Onera Pitches Greener, Wider Structure for A320 Replacement

 - June 30, 2015, 10:32 AM
Onera's Nova concept features semi-buried turbofans, an egg-shaped cross section and an upturned nose.

French aerospace research center Onera has devised a twin-aisle, 180-seat concept airliner that would burn 20 percent less fuel than an Airbus A320neo. Dubbed Nova, the aircraft could enter service by 2030.

The fuselage adopts an ovoid cross section, which creates relatively flat upper and lower surfaces. As a result, it contributes to lift, by a few percent. “Lift no longer collapses between the wings; having a more evenly distributed lift creates less induced drag,” research engineer Olivier Atinault told AIN.

However, the egg-shaped section does not withstand the strains exerted by pressurization cycles as well as a circular one. Therefore, structural reinforcements will make the ovoid cross section heavier. “But thanks to the seven-abreast layout, the fuselage will be made shorter and the bottom line will be a slightly lighter structure,” Atinault said.

Onera designers found another new tradeoff with downward-oriented winglets. Turned upwards, they would more effectively weaken turbulence and, thus, reduce drag. But conventional winglets also tend to increase the bending moment at wing root and, therefore, need some strengthening. Oriented downwards, winglets make the tradeoff between aerodynamics and structural weight better, Atinault emphasized. He noted the wing root dihedral might increase to ensure enough ground clearance at the wing tip.

The nose section appears “raised,” with strong longitudinal asymmetry. The shape accelerates the airflow above the upper surface and creates a small amount of lift over the first meters of fuselage, Atinault explained. He noted that designers took into account visibility through cockpit windows with virtual pilot dummies.

Ultra-high-bypass-ratio turbofans (over 16, much greater than today's 12.5 on a Pratt & Whitney PW1100G-JM) would power the Nova. Fewer but thicker and more robust fan blades can more easily “swallow” a distorted airflow. Therefore, the engines can be “semi-buried” to ingest the boundary layer. Seen from the turbofan, the boundary layer flows more slowly than the outside air. “Accelerating a slower airflow requires less power for a given thrust,” Atinault said.

The Nova concept aircraft could fly at a maximum speed of mach 0.82 and to a range of 3,000 nm at a slower speed. “All the technologies we have considered may definitely be ready for entry into service in 2030,” Atinault said. Onera did not consider potential production and cost issues.