This Paper will introduce the most developed concept of vertical take off and landing (VTOL) aircrafts and assess them. It will also analyse the key technology challenges and the legislative situation.
The world’s population is growing and people continue to move from rural to urban areas. This is accompanied by an increasing number of cars. As a result of this, traffic jams in densely populated areas and long commutes are becoming omnipresent. Extension possibilities for existing infrastructure, especially within urban areas, are very limited due to space. Consequently, innovative alternatives are required. Flying cars, also known as vertical take off and landing (VTOL) aircraft, still appear to be a future vision which seems to be far away. However, to date, more than 200 of such concepts around the world are being developed, some of which are even performing flight tests. The objective of this Master’s Thesis therefore is to evaluate if flying cars have a realistic potential to improve the overloaded ground infrastructure systems on a mid-term ten years basis.
In order to answer the research question, a conceptual examination and subsequent classification of the existing concepts is conducted. Based on this a profound content analysis of the four most mature aircraft is carried out. As a result, three significant technical challenges emerge: batteries, noise pollution and the autonomous flying capability. By performing another content analysis on these obstacles, their respective relevance and impact following an upcoming vehicle certification is investigated. Furthermore, VTOL aircraft operations would require legislative amendments. Hence, the current legal situations and actual activities in those regions are studied, where the four companies with the most mature concepts are based.
On that basis it can be concluded, that flying cars have a huge potential to relieve the overstressed infrastructure systems on the ground. Although more than ten years will be required to significantly improve this situation, the first flying cars will most likely be visible much sooner. Technical as well as legal challenges exist, but are not insurmountable and especially the latter are relatively well developed already to enable VTOL operations in an urban environment in the near future.
Table of Contents
I. Abbreviations
II. Figures
III. Tables
1. Introduction
2. Electrical Vertical Take-Off and Landing Concepts
2.1 Vertical Take-Off and Landing Overview
2.2 Methodology to Concept Analysis
2.3 The Lilium Jet
2.3.1 Technological Concept
2.3.2 Safety
2.3.3 Critical Analysis
2.4 Airbus A3 Vahana
2.4.1 Technological Concept
2.4.2 Safety
2.4.3 Critical Analysis
2.5 Aurora Flight Sciences Passenger Air Vehicle
2.5.1 Technological Concept
2.5.2 Safety
2.5.3 Critical Analysis
2.6 Kitty Hawk Cora
2.6.1 Technological Concept
2.6.2 Safety
2.6.3 Critical Analysis
2.7 Comparison of the Different Concepts
3. Key Technology Challenges
3.1 Batteries
3.2 Noise Pollution
3.3 Autonomous flying
4. Key Legislative Challenges
4.1 Organization of Aviation Law
4.2 Amendments to enable eVTOL Aircraft Operations
5. Conclusion
6. Outlook
7. References
7.1 Text References
7.2 Figures
7.3 Tables
8. Attachments
8.1 Initial Analysis of all existing eVTOL Aircraft
8.2 Convention on International Civil Aviation Annexes Overview
Executive Summary
The world's population is growing and people continue to move from rural to urban areas. This is accompanied by an increasing number of cars. As a result of this, traffic jams in densely populated areas and long commutes are becoming omnipresent. People could switch the means of transport and use the public transportation system instead, but that is at high or full capacity utilization already and does not always work for everybody everywhere. Exacerbating this situation further, extension possibilities for existing infrastructure, especially within urban areas, are very limited due to space.
Consequently, innovative alternatives are required. Flying cars, also known as vertical takeoff and landing (VTOL) aircraft, still appear to be a future vision which appears to be far away. However, to date, more than 200 of such concepts around the world are being developed, some of which are even performing flight tests. The objective of this Master's Thesis therefore is to evaluate if flying cars have a realistic potential to improve the overloaded ground infrastructure systems on a mid-term ten years basis.
