Optimized behavioural UAV formation flight controller design

In order to avoid external interference, the UAV cluster should keep electromagnetic silence as much as possible and send less electromagnetic wave signals to the outside world when conducting formation flight. In order to maintain formation flight, azimuth-only passive positioning method is proposed to adjust the position of UAVs, that is, some UAVs in the formation send signals, and other UAVs passively receive signals, from which orientation information is extracted for positioning. In this context, this paper studies the problem of pure azimuth passive positioning in UAV formation flight, and discusses the necessity of using pure azimuth passive positioning in UAV formation flight to cope with the limitation of electromagnetic interference on traditional positioning methods. The specific problem includes how to use the three-point positioning method to determine the position of the signal receiving UAV, whose receiving direction is determined by the Angle formed by the two UAV sending signals in the formation. Consider a circular formation containing 10 Uavs, where one UAV is located at the center of the circle and the remaining nine are evenly distributed on the circumference. By establishing mathematical models and geometric relationships, solutions are proposed to ensure positional accuracy under different measurement errors. This study provides a theoretical basis and practical method for improving the accuracy and stability of UAV formation flight.

A new set of analytical range equations (a modification of the traditional Bréguet range equation) suitable for formation flight at transonic flight speeds under realistic operating conditions (constant Mach number and altitude) is derived. Formations of two aircraft of the same type are analyzed to determine the effects of 1) weight differences between the aircraft, 2) altitude, and 3) the formation flight range on the potential fuel benefits and the associated optimum Mach number. In the case of a weight difference, the lightest aircraft should lead the formation to realize the largest fuel benefits. Overall, fuel savings of 6 to 12% for the total formation can be realized at the expense of a reduction in cruise Mach number from 0.85 to 0.80. The fuel benefit is much less (2 to 8%) when the formation is flown at the original design cruise Mach number. In terms of fuel benefits and Mach number, it is beneficial to fly in formation at higher altitudes. Formation flight step climb procedures are possible, but the additional fuel savings are minimal compared to a constant-altitude formation flight.

: In this research the close formation flight control problem is addressed. The formation consists of a lead and wing aircraft, where the wing flies in close formation with the lead, such that the lead's vortices produce aerodynamic coupling effects, and a reduction in the formation's drag is achieved. A controller, i.e., a formation-hold autopilot for the wing aircraft, is designed such that the formation's geometry is maintained in the face of lead aircraft maneuvers. In the formation flight control system, the wing and lead aircraft dynamics are coupled due to kinematic effects, and, in the case of close formations, additional aerodynamic coupling effects are introduced. In the research these additional aerodynamic coupling effects are properly modeled. The most significant aerodynamic coupling effect introduced by close formation flight entails the coupling of the lateral/directional channel into the altitude-hold autopilot channel. It is shown that formation hold autopilots designed ignoring the aerodynamic coupling effects, yield satisfactory performance in close formation flight.

This paper presents a consensus-based coordination protocol, using a fuzzy logic gain scheduling algorithm, for the formation flight of multiple quadrotors UAVs. The Newton-Euler approach is used to present the equations of motions for the multiple quadrotors UAVs. The formation flight consists of a distributed approach. Real-time experiments are presented in order to test the capabilities of the online tuning of consensus parameters, as well as a comparison with a fixed gain protocol. In effect, the variable gain consensus protocol shows a smoother output while maintaining a robust performance against induced wind gusts, in comparison with fixed gain coordination approach.

Avian formation flight has always inspired technology protagonists to mimic and harness associated benefits for the aviation industry. This paper discusses the performance benefits of similar and hybrid jet airliners flying in formation. The aerodynamic forces are modelled through potential flow theory. The lateral and vertical spacing is varied to estimate advantages in range. For simplicity, only cruise performance is analysed. By employing formation flying in wide-body aircrafts, an increase in range up to 65% is observed relative to standard flight. In addition to that, an optimal switching point during cruise flight is evaluated to give equal benefits to both aircrafts flying in formation. The study proposes a new concept of shared airspace where different aircrafts cooperate on long routes for fuel savings. However, the findings reported in this paper are of theoretical nature and high-fidelity models and experimentation is considered necessary to further evaluate the benefits of formation flying. Moreover, existing distancing restrictions between two aircrafts, imposed by regulatory authorities, are also a potential limitation in successful realisation of commercial formation flight.

Birds fly in formation to benefit from the upwash wake vortices created by their peer leader. Similar strategies can be employed on aircraft for fuel saving or for range extension. However, further understanding of wake vortices in the near field and mid field is needed for close formation flight (< 10 wingspans). This paper introduces a new method for wake vortex detection using small UAV formation. A NonLinear Dynamic Inversion (NLDI) based formation control law is adapted to the WVU Phastball UAV platform. The designed controller showed good tracking performance during close formation flight (5-10 wingspans) with typical errors of less than 3 meters during straight legs. Then, multiple sensor measurements from leader-follower UAV formation flights were used for the wake vortex detection, including angle of attack, angle of sideslip, accelerometers, and gyros. The collected flight data showed the feasibility of using UAV formation for the wake encounter detection.

ABSTRACT: This paper addresses a feedback linearization control problem for the nonlinear dynamics of an underwater glider system. We consider the buoyancy and moment as control inputs, which come from the mass variation and elevator control, respectively. Moment-to-force coupling increases the nonlinearities, which make the controller design difficult. By using a feedback linearization technique, we convert the nonlinear underwater glider to an equivalent linear model and design a linear controller. The controller for the equivalent converted linear system is designed using sufficient conditions in terms of linear matrix inequalities. Then, the control input of the nonlinear model of an underwater glider is formulated from the linear control input. An experimental examination is implemented to verify the effectiveness of the proposed technique.

