Unit 7,8GYROSCOPE:Gyroscopic PrinciplesIn aircraft instruments gyros are used in attitude, compass and turn coordinators. These instruments contain a wheel or rotor rotating at a high RPM which gives it two important properties: rigidity and precession. The rotor or gyro can be electrically, vacuum or pressure driven.Construction wise the gyro is fixed in the instrument by rings or gimbals and these give the gyro certain motions of freedom. It is these motions or movement in a plane which allow for the characteristics used in these instruments.VFR flying pilots will normally only fly on these instrument when getting out of IMC situations. Keep in mind that to be proficient in flying on instruments you will need regular training with a safety pilot, aka flying under the hood.Without being current on instruments, most if not all VFR pilots, will crash when attempting to do this.Rigidity & PrecessionThese two properties are unique to a rotating mass. Below an explanation of how they work and their application in aircraft instruments.RigidityWhilst small, the rotor of a gyroscopic instrument rotates at a very high RPM. Giving them inertia, also called rigidity and they maintain this alignment to a fixed point in space. This basically happens to every rotating object: wheel, propeller etc.. For example: this rigidity gives the moving bicycle its stability preventing it from falling over.A number of factors have their influence on rigidity: the mass of the rotor, its RPM or angular velocity and finally the distance of the mass to the axis of rotation. The larger the distance the greater the rigidity with equal rotational speed.PrecessionWhen you apply a force to a point around the spinning rim of the gyro, the rotor will tilt as if the force was 90 further in the direction of motion as shown in the image. This displacement of the force is called precession.The amount of precession depends on the following factors: strength and direction of the force applied, the amount of inertia of the gyro (mass concentration on the rim) and the RPM or rotational velocity of the gyro.To conclude: the rate of precession in a free gyro is directly proportional to strength of the force and inversely proportional to the RPM and the moment of inertia. Thus the more mass and RPM a gyro has the more stable it is and maintain its position to a fixed point in space.Gimbal ringsThe gyro rotor is held in place by rings or better known as gimbal rings. These allow for freedom of motion three dimensional planes as required by the instruments of the aircraft. Not all instruments will need all the planes of movement at the same time, this depends on their function, see the next pages.Planes of movementThere are three possible motions for a gyroscope: the plane of rotation of the gyro; the plane of applied force and as a result: the plane of precession. Refer to the image above.Turn IndicatorsThere are two types of turn indicators in aircraft. These are: the Turn and Bank Indicator (T/B) and the Turn Coordinator (T/C). Both are gyro driven and indicate the rate of turn but the turn coordinator can also indicate rate of roll. The T/B has a needle indicator where the T/C has an aircraft picture on the face of the instrument.Neither of these instrument give an direct indication of bank angle. For that you will need the speed of the aircraft and rate of turn to calculate the bank angle, or have an attitude indicator.Also note that these indicators are part of the basic six instruments in an aircraft the pilot needs for legal instrument flying. Nowadays you see more and more EFIS panels where the original T/C and T/B are used as standby and backup in case of failure.Rate GyroTurn indicators use a rate gyro (see image) to detect how fast the aircraft is changing direction. The T/B has a vertical needle and a slip ball; note that the Turn Coodinator has an aircraft picture. Both indicate a two minute turn, thus a 360 turn is completed in two minutes or put differently: three degrees/second (3/s, not that famous group) which is a rate one turn.The coordination ball indicates the direction of the g-forces and its the pilots job to keep the ball centered by 'stepping on the ball' with the rudder. Thus: ball to the right -> apply right rudder or trim (and less left rudder) and vice versa.

Rate gyro operationThis gyro has only one plane of freedom where it can move (not the plane of rotation). The tilting of the vertical axis though the aircraft causes precession and this is used to indicate the rate of turn about that axis. The amount of tilt (linear with the rate of turn) is balanced against a restraining spring.T/B or T/CIn a T/B the gyro is mounted in such a way that the rotation (or turn) axis is from wingtip to wingtip. In the T/C the turn axis gimbal is mounted on a 30 angle upward from the longitudinal axis of the aircraft, and this gives it the ability to sense rate of roll.SpringsThe springs used in the rate gyro give proper indication of rate of turn by being able to adjust the spring tension against the precession force of the gyro, without the springs the gyro would just bounce around. This is then indicated on the face place.DampingDue to air turbulence and aircraft movement by the pilot there will always be a force on the gyro causing precession and thus needle movement. To stabilize the indication the gyro has internal damping devices limiting these movements and presenting a stable indication.Mechanical stopsThe gimbal ring reaches a mechanical stop when the aircraft turns about 20/second. And with only one gimbal ring the gyro will not topple as with the attitude and heading gyro's.Instrument ErrorsThese are the result of mechanical design and limits due to contruction. Indication due to turbulence is not really an error by instrument design but it will cause erratic movement only.IndicationWhen the gyro rotor speed is not within limits the indication will suffer and be much slower. When the rotor speed is too high it will result in an excessive rate of turn as the precession forces will be greater than the preset tension of the calibrated springs. The instrument will look very much alive in this situationYawAnother error occurs when the aircraft subjected to a yaw movement together with positive g-forces, the indicator will then overread. Most noticeable when pulling out of a dive with the aircraft out of balance or with an unbalanced steep turn.

