• 09 Nov 2021 08:04 AM
• 0

The E-VTOL Flight Test Council’s Pioneering Year

Al Lawless, E-VTOL FTC Founder/Chairman
Vertiflite, Nov/Dec 2021

Last year, VFS helped establish a working group — connected through the VFS Electric Vertical Takeoff and Landing (eVTOL) Technical Committee and working with other professional societies — to advance the conversation on flight testing this new class of aircraft. Here’s what they have been up to.

Regular Vertiflite readers are well aware of the investment growth in large aircraft with novel power sources, such as electric, hydrogen and hybrid combinations. Small unmanned aircraft systems (sUAS) paved the way with continuous improvements in payload, range, reliability and — perhaps most importantly — nearly carefree handling and operations. While US Federal Aviation Administration (FAA) Part 107 rules successfully regulate commercial sUAS operation in the US, it’s clear that further capability advances combine with visionary ideas and venture capitalists to bring a new “Wild West” with rules yet unwritten.

Speculators are calling for aircraft configurations, operational uses and piloting scenarios that could lead to several aviation ecosystems operating in parallel. More than a few think out of the box simply because they don’t know the box for conventional aviation. Snake oil salesmen promise success, operational approval and deliveries on timelines that make responsible players wince. The demand for technical talent is fostering a Gold Rush of recruiting bonuses, poaching and intellectual property law suits akin to claim jumping.

This new West has many moving parts — each with specialists in engineering, operations, training, etc. At the risk of oversimplifying, these parts come together at the end of the line — flight test. To keep up with the innovators, flight testers should expect to think and work outside their box of conventional methods. We must get smart on new aircraft airworthiness topics, such as:

• Battery handling, storage, charging, mapping “personality” and operational histories
• In-flight energy monitoring, displays and contingency management
• Non-linear relation between battery capacity and power draw during powered-lift flight
• Testing “vibration swamps,” unlike helicopters or VTOL that operate at a single rpm
• Evaluating automation and human-machine interfaces (HMI) on behalf of new types of pilots and operators
• Evaluating ride quality on behalf of passengers
• Showing compliance with new certification standards
• Evaluating hazard levels and work-arounds for entirely new failure modes
• Flight into known icing for urban weather and (potentially stopped) propeller blades
• Stability and control margins during terminal operations with “urban canyon” wind gusts.

Airspace management is another field to plow in this West. Just as Part 107 segregates the smalls, speculators may promote other kinds of airspace, asking:

• Will every authority operating urban air mobility (UAM) vehicles adopt European “U-Space” as a public safety measure?
• To attract UAM providers, could local authorities allow a monopoly?
• Can UAM operations be a true “air taxi” service akin to Lyft or Uber?
• Will UAM operations be the “AeriaL” type — effectively a highly elevated (“el”) city train taking passengers between fixed platforms along fixed routes?
• Can electric short takeoff and landing (eSTOL) cargo aircraft take off from the roofs of hospitals and shopping malls?
• Will intercity regional air mobility (RAM) operators play by the conventional national airspace system (NAS) rules?
• How will high altitude long endurance (HALE) unmanned aircraft transit through the lower NAS?
• What distinguishes vertihubs, vertiports, vertistops and emergency landing spots?

Deciding these matters and many more is not in the flight test wheelhouse, but we still need to spool up to properly evaluate on behalf of the operators and the rules. Similarly, flight testers need to keep up with new rules for routing and deconfliction such as:

• Integrating with traditional aviation and UAM participants
• Providing instrument flight rules (IFR)-like controlled separation or expecting visual flight rules (VFR)-like self-separation
• Detect-and-avoid (DAA) systems for airborne traffic
• Pre-ordained evasive maneuvers suitable for unmanned aircraft
• Performance-based navigation (PBN) specifications • Datalink communication “robustitude” in multipath environments
• Resistance to malevolent signal spoofing or GPS denial
• Alternate navigation like Locata (ground-based GPS) or limited-capability inertial units

Yet another field in this new Wild West is piloting and automation — the least tangible and most subjective include the following:

• Clarifying new levels of onboard piloting capabilities — especially for simplified vehicle operations (SVO)
• Evaluating on behalf of a range of pilot skill levels (from former Harrier jump jet pilots through recreational pilots)
• Remote piloting equipment, displays, inceptors, feedback, lags and general interfacing
• Remote piloting capacity for multi-aircraft monitoring and override

As daunting as this partial list may be, consider the increased complexity when evaluating for different combinations of aircraft, airspace, facilities, operating rules and piloting options. Each combination is a different concept of operations (CONOPS). Until this Wild West settles, we must remain on alert — watching how test methods or metrics might change with the CONOPS.

