GKN Aerospace announced in January that it has delivered wing components as part of a major research program to test and measure the benefits of natural laminar flow (NLF) designs during trials on the wing of a flight test aircraft. The Breakthrough Laminar Aircraft Demonstrator in Europe (BLADE) project is part of the Clean Sky Smart Fixed Wing Aircraft (SWFA) program, an extensive, 50% European Union-funded, multi-partner activity aimed at lowering fuel consumption and emissions by reducing drag on next-generation.

“The SFWA BLADE program is allowing us to progress innovative technologies, concepts and capabilities with the potential to bring about a step change in aircraft fuel consumption,” said Russ Dunn, Senior Vice President, Engineering and Technology at GKN Aerospace.

GKN Aerospace has delivered the critical leading edge assemblies and upper covers that form part of the NLF wing section on the starboard wing of the Airbus A340 flight test aircraft. These structures offer NLF levels of performance through the adoption, by GKN Aerospace, of a totally new design approach and the application of novel manufacturing technologies that deliver the ultra-high tolerances and exceptional surface finish required.

During flight tests, taking place in 2017, this wing section will be used to test the performance characteristics of NLF wing architecture, helping prove predicted economic and environmental benefits: An NLF wing is expected to reduce wing drag by 8% and improve fuel consumption by approaching 5%.

“The key challenge with designing and manufacturing an NLF wing, with the many aerodynamic benefits that promises, stems from the need to tightly control the wing surface,” said Dunn.“It is vital to eliminate features such as steps, gaps, surface roughness and waviness or fastener heads as these all lead to more traditional ‘turbulent flow’ performance levels. The GKN Aerospace team has created these integrated, co-cured composite upper covers and very high tolerance leading edge surfaces using the same structured design and development process applied in commercial aircraft programs. As a result, our first part was of very high quality and has been delivered for the flight test program.”

The ground based demonstrator (GBD) of the wing developed a couple years ago was a 4.5 m x 1 m section of flight-representative wing leading edge attached to a partial wing box assembly. The leading edge accommodated a Krueger flap in two sections, which allowed GKN engineers to investigate two very different design philosophies.

The first "baseline" section applied a monolithic composite skin to the traditional rib design seen on the majority of metallic leading edges today. The second "innovative" section applied a more radical design to address issues experienced meeting NLF tolerances with the baseline design. This section comprised a lightweight leading edge sandwich panel incorporating electro-thermal wing ice protection technology with an integrated erosion shield and fastener-free outer surface.

Additive manufacturing processes were used to create a novel support structure for the Krueger mechanism, replacing the aluminum ribs in the baseline design. This allowed the leading edge panel to be supported by just three composite ribs: a single central rib and two closing ribs. These maintain the correct leading edge aerodynamic profile over the complete range of operating temperatures. The innovative section had a lower component and fastener count, was significantly lighter, and had greatly improved performance predictions compared to the baseline section.

The overall project was a collaboration between three GKN Aerospace technology centres in the U.K.: a team at the U.K.’s National Composites Center, at GKN Aerospace in Luton, and at the GKN Aerospace additive manufacturing center in Bristol.