The Natural Laminar Flow air foil is considered to be one of the key technologies to reduce drag and thus improve the performance of an aircraft, therefore reducing emissions. The Natural Laminar Flow Wing is recognized as a potential key technology for the next generation of aircraft.
The requirements of a Natural laminar flow wing differ significantly from a conventional turbulent wing, requiring changes to both the architecture of the wing, the aerofoil definition and the detailed design and manufacturing concepts.
The performance of a natural laminar flow wing requires very tight surface roughness and waviness tolerances and contamination free surfaces in the areas where laminar flow is to be maintained. Alternative leading edge moveable concepts and novel leading edge/wing box attachment concepts, and extremely slender LE sections also have to be addressed in the design.
In Phase 1 of the programme, the problem of how to achieve an aerodynamic surface of sufficient quality to support natural laminar flow had been addressed by GKN. In particular, a number of mechanical joint concepts had been evaluated against a very tight set of criteria including steps and gaps, surface finish, aerofoil profile, waviness and fastening techniques.
Phase 2 (of this project) formed the basis for the further development of the concepts for a ground-based demonstrator. The work on LE design was focused into five specific development activities: Innovative Wing Leading Edge Ribs and Integrated Leading Edge Cover solutions; Kruger flap integration into the D-Nose; Continued Investigations on potential Wing Ice Protection (WIPS) solutions; Lightning Strike protection for the Leading Edge zone; Bird strike risk assessment.
Phase two of the ground-based demonstrator (GBD) project was launched at the end of 2010 with the objective of developing a detailed design for the leading edge (LE) of a laminar flow wing. In the first half of the GBSSD (2) project the design was fluid. Although initially targeted at Kruegers two and six, after two months the investigation was refocused on the areas of Krueger four and Krueger five. This was a challenge for the design team because of the immaturity of Krueger mechanism design in this area. Many changes had to be made to datums, component locations and bolt positions to resolve clashes. As a result, the project was delayed by six months and ran over budget.
However, by the end of 2011 the mechanism design was finally established and work on detailed design could proceed. Concept down-select was achieved in April 2012 allowing the design to develop towards C-maturity and the detailed interfaces to be negotiated. The project was completed in July 2012 with a successful C-Mat review of the design.
The achievement of this design was an important milestone in the Clean Sky programme because it forms the 'baseline design' taken into GBD phase three. During GBSSD (2) work continued on establishing the feasibility of the wing ice protection system (WIPS) culminating in thermal fatigue testing of a representative section of the LE with integral WIPS.