Browse Topic: Attitude control
ABSTRACT 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
ABSTRACT 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
The presence of a slung-load during the flight of a quadrotor generates swing effects that can greatly influence the dynamics of the quadrotor. These effects have the potential to threaten the stability of the system’s attitude. This study presents a disturbance compensation strategy that is designed based on the utilization of an adaptive harmonic extended state observer (AHESO) in order to solve this problem and achieve precise attitude control. To derive the aforementioned algorithm, a comprehensive mathematical model for the quadrotor-slung-load system is built. The periodic features of disturbance are derived by considering the movement of the slung-load. Subsequently, by taking the periodic features of the disturbances into account, the AHESO for accurate disturbance estimation is designed. In this observer, an online frequency estimator for the harmonic disturbances is introduced. Lyapunov theory is introduced to examine the stability of the AHESO. In addition, backstepping
This document provides recommended practices regarding how System Theoretic Process Analysis (STPA) may be applied to safety-critical systems in any industry.
ABSTRACT The operation of helicopters on ships is one to most challenging tasks due to adverse weather conditions, the lack of visible cues, turbulent airwakes behind the ship and a moving confined landing spot on the ship. Currently, only a very limited number of pilot assistance systems are available to ease helicopter ship deck landings. The focus of this paper is the evaluation of a Head-Down Display (HDD), a Head-Mounted Display (HMD) and two different Attitude Command Attitude Hold (ACAH) flight control architectures for ship deck landings based on piloted simulation. A ship deck landing scenario at the research flight simulation facility Air Vehicle Simulator (AVES) has been extended to include turbulent ship airwakes from high-fidelity Computational Fluid Dynamics (CFD). The pilot assistance systems have been implemented at the simulator and evaluated by four helicopter pilots. In particular, the results show a favorable potential of the Head-Mounted Display and the flight
ABSTRACT This paper describes the design, development, and tethered flight testing of a quad-cyclocopter weighing 25 kilograms and 1.8 m x 1.4 m x 0.8 m in dimension. This cyclocopter features four cantilevered cyclorotors with a unique five-bar blade pitching mechanism. The cyclorotor design is chosen through systematic parametric studies using an in-house 2-D computational fluid dynamics (CFD) solver. Based on the parametric studies, the final design selected is a 6-bladed cyclorotor with 0.67 chord-to-radius ratio, symmetric NACA 0015 airfoil, and pitch amplitude of 45-degree because it provided high thrust and power loading (thrust/power) at a low operating rotational speed of 700 RPM. The cyclorotor blades are manufactured with a foam core and carbon fiber skin resulting in lightweight blades with large bending and torsional stiffness. The rotor supporting structure and transmission is designed to be lightweight and resilient to large centrifugal loads and dynamic torques
In the field of space technology, Centre Suisse d’Electronique et de Microtechnique (CSEM) has been a partner of the European Space Agency (ESA) for many years. One focus of their joint research is eliminating vibration emissions originating from components aboard satellites. In addition to limiting the precision of attitude control for satellites, these micro-vibrations lead to higher energy consumption and (in the case of imaging missions) cause deterioration of image quality.
ABSTRACT To achieve Level 1 Handling Qualities, Aeronautical Design Standard ADS-33E-PRF requires an Attitude Command Attitude Hold or Translational Rate Command response-type in Degraded Visual Environments while allowing a rate response in Good Visual Environments. The authors describe the design and analysis of a Blended Command Model that may offer the precision of the former and the aggressiveness of the latter. The command model, comprised of a single flexible transfer function and its parameter scheduling functions, produces attitude, rate, and blended responsetypes as functions of cyclic stick position. The authors explain the command model’s design considerations, test considerations, and its behavior through time domain and frequency domain perspectives. This effort precedes a handling qualities assessment aboard the U.S. Army’s JUH-60A RASCAL aircraft.
