Browse Topic: Fly-by-wire control systems
ABSTRACT Future military missions for Agile Combat Employment (ACE) and next generation Special Operations Forces need an aircraft with effective hover and the ability to operate in transonic cruise. Hover requires significant power that can only be mitigated by larger diameter rotors, but large diameter rotors become a detriment to achieving transonic flight. The stop-fold rotor configuration can “make the rotor disappear” in cruise and stands out as the most viable option for meeting these next-generation air vehicle requirements. This paper discusses the progress Bell has made in developing enabling technologies for a practical and scalable high-speed VTOL (HSVTOL) based on the stop-fold configuration. To this end, a unique Track-Guided Test Vehicle (TGTV) was developed at Bell and tested at the 10-mile High Speed Test Track at Holloman Air Force Base. The test vehicle integrates all subsystems required to demonstrate the key technologies in a representative environment, including
ABSTRACT This paper outlines observations from an FAA-sponsored research project that examined aviation Fly-By-Wire (FBW) accidents. The goal was to identify risk areas that will help guide a focus for FAA certification testing. Part of this study specifically focused on current powered-lift tiltrotors, identifying six general categories of causal factors for accidents, which will be discussed in detail regarding how they influenced flight control designs. The results of this survey, along with extrapolation to current designs, will be discussed and will illustrate why manufacturers are moving toward state-based flight control designs. In a state-based flight control scheme, the pilot does not have direct control over aircraft attitudes and motor tilt angles. Instead, the pilot requests a speed and or flight path with inceptor input, and the commanded attitudes and motor tilts are scheduled by the flight control computer. Additionally, recent lessons learned from electric Vertical
ABSTRACT A robust velocity stability augmentation system was developed for the CoAX 600/2D coaxial-rotor helicopter to enable safe testing of a fly-by-wire system on an optionally piloted variant of the aircraft, developed by Piasecki Aircraft Corporation. The control law design and subsequent stability analysis were based on a validated nonlinear model of the CoAX 600 rotorcraft. A subset of helicopter handling qualities were evaluated through both analytical methods and piloted simulations, conducted with and without the stability augmentation system. Additionally, flight test data contributed to the analysis, albeit to a limited extent.
ABSTRACT 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.
ABSTRACT The integration of automation and autonomy into modern aircraft has significant potential to simplify many piloting tasks. On the other hand, poor integration of automation and autonomy systems with the human crew has sometimes led to unintended consequences. With the goal of improving human-machine integration in piloting tasks, Bell Textron has conducted several autonomy demonstrations in both the simulator and aircraft. The team assessed automated terminal operations, enhanced station keeping, and maneuver tactile limit cueing in a flight simulator. Additionally, the V-280 technology demonstrator conducted autonomous flight profiles to explore these systems in an airborne environment. To mature autonomy systems for integration on future platforms, a Bell 429 was converted into the Aircraft Laboratory for Future Autonomy, completing its first flight last year with fly-by-wire controls at the evaluation pilot station. The influence of Bell autonomy demonstrations on the
ABSTRACT This paper describes the methodology, involving testing and simulation activities, to assess malfunction conditions of complex systems installed on fly-by-wire vehicles, including the evaluation of their effects. This paper provides also a description about how the system malfunction tests are designed, driven by input requirements and systems capability and behavior. With respect to prior publications, this paper includes some practical test examples, based on systems monitoring, logics and alerting functions. The case study described here comes from a portion of multiple laboratory certification tests done for AW609 Tiltrotor, focused on Avionics System malfunctions. These tests and simulations are a valuable Means of Compliance with respect to applicable airworthiness rules, and a suitable means to verify the design safety requirements. Three relevant examples are presented, grouped by input requirement and safety conditions. The effect of such malfunctions is evaluated
Over the past few decades, aircraft automation has progressively increased. Advances in digital computing during the 1980s eliminated the need for onboard flight engineers. Avionics systems, exemplified by FADEC for engine control and Fly-By-Wire, handle lower-level functions, reducing human error. This shift allows pilots to focus on higher-level tasks like navigation and decision-making, enhancing overall safety. Full automation and autonomous flight operations are a logical continuation of this trend. Thanks to aerospace pioneers, most functions for full autonomy are achievable with legacy technologies. Machine learning (ML), especially neural networks (NNs), will enable what Daedalean terms Situational Intelligence: the ability to understand and make sense of the current environment and situation but also anticipate and react to a future situation, including a future problem. By automating tasks traditionally limited to human pilots - like detecting airborne traffic and identifying
ABSTRACT The AH-64 would significantly benefit from an improved flight control system, particularly as the aircraft's requirements have evolved and continue to do so. To address this, multiple Vehicle Management System architectures are developed and presented for the AH-64 attack helicopter, each addressing several demanding and possibly conflicting future requirements, including Level 1 handling qualities, operating in degraded visual environments, autonomy, high-speed flight operation, and multiple vehicle coordinated operations. Architecture tradeoffs are performed with the understanding that the current AH-64 flight control system is mechanical with electrical partial authority augmentation, but also possesses a non-redundant full authority fly-by-wire emergency backup system. The various architectures are assessed as to how they satisfy the requirements. They are also assessed with respect to their relative costs, both for typical costs such as design, recurring, operating and
This document provides a description of a process for development of fly-by-wire actuation systems. Included are (1) the development of requirements for the servo-actuator hardware and the electronics hardware and software, (2) actuator and servo-electronics interface definitions and, (3) the required communications and interactions between the servo-actuator and the servo-electronics designers.
