Parafoil Systems Research Articles

Trajectory optimization for collaborative recovery of parafoil systems using unmanned vessel

Traditional trajectory optimization methods for the parafoil system set fixed-point landing as the objective. However, in recent payload fairing recovery missions, the recovery system comprising two parafoils is collaboratively recovered by a mobile vehicle, posing new challenges to the current trajectory optimization technique. In order to recover two parafoil systems autonomously with an unmanned surface vessel, this paper presents a trajectory optimization framework composed of three following component processes consecutively. Firstly, a feasibility judgment algorithm based on reachable boundary estimation is designed to determine the possibility of recovering two parafoil systems. Secondly, the decoupled-then-simultaneous strategy is proposed to enhance the convergence of solving the collaborative recovery problem. Thirdly, the finite-element collocation approach is utilized to convert the formulated trajectory optimization problems into nonlinear programming (NLP) problems, which are solved by a highly efficient NLP solver. Simulation results show that the proposed trajectory optimization framework can efficiently generate the optimal trajectory for recovering two parafoil systems with a vessel.

Trajectory tracking control of powered parafoil system based on sliding mode control in a complex environment

Powered parafoil systems are nonlinear systems that are easily affected by the surrounding complex environment. In this study, an eight-degree-of-freedom (DOF) model of a powered parafoil was established based on the Lagrange equation and dynamic constraints. A control methodology was then designed based on an extended state observer (ESO) and sliding mode control (SMC). By accurately estimating the influences of the complex environment using the ESO, the estimated disturbances could be compensated for in the SMC. Finally, the simulation results showed that this method could effectively overcome the influence of environmental disturbances and achieve accurate trajectory tracking control. Compared with the traditional proportional–integral–derivative (PID) controller and active disturbance rejection control (ADRC), this method has a higher control accuracy and better robustness.

Flexible modeling of parafoil delivery system in wind environments

Wind disturbances usually affect the motion states and aerodynamic distributions of a parafoil, changing the dynamics of the delivery system and deteriorating the control accuracy. This paper establishes an accurate flexible dynamic model for a parafoil delivery system in wind environments. Combined with identified wind fields, an accurate aerodynamic model is established, using aerodynamic coefficients calculated by fluid–structure interaction simulations to ensure its validity under crosswind effects. Good agreement between results of simulations and experiments demonstrates the accuracy of the dynamic responses. The model can be applied to the research of precise control algorithms for real parafoil systems.

Model-Free Adaptive Control for Parafoil Systems Based on the Iterative Feedback Tuning Method

Parafoil systems are strongly nonlinear due to the flexibility of the canopy and suspension lines, and this characteristic cannot be simulated accurately by existing dynamic models. Hence, model-independent control methods are necessary for parafoil systems. This paper introduces a model-free adaptive control method based on the iterative feedback tuning (IFT-MFAC) method for parafoil systems that is a data-driven control method in which only input/output (I/O) data are needed during construction. In this paper, the MFAC construction process and stability analysis are explained, and then the IFT method is used to tune the two stepping factors of the MFAC method. A six-degree-of-freedom (DOF) dynamic parafoil system model is built to assess the performance of the method in a simulation with disturbances added to imitate real flights. A series of simulations and hardware-in-loop (HIL) tests are designed to verify the performance of the IFT-MFAC controller, and it is compared with the PID control method, the active disturbance rejection control (ADRC) method, and the MFAC method.

An optimal‐multiphase homing methodology for powered parafoil systems

SummaryIn order to achieve the precise and agile homing control of the powered parafoil system, an optimal‐multiphase homing methodology is explored in this article. The proposed methodology is composed by a trajectory optimization method based on quantum genetic algorithm and a trajectory tracking method based on an improved active disturbance rejection control (ADRC). First, an improved optimization method combining the optimal and multiphase theory is proposed. The optimized trajectory consists of the simple trajectories, the standard lines and circles, while also satisfying the multiple constraints such as the wind disturbance, terrain avoidance, flared landing, and so on. Then, an improved active disturbance rejection controller is presented. For improving the agility of the system during the path switching and the disturbance rejection ability in windy environment, based on ADRC, a disturbance rejection control algorithm is designed for the horizontal controller of the system. By analyzing the aerodynamic characteristic of the system, the wind disturbance will be compensated previously with a feedforward compensation unit. It will be largely reduce the observation error of the extended state observer, while improving the control effect and the reaction speed. Finally, the hardware‐in‐the‐loop simulation is presented to prove the effectiveness of the proposed methodology. The results show that the optimization method can be achieved successfully and the optimized trajectory can be tracked by the improved ADRC controller precisely and agilely. The landing error is less than 15 m with the proposed homing methodology.

