Vertical Take-off And Landing Vehicle Research Articles

Transition flight of a concept of lifting-wing quadcopter

Abstract This paper presents the concept of a lifting-wing quadcopter unmanned aerial vehicle (UAV), a vertical take-off and landing vehicle (VTOL) with a rear wing, a canard at its front and four propellers. The aerodynamic surfaces are designed so that their mounting angle can be adjusted and fixed before flight, so its performance in transition flight can be studied for a combination of wing and canard mounting angles. A dynamic model using rigid-body equations of motion is presented, which is used to compute the transition flight trajectory from hover to cruise in horizontal flight. The trim conditions were computed for a range of fixed wing and canard mounting angles to study the effects of these variables on transition trajectory parameters such as required power, body pitch angle and propeller rotation speeds as a function of flight speed. Furthermore, a transition flight control algorithm is presented, which has a cascaded PID controller and a reference scheduler to switch between the proper reference states, controls and control allocation matrix. Finally, the transition control algorithm of the conceptual UAV is numerically simulated. Results show that this configuration can perform a fast and smooth transition from hover to cruise flight using the proposed flight control algorithm, substantially reducing required propulsive power in cruise of up to 64%. The application of the control algorithm made notable a transition manoeuver that consists of negatively inclining the aircraft at a negative pitch angle, initially at high intensity, and as the final cruising speed approaches, the inclination is attenuated until the equilibrium pitch angle is reached. Simultaneously with the negative inclination of the pitch angle, there is a slight drop in altitude, which is quickly resumed as the trajectory develops until the final cruising speed. Lastly, this aircraft configuration can be widely used in applications where performance gains in operations currently carried out by multicopters, which cover large distances and need long flight time, would bring great operational advantages.

Optimal Transition Trajectory of a Quadrotor Biplane Tailsitter

This work focuses on transition trajectory generation for a special class of hybrid vertical takeoff and landing (VTOL) vehicles called quadrotor biplane tailsitter. The transition refers to the change of flight modes for a hybrid VTOL vehicle. A transition maneuver is challenging as the vehicle undergoes in low-speed high angle of attack condition which is highly unstable. This work proposes methods to generate an optimal trajectory for the forward transition of the vehicle. A simplified 3-degree-of-freedom (3-DOF) model of the vehicle is considered for generating the transition trajectory. The optimization problem is solved using nonlinear programming with appropriate dynamic and physical constraints. The work considers multiple optimality conditions that include minimal control effort, minimal transition time, and a combination of them. The results of different approaches are compared considering the feasibility of implementation on a physical vehicle.

Design and Determination of Aerodynamic Coefficients of a Tail-Sitter Aircraft by Means of CFD Numerical Simulation

Vertical take-off and landing (VTOL) aircraft have become important aerial vehicles for various sectors, such as security, health, and commercial sectors. These vehicles are capable of operating in different flight modes, allowing for the covering of most flight requirements in most environments. A tail-sitter aircraft is a type of VTOL vehicle that has the ability to take off and land vertically on it elevators (its tail) or on some rigid support element that extends behind the trailing edge. Most of the tail-sitter aircraft are designed with a fixed-wing adaptation rather than having their own design. The design of the tail-sitter carried out in this work had the particularity of not being an adaptation of a quad-rotor system in a commercial swept-wing aircraft, but, rather, was made from its own geometry in a twin-rotor configuration. The design was performed using ANSYS SpaceClaim CAD software, and a numerical analysis of the performance was carried out in ANSYS Fluent CFD software. The numerical results were satisfactorily validated with empirical correlations for the calculation of the polar curve, and the performance of the proposed tail-sitter was satisfactory compared to those found in the literature. The results of velocity and pressure contours were obtained for various angles of attack. The force and moment coefficients obtained showed trends similar to those reported in the literature.