Hydraulic systems:Hydraulic systems in aircraft provide a means for the operation of aircraft components. The operation of landing gear, flaps, flight control surfaces, and brakes is largely accomplished with hydraulic power systems. Hydraulic system complexity varies from small aircraft that require fluid only for manual operation of the wheel brakes to large transport aircraft where the systems are large and complex. To achieve the necessary redundancy and reliability, the system may consist of several subsystems. Each subsystem has a power generating device (pump) reservoir, accumulator, heat exchanger, filtering system, etc. System operating pressure may vary from a couple hundred pounds per square inch (psi) in small aircraft and rotorcraft to 5,000 psi in large transports

Things important in selecting a fluid

ViscosityChemical stabiiltiyFlash pointFire point

The three principal categories of hydraulic fluids are:1. Minerals2. Polyalphaolefins3. Phosphate esters

Basic hydraulic system

Regardless of its function and design, every hydraulic system has a minimum number of basic components in addition to a means through which the fluid is transmitted. A basic system consists of a pump, reservoir, directional valve, check valve, pressure relieve valve, selector valve, actuator, and filter

Open Center Hydraulic SystemsAn open center system is one having fluid flow, but no pressure in the system when the actuating mechanisms are idle. The pump circulates the fluid from the reservoir, through the selector valves, and back to the reservoir. The open center system may employ any number of subsystems, with a selector valve for each subsystem. Unlike the closed center system, the selector valves of the open center system are always connected in series with each other. In this arrangement, the system pressure line goes through each selector valve. Fluid is always allowed free passage through each selector valve and back to the reservoir until one of the selector valves is positioned to operate a mechanism. When one of the selector valves is positioned to operate an actuating device, fluid is directed from the pump through oneof the working lines to the actuator. With the selector valve in this position, the flow of fluid through the valve to the reservoir is blocked. The pressure builds up in the system to overcome the resistance and moves the piston of the actuating cylinder; fluid from the opposite end of the actuator returns to the selector valve and flows back to the reservoir. Operation of the system following actuation of thecomponent depends on the type of selector valve being used. Several types of selector valves are used in conjunction with the open center system. One type is both manually engaged and manually disengaged. First, the valve is manually moved to an operating position. Then, the actuating mechanism reaches the end of its operating cycle, and the pump output continues until the system relief valve relieves the pressure. The relief valve unseats and allows the fluid to flow back to the reservoir. The system pressure remains at the relief valve set pressure until the selector valve is manually returned to the neutral position. This action reopens the open center flow and allows the system pressure to drop to line resistance pressure.

Closed-Center Hydraulic SystemsIn the closed-center system, the fluid is under pressure the power pump is operating. The three actuators are arranged in parallel and actuating units B and C are operatingat the same time, while actuating unit A is not operating. This system differs from the open-center system in that the selector or directional control valves are arranged in parallel and not in series. The means of controlling pump pressure varies in the closed-center system. If a constant delivery pump is used, the system pressure is regulated by a pressure regulator. A relief valve acts as a backup safety device in case the regulator fails. If a variable displacement pump is used, system pressure is controlled by the pumps integral pressure mechanism compensator. The compensator automatically varies the volume output. When pressure approaches normal system pressure, the compensator begins to reduce the flow output of the pump. The pump is fully compensated (near zero flow) when normal system pressure is attained. When the pump is in this fully compensated condition, its internal bypass mechanism provides fluid circulation through the pump for cooling and lubrication. A relief valve is installed in the system as a safety backup. An advantage of the open-center system over the closed-center system is that the continuous pressurization of the system is eliminated. Since the pressure is built up gradually after the selector valve is moved to an operating position, there is very little shock from pressure surges. This action provides a smoother operation of the actuating mechanisms. The operation is slower than the closed-center system, in which the pressure is available the moment the selector valve is positioned. Since most aircraft applications require instantaneous operation, closed-center systems are the most widely used

