Chapter 16: Structural Design Efforts

Kurzfassung

This chapter gives a summary on the considerations and efforts that drive the conceptual structural design of a novel configuration for an agile unmanned air vehicle at systems level within the NATO multinational research project AVT-251. Three key challenges drive the structural design of the MULDICON configuration: a shell structure with a flat “fuselage” section with large doors for engine, internal stores, and landing gears, the geometric shape of the flying wing configuration, which makes the vehicle prone to Body Freedom Flutter (BFF), and the stealth design objective, which precludes the placement of support structures outside of the vehicle’s external shape. The structural design concept is verified by a numerical analytical model which was created by a parametric approach. Capabilities of this tool are however limited to continuous assemblies of sub-components, which only exist in the outer wing panels of this configuration. Effects of smaller cut-outs can be approximated by reduced element thicknesses, but the larger ones require tedious manual modifications of the parametric model. Stiffness requirements for the fuselage box, the outer wing, and the control surface actuation system are defined by aeroelastic constraints derived from flutter, gust response and static aeroelasticity. While conventional flutter can be rather easily treated later in a design process by adjusting the structural stiffness properties or adding balance masses, BFF requires an early, multidisciplinary design approach because of the interaction with the basic vehicle’s flight dynamic characteristics. This also applies to the design of the vehicle’s flight control system. The control surfaces’ shape and mass properties together with the achievable stiffness of the actuation system must be designed together with the structure. While gust loads as well as flutter and static aeroelastic investigations are covered in three companion papers, this paper presents how the MULDICON structural design was approached to account for the conflicting requirements as much as possible within the scope of the AVT-251 project.