Aeroelasticity in Sailplane Design

Abstract

One of many problems in the field of sailplane design is that of aeroelastic stability. Practicing designers of gliders and light aircraft seldom have the opportunity to spend a great deal of time studying the difficult background of flutter. Therefore, the flutter engineers at the Institute of Aeroelasticity are traditionally consulted to test and to certify light aircrafts and gliders for flutter stability. In the paper, the basics for the mechanism of flutter are presented and the certification process is explained for a representative modern sailplane of the 18m-class starting with the requirements of the Joint Aviation Authorities (JAA). The objectives and methods of the ground vibration test are introduced to measure the vibration properties of the aircraft structure. These data are used to perform the flutter analysis in order to find possible flutter instabilities in the flight envelope. As the maximum flight speed of modern high performance sailplanes is further increased, costly modifications of the prototype are often necessary to satisfy a safe design. Therefore, a method is presented to estimate the flutter behavior during the design process.