A new remotely-controlled towing tractor containing drive technology from Siemens could be a reliable fuel-saving alternative for taking airplanes from the gate to the take-off position.
Airplanes currently use their own turbines to arrive at the take-off position. The taxiing consumes approximately one metric ton of fuel, depending on the size and distance covered. The diesel-electric tractor can attach itself to the nose wheel and pull the plane up to the runway. This results in the aircraft turning on it’s engines only when it is ready for take-off.
After extensive testing, Lufthansa has started using taxiing robots (TaxiBots) at Frankfurt International Airport. The tractors have contributed to savings of up to 11,000 metric tons every year since their deployment. TaxiBots is a joint project amongst Siemens, French TLD Group, Lufthansa LEOS and Israel Aerospace Industries.
TaxiBots produce less noise than turbines and also reduce the strain on aircraft engines, thereby increasing the maintenance intervals. They can tow narrow-body aircraft such as Boeing 737 and Airbus A320. These narrow-body TaxiBots save up to 150 kilograms of fuel with every taxiing mission.
Further trials are underway for Wide-Body TaxiBots for planes such as the Boeing 747-400 and Airbus A380 at the Chateauroux Airport, France.
TaxiBots for narrow-body aircraft has about 500 kilowatts drive output, and the Wide-Body model can generate 1 megawatt power. The four wheel pairs are driven using electric motors with each individual wheel containing it’s own drive motor.
Siemens is supplying these tractors with powertrains, consisting of electric motors, generators, converters, electronics and software. Most of the components, though based on ELFA hybrid drive system for buses, are specifically developed to the requirements of TaxiBots, which require high torsion and short response times.
The system contains two diesel engines drive-two generators for producing electricity. The converters turn electricity to a state usable by electric motors and based on the tractor models, they can be equipped with six to 16 converters.
Wide-Body TaxiBot systems can be separated to different pieces in case of a fault. This keeps the functionality of two-thirds of the drive system intact. In case of a short circuit, the electronics developed by Siemens switches off one third of the drive system automatically.
Siemens engineers developed the new wheel module consisting of it’s own motors. Engineers also optimized Wide-Body TaxiBot technology with permanent-magnet electric motors, which are much more efficient than conventional asynchronous machines.
An exciting feature of the wheels is that a TaxiBot can control the electric motor of it’s wheels separately. This is a major advantage while turning since the force required to turn the wheels while pulling an aircraft is considerably high. The TaxiBot can use different amounts of force to the two wheels or even drive them in opposite directions.
Airline regulations dictate that pilots should have sole control over an airplane. TaxiBot has been developed in line with these regulations. When the pilot brakes the plane using the landing gear, the TaxiBot responds in 130 milliseconds and brakes so that the nose wheel does not experience any strain.
The nose wheel is attached to TaxiBot using a special interface mechanism which registers the pilots steering and braking maneuvers, which is then translated as commands for the tractor wheels. The software for controlling these wheels is also made by Siemens.
Excerpts from Siemens. Image courtesy of Lufthansa LEOS
