Interaction and Usability: Fly-by-wire Systems - Coursework Example

Interaction and Usability (MOD002591) Due Date: 31st December 2014 Faculty: Science and Technology Department: Computing & Technology Module Code: MOD002591 Academic Year: 2013/2014 Semester: 2 Table of Contents Component 1 3 Brief description 3 Initial assumptions 3 Justification of goals 4 Component 2 5 Introduction 5 Critical Exploration 6 User Needs Analysis 7 Preliminary Design 10 Detailed Design 11 Implementation 13 14 Evaluation 14 References 16 Component 1 Brief description The Fly-by-wire (FBW) system replaces the standard manual flight controls through a hybrid electronic interface. Essentially, the system converts all movements of the flight controls into electronic signals that are then transmitted to the control panel through wires. At every control surface of the system are actuators whose movements are determined by flight control computers. This provides the desire response. There is also the possibility of sending automatic signals originated from the flight computers to perform some functions. This can proceed without the pilot noticing or even deciding. These systems assist in stabilizing the aircraft automatically (Crane, 1997). The basis of using the system as a replacement to the conventional manual or the hydro-mechanical systems then is to improve automation and increase efficiency. Initial assumptions The design process used for Fly-by-wire system is modification of current product to support the proposed method. The design process used for implementing and verifying Fly-by-wire system design. The Redundancy Component and debugging: The redundancy component in designing a Fly-by-wire system is a technique whose aim is to get rid of single points of failures within the system. Single point failures refer to a condition that breaks the entire system following the failure of only one device or design element. The Tools Component: hardware required for designing include sockets, wire-wrap wire PCB’s, IC’s, capacitors, resistors, copper wire and IDE ribbon cables. Circuit Boards for prototyping were also required. There are 4 boards that were used in this design that had display drivers, buffers for the interfaces, counter logic; Sockets for 3 IDE interface cables to external modules are visible at the bottom. Many modern jets, nevertheless, maintain computerized systems that not only control the movement of the aircraft but also its air inlets, engine throttle, fuel storage and distribution etcetera. For this reason, any possibility of sustaining less economic systems is minimal. Redundancy in the development of the Fly-by-wire system has been maintained and/or removed for several reasons. The main reasons regards malfunction. A hydraulic or a mechanical system would is sustained as an alternative to the digital fly-by-wire as exigency for failures of the digital system. Justification of goals The design is an important component of in designing Fly-by-wire (FBW) system. It involves understanding how the intended purpose of Fly-by-wire system that is about to be designed thereby allowing the designer to understand what should be incorporated in the processor at the design stage. One of the aspects that the design component has to consider for successful design of Fly-by-wire system from the standard manual flight controls. Component 2 Introduction Past experiences, accidents and incidents determine many developments in the aircraft industry. These lessons offer insights into what to modify, improve or discard as regards technology, systems design and system redundancy. The modern jet aircraft is a result of several transformations occasioned by incidents, ad particularly accidents. The flight control system has particularly developed thanks to many attempts at automation, improvement in efficiency and perhaps more so because of the many incidents of miscommunication that cause aircraft accidents. The fundamentals of aircraft control are explained in flight dynamics but the improvements in flight controls are best understood from system failures and redundancies thereof. Over time, the flight control system has therefore developed from the most basic mechanical systems used in the early 20th century (retained in some small aircrafts) to the hydro-mechanical systems that took into account the weight and complexity challenges in aircraft development. The later considerably increased the performance of aircraft control surfaces through aircraft feels systems that removed possibilities of overstressing the aircraft control surface movements that arise from hydro-mechanical systems. Another development in the hydro-mechanical system was the stick shakers, so called because they are fitted into the control column to shake it when the aircraft risks stalling. In aircrafts such as the McDonnell Douglas DC-10, the system is augmented by a back-up electrical power supply through which the pilot may use to make the stick shaker active again should the hydraulic connection to the stick shaker malfunction. Of these developments in aircraft control systems is the Fly-by-wire, so called because of its ability to control the aircraft through an electronic (wire) interface. When in use, the fly by wire system converts aircraft’s flight control movements into electronic signals that are transmitted through wires. The movement of actuators at control surfaces is determined by computers thereby providing the expected response. Essentially, this command system may proceed even without the pilot’s knowledge and therefore transforms flight control into an electronics sphere called avionics. In the following sections, I shall explore the FLY BY WIRE –FBW system. I will particularly discuss the system, its history and functionality as well as redundancy issues inherent, and why they may have been discarded or retained. I will also discuss implications of the challenges/failures of the system. Critical Exploration The fly-by-wire corresponds to the electronic systems