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
ABSTRACT A core mission of the CH-53K involves flying in severe brownout conditions, which increases pilot workload and can reduce mission success rates. With state of the art Fly by Wire capability, the CH-53K leverages the computational power of a flight control computer to provide higher order control modes which reduce pilot workload in all degraded visual environments such as brownout. The preliminary design of the flight control system included the inceptor system and low speed control architecture, which created an expansive design space. High fidelity simulations, cockpit mockup, and use of the NRC Bell 412 in-flight simulation Advanced Systems Research Aircraft surrogate aircraft allowed for a comprehensive development environment to narrow down to final control system design. The final design of the low speed maneuvering provided a command strategy similar to translational rate commend yet provided an approach profile that more closely replicated a piloted approach to a
Flight in icing for transport category aircraft certification presents a particularly challenging set of considerations to establish adequate safety commensurate with the associated risk while balancing design complexity and efficiency. A review highlighting important aspects of the regulatory evolution and guiding principles for flight in icing certification is presented, including the current standards and recent rulemaking activity. While historical icing certification relied on a simple yet subjective requirement to demonstrate that an aircraft is capable of operating safely within the prescribed icing envelopes, the certification requirements associated with demonstrating an adequate level of safety have progressively evolved into more explicit quantitative performance and qualitative handling qualities standards now scattered throughout the Federal Aviation Administration (FAA) Title 14 Code of Federal Regulations (CFRs) Part 25 Subpart B Flight standards which are largely
The development and qualification of distributed and highly safety-critical avionics systems implicate high efforts and risks. The resulting costs usually limit implementations like fly-by-wire systems to the military or commercial airliner domains. The aim of previous and ongoing research at the Institute of Aircraft Systems at University of Stuttgart is the reduction of these costs and therefore open up their benefits, inter alia, to general aviation, remotely piloted or unmanned aircraft. An approach for an efficient development is the application of a platform based development which supports the reuse of software and hardware components. The Flexible Platform adopts this approach. It is accompanied by a tool suite which automates the design and parameter instantiation, documentation generation and the generation of verification artifacts for a platform instance. This paper presents the approach for the requirement document generation compliant to ARP4754A and DO-178C. It is based
This SAE Aerospace Recommended Practice (ARP) provides general requirements for a generic “passive” side stick that could be used for fly by wire transport and business aircraft. It addresses the following: The functions to be implemented The geometric and mechanical characteristics The mechanical and electrical interfaces The safety and certification requirements
This SAE Aerospace Information Report (AIR) provides design information of various contemporary aircraft fly-by-wire (FBW) flight control actuation systems that may be useful in the design of future systems for similar applications. It is primarily applicable to manned aircraft. It presents the basic characteristics, hardware descriptions, redundancy concepts, functional schematics, and discussions of the servo controls, failure monitoring, and fault tolerance. All existing FBW actuation systems are not described herein; however, those most representing the latest designs are included. While this AIR is intended as a reference source of information for aircraft actuation system designs, the exclusion or omission of any other appropriate actuation system or subsystem should not limit consideration of their use on future aircraft.
