Evolution of Airfoils for Sailplanes

Abstract

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