development for aircrafts. Jet aircrafts particularly have enjoyed particular improvements in his are thanks to incidences of control failure that cause accident and therefore business concerns. Developments for major aircraft manufacturers have therefore been rather parallel. The control surface electronic signalling has a long history, having been tested for the first time in the 1930s. The Soviet Tupolev ANT-20 was the first to have developed a remote system to replace the long runs of mechanical and hydraulic control connections. This development, however, proceeded on an experimental basis until the Avro Canada CF-105 Arrow designed and flew the first non-experimental aircraft on a fly-by-wire flight control system in 1958 (Potocki, 2004). This fete was to stall, especially among production aircrafts until 1969, when the Concorde was developed. The design was an integration of an automatic search, a computerized navigation, and track radar. It was still flyable from ground control, in which data uplink and downlink was necessary. This ably provided real-time feedback (artificial feel) to the pilot. Nevertheless, the system in Concorde remained in a solid-state with inherited system redundancies (Whitcomb, 2008). A different development of the system was tried in the two-seater Avro 707B in the UK in early to mid-1960s. The Fairey system, as it was called, had a mechanical backup. However, the system was to be curtailed when the airframe of the Avro 707B ran out of flight time. User Needs Analysis Flight operations encompass the planning and movement of crew, freight, passengers and their belongings through specific airspace to particular destinations, on an aircraft. Flight operations comprise difficult tasks that involve the management of several resources. These resources at times prove to be hard due to congested airspace. Airspace congestion is a challenge that is not likely to go, thanks to the ever expanding airline industry. Even though, airline companies cannot effectively handle the problem of congested airspace, airline operations define the nature of substantial percentages of airspace congestion. The manner, in which airline companies manage time, influences their revenue and flying habits of their passengers. The administration of turnaround operations of an aircraft is vital as far as the achievement of quality airline operations is concerned. Cheaper and or busy airlines require quick and efficient flight operations in order to minimize disruption of airline return journey schedules, which could increase operating expenses. In view of this, most successful airline companies uphold two major operation tenets; the scramble for more passengers and the delivery of timely turnarounds. The subject of an airplane turnaround operation has been evaluated through the use of Critical Path Methods. Nonetheless, the employment of CPM to manage a turnaround process is that such a process does not provide options for uncertainties during flight operations, for instance flight postponement due to unfavourable weather The flight operations of a plane can be split into smaller categories, which are handled by different service providers, for instance, refueling of an aircraft, and provision of catering services. It is notable that turnaround operations of an aircraft demands the dispensing of many and different services. The operations take place almost at once within the planned turnaround period. This can be manifest in the way passengers are processed from the very minute they alight from an aircraft. The process of readying crew members also begins the very moment an aircraft occupies the departure lot waiting to be prepared for another flight. World airlines attain the amazing by securely moving almost five million passengers to distances exceeding 40 million miles of flight. Usually, however, most fail to effectively handle quite common things. Once the aircraft touches down, most of them move to a taxi way and wait, maybe for crew stationed at the airport to appear and unfasten a door so the passengers and crew disembark or for the passage to be cleared in case another aircraft is under maintenance. Even stick out, low-cost passengers lose baggage, keep important crew idle, leave late, and have large amounts of money in constantly underutilized airplane and other massively expensive resources. These extremes happen because airline companies have traditionally focused immense resources on safety, airplane technology, velocity, geographic coverage, and cabin and service features; on different regulatory limits and employment matters; and on the ever changing weather conditions and swiftly changing demand. Additionally, issues such as air ways, surfeit capacity, freight charges, and yield management vie with the airline services for interest. As a consequence, the companies have yet to give their operations industrial-engineering evaluation akin to that of a factory. Successful operators in equally heavy sectors have navigated their way through these shortfalls to deliver cheaper, high quality services that satisfy clients. Yet almost half of the expense structure of an airline consists of repairs, ground management and cabin services which provide communication services, and aircraft purchases; these operations are shaped by operational issues like plane downtime. A century since the discovery of powered air travel, it is notable that the airlines should be considered as fledged companies. Interestingly, this evaluation has triggered the application of better manufacturing measures that continue to modernize the process into an intensive business. The opportunity at stake revolves around the limiting of overall costs remarkably by employing more effective use of labour, resources and assets, to improve service delivery, and to uphold flight safety measures. Under normal circumstances, new members of crew would normally wait until the cabin cleaning process is complete before they can be allowed to board the aircraft. Once