Passengers looking out the window of a passenger plane will likely have noticed slats on the leading edge of the wing, along with the flaps on the trailing edge of the wing, being extended during takeoff and landing. These leading edge slats provide the lift necessary at low speeds, with the gap between the wing and the slats directing air from the underside of the wing to the top. Unfortunately, this gap also generates a lot of noise. A team of researchers has now developed a morphing leading edge that eliminates the gap and reduces noise and drag during landing.
The “smart droop nose” developed by researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) working with partners Airbus, EADS Innovation Works and Cassidian Air Systems, literally morphs into a different shape during takeoff and landing so that no separate slats – and no gap – is necessary.
In developing the new leading edge, the researchers faced a number of challenges. "On the one hand, the structure needs to be very elastic, to enable it to morph to the required shapes, but on the other it has to be very rigid,” said DLR Department Head Hans-Peter Monner. Ultimately, the leading edge must bear around one third of the weight of the aircraft during landing."
The material also had to produce wing surfaces that are as flat as possible to achieve laminar airflow. Concentrating on the glass- and carbon-fiber reinforced composites typically used by the aviation industry, they found that glass-fiber reinforced material best fit the bill.
The droop nose design concept also sees the skin on the front edge of the wing curved, rather than stretched to minimize the stress placed on the material. Individual layers are then placed on top of each other so that the skin creates a structure with a customized rigidity distribution. The leading edge them morphs into the desired shape using actuators and support elements integrated along the wingspan.
The researchers have tested the system’s operation and performance in in one of Europe's largest wind tunnels at the Russian Central Aerohydrodynamics Institute’s (TsAGI) Zhukovsky research facility south of Moscow and found that the morphing leading edge can be lowered by up to 20 degrees with virtually no loss of lift.
The team plans to continue development of the concept to meet industrial requirements, such as lightning protection, de-icing and the ability to withstand bird strikes.
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