To minimize fuel burn, noise, and environmental impact, novel technologies to move aircraft from gate-to-runway and runway-to-gate will be introduced. Rather than changing flight procedures, due to their comparative rigidity, airlines will more likely adopt integrated ground propulsion as a method of saving time and fuel. Of the multiple mechanisms of IGP studied, on-board systems produce the greatest reduction in emissions and the best cost-efficiency, while external systems reduce fuel burn at the cost of increased NOx emissions. Electric systems could also be adopted to enhance the process.
One concept is for tugs to be replaced by an APU powered motor-generators that drive the associated aircraft wheels. Another concept is for tugs to bring aircraft all the way from the gate to the runway. WheelTug is a fully integrated ground propulsion system for aircraft which puts a high torque electric motor into the hub of the nose wheel to allow for backwards movement without the use of pushback tugs and to allow for forward movement without using the aircraft’s engines. WheelTug will drive the aircraft with power supplied by the onboard APU (Auxiliary Power Unit). The first version was designed for the Boeing 737NG.
One recent design proposes an integrated vehicle dynamics control, or IVDC, algorithm. This system would use nonsingular fast terminal sliding mode (NFTSM) to coordinate active front steering and direct yaw movement, enhancing handling and providing vehicle stability. A non-automated system in the works at NASA involves turboprop technology. The SCEPTOR X-Plane, built with fold-out propellers and wingtip vortex propeller integration, is currently in the testing phase, with test flights scheduled to run until 2018. The goal is to increase propeller efficiency from 28% to 92%, while reducing noise by 15 dB on average.
Enhanced ground propulsion systems will have economic impacts as well as safety impacts. Data from WheelTug, presented at the IATA Singapore Conference in 2017, indicates that airline profitability is inversely correlated with aircraft ground time. The effect is consistent across multiple airlines in multiple nations.
- Runway incursions
- Ineffective new pilot interfaces
- Inadequate visibility from the flight deck
- Failure to complete engine run-up and checklists
- Damage to nose gear due to frequent coupling/uncoupling with propulsive tugs (for both towbar and no-towbar, wheel capture approaches)