In order to answer the research question, a conceptual examination and subsequent classification of the existing concepts is conducted. Based on this a profound content analysis of the four most mature aircraft is carried out. As a result, three significant technical challenges emerge: batteries, noise pollution and the autonomous flying capability. By performing another content analysis on these obstacles, their respective relevance and impact following an upcoming vehicle certification is investigated. Furthermore, VTOL aircraft operations would require legislative amendments. Hence, the current legal situations and actual activities in those regions are studied, where the four companies with the most mature concepts are based.
On that basis it can be concluded, that flying cars have a huge potential to relieve the overstressed infrastructure systems on the ground. Although more than ten years will be required to significantly improve this situation, the first flying cars will most likely be visible much sooner. Technical as well as legal challenges exist, but are not insurmountable and especially the latter are relatively well developed already to enable VTOL operations in an urban environment in the near future.
I. Abbreviations
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II. Figures
Figure 1 - Flying Car Vision in Movie
Figure 2 - Rolls-Royce eVTOL
Figure 3 - EmbraerX DreamMaker
Figure 4 - Trek Aerospace FlyKart 2
Figure 5 - Volocopter
Figure 6 - The Lilium Jet
Figure 7 - Engines of the Lilium Jet
Figure 8 - Airbus A3 Vahana
Figure 9 - Layout of the Engines of Airbus A3 Vahana
Figure 10 - Airbus A3 Vahana Recognition System
Figure 11 - Airbus A3 Vahana Cockpit View
Figure 12 - Aurora Flight Sciences PAV
Figure 13 - Kitty Hawk Cora
Figure 14 - Kitty Hawk Cora Top View
Figure 15 - Energy and Power Density of Batteries
III. Tables
Table 1 - Concept Status Overview
Table 2 - Specification Overview
Table 3 - Comparison and Scoring of eVTOL Aircraft
Table 4 - Comparison of Energy Density
Table 5 - Levels of Driving Automation
Table 6 - Ranking of eVTOL Aircraft
1. Introduction
The existing infrastructure on the ground is continuously getting busier, traffic jams are becoming a more frequent side effect and the necessity to accept long commutes is a growing circumstance for many people. In Rome for example, people wasted 254 hours in 2018 because they were stuck in congestion (1). Nevertheless, the number of cars is increasing by approximately 50M per year (2) which will exacerbate the situation further.
There are alternatives to the car, one could switch the means of transport to any public transport system, but that does not work for everybody everywhere, because the infrastructure is not available. For instance, specific regions are not covered completely, the travel time is too long compared to the car, one would have to change too often or the network is already at full capacity. Additionally, similar to the road network, the capacity of public transportation systems is limited; the railway just tolerates a certain number of trains, additional busses will cause more congestion on the streets, which are already highly populated, and the underground cannot be extended easily. Therefore, all incumbent local transportation systems are restricted regarding a potential expansion. Going further below ground, like 'The Boring Company' did in Los Angeles, with a tunnel project called Hyperloop (which would enable cars to quickly drive through the city subterraneously), does not seem to be a real alternative; the capacity is highly limited and existing subsurface infrastructure, like underground train systems or pipes, are complicating and further decelerating the construction work even more (3).
Simultaneously the world population is increasing. Every minute the population grows by 157 people and will reach 9.7M people by 2050, compared to 7.5M in 2018 (4). Aggravating this situation, urbanization, which is the shift of the population from rural to urban areas, is an omnipresent phenomenon as well (5).
What is the solution of a growing world population with a highly exhausted incumbent local transport system? Without appropriate countermeasures, traffic congestion will continue to grow. A seemingly science-fiction concept is becoming increasingly popular and evolving to the ideal solution - flying cars. Busy airspaces frequented by these, in fancy and ultra modern cities, with skyscrapers everywhere are a common feature of movies which depict the future. What many people do not realize however, is that such images may not be too far away. Many companies from all over the world are focusing on the development of flying cars.
Editorial note: Figure 1 was removed due to copyright issues.
