The scene is a familiar one to airline passengers around the world.  Gazing through the glass of the terminal building, one sees aircraft being pushed back from their stand when loaded, fuelled and ready to fly by powerful aircraft tugs.  However, the days of these tugs may be numbered.  Thomas Withington explains.

Early WheelTug hardware is seen being used to tow a Boeing 767. Production versions are designed to fit entirely within the wheel envelope, and will fly with the aircraft. (WheelTug)

Gibraltar-based firm called WheelTug PLC has developed an electric motor, powered by an aircraft’s Auxiliary Power Unit (APU) which is built into the nosewheel undercarriage to enable the aircraft to move off the stand and then taxi to the runway, without having to use its engines for propulsion.
The company has already demonstrated its design, outfitting an Air Canada Boeing 767 in 2005 with a nosewheel motor which was able to move the aircraft at similar speeds to those used for taxiing; proving that the WheelTug concept was sound.
Several companies are involved with building different parts of the WheelTug product: Luxell of Canada produces the motor’s cockpit controls.  Wire harnesses are provided by Cooperative Industries of the United States; meanwhile, ICE Corporation, also an American firm, is responsible for the motor’s control system, while Gibraltar’s Chorus Motors builds the two motors powering the nosewheel.  It was the development of high-torque motor technology that was the key factor in enabling WheelTug to be developed, according to Isaiah Cox, the company’s Chief Executive Officer.
One of the key attractions of WheelTug is that it saves the airlines cash by reducing the amount of fuel they need to burn to propel the aircraft across the Tarmac when taxiing.  This will also please the environmentalists keeping an eye on the quantity of exhaust emissions that airliners generate when maneuvering on the ground, and queuing up waiting for departure.
For airports, an airliner equipped with WheelTug potentially reduces the number of tugs needed and the number of staff required to operate those vehicles.  The tugs also produce their own carbon emissions so, by default, WheelTug reduces the environmental footprint of these vehicles too.  Other financial savings are possible by diminishing the wear and tear on the nosewheel undercarriage during pushback, and the amount of braking required during taxiing as the aircraft’s ground speed would be easier to regulate with the electric motor.  WheelTug has calculated that by using its product, individual aircraft could save around 600 hours of engine operations per year when maneuvering on the ground.  From a safety point of view, not using the aircraft’s engines for taxiing would also reduce the chance of them ingesting foreign objects that may be present in the ramp area.
Mr Cox notes that the savings offered by WheelTug: “cover the fuel burned during the aircraft’s forward taxi roll, not just during pushback.”  As a comparison when using conventional pushback, WheelTug says that the cost of fuel burnt during taxiing is around $82, with up to $25 spent during pushback.  Per year, per airliner, these costs can escalate to $132,000 and $40,000 respectively during an average scheduled of operations.  There is a weight penalty to WheelTug, of around 300lbs (136kg), although the company notes that other additions to aircraft such as winglets, which are also designed to improve fuel efficiency, come with a weight penalty, typically of around 500lb (226kg).  Moreover, this weight penalty can be offset against the fuel needed for taxiing.
Tests of WheelTug’s systems are currently ongoing to gather more information regarding their performance.  The company notes that Boeing’s 737 Next Generation airliner would be a natural aircraft to feature WheelTug as: “buyer furnished equipment”, according to Isaiah Cox.  Another natural fit could be the Airbus A320, with WheelTug again provided as a customer option.  He says that WheelTug could be offered; “just as an airframe builder offers an in-flight entertainment system.”
Furthermore, the company has said that retrofit is possible vis-à-vis older aircraft such as Boeing 757 or legacy 737s.  Mr Cox notes that this would be a way by which airlines could reduce their environmental impact in the short term: “You can install WheelTug very quickly and this can instantly make a legacy aircraft more fuel and environmentally efficient.”
In terms of the project’s future, electrical load tests performed on a Delta Airlines 737NG have confirmed that an APU can produce sufficient electricity to power the WheelTug.  The company has already designed the cockpit controls, along with the wire harnesses connecting these controls to the APU and to the motor control unit.  The motor itself has been designed and proven along with its control software, as has the
motor control system.
The work left to be done includes the modification of the nosewheel undercarriage strut to accommodate the motor, and the motor’s installation; although this will not change the undercarriage’s major components.  The firm estimates that these last two processes could take up to 20 months of development, testing and certification with the Federal Aviation Administration in the United States.
Once tested, it will be necessary to receive certification on a bilateral basis with several other regulatory authorities around the world such as the European Aviation Safety Agency, the Japanese Civil Aviation Bureau and Transport Canada.  WheelTug is now on the look-out for risk-sharing partners for further investment to take their prototype into production, something it is confident that it can achieve by 2012.