## 1 Introduction
To address the control and control allocation problem of a morphing aircraft, the NDOISMC method, which combined a nonlinear disturbance observer and incremental sliding-mode control, was proposed for morphing aircraft, and an SOCP-based control allocation was used to allocate the control of different actuators [18]. In reference [19], a super-twisting sliding-mode controller was designed for HMW trajectory tracking. In [20], an explicit model of a variable-swept-wing aircraft was proposed, considering the variations in aerodynamics, mass, and inertia, and an adaptive super-twisting sliding-mode controller was designed to track the reference trajectory. A morphing aircraft dynamic model based on the KANE method was also established, and an adaptive integral sliding-mode controller was proposed, which could stabilize the LPV system in finite time [21]. In addition, several advanced algorithms have been developed for morphing aircraft control. To address the control of morphing aircraft in a full envelope, a switching polytopic linear parameter-varying (SPLPV)-based gain-scheduled controller was proposed in [22]. In reference [23], a six-DOF model of a variable-swept-wing waverider was established, and a nonlinear model predictive controller considering system disturbance was proposed. Lateral weaving simulation showed that the morphing waverider had better ability in different flight conditions. To realize autonomous morphing and aerodynamic performance optimization for a new bionic morphing UAV, a deep deterministic policy gradient (DDPG) algorithm was developed for deformation control [24]. Aside from attitude and trajectory tracking control, some scholars have carried out research on the integrated guidance and control (IGC) of hypersonic morphing vehicles (HMVs). In reference [25], an IGC model with a terminal angular constraint of a hypersonic variable-span missile was established, and an adaptive dynamic surface control backstepping method was proposed. A simulation showed that span variety is useful for the fast and stable control of hypersonic morphing missiles. Similarly, an adaptive dynamic surface method was proposed with the IGC system for an HMV; the simulation results indicated that the HMV had lower velocity loss and larger terminal velocity than an invariable-span vehicle [1]. For HMWs, the system states are expected to converge in a short time. In the above-mentioned control approaches of morphing aircraft, the closed-loop system is usually finite-time stable, which means the system states will reach equilibrium in a finite time. However, for such a finite-time system, the settling time depends on the initial state. Since the states of the HMW in near space are under great uncertainty, there is an urgent need to develop a controller with a small bounded convergence time independent of initial states. Based on the finite-time convergence theory, [PERSON] [26] first proposed the fixed-time convergence concept and the stability analysis methods. Compared with the finite-time convergence system, the convergence time of the fixed-time system is independent of the initial system states. In reference [27], an adaptive fixed-time guidance law with attack angle constraint was proposed for intercepting maneuvering targets. In [28], a fixed-time cooperative guidance law with a desired terminal attack angle was proposed. A non-singular terminal sliding mode (NFTSM) controller was proposed for missile agile turning, and a fixed-time extended state observer (ESO) was applied to eliminate the chattering by online estimation of the disturbance [29]. In [30], a novel ESO-based NFTSM controller was proposed for a vertical take-off and vertical landing (VTVL) reusable launch vehicle. For a rigid spacecraft, a novel fixed-time attitude controller based on a backstepping technique and power integrator was proposed [31]. In [32], an event-triggered fixed-time attitude controller based on a multivariable sliding mode manifold was designed for an HMV.