Browse Topic: Control systems
ABSTRACT Over time, the National Institute of Standards and Technology (NIST) has refined the 4Dimension / Real-time Control System (4D/RCS) architecture for use in Unmanned Ground Vehicles (UGVs). This architecture, when applied to a fully autonomous vehicle designed for missions in urban environments, can greatly assist in the process of saving time and lives by creating a more intelligent vehicle that acts in a safer and more efficient manner. Southwest Research Institute (SwRI®) has undertaken the Southwest Safe Transport Initiative (SSTI) aimed at investigating the development and commercialization of vehicle autonomy as well as vehicle-based telemetry systems to improve active safety systems and autonomy. This paper will discuss the implementation of the 4D/RCS architecture to the SSTI autonomous vehicle, a 2006 Ford Explorer.
This organizational process survey provides insight into the technical aspects of approved airworthy aircraft modifications applied in government organization vertical lift flight test. The publication reviews processes applied by the National Research Council of Canada's Flight Research Laboratory (NRC-FRL) and its Airworthiness Control System to enable research flight testing. Dominated by the need for integrating experimental payloads, the NRC-FRL embeds a Design and Fabrication Service organization for modification of internal and external client projects and flight test aircraft. In context of experimental flight testing, this work reviews technical information on process, facilities, and methodology for airworthy integration of flight test payloads. Information is used to synthesize recommendations in experimental vertical lift flight testing that satisfy both formal (regulated compliance) and informal (compliance intent) airworthiness requirements.
This paper presents a reinforcement learning (RL)–based outer-loop controller for quadrotor UAV trajectory tracking and its real-world experimental validation. The proposed approach integrates RL into a standard cascaded flight-control architecture by replacing the conventional PID outer loop while retaining the onboard attitude and body-rate PID controllers. This hierarchical design preserves reliable inner-loop stabilization while leveraging RL to address nonlinear dynamics, coupling effects, and modeling uncertainty in translational motion. The controller is trained entirely in a physics-based simulation using Proximal Policy Optimization (PPO) and transferred directly to a Crazyflie quadrotor without additional tuning. Performance is evaluated through real-world figure-8 trajectory tracking experiments with varying time scales to impose increasing dynamic demands. Compared to a conventional PID outer-loop controller operating under identical conditions, the RL-based controller consistently reduces effective phase delay and achieves lower position and velocity tracking errors, particularly for aggressive trajectories. The results demonstrate robust sim-to-real transfer and highlight the potential of learning-based outer-loop control as a drop-in enhancement to classical quadrotor flight controllers.
A comprehensive numerical study was conducted to reduce helicopter rotor hub vibratory loads and fuselage vibrations using the Higher Harmonic Control (HHC) technique. A CAMRAD II model of a medium utility helicopter was developed for aeromechanical simulation, and a linear system model representing both hub vibratory load and fuselage vibration characteristics was identified offline. Optimal control inputs were then computed to minimize vibration responses under different weightings on hub vibratory load and fuselage vibration in the objective function. The predicted performance was verified through CAMRAD II simulations. Additionally, a closed-loop HHC system incorporating actuator amplitude limitations was investigated. A control algorithm regulated actuator amplitudes while maintaining phase consistency, dynamically adjusting control inputs after each iteration. The results demonstrate that the amplitude-limited closed-loop control limits excessive pitch link loads while maintaining effective vibration suppression, thereby maintaining structural safety and ensuring practical feasibility for real-world helicopter applications.
