Flight Controls PDF

Aircraft systems and Instrumentation  SYLLABUS UNIT 1 AIRPLANE CONTROL SYSTEMS Conventional Systems – Fully powered flight controls – Power actuated systems – Modern control systems – Digita...

Aircraft systems and Instrumentation  SYLLABUS UNIT 1 AIRPLANE CONTROL SYSTEMS Conventional Systems – Fully powered flight controls – Power actuated systems – Modern control systems – Digital fly by wire systems – Auto pilot system active control Technology,  FLIGHT CONTROL SYSTEMS Flying controls are hinged or movable airfoils designed to change the attitude of the aircraft during flight. PURPOSE 1.TO ENABLE THE PILOT TO EXERCISE CONTROL OVER THE AIRCRAFT DURING ALL PORTIONS OF FLIGHT. 2.IT ALLOWS TO MANOEUVRES IN PITCH,ROLL AND YAW. These can be divided in to 3 groups such as: (a) PRIMARY CONTROLS (b) SECONDARY CONTROLS (c) AUXILARY CONTROLS PRIMARY FLIGHT CONTROL SRUFACES Ailerons, Elevators and Rudder are the primary controls. These controls are used to maneuver the aircraft about its 3 axes. 1. ELEVATOR 2. AILERON 3. RUDDER  FLIGHT CONTROL SYSTEMS SECONDARY FLIGHT CONTROL SYSTEMS: Flaps, Spoilers, Slats or Leading edge flaps come under this category. Flaps and slats are the lift augmenting device. Spoiler again grouped as Ground spoiler and Flight spoiler. Ground spoiler extended only after the aircraft lands thereby assisting in braking action. The flight spoiler assists in lateral control by extending whenever aileron on the wing is moved up  FLAPS  SLATS  SPOILERS AUXILLARY FLIGHT CONTROL SYSTEMS: Tabs come under this category. Tabs are the small airfoils attached to the trailing edges of primary control surfaces. Its purpose is to enable the pilot to trim out any unbalanced condition which may exist during flight.  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : STABILATOR: It combines the function of a horizontal stabilizer and an elevator. When the stabilator moves, it varies the amount of force generated by the tail surface and is used to generate and control the pitching motion of the aircraft.  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : RUDDERVATORS: These flying control surfaces serve the function of the rudder and elevators. The surfaces are mounted at an angle above horizontal. When serving as elevators, the surfaces on each side of the tail move in the same direction, either up or down. When serving as rudder, the surfaces move in opposite direction, one up and one down. When combined rudder and elevator control movements are made, a control-mixing mechanism moves each surface the appropriate amount to get the desired elevator and rudder effect.  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : RUDDERVATORS:  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : FLAPERONS: These are the surfaces combine the operation of flaps and ailerons. These types of control surfaces are found on some aircraft designed to operate from short runways. The flaperon allows the area of the wing normally reserved for aileron to be lowered and creates a full span flap. From the lowered position the flaperon can move up or down to provide the desired amount of roll control while still contributing to the overall lift of the wing.  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : FLAPERONS:  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : ELEVONS: Elevons are aircraft control surfaces that combine the functions of the elevator (used for pitch control) and the aileron (used for roll control). It is found on Delta wing aircraft. On this type of aircraft the wings are enlarged and extend to the back of the plane. There is no separate horizontal stabilizer where you would find the elevators on conventional straight-wing aircraft.  