Demonstration to show airliners could manoeuvre on ground without engine power
An advanced electric-drive system that will enable crews to taxi and manoeuvre aircraft without using engines will be tested by Boeing on a 767 later this month.
The proof-of-concept on-board electric-drive device is being developed by Chorus Motor, an electric-drive technology specialist and subsidiary of Borealis Exploration, under a Boeing Phantom Works-led programme. Chorus, a "virtual" company based in Gibraltar, is providing a version of its Meshcon system.
The demonstration is being conducted on a 767 to prove the electric-drive system is powerful enough to handle large aircraft. "It could just as easily go on a 777 or a 747 because the technology is adequate to deal with any size of aircraft," says aerospace applications programme manager Robert Carman.
To get more torque out of an electric motor, it is necessary to increase the current handling capabilities of the inverter. However, this usually requires a larger, more expensive inverter, not all the capacity of which is usable because of limits on the total power available. The Meshcon system gets round this by regulating the voltage required by the inverter at various speeds, allowing the inverter to deliver all its power at reduced motor speeds.
Carman says the Meshcon system has been developed specifically for traction and increased low-speed torque loads, and applications for which starting torque requirements are higher than the continual torque requirements. The system uses multi-phase motors in which the windings are connecting several inverter terminals to each other, and not the ground. The different connectors act like different gear rates, and the motor can electronically change "gears" by operating the inverter at the harmonics of the drive frequency.
The system therefore uses harmonic drive to essentially fool the drive electronics into thinking they are operating at a higher speed. The net benefit is that the motor drive can achieve five times the torque speed of a similarly sized machine and is therefore much smaller and lighter.
"We believe the ability to integrate it into a weight-sensitive application is totally feasible," adds Carman. The demonstration is not representative of a flight-worthy system, suggesting that the drive system is being temporarily integrated into the nose gear bay and undercarriage leg rather than into the fuselage. The concept dovetails with Boeing's move to a more-electric aircraft philosophy, as is being pursued with the 787.
GUY NORRIS/LOS ANGELES
Source: Flight International
