Stefan R. Bieniawski

Control of Multiple UAVs for Persistent Surveillance: Algorithm and Flight Test Results

Interest in control of multiple autonomous vehicles continues to grow for applications such as weather monitoring, geographical mapping fauna surveys, and extra-terrestrial exploration. The task of persistent surveillance is of particular significance in that the target area needs to be continuously surveyed, minimizing the time between visitations to the same region. This distinction from one-time coverage does not allow a straightforward application of most exploration techniques to the problem, though ideas from these methods can still be used. The aerial vehicle dynamic and endurance constraints add additional complexity to the autonomous control problem, whereas stochastic environments and vehicle failures introduce uncertainty. In this work, we investigate techniques for high-level control, that are scalable, reliable, efficient, and robust to problem dynamics. Next, we suggest a modification to the control policy to account for aircraft dynamic constraints. We also devise a health monitoring policy and a control policy modification to improve performance under endurance constraints. The Vehicle Swarm Technology Laboratory-a hardware testbed developed at Boeing Research and Technology, Seattle, WA, for evaluating a swarm of unmanned air vehicles-is then described, and these control policies are tested in a realistic scenario.

Discrete, Continuous, and Constrained Optimization Using Collectives

Aerospace systems continue to grow in complexity while demanding optimal performance. This requires the systems to be both designed and controlled optimally. Aerospace systems are also typically comprised of many interacting components, some of which may have competing requirements. The optimization approaches used for aerospace systems usually require centralized coordination and synchronous updates. In addition, while the approaches treat the large numbers of variables, they may not take advantage of the fact that the coupling may only be between a relatively small number of the variables. Distributed optimization algorithms, such as the approach based upon collectives presented in this paper, attempt to exploit this aspect. A collective is deflned as a multi-agent system where each agent is self-interested and capable of learning. Furthermore, a collective has a specifled system objective which rates the performance of the joint actions of the agents. Although collectives have been used for a number of distributed optimization problems in computer science, recent developments based upon Probability Collectives (PC) theory enhance their applicability to discrete, continuous, mixed, and constrained optimization problems. This paper will present the theoretical underpinnings of the approach for these various problem domains. Several example problems are used to illustrate the technique and to provide insight into its behavior. The examples include discrete, constrained, and continuous problems. In particular a constrained discrete structural optimization and a continuous trajectory optimization illustrate the breadth of the collectives approach.

Fleet Assignment Using Collective Intelligence

Product distribution theory is a new collective intelligence based framework for analyzing and controlling distributed systems. Its usefulness in distributed stochastic optimization is illustrated here through an airline fleet assignment problem. This problem involves the allocation of aircraft to a set of flight legs in order to meet passenger demand, while satisfying a variety of linear and non-linear constraints. Over the cause of the day, the routing of each aircraft is determined in order to minimize the number of required lights for a given fleet. The associated flow continuity and aircraft count constraints have led researchers to focus on obtaining quasi-optimal solutions, especially at large scales. This paper proposes the application of this new stochastic optimization algorithm to a non-linear objective cold start fleet assignment problem. Results show that the optimizer can successfully solve such highly constrained problems.

Flutter Suppression for High Aspect Ratio Flexible Wings Using Microflaps

Miniature trailing edge effectors (MiTEs) are small flaps (typically 1% to 5% chord) actuated with deflection angles up to 90 degrees. Because of their small size, these devices provide the opportunity for high bandwidth control. The present study considers the use of many such control surfaces to increase the flutter speed of a high aspect ratio flexible wing. A finite element plate model is used to model the structural dynamics and an unsteady panel method provides the aerodynamic loads. Experimental flutter testing shows good agreement with the numerical stability analysis. The MiTE is modelled by a single panel element at the trailing edge with varying boundary conditions at its collocation point. In spite of the complex viscous aerodynamics of the MiTEs, the panel model proved to be adequate in simulating the steady and unsteady behavior. The use of these effectors for control is complicated by their nonlinear characteristics. Since the actuator is only effective at high deflection angles, it is only deflected in one of three positions: up, down, and neutral. The design of a nonlinear feedback controller has been performed using numerical optimization. Introduction The Gurney flap is a small (typically 1% ∼ 5% chord) flap used to increase the maximum lift of an airfoil section. It was developed and applied to racing cars by Robert Liebeck and Dan Gurney in 1960’s, although similar devices were employed in World War II aircraft such as the P-38 ∗Doctoral Candidate, Department of Aeronautics and Astronautics, AIAA Student Member †Professor, Department of Aeronautics and Astronautics, AIAA Fellow ‡Doctoral Candidate, Department of Aeronautics and Astronautics, AIAA Member Copyright c ©2002 by authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. and F8-F. Numerous wind-tunnel tests and numerical computations have been conducted on both single element and multi-element airfoils with Gurney flaps. These studies confirm that despite their small size, Gurney flaps with deflections near 90 degrees can increase maximum lift and the lift produced at a given angle of attack. Liebeck explained this effect, produced by a short region of separated flow directly upstream of the flap, with two counterrotating vortices downstream that effectively modify the trailing edge Kutta condition. This was verified to be correct for time averaged flow by flow visualizations and CFD simulations. In the present work, we consider the use of devices similar to Gurney flaps, not to increase maximum lift, but to provide high bandwidth, robust control. Miniature Trailing edge Effectors (MiTEs) are small movable control surfaces at or near the trailing edge, deflected to large angles to produce control forces and moments that may be used for flight control or structural mode control. The current study, begun in 1998, deals with the use of such actuators for aeroelastic control. MiTEs have distinct advantages over conventional control surfaces: High bandwidth actuation can be achieved due to their small size and inertia, enabling their use for flight control or for higher frequency structural mode control with significantly reduced power requirements. Spanwise variation and interdigitated deflections can produce rolling, pitching, and yawing moments, as well as the control of specific structural modes. Because the surfaces are deflected in a discrete manner (up, down, or neutral), no active servo-feedback is required, eliminating the expense of accurate, high-rate servo actuators and enabling a large number of these effectors to be fabricated at a low cost. The use of a large number of small, simple effectors also makes the system faulttolerant. The application of MiTEs for aeroelastic control is demonstrated here by designing an active control system that can suppress the flutter of a flexible wing. High aspect ratio flexible wings are of interest

