A Y-Shaped Tilting Wing UAV for Vertical Take-off and Landing Cargo

To address the growing demand for express cargo transportation within and between cities, this study presents a conceptual design of a Y-shaped tilting wing unmanned aerial vehicle (UAV) capable of vertical take-off and landing (VTOL). The design aims to overcome the limitations of existing UAV designs and combine the advantages of multi-rotor and fixed-wing aircraft. By incorporating fixed-wing features, the UAV offers an extended battery life and range, making it an ideal choice for urban express cargo transportation. Firstly, a master geometry model of the UAV is established. Subsequently, dynamic simulations are conducted to evaluate the UAV’s performance under different trajectories. The analysis of the research results verifies that the UAV can successfully complete its flight missions along predetermined paths.


Introduction
Amidst the rapid urbanization and growing logistics demands, express cargo transportation has assumed a pivotal role both within and between cities.Nevertheless, conventional modes of goods transportation confront obstacles such as traffic congestion, inefficiency, and elevated expenses.In response to these challenges, unmanned aerial vehicle (UAV) technology has emerged as a promising solution.This paper endeavors to investigate a novel application of UAVs specifically tailored for expeditious goods delivery within urban areas and across multiple cities.
Drawing upon a comprehensive review of existing UAV design schemes, this study systematically evaluates their respective merits and drawbacks.Subsequently, a cargo UAV design scheme is proposed, capitalizing on the advantages offered by the identified design approaches while mitigating their limitations.

Research status
Within the realm of early UAV design, numerous researchers and teams have dedicated their efforts to the exploration of diverse design schemes and technical performance parameters.Goraj et al. introduced the conceptual design of a high-altitude long-endurance UAV.Four aerodynamic layouts are proposed, and their performances are compared.In particular, the advantages of the biplane design are introduced [1].
Romeo et al. designed a high-altitude and extremely long-endurance wing-body fusion solar aircraft (SHAMPO), optimized the wing scheme, predicted the static and aeroelastic behavior of SHAMPO, and discovered the phenomenon of reduced flutter speed [2].
Researchers at the Warsaw University of Technology presented preliminary requirements for the design of a medium-altitude long-endurance UAV, describing the subsequent design stages of the PW-103 UAV [3].
Aksugu and Inalhan proposed a hybrid propulsion tail seat UAV design, which solved the problem that mini tail seat UAVs did not have efficient high-speed cruise flight capabilities at that time [4].
In recent years, the design and technology of UAVs have developed rapidly, and various innovative solutions have emerged.Li proposed a new design scheme for ducted coaxial dual-rotor UAV, which has better control performance and hovering efficiency compared with conventional ducted rotor aircraft.The aerodynamic characteristics of ducted single-rotor/coaxial dual-rotor are experimentally studied [5].
Tian et al. proposed a design scheme for a hydrogen-powered fixed-wing UAV, and the numerical simulation of the aerodynamic layout verified that the UAV has high aerodynamic performance [6].
Yang designed an amphibious tilting-wing UAV.The rotary-wing UAV can realize multiple working modes, such as rotor vertical take-off and landing and rotor-fixed-wing tilt transition [7].
Zhang proposed a coaxial water-air dual-power cross-medium UAV scheme, analyzed the mechanical properties of the scheme in cross-medium movement, and made a prototype for multi-working condition tests [8].
Zhao designed a design scheme for a six-rotor plant protection UAV and its automatic plant protection operation system.Various functional inspections, airworthiness judgments, and different flight mode tests were carried out on the UAV before it left the ground [9].
Chandrasekaran and Steck developed a bird flapper aircraft model and simulated validation of the improved adaptive controller.In this study, the gain study of the control structure was carried out by introducing new basis functions, and the concept of wing deformation was introduced [10].
Lombaerts et al. proposed an electric vertical take-off and landing UAV design scheme and designed a control law based on nonlinear dynamic inversion for its concept.The control law can reduce the dependence on the aircraft model, especially for urban air mobile aircraft [11].
Ong et al. proposed a new multi-rotor UAV design method with higher carrying capacity, which solved the thrust-to-volume ratio problem through the coaxial rotor system.They developed a multipackage delivery UAV capable of delivering up to four packages simultaneously using a novel morphing concept [12].
Panagiotou et al. proposed a preliminary design scheme for DELAER RX-3, a wing-body fusion tactical UAV, and described the research in configuration, optimization, internal layout, stability, and control in detail, and summarized the results of the aerodynamic design and conclusion [13].
Wang et al. proposed a trajectory optimization method for the EHang 184 UAV.Real-time trajectory optimization was achieved by conveying the optimal control problem.Preliminary results for the urban air transportation case were provided, and the effectiveness of the method was demonstrated [14].
Shandong University of Technology proposed a design scheme for an X-shaped coaxial double paddle plant protection UAV.Zhang et al. completed machine modeling, static load check, dynamic modal analysis, and field flight test, verifying the functionality and reliability of the design [15].
Han et al. proposed a design proposal for a small electric UAV.The aerodynamic optimization, structural design, and static simulation of the UAV were carried out.Then a prototype was made to verify the feasibility and accuracy of Solidworks 3D modeling [16].
Zhao and Shu proposed a new structure design and flight control algorithm for the eight-rotor UAV, which realized the independent controllability of six degrees of freedom.The new UAV has a simple structure and strong anti-interference ability.It uses an adaptive control algorithm to realize orbit and attitude control, and the feasibility and effectiveness are verified by Matlab [17].
Wang designed a lightweight fixed-wing UAV for remote sensing detection.The force and dynamic models were established, and the stability controller and path-following controller were designed.The flight control system was built, and outdoor experiments were carried out to verify the effectiveness of the control strategy [18].

