings that have sufficient structural capacity to be retrofit with a vertiport of certain size. In parallel, it is very important that property developers incorporate vertiport requirements into their plans from day 1, otherwise we will end up with loads of buildings that are useless for this purpose. This is something we’re doing at Skyports as well and it is increasingly sought after. And yes, in the future purpose-built towers with Skyport provisions are very likely. For example, Uber aims to convert entire buildings (car parks) into Uber Hubs for UberAir services.

Nick: With regards to the legislation and regulation, which body creates and upholds this?

Damian: In the UK this will be CAA again. All of our vertiport designs comply with existing ICAO (International Civil Aviation Organization) heliport standards and CAA adopts them. Therefore CAA will be the one giving us a stamp from a regulatory point of view.  On a local level, it will be the city authorities and planners giving us a permission to construct them and operate them.

Nick: I also note that Lilium, a potential future competitor to Volocopter, is also looking to create their own infrastructure. This will enable them to offer a complete service offering, rather than just an eVTOL product. Do you see the different eVTOL companies collaborating with one another to share transport hubs, or do you think that they will seek to create their own unique hubs?


Damian: I think that each organisation will seek to create it’s own individual hubs to start with, for example, I can’t see Volocopter and Lilium wanting to work together at this early stage when they are likely to be in competition with one another.

Skyports are already very close to most of the leading vehicle manufacturers alongside Volocopter. Our main principle is that all of our vertiports will be vehicle agnostic in the long term and everyone we have spoken with, including Volocopter and Lilium, agrees on this.

Nick: Looking at the established airline industry of today, most groundside operations and interfaces are standardised. These include refuelling, food and beverage logistics, as well as safety checks. Is work being done in order to standardise these and other items in the UAM sector?

Damian: There is some work being done in the U.S. looking at what should be standardised, however this is not the current priority of the eVTOL manufacturers. They are still very much looking at the overall systems design and how they can maximise the efficiency (cost / range / speed etc.) of their products.

Nick: I note also on the Skyports website that it is predicting drone deliveries over London by 2021. This statement was released almost a year ago. With the progress made since then, do you think that a 2021 date is still achievable?

Damian: Anything is achievable with enough resources! Joking aside, I think the way things are progressing, 2021 could be achievable for a point to point route, say for instance from one hospital to another. I think also that the route will need to run along the river. Once something like this has been fully proven then we may see an over land equivalent.

London is lagging some other locations. For instance, drone deliveries as I have just described are already happening in Switzerland and other parts of the world.

Nick: Are there any pertinent reasons why London is lagging behind?

Damian: Legislation and regulation are the biggest barriers to progress. This is not helped by the fact that London is notoriously ‘anti-helicopter’. In relative terms, London is a quiet city considering its size, and so helicopter noise pollution tends to be all the more noticeable, and therefore also unwelcome. This makes public percpetion and adoption of drones and other flying vehicles all the more challenging.

Nick: Well as a resident of London, I love the idea of flying taxis, but if it means I will have hundreds of helicopters flying above my head, I may quickly change my mind! Just how noisy are these eVTOL likely to be?

Damian: Volocopter and Uber Elevate have released white papers that hint on the estimated noise levels, which claim they are significantly quieter than traditional helicopters. But none of the other companies have. There seems to be quite a lot of secrecy surrounding this area. Without knowing the respective noise levels, it will be very difficult to get the legislation issues resolved.

Nick: Well Damian, I’d like to thank you once again for your time, this has been a very informative and enjoyable conversation.


For those of you who would like to learn more about the industry, I encourage you to check out their excellent blog at The Aviary Project: https://medium.com/aviaryproject. As mentioned above, this was set up by Damian and others with the prime purpose of promoting eVTOL and UAM.

eVTOL, interview: Simon Scott. Founder and Owner of Esprit Aeronautics

As a first for my blog, see below for my interview with Simon Scott; owner of Esprit Aeronautics espritaero.com a business focused on developing a manned vertical take-off aircraft. Simon has been active within this sector since the 1990’s, long before eVTOL and drones became media trendy.


This interview follows on from yesterday’s eVTOL blog entry: So are we finally going to live like the Jetson’s?? 

Nick: Hello Simon, firstly thank you for agreeing to the interview.

Nick: First off, please could you give a little detail upon your background, and how you became interested in the eVTOL sector?

