# Short Landing for Flying-Wing Unmanned Aircraft with Thrust Vector
## 1 Introduction  
The rapid development of unmanned aerial vehicles (UAVs) and thrust vector control technologies has opened up new possibilities for automatic landing operations, including vertical landing, shipborne rolling vertical landing (SRVL), and short-landing techniques. Among these, the short landing has gained popularity, as it reduces runway reliance by lowering the touch-down speed and enhances the aircraft's bring-back capability. However, the application of thrust vector control to short landings poses significant challenges. First, the landing process requires careful consideration of the trim problem that arises from balancing the aerodynamic and direct forces generated by the thrust vector. Second, a proper control allocation strategy must be developed to account for the varying dynamic responses of the actuators involved. Third, a unified control framework that can adapt to control-mode switching is crucial for simplifying the controller design. Fourth, the control objects for each landing phase must be defined to ensure smooth operation. Finally, the control system must be robust to model uncertainties during the short-landing process. Addressing these challenges is critical to ensure the safety of short landings with thrust vector control. By fully considering the above five points, a well-designed control system can facilitate the successful execution of short-landing techniques, bringing new possibilities and benefits to UAV operations. Thrust vector control has been extensively researched, with several notable advancements. Integrated thrust-vector (ITV) control technology has been widely used in post-stall envelope expansion by implementing the engine nozzle [1]. In history, there have been attempts to apply thrust vectoring for the takeoff and landing of the Harrier aircraft [2; 3]. The Lianistry of Defence has led the development of shipborne rolling vertical landing (SRVL) technology for F-35B carrier aircraft landing, and thrust vector control has been applied to improve the performance of a damaged fighter [4]. The F-35B is well-known for its short takeoff and vertical landing (STVL) capabilities [5], which are supported by thrust vectoring technology. Additionally, the UK Ministry of Defence [6; 7] has improved the payload performance of weapons--as this was previously a weak point for vertical landings--through the use of thrust vectoring. On 13 October 2018, British pilot [PERSON] successfully completed the first SRVL flight [8], landing the F-35B 755 feet above HMS Queen Elizabeth's ski-jump deck, and then taxed 175 feet before using the aircraft's brakes to bring it to a standstill from 40 knots. Compared to vertical landing, SRVL lands at a slow forward speed and uses wing lift to supplement the propulsion system. Reference [9] developed the optimal trajectory transition controller for a thrust-vectored V/STOL aircraft. In Reference [10], the problem of the short takeoff curve was solved with the optimal tilt angle optimization. Different from the straight-line approach [11; 12] taken by the F-35B in SRVL, [PERSON] et al. [13] used a curved approach with a fixed-wing UAV and evaluated the predefined spline path, using flight tests. Furthermore, fast transition maneuvers along curved trajectories can reduce landing times [14]. Flying-wing unmanned aircraft, with their blended wing body layout [15], have a high lift-to-drag ratio but suffer from bad static heading stability [16] and control coupling, posing a significant threat to flight safety. To address this, [PERSON] et al. [17] used the eigenstructure assignment (EA) method to realize three-axis decoupled control, which considers flying quality specifications during the control law design process. In addition, nonlinear dynamic inversion control (NDI) is utilized to deal with nonlinear coupling dynamics, as X-35B did [18]. However, these model-dependent design approach produce an unsatisfying result in the presence of model uncertainties.