Natural Laminar Flow was one of the principal new wing technologies to be applied in the near future to reach the challenging fuel consumption and emission reduction objectives stipulated in ACARE’s Vision 2020. NLF air foils are shaped in such a way to avoid laminar to turbulent flow transitions in cruise which creates increased viscous drag, hence larger fuel consumptions and more emissions.

Krueger flaps are suitable as high lift devices for NLF, because they leave the upper wing surface clean when retracted. Furthermore, when fully deployed during take-off and landing, the main Krueger panels form a kind of deflector that protects the fixed leading edge from accumulation of insects or dirt and from surface erosion due to rain or hail during low-altitude flights. Such accumulations and erosions, resulting in wing surface discontinuities, could significantly increase friction drag by causing loss of laminar flow in the affected areas.

In the frame of DEAMAK, ASCO Industries N.V., a Belgian company involved in the development of the high-lift devices on all recent major aircraft programs (A380, A400M, Boeing 787, A350XWB, Bombardier C Series), designed and manufactured the Krueger flaps and the corresponding interface struts that were mounted on the new NLF outer wing sections of the A340 Flight Test Demonstrator. This aircraft was used within Clean Sky’s SFWA-ITD to among others assess the leading-edge insect-shielding efficiency of Krueger flaps during landing and take-off.

The proposed technical work was divided into four work packages dealing with the design, the manufacturing, the handling and transport as well as the validation and verification of the Krueger flap and wing interface struts. The project lasted 73 months in total. The budget was estimated to be €759,840.