Maximum Turn Rate Research Articles

Control Authority of a Single-Surface Parafoil with Bleed-Air Spoilers

Bleed-air control of ram-air parafoils is a lightweight and cost-effective mechanism that enables significant landing accuracy improvements compared to traditional trailing edge brake control due to the addition of direct glide slope control. Single-surface parafoil canopies have been shown to be lightweight and possess similar flight behavior as their ram-air counterparts. The design of bleed-air spoilers is more challenging for single-surface canopies, which lack the internal ram-air that provides a high pressure differential at any chordwise location. This paper explores bleed-air spoilers on single-surface parafoils with a focus on turn rate and glide slope control capabilities. Through a flight test campaign, it was shown that bleed-air spoilers on a single-surface parafoil provide both turn rate control from asymmetric vent opening and glide slope change from symmetric vent opening. Vents located far forward at the 10% chord location yield substantial control response with a maximum turn rate response of 38 deg/s and a maximum glide slope change of 58%. Vents located farther aft at 30, 50, and 70% chords demonstrated diminished control authority. Varying the spanwise locations of the spoilers revealed that the outermost vents had negligible lateral and longitudinal control authority.

Conceptual design modeling by the novel aircraft conceptual design and analysis system (ACDAS)

PurposeThroughout an aircraft development process, the conceptual design phase is an extremely important milestone; hence, the quality and success of this step directly affect the overall cost and lead time of the project. Because of this fact, the purpose of this study is to provide outputs and suggestions to the designing engineer regarding the requirements for reducing overall design time as well as costs and creating an ideal design at the early phases of the project by optimizing the aircraft development process.Design methodology approachThe system has been prepared parametrically and presents some performance specifications for the aircraft in the early phases of the design, for example, coefficients for lift CL as well as drag CD and weight as well as fuel estimations. The software uses a combination of well-known design techniques within just one platform in contrast to many other applications. Because of this feature, it is not needed to use different sub-platforms which would require an appropriate environment and even though would lead to complications with regard to the connectivity. The system also presents relevant information about the aircraft performance like velocity versus load factor (V-n) diagrams, maximum turn rate of climb, turn rate and climb angle graphs in contrast to many other open-source conceptual design platforms.FindingsIn this study, authentic General Dynamics F-16 Fighting Falcon and McDonnell Douglas F-15 Eagle data were used as input to the system, and advanced geometric and/or performance graphs were obtained and compared to the literature where a good agreement of the results was observed. These results with regard to the aircraft performance are typically product specific and quite rare in the literature. These data obtained by use of the software during the aircraft design are, thus, of major interest, especially for the design of new aerospace platforms. In this study, all of these graphs (especially the remarkable V-n diagram) are obtained on one platform.Originality valueThe aircraft conceptual design and analysis system software provides information and suggestions regarding the requirements for reducing the overall design time, reducing the design costs and creating an optimized design at the early phases of a project by optimizing the aircraft development process within just one convenient, that is, user friendly, platform, where it uses a combination of varying methodologies. Besides presenting one interface, which is quite typical for conceptual design tools, it allows applications of methods like vortex lattices and finite differences for obtaining aerodynamic performance parameters.

Flight Trajectories Optimization of Fixed-Wing UAV by Bank-Turn Mechanism

This paper addresses an optimization of Unmanned Aerial Vehicle (UAV) flight trajectories by bank-turn mechanism for a fixed-wing UAV at a constant altitude. The flight trajectories should be optimal and stay in the UAV flight operational area. The maneuver planning is conducted in two steps, which are UAV path planning and UAV flight trajectory planning. For the first step, the Bezier curve is employed as a maneuvering path. The path planning optimization objective is to minimize the path length while satisfying maximum curvature and collision avoidance constraints. The flight trajectories optimization objective is to minimize maneuvering time and load factor considering, minimum/maximum speed, minimum/maximum acceleration, maximum roll angle, maximum turn rate, and aerodynamics constraints. The variable speed trajectory generation is developed within allowable speed zone considering these UAV flight constraints by employing meta-heuristic optimizations. Results show that the PSO have outperformed the GA and the GWO for both steps of path planning and trajectory planning. The variable speed has succeeded in reducing the load factor during the bank-turn mechanism using the Bezier curve. The variable speed is recommended to be conducted when the result of the maneuvering path involve the lower turning radius. A simultaneous on arrival target mission has also succeeded to be conducted using the combination of the variable speed and constant speed strategies.

