The Influence of Materials on the Development of Sailplane Design

Abstract

The evolution of sailplanes in the past century is a product of both the progress in aerodynamics as well as the usage of new materials including constructive and technological solutions. The focus of this contribution is to highlight the importance of new materials and their application in the development of sailplane design. Three periods are classified. The first beginning with the flights of O. Lilienthal in 1891 is characterized by wire braced, cloth covered willow, bamboo and wood constructions of the wings with thin airfoils. New possibilities were discovered in 1921 with the Vampyr where by means of plywood a cantilever single beam design including a D-tube leading edge of high torsion stiffness allowed a thick airfoil wing without wire braces. In this period also some important metal designs can be found. The end of this period which culminated in the HKS and KA6 constructions was rung in with the Phoenix in 1957 which was completely designed in glass fiber reinforced plastics (GFRP). The introduction of high strength and high modulus carbon fibers finally enabled further possibilities to increase the glider per-formance. Composite materials have been dominating the development of sailplanes now for nearly 50 years. Nevertheless, there are still problems to be solved such as the missing confidence in the very good fatigue properties of FRP. Thus, also lifetime certification and evaluation items are discussed, too.