This proposal covered all actions from the university side required in the call JTI-CS-2010-1-SFWA-01-020 for the development and testing of two designs of an integration of active flow control concepts on a trailing edge of high lift devices, namely:
- the design, including an optimisation of the structure
- the manufacturing of coupon specimens and a mock-up
- the structural testing of the specimens
The main technical challenge was the introduction of outlets in the highly loaded skin of the flap. Therefore, this was the main subject of the project, which led beyond the state of the art.
For this purpose two universities cooperated and relied on the work of EADS-IW as a partner within the Clean Sky consortium, making sure that new ideas on the integration of active flow control devices into the flap structure are investigated, and on the other hand that industrial manufacturing standards and certification rules are followed.
The DoW contains all work specified in the previously evaluated proposal but without the EADS-IW work share.
This project had one main aim, namely to find a structural solution for a flap with active flow control features like slits in the outer skin and actuators and a plenum inside the structure. The solution was found for exactly the actuator type developed in the parallel FloCoSys project. The outer flap design was chosen according to a flap of the FNG wing, but – due to the active flow control features – the flap only needs 70% of the cordwise dimension of the original flap. According to the reduction in this dimension, other dimensions like the thickness also had to be reduced, which means that the space for internal installations is also smaller than for the original flap.
The special challenge of the project was to find a unique concept for such a flap. It is obvious that small slits in the outer skin will result in a damage/fatigue prone design and will result in lower overall stiffness, at least with respect to torsion and shear from bending of thin-walled profiles. The direction of the pulsed airflow with respect to the upper skin of the flap was requested to be 45°. This has a large impact on the internal structural design, since the actuators have to be positioned accordingly.
Many concepts have been discussed for this case. The result was to use a multi-spar concept for most of the flap. This not only offers some manufacturing advantages, but also the chance to use the forward cell of the flap as plenum. In order to combine the use of the forward cell as plenum and the installation of the actuators under 45° results in an unusual spar design in this area. The overall multi-spar design has then been optimized by special structural design code. Sizing of the structure by means of detailed finite element simulations has been performed likewise.
The flap design was – due to the fact that the overall design was only possible by including the new actuator type into the structural design – triggered both, system-wise as well as structural-wise. So, tests have been performed with regard to both aspects, and although this was not planned beforehand, the demonstrator includes the original actuators and it also includes more structural elements in cordwise direction than originally planned. The concept has been tested by a set of tests. Test articles have been manufactured by the partners. The tests include many flat CFRP plates with a set of three aligned slits. The size of these specimens ranged from wide coupon tests to plates with a dimension of approximately 750 x 750 mm2. Static and fatigue tests have been performed under a range of loading conditions. This includes tension in a direction perpendicular to the aligned slits as well as under 45° and under shear loading. A very high remote strain state has been used in these tests to challenge the disturbed plate design. Even at this high strain the performance was quite satisfying. As a kind of final verification, a demonstrator – as mentioned above – with 2 m span has been tested under static and cyclic fatigue loading. The type of loading was a combination of bending and torsion. Finally, a mock-up demonstrator of a full-sized section of a flap has been manufactured and handed over to the WP leader of the Clean Sky project.
The partners involved in the project were:
- Institute of Aircraft Design and Lightweight Structures, TU Braunschweig (IFL)
- Institute of Aerospace Engineering, TU Dresden (ILR)
- Institute of Lightweight Engineering and Polymer Technology, TU Dresden (ILK)
In addition, from CleanSky consortium Airbus Group Innovations was heavily involved.