Figure 1 - Flying Car Vision in Movie
Uber, which is famous for the disruption of the existing taxi industry globally, started its Elevate project in 2016 (6). It is the project focused on revolutionizing the system again through aerial ridesharing. For this, they hold global summits on a yearly basis and partner with six companies who are currently working on the development of a flying car. One of these partners, and its concept, is introduced within this Paper. In addition, Uber also partners with universities, consulting companies and authorities to transform their vision into reality by 2023. It is not just Uber that works in this space, in Germany in September 2019, an autonomously flying taxi successfully performed a four-minute test flight over the city of Stuttgart (7). Start-up companies around the world are developing and testing both full-scale and smaller sized prototypes of flying cars at this very moment.
But are flying cars really the solution for the overcrowded incumbent ground transportation infrastructure? Is technology at a mature enough level to allow a small aircraft to fly in urban areas with all the noise pollution one knows from conventional aircraft? Would people really accept these innovations with all the associated risks which are attributed to aviation generally? Are they even aware of how close the market introduction of flying cars is at all?
And irrespective of that, is there any chance to amend the legal framework adequately? This Master's Thesis will provide clarity and answers on all those questions with the overall objective to evaluate if flying cars have a realistic potential to improve the overloaded ground infrastructure systems on a mid-term (ten year) basis.
To answer the objective question, a qualitative research has been conducted. To date, companies around the world are working on more than 200 different concepts which could be classified as a flying car to an extent (8). The superordinate term for these concepts is Vertical Take-Off and Landing (VTOL) aircraft, which will replace the term 'Flying Car' in this Paper henceforth. There are four different groups in which VTOL aircraft can be structured:
- Personal flying devices, also known as hover bikes;
- Rotorcraft aircraft, which can be summarized as hybrid or electric helicopters with a thruster just for lift;
- Aircraft with separate, independent thrusters for lift and cruise; and
- Aircraft controlled by thrust vector control (TVC), where tilted rotors are used for both, lift and cruise.
The total scope that is assessed within this Paper will be limited to the last two groups of VTOL aircraft, i. e. thrust vector controlled and independently powered thrust aircraft. Personal flying devices as well as rotorcraft aircraft are consequently not part of this Thesis. Personal flying devices are not being considered since a vehicle which requires a pilot license will not improve the busy traffic situation on the ground, at least not noticeably. Additionally, it is not realistic that this could be enabled by a vehicle for a single person only. Rotorcraft aircraft are excluded, because, although there are innovative concepts and more lasting hybrid or even electrical propulsion systems in development, it generally is not a new technology (helicopters have existed for a long time already).
For the vehicles in scope of this Paper, the focus will be on purely electrically powered aircraft to reflect the increasing public environmental awareness and demand for sustainable means of transport. This special feature expands the VTOL capability to 'electrical vertical take-off and landing', abbreviated by eVTOL. Even by considering the limitations referenced above, the total number of concepts to be assessed is still 107. In order to evaluate the potential of these as a real alternative for incumbent ground transportation systems, it is required to perform an analysis of all the concepts which are publicly known. To do so, a qualitative research in the shape of database and internet research is conducted initially. This is required because there are no classic literature sources available which contain information about the respective providers and concepts. Information from a variety of different sources are collected and summarized in a Microsoft Excel spreadsheet (see Attachment 8.1) which subsequently provides the basis for a more detailed analysis. By working through the spreadsheet and identifying those, which did perform a full-scale flight test already, the time-critical aspect of the objective of this Paper (being an alternative until approximately 2030) is considered and the number of aircraft for a detailed analysis is reduced to a manageable amount. With the qualitative empirical research method of summarizing content analysis, this reduced number of four aircraft concepts is examined through several different sources. Again, these are mainly internet sources because the companies and concepts have just been founded in the last few years.