Characterization of rotor–rotor wake interactions and their influence on flight dynamics is an important step toward advancing control system design and evaluating the performance of next-generation Mars multirotors. In this work, a Viscous Vortex Particle Method (VVPM) is utilized to generate rotor–rotor interference data for the Chopper Mars Helicopter platform, a large-scale hexacopter concept designed to be capable of carrying payload and pursuing independent science tasks. A reduced-order model compatible with finite state dynamic inflow is derived from the database. Interpolation strategies for continuous look-up are evaluated, with Gaussian Process Regression providing up to 20% improvement in prediction accuracy over linear interpolation of the interference data, although its scalability is limited by the large number of output channels. The interference model is implemented in HeliCAT, the flight dynamics analysis framework used for the Ingenuity Mars Helicopter, to assess the impact of rotor–rotor interference on trim, open-loop response and key stability derivatives. For Chopper, the first-order impact of rotor–rotor interaction on flight dynamics in hover is small, but with an observed increased pitch and roll damping. In forward flight, on-axis bare airframe responses exhibit attenuation at the lower frequencies due to interference, and increased sensitivity of the pitch response to vertical perturbations in cruise. Finally, a real-time closed-loop simulation is performed with and without the interference model to assess the impact on rotor power during a representative science mission flight trajectory on Mars, showing that total increase in mechanical shaft power due to multirotor wake interactions does not exceed 5% throughout the flight.
Neonatal patients in need of specialized care may require transport by rotary-wing air ambulances. These patients are subjected to environmental stressors during transport, including elevated levels of mechanical vibration. Aircraft vibration is transmitted through the transport system and incubator to the patient. The unique vibration profile is dependent on vehicle model and phase of flight. To improve safety for these patients, we aim to evaluate the vibration exposure across this complex system. The purpose of this paper is to present and evaluate the methods used for aircraft data collection and replication of aircraft vibration profiles in a laboratory setting. Our current focus is on neonatal transportation in Ontario, Canada, where Leonardo AW139 helicopters are used for patient transport. AW139 field data were collected and processed to generate excitation profiles for discrete phases of flight. The vehicle data were used to drive a series of laboratory shaker-table experiments, in three axes, to evaluate the response of different configurations of the transport system. We present the methods used to simulate transport conditions, from vehicle data collection to laboratory shaker experimentation, and evaluate the behavior of the test apparatus. The simulated motion has been verified against the aircraft data to identify sources of error in the experimental setup. Some limitations in the shaker and control system present inherent differences in the input and response; however, it was found that the greatest spectral error occurred outside the frequency range of interest (>80 Hz), and that the shaker controller successfully replicates the energy levels recorded in the aircraft. The shaker experiment results, such as the response of the transport system and incubator, will be analysed in future work to identify equipment configurations and/or modifications which can reduce neonatal patient vibration exposure during rotary-wing transportation.
In April of 2024, Sikorsky flight tested an open loop Higher Harmonic Control system on an S-97® helicopter. The S-97® helicopter is a prototype aircraft, based on Sikorsky's X2 Technology™, that first flew in May 2015. It has contra-rotating, stiff in-plane main rotors with fly-by-wire controls, and a pusher propeller. This paper describes the HHC design, how it was implemented on the aircraft, how it was tested, and what the test results were.
This study investigates the fault tolerance of a large-scale coaxial quadrotor Electric Vertical Takeoff and Landing (eVTOL) under motor failure through high-fidelity software-in-the-loop (SIL) simulations using PX4-Gazebo environment. The objective is to evaluate the vehicle's ability to maintain flight stability and complete critical missions under various propulsion failure scenarios, without the control system being explicitly aware of which motors have failed. Four motor failure cases-single, two adjacent, two diagonally opposite, and three distributed motor failures-were introduced during takeoff, hover, cruise, and hover under crosswind missions. Results show that the eVTOL maintained controllability and mission completion under all scenarios, with increasing levels of performance degradation under more severe failures. Notably, considerable yaw instabilities of about 10 degrees occurred under two diagonally opposite motor failures. The highest thrust demands after motor failures were observed during cruise mission, with some motors demanding about 80% to 90% of their maximum throttle. Hover under crosswind revealed compounded challenges in attitude control during descent under severe failure cases compared to calm weather. These findings underscore the robustness of the integrated control system and vehicle configuration in managing motor failure scenarios.