In-flight Wind Field Identification and Prediction of Parafoil Systems

The wind field is an essential factor that affects accurate homing and flare landing of parafoil systems. In order to obtain the ambient wind field during the descent of a parafoil system, a combination method of in-flight wind field identification and prediction is proposed. First, a wind identification method only using global position system information is derived based on the flight dynamics of parafoil systems. Then a wind field prediction model is constructed using the atmospheric dynamics, and the low-altitude wind field is predicted based on the identified wind field of high-altitude. Finally, simulations of wind field identification and prediction are conducted. The results demonstrate that the proposed method can identify the wind fields precisely and also predict the wind fields reasonably. This method can potentially be applied in practical parafoil systems to provide wind field information for homing tasks.

Trajectory Tracking Control for Parafoil Systems Based on the Model-Free Adaptive Control Method

Parafoil systems are unique steerable decelerator systems. However, due to the strong nonlinearity caused by the flexibility of the canopy and the suspension lines, the existing dynamic models of parafoil systems are not sufficiently accurate enough; and hence, existing model-dependent control methods are not suitable for practical applications. To effectively eliminate the influence of inaccurate models on trajectory tracking, this paper introduces a novel real-time model-independent control method named the model-free adaptive control (MFAC) method. The stability of the MFAC method is theoretically deduced, and the robustness of this approach is analyzed and demonstrated by the Monte Carlo method. To assess the performance of the MFAC method, a six-degree-of-freedom (DOF) dynamic model is built, and then a series of simulations are performed under different conditions. The simulation results demonstrate the effectiveness of the proposed MFAC method in trajectory tracking. Compared with the proportional/integral/derivative (PID) control method and the active disturbance rejection control (ADRC) method, the MFAC method has higher precision and lower energy consumption, especially under complex disturbance conditions.

Design, modelling and control of collaborative samara autorotating wings (SAW)

Current methods of airdropping payloads accurately use the autonomously guided parafoil systems. Such approaches have limited trajectory options, hence limited accuracy, and could deliver only one payload with one airdrop. The Samara Autorotating Wings (SAW) is disposable type of aerial deployment system proposed in this paper to drop light-weight electronic payloads to remote locations accurately. Using autorotation as its main technique of lift creation, the concept borrows the natural dispersion method from maple seeds and takes advantage of the gyroscopic stability of a spinning mass. It does not require any propulsion system on-board and is equipped with an actuator to change the angle of attack of the wing for directional control. The concept also features a collaborative autorotation mode whereby multiple wings are attached together to form a larger rotor hub that benefits from increased angular momentum and control authority which is especially important at higher altitudes where the air is less dense. Although there have been other works on using autorotation to deliver payloads, this is the first documented effort in using a collaborative form of autorotation. The chordwise geometrical wing shape of SAW is optimized to achieve the maximum lift force during its autorotating descent. A nonlinear control method is conceived to regulate the descent direction and speed of SAW. This proposed control scheme enables an omni-directional guide slope, allowing SAW to be more maneuverable than parafoils or fixed-wing type of aerial deployments. SAW with different numbers of wings are tested against each other for drop characteristics and control performance, in simulated models and in physical experiments that involve a vertical wind tunnel with and integrated motion-captured system and free-fall drop tests.

A Generalized Predictive Control-Based Path Following Method for Parafoil Systems in Wind Environments

Parafoil systems represent flexible wing vehicles. In case a vehicle is flying at low altitude, it is well known that the vehicle is more susceptible to winds. Also, due to the nonlinear, large inertial existing within the system, traditional control methods, such as traditional proportional-integral-derivative (PID), cannot guarantee the quality of path following. Therefore, we here apply generalized predictive control (GPC)-based method for parafoil systems to follow the designed path for a better control effect. To achieve this, we first propose a novel modeling method based on computational fluid dynamics to build a dynamic model of the parafoil system in windy environments. Afterward, a guidance law is designed according to a hybrid approach that combines the cross track error and the line of sight. In addition, the path following controller is established by using GPC. Finally, we generate and interpret numerical results to demonstrate the feasibility of the horizontal path following method in windy environments by utilizing the semi-physical simulation platform. The achieved results show that the GPC controller achieves high precision path following. More precisely, it possesses a better anti-wind ability and tracking accuracy and, therefore, the method outperforms PID controller.

