IN EARLY December, German MRO Lufthansa Technik (LHT), in partnership with L-3 Communications, successfully completed the first taxi trials of an aircraft powered by electric motors attached to the main undercarriage.
Developed as a proof-of-concept demonstrator, the e-taxi system uses water-cooled, permanent magnet motors attached to the inboard wheels of each main landing gear to propel the aircraft both forwards and backwards – with power being supplied from the Auxiliary Power Unit (APU), the aircraft is able to manoeuvre on the ground without using its main engines.
A Lufthansa Airbus A320 underwent two days of modification at LHT’s Frankfurt facilities ahead of the trial, with the two electric motors being fitted in place of two braking units. The temporary nature of the installation was immediately apparent with power cables and coolant hoses running from an open passenger window to the motors via the wing trailing edge. Ancillary equipment was installed behind a modified panel in the aft cargo hold, and operational controls were fitted on the flight deck.
With the ultimate aim of integrating the system into conventional airport operations, the five-day trial covered 40 criteria over a variety of ground manoeuvres, including sustained taxi at a speed of over 15mph (25km/h), runs up inclined surfaces and a range of reverse movements. Other parameters examined the break-away momentum required to move the aircraft from a standing start, acceleration, heat development within the motors and energy consumption during various phases.
Christian Mutz, LHT’s Programme Manager – Innovation, spoke enthusiastically about the project, remarking that although the performance of the e-taxi system was as good as he had expected, he was “surprised” by the remarkable agility shown by the A320 during manoeuvres such as pivoting on the spot around the main landing gear in both forward and reverse directions. Indeed, on the evening of December 6, the aircraft operated around Frankfurt Airport amongst conventional traffic and demonstrated the ability to complete a 180-degree turn on a 130ft (40m)-wide taxiway; barely wider than the A320’s wingspan.
“This revolutionary system utilises green technology to improve aircraft autonomy and provide more environmentally-friendly ground operations. Studies demonstrate single-aisle aircraft can burn more than 3% of the total fuel during ground operations. We are convinced that this system will provide significant economic and environmental benefits to the aircraft operators and airport service providers,” said Joe Hoffman, Vice President and Executive Programme Manager of L-3’s team.
He added that: “As a feasibility study, the e-taxi trial appears to have met its objectives, though the main driving factor in moving the project forward will be whether it is economically viable.” Mr Mutz commented that the electronic motors are over-engineered in their current form (the aircraft was able to taxi using just one of the two motors installed) but had allowed LHT to demonstrate the technology. Any longer term refinements would take into account lessons learned during the trials, while obvious problems such as compromised braking performance due to the removal of two brake units would also be considered.
“The system offers significant fuel savings, improved turnaround times and reduced engine maintenance,” Mr Hoffman remarked, noting that e-taxi would appear to be well suited to aircraft operating high-cycle, short-haul routes.