Ricardo worked with Israel Aerospace Industries (IAI) over a period of about 15 months to engineer and deliver TaxiBot, a demonstrator robotic, pilot-controlled tow vehicle capable of operating with both wide- and narrow-bodied commercial airliners. Its anticipated widespread use is expected to require no modification to aircraft, taxiways, or runways, and only minor changes to airport infrastructure, while reducing both noise and air pollution.
Ricardo based the first fully operational TaxiBot vehicle on a Krauss-Maffei PTS-1 aircraft towbar-less tractor donated by Lufthansa LEOS. Ricardo heavily redesigned, modified, and rebuilt the vehicle, part of which included installing IAI's patented turret concept as well as energy absorption systems and controls.
Three key modifications engineered by Ricardo were the installation of the turret, to which the aircraft nose wheel is clamped; a platform that can tilt and move axially; and chassis extensions, including an additional axle set. The resulting six-wheeled vehicle is capable of towing Boeing 747 and Airbus A340 airliners.
The demonstrator vehicle has a mass of 52 t (57 ton) and is powered by twin, 500-hp (370-kW) V8 diesel engines. It features a hydrostatic drive system and hydraulic systems that handle the four-wheel steering and aircraft pickup and clamp actuators. Dual Ricardo rCube electronic controllers manage the forces applied to the nose landing gear as well as vehicle speed and all the communications with the electronic systems for navigation, speed setting, and control tower integration, as well as the operational logic of the vehicle systems and the pilot interface.
To get a sense of how the vehicle works, on engaging with the TaxiBot, the nose wheel of the aircraft enters the turret and is clamped securely into position. As Ricardo explains, the turret is able to rotate freely and can take steering and braking requests directly from the nose wheel in such a way that the pilot should normally not notice he or she is being towed.
Ricardo says that one particular “crucial aspect” of the TaxiBot design is that the aircraft brakes slow the aircraft down, not the tug. With the TaxiBot engaged, the flight crew can maneuver the aircraft around the taxiways of the airport, relying solely on auxiliary power units for onboard power and air-conditioning needs.
IAI developed and provided a “high-level” vehicle controller that will integrate with airport control towers and provide speed targets, towing force, and other mission data while constantly monitoring geographical position. While the current demonstrator assumes that an operator is present in the vehicle, the control architecture of the vehicle is already in place to support autonomous tug operation so that “in the near future” no tug driver would be needed for taxiing.
To test the TaxiBot prototype demonstrator, Ricardo designed and built, in parallel with the vehicle program, a 100-t (110-ton) test trailer equipped with a hydrostatic dynamometer capable of simulating large passenger aircraft tire drag. The trailer uses an actual 747 cockpit and nose landing gear to fully replicate the processes both of towing and flight deck control of the tug. Extensive testing of the TaxiBot with the trailer is currently under way by Ricardo at Dunsfold Aerodrome in Surrey.
Once that testing is complete, the demonstrator vehicle will be shipped to Toulouse airport where it will be used in further tests probably in February with a 350-t (385-ton) A340-600. The Ricardo team on the TaxiBot program will continue to support the development work throughout that next phase.
After further testing and development, TaxiBot may potentially play a significant role in the reduction of fuel costs and emissions. According to IAI and Airbus, taxiing to and from airport terminal gates using the aircrafts' main propulsion engines results in a fuel consumption forecast to cost around $7 billion by 2012, CO2 emissions of approximately 18 million t (20 ton) per year, and a significant amount of foreign-object-debris damage, costing around $350 million per year.