IEEE Electrification Magazine - December 2017 - 11

Electric Taxiing Systems
The more-electric-architecture (MEA) and energy-optimized aircraft initiatives continue to be
dominating trends in the aerospace industry, as they have for the last two decades. The commercial aircraft business is increasingly using no-bleed air environmental control systems, variable frequency (VF) and dc power distribution buses, and electrical actuation, e.g., the Boeing
787 platform. The next-generation Boeing and Airbus narrow-body airplanes will most likely use
MEA. Some military aircrafts already utilize MEA for both primary and secondary flight controls.
Substantial progress in replacing hydraulic and pneumatic systems with electric systems has
been achieved.
The aerospace industry and the airlines have expressed interest in performing a taxiing
operation without the use of the main engine because of fuel savings and environmental
benefits. Other advantages for the aerospace industry and airlines include the reduction of
brake wear and the elimination of ground-tug operations. The next logical step is to implement electric taxiing using the electric power generated by the existing APU or alternative
sources, i.e., fuel cells or batteries. To justify various approaches, different companies and
universities have performed analyses and calculated estimates; many of their results have
been shared publicly.
For the first time, Teo et al. provided results of a comprehensive study of the technical feasibility of an electric wheel-drive taxiing system using publicly available aircraft and runway coefficient data. The study shows the potential for overall mission fuel burn reductions, particularly for
short-haul aircraft with a relatively long taxi time. The study also highlights that the wheel-drive
system needs to be considered as an integral part of the design of next-generation MEA, as it has
implications for other systems onboard the aircraft. Another important conclusion is that the
main-wheel-drive configuration offers greater applicability than the nose-wheel-drive configuration due to its better traction.
In his article, Re presents a tool to assess the global benefits in terms of fuel consumption and
emissions. Re considers the concept of an aircraft-integrated ground propulsion system and
determines its performances and weights, assuming the power source for the system is the APU
or a zero-emission device, (e.g., a fuel-cell). A model of the propulsion system integrated into an
object-oriented, midsized aircraft is generated, capable of precisely simulating an entire aircraft
mission. The results show a potential overall fuel savings of up to 2.6%, depending on the flight
mission and the duration of the taxi phases. The associated CO2 emissions may decrease by the
same amount.
Furthermore, nitrogen oxide, carbon monoxide, and hydrocarbon emissions might be reduced
by 64-80% compared to conventional ground operations. The aircraft model used in this article
has proved a powerful tool for assessing the performance of an electrical taxiing system and
comparing it with different real-world scenarios.
Oyori and Morioka focus on electric taxiing that does not require the use of jet engines or
the APU during taxiing, either from the departure gate to takeoff or from landing to the arrival
gate. The proposed approach examines these systems and proposes an ecologically sound
solution for reducing aviation emissions at airports for a 3% fuel burn reduction. Kjelgaard
provides a top-level comparison between the Honeywell/Safran eTaxi approach and the frontwheel-driven hybrid approach of WheelTug. However, this article concentrates primarily on
the EDS and its components rather than the entire eTaxi.

WIKIMEDIA COMMONS, JULIAN HERZOG

EDS
The commercial aircraft business is moving toward more fuel-efficient and environmentally
friendly operations. The high-power EDSs will play a significant role in this trend. In the eTaxi
applications, an Airbus A320 airplane is utilized to demonstrate use of the APU to power EDS to
taxi in and/or out of a runway. The EDS is the heart of the eTaxi. The function of the EDS is to utilize power from the APU electric generator and drive the wheels on each of the main landing
gear. In this way, it propels the aircraft in either the forward or the reverse direction as commanded by the pilot. The EDS is commanded by the system controller so that the aircraft can
move at a constant commanded speed or with a constant commanded acceleration. The pilot is
not required to constantly adjust the main-engine throttles and/or ride the brakes to control
taxiing speed. Consequently, the control of the aircraft is more efficient.
IEEE Elec trific ation Magazine / D EC EM BE R 2 0 1 7

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2017