ABSTRACT Flight testing of explicit rotor-state feedback (RSF) fly-by-wire control laws showed that measuring rotor tip-path-plane (TPP) flapping, via a laser measurement system, provided additional lead to the control system. This resulted in superior handling qualities in turbulence and heavy winds and improved stability margins. However, a significant impediment to the adoption of explicitly measured RSF has been the difficulty in extracting reliable rotor measurements. Therefore, this paper describes the development of a Kalman filter that was designed to estimate rotor TPP coordinates, and remove noise from the flapping signals while retaining the useful information without introducing large time delay, as would be the case for conventional low pass filtering. A new method for the design of the process noise covariance matrix using optimization of frequency domain specifications was implemented using flight test data from the UH-60 Black Hawk. The design was integrated into an
This SAE Aerospace Information Report (AIR) supplies information on the flight control systems incorporated on various current and historic fixed wing, rotary wing, and tilt rotor aircraft. A brief description of the aircraft is followed by a description of the flight control system, some specific components, drawings of the internal arrangement, block diagrams, and schematics. System operation redundancy management is also presented.
ABSTRACT Advances in technology have made rotorcraft more comfortable, more capable, and more complex. With these advances, operators rely more on automated systems to reduce flight crew workload and to elevate safety. Correspondingly, flight-critical systems must remain operational at all times. Mechanical vibration or impact shocks such as bird strikes must not lead to a system failure. The approach for making the Bell 525 as safe as possible uses the guidelines of ARP4754A. The 525 is a commercial entry in the new super medium class of helicopters, and is the only commercial helicopter with fly-by-wire (FBW) flight control technology with state-of-the-art avionics. Safety requirements and certification regulations mandate the ability for continued safe flight following a bird strike incident. Improvements in computer simulation capabilities enable relating mechanical shock qualification tests with in-flight impact threats.
ABSTRACT This paper describes selected benefits of Adaptive Vehicle Management System (AVMS) tactile-cueing technologies that were demonstrated using an MH-47G Chinook equipped with an Active Parallel Actuator Subsystem (APAS). Rather than immediately proceeding to a full-authority Fly-By-Wire (FBW) system, the APAS adds tactile cueing and backdrive capabilities while retaining the existing Chinook hydromechanical primary flight controls with partial-authority augmentation. The flight-tested AVMS technologies include Carefree Maneuvering, Regime Recognition, and Task-Tailored Control Laws. Both simulation and flight test results are presented using technical performance metrics and pilot comments. Features of the APAS and AVMS control law software are described. The flight testing not only demonstrated the value of the technology, but also reduced technical risk to facilitate technology transition into a production environment. Having been successfully demonstrated in a flight
ABSTRACT Rotor-state feedback (RSF) technology uses tip-path-plane measurements of the rotor to improve the tracking response of the aircraft in winds and turbulence, and provide improved stability margins. Three fly-by-wire control systems were designed and flight tested on the RASCAL JUH-60A aircraft to determine the benefits of RSF. A Baseline control system that used only conventional fuselage feedback but was optimized for Level 1 performance was compared to two control systems that used both rotor-state and fuselage feedback (and were also optimized for Level 1). The Implicit RSF control system implemented fuselage feedback and estimated (implicit) rotor-state feedback. The Explicit RSF control system implemented fuselage feedback and measured (explicit) rotor-state feedback via a laser measurement system installed on the aircraft. The sensor characteristics, frequency response validation, handling qualities ratings, and MTE tracking performance for hover/low-speed are discussed
This SAE Aerospace Information Report (AIR) provides a description of the interfaces and their requirements for generic and specific hydraulic actuation systems used in the flight control systems of manned aircraft. Included are the basic control system characteristics and functional requirements, and the essential interfaces (structural, mechanical, hydraulic power, control input, status monitoring, and environment). Major design issues, requirements, and other considerations are presented and discussed.
ABSTRACT Transport Category Certification requires the ability to safely land or continue flight after an engine failure during all phases of flight. The maximum transport category gross weight is a key parameter that can strongly influence the success of an aircraft. Due to its unique configuration, the tiltrotor offers unique challenges and abilities for surviving an engine failure during its critical mission phase. Challenges include energy management and thrust maintenance for a low inertia, high disk-loading rotor. Unique capabilities include rapid acceleration due to tilting of the thrust vector via the nacelles, which is a powerful method of improving takeoff performance and ground clearance for continued flight after a single engine failure. With its fly by wire flight control system and integrated engine controls architecture, the AW609 offers an unparalleled ability to evaluate, tune, and improve transport category performance, specifically during the critical flight phases
ABSTRACT Vertical speed is a critical limit for rotorcraft at low height above terrain and low speed flight conditions. In this paper an adaptive estimation algorithm is proposed to estimate allowable control travel on the collective axis at the onset of pre-defined vertical speed limits. A concurrent learning neural network based framework is used to model vertical speed online and used to predict future values of the vertical speed for given collective inputs. The generated online model is used to estimate the control sensitivity of the collective axis to formulate the allowable control travel. A generic nonlinear utility helicopter model is used to show estimation and avoidance of vertical speed limits.
