Aerospace Insight Blog

BILL READ reports on the acceleration in green e-taxiing technology for airliners - promising fuel savings for airlines while still on the ground.

The WheelTug system can be fitted to an aircraft nose wheel in under two hours, according to the company (WheelTug).

In addition to the widely publicised air displays and big order announcements at the recent Farnborough Air Show , there was also much of interest to be seen in the exhibition halls – including two innovative solutions designed to save airlines’ fuel while taxiing at airports.

Currently, departing aircraft need to be pushed backwards from the ramp using a tug, after which they use their engines to move forward to and from the runway. However, running the main engines while the aircraft is taxiing uses up fuel and increases costs for an airline, particularly if there is a lengthy queue for take-off or to be allocated a gate at the airport terminal. Running the engines also creates CO2 emissions and local noise, as well as the running risk of foreign object damage (FOD) from debris on the ground.

Front wheel drive

WheelTug’s electric drive system being tested on a Germania 737-700 at Prague Airport. (WheelTug)

Two companies at Farnborough were exhibiting different alternatives to using aircraft engines for taxiing. WheelTug has developed an electric motor powered by the aircraft’s auxiliary power unit (APU) to which can be fitted to an aircraft’s front nose wheel, enabling the pilot in the cockpit to control push back and taxiing to and from the runway. Designed for Boeing 737 and Airbus A320 aircraft, the system can be installed or removed within two hours.

In June Gibraltar-based WheelTug conducted a four-day trial of its electrically-powered nose landing-gear system using a Germania  Boeing 737-700 at Prague Ruzyne Airport. The tests proved that the system had sufficient power from the APU to move the aircraft in wet weather conditions, on oily ground or on a slope, as well as when the 737 was fully loaded (for this test, the rear cargo compartment was filled with water containers to move its centre of gravity aft).

WheelTug’s estimated fuel savings for ground operations per aircraft. (WheelTug)

WheelTug claims that its system can save airlines up to 80% of fuel during ground operations. A Boeing 737 uses between 24- 27lb of fuel per minute taxiing using its engines, while using its powered wheel system will only use 4lb of fuel per minute from the APU. The company estimates that airlines could save over $500,000 per aircraft per year.

“We’ve aiming for certification by the end of 2013,” says WheelTug’s operations analyst Joseph Cox. A number of airlines have already expressed interest in acquiring the system for Airbus A320s and Boeing 737s, including Alitalia in Italy, Israeli carriers El Al  and Israir and Jet Airways  in India. These customers were supplemented by Turkish operator Onur Air which signed a letter of intent during the air show to lease the system for 22 A320s and A321s.

Taking the tug

The TaxiBot concept – in model form …

An alternative system was on offer from Israel Aerospace Industries (IAI)’s TaxiBot which involves towing aircraft to and from runways using a semi-robotic tractor tug supporting the nose wheel. The nosewheel is connected to a rotary table and the tug can be moved and steered from the cockpit using a special interface system linked to special sensors. As well as offering the environmental benefits of engineless taxiing, TaxiBot claims that its system has the additional advantages that it does not require any alterations to the aircraft or its APU, no modification downtime or the addition of extra weight.

Developed by IAI in co-operation with Airbus and the TLD Group, the TaxiBot system was first tested in the spring of 2011 on an Airbus A430-600 at Chatoroux Airport in France and on a Lufthansa  747-400 at Frankfurt Airport in Germany. During 2012, the company will develop maintenance and training techniques, after which a second set of tests are planned at Frankfurt Airport in mid 2013 in which three narrowbody TaxiBot tractors will be used to tow Lufthansa 737s in regular day-to-day service (a letter of intent for which was signed at the show). These ‘beta’ tests, which will be carried out in conjunction with Lufthansa’s ground-handling division Lufthansa LEOS, are intended to provide operational data on the system which can be used to develop the tractors towards full series production by ground support equipment specialists TLD France using electric drivelines from Siemens. If the tests are successful, Lufthansa is expected to place orders for the system while US equipment leasing company Bankers Capital has already signed a letter of intent to buy TaxiBot tugs for use in North America. A version of the TaxiBot suitable for larger widebody aircraft is scheduled to be developed a year after the narrowbody version.

And in reality. (TaxiBot)

IAI estimates that the TaxiBot system could reduce a typical Boeing 747 fuel consumption on the ground from 1,250litres to 25-30litres. If used by the total worldwide fleet of narrow bodied aircraft, it could reduce total annual ground taxi costs from $8.7bn down to $2.9bn and for all widebody aircraft from $23bn to $3bn.

Safran and Honeywell are trialing e-taxiing with this A320. (Safran)

Other companies are also developing non-aircraft engine taxiing systems, including two main wheel electric drive systems being developed by Safran and Honeywell, as well as by L-3 Communications in the US in partnership with UK-based Crane Aerospace.

Greener taxiing is on the way.

Germany's DLR electric taxiing system would use a fuel cell to be even greener.