FLIGHT CONTROL SYSTEMS COMBINATION FLYING CONTROLS : ELEVONS:  FLIGHT CONTROL SYSTEMS TABS: TABS are small secondary flight control surfaces set into the trailing edges of the primary surfaces. These are used to reduce the work load required of the pilot to hold the aircraft in some constant attitude by “loading” the control surface in a position to maintain the desired attitude. It may also used to aid the pilot in returning a control surface to neutral or trimmed-center position. It controls the balance of an aircraft to maintain straight and level flight without pressure on CONTROL COLUMN or rudder pedal. Movement of the tab in one direction causes a deflection of the c/ surface in the opposite direction  FLIGHT CONTROL SYSTEMS TYPES OF TABS: FIXED TRIM TAB BALANCE TAB ANTI-SERVO TABS SERVO TAB SPRING TABS  FLIGHT CONTROL SYSTEMS TYPES OF TABS: FIXED TRIM TAB: A fixed trim tab is normally a piece of sheet metal attached to the trailing edge of a control surface. This fixed tab is adjusted on the ground by bending it to appropriated direction. Adjustment is only trial and error method and the aircraft must be flown and the trim tab adjusted based on the pilot’s report. Found on light aircraft and are used to adjust rudders and ailerons.  FLIGHT CONTROL SYSTEMS TYPES OF TABS: BALANCE TABS: To decrease the very high control forces the balance tabs are used. In this arrangement, when the control surface is moved, the tab moves in the opposite direction. Thus the aerodynamic force acting on the tab assists to move the main control surface..  FLIGHT CONTROL SYSTEMS TABS:  FLIGHT CONTROL SYSTEMS TYPES OF TABS: ANTI-SERVO TABS:  The tab moves along the same direction as the control surface itself increasing the aerodynamic forces.  The higher the speed the higher the forces become. For example if the pilot pulls back the control column, the control surface moves up, so does the tab. They both create a down force making it more and more difficult to bring a pitch change.  We see these type of tabs in airplanes that uses stabilators instead of tailplane and elevator combination.  FLIGHT CONTROL SYSTEMS TYPES OF TABS: ANTI-SERVO TABS:  FLIGHT CONTROL SYSTEMS TYPES OF TABS: SERVO TABS:  It reduces the stick force. Here, the pilot controls the tab not the control surface.  The movement of the tab makes the control surface move. The tab moves in one direction, while the control surface move in the other direction.  Servo tabs are mostly used as a backup in large airplanes in case the hydraulics fail. As the control surfaces of these airplanes are quite heavy and the forces they generate are also incredibly large, a servo tab is essential to reduce the stick forces.  FLIGHT CONTROL SYSTEMS TYPES OF TABS: SPRING TABS:  A control surface may require excessive force to move only in the final stages of travel.  When this is the case, a spring tab can be used. This is essentially a servo tab that does not activate until an effort is made to move the control surface beyond a certain point.  When reached, a spring in line of the control linkage aids in moving the control surface through the remainder of its travel POWER ASSISTED & POWER OPERATED FLIGHT CONTROL  POWER ASSISTED Movement of the control column will move both the flying control and the pilot valve  POWER OPERATED Movement of the control column only moves the pilot valve.  FLIGHT CONTROL SYSTEMS METHODS: 1. PUSH-PULL CONTROL ROD SYSTEM 2. CABLE AND PULLY SYSTEM FLIGHT CONTROL SYSTEM COMPONENTS OR COMPONENTS OF MECHANICAL LIKAGES FLIGHT CONTROL SYSTEM: 1. CABLES 2. PULLEYS 3. TURNBUCKLES 4. PUSH PULL RODS 5. BELL CRANKS 6. TORQUE TUBES 7. CABLE GUARDS  FLIGHT CONTROL SYSTEMS COMPONENTS OF MECHANICAL LINKAGES 1. PUSH PULL ROD: Many airplanes and almost all helicopter use push pull rods rather than control cables for control system. Made of heat treated aluminum alloy tubing with threaded ends riveted to its ends. End fittings which have a drilled hole are screwed on to these threads and to be sure that the rod ends are screwed far enough in to fitting a safety wire when inserted in to the hole it should not pass through the fittings. A check nut is screwed on to the rod end and when the length of the push pull rod is adjusted the nut to be screwed up tight against the end fitting. Push pull rods are extensively used along with bell cranks to change direction and to gain or decrease the mechanical advantage of control movement.  FLIGHT CONTROL SYSTEMS PUSH PULL ROD:  FLIGHT CONTROL SYSTEMS TORQUE TUBE: Torque tube is a hollow shaft by which the linear motion of cable or push pull rod is changed to rotary motion. A torque arm or horn is attached to the tube by welding or bolting and imparts motion to the tube as the arm is moved back and forth.  