Through the profound analysis and comparison of the four different aircraft concepts, several common key technological challenges emerge. These are described and assessed in detail by conducting another content analysis with the help of specialized literature. Irrespective of the technological challenges, the legislative framework cannot be ignored while assessing the potential of a new technology. So, a variety of relevant statutory texts and publications is examined accordingly in consideration of the geographical locations of the four aircraft providers. This approach is providing the overall structure of this Master's Thesis. Chapter 2 consequently starts with an introduction into several different eVTOL concepts. In total there are four concepts which are analyzed within this Paper. In Chapter 3 the key technical challenges, which were identified in Chapter 2, are examined and assessed i.e. how critical these are for the short to mid-term development of eVTOL aircraft. Chapter 4 deals with another potential blocker; the legislative framework. After a quick introduction into the organization of aviation law in general, some already implemented amendments are presented.
2. Electrical Vertical Take-Off and Landing Concepts
This Chapter deploys an outline of eVTOL in general and the different groups in which these aircraft can be classified. In order to provide the full overview, also those two types will be introduced, which have been excluded in the Introduction in Chapter 1. After this first general summary, the method to identify the most developed concepts is illustrated. Subsequently the detailed analysis of these follows. This analysis is done completely neutral without contrasting any other concept. It purely is limited on the respective aircraft. To ensure equivalence, the approach always follows the same structure.
2.1 Vertical Take-Off and Landing Overview
VTOL itself is not a new technology. Helicopters, for example, are a common transport vehicle, especially in big metropolises, for decades. Mostly prosperous or vulnerable persons use them to quickly travel from one place to another. However, there are several disadvantages related to helicopters, which disqualify them for being a real alternative means of mass transportation to the existing ground systems. A lack of heliports, the noise pollution or the high costs are just a few of them. Nevertheless, VTOL is a key capability to basically enable flying cars in urban areas. Long runways, which are used in conventional aviation business, are obviously not suitable. Cities usually suffer from limited space availability, which make VTOL aircraft to the only appropriate solution. Big rotating blades, which create strong winds as well as loud noise, are inconceivable for a common mass utilization. Alternate options are needed and the aforementioned issues with helicopters concurrently build the key requirements for a mundanely used VTOL aircraft in an urban environment. Although it is not an absolute necessity for such a vehicle to be fully electrically driven, the continuously increasing environmental awareness and emerging demand for sustainable transportation solutions in the society, underline the importance of such a solution. And whilst the vast majority of companies still is in the development phase of their product, it just makes sense to concentrate on this type of propulsion technology now.
As already described in the Introduction, there are four different groups in which VTOL aircraft can be classified. Some vehicles are controlled by TVC. This means that all engines of an aircraft are equally used for gaining altitude as well as generating thrust. This is done by any kind of tiltable rotor. By tilting the engines towards the ground, lifting force is generated. Once the aircraft has reached an acceptable flight level, the engines are tilted horizontally to generate forward thrust. Examples for this type of VTOL aircraft are the Lilium Jet and Airbus A3 Vahana, which are introduced in detail in Subchapters 2.3 and 2.4, or the eVTOL project of Rolls-Royce (Figure 2).
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Figure 2 - Rolls-Royce eVTOL
Alternatively, rather than using tilting rotors for the different types of propulsion, there are aircraft with two disparately directed fixed rotors. In order to take-off, they use the horizontally rotating propellers, like helicopters do. Once they gained appropriate altitude, the vertically rotating propellers provide the necessary thrust for cruise mode. Examples for this type of aircraft are Aurora Flight Sciences PAV and Kitty Hawk Cora, which are introduced in detail in Subchapters 2.5 and 2.6, or the EmbraerX Dream Maker (Figure 3).
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Figure 3 - EmbraerX DreamMaker
Another type of aircraft, which belongs to the overall VTOL classification as well, are personal flying devices. There is a big variety of different concepts and technologies within this group and it might be very interesting to analyze these in more detail. However, the objective of this Paper is to evaluate the potential of eVTOL aircraft as a real alternative for the existing ground infrastructure which requires space for more than just one single person. Also, by working through the different providers of personal flying devices, the majority of concepts seems to be more focused on leisure activities rather than solving an existing and growing problem. Hence, they are not considered in this Paper but should be listed and briefly presented in this introduction about VTOL aircraft.