An exemplary definition of a vertidrome's airside concept of operations

In many cities the (public) transportation system already faces challenges to adjust appropriately to the growing population. Lifting the transportation offer into the third dimension by introducing Urban Air Mobility (UAM) may be a promising step towards an improvement. But what characteristics does UAM need to offer in order to represent successfully an extension to our traditional (public) transportation system and to fit into the concept of Mobility-as-a-Service (MaaS) where various modes of transportation are bundled and accessible on demand? On the one hand, the supporting ground infrastructure specialized in accommodating UAM and vertical take-off and landing (VTOL) operations, in this research named vertidrome, and on the other hand a consortium of stakeholders (vehicle operator, vertidrome operator, air traffic management, passenger, city councils, etc.) will determine a considerable portion of these requirements. The vertidrome is a UAM traffic junction, which merges airside and landside operations and interactions between the vertidrome infrastructure components, the vehicles and the passengers. This research work focuses on the exemplary development of a vertidromes airside operation considering a UAM application at the Munich trade fair (Germany). Following this objective, we analyze the unique characteristics of UAM, review the current state of the art regarding UAM ground infrastructure designs and introduce a new and VTOL-specific terminology vertidrome. In addition, we define an exemplary vertidrome concept of operations: a linear and expandable drive-through (LIEDT) topology, distinct approach and departure mission profiles based on the VTOL vehicle Volocopter 2X, as well as operating (airside air) and traffic (airside ground) rules for arriving and departing vehicles. The results will contribute to the development of a corresponding discrete event-based simulation (DES) depicting the elaborated vertidrome's airside structure and operations followed by the development of a performance assessment method evaluating a vertidrome's airside traffic flow (Vertidrome Airside Level of Service - VALoS).

A high-fidelity aeroacoustic simulation of a VTOL aircraft in an urban air mobility scenario

This paper concerns a high fidelity computational approach for the prediction of the acoustic impact of a VTOL vehicle operating in a urban area. The aerodynamic problem is solved with a free-wake vortex lattice boundary element method whereas the challenging acoustic scattering problem by a large urban area is carried out by coupling a Ffowcs Williams and Hawkings approach (FW-H) with a Boundary Element Method (BEM), accelerated with an Adaptive black-box Fast Multipole Method (AbbFMM). This work also demonstrates the set-up of a comprehensive numerical chain for assessing the noise of vertical take-off and landing (VTOL) vehicle during their whole operations meanwhile producing highly accurate noise shielding predictions when they are approaching in proximity of the urban areas.

Optimisation Studies for an Efficient Aerodynamic Configuration of a Blended Wing Unmanned Aerial Vehicle

There are various configurations and parameters that contribute to the Design of Unmanned Aerial Vehicles for specific applications. This paper deals with an innovative design of an unmanned aerial vehicle for a specified class of UAVs that require demands such as long endurance, minimized landing space with vertical take-off and landing (VTOL) capabilities. The focal point of this design is superimposing the high endurance blended wing design into tri-copter to address these parameters. The preliminary calculations are initially performed for the blended wing VTOL vehicle based on the required payload capacity and endurance. Superimposing the tri-copter will decrease the aerodynamic efficiency of the vehicle. Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical methods and algorithms to solve complex problems involving fluid flow which will effectively employed to reduce the cost and time during the conceptual and preliminary design stages. CFD analysis was carried out to estimate the major parameters like lift, drag, lift coefficient (CL) and drag coefficient (CD) for various Angle of Attack (AoA) for configurations of blended wing vehicle with and without tri-copter system in the cruise condition. Thus, the vehicle design and propulsion system is effectively optimized using this drag estimation.

Enhancing VTOL Multirotor Performance With a Passive Rotor Tilting Mechanism

This article discusses the benefits of introducing a simple passive mechanism to enable rotor tilting in Vertical Take-Off and Landing (VTOL) multirotor vehicles. Such a system is evaluated in relevant Urban Air Mobility (UAM) passenger transport scenarios such as hovering in wind conditions and overcoming rotor failures. While conventional parallel axis multirotors are underactuated systems, the proposed mechanism makes the vehicle fully actuated in SE(3), which implies independent cabin position and orientation control. An accurate vehicle simulator with realistic parameters is presented to compare in simulation the proposed architecture with a conventional underactuated VTOL vehicle that shares the same physical properties. In order to make fair comparisons, controllers are obtained solving an optimization problem in which the cost function of both systems is chosen to be equivalent. In particular, the control laws are Linear-Quadratic Regulators (LQR), which are derived by linearizing the systems around hover. It is shown through extensive simulation that the introduction of a passive rotor tilting mechanism based on universal joints improves performance metrics such as vehicle stability, power consumption, passenger comfort and position tracking precision in nominal flight conditions and it does not compromise vehicle safety in rotor failure situations.

