< PREVIOUS: NEXT > The rudder pedals directly command rudder surface movement via cables. Another function of flight control laws is to assess the performance of the aircraft under various conditions, such as takeoff, landing or normal cruise when flight control computers partially or completely fail. Failures can occur singly or in combination to render systems inoperative. However, the protection functions of the system do not reduce or limit pilot control authority. For manual turns up to 33° bank, no sidestick back pressure is required as the system automatically trims the aircraft to maintain level flight. Many newer aircraft replace these mechanical controls with fly-by-wire systems. Boeing's direct mode removes many of the computational 'limitations'. The air flight simulator, also known as the variable stability aircraft, can make the dynamic characteristics of the machine change or simulate the response characteristics of different objects in a large range through the variable stability telex system. Two Flight Control Data Concentrators (FCDC) also acquire data from the Primary and Secondary Flight Control Computers and send it to the Electronic Instrument System (EIS) to feed pilot displays and to the Central Maintenence Computer (CMC). • Map the Pilot Commands and Feedbacks into the Desired Aircraft Accelerations, not Aircraft Surface Commands Roll Regulator Example Roll Regulator + Cmd roll-P s 1/τ roll P s (1/τ roll)----- = -----Cmd roll (s + 1/τ roll) Simple Dynamic Inversion Roll Control Law Provides a Classical First Order Roll Response P s desired. The aural warning "Speed Speed Speed" indicates to the pilot that aircraft energy has become too low and that power must be added to recover a positive flight path angle. Aircraft with fly-by-wire flight controls require computer controlled flight control modes that are capable of determining the operational mode (computational law) of the aircraft. Flight control mode or flight control law both refer to the computer software that transforms the movement of the joystick, made by an aircraft pilot, into movements of the aircraft control surfaces. To overcome these problems, a flight control law design method that couples the longitudinal axis with the lateral-directional axes is proposed. Section 4A. Ground Mode: Active when aircraft is on the ground. The relationship between sidestick input and the aircraft response is called the flight control law. Information from numerous sources including pilot sidesticks and rudder pedals, the Air Data Inertial Reference Units (ADIRUs), the Landing Gear Control Interface Units (LGCIU), the Slat Flap Control Computers (SFCC), the Flight Management Guidance Computers (FMGC) and the accelerometer is sent to the five flight control computers. Some surfaces, such as the rudder and the horizontal stabilizer, can also be mechanically controlled. In many cases some form of automatic flight control is used. High Speed Protection will engage to automatically recover from high speed upset. If you wish to contribute or participate in the discussions about articles you are invited to join SKYbrary as a registered user. Modern large commercial transport aircraft designs rely on sophisticated flight computers to aid and protect the aircraft in flight. Boeing Secondary mode is somewhat similar to the Airbus Alternate Law. The legislation applicable to UK merger control is the Enterprise Act 2002 (the “Act”). Aviation accident: Any situation or condition that could lead to an aircraft accident or incident. At low speed, a nose down demand is introduced based on IAS (instead of AOA) and Alternate Law changes to Direct Law. There, dependent upon the active control law, the aircraft speed, altitude, configuration, attitude, phase of flight and numerous other parameters, the sidestick and rudder pedal or autopilot commands are interpreted and the appropriate control deflection signals are sent to the control actuators. Pitch mode is in Alternate Law. Mechanical Backup These aircraft have flight control computers which send electronic signals to operate control surfaces or engine controls, inform the pilot and provide performance information. Load Factor and Bank Angle Protections are retained. Control surface motion is directly related to the sidestick motion. While all flight control surfaces remain operative, the elevator and rudder are more sensitive at some airspeeds. Apply to Communication Specialist, Mechanical Designer, Technician and more! Failure of any single computer does not affect normal law. α-Floor protection is available and will engage if pilot actions are inappropriate or insufficient. Failure of certain systems or multiple failures will result in degradation of Normal Law to Alternate Law (ALT 1 or ALT2). The PFCs verify these signals and utilise information from other airplane systems in order to compute control surface commands. Normal Law consist of three modes of operation that includes; The ground mode and flare mode are direct law with no active protections and no automatic trimming. Guest editors: ... 