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Figure 4 - Trek Aerospace FlyKart 2
The last group are rotorcraft aircraft. They can be described as helicopters or helicopter like vehicles. The main differences between the latest versions and conventional helicopters are that they are hybrids or completely electrically driven, quieter than previous models and that the rotors have been rearranged. Nevertheless, the design and functionality still are similar to a helicopter which everybody is aware of, hence is less innovative and consequently excluded for the analysis within this Paper. One example is the Volocopter (see Figure 5).
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Figure 5 - Volocopter
2.2 Methodology to Concept Analysis
To date, there are more than 100 different concepts being developed which belong to either TVC or fixed engine-controlled aircraft. During the research phase of this Thesis all of these different companies and their respective aircraft have been analyzed in order to determine the current status of development. For a consistent categorization among the high number of concepts, seven statuses have been defined and used by the author of this Paper:
- Defunct
- Preliminary Design
- Prototype
- Low-Scale Flight Test
- Full-Scale Flight Test
- Certified
- Commercially operating
The following overview points out the numbers of concepts in the respective statuses. The whole analysis with more details can be found in Attachment 8.1.
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Table 1 - Concept Status Overview
Considering the overall objective of this Paper, which is oriented on a mid-term improvement of the incumbent transportation system through eVTOL aircraft until approximately 2030, the profound analysis and assessment is limited to those aircraft, which have successfully completed their first full-scale flight test already. This leads to eight remaining aircraft out of that four additional ones are removed, because they either are single-seater (in flight tests, but no hoverbike, because seats should be extended in further development) or hybrids. As a result of this, four concepts are left which will be presented in detail in the following Subchapters.
To collect comprehensive data regarding the respective aircraft a qualitative research has been carried out. The information on the online presences of the companies are the basis to provide an initial overview of each concept which is extended through the research in databases, the scrutiny of reports and trade magazines and by watching videos from test flights. Typical for this type of data are its ephemerality and frequent updates, which especially applies for the online presences of the companies. Also, it must be stated that the total number of sources obviously is limited for such a comparably new and innovative topic. This was no surprise and previously known but must be considered. In order to analyze the gained information consistently, all aircraft are explored in the same structure. First of all, the technological concept is described, followed by the safety related aspects and completed with a critical engagement of the preceding but also concerning the financial background, potential partnerships etc. After summarizing these key aspects of each aircraft, a competitive comparison is concluding this Chapter 2. The carved-out details are assessed among the concepts with regard to technology in general and more particular in terms of noise, pilot mode and safety. Additionally, the financial resources and the public management are evaluated. Since not all criteria are equally important, the rating is extended with a weighting which will end up with a ranking of the introduced aircraft.
The described research methodology above is reliable, because it follows a clear structure. The initial description of similar aspects of each aircraft is followed by a transparent and sensible assessment against weighted criteria which should be completed similar by different people.
2.3 The Lilium Jet
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Figure 6 - The Lilium Jet
Lilium GmbH is a German company based in Weßling, Bavaria, nearby Munich. The company was founded in 2015 by four students of the Technical University of Munich with different degree programs ranging from Aerospace and Mechanical Engineering, via Aerodynamics through Robotics (9). Their vision was to establish 'the leading company in on-demand air transportation by providing quiet, eco-friendly and exceptionally designed VTOL jets and a magical user experience'.
Since 2015 they have achieved a lot - a successful full scale two-seater prototype test flight just two years after foundation in April 2017 (10), millions of investments from external companies (11), more than 50 employees on an annual average basis in 2017 (12) and more than 136 open vacancies in September 2019 (13). In 2018 Lilium won the Early Stage Company of the Year award produced by Cleantech Group which honors the most innovative and promising ideas which will contribute to the clean technology challenges of the future (14).