FLIGHT CONTROL SYSTEMS BELL CRANK:  A lever with two arms which have a common fulcrum at their junction.  It is used to transmit force and permit a change in direction of force.  Normally a push pull rod is used with bell crank lever.  FLIGHT CONTROL SYSTEMS FAIRLEADS It serves as a guide to prevent wear and vibration of a cable. Made of phenolic material, fiber, plastic or soft aluminum. It is of either split or slotted to install a cable. TURN BUCKLE  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: BLOWN FLAPS KRUEGER FLAP PLAIN FLAP SPLIT FLAP FOWLER FLAP SLOTTED FLAP  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: BLOWN FLAPS: Systems that blow engine air over the upper surface of the flap at certain angles to improve lift characteristics.  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: KRUEGER FLAP :  They are lift enhancement devices that may be fitted to the leading edge of an aircraft wing.  Unlike slats or drooped leading edges, the main wing upper surface and its nose is not changed. Instead, a portion of the lower wing is rotated out in front of the main wing leading edge.  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: PLAIN FLAP: It is attached to the trailing of main plane and rotates on a simple hinge.  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: SPLIT FLAP: It is hinged at the bottom part of the wing near the trailing edge. The lower surface operates like a plain flap, but the upper surface stays immobile or moves only slightly.  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: FOWLER FLAP: It slides backwards on tracks before hinging downwards, thereby increasing both camber and chord, creating a larger wing surface better tuned for lower speeds. It also provides some slot effect. The Fowler flap was invented by Harlan D. Fowler.  FLIGHT CONTROL SYSTEMS TYPES OF FLAPS: SLOTTED FLAP: A slot (or gap) between the flap and the wing enables high pressure air from below the wing to re-energize the boundary layer over the flap. This helps the airflow to stay attached to the flap, delaying the stall. ENGINE CONTROL SYSTEMS  To allow the engine to perform at maximum efficiency for a given condition Aids the pilot to control and monitor the operation of the aircraft's power plant Originally, engine control systems consisted of simple mechanical linkages controlled by the pilot then evolved and became the responsibility of the third pilot-certified crew member, the flight engineer.  By moving throttle levers directly connected to the engine, the pilot or the flight engineer could control fuel flow, power output, and many other engine parameters. Following mechanical means of engine control came the introduction of analog electronic engine control. Analog electronic control varies an electrical signal to communicate the desired engine settings  It had its drawbacks including common electronic noise interference and reliability issues Full authority analogue control was used in the 1960s. It was introduced as a component of the Rolls Royce Olympus 593 engine of the supersonic transport aircraft Concorde. However the more critical inlet control was digital on the production aircraft.  In the 1970s NASA and Pratt and Whitney experimented with the first experimental FADEC, first flown on an F-111 fitted with a highly modified Pratt & Whitney TF30 left engine  Pratt & Whitney F100 – First Military Engine Pratt & Whitney PW2000 - First Civil Engine fitted with FADEC Pratt & Whitney PW4000 - First commercial "dual FADEC" engine. The Harrier II Pegasus engine by Dowty & Smiths Industries Controls - The first FADEC in service  FUNCTIONS FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many other parameters The inputs are received by the EEC and analyzed up to 70 times per second Engine operating parameters such as fuel flow, stator vane position, bleed valve position, and others are computed from this data and applied as appropriate  It controls engine starting and restarting. Its basic purpose is to provide optimum engine efficiency for a given flight condition. It also allows the manufacturer to program engine limitations and receive engine health and maintenance reports. For example, to avoid exceeding a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.  