European airframers are looking for a technological leap in aircraft wing design that will yield major cuts in carbon dioxide emissions

While a major reduction in weight will likely be achieved through progressively greater use of composite materials, this alone will not be sufficient to reach the ACARE goals for 2020, where nearly half the 50% reduction in CO2 is to be delivered through airframe innovation.

The steady pace of incremental improvements over the last 50 years has in somewhat disappointing fashion led to the shape and configuration of large and small transport aircraft converging to produce what has become an almost universal configuration: a highly efficient passive wing with moveable surfaces, under-wing high by-pass ratio engines or rear fuselage engines, and rear vertical and horizontal tails.

It is against that background that the novel concept of an active wing and new configuration allied to a step change in aerodynamics and flight physics performance is being examined by the European aeronautical industry.

The Clean Sky integrated technology demonstrator Smart Fixed Wing Aircraft (SFWA) represents a pioneering effort to enter this still-unexplored field of serious investigation. The purpose of the SFWA flying demonstrator is to develop and validate up to Technology Readiness Level (TRL) 6 innovative technologies, concepts and capabilities currently only investigated at TRL 3 in an effort to show the potential of step change advances in the critical areas of fuel consumption and noise.

To this end, SFWA will integrate active wing and innovative airframe concept technologies, largely based on the results of other European research and technology projects such as AWIATOR and NACRE, with the acid test assessment of the benefits of such a radical multidisciplinary approach eventually validated on a representative flying aircraft.

Most Challenging

Jens König of Airbus's Future Projects Office reports that the SFWA, which at Euro393 million ($620 million) represents the second largest slice of the Euro1.6 billion total Clean Sky budget, will be co-led by Airbus and Saab. The leading European industry primes will be given 50% of that budget with the remainder equally divided between academic and small and medium sized enterprises. "It is not possible to do everything so we had to pick out the most important, the most challenging," says König.

Within the division of responsibilities for SFWA technologies to be developed and integrated, Dassault will lead the bid to taking natural and hybrid laminar flow and active and passive load control to TRL 4, "It is at this level that we want to start the demonstration," says König.

SAAB will head the definition of new wing concepts alongside SFWA technologies to permit the technology readiness to be advanced to TRL6. This endeavour will also focus on how to integrate innovative engine concepts such as counter rotating open rotor technologies into novel airframes using new materials and manufacturing methods, the product of separate ITDs such as Systems for Green Operations and Sustainable and Green Engines.

The end result will be the creation of four large scale flight demonstrators which, led by Airbus, will attempt to validate these new technologies and wing concepts integrating equally as innovative powerplants and empennage. Areas that will be examined here will include the impact of the airframe flowfield on propulsion design as well as impact of open rotor configurations on the aircraft, tackling what König terms the "traditional showstopper issue of structural vibration".

"These have never been tested so comprehensively in a funded programme," he says.

These four flight demonstrators will account for around 50% of the entire SFWA budget, which will force the ITD leaders to carefully select them for their pertinence within realistic and relevant operational conditions in an industrial context.

"We are not starting research from scratch or else we would never get anywhere within seven years. We want to start at TRL 4 and hope to end at TRL 6 or 7," says König. "We have to really have the confidence that we can use these technologies on a real size aircraft. It is very different from other types of demonstrator to date and therefore has to be very close to the industrial operation and not too research led. We also have to measure any benefit in precise percentage terms."

Validating Drag Solutions

A high-speed flight demonstrator will be developed for large scale flight testing of passive and active flow and loads control solutions on all new innovative wing concepts in an effort to validate low drag solutions at representative Mach and Reynolds Numbers. Aircraft options here include using an unmanned air vehicle, a Dornier/Dassault-Breguet Alpha-Jet or even an Airbus A340 with modified wing, something that König says would be the most expensive and complex option but still one worth investigating.

A low-speed flight demonstrator will aim at validating a high lift solution to support and/or enable innovative wing low drag concepts on either a Dassault Falcon or an Airbus A320.

Aircraft options for an engine demonstrator flying testbed that aims to demonstrate the viability of full scale innovative engine concepts in operational conditions are still under investigation. A long-term technology flight demonstrator that will validate the durability and robustness of wing technologies in operational environment may use either an Airbus A300 Beluga or Airbus A320, or alternatively an in-service transport aircraft. König reports that here the ITD leader is seeking the co-operation of a large airline running many regular flights, although the contribution will be "nothing too challenging".

Source: Flight International