Discrete-time fault tolerant control for semi-Markov jump systems with finite sojourn-time

This paper presents an active fault tolerant control scheme for discrete-time semi-Markov jump systems. The semi-Markov kernel approach and the finite sojourn time restriction are employed to obtain finite stability sufficient conditions for stability and stabilization. Semi-Markov processes are applied to model the faults occurrence of the actuators and the fault detection process. To guarantee the stability of the resulting closed loop system, an elapsed-time-dependent controller design method is applied. Finally, a numerical example and a vertical take-off and landing vehicle (VTOL) example are shown to illustrate the effectiveness and potential of the proposed design technique.

Extended Modeling of Vertical Axis Motion Dynamics of VTOL Vehicle

Development of a reliable high-performance multirotor unmanned aerial vehicle (UAV) requires an accurate and practical model of the vehicle dynamics. This paper describes the process and results of the dynamic modeling of an unmanned aerial platform known as quadrotor. To model a vehicle dynamics, elementary physical and aerodynamical principles has been employed. Parameter estimations, from a UAV design have been obtained through direct and indirect measurements. In addition to standard configuration of VTOL (Vertical Take-Off and Landing) platform, the amortized landing gear, modeled as spring-damper system, has been added. The resulting model has been implemented in a simulation environment under MATLABs toolbox, SIMULINK. Some numerical results are presented to illustrate response of the open loop system to specific commands.

Landing a VTOL Unmanned Aerial Vehicle on a Moving Platform Using Optical Flow

This paper presents a nonlinear controller for a vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV) that exploits a measurement optical flow to enable hover and landing control on a moving platform, such as, for example, the deck of a sea-going vessel. The VTOL vehicle is assumed to be equipped with a minimum sensor suite [i.e., a camera and an inertial measurement unit (IMU)], manoeuvring over a textured flat target plane. Two different tasks are considered in this paper. The first concerns the stabilization of the vehicle relative to the moving platform that maintains a constant offset from a moving reference. The second concerns regulation of automatic vertical landing onto a moving platform. Rigorous analysis of system stability is provided, and simulations are presented. Experimental results are provided for a quadrotor UAV to demonstrate the performance of the proposed control strategy.

Design and implementation of a hybrid fuzzy logic controller for a quadrotor VTOL vehicle

Helicopters have generated considerable interest in both the control community due to their complex dynamics, and in military community because of their advantages over regular aerial vehicles. In this paper, we present the modeling and control of a four rotor vertical take-off and landing (VTOL) unmanned air vehicle known as quadrotor aircraft. This model has been generated using Newton-Euler equations. In order to control the helicopter, classical PD (proportional derivative) and Hybrid Fuzzy PD controllers have been designed. Although fuzzy control of various dynamical systems has been presented in literature, application of this technology to quadrotor helicopter control is quite new. A quadrotor helicopter has nonlinear characteristics where classical control methods are not adequate especially when there are time delays, disturbances and nonlinear vehicle dynamics. On the other hand, Fuzzy control is nonlinear and it is thus suitable for nonlinear system control. Matlab Simulink has been used to test, analyze and compare the performance of the controllers in simulations. For the evaluation of the autonomous flight controllers, some experiments were also performed. For this purpose, an experimental test stand has been designed and manufactured. This study showed that although, both of the classical PD and the Fuzzy PD controllers can control the system properly, the Fuzzy PD controllers performed slightly better than the classical PD controllers, and have benefits such as better disturbance rejection, ease of building the controllers.

A terrain-following control approach for a VTOL Unmanned Aerial Vehicle using average optical flow

This paper presents a nonlinear controller for terrain following of a vertical take-off and landing vehicle (VTOL). The VTOL vehicle is assumed to be a rigid body, equipped with a minimum sensor su...

Design Considerations of a Prototype VTOL Robotic Vehicle through Market Survey Data Collection

A detailed technical design and performance comparison of current unmanned Vertical Take-Off and Landing (VTOL) vehicles is presented as a function of vehicle maximum speed, payload, range, endurance, and propulsion configurations. Mission applications and VTOL market characteristics are used to define design specifications for a new prototype unmanned VTOL vehicle suitable for a wide range of (mostly) civilian applications. The proposed VTOL vehicle's design phase is presented, including: performance capabilities calculation, fuselage strength evaluation and weight optimization via crash/drop tests. Drop tests performed have followed standard regulations used for airworthiness certification of such vehicles. The proposed VTOL vehicle is currently under prototype development.