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Cutting edge

Airbus is using its Airbus A340-300 prototype to investigate laminar flow wing sections as part of the BLADE project. Ian Harbison reports from Tarbes
 

BLADE stands for Breakthrough Laminar Aircraft Demonstrator in Europe, for which Airbus is the project leader. Launched in June 2008, it is part of the €1.6 billion EU/industry-funded Clean Sky Programme, which, in turn, is part of the EU Commissions ACARE Vision 2020, which called for a 50% reduction in noise and an 80% reduction in fuel burn by 2020 (based on 2000 standards).

 

Within Clean Sky, it is designated as a Smart Fixed Wing Aircraft – Integrated Technology Demonstrator (SFWA-ITD). This aims to take innovative technologies, concepts and capabilities that are currently at Technology Readiness Level 3 (defined by the EU Commission as an experimental proof of concept) and developing and validating them at TRL 6 (technology demonstrated in its relevant environment).

 

In total, there are 21 organisations involved in BLADE:

 

 • Industrial partners: Aernnova, Airbus, Dassault Aviation, Eurecat, GKN Aerospace, Romaero, Saab, Safran

 

 • SMEs: 5micron, ASCO, Aritex, FTI Engineering, Sertec, VEW

 

 • Research institutes: BIAS, DLR, DNW, INCAS, ITAINNOVA, NLR, ONERA.

 

Natural laminar flow (NLF) employs a careful aerodynamic design of the wing section that allows the airflow to remain attached to the surface for longer, before it separates and produces turbulence, hence drag. Keeping the flow attached can provide a drag reduction of up to 50%, which translates to a 5% reduction in fuel burn over an 800nm sector for a single aisle aircraft. Unfortunately, wind tunnel tests have shown that the attachment is extremely sensitive, and separation can be caused by a wide range of factors, including leading edge and wing contamination (insects, grease, deicing fluids, scratches, dents, erosion, dust), atmospheric disturbances, acoustic disturbances and vibrations, fastener head deformation, joint and filler deformation, and local and global wing deformation.

 

In addition, says Axel Flaig, Head of Research & Technology at Airbus, the technology up to now has not been mature enough, nor fully tested in flight. However, recent rapid developments of numerical flow simulation tools now enable aerodynamicists to design, build, demonstrate and validate an optimised NLF wing.

 

As noted above, a NLF wing is best suited for single aisle aircraft with a 20° wing sweep and a cruise speed of M0.75, such as the A320 Family. However, fitting a prototype wing to such an aircraft would be extremely complex and costly, and would almost require a new certification programme as it would involve engine and landing gear attachments and aircraft systems.

 

Instead, Airbus decided to use its A340-300 prototype (MSN 01), which had been in storage for some time. While this has a wing sweep of 30° and a cruise speed of M0.82, the aircraft configuration means the wing section, at Rib 27, beyond the outer engines, may be removed and a sample NLF section attached on each side.

 

This provided an opportunity to test two different designs simultaneously. On the port wing, there is a completely integrated composite design from Saab, with a single piece upper cover including the leading edge, while the starboard wing has a composite upper cover joined to a metallic leading edge, with a joint on the upper surface. This was produced by GKN Aerospace. The single piece is theoretically the optimal solution, as the joint could be a separation trigger. The results from the flight trials will be used to specify manufacturing tolerances for a laminar wing and components for next generation commercial aircraft. >>

 


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