This SAE Aerospace Information Report (AIR) has been prepared to provide information regarding options for optical control of fluid power actuation devices. It is not intended to establish standards for optical fluid power control, but rather is intended to provide a baseline or foundation from which standards can be developed. It presents and discusses approaches for command and communication with the actuation device via electro-optic means. The development of standards will require industry wide participation and cooperation to ensure interface commonality, reliability, and early reduction to practice. To facilitate such participation, this document provides potential users of the technology a balanced consensus on its present state of development, the prospects for demonstration of production readiness, and a discussion of problem areas within this technology. The intent is to inform the user/designer of the options available for interfacing photonics (optics) to hydraulic power
Business Jets Bounce Back The business jet segment suffered badly from an extended economic downturn but is now seeing a new generation of airplanes becoming available, introducing features and technologies that are equal to, and in some cases superior to, jets in airline service. The business jet market has a resilience all its own. While defense spending has sharply declined, the commercial sector is over-flowing with multi-thousand order backlogs. But if business jet orders can tail off dramatically and then bounce back so quickly, what accounts for this collective long-term immunity to volatile market demands? One answer is competition. There are now so many manufacturers of business jets in the world there are niche markets within the sector that enable products to be offered for almost any need, from a private Airbus Corporate Jet (ACJ) A380 down to a 4-6 seat entry-level jet.
Advanced commercial aircraft increasingly use more composite or hybrid (metal and composite) materials in structural elements and, despite technological challenges to be overcome, composites remain the future of the aviation industry. Composite and hybrid aircraft today are equipped with digital systems such as fly by wire for reliable operations no matter what the flying environment is. These systems are however very sensitive to electromagnetic energy. During flight, aircraft can face High Intensity Radiated Fields (HIRF), static electricity, or lightning. The coupling of any of these threats with airframe structure induces electromagnetic energy that can impair the operation of avionics and navigation systems. This paper focuses on systems susceptibility in composite aircraft and concludes that the same electromagnetic rules dedicated to all metal aircraft for systems and wiring integration cannot be applied directly as such for composite aircraft.
ABSTRACT After supplying a first-generation Active Inceptor System (AIS) for the Boeing Vehicle Management Systems Integration Technology for Affordable Lifecycle cost (VITAL) AH-64 Apache helicopter, BAE Systems has produced a range of flightworthy AIS products for several military and commercial aircraft. The latest fifth-generation AIS is in development for the civil marketplace. Most recently, BAE Systems worked collaboratively with Boeing Helicopters to define a new type of tactile cueing solution, the Active Parallel Actuation Subsystem (APAS) that provides the benefits of tactile cueing to vehicles that are not Fly-By-Wire (FBW). Initially aimed at the H-47 Chinook platforms, the APAS equipment provides synthetic force feedback and tactile cues to pilots of any aircraft having mechanically interconnected pilot stations and displacement-trim flight controls. The solution leverages Commercial-Off-The-Shelf (COTS) components, software, and civil certification artifacts from the
ABSTRACT Since its formal launch in 2012, designers of the Bell 525 Relentless have sought feedback and utilized input from a Customer Advisory Panel (CAP) comprised of industry-leading global helicopter operators. The top initiative of this group is to adopt the features of a next generation helicopter that provides enhanced margins of flight safety. In response, the Bell 525 will be the first commercial helicopter to offer full authority fly-by-wire digital flight controls. Helicopter safety reviews have consistently found that human factors and situational awareness are the leading cause of helicopter accidents. With this history, safety clearly points to the need for careful consideration of pilot workload, especially in demanding situations such as hovering near multiple obstacles or performing in Degraded Visual Environments (DVE). Design-for-safety enhancements include Translational Rate Command / Position Hold control laws at low speed, automatic computer assisted entry into
On September 30, 2011, certification authorities released Advisory Circular 20-174[1], Development of Civil Aircraft and Systems, which recognizes the Society of Automotive Engineers (SAE) Aerospace Recommended Practice (ARP) 4754A and the European equivalent ED-79A [2], in order to address “the concern of possible development errors due to the ever increasing complexity of modern aircraft and systems.” ARP4754A/ED-79A describes a process of development assurance which helps reduce the risk of design errors in the development of aircraft systems. This process is necessary for complex systems not easily comprehended by deterministic analyses or tests. This ARP was developed “in the context of Title 14 of the Code of Federal Regulations (14 CFR) part 25,” a category which includes complex systems such as full fly-by-wire flight controls. However, this paper shows that such systems are the exception to most, recent civil airplane designs. Of new airplanes designed in the last 10 years