This research analyzes flight safety occurrences such as incidents and accidents in the vertical lift community over the last two decades. A study of civil vertical lift occurrence data was performed for flight occurrences from 2000 to 2024. Focusing on North America (Canada, United States), research data was acquired from the respective government Transportation Safety Board agency of either country. The study data set consisted of 4623 occurrences (occ.) or observations (i.e.; 861 for Canada and 3762 for the United States). The research methodology involved a 6-step process to analyze data quantitatively (descriptive statistics) and qualitatively (trends, mitigation projections). For the study period, quantitative findings indicated occurrence rates (4.53 occ. per 100k flight hours (Canada); 3.39 occ. per 100k flight hours (United States)), occurrence rates of change (declining Canadian and United States rates (-2.3%/yr. & -2.2%/yr.) respectively), and occurrence event types (in Canada, Engine Failures (121 occ.) while in United States Loss of Control (589 occ.) events indicated the most occurrences). For this investigation, qualitative findings highlighted a series of general groupings or conditions in areas of System Failures, Flight Control, Vehicle Collisions, Flight Operations, and Pilotage. It was projected that technologically, open-loop and closed-loop control systems may provide the best potential for occurrence mitigation. Key pilot assistance domain systems include envelope/limit protection, detect/avoid, perception, and flight control (stability, trajectory following, navigation).
This paper presents a robust and adaptable control system for tilt-wing aircraft, developed by Dufour Aerospace. The transitional tilt-wing aircraft, Aero2, combines the vertical takeoff/landing capabilities of helicopters with the high-speed range of fixed-wing aircraft. Addressing the inherent control complexities required to maintain control and stability, the developed system employs established control techniques, utilizing linearization at trim points and gain scheduling based on wing tilt. The architecture comprises a Control Allocation module for optimal actuator management, a Control Augmentation System utilizing an LQRI controller enhanced with a feedforward component for precise attitude tracking, and a Unified Velocity Controller for seamless transitions between ground speed tracking in hover and airspeed tracking in cruise. Special challenges unique to transitioning aircraft to ensure control in all axes, including in windy conditions are addressed with operational strategies and control system modifications, validated through flight testing of a subscale and Aero2 aircraft. The resulting control system demonstrates effective velocity and attitude tracking across the flight envelope, enabling reliable piloted flight and automated missions.
This paper presents an experimental and analytical investigation of whirl-flutter stability in tiltrotor aircraft, focusing on the influence of pitch-flap coupling on stability boundaries. Wind-tunnel tests were conducted using the TiltRotor Aeroelastic Stability Testbed (TRAST), a semi-span model designed for test-analysis correlation. This study examines variations in pitch-flap coupling and compares measured frequency and damping trends with predictions from RCAS and CAMRAD II. Results indicate that less pitch-flap coupling increases stability, with both analytical models capturing general trends. The analysis accurately predicts the wing inplane mode stability, but larger deviations are observed in the vertical bending mode, suggesting missing physical effects in the modeling approach. Differences in damping trends at higher speeds indicate that improvements in modeling may be necessary to refine stability predictions. These results provide valuable insights into the capabilities and limitations of current whirl-flutter analysis methods and inform future refinements in tiltrotor aeroelastic modeling.
The next generation of Mars rotorcraft may involve an increase in scale and number of rotors. A key focus area that has been identified is to increase the fidelity of rotor wake modeling, including its impact on flight dynamics. To that end, this paper pursues the use of a Viscous Vortex Particle Method (VVPM) for mid-fidelity rotor wake predictions in Mars atmospheric conditions. Simulated aerodynamic hover performance, as well as control efforts in trimmed forward flight, of the Ingenuity Mars Helicopter with a VVPM wake is shown to correlate well with available experimental data. Qualitative and quantitative coaxial wake effects for Ingenuity-type rotors in hover and forward flight as predicted with VVPM are studied. Utilizing VVPM to evaluate rotor-rotor interference effects in a large-scale Mars hexacopter across a wide range of flight conditions showcases the capability to comprehensively model the induced wake of complex multi-rotor configurations within feasible computational cost. An approach to emulate interference effects derived from the VVPM data that is compatible with finite-state dynamic inflow models is demonstrated, exemplifying how VVPM can be adopted to inform flight dynamics analysis and control system design of next-generation Mars rotorcraft.