2.3.1 Technological Concept
The Lilium Jet should be created as a five-seater eVTOL aircraft without the disadvantages of existing VTOL alternatives like helicopters which are comparably slow but at the same time have a high fuel consumption (15). So Liliums objective was clear - they wanted to 'define a transition aircraft concept with better performance in safety, noise, speed, range and payload than existing concepts' (16). Simultaneously they aim to reduce the complexity to one third compared to VTOL alternatives.
The jet generally consists of a fuselage with two rigid wings, one in the front of the aircraft and a longer one at the back (16). The wings include 12 moveable flaps, four on the smaller one in the front and eight on the bigger one in the back. Each flap then again consists of three electric jet engines. This functionality enables the Lilium Jet to adjust the flaps and thus also the engines depending on the respective flight mode. In order to take-off the flaps are tilted vertically to lift the jet. Once the required flight altitude is reached, the flaps gradually tilt into a horizontal position and the aircraft gathers speed. In cruise mode, i. e. in a full horizontal position of the flaps and engines, all lift which is necessary to keep the jet airborne, is provided by the pair of wings. Lilium calls that 'high-lift system'. Its objective is to increase the lift even at lower speed. This will be supported by the engines which are designed in an aerodynamic manner to ensure a very low drag coefficient during cruise flight.
In terms of simplicity the Lilium Jet does not need a gearbox, no kind of propellers, no watercooling, no steering flaps, no variable pitch and no stabilizing tail (16). All functions which are usually provided by the aforesaid are provided by the 36 tiltable electric engines.
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Figure 7 - Engines of the Lilium Jet
These engines generally work just like typical turbofan jet engines where - very simply described - air is sucked into the engine by the turning fan blades in the front of the engine which is then squeezed by a compressor and finally blown out at the back of the engine to create thrust (17). Conventional turbofan jet engines utilize jet fuel to power the engine. Contrary to that the Lilium Jet engine compressor fan is turned by a high performance electric motor (16). Another big difference compared to gas engines is the fact that there is just one single moving part in the Lilium engine which is the central shaft of the rotor holding the fan in the front as well as the magnets of the electric motor. During a presentation at World.Minds Mobility, a community of leaders in science, the arts and business (18), which took place in May 2018 in Zurich, Switzerland, one of the Co-Founders and CEO of Lilium, Daniel Wiegand, mentioned, that this single moving part leads to not a single maintenance requirement for the engines over the whole lifecycle period of the aircraft (19). Another advantage of the electric engines is that they do not transmit any vibrations into the passenger cabin, like Helicopters for example do (16). Considering the most likely field of application for the Lilium Jet, flying in urban areas as an air taxi, noise pollution is an important topic. Conventional jet engine noise would be inconceivable but the electric engines used by Lilium shall cause much less noise for people on the ground and are even called ultra-low noise by the company. There are comparisons in the internet that the engines are causing noise like a truck or a car with 100 kilometers per hour (20). But there are no detailed information or a specific decibel-level available.
In terms of flying and maneuvering the aircraft uses a fly-by-wire system (16). This means, that it will be equipped with multiple computers which are responsible for transmitting the commands that the pilot is doing with a joystick. This shall be as easy as flying a toy quadcopter according to the company.
There are some topics which are not clear or completely described on the company's website. These subjects have been sent to the Press department of Lilium by the author of this Paper (see Attachment 8.2). The aim was to get answers on the following questions:
- 'The Lilium Jet uses an integrated high-lift system' (mentioned on the website)
o What exactly is the high-lift system? Is this a specific 'system' or just the design of wings?
- Which materials are used? There's a lot of information around technology but not regarding the material.
- In decibel, how loud is the jet during take-off, cruise and landing?
- Could you provide more information regarding the batteries which will be used?
The response was received within a day but did not provide further information because of capacity issues according to Oliver Walker-Jones, Head of Communications at Lilium GmbH.
