research for cleaner skies

Airbus is studying four natural laminar flow wing designs with varying sweep and Krueger configurations – assessing them for aerodynamic performance, weight, lift characteristics, cost and maintenance. This work includes studies on how to create and maintain the very high surface tolerances needed for laminar flow – including profile and finish – as well as keeping these tolerances once the aircraft is in daily service.

Initial flight testing of a laminar 'glove' fitted on a smaller testbed aircraft is being considered to ascertain the tolerances of natural laminar flow to a wing’s surface roughness and imperfections, as well as see how atmospheric ice crystals would change wing airflow patterns. Further work will be done to determine how in-service damage could change the laminar flow characteristics, as well as to develop concepts for wing leading-edge repair or replacement to ensure that natural laminar flow can be maintained over an airliner’s service life. Major demonstrations are also planned as part of the European Clean Sky Smart Fixed Wing collaborative research programme, culminating in the flight test of an A340 with modified laminar outer wings.
 

Open rotor engine

An important target for research at Airbus is the future single-aisle airliner that could eventually succeed its best-selling A320 in the 2025 timeframe. A candidate propulsion system for such a follow-on aircraft is the contra-rotating open rotor engine, which offers the potential for 'game-changing' reductions in fuel consumption. This innovative design utilises two rotors – one located behind the other – which rotate in opposite directions. These rotors are in the open, as the propulsion system does not utilise a traditional jet engine’s nacelle, which helps limit noise levels and provides protection from debris in case of engine failure.

The open rotor concept offers the promise of major improvements in fuel efficiency due to its ultra-high bypass ratio, but also raises various questions that include higher noise levels, both externally and inside the passenger cabin; more intense acoustic and vibration environments; different aerodynamics when compared with traditional jet engines; and issues concerning specific certification by the airworthiness authorities – particularly due to threat from the blades to the aircraft.

An industry-wide project

To better understand these issues, Airbus has been participating in open rotor test rig evaluations performed by the major engine manufacturers. This included testing in 2008/2009 with Rolls-Royce in major European wind tunnels, and in 2010 with GE and its CFM International joint-venture during validations conducted at the U.S. National Aeronautics and Space Administration’s Glenn Research Center in the state of Ohio.

On top of many intellectual property issues for such a new technology that could limit Airbus’ access to data on the new propulsion concept, there is a need to completely master propulsion system integration. Therefore, Airbus decided to develop its own evaluation strategy, including wind tunnel testing to better understand the open rotor system’s aerodynamic and acoustic aspects. Using a configuration with 11 blades in the front rotor and nine blades in the back, Airbus' generic open rotor configuration will be evaluated within the European Clean Sky Smart Fixed Wing Aircraft programme, involving the participation of engine manufacturers (Rolls-Royce, Safran), European research centres (DLR, ONERA, NLR) and specific partners selected through calls for proposal.