Research value
In the current research field, the design schemes of UAVs mainly focus on two types: multi-rotor and fixed wing.The configuration of the multi-rotor aircraft is relatively fixed, and its flight time and range are relatively short.Fixed-wing UAVs usually do not have the ability to take off and land vertically, but they have obvious advantages in terms of endurance and range compared with rotorcraft.Therefore, in order to meet the needs of express cargo transportation within and between cities, this paper proposes a conceptual design scheme for a VTOL Y-shaped tilting wing UAV.
The fixed-wing design plays a crucial role in the overall UAV configuration.The fixed wings serve the purpose of enhancing aerodynamic stability, increasing lift efficiency, and enabling sustained longdistance flights.By employing a straight-wing configuration, the UAV achieves favorable lift characteristics, particularly during extended cargo transportation between cities.
The primary focus of this paper encompasses the following aspects: utilizing Catia software for precise solid modeling of the Y-shaped tilting wing UAV; employing Adams and Matlab/Simulink software for conducting dynamic simulations of the entire aircraft under diverse predetermined trajectories.

Formation of UAV shape
The development of an aircraft concept begins by identifying its intended purpose and establishing tactical and technical requirements.In the case of our cargo UAV, the primary objective is to transport cargo within and between cities.It is necessary to consider the realization of both short-distance freight and long-distance freight capacity.
First and foremost, when transporting express goods within urban areas, it is essential for unmanned aerial vehicles (UAVs) to possess vertical take-off and landing capabilities due to spatial limitations.To accommodate express cargo transportation between cities, UAVs must exhibit long-range endurance, thus necessitating the implementation of fixed-wing aircraft designs for long-distance travel.Moreover, considering concerns related to environmental pollution and endurance, the utilization of a gasolineelectric hybrid system proves to be the most suitable choice for UAVs.In accordance with the aforementioned design requirements, this chapter undertakes the development of a Y-shaped tilt-wing UAV featuring vertical take-off and landing capabilities and proceeds with the creation of a comprehensive 3D model for the UAV.
In order to facilitate efficient cargo handling, a high-wing configuration is adopted.Additionally, to ensure optimal lift characteristics for long-distance cargo transportation, a straight-wing configuration is employed.Considering the ability of symmetric airfoils to generate symmetrical lift and stability for cargo UAVs, the NACA2412 airfoil has been selected for implementation.
It is noteworthy that, in order to achieve wing tilting, a design employing direct servo actuation has been adopted.Specifically, this involves utilizing dual-axis servos to generate rotational torque, thereby facilitating the desired wing tilting motion.
The propellers are evenly distributed on both sides of the wings, while the arrangement of the tail section differs from that of conventional fixed-wing aircraft.Drawing inspiration from rotorcraft design principles, a configuration featuring propellers with distinct upward and downward orientations has been implemented at the rear of the aircraft.This arrangement enables the aircraft to accomplish flight missions resembling those of a Y-shaped UAV when the wings are tilted at a 90° angle.
Furthermore, the nose section of the aircraft possesses the functionality of upward-opening, facilitating the loading and unloading of bulky cargo.Additionally, four controllable mechanical grapples have been strategically positioned beneath the fuselage, allowing for the suspension and release of smaller cargo items.
In the conceptual design scheme stage, its main parameters are initially determined: the wingspan is 9 m, the length of the fuselage is 8.5 m, and the height is 1.46 m.The master geometry model of the UAV is shown in Figure 1.

