Next generation wings for long range aircraft: hybrid laminar flow control technology drivers
Creators: name: Haase, Thomas
name: Ropte, Sven
name: Kamp, Bram Van De
name: Pohya, Ahmad Ali
name: Kleineberg, Markus
name: Schröder, Andreas
name: Johanna-Lisa Pauly
name: Kilian, Thomas
name: Wild, Jochen
name: Herrmann, Ulrich
Publisher: name: Zenodo
Year: 2020
Subjects: hybrid laminar flow, tubeless suction system, inductive heatinfg

description: Due to the societal need for mobility of more and more people, the need to reduce CO2 emissions in civil<br> aviation is very high and led to Europe’s effort labeled “Green Deal”. New aircraft with (hybrid) electric &amp;<br> distributed propulsion for short &amp; mid-range are the focus of actual research. In contrast, long-haul aircraft<br> will continue to have jet engines in the future. Therefore, a rather classical two wing mounted engine<br> configuration, but with significantly boosted performance and reduced emissions footprint is very likely.<br> Beside the use of synthetic fuels and more efficient engines, drag reduction for transonic aircraft (approx.<br> Mach 0.85) has to be obtained. Hybrid laminar flow control (HLFC) technology offers a remarkable drag<br> reduction potential. Aerodynamic efficiency of hybrid laminar flow control has been demonstrated in<br> several wind tunnel and flight tests from the physics point of view. The major drawbacks preventing the<br> application of this technology are the complexity and the high production &amp; operating cost associated.<br> Fighting these major drawbacks is the objective of the HLFC projects under the CleanSky2 umbrella. In<br> this article, overviews of the important technology elements developed by DLR for HLFC purposes are<br> presented. The following technology bricks are described:<br>  Tubeless suction system<br>  Inductive heating based wing ice protection system (WIPS)<br>  (resulting) Aircraft performance assessment<br> By using distributed compressors and consequent structural integration, an almost tubeless suction<br> system can be realized. Hence, large vacuum tubes can be avoided and the space allocation for the<br> leading edge is relaxed. In order to reach such a tubeless suction system, the structural integration and<br> the development of a lightweight compressor with suitable mass flow are addressed.<br> The integration of a WIPS in an HLFC wing is very challenging. Classical bleed air WIPS consumes a lot<br> of energy and requires tubing; electro-thermal WIPS with heating stripes induces a lot of blockage to the<br> perforated outer skin. A promising alternative solution is the inductive heating, which can induces heat in<br> the titanium skin contactless. The maturity of inductive WIPS is low, but the opportunities seen for the<br> HLFC technology outweigh their risks, which is why this technology was chosen.<br> In order to enable laminar flow, high surface tolerances have to be ensured for the laminar flow part of the<br> wing (beyond the leading edge). In order to ease the operability of a HLFC wing, a design with a<br> removable outer skin for the active part performing suction is developed. In case of contamination or<br> damage (e.g. by insects or hail) the perforated outer titanium skin can be replaced individually. It is<br> therefore not necessary to replace the complete wing leading edge during operation of the aircraft.<br> To constantly feed the design process, the overall aircraft assessment is used to identify the correct balance between the figures of merit (drag reduction, mass and power off-take) and the cost of the envisaged design including materials, manufacturing and assembly.<br> At the moment, the project is right before Technology Readiness Level (TRL) 3 where all relevant sub-technologies<br> are down selected and an overall wing concept is established. The preliminary assessment reveals a<br> 5.5% drag reduction. The overall concept will be now matured by analysis of small scale demonstrators<br> focusing on key technical challenges to verify the initial performance gain level.<br>
description: Acknowledgement: This project has received funding from the Clean Sky 2 Joint Undertaking (JU) under grant agreement No 945583. The JU receives support from the European Union's Horizon 2020 research and innovation programme and the Clean Sky 2 JU members other than the Union. Disclaimer: The results, opinions, conclusions, etc. presented in this work are those of the author(s) only and do not necessarily represent the position of the JU; the JU is not responsible for any use made of the information contained herein.