Control and Management of an Indoor, Health Enabled, Heterogenous Fleet

Coordination of multiple, autonomous unmanned aerial vehicles is a growing topic within the research community. Universities and industry players are investing in Multi-vehicle, unmanned testbeds in order to better understand the benets and logistics of vehicle coordination. Boeing operates an indoor ight facility to enable hardware-in-the-loop, System of Systems evaluations in utilizing a heterogeneous autonomous eet of air and ground vehicles. Aside from providing a cost eective means of evaluating new autonomous vehicle technologies, the facility includes an existing eet of heterogeneous helicopters that are used to test high level, health based mission management concepts. This paper discusses the control and health-based management concepts required for the safe, reliable and ecient operation of vehicles in the facility. Details and advantages of the modular facility hardware architecture, which is key to rapid integration of new vehicle concepts, is described. A rapid control law design process, suitable for all types of helicopters, is also discussed and the actual ight performance of all vehicles is presented. Finally, the safety and reliability benets of autonomous, health based vehicle monitoring and behavior are discussed.

Cooperative avoidance control for UAVs

The objective of this paper is to present the application of a methodology for designing cooperative control laws that guarantees safe coordination of unmanned aerial vehicles (UAVs). In parallel, an optimal control law and an avoidance control law are designed for each UAV of the multi-vehicle system. These two control laws are combined, guaranteeing that each UAV arrives at their desired state and that their path remains collision free.

Formation Flight for Aerodynamic Benefit Simulation Development and Validation

The Air Force Research Lab and DARPA have been investigating the challenges and opportunities associated with flying aircraft in formation for aerodynamic benefit. Under the Surfing Aircraft Vortices for Energy (SAVE) concept, aircraft are flown autonomously at longitudinal separations of 3000-8000ft at offsets from the wake sufficient to obtain significant aerodynamic benefit. A baseline C-17 simulation is updated to include the dynamics and the aerodynamic effects of a lead aircraft wake on a trailing aircraft. Details of the wake dynamic and aerodynamic models are provided, including how CFD based models are integrated into a real-time simulation. Flight test data analysis is conducted to extract the actual aerodynamic influences and the results are compared to the CFD based models. The simulation models are updated based on the flight test data and the final results are compared to flight test maneuvers and flight test derived fuel burn measurements.

Micro-Aerial Vehicle Flight in Turbulent Environments: Use of an Indoor Flight Facility for Rapid Design a nd Evaluation

One of the most significant challenges facing Micro-Aerial Vehicles (MAVs) is flight within the turbulent environments they typically encounter. Their small size makes them particularly sensitive to the gusty wind environment around buildings and in close proximity to the ground. The turbulent flight environment also presents an opportunity for designs that are able to extract energy from the turbulent environment. Recent studies have shown the feasibility of energy extraction for vehicles larger than typical MAVs. Further, the potential benefit increases as the size of the vehicles becomes smaller, indicating MAVs may even further benefit. The wide range of MAV configurations that have been explored and are possible indicates the need for an environment where designs can be rapidly developed and evaluated. A further challenge with developing both the MAVs and the associated energy extraction algorithms is repeatability in the stochastic turbulent environment. This paper describes the use of an indoor flight facility that can address these needs. The facility provides an opportunity to quickly evaluate a variety of vehicle designs and control algorithms in a controlled, repeatable environment. This environment can then be modified to include more stochastic elements as added realism is required. The basic facility capabilities, as well as several aspects of the vehicles themselves, are described. Initial results are shown for two classes of MAVs.

Using Multiple Information Sources to Construct Stochastic Databases to Quantify Uncertainty in Certification Maneuvers

Understanding how a new aircraft configuration will perform during certification maneuvers is important during the conceptual design phase. Most current methodologies require a complete aerodynamic database be constructed without a way to determine how the uncertainty in the database affects the resulting maneuvers. Building upon previous work in combining multiple information sources to build a stochastic aerodynamic database for the configuration of interest, this paper contains a methodology to estimate what location in the flight envelope has the dominant impact on the uncertainty in the quantity of interest. This is done by estimating the aerodynamic characteristics at a set of Latin Hypercube Sampling locations. The maneuver is then run multiple times using deterministic samples of the stochastic database incorporating each of the LHS locations separately. Fitting a Gaussian Process between the vehicle conditions (angle of attack (α), Mach number, control surface deflection, etc.) and the quantity of interest (a measure of the uncertainty in the maneuver), we found the best results could reduce the 90% Confidence Interval of the time to descend in the emergency descent case by approximately 70% when adding 5 new high fidelity points.

Guidance & Control of Micro Air Vehicles: Rapid Prototyping & Flight Test

own autonomously within the laboratory in order to conducted hardware in the loop testing of advanced ight control technologies. This paper covers the process employed to rapidly design the autonomous, xed-wing MAVs own within Boeing’s indoor test facility. Specically, Vortex Lattice modeling and subsequent LinearQuadratic Tracker control design are discussed. A Nonlinear attitude control law and a smooth, spline based guidance scheme are presented and their advantages are discussed in the context of ying within the 10x20 meter connes of the indoor laboratory. Finally, ight tests and parameter identication results for a 20 inch diameter, 150 gram ying disc are presented.