Drift-free solar sail formations in elliptical Sun-synchronous orbits

Nowadays the feedback linearization and backstepping techniques are introduced as methods for linearization of a system with coordinate transformation and nonlinear designing, respectively. The feedback linearization and backstepping techniques are robust methods, however this study indicates that combining of them and adding nonlinear disturbance observer increases the system robustness. In this paper, the system linearization with backstepping process has been studied. Combining of above mentioned techniques has been used for linearization in this method. The systems have been practically exposed to disturbances and uncertainties. Nonlinear disturbance observer has a good ability to estimate disturbances and nonlinear dynamics, so it is useful method for increasing performance of control methods, reducing the effects of disturbances and system uncertainties. The presented control method with nonlinear disturbance observer improves the system robustness against different types of uncertainties, so this method is a modified technique. The proposed design process consists of two steps: First, the nonlinear disturbance observer has been designed to estimate the uncertainties and external disturbances applied to system. Second, a controller has been designed using combined feedback linearization-backstepping method that used prior estimations to decrease the effects of external disturbances and uncertainties in the control input.

Robust adaptive three-dimensional trajectory tracking control scheme design for small fixed-wing UAVs

In this article, the robust control of an electromagnetic levitation system using an integral optimal sliding mode control technique is proposed. The feedback linearization technique is developed to obtain the linearized controllable model. The linearized model is used to design optimal controller gain with a linear quadratic regulator using the algebraic Riccati equation. The main goal of the proposed technique is to keep the levitated object in the desired position while removing the chattering effect on the control input. Stability proof of the designed control scheme is developed using Lyapunov's method. The simulation experiments validate the proposed technique's robustness. The presented work also elaborates on the comparison of sliding mode control with integral optimal control and proves the robustness of the proposed controller.

A guidance-based approach to formation flight of unmanned air vehicles is presented. Most of the works related to formation flight deal with the control of the relative positions between the vehicles in the formation. In the proposed approach a pursuit law replaces the control law. A new rule of pursuit denoted as detective deviated pursuit is then developed based on known guidance rules. The proposed guidance law regulates the distances between vehicles and the heading angles with respect to the lines of sight. We show that the detective deviated pursuit rule can be applied to formation flight, where the formation geometry determines the guidance-law parameters. The work discusses the conditions for a stable formation flight in the case of a maneuvering leader and proposes a control scheme for implementation. The performance of the new guidance-based formation flight is evaluated via simulations. Nomenclature C D = drag coefficient CL = lift coefficient D = drag g = acceleration caused by gravity K = drag polar constant K xI = integral controller for the x state K xP = proportional controller for the x state n = load factor R = radius r = leader‐follower range T = thrust t = time V =v elocity W = weight X = states vector x, y = inertial coordinates

Autonomous formation flight has been a fast growing research area during the last decade. Unmanned aerial vehicles (UAVs) can achieve a wide range of benefits from formation flight, such as fuel saving and aerial refueling. In this paper, the development of a small UAV system, called Swallow UAV system, as testbed of formation flight, is presented. Swallow UAV system includes Swallow UAV itself and a Hardware-In-the-Loop Simulation Environment (HILSE). Swallow UAV is a fixed wing, pusher-type, electric motor driven aircraft with 1.4 meter wing span. Its avionics system includes an onboard computer and a sensor system with GPS, IMU, air data sensor, and motor monitoring unit to provide position, velocity, inertial data, and system health. Communications between UAVs and the ground control station (GCS) are conducted by wireless modem. A fuzzy navigation and control system (FNCS) is developed for the waypoint navigation and attitude control of the aircraft. GPS velocity based pseudo attitude and fuzzy logic control are applied to FNCS for attitude estimation and fast implementation of controllers. HILSE is built to verify FNCS with onboard computer on the ground. X-Plane flight simulator is applied to simulate aircraft dynamics and output sensor data. GCS software, built with data distributor, transmits these data to the onboard computer and receive control signal from it so the onboard computer can control the aircraft in X-Plane. HILSE can perform pre-flight test for software debug, which improves safety and efficiency of flight test. The design of Swallow UAV is verified by flight test and the result shows that it has sufficient flight performance with waypoint navigation and attitude control capability to be used as a formation flight testbed.

This paper introduces a multi-fidelity computational framework for the analysis of aerodynamic performance of flight formation. The Vortex Lattice and Reynolds Averaged Navier–Stokes methods form the basis of the framework, as low- and high-fidelity, respectively. Initially, the computational framework is validated for an isolated wing, and then two rectangular NACA23012 wings are considered for assessing the aerodynamic performance of this formation; the optimal relative position is through the multi-fidelity framework based on the total drag reduction. The performance estimates are in good agreement with experimental measurements of the same configuration. Total aerodynamic performance of formation flight is also assessed with respect to attitude variations of the lifting bodies involved. The framework is also employed to determine the optimal position of blended-wing-body unmanned aerial vehicles in tandem formation flight.

Helicopters have many good flight characteristics. Recently, helicopters are used for various situations. However, there are few studies about cooperative control between different scale helicopters. In this paper, an approach to cooperative control between different scale helicopters is proposed to expand the field of application of using helicopters. Leader-following is applied for the control scheme of formation flight to multiple autonomous helicopters. Two helicopters model is discussed as a first step for formation flight of multiple helicopters in this paper. The cooperative control system is based on the weighted pseudo-inverse matrix and null-space. This proposed system is scalable. Therefore the control system can be expanded easily. Additionally, the control input generator is designed with cascade controller. Four control inputs should be generated suitably to control 6-DOF of the helicopter because helicopters are the underactuated robots and there are nonholonomic constrains. The workspace observer are adopted in order to compensate disturbance, parameter uncertainty, interaction of helicopters, influence of the wind, and so on.