2.3.2 Safety
Lilium calls it safety concept as ultra-redundant (16). This is achieved by separating the different components of the jet into several parts, e. g. the high number of engines to allow the aircraft to continue its flight in case of an engine shut down, the assembly of three engines per flap respectively in case a flap stops to work and so on. The big benefit of VTOL aircraft generally is that they can land nearly everywhere if an emergency touchdown is required whereas conventional aircraft have to approach the next available airport which is in accordance with the needed requirements like runway length.
The computers which are transmitting the pilot commands (as described in 2.3.1) are fully redundant (16). In addition, the computers are ensuring that specific regulations, e. g. speed limits or the maximum angle to roll and pitch, are still within the admissible values during a manual and dangerous maneuver of the pilot.
The engines of the Lilium Jet are shielded (16). That means that two neighboring engines will not be affected both in case of an event which destroys one engine, such as the loss of a fan blade during the flight. The duct, which is covering the fan, is specifically designed to keep a dropping fan blade, so it is shielding the engines.
The energy supply through the batteries again is designed in a multi-redundancy way (16). Even if multiple units of the several thousand Lithium-Ion cells battery pack are stopping to work the remaining batteries will be sufficient to provide the jet with the appropriate power to safely land. If all the batteries are corrupt or any other event occurs which is impacting the ability of the aircraft to fly, it will be equipped with a parachute which would allow the jet to land slow and safe. Even a water landing would be possible, because the cabin will be water-resistant.
2.3.3 Critical Analysis
The main objectives of Lilium are low noise, simplicity, high speed, emission free and low operating costs (21). 'Emission free' might be the most obvious one considering that the Lilium Jet is purely powered by electrical energy. In terms of speed, 300 kilometers per hour in an urban civilian environment definitely can be called 'high speed'.
The noise level is not that clear to assess. As matters stand today, there is no specific noise level published anywhere, which the jet will cause. There are just comparisons available but no values. Upon request through the Lilium communications team the author of this Paper asked for specific decibel values. The team responded very quick but just with the information, that they do not have the time to provide more details. This can be true but the fact that there is no information published on noise levels anywhere and that a short information upon request would not have taken too much time, creates the impression that Lilium is not achieving values which would generally be accepted as 'low noise'. This is also underlined by the noise which can be heard in the video of the first flight of Liliums five- seater. It shows the start of the aircraft and between 1:48 and 1:55 one can get an impression of the noise level (22). Of course, it should be considered that this is just a very short sequence of a video with background music but nevertheless the noise level does not seem to be too low.
'Simplicity' really has been considered during the design and conceptual preparation phase of the jet. Comparing the design of Lilium with that of a conventional aircraft, one quickly realizes missing components of standard aircraft, like the missing rear including the rudders or all other parts mentioned above. But also, the planned concept for the air taxi service, i. e. the ordering process with an app, energy stations throughout the city for a quick recharge etc. seems to be simple (23). However, how easy this concept will be implemented in reality and how easy it really is in the end will not be possible to analyze before the first production jet starts its operation.
The same applies to the 'low operating costs'. Liliums aim is to offer the service for the same costs as a normal car taxi which would make low operating cost to a key requirement. However, the costs are very hard to calculate. One could calculate the approximate aircraft related costs, like maintenance or charging costs. But within a completely new industry there are many hidden costs which just cannot be calculated at the moment, like potential charges for the utilization of the airspace or takeoff and landing and fees which might be accompanied with the registration and operation of an aircraft. All these costs can be considered in the budget planning of a company which starts a business within an existing industry, because cost structures and transparency are available. But in this case, it is just not possible to capture all associated costs. So low operating costs are generally a reasonable target and the simplicity of the aircraft design comes along with that, but if the Lilium Jet will really be able to achieve that is not predictable today. The rare maintenance requirements, which have been mentioned above, underline that the company is on the right way but it's just a vision so far and legal authorities have not agreed to these plans yet.