The flight crew first enters flight data such as wind conditions, runway length, or cruise altitude, into the flight management system (FMS). The FMS uses this data to calculate power settings for different phases of the flight. At takeoff, the flight crew advances the throttle to a predetermined setting, or opts for an auto-throttle takeoff if available. The FADECs now apply the calculated takeoff thrust setting by sending an electronic signal to the engines  There is no direct linkage to open fuel flow. This procedure can be repeated for any other phase of flight In flight, small changes in operation are constantly made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but limitations can’t be exceeded The flight crew has no means of manually overriding the FADEC  The full authority digital engine controls have no form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer If a total FADEC failure occurs, the engine fails If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an EEC or ECU. An EEC, though a component of a FADEC, is not by itself FADEC. When standing alone, the EEC makes all of the decisions until the pilot wishes to intervene.  SAFETY With the operation of the engines so heavily relying on automation, safety is a great concern. Redundancy is provided in the form of two or more, separate identical digital channels. Each channel may provide all engine functions without restriction. FADEC also monitors a variety of analog, digital and discrete data coming from the engine subsystems and related aircraft systems, providing for fault tolerant engine control  APPLICATIONS FADECs are employed by almost all current generation jet engines, and increasingly in piston engines for fixed- wing aircraft and helicopters. The system replaces both magnetos in piston-engined aircraft, which makes costly magneto maintenance obsolete and eliminates carburetor heat, mixture controls. Since, it controls each engine cylinder independently for optimum fuel injection and spark timing, the pilot no longer needs to monitor fuel mixture.  More precise mixtures create less engine wear, which reduces operating costs and increases engine life for the average aircraft. Tests have also shown significant fuel savings  ADVANTAGES Better fuel efficiency Automatic engine protection against out-of-tolerance operations Safer as the multiple channel FADEC computer provides redundancy in case of failure Care-free engine handling, with guaranteed thrust settings Ability to use single engine type for wide thrust requirements by just reprogramming the FADECs Provides semi-automatic engine starting Better systems integration with engine and aircraft systems  Can provide engine long-term health monitoring and diagnostics Reduces the number of parameters to be monitored by flight crews Can support automatic aircraft and engine emergency responses (e.g. in case of aircraft stall, engines increase thrust automatically).  DISADVANTAGES No form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. In the event of a total FADEC failure, pilots have no way of manually controlling the engines for a restart, or to otherwise control the engine. High system development and validation effort due to the complexity  FLY BY WIRE CONTROL SYSTEMS IT IS ONE IN WHICH WIRE CARRYING ELECTRICAL SIGNALS FROM THE FLIGHT CONTROLS BY REPLACING MECHANICAL LINKAGES. TYPES OR THE WAYS OF USING FBW: ANALOG FBW DIGITAL FBW  FLY BY WIRE CONTROL SYSTEMS ANALOG FBW: In analog fly by wire system operation, movements of the control column and rudder pedals, and the forces exerted by the pilot, are measured by electrical transducers, and the signals produced are then amplified and relayed to operate the hydraulic actuator units which are directly connected to the flight controls surfaces. The fly by wire control employed in the Boeing 767 (spoiler) as illustrated in the figure is appended in the next slide: The main components involved in this system are as follows: 1. POSITION TRANSDUCER (RVDT) 2. SIGNAL CONTROL MODULE 3. LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT) 4. POWERED FLYING CONTROL UNIT (PFSCU) FLY BY WIRE CONTROL SYSTEMS  FLY BY WIRE CONTROL SYSTEMS DIGITAL FBW: A digital FBW system is similar to its analogue counterpart. However the signaling processing is done by digital computers. The pilot can literally say “fly-via-computer”. This increases flexibility as the digital computers can receive input from any aircraft sensor. It also increases stability, because the system is less dependent on the values of critical electrical components as in analogue controller.  