IEEE - Aerospace and Electronic Systems - May 2023 - 18

Feature Article:
DOI. No. 10.1109/MAES.2022.3200933
Flight Guidance Concepts to Mitigate Flight Control
System Degradation in Urban Air Mobility Scenarios
Milan Vrdoljak , University of Zagreb, HR-10002 Zagreb, Croatia
Omkar Halbe
, Tim Mehling , and Manfred Hajek, Technical University of
Munich, 85748 Garching, Germany
INTRODUCTION
Urban aerial mobility (UAM) promises to revolutionize ondemand,
point-to-point passenger and goods transportation. At
the center ofthis revolution are hybrid-electric and all-electric,
heavier-than-air vertical takeoffand landing vehicles, abbreviated
as eVTOLs in the popular literature. eVTOL configurations
depart significantly from the conventional single main
rotor and tail rotor helicopter configuration that has dominated
low-altitude airspace for decades. Electric propulsion and flyby-wire
control systems offer far greater design freedom and
room for creativity than conventional helicopters. The diversity
among eVTOL aircraft configurations is also noteworthy, with
designs ranging from vectored thrust to fixed multicopters,
along with single-person configurations such as hover bikes
andpersonal flyingdevices.As oflate 2021, several innovative,
distributed, multirotor eVTOL configurations have been conceived.
In fact, there exist more than 500 eVTOL concepts
worldwide, up frommerely halfa dozen in 2016.1 While many
1See https://evtol.news/aircraft for an exhaustive list of eVTOL
concepts.
Authors' addresses: Milan Vrdoljak is with the Department
of Aeronautical Engineering, Faculty of Mechanical
Engineering and Naval Architecture, University of Zagreb,
HR-10002 Zagreb, Croatia (e-mail: vrdoljak@fsb.hr).
Omkar Halbe was with the Institute of Helicopter Technology,
School of Engineering and Design, Technical University
of Munich, 85748 Garching, Germany; he is now
with the CSIR-National Aerospace Laboratories, Flight
Mechanics and Control Division, 560 017 Bangalore, India
(e-mail: omkar.halbe@gmail.com). Tim Mehling and
Manfred Hajek are with the Institute of Helicopter Technology,
School of Engineering and Design, Technical University
ofMunich, 85748 Garching, Germany (e-mail: tim.
mehling@tum.de; hajek@tum.de).
Manuscript received 15 November 2021, revised 19 May
2022; accepted 19 August 2022, and ready for publication
23 August 2022.
Review handled by Omar Garcia Crespillo.
0885-8985/22/$26.00 ß 2022 IEEE
18
concepts are still on the drawing board, a few are already in the
advanced stages of development and flight testing, including
one eVTOL aircraft type having received military airworthiness
approval [1].
The ultimate objective of eVTOL manufacturers and
operators is to deploy these aircraft in commercial operations
for goods and passenger transport. However, obtaining
approval for commercial eVTOLUAMoperations over populated
areas or critical infrastructurewill require both the manufacturer
and the operator to demonstrate a level of safety that
is equal to or better than those applicable to current civil aircraft
types and operations. This is because commercial air
transport operations entail high operational risks to both the
aircraft occupants and third parties. Moreover, the sheer level
of novelty, configuration diversity, and lack of prior data and
experience imply that certification agencies will likely scrutinize
design artifacts more closely to assure safety and airworthiness
ofthe aircraft, its installations and occupants, and third
parties. To this end, the European Union Aviation Safety
Agency has published VTOL special conditions aimed at
establishing an overarching set ofsafety and design objectives
for eVTOL aircraft [2]. An important requirement therein is
to assure continued safe flight and landing after any single system
failure or a combination of system failures that are not
classified as catastrophic. The requirement additionally states
that continued safe flight and landing should not require
exceptional piloting skills. Here, piloting skills may be understood
in the context of the handling qualities of the aircraft
under consideration. Awidely accepted definition ofhandling
qualities was given by Cooper and Harper in [3]: " ...those
qualities or characteristics of an aircraft that govern the ease
and precision with which a pilot is able to perform the tasks
required in support of an aircraft role. " Cooper and Harper
proposed a decision tree to allow test pilots to rate their task
performance and aircraft characteristics. The outcome of the
decision tree is a handling qualities rating on a scale from 1 to
10 and a corresponding handling qualities level on a scale
from 1 and 3. Level 1 handling qualities indicate desired aircraft
characteristics and desired task performance with minimal
pilot compensation, whereas level 3 represents major
deficiencies. The key terms in the definition of handling
IEEE A&E SYSTEMS MAGAZINE
MAY 2023
https://orcid.org/0000-0002-2948-3523 https://orcid.org/0000-0002-7119-3239 https://orcid.org/0000-0002-3853-9904 https://evtol.news/aircraft
IEEE - Aerospace and Electronic Systems - May 2023

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