Optimal motion controllers for an unmanned surface vehicle to track a maneuvering underwater target based on coarse range-bearing measurements

This paper handles the situation in which an Unmanned Surface Vehicle (USV) tracks a maneuvering underwater target (UT) based on coarse range-bearing measurements. Here, we consider an USV equipped with cheap sensors providing coarse range-bearing measurements of a maneuvering UT. As a method to improve the tracking effectiveness, this paper introduces the optimal motion controllers for the USV. The USV has motion constraints, such as the maximum turn rate. Moreover, bearing standard deviation may vary as the ship-relative bearing varies. As far as we know, the proposed motion controllers are unique in achieving following two goals simultaneously: 1. Considering both the USV's maximum turn rate and its bearing standard deviation, the USV approaches the UT while estimating the UT's location using coarse range-bearing measurements. 2. Avoid getting too close to obstacles. The effectiveness of the proposed method is verified utilizing simulations.

Control laws to avoid collision with three dimensional obstacles using sensors

Collision avoidance in 3D environments is important to the problem of planning safe trajectories for an autonomous vehicle. Existing literature on collision avoidance assumed that obstacle shapes are known a priori and modeled obstacles as spheres or bounding boxes. However, in 3D environments, an obstacle shape is unknown to the autonomous vehicle, and the vehicle detects an obstacle boundary using 3D sensors, such as 3D sonar. In this paper, we introduce control laws for collision avoidance, considering scenarios where a vehicle detects arbitrarily shaped and non-convex obstacles using sensors. Moreover, our control laws are designed considering motion constraints, such as the maximum turn rate and the maximum speed rate of the vehicle. The effectiveness of our control laws is verified using MATLAB simulations.

Stealth path planning for a high speed torpedo-shaped autonomous underwater vehicle to approach a target ship

Let us consider a scenario where a high speed torpedo-shaped autonomous underwater vehicle (AUV) approaches a target ship. In an underwater environment, radio waves are easily dissipated. Thus, sound is the main energy transmitted from the AUV to the target ship. We plan the path of the AUV to reduce both the time required to meet the target ship and the AUV’s sound measured by the target. We consider a torpedo-shaped AUV equipped with backward propellers to move forward and fins for heading control. For this type of vehicle, there is an instantaneous maximum turn rate for its motion. In order to increase the safety of path, we plan the AUV’s path so that a sharp corner along the path is avoided. We verify the effectiveness of our stealth path planning method using MATLAB simulations.

Time-Optimal Path Planning for a Kinematic Car with Variable Speed

This paper investigates the minimum-time path-planning problem for a kinematic car with variable speed and turn rate controls. The speed is strictly positive, ranging from a lower to an upper limit, and the turn rate limits are symmetric about zero. The minimum principle is used to characterize the extremal controls and, using additional geometric arguments, a finite and sufficient set of candidate optimal controls is derived. It is found that, in addition to straight and maximum rate turning segments at maximum-speed, minimum-time paths may include “cornering” turns at the minimum forward speed and the maximum turn rate. A procedure is proposed for solving the path synthesis problem of constructing the minimum-time path between two “oriented points” in the plane.

Constrained Linear Quadratic Tracker for Optimal Performance Flight

M ODERN autonomous vehicles are able not only to follow certain low-level directives, such as airspeed, altitude, and heading, but also to track computed optimal trajectories in the sense to minimize fuel consumption and time of arrival at a certain waypoint while avoiding collisions with known and unknown obstacles, the terrain and other aerial vehicles. Substantial effort has beenmade recently to develop several techniques to compute optimal constrained trajectories for manned [1] and unmanned aircraft [2,3]. A common characteristic of these methods is their strong dependency on the maneuverability properties of the vehicle under consideration. Variables such as flight-path angle, turning rate, and turning radius are considered as constraints in the related optimization problems. Thus, larger values of flight-path angle and turning rate and a reduced radius of turn are desirable, because these improvements would allow for the operation of the vehicle in a wider set of scenarios. However, the inclusion of performance and maneuverability constraints is often accomplished in terms of maximum and minimum bounds without accounting for the fact that, in an aerial vehicle, optimal performance is always related to airspeed or Mach number [4]. For example, it is unlikely to simultaneously achieve maximum airspeed and maximum turning rate. The aircraft flight envelope, i.e. the combination of all achievable steady-state conditions, is more complex than a simple rectangle formed by minimum and maximum admissible values. Once the flight envelope is properly defined for operational purposes, the next task is the proposal and synthesis of a controller concerned with the defined limitations. This controller function, commonly referred to as an envelope protection system, is now widespread in the aeronautics industry [5] and remains a current topic of research. Unnikrishnan and Prasad [6] presented a protection system inwhich the operational limitations are treated as obstacles to be avoided. Falkena et al. [7] investigated several approaches to the problem of envelope protection, including a nonlinear constrained control law based on model predictive control (MPC). One of the challenges to designing envelope protection systems is the need to predict not only the future steady-state level of the constrained variable but also its transient characteristics, especially the peak value. Thus, a natural approach to this problem takes into consideration constrained control techniques, amethodology that has been validated by numerous studies [8–10]. The key mathematical element of these stable constrained controlmethods is the presence of an invariant set [11]withinwhich the state and input are guaranteed to lie, in accordance with the system constraints, indefinitely. Thus, strategies based on the invariant setmembership of the statevector are adequate to handle the envelope protection problem. Based on the aforementioned problems and current state-of-art solutions, this Note presents a constrained control technique called the constrained linear quadratic tracker (CLQT). The proposed method is a simplified variant of the MPC method known as the feasible target tracking MPC [10]. In addition, a new method to represent theflight envelope is proposed, based on linear inequalities. The denominated polyhedral flight envelope is constructed from the computed solutions of the nonlinear free-body equations with the advantage of providing achievable speed schedules for maximum performance maneuvers, such as maximum climbing flight-path angle, maximum turn rate, or a combination of both. Simulation results of the complete system composed of the polyhedral flight envelope representation and CLQT, using the Acaua test vehicle model (Fig. 1), are obtained in calm and turbulent air. The results demonstrate suitable tracking performance and protection against stall, even in a severely turbulent environment, with a relatively low computational execution time.

