# Roll Control of Morphing Aircraft with Synthetic Jet Actuators at a High Angle of Attack
## 1 Introduction  
According to the instantaneous flight state, a morphing aircraft can alter its configuration to achieve a higher fuel-efficiency and maneuverability for multi-role missions, such as long endurance loiter, dash, and high-speed maneuvers [1, 2, 3, 4]. The morphing part of an in-plane morphing aircraft, on the other hand, can be considered a control surface to replace an aileron [5]. Many control methods can be used for flight control, such as optimal feedback control [6], robust control [7], adaptive control [8, 9, 10], fuzzy control [11], and time-delayed feedback control [12, 13]. However, the above-mentioned control schemes are mainly applied in aeroelastic control of fixed wing aircraft. [PERSON] and [PERSON] adopted the developed Active Disturbance Rejection Control (ADRC) to maintain roll control of morphing aircraft and found that the variable-sweepback-based control consumes less energy than approaches using the conventional control surface [14]. [PERSON] modeled the roll dynamics of a morphing-span wing mathematically and pointed out that variable-span morphing could modify the damping of the total system of the aircraft [15]. To replace the conventional aileron, [PERSON] et al. used the morphing wing to maintain roll motion over the flight envelope and found that 20% symmetric span morphing is the optimum value forreducing the overall drag [16; 17; 18; 19]. The published studies were mainly focused on flight control via the morphing part at a low angle of attack (AoA), while the situation under a high AoA has not yet been considered.  
To tackle the problem of the flight control of morphing aircraft at a high AoA, the morphing project proposed by NASA, whose objective is to assess the advanced technologies to enable efficient, multi-point morphing in flight vehicles, provided a feasible approach [20]. One major idea of this project is micro-aero adaptive control, including active flow control via a synthetic jet actuator (SJA), so as to delay the separated flow at a high AoA [21]. However, the synthetic jet technology has not been developed in the roll control of morphing aircraft. For fixed-wing aircraft, [PERSON] et al. replaced control surfaces with SJA and employed adaptive compensation control to cancel the nonlinearity of SJA in the Barron Associates Nonlinear Tailless Aircraft Model (BANTAM) [22]. [PERSON] et al. applied Bang-Bang control to the simplified roll dynamics with plasma actuators, and found that a small plasma-induced roll moment could fulfill the maneuver task well [23]. By taking the effect of roll damping into account, [PERSON] and [PERSON] developed [PERSON]'s model and provided a robust Linear Quadratic Regulator (LQR) method, only using SJA for roll control [24].  
It has been proven that flight control can be achieved by means of the morphing span and SJA, respectively. In this paper, flight control at a high AoA is integrated with both the morphing span and active flow control with SJA. Furthermore, the input saturation induced by the morphing span is considered, so as to make the control more applicable in practice. The contributions of this article are as follows: (1) A novel model of morphing aircraft using SJA with an optimized cavity shape for roll control at a high AoA is established, which can provide a foundation for further research on the flight control of morphing aircraft, and (2) to maintain the pure roll motion and meet flight quality specifications, integrated fight control via SJA and the morphing span is designed.  
The remainder of this paper is organized as follows. In the second section, the model of morphing aircraft with SJA for roll control at a high AoA is established. In the third section, the sliding mode control is designed and the Radial Basis Function (RBF) neural network is introduced to compensate for the input saturation. In the fourth section, the numerical simulations are given to perform the control effects of the integrated flight control for tracking the reference roll signal. The last section concludes this paper.