Simon: Both my grandparents had served in or supporting the Royal Air Force and my youth was spent either making model aircraft or visiting air shows and museums in Europe. After leaving school at 15 I studied engineering before becoming an assistant metallurgist for a specialist castings company that supplied the aerospace industry.  At 19 years of age I joined the military as a guided weapon’s controller before working closely with the Army Air Corp on several operations. On leaving the military in the late 90’s my fascination had not diminished and I started to look at the research being done by Mark D. Moore (currently UBER Engineering Director of Vehicle Systems) when he was at NASA Langley Research Centre and following several email exchanges I started my own research into Personal Air Vehicles which led me towards hybrid propulsion and electric aircraft in the early 2000’s.

Nick: So this is not a recent venture for you, this is an area that you have been working upon for many years. You also have significant experience in the creation of drones. Does your ePAV carry a lot of design heritage from Esprit Aero’s drones? What are the key differences?

Simon: I’ve always been a believer in building something, not just a nice 3D CAD rendering. It is also better to build and test a real platform in nature as CFD (Computational fluid dynamics – used for aerodynamic analysis) may be a very useful tool but nature is unpredictable in many cases. I’ve also carried out testing at higher elevations, usually starting at 500m ASL unlike many which tend to test at scale and at sea level.

You learn a great deal from failure and I have experienced plenty in the early years with drone flight controllers and sensors far less capable than current versions, but I have also seen my designs carry out flights lifting payloads far greater than even some of the well-known drones of today cannot handle.

As far as heritage goes, if you can fly a conventional quad copter drone competently today you could fly one of our eVTOL platforms, it is that simple to fly.

Finally there are many differences between drones and manned vehicles, most notably, safety is of utmost importance, when carrying a “Live” cargo.

Nick: I think most will agree that public awareness of the future eVTOL market has rapidly increased in recent times. This awareness has been amplified due to the concept designs shown at this year’s Paris Airshow, and claims that cities such as London will be serviced by air taxis as early as 2025. Do you think that these 2025 claims are realistic?

Simon: I will say I am very sceptical of timelines as I have first-hand experience of just how long it takes to turn ideas and concepts into reality. There are far more barriers to market for eVTOL air taxis in the Urban Air Mobility sector than many openly admit to.

Obviously there are some exceptions when it comes to platforms we are already seeing in test videos online but we have yet to see any fly in an urban environment never mind carry a fare paying passenger between two vertiports in a city.

Nick: What do you think are the main barriers to achieving this 2025 target?

Simon: Obviously legislation requirements, not only for vehicle certification but also flight restrictions, noise levels and flight corridors over populated areas.

Social acceptance is key so safety requirements need to be much higher and the costs associated with using such means of transportation needs to be cost effective for passengers. Most people would enjoy saving an hour a day travelling but not if it costs them twice as much as using conventional means, which reduces the potential passenger numbers willing to pay for that time saving.


Nick: So legislation and regulation will be key, unsurprisingly, but you also consider that there is high risk of the short to mid-term business case being unviable. With such significant barriers remaining before city air taxis are accepted for use, and with the recent rapid increase in eVTOL businesses across the world, it looks like at least some of these ventures will not end with success. Considering this, what is Esprit Aero’s planned product and service offering?

Simon: We are targeting Rural Air Mobility (RAM) and at first, we are looking at the use of single and dual seat platforms for first responders. Many rural areas are receiving very little support from emergency services due to budget cuts and low staffing numbers. Smaller ePAV solutions are force multipliers and allow a greatly increased response time.

Nick: So, you are looking to provide highly mobile transport solutions for emergency services in remote locations where there is a high need. In affect you are proposing to offer a smaller, quieter, more cost-effective and easier (safer) to fly, alternative to a helicopter? If the eVTOL consumer taxi market is delayed, do you see this space being targeted by the eVTOLs taxi companies, while we wait for the certification and regulation hurdles to be overcome?

Simon: Most of the air taxi designs could be modified but the focus by the main player’s remains air taxis. Would a local authority pay £4,000,000 GBP for an eVTOL air taxi platform when they could purchase a dual seat ePAV for less than £200,000 GBP? There is also the platform footprint to consider as some of the eVTOL designs being developed are nearly as large as conventional helicopters.

Nick: Regarding the seemingly booming eVTOL industry, have you found that this has helped or hindered your business development strategy? Are you finding it easier to find both customers and suppliers now than say two years ago?

Simon: We tend to get far more suppliers interested in us now as many read the analysis & market predictions believing it to be a good opportunity for them at an early stage. Customer interest is growing but many are “tyre kickers” and are wisely waiting until they see the real platforms working before committing.

Nick: With so many different types of eVTOL being developed, do you think that there will be key areas where parts will become homogeneous? Are there any of these products that you plan to specialise in, or in fact outsource to a specialist supplier, rather than create yourselves?

Simon: We have a plan and that has to be flexible as nobody can predict the future so we will keep a keen eye on the industry & market and react accordingly.

