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An accurate aeroelastic assessment of powered HALE aircraft is of paramount importance considering that their behaviour contrasts the one of conventional aircraft mainly due to the use of high aspect-ratio wings with distributed propulsion systems. This particular configuration shows strong dependency of the wing natural frequencies to the propulsion distribution and operating conditions. Numerical and experimental investigations are carried out to better understand the behaviour of flexible wings, focusing on the effect of distributed electric propulsion systems. Several configurations are investigated, including a single propulsion system using an engine pod (a weight with embedded electric motor, a propeller, and the wing-attached structure) installed at selected spanwise positions, and configurations with two and three propellers.

The problem of wing shape modification under loads in order to enhance the aircraft performance and control is continuously improving by researchers. This requirement is in contrast to the airworthiness regulations that constraint stiffness and stress of the structure in order to maintain structural integrity under operative flight conditions. The lifting surface modification is more stringent in those cases, such as UAV configurations, where the installed power is limited but the variety of operative scenario is wider than in conventional aircraft. A possible solution for adaptive wing configuration can be found in the VENTURAS Project idea. The VENTURAS Project is a funded project with the aim of improve the wind turbine efficiency by means of introducing a twisting capability for the blade sections according to the best situation in any wind condition. The blade structure is composed by two parts: 1) internal supporting element, 2) external deformable envelope.

Weight reduction in structural aerospace configuration is based both on specific material selection and on the selection of specific shape and sections. UAS structures need both the introduction of new advanced composites and the definition of light weight construction based on thin walled configuration. With this idea in mind, Stiffening concepts are frequently used to increase structural performance, i.e. buckling characteristics, of a thin plates. Manufacturing of composite stiffened structures can give rise to the presence specific damaged situations such as skin/stiffener de-bonding. Such kind of defect can cause buckling prior to the designed critical condition and can cause a reduction in global strength. The presence of cyclical loading and fatigue effect can have important consequence on damage propagation and structural integrity. The static structural behavior of a damaged stiffened composite panel is summarized from previous research investigation and presented.