Lufthansa and technology company L-3 Communications have conducted taxi trials with an Airbus A320 equipped with electrical motors on both main landing gears (MLG) as part of a feasibility study to gain initial operational experience and data about a MLG-fitted electrical drive system.

The motors and control units were temporarily installed on the aircraft at Frankfurt International airport earlier this week. They are based on existing industrial components manufactured by L-3's Magnet Motor subsidiary in Starnberg, near Munich, and already in use on other applications such as ground vehicles.

An engineering team comprising staff from Airbus, L-3 and Lufthansa Technik (LHT) replaced the brake assemblies of the inboard MLG wheels with drive units, each one containing a liquid-cooled electrical motor, powered by the aircraft's APU, and planetary gearbox.

Lufthansa e-taxi

© Michael Gubisch/Flightglobal

Power supply cables and coolant hoses were installed along the rear of the MLG, across the landing flap trailing edge, upper wing surface and through opened passenger windows into the aircraft's interior.

System control and ancillary equipment was installed in the twinjet's aft cargo compartment, which had been fitted with a special door with two large openings for cooling.

Operational controls were fitted on the flight deck and coupled with the nose wheel steering system. The two drive units were synchronized so that if, for example, the nose wheel was deflected to its 75-degree maximum, the motor on the respective inside wheel was stopped.

Lufthansa e-taxi

© Michael Gubisch/Flightglobal

The pilots reported that the demonstrator system not only handled well, but was more responsive than the main engines normally used for the task, said Christian Mutz, project manager innovation at LHT.

The team trialled a broad range of ground manoeuvres, including sustained taxiing up to a maximum speed of 25kph (13.5kts), a 180-degree turn on a 40m-wide (130ft) taxiway, runs on sloped surfaces, and various self-powered reverse movements.

Approximately 40 test points were covered to assess values such as brake away momentum for taxi start from standstill, acceleration, energy consumption, heat development and tyre deformation in different conditions.

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© Michael Gubisch/Flightglobal

The team varied tyre pressure, switched off one of the two drive units, and trialled taxiing with a fully fuelled aircraft.

Despite strong winds, with gusts up to 70kt, at Frankfurt airport on 7 December, no adverse handling was encountered with the electric taxiing system, said Mutz.

Acceleration values were a key focus particular in regard to crossing runways, for which aircraft usually must have two engines running in case of redundancy.

The flight crew also operated the system while the engines were running. Mutz said that while the powerplants provided sufficient thrust at ground idle to move the aircraft forward, the drive units were still able to reverse the twinjet. This was not only possible along a linear track, but the pilots were able to do S-turns and tight turns, he said.

Mutz added that the team was surprised about how agile and mobile the aircraft had become, and how easily the pilots adapted to the controls.

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© Michael Gubisch/Flightglobal

The test data will now be evaluated and flow in the specification of a potential electric drive system in the future.

L-3 and Lufthansa Technik are planning to design a system which could be retrofitted to in-service aircraft.

Installation of the demonstrator system took two days before tests began on 6 December. The equipment is currently being removed again, and the aircraft (reg. D-AIZF) is due to re-enter passenger service on 10 December.