Adaptive Control of Precision Guided Airdrop Systems with Highly Uncertain Dynamics

The bulk of research in the field of precision guided airdrop systems has focused on improving landing accuracy in the presence of atmospheric winds that can exceed vehicle airspeed. One important challenge of parafoil systems is their highly uncertain flight dynamic behavior and control response, which can result from canopy degradation or an offnominal inflation event. This significantly impacts the ability to reach the target and can often lead to very large miss distances. This work addresses guided airdrop system model uncertainty with a novel combined direct and indirect adaptive control strategy to quickly characterize vehicle dynamics and lateral control sensitivity in flight. Extensive simulation and experimental flight testing indicate that the proposed adaptive algorithm is capable of high-accuracy landing in a large variety of degraded conditions, including unknown nonlinear changes in control sensitivity as well as control reversals. In comparison, current industry standard algorithms experience over an order of magnitude decrease in accuracy when tested under identical scenarios.

Global Positioning System Denied Navigation of Autonomous Parafoil Systems Using Beacon Measurements From a Single Location

Precision-guided airdrop systems have shown considerable accuracy improvements over more widely used unguided systems through high-quality position, velocity, and time feedback provided by global positioning system (GPS). These systems, like many autonomous vehicles, have become solely dependent on GPS to conduct mission operations. This necessity makes airdrop systems susceptible to GPS blackout in mountainous or urban terrain due to multipathing issues or from signal jamming in active military zones. This work overcomes loss of GPS through an analysis of guidance, navigation and control (GNC) capabilities using a single radio frequency (RF) beacon located at the target. Such a device can be deployed at the target by ground crew on site to retrieve package delivery. Two novel GNC algorithms are presented, which use either range from or direction to a RF beacon. Simulation and experimental flight testing results indicated that beacon-based methods can achieve similar results as GPS-based methods. This technology provides a simple and elegant solution to GPS blackout with best method studied showing only a 21% decrease in landing accuracy in comparison to GPS-based methods.

Computational fluid dynamics based dynamic modeling of parafoil system

The calculation of aerodynamic coefficients has been one of the key issues when modeling parafoil systems, that directly affects model precision. This study relates to investigate limitations of traditional calculation methods. As a result, we achieve aerodynamic parameters of a parafoil using computational fluid dynamics simulations. Also we employ the least square method as a tool for the rapid identification of deflection factors of aerodynamic coefficients. The estimated aerodynamic coefficients of the system were incorporated into the dynamic equations of the parafoil to implement a six degree of freedom model of a parafoil system according to the Kirchhoff equations. Numerical results generated by simulation and airdrop testing demonstrate that the established model can accurately describe the flight characteristics of the parafoil system.

Trajectory tracking of powered parafoil based on characteristic model based all-coefficient adaptive control

One of the primary difficulties in using powered parafoil (PPF) systems is the lack of effective trajectory tracking controllers since the trajectory tracking control is the essential operation for PPF to accomplish autonomous tasks. The characteristic model (CM) based all-coefficient adaptive control (ACAC) designed for PPF systems in horizontal and vertical trajectory control is proposed. The method is easy to use and convenient to adjust and test. Just a few parameters are adapted during the control process. In application, vertical and horizontal CMs are designed and ACAC controllers are constructed to control vertical altitude and horizontal trajectory of PPF based on the proposed CMs, respectively. Result analysis of different simulations shows that the applied ACAC control method is effective for trajectory tracking of the PPF systems and the approach guarantees the transient performance of the PPF systems with better disturbance rejection ability.

Avoiding Lockout Instability for Towed Parafoil Systems

Many towed systems consist of a parent platform moving along the ground, air, or water surface connected to a towed vehicle via a tether line. Motion of a towed parafoil system can be complex and is driven by motion of the parent platform, canopy control inputs, and wind disturbances. A particularly problematic flight dynamic instability for this system is canopy lockout, in which the canopy attains a large lateral offset and bank angle resulting in high line tension. It is possible to use left and right brakes to return the system to its nominal position; however, if the lateral offset and bank angle are too large, it is not possible to restore the system to a nominal position, and the lateral offset and bank angle grows until impact with a ground surface. This paper explores the lockout phenomena using a multibody simulation and identifies passive means to avoid the instability by locating the tether connection point forward on the cradle in combination with sufficiently high cradle–canopy yaw stiffness. Moreover, it is shown that an active control system that regulates canopy roll angle with parafoil brake inputs can eliminate the instability for the tested configuration.