Hydraulic System ComponentsAs with all systems working with fluids they, at least, will have a reservoir, pump and filter and some valves / actuators and a pressure gauge to monitor the working pressure. We will describe these parts and their function below.ReservoirThis must contain enough fluid so that all actuators can operate at the same time. There must be some amount of reserve in case of a leak so that the system can operate for a period of time.The reservoir functions as an expansion chamber (when the fluids heats up) and traps air bubbles should they enter the system somewhere. It can be pressurized for aircraft flying at high altitudes. Returning fluid must enter the reservoir without causing foaming and bubbles.PumpThe main pump is driven by the engine or by an electric motor. Pressure is held in a accumulator. With hydraulic landing gear aircraft you will find a hand operated backup pump in case the gear fails to extend by the main pump. This will require a large number of manual pumps from the pilot at a time where stress is higher than normal.These pumps are available in different types depending on the volume and pressure requirements: vane, spur gear and the fixed angle piston type.Vane and spur gearThis is a constant displacement low pressure/high volume pump (vane) or medium volume/pressure (gear) pumps. Both require a pressure relief to prevent damage to the system due to increased RPM of the pump.Fixed angleSome are constant displacement types but others are a variable displacement/constant pressure pumps and the latter obviously will not need a pressure regulator. They are capable of very high pressures up to 3000 - 3500 psi but with low volumes.Pressure regulatorTo prevent damage we need to keep the pressure within the design limits of the system. Normally if a pump moves fluid and there is no restriction, there will be no pressure. The fluid just moves around. But when there is a restriction (such as in a closed circuit) the pressure will build up until the regulator kicks in.AccumulatorA two part pressure vessel in which the sections are divided by a bladder. One parts contains a gas (air or nitrogen) and the other half contains the working fluid. The gas is pressurized to half the working pressure of the system.Constructed this way the gas will act as a damping device and levels out pressure fluctuations and it also serves as backup pressure should the pump fail.ValvesThere are three types of valves used: check, pressure relief and selector. The check valve is a non-return type, basically a hydraulic form of the electronic diode. The pressure relief valve limits the amount of pressure if it exceeds a preset level. And the selector valve is operated by the pilot to initiate the movement of an actuator.Actuators and filtersActuators are the main moving parts, they convert pressure into a mechanical movement to do useful work. They come in different sizes and shapes, this depends largely on the object it needs to move.Filters keep the operating fluid clean from contamination as microscopic particles can ruin valves, pumps resulting in a leak and possibly worse. Some filters have a bypass should the filter material become clogged.

Sources of Pneumatic Power:

1. Engine bleed air2. Auxiliary Power Unit (APU)3. Ground source1.It is tapped from the appropriate stage of a high pressure compressor. A pre-cooler system controls the engine bleed air temperature.2. The APU supplies bleed air to the pneumatic manifold3. pneumatic manifold system gets bleed air from ground source too.

High pressure systemsAn engine driven compressor feeds air via an unloading valve tot the system keeping the pressure around 3000 psi, but this may vary from aircraft manufacturer to another. There will usually also be a ground valve on the aircraft to enable the system to be pressurized when the main engines are not running.You will also find a moisture separator, dryer (desiccant) and filter to keep the air clean and free from water before it is stored in the high pressure bottles.Pressurized air at 3000 psi is reduced before it is routed to valves and actuators, this reduced pressure is monitored by gauges. Actuators can be a single acting device where air moves them one way and a strong spring inside pushes the piston actuator back, or can they be double acting. These are sometimes used with flap extension systems.

Low pressure system:

These are pressurized up to about 1000 psi and use an engine driven vane type pump and they are used to drive the aircon, door seals, de-icer boots, mainly small low power applications.Pneumatic system components:1. Air filter2. Check valve3. Desiccant / Chemical Dryer4. Moisture Separator5. Bleed air isolation valve6. Pressure reducing valve7. Relief valve8. Shuttle valve Air filter:Used in system lines to remove any foreign matter. It have micronic type paper element, which must be replace periodically. Check valveUsing flap type, which are one directional flow control valves Desiccant/ Chemical DryerPurpose is to absorb the moisture. It contains replaceable cartridge (blue color). Change in color says the cartridge is contaminated with moisture and need to replace Bleed air isolation valveIt separates the pneumatic manifold into right and left sides, also it connects the right and left sides of pneumatic manifold for cross bleed operation Pressure reducing valveIt reduces the air pressure in cylinder to a workable pressure required for operation of certain components Relief ValveIt protects the system from over pressurization and acts as a pressure limiting unit. At normal pressure, the valve remain closed, but under high pressure it opens and vent excess air

Shuttle ValveIt allows the pneumatic system to operate from the ground source. When pressure from external source is higher then isolates the compressor. It also used for emergency backup for landing gears.

