## 1 Introduction  
The vertical take-off and landing fixed-wing UAV can achieve zero-speed take-off and landing without the need for a runway as in the case of the conventional aircraft. In the vertical take-off and landing mode, it is capable of hovering. In fixed-wing mode, high-speed and long-term flight can be achieved. It is one of the best choices to perform reconnaissance and monitoring tasks in special environments [1; 2; 3; 4; 5]. In this work, a ducted vertical take-off and landing fixed-wing UAV scheme is proposed. For this type of vertical take-off and landing fixed-wing UAV, the transition flight corridor (envelope) is studied. There are many studies on the tilting corridor of the tilt-rotor vertical take-off and landing aircraft. [PERSON] [6] studied a vertical take-off and landing unmanned aerial vehicle, presented with a quadrotor design for propulsion and attitude stabilization and an annular wing that provides lift in forward flight. [PERSON] [7] focused on the Dual Tilt-Wing UAV, a vehicle capable of performing both flight modes (VTOL and CTOL). The complete dynamic model of a UAV was obtained using the Newton-Euler formulation, which includes aerodynamic effects as the drag and lift forces of the wings, which are a function of airstream generated by the rotors, cruise speed, tilt-wing angle, and angle of attack. The airstream velocity generated by the rotors was studied in a test bench. [PERSON] et al. (2018) took the scaled-down prototype as the research object, then predicted the transition corridor of the tilt-rotor aircraft through blade element theory and momentum theory, and compared the nacelle inclination angle and flight speed envelope with experimental test results. After a series of flight tests, they determined the transition from helicopter mode to fixed-wing mode. [PERSON] (2018) studied unmanned aerial vehicles operating in this configuration, which were also categorized as hybrid UAVs due to dual flight envelope--hovering like a multi-rotor and cruising like a traditional fixed-wing, the two different dynamics enable UAVs to carry out complex missions. [PERSON] et al. (2018) discussed the overall conceptual design, dynamic modeling, computational simulation, and experimental analysis of the novel hybrid fixed-wing bicopter with thrust vectoring capabilities, with the aim of substantially increasing the flight range and endurance compared to conventional aircraft rotorcraft configurations. [PERSON] (2018, 2019) proposed a power system of the tilt angle-speed envelope of the transitional flight from vertical take-off and landing to horizontal flight for this kind of aircraft. The envelope analysis method was studied from the two aspects of low speed and high speed, the matching relationship of each power in the transition process was analyzed, and the tilt-speed envelope of the wing stall limit was determined. [PERSON] (2019) aimed to determine the range of values of the attitude angle of the tilt-rotor aircraft during flight trim. Taking the XV-15 aircraft as an example, the transition corridor was calculated and determined, and a transition route was found within the envelope of the transition corridor, for which the trim attitude angle of the XV-15 was the smallest during the transition flight. [PERSON] et al. (2019) aimed at studying the complex control characteristics of the tilt-rotor aircraft with both vector dynamic control and aerodynamic rudder surfaces. The transitional states were balanced and trimmed, the control quantities of each state were calculated, and the transition corridor was designed. [PERSON] et al. (2019) established the aerodynamic model of the body parts for high-speed helicopters with fixed wings. Furthermore, a full dynamics model of the entire machine was established, and on this basis, the state point analysis method was used to determine the safe transition corridor of the high-speed helicopter.