While settling the above is in everyone’s interest, there is no single sheriff to lay down the law. Today, the various Standards Development Organizations (SDOs) — such as SAE International, ASTM International, ARINC, etc. — provide venues to deliberate on the many topics. Similarly, flight testers need to collaborate to determine acceptable practices for developmental testing and showing compliance with the standards. If pending standards or rules appear untestable or unsafe, we should collectively engage the SDOs and authorities to “head them off at the pass.”

Flight testing collaboration makes sense, but there was a void. Although large electric aircraft flight testing expanded in recent years, professional societies such as VFS, the American Institute of Aeronautics and Astronautics (AIAA) and the Society of Flight Test Engineers (SFTE) saw very papers published regarding flight testing of electric aircraft. While understandable for sUAS testers, the recent expansion in aircraft size, investment and risk certainly justifies engagement. The stage was set to fill the void with an international posse.

Beginning in 2019, discussions with fellow testers made clear there was broad enthusiasm to cooperate in this new niche. These conversations shifted away from simply promoting papers towards actively collaborating on flight test matters. With encouragement from colleagues, SFTE and VFS leaders, representatives from other professional societies and FAA members, August 2020 saw the launch of an entirely new inter-organizational council focused on flight testing novel electric-powered aircraft, now often referred to as advanced air mobility (AAM). This council’s scope would cover the new generation (i.e., not your father’s VTOL aircraft). Helicopters and turbine powered-lift aircraft have been served well with activities and with papers in the archives of VFS, SETP and elsewhere. To give equal recognition to electrified airplanes plus VTOL, we became the “E-VTOL Flight Test Council” (written thus to show that it was not just for eVTOL aircraft).

This council’s first foundational feature is independence. Instead of being wholly under any single professional society, it invites all to become joint sponsors. Joint sponsor obligations are minimal: pass council announcements to members and inform the council when members have news in our wheelhouse. This is a win-win because passing news conveniently serves their members. Furthermore, reciprocating by sharing their news gives joint sponsors a megaphone for promoting their activities, papers and corporate sponsors.

The second foundational feature is the council complements — not competes with — joint sponsors. We encourage council members to contribute by publishing via their home organization. We don’t charge membership dues or host in-person symposiums outside the auspices of a joint sponsor. This council is a lean, transparent operation.

With these foundations, our charter and mission statement became a focused version of what professional organizations typically do:

The council is an open forum for flight testers of electric and novel VTOL aircraft configurations, covering the spectrum of sizes, categories, classes, payload/passenger combinations and piloting options. The complexity and energy concerns for large aircraft bring priority to those above the FAA Part 107 (>55 lb) limit. With emphasis on eVTOL, the council’s mission is to promote flight test safety, efficiency and knowledge for electric aircraft development, certification and qualification. The spirit is to advance knowledge through reciprocal contribution of non-proprietary information. The means is to openly collaborate on best practices and to share all council discussions, papers and recordings across three mutually beneficial areas: safety, rulemaking & standards, and efficiency.

Our last chartering discussion settled how to broadly proceed.

• Promote various digital, virtual or in-person collaboration forums for discussions
• Manage a repository for unpublished papers, internal discussions, guidelines and other content germane to electric and powered-lift flight testing
• Promote collegiate and technical talent networking
• Launch standing or ad-hoc committees for popular but narrowly focused topics

With all the above established, we formed a structure to execute, weaving three venues to continually communicate and archive.

1. Email for communicating all reports, announcements and reminders.
2. Video conferencing for real-time collaboration. SFTE host some council meetings while VFS does so regularly and hosts large-audience webinars, posting some on the VFS YouTube Channel (www.youtube.com/VTOLsociety).
3. Website for archiving and sharing content. While the council offers all its work openly, so far only VFS established an E-VTOL FTC library. The left side of the screenshot succinctly shows its organization. Everything we produce is shared here, ranging from meeting reports and session recordings to open papers, member synopses and our mission statement. Also shared are reviews and links to material owned outside the council. We encourage vendors to advertise relevant services and encourage participants to add to our training folder, and our words, acronyms, terms and abbreviations (WATA) list. The right side of this screenshot shows the most recent posts.

As a bonus, our community on the VFS Hover site (https://hover.vtol.org) includes a Discussion Forum, Members List and Community Home page showing recent posts. Beyond VFS’s generosity in hosting meetings and maintaining this site, they grant access to all council participants. The E-VTOL FTC greatly appreciates these contributions to our mission.

Common throughout the weave is our biweekly meetings, each of which begins with the following regular updates.