A multi-axis serially redundant, single channel, multi-path FBW (FBW) control system comprising: serially redundant flight control computers in a single channel where only one “primary” flight control computer is active and controlling at any given time; a matrix of parallel flight control surface controllers including stabilizer motor control units (SMCU) and actuator electronics control modules (AECM) define multiple control paths within the single channel, each implemented with dissimilar hardware and which each control the movement of a distributed set of flight control surfaces on the aircraft in response to flight control surface commands from the primary flight control computer, and a set of (pilot and co-pilot) controls and aircraft surface/reference/navigation sensors and systems which provide input to a primary flight control computer and are used to generate the flight control surface commands in accordance with the control law algorithms implemented in the flight control
Aircraft utilize electrical power for many functions ranging from simple devices such as resistive heaters to highly advanced and complex systems responsible for communications, situational awareness, electronic warfare and fly-by-wire flight controls. The operational states of these electronic systems affect safety, mission success and the overall economic expense of operation and maintenance. These electronic systems rely on electrical power within established limits of power quality. In recent years, electrical power quality is becoming excessively degraded due to increased usage of nonlinear and dynamic loads coupled to aircraft power systems that were neither designed nor tested for these loads. Legacy power generation systems were designed for electrical loads with resistive and inductive properties, which previously represented the majority of actual aircraft electrical loads. As more complex and advanced electronic systems were invented, mostly due to developments in
This SAE Aerospace Recommended Practice (ARP) provides general requirements for a generic “passive” side stick that could be used for fly by wire transport and business aircraft. It addresses the following: The functions to be implemented The geometric and mechanical characteristics The mechanical and electrical interfaces The safety and certification requirements
If you're in the business of making machine tools for aerospace applications, you're probably working on improvements in cutting tough metals and composites. How's this for a challenge to makers of machine tools for aerospace applications: “95% of the new materials used in the new aircraft programs are impossible to machine with conventional CNC machines.” So says Scott Walker, President of Mitsui Seiki North America. His company and others are hard at work developing the technologies to make the impossible possible, especially as it relates to titanium.
This guide provides detailed information, guidance, and methods related to the Federal Aviation Administration (FAA) Advisory Circular (AC) 20-158 and European Aviation Safety Agency (EASA) draft Advisory Material Joint (AMJ), both titled "The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-Intensity Radiated Fields (HIRF) Environment". The AC provides acceptable means, but not the only means, of compliance with Title 14, Code of Federal Regulations (14 CFR) 23.1308, 25.1317, 27.1317, and 29.1317, High-Intensity Radiated Fields (HIRF) protection for Aircraft Electrical and Electronic Systems, and applicable FAA HIRF Special Conditions to prevent hazards to aircraft electrical and electronic systems due to HIRF produced by external transmitters. It is also intended for this guide to provide the same information, guidance, and methods to the European Aviation Safety Agency (EASA) interim HIRF policies certification requirements. This guide is neither
This SAE Aerospace Information Report (AIR) provides a description of the interfaces and their requirements for generic and specific hydraulic actuation systems used in the flight control systems of manned aircraft. Included are the basic control system characteristics and functional requirements, and the essential interfaces (structural, mechanical, hydraulic power, control input, status monitoring, and environment). Major design issues, requirements, and other considerations are presented and discussed.
This SAE Aerospace Information Report (AIR) has been prepared to provide information regarding options for optical control of fluid power actuation devices. It is not intended to establish standards for optical fluid power control, but rather is intended to provide a baseline or foundation from which standards can be developed. It presents and discusses approaches for command and communication with the actuation device via electro-optic means. The development of standards will require industry wide participation and cooperation to ensure interface commonality, reliability, and early reduction to practice. To facilitate such participation, this document provides potential users of the technology a balanced consensus on its present state of development, the prospects for demonstration of production readiness, and a discussion of problem areas within this technology. The intent is to inform the user/designer of the options available for interfacing photonics (optics) to hydraulic power
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