This paper demonstrates methods of aircraft sizing, flight dynamics modeling, and performance analysis using a lift+cruise concept vehicle with an electric powertrain and variable-speed rotors. The central focus is the development of methods to relate the aircraft design sizing constraints to achievable maneuverability and predicted handling qualities. A toolchain is demonstrated that performs aircraft sizing, mass moment of inertia estimation, powertrain modeling, trim optimization, dynamics linearization, handling qualities prediction, and quantification of achievable maneuverability under both nominal conditions and control effector failures. A convex optimization problem framework is introduced to compute agility bound estimates without requiring control system design or control allocation, potentially supporting rapid design iteration as well as early detection of deficiencies and undesirable operating conditions. This analysis is supplemented with more conventional methods of analysis to provide additional perspective and observations. Overall, the results suggest that each modeling and analysis element in the demonstrated toolchain adds significant value, with the combined approach supporting a more efficient and comprehensive exploration of trade-offs within the design space.
The transition phase of eVTOL aircraft poses a challenge in balancing energy efficiency and stability. This study presents the development and evaluation of an automatic flight control system for eVTOL transition phases, focusing on minimizing energy consumption while ensuring robust performance. The control architecture implements a hybrid response type combining Translational Rate Command below 5 knots and Acceleration Command Speed Hold above 5 knots, with control allocation dynamically adjusted based on airspeed and rotor shaft angle. Stability analysis reveals surge mode instability at high shaft angles due to negative speed stability derivatives, stabilized through carefully tuned feedback control. The system demonstrates Level 1 handling qualities against bandwidth, quickness, and disturbance rejection criteria when evaluated against MIL-DTL-32742 and MIL-STD-1797B standards. Simulation results verify the control system's ability to maintain precise acceleration/deceleration rates and attitude control while ensuring passenger comfort through limited pitch excursions. The control strategy achieves minimum energy transitions by locking rotor shaft angles to optimal schedules while avoiding excessive hub moments. Flight test maneuvers developed specifically for conversion phases confirm the system's capability to execute efficient transitions within defined performance boundaries. This research establishes a framework for certifiable eVTOL flight control systems that balance energy efficiency with robust performance across diverse flight regimes.
Complex vertical takeoff and landing configurations that transition between vertical and forward flight modes necessitate advanced flight control systems to substantially reduce pilot workload. Prior work demonstrated the Trajectory Control System, a flight control architecture that enables such Simplified Vehicle Operations. However, there may also be scenarios or applications that require more aggressive maneuvering with rates and attitudes that exceed the nominal envelope. This paper demonstrates a flight control architecture with a middle-loop that harmonizes the Trajectory Control System with a Tactical Maneuvering System that enables more aggressive maneuvering, with seamless in-flight transitions between the two. In both cases, the middle-loop is linked with an explicit model-following inner-loop control system. Flight test results for the Trajectory Control System and maneuver simulation results for the Tactical Maneuvering System are shown for a subscale tilt-wing configuration.
ABSTRACT Automatic guided vehicles (AGV) have made big inroads in the automation of assembly plants and warehouse operations. There are thousands of AGV units in operation at OEM supplier and service facilities worldwide in virtually every major manufacturing and distribution sector. Although today’s AGV systems can be reconfigured and adapted to meet changes in operation and need, their adaptability is often limited because of inadequacies in current systems. This paper describes a wireless navigated (WN) omni-directional (OD) autonomous guided vehicle (AGV) that incorporates three technical innovations that address the shortfalls. The AGV features consist of: 1) A newly developed integrated wireless navigation technology to allow rapid rerouting of navigation pathways; 2) Omnidirectional wheels to move independently in different directions; 3) Modular space frame construction to conveniently resize and reshape the AGV platform. It includes an overview of the AGVs technical features and how the flexibility and agility can be adapted to fit military and commercial application. The AGV is being evaluated as a mobile work station platform and a precise material handling robot.