Flight principle
The UAV exhibits level wings during stationary periods and long-distance flights.During extended flights, the wings primarily generate lift characteristics and alleviate the lift load solely borne by the tail propellers.Conversely, during vertical take-off, landing, and short-distance flights, the wings are tilted upwards at a 90° angle, with the four propellers providing lift and enabling control over various flight attitudes.To counteract the anti-torque effect, the propellers on both sides of the wings rotate in opposite directions, while the two propellers on the tail also rotate in opposing directions.Precise control over the UAV's movement is achieved through the coordinated speed regulation of each motor.In this simulation experiment, to simplify the UAV's motion, the contact force was employed as a substitute for the propeller-generated driving force.

Trajectory planning
In this simulation experiment, we devised and executed four distinct trajectories to replicate the flight process of an actual UAV.Firstly, a takeoff-hover-landing trajectory was simulated to emulate a standard flight sequence.Secondly, a vertical plane rectangular flight trajectory was simulated to mimic the urban flight scenario.It is crucial to note that during the lower boundary segment of the rectangular flight, the UAV's wings were continuously tilted upwards at a 90° angle to accurately replicate the flight characteristics of a Y-shaped rotorcraft.Thirdly, a horizontal plane rectangular flight trajectory was simulated to replicate the urban flight scenario.Lastly, a triangular flight trajectory on the horizontal plane was simulated to emulate the long-distance flight scenario of the UAV between different cities.
Trajectory 1. Takeoff-Hover-Landing simulation.The UAV goes through a series of phases, which include a ground phase, a take-off phase, a hover phase, and a landing phase.During the ground phase, the UAV's wings undergo a 90° upward tilting angle.Subsequently, the UAV enters the takeoff phase, gradually ascending to a certain flight altitude, during which the wings gradually return to their original position.Following this, the UAV enters the hovering phase, maintaining a relatively stable flight state.Finally, the UAV's wings tilt 90° once again, transitioning into the landing phase.By utilizing the step function to precisely control the wing tilting and adjusting the contact force, we obtained the temporal trajectory of the UAV's center of mass, as depicted in Figure 3.The height of the UAV remains basically unchanged between 4 s to 8 s.We can think that the UAV can basically take off, hover, and land.
Trajectory 2. In a rectangular trajectory simulation in the vertical plane, the UAV goes through a ground phase, a take-off phase, a flight phase, a descent phase, and a return-to-origin phase.During the initial ground stage, the UAV's wing tilt angle achieved a vertical orientation of 90° upwards.Subsequently, the UAV progressed into the take-off stage, gradually ascending to a predetermined flying altitude, accompanied by a gradual return of the wings to their original position.Following this, the UAV executed a leftward flight maneuver, reaching the designated target location, after which the wings once again tilted upwards by 90°.Subsequently, the UAV commenced its descent, maintaining the wings in their original position once it reached a specific height.Ultimately, the UAV, assuming the configuration of a Y-shaped rotorcraft, returned to its initial point of origin.The trajectory of the UAV's center of mass movement was derived and depicted in detail in Figure 4. Trajectory 3. In a rectangular trajectory simulation in the horizontal plane, the UAV continues to fly in the form of fixed wings after takeoff.In order to control the yaw angle of the UAV to 90° each time, we adopted the co-simulation method of Adams and Matlab.Firstly, the mechanical system model is established in Adams, and then the corresponding control scheme is designed in Matlab.The data exchange is carried out through the Adams/Control interface module.The Adams/Control module settings are shown in Figure 5.The establishment of the control scheme is completed in Matlab/Simulink, and the specific schematic diagram is shown in Figure 6.

Conclusions
Aiming to address the demand for express cargo transportation within and between cities, this study presents an innovative conceptual design scheme for vertical take-off and landing cargo UAVs.The performance of the UAV is evaluated through flight simulation.The UAV incorporates tilting wings to enable vertical take-off and landing while utilizing the step function to simulate take-off, hover, landing, and following rectangular trajectories in the vertical plane.Additionally, employing the co-simulation method of Adams and Matlab/Simulink, successful simulation of the UAV's flight in the horizontal plane is achieved, following predetermined rectangular and triangular trajectories.By conducting these simulation experiments, this research provides a valuable reference and guidance for the design and application of vertical take-off and landing cargo UAVs.

Figure 1 .
Figure 1.Different views of the prototype in Catia

Figure 2 .
Figure 2. Simulation model in Adams

Figure 3 .
Figure 3. Dependence of the height of center of mass of the UAV over time

Figure 4 .
Figure 4.The movement trajectory of the center of mass of the UAV

Figure 5 .
Figure 5.The Adams/Control module settings

Figure 6 .
Figure 6.The control schemes

Figure 8 .
Figure 8.The triangular trajectory in the horizontal plane