ABSTRACT In application, the Aeronautical Design Standard for the handling qualities of military rotorcraft, ADS-33E-PRF, provides the means to effectively predict rotorcraft handling qualities via validated criteria and demonstrate actual handling qualities in flight test using mission task elements. Besides a definition, a note that rotorcraft shall have no tendencies, and a note regarding Attitude Command Response-Types and gain bandwidth frequency, the topic of pilotinduced oscillations (PIO) is not addressed via specific criteria or flight test techniques. As the use of full authority fly-by-wire flight control continues to expand in Vertical Takeoff and Landing (VTOL) aircraft, the likelihood of encountering PIO will also expand. In the fixed wing world where PIO has been commonplace, at least in developmental test if not operations, predictive analytical methods that can also be used for detection of PIO in realtime have been developed, which can also be applied to rotorcraft
These recommendations cover the mechanical and electrical installation and installation test procedures for automatic pilots of the type normally used in transport type aircraft. The material in this ARP does not supercede any airworthiness requirement in the Civil Air Regulations.
When firing artillery, there is typically a maximum angle that the platform cannot exceed relative to the Earth plane. This is due to the large recoil forces involved and the risk of destabilizing the platform the weapon is mounted to. Mobile systems are particularly sensitive to this as the attitude of the platform relative to Earth is constantly changing. A simple solution is to add pitch and roll sensors directly to the platform. However, many mobile systems already have an assortment of sensors that can be used to calculate the platform attitude.
NASA’s Small Spacecraft Technology Program is on the countdown clock to advance communications and proximity maneuvering capabilities for CubeSats with the Integrated Solar Array and Reflectarray Antenna (ISARA) mission.
In designing of the Attitude Control System (ACS) is important take into account the influence of the structure’s flexibility, since they can interact with the satellite rigid motion, mainly, during translational and/or rotational maneuver, damaging the ACS pointing accuracy. In the linearization and reduction of the rigid-flexible satellite mathematic model, usually one loses some important information associated with the satellite true dynamical behavior. One way to recovery this information is include to the ACS design parametric and not parametric uncertainties of the system. The H infinity control method is able to take into account the parametric uncertainty in the control law design, so the controller becomes more robust. This paper presents the design of a robust controller using the H infinity control technique to control the attitude of a rigid-flexible satellite. The satellite model is represented by a flexible beam connected to a central rigid hub considering a set of
ABSTRACT The present contribution aims at providing a comprehensive illustration of a structured approach to the design, implementation and testing of a new rotor state measurement system for rotorcraft applications. This effort has been carried out in the framework of a Clean Sky collaborative project in which the novel sensor system plays a fundamental role by enabling the real-time estimation of non-measurable quantities that govern the rotorcraft running acoustic emission, in view of external noise alleviation. Furthermore, the availability of the new sensor system capable to accurately capture rotor blade motion allows the derivation of enhanced attitude control laws based on rotor state feedback. We detail the complete process that led to the full-scale development of a stereoscopic vision-based measurement system mounted on the rotor head, which has been fully integrated on board a prototype helicopter for ground and flight testing.
ABSTRACT This paper describes the design, development and flight testing of a meso-scale cyclocopter. Weighing only 29 grams, the present vehicle is the smallest cycloidal rotor based aircraft ever built. Unlike the previous cyclocopters, the current prototype utilizes a novel, light weight (3 grams) cycloidal rotor design, with cantilevered blades, having semi-elliptical planform shape and no exposed rotor shaft. To minimize bending deflections the blades use a unique, lightweight (0.15 grams each) but high strength-to-weight ratio unidirectional carbon-fiber based structural design and are fabricated using a specialized manufacturing process. The cycloidal rotor design was chosen through systematic performance measurements conducted using a custom-built miniature three-component force balance. Based on experimental parametric studies, a 4-bladed rotor and symmetric blade kinematics with pitch amplitude of 45° provided the highest thrust and power loading (thrust/power) and was used
ABSTRACT A joint research project (2010-2014) between Delft University of Technology and Boeing Mesa was conducted in SIMONA Research Simulator (SRS) at Delft University with the goal to develop advanced flight control laws for handling qualities (HQs) improvements of the Apache AH-64 helicopter. The goal of the present paper is to concentrate on implementation and simulator testing of modern control laws for Apache's AH-64D Longbow helicopter to provide improved handling qualities for hover and low speed flight in degraded visual environment. The paper will implement an "Incremental Nonlinear Dynamic Inversion (INDI)" controller into the Boeing's FlyRT AH-64 Apache baseline model for the existing partial authority stability augmentation system (SAS). The INDI will be used to provide both attitude command attitude hold and translational rate command response types based on the requirements in ADS-33E. Implementation of the INDI into Apache's FlyRT proved to be challenging because the
