Regional airlines may have shed their humble origins as commuter carriers, but regional aircraft are still best known for their simplicity and economy, rather than their technology. But that must change if the sector is to make its contribution to the aviation industry's commitment to reduce its environmental impact.

The important reductions in fuel burn and greenhouse-gas emissions now possible with the latest long-haul airliners such as Boeing's 787, and promised for next-generation single-aisle aircraft such as Airbus's A320NEO, are harder to achieve with smaller regional types making many short hops a day.

Significant improvements in efficiency and reductions in emissions on short flights require new technology but, over the decades, there has been little research directed specifically at the regional sector. The airlines' demand for low equipment prices has made it hard to get a return on such investments.

But that is changing with the inclusion of regional aircraft under Europe's Clean Sky research program. Launched in 2008, Clean Sky is a seven-year, €1.6 billion ($2.1 billion) technology initiative funded equally by the European Commission and industry with the goal of developing technology for cleaner and quieter aircraft.

The result could be a new 90-seat regional turboprop with composite airframe, laminar-flow wing, low-noise landing gear and all-electric systems, or a new 130-seat small airliner with similar technologies and either geared-turbofan or open-rotor propulsion.

Clean Sky's Green Regional Aircraft (GRA) technology demonstration is lead by Alenia Aeronautica, a partner in the ATR aircraft consortium.

The GRA project's objectives are to mature new technologies in five domains: low-drag, low-noise aerodynamics; lightweight materials and structures; all-electric systems; avionics architectures and trajectory management; and new aircraft configuration. These technologies are to be raised to a readiness level of 5 or 6 through ground demonstrations, wind-tunnel and flight tests.

Combined with new powerplants developed under Clean Sky's Sustainable and Green Engines project, these technologies have been shown in simulations to enable advanced regional aircraft configurations to meet the Clean Sky target of reducing carbon-dioxide emissions by 10-20% and noise by 10 db relative to 2000 technologies, says Andrzej Podsadowski, GRA project officer.

“There are three main full-scale ground demonstrators: the composite fuselage barrel demo, the composite cockpit demo and the composite wingbox demo,” he says. “All of these apply to a 90-passenger turboprop.” Tradeoffs between advanced metallic and composite materials and manufacturing concepts have been conducted, leading to the selection of composite technologies for final demonstration.

“They are based on considerable weight reduction due to more innovative multi-functional layer and multi-layer architectures that ensure electrical conductivity and lightning resistance without additional weight,” says Podsadowski. “In addition, we will see better acoustic insulation, increased hail impact resistance and the possibility to embed sensors in the composite to monitor the health status of the structure and report any degradation of its mechanical properties.”

Other technologies have been down-selected across the airframe, from cockpit and cabin to wing. “For the wing, we are focused on high-performance devices for noise reduction,” he says. According to Podsadowski, the biggest challenges are a natural laminar-flow wing for reduced drag and fuel burn; load control and alleviation to save structural weight; and reducing external noise from high-lift devices and landing gear through aerodynamic optimization to reduce the turbulence they generate.

Construction and testing of the demonstrators planned under GRA runs from late 2012 to the end of 2015. Flight demos will focus on reducing or eliminating hydraulics and pneumatics and replacing them with electrical systems for ice protection, cabin pressurization and air conditioning, flight controls, landing gear operation and braking activation. This bleedless architecture will enable the engines to be more efficient at producing thrust. “This will be the first step toward the so-called all-electric aircraft, where all onboard utilities will use only the electrical power from generators driven by the engines.”

Technologies selected for flights testing on a modified ATR 72 include electrical environmental control and energy management systems, the latter providing 270-volt DC power distribution and control logic with electro-mechanical actuators for the rudder and landing gear providing electrical loads.

Wing load control and alleviation will be tested in the wind tunnel. Tunnel tests of low-nose nose and main landing-gear designs are scheduled for mid-2015. Also planned for 2015 are wind-tunnel tests of advanced regional-aircraft configurations: a 90-seat turboprop and two 130-seat aircraft, one powered by geared turbofans and one by open rotors. “Tradeoff studies are being performed on 130-seat configurations with under-wing and rear-fuselage geared engines,” says Podsadowski.