Airbus says the drag-reducing effects of the experimental wings on its laminar-flow demonstrator aircraft are proving better than previously thought, making application of the technology on a next-generation aircraft more feasible.
In September 2017, the airframer began a flight-test campaign with an A340 that has been modified with reshaped outer wing sections to assess natural laminar flow on the aerofoil's upper surface.
Some 66 flight hours have been completed under the partly EU-funded project – dubbed Breakthrough Laminar Aircraft Demonstrator in Europe (BLADE) – said Airbus senior vice-president research and technology Axel Flaig, speaking at the ILA air show in Berlin on 25 April.
He says laminar flow could be observed from the aircraft's first flight and that the flow is more stable than expected.
While the theory and potential benefits of having an orderly, laminar, rather than turbulent, air flow in the boundary layer around the wings have been known since the 1980s, the challenge has been to manufacture wings on an industrial scale that are smooth and aerodynamically stable enough to sustain the benefits in regular airline operations.
A key area of the BLADE project has been to assess how robust the laminar flow is when the wing flexes and twists in the air, and which design methods can be employed to build such aerofoils.
Airbus and its industrial partners constructed the left wing laminar-flow section with an integrated upper-wing surface and leading edge, which was made of carbonfibre and required an extremely high degree of accuracy.
The right wing section followed a more conventional design with a carbonfibre upper wing surface and a separate metallic leading edge.
Flaig acknowledges small differences in aerodynamic effects between the two structures, but says both wings sustainably generate the desired effect.
The manufacturer is "very confident" that the project will achieve "more than we targeted", he says.
Airbus estimates that laminar-flow wings could reduce drag by around 10%, cutting fuel burn by up to 5% on an 800nm (1,480km) sector.
Furthermore, the aerodynamic benefits could be sustained during the flight tests at Mach 0.78 – a typical cruise speed for A320-family jets – while Airbus previously predicted that the aircraft would need to fly at M0.75 to deliver the fuel savings.
Flaig says the test have shown "the door is wide open" to employ the technology on a potential next-generation single-aisle aircraft from the late 2020s.
Test are scheduled to continue until 2019, with a plan to assess the effects of wing contamination on the laminar flow and to install a fixed Krüger flap.
Such a device is being considered as potential protection against insect contamination on the leading edge – which could disturb the laminar flow – and as a high-lift device for take-off and landing.