Comparison of Design Gust and Turbulence Loads Prescribed in Certification Specifications on a Long-Range Transport Configuration

Abstract

This work discusses three approaches for gust/turbulence load calculations prescribed in the certification specifications (CS23 and CS25) of the European Union Aviation Safety Agency (EASA): quasi-steady load factor, dynamic discrete gust, and continuous turbulence approach. Underlying gust and turbulence loads are calculated in MSC.Nastran in combination with a long-range transport configuration, featuring a high aspect ratio of 12.0. Under the requirement of considering aircraft elasticity in all approaches, wing bending moment results exhibit very good agreement throughout all calculations. In the context of the wing torsion moments, deviations caused by the fundamental differences in the approaches become apparent. Due to the absence of structural oscillations, the load factor approach generates the smallest amplitudes, followed by the discrete gust, and finally the continuous turbulence approach. In the latter case, the relation between a low mode damping ratio and high turbulence loads is elaborated. For structural sizing in early design stages, the deviation in the torsion moments are not expected to yield significant differences in the load-carrying wing masses. Nevertheless, the impact of aircraft elasticity on the quasi-steady gust loads are found to be crucial. Hence, the research suggests aircraft elasticity to be considered as early as possible during the aircraft design process. This finding gains in significance for flexible configurations, such as the reference aircraft.