Apart from Liliums own ambitious targets there are doubts of aviation experts that the speed-range combination, i. e. 300 kilometers per hour speed and 300 kilometers range, is achievable with current battery technology. Of course, both values are just the respective maximum values but generally the predictions of Lilium are criticized because it is the most extreme forecast of all eVTOL companies around the globe (24). Since battery technology and its weight are one of the most critical components of eVTOL aircraft generally, this Paper will touch upon the battery technology in detail in Chapter 3.1.
The Lilium Jet is one of the most developed eVTOL aircraft around the globe. With the first flight of the full-size five-seater in May 2019 they demonstrated their extreme willingness to adhere to previously set milestones and the great ambition within the team. The maturity of the aircraft and the trust in the team are underlined by investments of more than 100M USD (25) from big investment companies like Atomico or e42, the company of the famous German founder Frank Thelen (26). In terms of its personnel, Lilium managed to hire some very interesting characters in the past with a proven track record. In April 2019 they appointed Christoph Delbrück as first CFO who previously hold several senior positions at German based electric utility company E.ON (27). At the end of 2018 Lilium hired several people for key roles from Airbus, Audi and Rolls-Royce. The most famous appointment they made in April 2018, when Frank Stephenson joined the company as Head of Product Design. Stephenson is one of the most renowned and influential car designers of the world and designed cars like the BMW X5, Ferrari F430 or Maserati MC12. These appointments are showing the trust of very experienced and senior people into the company and its strategy. Although there are not many information published about the jet, like next key milestones for example, the project seems to be on a strong successful way forward. On August 17, 2019, the company had published 146 open vacancies both, at their home base in Munich and London (28) which also speaks for itself. Considering the major achievements which could be made from the foundation in 2015 until today and the positive facts mentioned above, the Lilium Jet will be one of the most important key players within the eVTOL industry in the next years.
2.4 Airbus A3 Vahana
The Vahana project started in 2016 at A3, the innovation center of Airbus at Silicon Valley (29). The objective of A3 is to secure Airbus a leading position in future aerospace markets. Apart from Vahana, other current projects are 'Wayfinder', a solution which aims to enable autonomous flight and self-piloted aircraft operations, and 'Adam', a transformation program which shall change design and manufacturing processes through digital innovation. The Vahana aircraft had its first full-size flight test in January 2018, after less than two years of development (30). It is designed as a single-person or cargo jet specifically for urban areas to provide additional travel opportunities to conventional vehicles. Also, the aim of Vahana is to make it the first certified passenger aircraft which flies autonomously without a pilot (31). Already in 2020, the company plans to have a demonstrator available which can be manufactured in series and is then able to serve 1 billion flight hours every year.
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Figure 8 - Airbus A3 Vahana
2.4.1 Technological Concept
Vahana is equipped with eight variable-pitch and counter-rotating variable-speed fans, two tandem tilting wings and four control surfaces (32). The total horse power is 480 hp (360
kW) (31). Figure 9 shows the layout of all these (33). 1-16 are variable pitch fans, 17 and 18 are tilting wings and 19-22 are control surfaces.
Abbildung in dieser Leseprobe nicht enthalten
Figure 9 - Layout of the Engines of Airbus A3 Vahana
The radius of the speed fans is 0.75 m (33). The total width is 6.2 m with a total length of 5.7 m. It is 2.8 m high and has a total take-off weight of 745 kg. With its tilting wings the aircraft is able to vertically take off and land and transition into cruise mode. Although it has flown already, that transitioning maneuver still is one of the biggest challenges of the engineers because of the unsteady aerodynamic interference phenomena between wings and rotors wake systems (32). Intensive computing scenarios and flight tests are ongoing to meet this challenge.
Information about the materials which are used to build the aircraft are not provided. However, upon request through the A3 Communications team, some details were provided. The majority of the primary airframe structure is carbon fiber composite (34).
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