Abstract This paper presents a software framework developed for the simulation of vehicle-level control systems for modern (existing or conceptual) ground vehicles, targeted for high-performance platforms (Linux clusters). The framework augmented existing ground vehicle simulation environments (such as CREATE-GV MERCURY or other object-oriented software packages) making it possible to perform a comprehensive evaluation of a ground vehicle’s performance when equipped with vehicle level controllers to determine the effectiveness of the control systems on the vehicle. The framework, implemented as part of the PACE (Powertrain Analysis Computational Environment), was comprised of software components (a C++ objects library) simulating various vehicle-level controllers, an Application Programming Interface for the development of new components to be used within the framework, and C++ code for integrating these components into simulations of control systems within a ground vehicle simulation environment.
A key technology in automation of rotorcraft flight is collision-free guidance. Especially in operations close to the ground, detection and automatic avoidance of ground-based obstacles and aircraft is a demanding task. This paper presents a sampling-based model predictive approach for collision-free guidance of rotorcraft. The method calculates control inputs for the flight controller by predicting the closed-loop dynamics of the rotorcraft for a short time horizon and evaluating the predictions with a cost function, which can take an arbitrary form. The approach implements a simple algorithm, mitigating the need for iterative optimization and allowing for deterministic execution time. The cost function is set to ensure collision-free maneuvering while following a desired path, as well as considering constraints of the rotorcraft states and control inputs. The path following performance is tested in closed-loop simulations with a non-linear helicopter model. The algorithm is implemented on a graphics processing unit for parallel execution, strongly decreasing the computation time.
ABSTRACT The present study considers two notional rotorcraft models: a conventional utility helicopter, representative of an H-60, and a wing-only compound utility rotorcraft, representative of an H-60 with with a wing similar to the X-49A wing. An Explicit Model Following (EMF) control scheme is designed to achieve stability and desired Rate Command / Attitude Hold (RCAH) response around the roll, pitch and yaw axes, while alleviating vibratory loads through both feed-forward and feedback compensation. The harmonic decomposition methodology is extended to enable optimization of primary flight control laws that mitigate vibratory loads. Specifically, Linear Time Periodic (LTP) systems representative of the periodic rotorcraft dynamics are approximated by Linear Time Invariant (LTI) models, which are then reduced and used in LQR design to constrain the harmonics of the vibratory loads. The LQR gains are incorporated in the EMF scheme for feedback compensation. One innovative approach is the addition of rotor state feedback to standard rigid body state feedback. A Pseudo Inverse (PI) strategy is incorporated into the EMF scheme for redundant control allocation. Finally, simulation results with and without load alleviation are compared and the impact of PI feed-forward and rotor state feedback compensation on handling qualities is assessed in terms of ADS-33E specifications.
ABSTRACT A new simulation model to predict tail rotor drivetrain maneuver loads at hover is developed. The model consists of a high fidelity dynamic engine simulation coupled to a multibody dynamics simulation of the main rotor system, tail rotor and drivetrain, including torsional flexibility of drivetrain shafts. Simulations of yaw doublets at hover demonstrate that tail rotor drivetrain loads can be reduced without compromising handling qualities for moderate amplitude heading changes. A full autonomous heave/yaw hover control law is developed with a nonlinear element in the heading feedback loop. The nonlinear element specifies the aggressiveness level (gain) as a function of heading angle change. It allows the flight control system engineer to simultaneously minimize tail rotor drivetrain maneuver loads whilst maintaining level 1 handling qualities. The nonlinear flight control system is evaluated for the ADS-33 hover turn mission task element and compared to a conventional linear control system. Level 1 performance is achieved with both control systems and dynamic tail rotor drivetrain loads are reduced up to 58% by the nonlinear element.
A high-fidelity flight simulator is used to effectively train and evaluate pilots. The simulator must, however, be previously qualified by authorities by comparing the responses of the simulator to those of flight tests for several maneuvers. The use of a controller is permitted to make corrections to the simulator input signals. The simulator inputs and outputs must, however, be within tolerance bands defined by the authorities, compared to flight test data. This article presents a model predictive controller (MPC) and its evaluation on a takeoff and landing case. The method is already promising because these results were obtained after very few tuning iterations, which could result in significant time and cost savings. This is made possible by the clear meaning of the impact of the MPC tuning parameters on the simulator inputs and outputs and also by the ability to intrinsically consider the interactions and constraints of the multivariable system.
