Structural and Aeroelastic Design of a Joined-Wing UAV

The Italian Aerospace Research Center (CIRA) is currently designing an unmanned aerial research system that is lightweight and has high-structural flexibility, code named the High Altitude Performance Demonstrator (HAPD).The project is framed within the Italian Aerospace Research Program, under the Unmanned Aerial Vehicle (UAV) Chapter. This unmanned aerial system is mainly aimed at developing and validating advanced modeling methodologies for flexible aircrafts. A compendium of the system is provided in this paper, together with a deeper discussion of how CIRA developed the structural and aeroelastic design of HAPD. Some experimental tests performed to validate the main concepts are also presented. The vehicle has an unconventional joined-wing configuration that mitigates undesired extreme flexibility, but that results in a more complicated design. First, aeroelasticity has been taken into account from the preliminary stages of design because flexibility significantly affects aircraft behavior. Second, the HAPD structure is redundant with regard to constraints (because of its joined wing), thus making the internal forces dependent on the stiffness distribution. For these reasons, the availability of an integrated methodology that can support the structural design is mandatory. The output of such a methodology consists of primary structure stiffness distributions (fuselage, wings, and vertical tail), compatibly with the absence of any aeroelastic instability, and structural failure under operative loads.