The Natural Laminar Flow (NLF) aerofoil is a potential key technology for the next generation of aircraft, improving the performance by reducing drag, and hence reducing emissions.
The requirements of a NLF wing differ significantly from a conventional turbulent wing, requiring changes to both the wing architecture, aerofoil definition and the detailed design and manufacturing concepts. The performance of a NLF wing requires very tight surface roughness and waviness tolerances and contamination free surfaces in the areas where laminar flow is to be maintained. NLF wings also require alternative Leading Edge (LE) moveable concepts, novel LE/Wing-box joints, and slender LE sections.
This proposal was for the design of the starboard LE and Upper cover for a NLF Wing flight demonstrator. The baseline solution was a metallic LE and composite Top Cover. The LE and Top cover was joined to a wing-box (outside of scope) and attached to the flight test demonstrator which will be an A340, with the outer third of a starboard wing (from Rib 28 to wingtip) replaced.
The demonstrator aimed to validate that a jointed wing concept (LE + Top cover) can be manufactured in realistic high rate and repeatable conditions appropriate to a civil short-range aircraft to the required level of aerodynamic surface quality to achieve laminar flow.
From experience on existing Clean Sky Smart Fixed Wing Aircraft (SFWA) calls, current LE and Top Cover design and manufacture capability, and thorough investigation into the Call, GKN recognised the very demanding tolerance and hence manufacturing requirements to achieve a successful demonstrator outcome.
It is understood that any proposed solutions, for LE or Top Cover design, must be developed and proved to such a level that the components can obtain flight clearance for test. GKN believed that ‘traditional’ wing manufacture and assembly techniques will be unable to achieve the required tolerances at an acceptable cost, and therefore novel techniques and concepts will need to be investigated.
The NLFFD program is an ongoing area of research aimed at developing the capability and understanding of Natural Laminar Flow (NLF) for the next generation of civil aircraft. It is undertaken in support of the Smart Fixed Wing Aircraft (SFWA) program to mature a NLF technology stream for a future short range transport aircraft and is intended to support the TRL process by the design, manufacture, test and demonstration of an integrated NLF wing leading edge assembly, as a flight test demonstrator
The NLF aerofoil coupled with improved aerosmoothness, offers higher efficiencies in aerodynamic performance and a reduction in drag, contributing to an overall increase in an aircraft’s efficiency. This in turn allows for potential reductions in aircraft emissions by reducing fuel burn. Achieving these reductions would be a significant step towards reaching the ACARE goals for 2020, including a 50% reduction in CO2 emissions and an 80% reduction in NO emissions.
The requirements of a NLF wing differ significantly from a conventional turbulent wing, requiring changes to the architecture of the wing, the aerofoil definition, the detailed design concepts and manufacturing processes. The aerodynamic performance of a natural laminar flow wing is highly dependent on meeting very high aero-smoothness tolerances including steps and gaps, surface roughness and surface waviness tolerances, in the regions where laminar flow is to be maintained.