ANALYSIS: Green taxi systems gather momentum

Farnborough
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With airlines increasingly keen to examine every area of potential fuel saving, companies offering electric or automated taxi systems were present in force at the show.

The goal for airlines is to move aircraft between the ramp and the runway without running the main engines. As well as cutting fuel use - and CO2 emissions - engine wear is reduced along with the likelihood of foreign object damage.

As soon as the show gates opened on 9 July, US technology group L-3 Communications revealed a partnership with UK-based Crane Aerospace to jointly develop an electric wheel drive system for main landing gears.

The move follows a demonstrator test in Frankfurt last December, where L-3 installed a non-flyable drive system on a Lufthansa Airbus A320, using off-the-shelf components. The test was aimed at gathering specification data and exploring the concept of manoeuvring aircraft on the ground, using electricity taken from the auxiliary power unit (APU).

L-3 will be responsible for the motors and a clutch mechanism and Crane will provide the wheel drive and brake controls, power conversion electronics as well as integrate all the equipment in the aircraft systems monitoring architecture. A prototype system should be ready by the end of 2013, with certification to follow in 2015.

The news from L-3 was swiftly followed by an announcement from Israel Aerospace Industries, unveiling a six-month trial of its Taxibot pilot-controlled aircraft tow-tractor in partnership with Lufthansa. Starting in May 2013, the German carrier will employ three of the hybrid-powered tugs in Frankfurt to move its Boeing 737 fleet on scheduled flights.

The Taxibot still requires a driver like a conventional tractor to connect the vehicle to the aircraft and return it from the runway after take-off. However, Ran Braier, IAI's Taxibot programme director, says the cost of the driver will be "negligible" compared with the potential fuel savings. The aircraft will also require only minor modifications and gain no additional weight, unlike onboard drive systems.

If the test results are positive, Lufthansa will buy the system as launch customer, says Braier. Certification is planned for next year, with entry-into-service to follow in 2014.

The third company in the race is WheelTug. In June, the Gibraltar-headquartered engineering firm tested the first demonstrator of its nose landing-gear drive system, where motors were installed into both wheels of a Germania-owned Boeing 737-700. Previous tests employed drive mechanisms where the motors were not integrated into the aircraft's wheels.

The trial at Prague airport proved that the standard APU and generator set-up supplies "more than enough" electrical energy to move the aircraft and that the motors fit into the wheels, says WheelTug director Jan Vana. It also verified that the nose wheels have sufficient traction to move the aircraft even in adverse conditions such as wet weather or on a slope, he adds.

The test involved loading water containers in the rear cargo compartment, which brought the centre of gravity aft, with the aircraft being "close to the maximum take-off weight", says Vana.

WheelTug has accumulated five tentative clients - Alitalia, El Al, Israir, Jet Airways and, announced at Farnborough, Turkey's Onur Air - to equip a total of 232 Airbus A320 and 737 aircraft. Certification is planned for the fourth quarter of 2013.

Lastly, Safran and Honeywell are working on a main wheel drive system which, in principle, is similar to the L-3 project. The partnership has gathered specification data with a conventionally-powered A320 and 737. A prototype of the system is to be tested on an A320 by UK budget carrier EasyJet next year. Entry into service is planned for 2016.