Flight Control System Design and Sizing Methodology for hypersonic cruiser

Flight Control System is considered a key enabler for future high-speed aircraft and therefore, the anticipation of its impact onto the aircraft layout and performance is crucial. On one side, a preliminary characterization of the control surfaces is essential for a precise estimate of the aerodynamic characteristics of the vehicle throughout the mission. On the other side, traditional design approaches widely used in subsonic aircraft design and based on on-design and standalone system sizing, may lead to wrong estimates of the peak power demand. Conversely, typical supersonic and hypersonic design solutions are investigated by means of numerical simulations which guarantee higher accuracy but may not be directly applicable during the early design stages. Therefore, this paper discloses an innovative methodology (i) to anticipate the Flight Control System design of future high-speed aircraft at conceptual design stage, (ii) to properly consider the interactions with other subsystems and (iii) to properly predict the behavior of the Flight Control System throughout the entire mission. The integrated subsystems design methodology disclosed in this paper starts with the suggestion of the most promising semi-empirical models for control surfaces geometrical definition. The newly defined surfaces can be analyzed to predict their single contribution to the vehicle lift and drag coefficients. At this stage, the interaction with the propellant system is fundamental to identify the minimum surfaces deflections required to guarantee the aircraft trim. Indeed, in order to minimize the exploitation of control surfaces and thus limiting the detrimental effects onto the aerodynamic efficiency, propellant tanks can be properly shaped and integrated on board, and ad-hoc depletion sequencies can be adopted to match the desired center of gravity shift throughout the mission. Maximum required control surfaces deflections are used as inputs for the estimation of hinge moments to be counteract by the actuation system. A novel approach is here suggested to extend the formulation available in literature beyond the transonic regime. Eventually, the Flight Control System design is completed with the selection of actuators and finalization of the System architecture including power distribution lines and connections with the avionic system. The integrated design methodology has been developed in the context of the H2020 STRATOFLY Project and it has been exploited for the design and sizing of the Flight Control System of the STRATOFLY MR3 vehicle, a Mach 8 waverider concept for civil antipodal flights.