Analysis of Dynamic Flight Loads

Abstract: This thesis deals with the determination of loads on an aircraft struc- ture during flight. The focus is on flight conditions where the loads are significantly time-dependent. Analysis of flight loads is primarily motivated to ensure that structural failure is avoided. The ability to ac- curately determine the resulting structural loads which can occur during operation allows for a reduction of the safety margins in the structural design. Consequently it is then possible to decrease the aircraft struc- tural weight. The demand for safe and fuel efficient aircraft creates a desire for efficient and accurate methods for determining the structural loads.The first paper of this thesis discusses the use of control laws for robust atmospheric turbulence load alleviation in the time domain. A numerical aircraft model including structural elasticity and unsteady aerodynamic effects is used. A limited set of longitudinal flight mechanic degrees of freedom are considered and two methods for structural load analysis are compared for evaluation of the wing root bending moment.In the second paper a method to perform time domain simulation of both motion of center of gravity and elastic deformation is described. The intention with the development of this simulation method is to enable efficient analysis of dynamic flight loads.A third study is finally included, where steady and unsteady pressure measurements have been carried out during wind tunnel testing. The motivation for performing these experiments is that knowledge about the aerodynamic force distribution which affect an aircraft structure is needed to correctly determine the structural loads.