- 10 Feb 2022
- Ken Elliott
- Avionics for Biz Av
What factors will drive and regulate the development of avionics aboard the emerging eVTOL aircraft? Ken Elliott takes a look...Back to Articles
Electric Vertical Take Off and Landing (eVTOL), also collectively termed Urban Air Mobility (UAM), is one of the new thrusts in civil aviation platform development. Inevitably as they become a reality on the market, they will have their own requirements with regard to the avionics they use…
Almost as though straight out of the Jetsons, the emerging eVTOL sector has only been in development for just over 10 years. The main distinctions of eVTOL from other aircraft is electric/hybrid propulsion, vertical take-off and landing, and an operating architecture intended for urban air mobility/air taxi services.
To understand the avionics required for eVTOL, it’s essential to review the broader eVTOL platform as one category of air transport:
1. Light & Sport Aircraft
4. Supersonic (emerging)
5. eVTOL (emerging)
6. Unmanned Aircraft Systems (emerging)
7. Flying Cars (future).
Both fixed-wing aircraft and helicopters can be electric. Both, however, are not strictly eVTOL. Aircraft models in the eVTOL category can be designed and developed for Military, Commercial (Passenger and Cargo), Business and General Aviation, Urban Air Transport, Urban Air Mobility (Urban), and Advanced Air Mobility (Inter-Urban).
The independent category of eVTOL platforms, mostly in development, fall into the following types of intended power source.
1. Fully Electric
3. Electric and Fossil Fuels
4. Electric and Fossil Fuel Derived (such as Hydrogen Fuel Cell).
Another crucial metric for any eVTOL aircraft is how it will be piloted. There will be three generations of eVTOL development and acceptance, as follows:
1. Generation 1: Piloted 1a) Traditional Pilot 1b) Passenger ‘Piloted’
2. Generation 2: Remotely Piloted
3. Generation 3: Autonomous – No piloting required.
Some eVTOL developers, such as China’s EHang, are heading straight for the third-generation where, initially, there could be strict operating limitations. Alternatively, their business model may support the necessary certification path, specific to the locations they intend to operate. Note that autonomous can also be partial, where the passenger plays a minimized piloting role via a tablet device.
Avionics requirements for autonomous platforms will be very different than for piloted and, later, remote piloted. Aircraft developers, such as Joby and Lilium, are currently relying on piloted versions using evolutionary versions of the latest legacy aircraft avionics.
Finally, to further understand the different eVTOL platform designs, it is necessary to know where the aircraft will operate. UAM can involve different environments and the operation in each will commence in different stages:
1. Urban (in city)
2. Urban airport to city
3. Urban city to outer suburbs
4. Intra-regional (city to city)
5. Metroplex operations to maximum permissible range.
From an air traffic control perspective, the lower urban environment is to be predominantly occupied by drones and future flying cars, with eVTOL mostly operating above them, and traditional aircraft above eVTOL.
Summary of eVTOL Models
The data summarized in Table A is subject to change, and is approximated only. eVTOL platforms are all still under development and at different levels of initial certification. Takeaways to derive include:
eVTOL Avionics Considerations
Critical guidance for eVTOL avionics must include the two major considerations of SWaP(c) [Size, Weight & Power, plus cost] and Operating Environment. The former impacts hardware while the latter affects operating architecture and software, with significant crossover elements between both.
Power is the big unknown when it comes to the reality of eVTOL. Some platform developers such as Joby, Lilium and EHang have been flying demonstrator aircraft, while some others are flying scaled-down versions. Until completed, full-scale aircraft are flown the true range and performance capability are mere estimates.
Completed aircraft implies SWaP considerations are realistic, where the size is full, the weight reflects the final airframe version (including equipage, passengers, baggage or cargo load), and the power source is the final configuration.
Interestingly, while a full scale aircraft can be certified and operated for passenger UAM, a sub-scale (smaller, but to scale) version can be used for small package delivery, line inspection and other tasks. While full scale versions can be piloted, sub-scale will remain as remote piloted or autonomous.
Assuming the power is exclusively electric, and adequate for an average advertised mission, the aircraft must have sufficient ‘fuel’ and power management to reach an alternate vertical port. This is in case of preferred port closure, or inclement weather at the original destination.
And remember, with no fuel burn, that for any all-electric eVTOL the take-off weight will be the same as the landing weight. eVTOL platforms will need to be smart in every way imaginable, since it will need to react to rapid changes of physical environment, dense traffic, and additional maneuverability.
The subsequent data requirements and constantly variable demand on the aircraft’s power source, will need to be managed by the avionics. Moreover, the avionics will include flight control, full-time cloud connectivity, and the traditional avionics Communication, Navigation and Surveillance (CNS) systems – all of which will be different to what’s installed in other categories of aircraft.
Generation 1 piloted eVTOLs assume a licensed pilot at the controls. However, there’s a strong desire from developers to allow for passengers to act as pilots by offering greater redundancy, plus intuitive and autonomous technology. In certain parts of the world this may be an acceptable compromise to reduce weight and cost.
By offering aircraft recovery systems and ‘direct to home’ commands in the instance of an emergency, it is possible airworthiness authorities will consider the safety margins to be sufficient, to have passengers perform as pilots.
Not only is there concern for those on board, but also those in buildings or on the streets. Liability is a big factor in providing flight permits, especially for any commercial operation, where money changes hands.
From an avionics perspective, system reliability is paramount, and a Systems Safety Assessment (SSA) for any UAM aircraft will require up to quadruple primary avionics equipage, to ensure no single point of failure can compromise the flight.
This will require smaller and lighter avionics to be developed, under the Integrated Modular Avionics (IMA) design criteria.
