ATR’s contribution to Europe’s Clean Sky research effort manifested itself most recently with the completion earlier this month of a second round of flight trials dedicated to testing an all-electric systems architecture on an ATR 72 turboprop. The team led by ATR shareholder Finmeccanica logged some 15 test hours during eight flights. The main industry partners involved Liebherr (for pressurization) and Thales (for the electric generator).
On the test aircraft, Liebherr’s environment control system drew a large electric load, Alessandro Amendola, ATR’s senior v-p for engineering, explained. The team simulated the other loads by, for example, using electric actuators for the control surfaces.
In flight, the systems—real or simulated—could turn on and off, depending on the flight phase. The automated system optimized power demand in real time, Amendola said. For example, the actuation system demands less power when in cruise. The energy management system is transparent to the pilot.
“Power is made available to the system that really needs it,” Amendola said, a way to achieve the design goal of cutting peak demand. Engineers can then design electric generators at the correct power level.
A major objective in designing an all-electric architecture centers on eliminating the engine’s bleed air offtake, thereby improving engine efficiency, Amendola emphasized. The Boeing 787 remains the only commercial aircraft to implement the concept.
For a regional turboprop, challenges differ. “We don't know yet whether the net balance is positive because, on the other side, the demand for electric power increases a lot, with associated weight penalties,” Amendola pointed out. Storage capacity must increase.
But new technology is now allowing for a favorable balance. Lithium-ion batteries weigh at least 30 percent less than those used just a few years ago. The power electronics used for generation enable better control and weigh less, too. For electric actuation, however, weight remains an issue.
ATR’s first Clean Sky test campaign took place last July. It concentrated on structures. An innovative composite material using a new resin with thermoplastic injection showed better impact resistance. Moreover, a visco-elastic insulation layer embedded in the layup reduced the higher noise normally associated with composites.
The new insulation material, however, introduces heterogeneity, which negatively affects the airframe’s material resistance. Engineers purposely created “micro impacts” to see if and how small cracks propagated and measured them in flight thanks to optic fibers. Analysis continues.