FLY BY WIRE CONTROL SYSTEMS DIFFERENCE BETWEEN ANALOG AND DIGITAL FBW SL. ANALOGUE FBW DIGITAL FBW NO. 01 The FBW eliminates the This increases flexibility as the digital complexity, fragility and weight computers can receive input from any of the mechanical circuit of the aircraft sensor. It also increases electronic hydromechanical flight control stability, because the system is less systems and replaces it with an dependent on the values of critical electrical electrical circuit. components in an analog controller. 02 The hydraulic circuits are similar The computers "read" position and force except that mechanical servo inputs from the pilot's controls and aircraft valves are replaced with sensors. They solve differential equations electrically-controlled servo to determine the appropriate command valves, operated by the signals that move the flight controls in electronic controller. This is the order to carry out the intentions of the pilot. simplest and earliest configuration of an analog fly-by- wire flight control system,  FLY BY WIRE CONTROL SYSTEMS DIFFERENCE BETWEEN ANALOG AND DIGITAL FBW SL. ANALOGUE FBW DIGITAL FBW NO. 03 In this configuration, the flight The programming of the digital computers control systems must simulate "feel". enable flight envelope protection. In this The electronic controller controls aircraft designers precisely tailor an electrical feel devices that provide aircraft's handling characteristics, to stay the appropriate "feel" forces on the within the overall limits of what is possible manual controls. given the aerodynamics and structure of the aircraft. Software can also be used to filter control inputs to avoid pilot-induced oscillation. 04 In more sophisticated versions, Side-sticks, center sticks, or conventional analog computers replaced the control yokes can be used to fly such an electronic controller. Analog aircraft. While the side-stick offers the computers also allowed some advantages of being lighter, mechanically customization of flight control simpler, and unobtrusive, characteristics, including relaxed stability.  FLY BY WIRE CONTROL SYSTEMS DIFFERENCE BETWEEN ANALOG AND DIGITAL FBW SL. ANALOGUE FBW DIGITAL FBW NO. ----------------------- 05 As the computers continuously "fly" the aircraft, pilot workload can be reduced. It is now possible to fly aircraft that have relaxed stability. The primary benefit for military aircraft is more manoeuvrable flight performance and so-called "carefree handling" Digital flight control systems enable -------------------------- 06 Improves combat survivability because it avoids hydraulic failure. With a fly-by-wire system, wires can be more flexibly routed, are easier to protect and less susceptible to damage than hydraulic lines. 07 Digital fly-by-wire systems is reliability, even more so than for analog systems.  FLY BY WIRE CONTROL SYSTEMS ADVANTAGES: 1. WEIGHT SAVING 2. REDUCED MAINTENANCE TIMES 3. LESS SPACE 4. IMPROVED HANDLING 5. Fuel saving: 6. Automatic maneuver envelope protection 7. Gust load alleviation (lessening) ADVANTAGES OF FBW: 1. WEIGHT SAVING 2. REDUCED MAINTENANCE TIMES 3. LESS SPACE 4. IMPROVED HANDLING AUTOPILOT SYSTEM ACTIVE CONTROL TECHNOLOGY: AUTOPILOT IS A SYSTEM OF AUTOMATIC CONTROLS WHICH HOLDS THE ARICRAFT ON ANY SELECTED MAGNETIC HEADING AND RETURNS THE ARICRAFT TO THAT HEADING WHEN IT IS DISPLACED FROM IT. PURPOSE: TO REDUCE THE WROK STRAIN AND FATIQUE OF CONTROLLING THE AIRCRAFT IN FLIGHT BY THE PILOT. COMPONENTS: 1. GYROS (TO SENSE WHAT AIRPLANE IS DOING) 2. SERVOS (TO MOVE CONTROL SURFACES) 3. AMPLIFIER (TO INCREASE THE STRENGTH OF GYRO SIGNALS TO OPERATE SERVOS) THREE CHANNELS. 1. RUDDER CHANNELS 2. AILERON CHANNES. 3. ELEVATOR CHANNELS