As for the avionics systems themselves, there is significant commonality with fixed-wing aircraft systems (at least initially), until both the UAM traffic system and new 5G-based technology are mature. The more autonomous the eVTOL aircraft, the more reliance there will be on datalink and cloud-based services.
IMA products will be sub-modules within packages, capable of a wide variety of functions. There will be several identical modules, each operating independently and ready to take over the reins if any one module drops offline.
It’s hoped (yet unlikely) that an open architecture policy will apply. In reality, there’s too much vested self-interest for that to occur anytime soon, despite apparent promises. And that will be tough for pilots moving between platforms and simulators.
Table B lists a complete avionics package for an advanced piloted eVTOL aircraft. There are four important considerations when reviewing the list.
For any aircraft, there are two independent components of the overall process: The certification of the equipment that will be installed on the aircraft, and certification of the aircraft itself.
Equipment: For the equipment, there’s a Technical Standing Order (TSO) developed and then used by any manufacturer of that system (i.e., a TCAS or a GPS Receiver). While there are other avenues for approval, these are more specific to the function, or where it will be used, and may involve Issue Papers to resolve. This was the case for Head-Up Displays (HUD), for example.
Once the design is approved there is an additional approval required for equipment production, ensuring that each item is produced in accordance with the design, and in identical replication.
Aircraft: For the aircraft, there is the development of a ‘type design’ for the issuance of a Type Certificate (TC). Anything added later is then developed under a Supplemental Type Certificate (STC). As with equipment, there is an additional step required for production approval.
Once produced the aircraft and its crew must be approved to operate, and that could be an ever-evolving process as operators seek to fly their aircraft in different urban environments and conditions.
Avionics: For avionics, the process is initially the same as for equipment, followed by a collective approval under the aircraft TC for that make and model of aircraft only (unless added later). Most avionics that are added later must undergo an STC process, for which there are a few different ways to go.
Avionics are developed under a variety of design requirements and four of the most important that will certainly apply to eVTOL are:
eVTOL: For eVTOL and corresponding avionics, the process will be much the same. Hopefully many of the smaller aircraft will be developed to Part 23 eVTOL standards and larger ones to Part 25. There is also a possibility of Part 27 and 29 (Helicopter Certification) being applicable. However, if the intent is to operate commercially, Part 135 (scheduled), Part 91 (unscheduled), or 91K (fractional) will be required, with Part 135 raising the bar for compliance, necessitating higher standards for the aircraft and its equipage.
Because of the ‘novelty’ of some of the new avionics for eVTOL, the equipment certification path will be littered with Issue Papers, Special Conditions, and interesting ‘show compliance’ requirements. Moving from piloted to autonomous will extend the ‘special categories and certifications’ even further, offering unique challenges to this fledgling industry.
Lastly, for eVTOL certification there is much to leverage from fixed-wing horizontal flight, and now, too, from the significant effort expended in unmanned aircraft systems or drones. The latter includes remote pilot, beyond line-of-site, and other non-traditional ways of flying in 3D airspace (soon to be operating as 4D with time-based operations).
Operations and Infrastructure
With respect to 4D time-based operations, an urban traffic management (UTM) may appear as if an underground rail network, but from trains to planes, and from stations to vertiports. As with trains, there are stops along the way, and central hubs.
While trains operate along 2D tracks, with timing as a third dimension, eVTOL will be operating in 3D air corridors, with timing as 4D.
Understandably, the challenge to control 3D operations with precision timing, will necessitate the use of 5G speeds and bandwidth for connectivity. Initially, however, we can expect prototype operations in specific urban locations for single operators. Several adequately funded collaborations are underway between the three elements of an eVTOL environment: Vehicle provider, Operator, and UTM.
From an avionics perspective, a successful eVTOL operation requires continual connectivity to a reliable and capable ground infrastructure, where nothing is left to chance. This will take time to fully develop, as prototype operations carve out tried, tested and approved UTM processes that everyone can trust.
The avionics will need to control the aircraft in structural environments, where micro-climates form rapidly around buildings, or where electro-magnetic interference (EMF) is more likely.
Training and Support
Any company contemplating the development of eVTOL avionics and infrastructure will need to transition from creative innovator to an aviation-approved manufacturer, which is a tall order. Often overlooked, training and support are key components of a manufacturer’s portfolio, and should be considered early. Two time consuming and costly considerations are:
Companies developing eVTOL, such as Embraer, have this figured out – including for the avionics. Others are still at the creative innovation stage. As the next few years unfold, it’s reasonable to anticipate a drop-off of eVTOL programs as the ‘rubber meets the road’. The market is prime for mergers and acquisitions.
The exciting new and evolving field of eVTOL has so much to offer to future generations. Avionics is one small piece of that future, and, when viewed through a ‘look- ahead-telescope’, appears as a large virtual cloud of autonomous connectivity to an aircraft hosting very little in the way of equipment.
The passenger or remote operator (cargo) uses voice or touch screen to request a route, and all computation is completed off-board. The future air vehicle will be a sensory wizard, always aware of its surroundings, like a bird.
The combined sensory data is also processed off-board, in real-time. Flight control commands are then provided from the same cloud, as a stream of multiple maneuverability instructions, and the aircraft operates autonomously from there.
That prospect is likely to come after 2030, or even 2040. Reaching that goal will be a long, steady, inching forward of eVTOL avionics development, in lock-step with airspace redesign, UTM, and UAM certification evolution.
Anyone pushing the envelope for disruptive change should hang in there, but understand that one single accident that results in a fatality, could set the wider eVTOL program back, and require even greater stringency with closer scrutiny.
The disruption can only come about through verification and validation of each avionics advancement, and that will require additional time and cost.