in, the aircraft will not be flagged off if the communication between the crew and the airport control tower is not successful. Moreover, a number of aircraft service operations handled separately during the course of aircraft turnaround exist. These may include engineering verifications. The entire procedure of readying an aircraft for another flight, therefore, comprises of series of activities and separate service operations. It is notable that these aspects of flight are quite involving, difficult to monitor and demands more technical knowhow. Practically, an effective model that eases the management of aircraft turnaround operations should create room for operational emergencies, which prompt the postponement of a turnaround plane. Moreover, a model for turnaround aircrafts should give room for the evaluation of comprehensive operational activities, as this would lead to the detection of probable weaknesses in turnaround flight operations. Development of the fully digital versions of the Fly-by-wire system started in earnest in the 1970s when the first such system without any mechanical back-up was developed in the an F-8 Crusader. The F-8 Cruader took the air as a test aircraft in 1972 with modifications of the system by the US’ National Aeronautics and Space Administration (NASA, 2008). For its control, the aircraft used a digital computer backed up by three analogue channels. A similar development was undertaken in the Sukhoi T-4 in the USSR and in a British Royal Aircraft Establishment version of the Hawker Hunter in the UK (flightglobal.com, 1973). The latter had the new developments on the pilot’s right-seat while the left-seat retained the conventional flight controls for safety reasons. Since then, the fly-by-wire systems has been tested and perfected in a host of other jet aircrafts. In many modern versions of these, the fly-by-wire is a stand-alone system that has increased aircraft control efficiency and experience. Preliminary Design This type of design shows the ability of the system to function. This ensures that it hardware is correct in operation. Any malfunction will be debugged as any hardware that is not compatible may not function. Software and software development tools: software is critical to design as they make the system work. The software can valuable in debugging. Compiling, simulation and execution cannot be carried out without debugging. It is also relevant during the selection of specific design choices at the process’ subsystem level and for the determination of the sensitivity of the overall system selection to change in weights and ratings accorded to various architectural alternatives. Functional analysis is the process of identifying the set of inputs, behaviour, and outputs of software. Analysis may involve a description of technical details, calculations, manipulation of date or other specific classification of functionalities that a system is to accomplish. Use cases are used to describe behavioural requirements for system functionality. Generally, functions are expressed in the form of a task that the system must undertake. For instance, “system must do , to produce . So defined, the functions are used to drive the application architecture of a system. The essence of ascertaining software reliability is in the interest of vendors who need confirmation that their customers will utilize them without failures. Software reliability models are therefore used to ascertain this functionality. They provide information about the reliability of software either by predicting the same from design parameters or from test data. Predicting software reliability from design parameters is a kin to ascertaining the level of defect in the software, thus they are referred to as “defect density” models. These models used code characteristics such as through nesting of loops, lines of code, input/outputs, or external references in estimating the degree of defect in software. Models that test software from test data are akin to testing reliability in growth, thus they are referred to as “software reliability growth” models. The models use statistical correlations to find the relationship between known statistical functions and defect detection data. Good correlations are then used to predict software behaviour in the future. Detailed Design The operation of a fly-by-wire works on a relatively simple command- a simple feedback loop that, in reality, is quite complex. When the pilot moves the side stick (control column), a signal is transmitted to a computer through a number of wires (called channels). This is to ensure that the signal is received by the computer. A triplex channel, for instance, includes three such channels. After the computer receives the signal, it performs a number of calculations chief of which involves adding signal voltages, before dividing them by the number of channels received. This gives he average signal voltage. Another channel is then added to the three signals, and the four signals then sent to the actuator on the control surface. This moves the surface. A series of potentiometers within the actuator then returns a signal to the computer to report the current position of the actuator. This signal is usually a negative signal. When the desired position of the actuator is attained, the outgoing and incoming signals cancel out each other thereby stationing the actuator at its present position. The automatic stability systems of fly-by-wire enable the control of an aircraft with only little or no input from the pilot. Usually, sensor-fitted gyroscopes are mounted in an aircraft. These sensors are capable of sensing any changes in movement- pitch roll and yaw axes- of the aircraft. With these, any movements such as from level flight or straight flight cause signals to be sent to the computer. These signals cause automatic movements in control actuators thereby stabilizing the aircraft. The automatic stabilizing systems may be analog or digital. The analog systems are similar to the