1 – Meeting of team in front of the NLF-wing sections of GKN and Saab at the Final Assembly Line at Aernnova in Spain; 2 – A340 in the SFWA-Hangar in Tarbes; 3 – Flight Test Instrumentation on A340; 4 – Wing upper cover section prepared for entering the Autoclave for curing.
- Application of Natural Laminar Flow (NLF) on Short Range Aircraft and Business Jets with low sweep lifting surfaces;
- Application of advanced technologies for achieving a high technology readiness level including high wing surface quality.
- Application of innovative aerodynamic design tools, large scale wind tunnel tests, Ground Based Demonstrators and comprehensive flight tests
1.1 Challenges and approach taken
The primary challenge of this Technology Stream is the realisation of laminar flow at full scale, high Reynolds number industrial wing; the data is needed to validate the applied design criteria for future industrial laminar wing designs. Advanced wind tunnel facilities such as the European Transonic Wind Tunnel (ETW), as well as innovative instrumentation (e.g. for wing deformation measurement) were used to prepare the A340 Natural Laminar Flow test flights.
Other major challenges had to be tackled during the manufacturing and assembly process for the large composite surface panels for the A340 outer wing test sections
- Completely new technologies and production processes were required to enable design and production of those very large and complex innovative all-composite structures with extremely high requirements on tolerances, shape and surface quality
- Specific tooling and jigs for wing disassembly and join-up were necessary (Figure 2)
Figure 2 Assembly of the BLADE NLF Wing in the Jig (developed by Aernnova-Sertec)
- Knowing the exact bending of the wing during the test flights is crucial for the interpretation of the flight test results. Reflectometry, an optical tool for measuring the state of the surface, was employed for this purpose (Figure 3)
Figure 3 Wing Reflectometry by 5 microns GmbH (qualifying tests on A320, Nov 2014)
Major achievements and benefits
Successful experiments have been conducted to better understand and control the laminar-turbulent transition phase, e.g. the impact of isolated holes, steps and gaps (Figure 4). These tests prepared the groundwork for the full-scale wing design and flight test; specifically for large transport aircraft, it is the first time such realistic test data has been available for future aircraft design.
Figure 4 High Reynolds Business jet testing of laminar wing at ETW
As part of the push towards Technology Readiness Level 6 and to be representative of a real design and production environment for the NLF Structural Concept, a typical full scale element of a Short Range Aircraft leading edge was designed and manufactured including all relevant systems (Figure 5)
Figure 5 Ground Based Demonstrator (4,5m long by 1m wide, on equipping fixture)
The flight test demonstrator has been conducted in the BLADE (Breakthrough Laminar Aircraft Demonstrator in Europe) project of the SFWA ITD.
Major steps of the ambitious and challenging demonstrator are:
- The detailed design of the laminar wing elements which started in 2011 under the constraint that modifications of the Airbus A340-300 test aircraft, apart from replacing the outboard wings, should be kept to a minimum.
- Manufacturing of special components for the flight test:
- a large Aero-Fairing to separate the outboard laminar wing section from the remaining, turbulent inboard wing.
- a wing-tip pod to assure a defined flow pattern at the outboard end of the laminar wing section and to provide containment for flight test instrumentation, with optical access close to the laminar wing, a diffusion zone passing the wing loads and torque form the laminar wing to the datum wing structure.
- A digital Mock-up (DMU) of the laminar wing outside of the outer port engine of the Airbus A340-300 datum wing as shown in Figure 6.
Figure 6 Digital Mock up (DMU) of the laminar wing attached to the Airbus A340-300 datum wing
- The port wing has been designed and built as a large panel fully integrated leading edge – upper cover in CFRP under leadership of SFWA ITD member SAAB; the starboard wing is designed and built with a metallic leading edge connected to a CFRP large panel upper cover. The assembly of the wing is ongoing at SFWA consortium member Aernnova in Vitoria, Spain (Figure 7)
Figure 7 Left and right wing sections at the final assembly lines of Aernnova
The main working party of BLADE started in January 2016 and will last until the end of February 2017, mostly in a fully dedicated hangar at the Tarbes Airport in southern France. (Figure 8)
Figure 8 Wing join-up assembly rig for A340 modifications in BLADE
The flight test campaign directly associated with SFWA in the fourth quarter of 2017 comprises 45 flight test hours; it is primarily intended to validate the area of laminarity that can be achieved for a large variety of cruise flight conditions with respect to altitude, flight Ma-Number and wing loading.
For a typical short-medium range aircraft, the calculated drag benefit is up to 8% at typical Ma 0,75 cruise flight at aircraft level, which translates to ~4,5% fuel burn reduction for a typical mission.
- Continuation in German and UK national frames and Clean Sky 2 for the reduction of lead time for manufacturing and cost, surface quality and optimization of high lift systems, electrical de-icing, etc.
- Further improvements, potentially in the Clean Sky 2 framework of the innovative Flight test instrumentation that has been developed for the BLADE project such as reflectometry and Infra-red measurements.
- Potential application on new Short Medium Range aircraft wings for the next generation of business jets.