The ongoing development of numerous novel vertical takeoff and landing configurations necessitates flight control system design that enables the Simplified Vehicle Operations paradigm. This paper shows flight test results for one subscale lift-plus-cruise and one tilt-wing configuration employing such a flight control system architecture. Pilot inceptor inputs are used to synthesize trajectory commands that are processed by a full-envelope trajectory control system that generates propulsor thrust commands, a wing angle command, and attitude and rate commands for linear quadratic integral and explicit model-following inner-loop control systems. Commonalities and differences in the flight control implementation for the two configurations are highlighted. Results are shown for both configurations subject in manually piloted flights. The flight test results demonstrate that the flight control system designs allow a minimally trained operator to operate the two flight test vehicles safely and proficiently.
ABSTRACT Wind-tunnel tests of a heavy-class helicopter model were carried out to evaluate the effectiveness of passive flow control system in alleviating the fuselage parasite drag. An array of counter rotating vortex generators was selected to reduce/remove the flow separation occurring on the rear loading ramp responsible of the high pressure drag. Different technical solution for the VGs design and location were selected with respect to previous work. The basic fuselage geometrically scaled 1:7 of a heavy class helicopter was investigated with and without passive flow control system. The comprehensive experimental campaign involved the use of different measurement techniques. Indeed, pressure measurements and stereo particle image velocimetry surveys were performed to gain a physical insight about the results of load measurements. This paper addresses the promising results obtained during the wind-tunnel campaign, since significant drag reduction was achieved for a wide range of fuselage angles of attack and side slip angles without the detriment of the other aerodynamic characteristics.
ABSTRACT A flight simulation model for the UH-60 Black Hawk based on Sikorsky's GenHel model is modified to simulate a locked failure of a main rotor swashplate servo actuator and is compensated by using the stabilator as a redundant control effector. Steady state trim analysis is performed to demonstrate feasibility of trimmed flight in various conditions with different locked servo actuator positions for the forward, aft, and lateral actuators. A model-following, linear dynamic inversion controller is implemented and modified to account for locked actuator position. Post-failure, the control mixing and feed-forward control coupling terms are reconfigured to partially reallocate the control authority in the longitudinal axis from the main rotor longitudinal cyclic to a symmetric deflection of the stabilator. This is done by manipulation of only the control allocation relating pilot stick inputs to servo actuator positions, the feedback control gains and mechanical rigging between servo actuators and rotor pitch controls remain identical to the baseline controller. Flight simulation results demonstrate the ability of this reconfiguration to compensate for locked failure of the forward main rotor swashplate servo actuator, as well as the ability of the aircraft to decelerate from cruise at 120 knots to 50 knots which is less than the published safe rolling landing speed of 60 knots. A similar range of locked positions of the forward and aft actuators is demonstrated to be feasible for aircraft recovery using control of the stabilator. Feasibility of aircraft recovery for locked positions of the lateral servo actuator is also considered.
The DoD enterprise requires a blueprint for each service and industry base to develop, integrate, and connect crewed and uncrewed platforms across the aviation and ground domains to satisfy the goals of programs such as Replicator, Human Machine Integrated Formation (HMIF) and Joint All Domain Command and Control (JADC2) as a whole. Thanks to years of architecture work by Program Executive Office (PEO) Aviation, PEO Ground Control System (GCS), and the Ground Vehicle Services Center (GVSC), the necessary open standards-based reference architectures, objective architectures, Major System Components (MSCs), and Major System Interfaces (MSIs) can be leveraged to create an executable plan for the Army, the DoD, and the international community as a whole. This paper proposes how to leverage government-owned elements across multiple Army offices to provide a Modular Open Systems Approach (MOSA) that achieves the speed, portability, and interoperability of capabilities needed for the conflicts of tomorrow.
