Hybrid Laminar Flow Technology (HLFC), a combination of active flow control and specific laminar profiles, is a promising possibility to reduce the drag of aircraft wings and empennage. While the basic idea has been known for a very long time and has already been experimentally investigated and validated, this technology has hardly been able to establish itself in series applications. The main reasons for this are, besides the high system complexity, especially the very high manufacturing costs and the unclear behaviour of the suction noses during continuous use. This is precisely where the DLR developed Tailored Skin Single Duct (TSSD) design comes into play: significantly reducing manufacturing costs, especially for the microperforated outer skin, and opening up new possibilities for cleaning and maintenance thanks to its complete dismantlability.
The TSSD design is based on a multilayer outer skin, consisting of a microperforated cover film and several metal fabrics. The hole diameter of the cover layer is approx. 50 µm. Even the smallest changes in the drill channel geometry or diameter lead to large deviations in the flow properties. Due to the specific design, it is possible to omit the challenging perforation of large areas by laser drilling. Instead, the fine etching can provide very precise perforations, repeatable for large areas. A local distribution of pressure loss can be achieved by selecting individual fabric layers. This allows a suction distribution with respect to aerodynamical requirements. State-of-the-art would need a complex internal chambering to achieve this distribution.
The specific design of this TSSD outer skin results in a cost-effective production, a separation of aerodynamic and structural requirements as well as the possibility to make the entire leading edge completely dismountable. Thus, the entire structure can be cleaned in order to maintain its performance. Furthermore, in case of minor damages, for example due to hail strikes, individual components can be replaced quickly and efficiently.
The described TSSSD design was developed within the Clean Sky 2 project NACOR (New Innovative Aircraft Configurations and Related Issues, Grant Agreement Nr. 945521) and will be validated by a large-scale wind tunnel test campaign in 2021. The design was commonly developed by the Institute of Structures and Design in Stuttgart and the Institute of Aerodynamics and Flow Technology in Braunschweig.
This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 Research & Innovation programme under grant agreement No 945521.