Aerodynamic Decelerator Systems-Diverse Challenges and Recent Advances

HIS special section of the Journal of Aircraft is devoted to recent advances in aerodynamic decelerator systems technology. Parachute systems are often taken for granted. As will be seen in this section, the controlled deceleration of a payload is a vital part of many aerospace missions that involves signie cant technological challenges and creative engineering solutions. These diverse challenges are highlighted by e ve papers that cover parafoil systems, computer simulation, guidance and control, design and testing, and aerodynamic modeling. Anoverviewof theNASAX-38 CrewReturnVehicle (CRV)programisgivenbyMachinetal.ThechallengeconfrontingNASAwas to develop a robust emergency return vehicle for seven crew members aboard the International Space Station (ISS). Their solution utilizes a three stage decelerator system (pilot, drogue, and parafoil parachutes) as the primary recovery system. A novel parafoil with a span of 121.5 ft. and chord of 45 ft. is used with an autonomous Guidance, Navigation and Control (GNC) system to maneuver and land the 15,000 lb. CRV. Stein et al. present the state-of-the-art in computer simulation of parachutesystems.Here,itisnecessarytomodelthecoupledbehavior of the parachute system and the surrounding air e ow which are both highly transient and nonlinear. To capture this complex behavior, large-scale e nite element models are used that are executed on massively parallel computers.The results from these computer simulations provide a predictive capability to understand the complex dynamic behavior of parachute systems and supplement information obtained by full scale drop tests which are expensive and time consuming to perform. Another major challenge in parachute system design is to accurately and reliably deliver the payload to a specie c landing point with limited knowledge of prevailing wind conditions. Dellicker et al. describe a novel approach to accomplish this task. The AGAS system utilizes four Pneumatic Muscle Actuators (PMAs) as the parachute risers to control the system trajectory. The parachute is maneuvered by changing the lengths of the PMAs which are controlled by a GNC ssytem is response to the current and planned e ight trajectories. The paper by Heindel and Wolf illustrates the stringent mission requirements that are frequently faced by parachute system designers and presents their design solution and results from full scale prototype drop testing. In this mission, a long-duration stable descent is required for an air launched missile system. The design utilizes a cluster of four reefed G12 parachutes with two additional ringslot parachutes for stabilization. Following the initial design, a progressive series of drop tests were performed to evaluate and modify the design. Finally, in the paper by Potvin et al., the aerodynamics of parachute ine ation is addressed using a theoretical approach that is validated with experimental data. The parachute ine ation phase is of critical importance in parachute design but is still not well understood. The fundamental work presented here gives a simple yet comprehensive tool to simulate the ine ation of parachutes that include “ sliders” . Sliders are commonly used on the parachute suspension lines to control the opening shock during ine ation.

Guidance and Control for Flat-Circular Parachutes

The Affordable Guided Airdrop System (AGAS) is being evaluated as a low-cost alternative for meeting the military’ s requirements for precision airdrop. Designed to bridge the gap between relatively expensive high-glide ratio parafoil systems and uncontrolled ballistic parachutes, the AGAS concept offers the benee ts of high-altitude parachute releases as well as the potential for highly accurate point-of-use delivery of material. The design goal of the AGAS development is to provide a guidance, navigation, and control system that can be placed in line with cargo parachute systems, for example the G-12 e at-circular parachute, and standard delivery containers (A-22) without modifying these e elded systems. The AGAS is required to provide an accuracy of 328 ft (100 m), circular error probable (CEP), with a desired goal of 164 ft (50 m) CEP. The feasibility of this concept was investigated through modeling and simulation. A three-degree-of-freedom (3DOF) point mass e ight dynamics model, sensor models of a commercial global positioning system (GPS) receiver and magnetic compass, and a model of the control and actuator system were incorporated into a Monte Carlo simulation tool. A bang-bang controller was implemented with trajectory tracking algorithms using position and heading information. Flight testing, using a radio-controlled scaled prototype, provided parachutedynamic and control response data to support themodeling efforts.Thestudy demonstrated thatthisconcepthas thepotential to providecontrolofpreviously unguided round parachutes to accuracies of approximately 210 ft (64 m) CEP. The program is now continuing into the next phase to include the development of a full-scale prototype system for payloads up to 2200 lb (1000 kg).