75.7 deg, with sufficient stability. Pilots must be able to control the aircraft with any or all of the fly by wire protections and control enhancement not functioning. DIR is entered if there is failure of all three inertial reference units or all three primary flight computers, faults in both elevators or flame out of both engines concurrent with loss of PRIM 1. The following functions are inoperative or degraded during Secondary mode operations: Direct mode On both aircraft, a single flight control computer is capable of providing complete aircraft control in the most basic of Airbus control laws, Direct Law. Secondary mode Normal mode Depending upon the status of the fly-by-wire system, three sets of control laws are provided, i.e. These newer generation of aircraft use the lighter weight electronic systems to increase safety and performance while lowering aircraft weight. Full functionality is provided including all enhanced performance, envelope protection and ride quality features. Dependent upon the failure, autopilot may not be available. The flight mode provides flight envelope protection that includes: YAW NORMAL LAW - Yaw in normal law uses the rudder for turn coordination and yaw damping. The system freezes the auto-trim when the angle of attack becomes excessive, the load factor exceeds 1.3g or when the bank angle exceeds 33°. Civil Aviation Law 11 39. The rudder pedals directly command rudder surface movement via cables. If these situations occur as the result of a deliberate manoeuvre, the pilot must apply back pressure on the sidestick to maintain the selected attitude. These newer aircraft, including the AIRBUS A-320, A330 Family, A340 Family, A350 and AIRBUS A-380-800 operate under Airbus flight control laws. It also reduces the sidestick nose down authority and applies a permanent nose up order to help reduce speed and recovery to normal flight. Activation of High Speed Protection results in automatic autopilot disengagement. High AOA protection (Alpha Prot, Alpha Floor, and Alpha Max), Load Alleviation Function (on earlier aircraft). In the case where the ideal model is fixed, the aircraft characteristics and the control law jointly affect the overall system dynamics. Two aircraft manufacturers produce commercial passenger aircraft with primary flight computers that can perform under different flight control modes (or laws). Airbus fly-by-wire: a process toward total dependability, https://www.skybrary.aero/index.php?title=Flight_Control_Laws&oldid=135151. There are three basic reconfiguration modes for the Airbus fly-by-wire aircraft, Alternate Law, Direct Law and Mechanical Back Up. Aircraft designers have created a set of flight control modes that include redundant electronics to safeguard against system failures. This paper is devoted to the research of the air flight simulation control law of large aircraft, and designs the five degree of freedom variable stability … The flight controls on Airbus fly-by-wire aircraft are all electronically controlled and hydraulically activated. Thus, the 1963 Tokyo Convention obliges contracting states to take all appropriate measures to restore control of an aircraft hijacked in flight to its lawful commander, and obliges the state in which the aircraft lands to allow the passengers and crew to continue their … With full sidestick deflection, the maximum acheiveable bank angle is 67°. Normal Law, Alternate Law and Direct Law. In older aircraft the pilot's mechanical controls are resisted by the forces acting on the control surface, but nothing prevents the aircraft from stalling, over-speeding or an excessive bank angle at high speed. As is the case with ALT1, some failure cases that result in ALT2 will also cause the autopilot to disconnecnt. Normal Law, Alternate Law and Direct Law. When the auropilot is engaged, the autopilot system sends commands to the PFCs. Model flying is governed by the same set of laws as manned aviation (the Air Navigation Order - ANO) and from the 1st July 2018, some of the laws governing the flight of all small unmanned aircraft (including model aircraft and multi-rotors) changed. Aircraft incident: Any occurrence that is not included in the definition of an aircraft accident, and is associated with the operation of an aircraft and affects, or has the potential of affecting, safe operation thereof. RECONFIGURATION OF FLT CTL LAWSIf multiple system failures occur, the flight control computers will reconfigure to a degraded flight control law. These are governed by computational laws which assign flight control modes during flight. The design principle adopted is to provide a system that responds similarly to a mechanically controlled flight control system. Limited mechanical control modes are also available to allow continued aircraft control during the reset process following a transient loss of all flight control computers. A reduction of electronic flight control can be caused by the failure of a computational device, such as a flight control computer, an information providing device, such as the Air Data Inertial Reference Unit (ADIRU) or the failure of multiple systems (dual hydraulic failure, dual