Nick: What do you see as your key objectives in the mid-term, once you have achieved certification and the ePAV is in use in the UK? Do you plan to develop business overseas? Also, are you planning to develop any additional vehicles to the ePAV in the future? If you were to develop an additional product offering to the ePAV, what differences would it have (eg. What do you see as a strong second market)?

Simon: At this stage we are focused on finding the right investment for us and our plans to get our designs into the air safely and legally.

Obviously there is international interest and due to our experience with international suppliers and the wider aerospace industry we can visualise dealerships across the globe in the future as well as the international support infrastructure that will be needed.

We are aware that certain clients require bespoke solutions that will need to be built “in-house” for security reasons.

Nick: So it sounds like you will need at least a small manufacturing facility, with the option of outsourcing high volume orders on build to print licences as and when customer demand deems it necessary.

Many thanks for your time Simon, it has been very interesting to speak with you. I think considering the current market, your business development strategy is smart; offering a product with low unit cost that offers clear advantages over existing products (e.g. helicopters), and will also open the market to users who may not have previously considered flying vehicles as a viable option. I look forward to hear about further developments!


For those who are reading this blog, if you would like to learn more about what Simon and Esprit Aeronautics are developing, please check the links below:

The business case for Rural vs Urban air mobility: https://www.espritaero.com/ram-rural-air-mobility

The ‘barriers’ to Urban air mobility: https://www.espritaero.com/are-evtol-air-taxi-s-the-only-solution

So are we finally going to live like the Jetson’s??

Human’s have been buzzing around in flying cars since before we landed on the moon, in cartoon form at least. However, if the hype is to believed then maybe 60 years after the first Jetsons episode, we in the real world are finally catching up…


Although I’m not old enough to have witnessed the first showing of the Jetsons, which aired in September 1962, I do fondly remember their 80’s shows. The life and times of the Jetson family was given to us as a futuristic alternative to the Flintstones, and the notion of flying cars as well as other futuristic inventions left a lasting impression upon me.

However, despite the optimism that us pre-millennials carried with us through the 80’s, it didn’t seem to translate into reality. Our wide eyed vision of the future was most likely fueled by our parents witnessing the moon landings when they were a similar age to us, together with the emergence of the computing age; which would seemingly make anything possible. I remember reading children’s books that were telling me by the year 2000 we would no longer be using petroleum fueled cars. I also remember watching Back to the Future II in 1988, which told me that by the time I was 35 I would be whizzing around on a flying hover-board.

BTFII Hoverboard.png

You can’t deny that the impact that the likes of Mark Zuckerburg has had on our lives is both significant and unpredicted. But in terms of tangible inventions, when compared to what was being predicted, it’s certainly a case of must try harder. Sure, I love the fact that I can make my face look older than it really is just by using a special app, but how come it still takes me 24 hours to get to Australia? and while I’m at it, how come my journey out of London for a weekend retreat now takes longer than it did for my parents at my age??


Well documented studies have shown that social media isn’t actually that social, and with climate change becoming ever more of an issue, the challenge of physically connecting people seems to be becoming much more difficult than the now solved challenge of virtually connecting people.

I mean, if you have a vacuum cleaner manufacturer has decided that they can make better electric vehicles than incumbent vehicle manufacturers, then surely the industry is in need of a shakeup?


Well, finally we might be getting there… following on from Elon Musk’s foray into the electric vehicle market with Tesla, companies are starting to take this one step further and combine electric propulsion with air travel.

lilium jetThis year has seen a marked increase in media exposure for where we hope the next generation of aircraft will take us. The 2019 Paris Airshow displayed several electrical powered concepts, including an offering from both Airbus and Boeing. Roland Berger, an aerospace thought leader, have stated there are now 170 different ‘e’planes globally Roland Berger Study. Of these 170, there are two German based start ups, one who is aiming to serve London with air taxis by 2025 Lilium Jet’s 2025 target, and another who is aiming to go one further and provided automated flying taxis. I challenge you to watch the video clip below and not get excited…

Having been rather blown away by these claims, my imagination was quickly kicked into overdrive with what possibilities and opportunities such developments will bring; from transformational commuting experiences to exciting employment opportunities. However, as the saying goes, once bitten twice shy. With the broken promises of Marty McFly and Doc Brown still fresh in my memory, I thought it only right to investigate further into this fresh and exciting sector. Just how real are these claims?

I will be sharing my findings upon this blog, so you will be the first to know. Starting with an interview with a business owner who is developing a manned eVTOL (electrically powered vertical take-off and landing) vehicle, which I will post tomorrow…