Coupled powerplant and rotorcraft flight dynamics simulations are commonly carried out in the non-linear time-domain framework (e.g. for pilot-in-the-loop handling qualities assessments), although these integrated models are generally not fully accurate from drivetrain dynamics perspective. Nevertheless, there is interest to verify that usual assumption of decoupled torsional stability (including rigid drivetrain analysis) and aircraft rigid body stability is valid, and up to what extent. The process described in the paper entails the automatic assembly of relevant subsystems (bare aircraft flight dynamics, Flight Control System including fly-by-wire actuation, sensors, and Control Laws software, drivetrain dynamics, powerplant dynamics) state space matrices through a Company developed Matlab toolbox. The proposed approach is control system design oriented, i.e. it does not require detailed flexible multibody modelling of the entire aircraft including dynamic systems and it is a natural extension of the process generally carried out by Control Laws and Flight Mechanics discipline for rigid-body stability assessment. The paper specifically addresses, as case study, the coupled torsional dynamics analysis of Next Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD) in Helicopter configuration. The NGCTR-TD project is developed under the EU Clean Sky 2 program for defining novel technology for future civil Tiltrotor platforms. The proposed coupled torsional stability modelling process is described, and the main outcomes valid for NGCTR-TD trimmed in hover and near-hover conditions presented. It is shown that the proposed methodology provides consistent outputs against the original NGCTR-TD linear stability results (from individual flight dynamics and drive system models). Analysis of Modal Participation Factors is used to quantify the coupling existing between drive system and flight dynamics state vectors, in nominal and failure conditions (Inter Connect Drive Shaft failure).
In this paper, an offline path planning module, which is capable of generating dynamically feasible 3D trajectories for a class of Vertical Takeoff and Landing (VTOL) vehicles is presented. Input to the module is a flight plan defined by a set of way-points and its output is twofold: first, it produces an improved flight plan introducing additional waypoints and speed changes based on the heuristics and dynamical constraints of the vehicle. This new plan facilitates the pilot by providing information on specific locations and changes of the original flight path. Second, it generates a set of reference points, which can be used as the initial set of inputs for an online reactive trajectory optimization algorithm. The proposed development is capable of processing both climbs and descents as well as both fly-by and flyover waypoints, and speed changes in between those way-points. The module was also designed to capture the pilot's perspective of an abstract way-point mission. NRC has implemented a nominal Nonlinear Model Predictive Control (NMPC) based online planner using the reference trajectories generated by the proposed offline planning module successfully. The generated improved mission was implemented on a simulator having Bell 412 flight dynamics and promising results were obtained.
The inherent complexities of maritime environments make the helicopter shipboard operations exceptionally demanding to the pilots. This paper presents current research on development of a combination of different advanced control modes to automatize different parts of a ship deck landing maneuver in the maritime simulation environments of both DLR (German Aerospace Center) and ONERA (The French Aerospace Lab). The proposed advanced control modes involve ship relative Velocity Hold and Position Hold capabilities for pilot assistance and further enhancing the safety levels of the shipboard operations. Control augmentation is based on a model following control system featuring a translational rate command at DLR, however at ONERA a feedforward control strategy is used. The paper describes the simulation setup of a helicopter-ship dynamic interface, test methodologies and evaluation methods at both DLR and ONERA. Simulation results demonstrate an evaluation and comparison of the implemented control augmentation for different helicopter types namely, an EC135 at DLR and an EC225 at ONERA for shipboard operations.
The complex vertical takeoff and landing configurations currently under development necessitate flight control system design that enables substantial reductions of pilot workload through Simplified Vehicle Operations. This paper shows optimization and simulation of such a flight control system architecture for a subscale vectored thrust aircraft configuration. A full-envelope Trajectory Control System for longitudinal dynamics was coupled with explicit model-following inner-loop controllers, and a scheduled control allocation logic. Control system parameters were determined using a genetic algorithm optimization scheme subject to dynamic stability, robustness, and control responsiveness constraints. Flight simulation results for a series of representative maneuvers including departure and arrival transitions and forward flight maneuvers are presented to demonstrate the effectiveness of the proposed flight control system architecture.