engine failure etc). However, due to the degraded mode of operation, the PFCs use "simplified" computations to generate the flight control surface commands. However, without changing the control law, when the controlled object model is replaced by the elastomer model, the control system in the vicinity of 8 Hz is in the situation of … FLIGHT CONTROL LAWS SUMMARY : NORMAL LAW: Normal operating configuration of the system. This mode is automatically engaged when the radar altimeter indicates 100 feet above ground and provides for a direct sidestick to elevator relationship. Mergers (including, acquisitions and full-function joint … The autopilot commands move the flightdeck controls to provide autopilot feedback to the pilots. In addition to those functions lost during Secondary mode operations (as listed previously) the manual rudder trim cancel switch is inoperative. If a pilot overrides the autopilot with control inputs, the PFCs will disengage the autopilot and utilise the pilot control inputs. The relationship between sidestick input and the aircraft response is called the flight control law. Airbus aircraft designs subsequent to the A300/A310 are almost exclusively controlled by fly-by-wire equipment. Mark Drela Abstract: In order to solve the robustness problem of regular explicit nonlinear dynamic inversion (NDI) control law, the incremental version NDI control law is designed via the implicit dynamic inversion (DI) method and singular perturbation theory, in which the state acceleration (derivative) is feedback to measure the effects of the aircraft model perturbation and the current position information of the … 63% Max τ roll In addition, Low Speed Protection is available in certain phases of flight. Pitch control degrades to Direct Law and automatic trim is inoperative requiring stab trim to be adjusted manually by the pilot. In addition, flying wing aircraft uses drag rudders for yaw control, which tends to generate strong three-axis control coupling. While in normal flight the computers act to prevent excessive forces in the pitch and roll axes. 3.6 Are there any rights of appeal to the courts from the decision of a court or arbitral tribunal and, if so, in what circumstances do these rights arise? In Normal mode during manual flight, the ACEs receive pilot control inputs and send these signals to the three PFCs. This mode is intended to allow the pilots to maintain level flight while resetting flight control computers after a temporary total loss of power. Once the speed has decreased below VMO/MMO, Normal Law is restored and the autopilot can be re-engaged. This is done via electronically controlled backdrive actuators (controlled by the ACE). ALT2 is entered when both engines flame out, with faults in two inertial or two air-data reference units, with faults to all spoilers, certain aileron faults or with a pedal transducers fault. High Speed and High Angle of Attack Protections enter Alternate Law mode. The PFCs generate control surface commandas which are sent to the ACEs in the same manner as pilot control inputs. Several applications and adaptations of multivariable control theory for aircraft control law developments are described. Roman law and other ancient lund systems generally granted all rights in airspace to the owner of the underlying land. Because the B777 system is controlled electronically, it is also able to provide flight envelope protection. Power of Central Government to exempt certain aircraft. With High Speed Protection active, release of the sidestick will cause the aircraft to return to a wings level (0° bank)attitude. Aircraft handling characteristics are very similar to those encountered while in Secondary mode. 40. In aircraft in which the flight control system is fly-by-wire, the movements the pilot makes to the joystick in the cockpit, to control the flight, are converted to electronic signals, which are transmitted to the flight control computers that d… The horizontal stabilizer is automatically set to 4° up but manual settings (e.g. Depending upon the status of the fly-by-wire system, three sets of control laws are provided, i.e. If the autopilot is engaged, it is automatically disengaged with activation of High Angle of Attack Protection. The ACEs control actuators (from those on pilot controls to control surface controls and the PFC) and the PFC determines the applicable control laws and provide feedback forces, pilot information and warnings. Since these systems can also protect the aircraft from overstress situations, the designers are able to reduce "over-engineering" on various components further reducing weight. Integrated design of flight control surfaces and laws for new aircraft configurations Y. Denieul∗ J. Bordeneuve-Guib´e∗∗ D. Alazard∗∗∗ C. Toussaint∗∗∗∗ G. Taquin† ∗ PhD Student, University of Toulouse, ISAE-SUPAERO, 10, Av. Section 4. α-Floor (automatic application of TOGA thrust) may be activated by the autothrust system if engagement parameters are met. ALT1 control law degradation will result from some faults in the horizontal stabilizer, a single elevator fault, loss of a yaw-damper