ABSTRACT We give a comprehensive illustration of a new approach to rotorcraft noise abatement carried out in the framework of the Clean Sky collaborative project MANOEUVRES. This approach is based on technologies and tools for real-time, in-flight monitoring of the emitted noise. By means of a new cockpit instrumentation, the Pilot Acoustic Indicator (PAI), the current noise impact is presented to the pilot in a condensed, practical form as an aid in performing quieter maneuvers. The PAI algorithm makes use of several ingredients that have been implemented and tested within the project, including offline steady and unsteady acoustic predictions, and estimation of flight mechanics parameters based on the measurements derived from a new contactless rotor state measurement system. The latter is capable to accurately acquire the motion of the rotor blades, allowing the computation of non-directly-measurable quantities such as tip-path-plane angle of attack and thrust coefficient, and
ABSTRACT The vast majority of the U.S. Army's helicopter fleet consists of aircraft initially developed in the 1960s and 1970s and which were designed based on the handling qualities and flight control requirements of the time for flight in good visual environments (GVE). The Army today uses helicopters at night and in brownout and other degraded visual environment (DVE) conditions but with the same control laws of the original models; the major exception being the CH-47F and MH-47G DAFCS, which have been highlighted as a successful partial authority flight control system upgrade to provide improved handling qualities. The U.S. Army Aviation Development Directorate–AFDD has partnered with the U.S. Army Utility Helicopter Program Office's Futures Team and the RDECOM DVE Mitigation Program to further develop and test the UH-60 Modernized Control Laws (MCLAWS). Previous work implemented a model following control system architecture which provided an attitude command/attitude hold response
Typical spacecraft thruster configurations are often unable to provide full six-degree-of-freedom control and may have unwanted interaction between their attitude control and trajectory control functions, have undesirably high instantaneous electrical power demands, and use more thrusters than desirable. These last two potential problems gain increased significance if a spacecraft is required to have especially small size and mass, and have very low cost.
Preliminary data was recently provided for a reaction sphere prototype on NASA’s zero-gravity parabolic flight vehicle. Gyroscope telemetry indicates that reaction spheres were successfully commanded at 10- to 20-ms pulses during a handful of parabolas in each flight. This is the first publicly disclosed validation of a freely rotating reaction sphere in a standalone compact package. At dimensions of
ABSTRACT A previous investigation studied the use of advanced response types and non-linear dynamic inversion (NLDI) control to improve handling qualities for shipboard operations from a moving ship deck with unsteady airwake. The results showed potential for ship-relative Translation Rate Command (TRC) control modes to significantly reduce pilot workload, at least in mild sea states. The paper extends the investigation to better understand the bandwidth and the disturbance rejection requirements of the NLDI controller (and for rotorcraft control characteristics in general), when operating in a range of sea states and airwake conditions. The US Army's rotorcraft handling quality specification, ADS-33E-PRF, provides no specific design guidance on bandwidth or disturbance rejection properties for maritime operations. A family of controllers was developed to test varying levels of bandwidth and disturbance rejection proper-ties of Attitude Command / Attitude Hold (ACAH) and TRC control
This study is made on a simplified pitch model of an armored fighting vehicle. Jerks and angular acceleration inside the vehicle compartment Affects accurate firing attack and reduced fatigue to the occupants in Vehicle. The Stability Augmentation Technique can enhance the stability and ride comfort of the vehicle platform from road and firing disturbance. The force requirement for stabilizing the platform is calculated from the displacement of vehicle body in terms of pitch angle and Heave displacement with respect to the equilibrium position, the equivalent force at suspension mounting points required to stabilize the platform is calculated using a force transformation technique. The required force is given by an active Damper for stabilization, within the limit of damper capacity. From simulation conducted and comparison with passive suspension it is perceived that the Stability of vehicle platform is increased together with a reduced VDV (Vibration Dose Value) and rms acceleration