Liaison reports. Our liaison roster includes VFS, SAE, SFTE, the Flight Test Safety Committee, EASA, EUROCAE, the AIAA Flight Test Technical Committee and several working groups within ASTM. Liaison expectations are simple: inform your people about council activities interesting to them and vice-versa.

Rosetta Stone. This simple file captures WATA unique to our niche. It is called the Rosetta Stone to invite competing definitions or descriptions and better understand what each of us mean.

Technical papers relevant to our work. With tipoffs from liaisons and others, we pursue a comprehensive compilation. This searchable file contains titles, synopses and links to published papers from sources around the globe. Akin to film critic reviews, this is known as Pec’s Picks, recognizing Ryan Pecoraro’s (Boeing) initiative and curating perseverance.

External Events. Conferences, talks and webinars hosted outside our council.

Internal Events. Less regular, but always on our radar, are opportunities to host webinars for members or a wider audience. For the latter, we ask joint sponsors to spread the word. Any relevant topic is fair game, with our first year covering SVO, the NASA AAM National Campaign, systems theoretic process analysis (STPA) and “eVTOL Certification 101.”

Electric Flight Test Committee. Chaired by Peter Schmidt (Transcend Air), this addresses batteries, the peculiarities of converting conventional takeoff and landing (CTOL) to eCTOL, lessons and distributed electric propulsion (DEP).

MOC Harmonization Committee. Chaired by Tony Mumford (Overair), they discuss the testability of and compatibility between proposed means of compliance (MOC) standards. Here is an informal yet informed feedback venue to build industry consensus. Always fast-paced, the above updates take 10 to 30 minutes, leaving the rest of the time to dig into the topic of the day. A few of our first year’s topics included:

• EASA’s proposed text for MOC 2, “Special Conditions for VTOL Aircraft”
• EUROCAE’s proposed standards for flight test maneuvers for VTOL aircraft
• Certification 101 and 102
• Simulator validation for training or taking Subpart B (“Performance and Flight/Ground Characteristics”) credit
• Separating aircraft airworthiness certification vs automation certification
• Flying FAA Flight Standards in the NASA Langley Cockpit Motion Facility
• Applicability of ADS-33 and the new AVT-296 report
• Approach angle constraints and susceptibility of RPM-controlled rotors to vortex ring state (VRS)
• Disturbance rejection methods, the Dryden disturbance model, control equivalent turbulence input (CETI)

Note: Council deliberations avoid the word “autonomy” when possible. Its misuse causes confusion about what it entails and unnecessarily rings alarms about crossing the human oversight Rubicon to the Terminator’s ‘singularity.’ We more accurately refer to “levels of automation” (see also, “Coming to Terms: ‘Levels of Autonomy’ is Unsound,” Vertiflite, Jan/Feb 2021).

Just a few topics on our to-do list include:

• Part 29.779 motion and effect of cockpit controls
• Flight test emergency procedures (numerous failure and recovery modes)
• Evaluating normal, degraded and emergency modes
• Dynamic Interface between aircraft, structures and winds
• How VTOL power relationships differ from rotorcraft
• Common facilities, safety equipment, instrumentation
• Testing communication/navigation system for UAM, including degraded communication
• UAS detect and avoid spectrum
• Safety paradigm shift (no longer relying on the pilot to compensate for system failures)
• Best practices for test hazard analysis
• Testing via remote vs onboard piloting

Because this Wild West is only temporarily lawless, organizations designing novel aircraft in a vacuum of assumptions are doomed. Just as entrants should keep apprised and influence the appropriate SDOs, they should recognize value in professional societies. The fledgling E-VTOL Flight Test Council serves this niche.

During our pioneer year, we gained excellent support from testers and organizations and saw membership grow to 230 people, discussing topics they nominate. Our independent, open council strives to be a universal venue linking content throughout this emerging niche. With everything in place, it remains for members to keep their end of the bargain by sharing non-proprietary knowledge, flight test experience and collaborating on best practices. Working through this Wild West, we are looking forward to the “Golden Age” of E-VTOL flight testing.

About the Author

Alan Lawless is a flight test subject matter expert at Aurora Flight Sciences, a Boeing Company. He joined Aurora in February 2019 after leading flight test and flight test engineering efforts at Honda Aircraft, Grob Aerospace and Cessna Aircraft. He started his career as a flight test engineer for the US Air Force and was the Chief of Academics and an Instructor at the National Test Pilot School, in Mojave, California. He has been active with SFTE since 1987, serving in several leadership positions, including as a Board Director, and served as the Technical Council Chairman from 2004-2020. He is an SFTE Fellow and an FAA Designated Engineering Representative (DER).