conventional hydraulic circuits except that electrically controlled servo valves replace the mechanical ones. These valves are then operated by a electronic controller. The simple analog configuration allows the “feel” to be simulated through the control of electrical feel devices. These devices provide the necessary "feel" forces onto the manual controls and were first used in the Concorde (flightglobal.com, 1986). In other sophisticated versions of the analog stabilizing system, the electronic controller is replaced by analog computers as it was used in the Avro Canada CF-105 Arrow, a 1950 Canadian supersonic intercepter. Through the analog computers, other customizations of flight control characteristics, such as relaxed stability were achieved. In the pioneer versions of F-16, for instance, this was used to give an impressive maneuverability. The digital fly-by-wire flight control system is a complete makeover of the analog and mechanical operations of the conventional flight control systems. The first completely digital fly-by-wire controls system was developed for the Airbus A320. In this system, signal processing is undertaken through a series of digital computers, thereby enabling the pilot to literally fly via computer. The flexibility of the flight control system is improved tremendously because the computers are capacitated to receive signals from a myriad of sensors like the pilot tubes and the altimeters. The digital system also increases electronic stability since the control system depends less on the input values of critical electrical components as it happens in the analog systems. Once the computers have sensed force inputs and positions from sensors and pilot controls, they manipulate a series of differential equations to determine which of the command signals is appropriate to best execute the pilot’s intentions. In essence, the digital systems are programmable units with flight envelope protection that effectively tailor the handling characteristics of the aircraft. The pilot’s workload in operating such aircrafts is grossly reduced. Moreover, stability is relaxed thereby increasing the aircraft’s maneuverability. Examples of this system in use today are the control systems of Dassault Falcon 7X, which pioneered as the first commercial jet to have the system. Another is the Airbus A320, which became the first airliner to use an all-digital system, fly-by-wire control system (Moir et al, 2003). Implementation Redundancy in flight-control for airlines is aimed at improving safety. This must be balanced by the economy, in weight reduction achievable through fly-by-wire systems. Many modern jets, nevertheless, maintain computerized systems that not only control the movement of the aircraft but also its air inlets, engine throttle, fuel storage and distribution etcetera. For this reason, any possibility of sustaining less economic systems is minimal. Redundancy in the development of the Fly-by-wire system has been maintained and/or removed for several reasons. The main reasons regards malfunction. A hydraulic or a mechanical system would is sustained as an alternative to the digital fly-by-wire as exigency for failures of the digital system. Evaluation In fly-by-wire systems, the main worry regards possible insanity by electromagnetic pulses. In earlier versions of the fly-by-wire, the digital system was backed up by an analog electrical system. It is now planned that if one flight-control computer crashes, another computer should overrule the faulty one and flies the aircraft to safety. There are possibilities of rebooting the faulty computers or overruling any computer whose results disagrees with the others, a process called “voting-out.” Similarly, variants of back-ups have also been developed to reduce the risks of exposing the entire flight-control-system to failure, arising either from the malfunction of general-purpose flight software. In this case, a standby system of computer and software makes up for the failure. Different flight control modes are to be found in different commercial jets. The Airbus and Boeing commercial jets, for instance, present different variations of the system. The former has a flight-envelope control system that retains the ultimate control, and so do not permit any flight outside these confines by pilots. The aircraft, however, has a back-up system that cushions for multiple system failures, especially for pitch trim and rudder functionalities. A redundant electrical rudder control system is sustained in the A340-600, for instance (Le Tron, 2007). In the Boeing 777, a different variant exists in which the two pilots have the capacity to override the electronic flight-control system thereby permitting the pilots to fly beyond the limits of the system, especially during emergencies (Briere & Traverse, 1993; North, 2000). References Briere, D., and Traverse, P., 1993. Airbus A320/A330/A340 Electrical Flight Controls: A Family of Fault-Tolerant Systems. Proc. FTCS, 616-623. Crane, D. (1997). Dictionary of Aeronautical Terms, third edition. Aviation Supplies & Academics. flightglobal.com. (10 August 1972). RAE Electric Hunter. Flight International. Accessed 30 December 2014, from http://www.flightglobal.com/pdfarchive/view/1973/1973%20-%201822.html flightglobal.com. (1986). The Tay-Viscount was the first airliner to be fitted with electrical controls Flight 1986. Accessed 30 December 2014, from http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%200838.html Le Tron, X. (27 September 2007). A380 Flight Control Overview Presentation at Hamburg University of Applied Sciences. Accessed 30 December 2014, from http://www.fzt.haw-hamburg.de/pers/Scholz/dglr/hh/text_2007_09_27_A380_Flight_Controls.pdf NASA. F-8 Digital Fly-By-Wire Aircraft.12-02.09. www.nasa.gov. Accessed 30 December 2014, from http://www.nasa.gov/centers/dryden/news/FactSheets/FS-024-DFRC.html North, D. (2000). Finding Common Ground in Envelope Protection Systems. 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