ABSTRACT In June 2013, NASA and the U.S. Army jointly conducted a simulation experiment in the NASA-Ames Vertical Motion Simulator that examined and quantified the effects of limited-authority control system augmentation on handling qualities and task performance in both good and degraded visual environments. The vehicle model used for the experiment was the OH-58D with similar size, weight and performance, and the same 4-blade rotor system as the Bell 407 civilian helicopter that is commonly used for medical evacuation and emergency medical services. The control systems investigated as part of this study included the baseline aircraft Rate Command system, a short-term Attitude Command/Attitude Hold system that uses lagged-rate feedback to provide a short-term attitude response, Modernized Control Laws that provide an Attitude Command/Attitude Hold control response type, and Modernized Control Laws with an additional Position Hold function. Evaluation tasks included the ADS-33 Hover
ABSTRACT Piloted simulation tests were conducted to develop and evaluate advanced control laws and optimal response types for ship-based rotorcraft. Simulations used the GENHEL-PSU model integrated with the Penn State rotorcraft flight simulator. The simulation includes ship motion, a visual model of a FFG-7 frigate, and the Control Equivalent Turbulence Input (CETI) model for airwake turbulence. The controller uses a Non-Linear Dynamic Inversion scheme to accurately track a variety of response types. An Attitude Command / Attitude Hold (ACAH) control mode was used as the baseline control law. Different variants of Acceleration Command / Velocity Hold (ACVH) and Translational Rate Command / Position Hold (TRC/PH) response types were designed to make use of ship deck motion measurements. Filtered deck states are fed into the control laws to command velocity and position relative to the landing spot. Piloted simulation tests were performed for a variety of control configurations with and
ABSTRACT Multicopter type helicopters have become prevalent in the past ten years with applications in military, academia, commercial, and recreational use. These aircraft benefit from their inherent simplicity, robust design, and ease of control. This paper discusses the design of an attitude control system for a large-scale gas powered multicopter and the challenges overcome in the development of the system. A nonlinear model was developed for simulation purposes and a simplified linear model was developed for control system design. The resulting control system architecture and design was implemented and successfully tested on an eight-engine prototype aircraft with 880 horsepower and a max gross weight of 4,400 lb.
A paper describes a process for imposing safety constraints on a spacecraft trajectory design. The conventional process has the ACS (Attitude Control System) team define geometric constraints, then the NAV (Navigation) team produces a compliant thrust direction profile for the spacecraft to execute. With time-varying thrust profiles, merely specifying geometric constraints is not sufficient. Because low thrust implies low agility under thrust vector control (TVC), even slowly developing spacecraft dynamics can be significant and geometric constraints can have dynamic implications. The thrust profile design process was modified to incorporate a new tool, known as qSTAT, which analyzes candidate thrust profiles for compliance with geometric and dynamic constraints by simulating an appropriately reduced set of spacecraft dynamics. qSTAT gives the navigation team a simplified attitude control simulation tool that can quickly be used to analyze multiple candidate thrust profile designs. The
A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted.
Hybrid systems are characterized by a composition of discrete and continuous dynamics. In particular, the system has a continuous evolution and occasional jumps. The jumps are caused either by controllable, uncontrollable external events or by its continuous evolution. Inevitably, this type of system is present in mobility devices such as cars, ships, and aircrafts. Efforts to develop this type of system have increasingly suffered from cost and schedule overruns. In fact, the verification of such systems has become a key activity in the development life cycle. Historically, such activity demands experts and high efforts, and uses ad-hoc methods. Therefore, the aim of this work is to apply finite state-machine verification to hybrid systems. To do that, a small part of the vast theory of automatic test suite generation for this type of discrete behavior and system is applied in a model-based testing approach, showing an effective and reproducible alternative for automatic test suite
This document sets forth design and operational recommendations concerning the human factors issues and criteria for airborne terrain separation assurance systems. The visual and aural characteristics are covered for both the alerting components and terrain depiction/situation components. The display system may contain any one or a combination of these components. Although the system functionality assumed for this document exemplifies commercial aircraft implementation, the recommendations do not exclude other fixed wing aircraft types. Because of their unique operations with respect to terrain, rotorcraft will be addressed in a separate document. The assumptions about the system that guided and bounded the recommendations included: the system will have a human centered design based on the "lessons learned" from past systems; the system is not intended to replace the Ground Proximity Warning System (GPWS) function; the system is an on-board system that is not dependent on ground
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