Guaranteed infinite horizon avoidance of unpredictable, dynamically constrained obstacles

This paper presents a new approach to guaranteeing collision avoidance with respect to moving obstacles that have constrained dynamics but move unpredictably. Velocity Obstacles have been used previously to plan trajectories that avoid collisions with obstacles under the assumption that the trajectories of the objects are either known or can be accurately predicted ahead of time. However, for real systems this predicted trajectory will typically only be accurate over short time-horizons. To achieve safety over longer time periods, this paper instead considers the set of all reachable points by an obstacle assuming that the dynamics fit the unicycle model, which has known constant forward speed and a maximum turn rate (sometimes called the Dubins car model). This paper extends the Velocity Obstacle formulation by using reachability sets in place of a single "known" trajectory to find matching constraints in velocity space, called Velocity Obstacle Sets. The Velocity Obstacle Set for each obstacle is equivalent to the union of all velocity obstacles corresponding to any dynamically feasible future trajectory, given the obstacle's current state. This region remains bounded as the time horizon is increased to infinity, and by choosing control inputs that lie outside of these Velocity Obstacle Sets, it is guaranteed that the host agent can always actively avoid collisions with the obstacles, even without knowing their exact future trajectories. Furthermore it is proven that, subject to certain initial conditions, an iterative planner under these constraints guarantees safety for all time. Such an iterative planner is implemented and demonstrated in simulation.

In-Flight Trajectory Planning and Guidance for Autonomous Parafoils

This paper presents a framework for onboard trajectory planning and guidance for a large class of autonomously guided parafoils. The problem is for the parafoil to reach a given location at a specified altitude with a specified final heading. Through appropriate change of the independent variable, the trajectory planning problem is converted from a three-dimensional free-final-time problem to a two-dimensional fixed-final-time problem. Using the wellknownDubinspath synthesis andknownparafoil performanceparameters, a concept of altitudemargin is developed as aquantitativemeasure of the availablemaneuvering energy for use in trajectory planning.Ahybrid strategy using two methods to generate kinematically feasible fixed-time trajectories is presented, each targeting a different range of initial values of the altitude margin. The trajectory can be replanned onboard in every guidance cycle, making the guidance effectively closed-loop, or replanned whenever the actual deviation of the actual condition from the reference trajectory exceeds a threshold. The proposed planning and guidance algorithm applies to a large class of parafoil canopies and payloads, which encompasses wide variations in the lift-to-drag ratio, wing loading, and maximum turn rate. The guidance logic has the potential of requiring little or no tuning to accommodate variations in canopy performance. Monte Carlo simulations are conducted to evaluate the effectiveness of the algorithm with dispersions in canopy performance, loading, wind profile errors, navigation uncertainty, using lateral control only, and using both longitudinal and lateral control.

Performance Flight Testing of Small, Electric Powered Unmanned Aerial Vehicles

Flight testing methods are developed to find the drag polar for small unmanned aerial vehicles powered by electric motors with fixed-pitch propellers. Wind tunnel testing was used to characterize the propeller-motor efficiency. The drag polar was constructed using data from flight tests. This drag polar was then used to find the following performance parameters: maximum velocity, minimum velocity, velocity for maximum range, velocity for maximum endurance, maximum rate of climb, maximum climb angle, minimum turn radius, maximum turn rate, and maximum bank angle. The developed flight testing methods are used to characterize the performance of a small UAV.