An unmanned aerial system automation qualities framework (previously known as the unmanned aerial system handling qualities framework) has been in development to determine a set of criteria and mission task elements for evaluating the airworthiness of unmanned aerial systems. The framework is being developed to apply across a range of unmanned aircraft from Group 1 to Group 4-5, via scalable predicted (quantitative) automation qualities metrics as well as scalable mission task elements. Prior work has developed scalable mission task elements and predictive attitude response criteria, scaled from MIL-DTL-32742 (which supersedes ADS-33E-PRF). This paper extends the UAS automation qualities framework to provide predictive (quantitative) criteria for velocity and position responses. The paper evaluates Froude scaled velocity disturbance rejection bandwidth and position disturbance rejection bandwidth requirements from MIL-DTL-32742 and describes and evaluates two new metrics, velocity bandwidth and tracking bandwidth, as possible new criteria. These metrics are defined in the paper and were evaluated as predictive quantities for automation handling qualities level using lateral reposition and depart/abort mission task elements. The evaluation was conducted by modifying the control system to achieve parametric variation of the metrics of interest and then assessing the performance with simulation and flight test of mission task elements. Three small unmanned vertical lift aircraft were used in this study; the University of Portland hexacopter, the USNTPS X8-M coaxial quadcopter and Synergy 626 single main rotor helicopter. It was found that the newly defined tracking bandwidth and velocity disturbance rejection bandwidth are key predictive criteria for automation qualities level for automated mission task elements on the test aircraft.
ABSTRACT Rotorcraft shipboard landing continues to be challenging due to increased pilot workload in dealing with effects of ship air wake turbulence on vehicle motion and random ship motion. Some of the recent work has proposed a pilot assist function for reduced pilot workload using model predictive control methods. This paper explores the use of a recently developed Model Predictive Path Integral (MPPI) method based on a stochastic optimal control framework for trajectory guidance solution to the shipboard landing problem. First, a proof-of-concept study is presented by applying the MPPI method to a simple point mass approximation of helicopter dynamics represented in the form of a first-order command acceleration model, representative of helicopter trajectory motion in the vertical plane. Next, the MPPI method is used in conjunction with a six degrees-of-freedom linear model of a helicopter in order to gain further insight into the applicability of the MPPI framework to the rotorcraft shipboard landing problem. The paper concludes with key observations and inferences gained in this study.
ABSTRACT A novel method for the automated control of helicopters in landing maneuvers on ship decks is proposed, which combines integer programming and model predictive control (MPC). The helicopter is first brought sufficiently close to the landing deck using a standard MPC. In the final phase of the mission, termed the rendezvous phase, implementation of the novel control design method allows the MPC to rapidly adapt to the landing deck state via a variable prediction horizon. The control design problem includes an integer variable vector which is used to frequently estimate an appropriate prediction horizon for the MPC during the maneuver. This process mimics the manner in which human pilots act, by repeatedly estimating how long ahead during the ship landing maneuver their actions are effective to safely accomplish the mission. The performance of the proposed procedure is evaluated via numerical simulations using a nonlinear helicopter-ship dynamics interface that captures significant characteristics of the helicopter and ship dynamics, as well as the ship airwake effects. These simulations show that the proposed method can be effective in satisfying rendezvous conditions for helicopter ship landing even when the moving deck has a very high energy index.
The Adaptive Digital Automated Pilotage Technology (ADAPTTM) flight control software package aims to take advantage of redundant controls to improve safety, survivability, and performance for advanced rotorcraft. Vehicle Maneuver Optimization (VMO) is one component of the ADAPTTM architecture intended to increase maneuverability. VMO uses feedforward actuation within the control null space of over-actuated aircraft to minimize power required during quasi-steady maneuvers. In this study, the system is applied to a generic tiltrotor aircraft and evaluated in piloted simulations at the Penn State Rotorcraft Simulator. In this application, VMO uses flap deployment and nacelle tilt to reduce power required in turn maneuvers. Piloted simulation results show that the system effectively reduces power required during Break Turn and Maximum Performance Turn Mission Task Elements (MTE), while handling qualities are equivalent to the baseline controller without VMO. The system was also tested for a terrain flight mission scenario. Pilot comments indicated better handling with VMO in the aggressive maneuvering phases of the flight.
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