Abstract:The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag reduction is seen in laminar flow control by boundary layer suction. While most of the research so far has been on partial laminarization by application of Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC) to wings, complete laminarization of wings, tails and fuselages promises much higher gains. The potential drag reduction and suction requirements, including the necessary compressor power, are calculated on component level using a flow solver with viscid/inviscid coupling and a 3D Reynolds-Averaged Navier-Stokes (RANS) solver. The effect on total aircraft drag is estimated for a state-of-the-art mid-range aircraft configuration using preliminary aircraft design methods, showing that total cruise drag can be halved compared to today's turbulent aircraft.

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A simplified procedure is presented for the design of a leading-edge fairing of a wing-body combination. The design aims at optimizing the design of the fairing, which is to serve the double purpose of eliminating separation near the wing-body junction, as well as minimizing leading-edge contamination of the laminar wing. The design optimization procedure is based on the analysis of the viscous-flow performance of a fairing of prescribed geometry. First, a panel method is used to determine the inviscid flow around the fairing. This is then followed by an integralmethod calculation of the boundary-layer development on the attachment line along the body and the fairing. As an application, a fairing was designed for a straight NACA0015 wing mounted on a flat plate. Tests in the wind tunnel confirmed the effectiveness of the fairing. NomenclatureH , H 1 = boundary-layer shape factors Re = Reynolds number r = crossflow model switching parameter U e , W e = external flow velocity components U ∞ = freestream velocity u, v, w = velocity components x, y, z = Cartesian coordinates δ = boundary-layer thickness δ * = displacement thickness θ = momentum thickness µ, µ T = dynamic viscosity; turbulent viscosity ν = kinematic viscosity, µ/ρ ρ = density τ = shear stress

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About 110 years a8o O. Lilienthal built his gliders wiih cambered plate wings which werc stiffened out by a plen ty ofstrut wires. Analysis of this type of airfoils show their narrow range of angles of attack and their rapid loss of lifi at stall conditions. The development of ihe ihick airfoils of the Cciitingen sedes l€d to the constnction of the Vampyr wiih a strut fr€e wing and a torsion leading edge box. The quality of the surfacc arld the maximum ihickness close to the leading eclge did not allow reasonable extentoflaminar flow The big advantages oflaminar flow airfoils have been discovered in the late thirties and have been systematically investigated by the NACA. Bui only the combination of arl airfoil designed for laminar flow and the excellent surface quality of a sandwich construction of glass fibre reinforced plastics and solid foam made the big success oflaminar airfoils for saiiplanes possible. This is shown by way of the example of the Ka 6 and the Phdnix. Examples of typical airfoils demonstrate turther developments: Airfoils with, out and with flaps; problem of laminar separation brbbles, use of destabilisation zones and use of turbulators. An attempt to assess future possibilities for performance improvemcnts of sailplanes closed th€ paper