actuator, loss of slat or flap position sensors or a single air data reference fault. This results in all three state variables being output such that they may be used by the state-feedback control law. Mechanical Back Up is incorporated into the system design to allow limited control of the aircraft while recovering from a temporary total electrical failure. If either Angle of Attack or High Speed Protection are active, full sidestick deflection will result in a maximum bank angle of 45°. Low Energy Protection is replaced by Low Speed Stability meaning that the aircraft no longer has automatic stall protection. Unlike conventional controls, in Normal Law flight mode the sidestick provides a load factor proportional to stick deflection which is independent of aircraft speed. The ACEs automatically revert to Direct mode when they detect the failure of all three PFCs or when they are unable to communicate with the PFCs. Load Alleviation Function (on earlier aircraft) YAW NORMAL LAW - Yaw in normal law uses the rudder for turn coordination and yaw damping. These modes include: Ground mode is active whilst the aircraft is on the ground. See Reconfiguration of FCL Diagram. Pitch Attitude Protection is lost. If not all three state variables can be measured, then an observer needs to be designed. Alternate Law is further subdivided into Alternate Law 1 and Alternate Law 2. The control surface movements depend on which of several modes the flight computer is in. The design philosophy is: "to inform the pilot that the command being given would put the aircraft outside of its normal operating envelope, but the ability to do so is not precluded." In addition to those protections lost in ALT1 (Pitch Attitude and Low Energy Protection), Bank Angle Protection is also lost. In all cases, Load Factor Protection automatically limits the control inputs so that the aircraft remains within AOM "g" limitations and Pitch Attitude Protection limits the aircraft attitude to a maximum of 30° nose up or 15° nose down. Bank Angle Protection limits the maximum bank angle of the aircraft. The protection engages when the angle of attack is between α-Prot and α-Max and limits the angle of attack commanded by the pilot's sidestick to α-Max even with full sidestick deflection. Load factor protection is retained. In the above, the State-Space Block is defined as shown below, where the matrix is the identity matrix. In Direct Law, autopilot function is always lost. Control law design for elastic aircraft based on intelligent variable structure Issue title: Special Section: Recent Advances in Machine Learning and Soft Computing. A reduction of electronic flight control can be caused by the failure of a computational device, such as a flight control c… There are three primary flight control laws - Normal Law, Alternate Law and Direct Law. Boeing also has two other, recently in-service, commercial aircraft, the 787 and the 747-8, which use fly-by-wire controls. The degradation to one or the other of the Alternate Law options is dependent upon the type of failure. First, the three-axis coupled control augmentation structure is specified. Within the normal flight envelope, if the sidestick is released when bank angle is above 33°, the bank angle is automatically reduced to 33°. Has 3 modes according to phase of flight. At one extreme the control ‘law’ could be trivial: simple cables and pulleys connected to the control stick and rudder pedal at one end, to the control surfaces at the other end. Designers build in the ability to by-pass the computers or for the standby systems to operate without the computers. The following discussion is based on the A330 but much of the information also applies to other Airbus types. There are two speed limitations for high altitude aircraft, VMO (Velocity Maximum Operational) and MMO (Mach Maximum Operational). into account, ISP control laws must be as simple as possible to implement them in the airborne computers. This fact gives the possibility of direct measurement of the aircraft’s body (6.19). In Alternate Law 2 (ALT2), Normal Law lateral mode is lost and is replaced by roll Direct Law and yaw Alternate Law. Covers 3-axis control, flight envelope protection, and load alleviation. In Direct Law (DIR), lateral modes are the same as ALT2; that is roll Direct Law and yaw Alternate Law. The autotrim feature is turned off and there is a direct relationship between sidestick deflection and elevator response. The flight mode of Normal Law provides five types of protection: pitch attitude, load factor limitations, high speed, high-AOA and bank angle. There are some differences in the electrical architecture, the number and the naming of the flight control computers between types. In the event of a complete electrical system shutdown, cables from the flight deck controls to the stabiliser and selected roll spoilers allow the pilots to maintain straight and level flight until the electrical system can be restored. Each of the three laws has different sub modes inclusive of ground mode, flight mode and flare mode. 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