Aircraft instruments:1. Classified according to function in following categories: Flight and navigation instruments provide information on flight speed, altitude, a/c condition, heading, R/C or descent etc. Power plant instruments provide information on operation of engine, its rpm, EGT, pressure ratio, etc. System instruments provide specific information relevant to various a/c systems 2 Classified according to the principles used in giving the desired information: Pressure type instruments Gyro instruments Mechanical type instruments Direct indicating instruments Electronic instruments Pressure type instruments P can be measured by applying the fluid force to a moveable bellow / by converting the P energy into an electrical signal (P transducer) Different ways to measure P are:1. Absolute P2. Gauge P3. Differential Pressure Absolute P The measurement of P relative to the total vacuum (P = 0). It is used on the a/c in comparison to other P through a device called aneroid capsule. It measure the difference in P b/w the vacuum inside the sealed chamber and the ambient P around it. The difference in these two values gives the absolute P. Gauge P it is the difference b/w the atmospheric P and the P being measured. The absolute P is applied on one side of the bellow and atmospheric P on the other side of the bellow, the resulting force is indicated by the gauge P. Differential P it is the comparison b/w two different P. Most commonly used differential P gauge is the air speed indicator. It measures the difference b/w ram air or pitot P and the static / ambient P. most useful type differential P instrument is the differential bellow type, have 2 bellows, each filled with the associated P to be measured. Pitot - static system This a/c system measures the total P by the forward motion of the a/c and the static P surrounding the atmosphere. These P are used to calculate flight parameters such as airspeed and altitude. The system connected to the 3 primary flight instruments 1. airspeed indicator, 2. altimeter and 3. vertical speed indicator.Altimeter all the altimeters have P sensing elements made up of 3 aneroid capsules staked together to increase the sensitivity of the instrument. The altimeter measures the Pressure altitude.

Air speed indicator it measures the difference in pitot P and static P. The P sensing element is the metallic capsule. The speed indicated on the airspeed indicator is referred to as the indicated airspeed (IAS). The error in airspeed indication caused by the change in P is referred as position error. Indicated speed corrected for position error is called the calibrated airspeed (CAS). True airspeed (TAS) is derived from the calibrated airspeed when it is corrected for non-standard P and T. TAS is not used for controlling the a/c during the taxiing, T/O, climb, descent, approach or landing; for these purpose the IAS is used Vertical speed indicator- it is also known as the R/C indicator designed to indicate the rate of altitude change from the change of static P alone. It is a type of differential P gauge. It measures only change in P. When the a/c flies at constant altitude, the air P doesnt change. As the a/c climbs air becomes less dense and the P changes, so the indicating needle deflection shows R/C.

AIRCRAFT NAVIGATION SYSTEMS INCLUDE VHF OMNIDIRECTIONAL RANGE (VOR) INSTRUMENT LANDING SYSTEM (ILS) DISTANCE MEASURING EQUIPMENT (DME) AUTOMATIC DIRECTION FINDERS (ADF) DOPPLER NAVIGATION SYSTEM INERTIAL NAVIGATION SYSTEM VHF Omni Directional Radio Range (VOR) is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine their position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons.Distance measuring equipment (DME) is a transponder-based radio navigation technology that measures slant range distance by timing the propagation delay of VHF or UHF radio signals.

A course deviation indicator (CDI) is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a course. If the location of the aircraft is to the left of course, the needle deflects to the right, and vice versa.

A radio direction finder (RDF) is a device for finding the direction, or bearing, to a radio source. The act of measuring the direction is known as radio direction finding or sometimes simply direction finding (DF). Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately, using two or more measurements of known transmitters, the location of a vehicle can be determined. RDF is widely used as a radio navigation system, especially with boats and aircraft.An automatic direction finder (ADF) is a marine or aircraft radio-navigation instrument that automatically and continuously displays the relative bearing from the ship or aircraft to a suitable radio station.[10][11] ADF receivers are normally tuned to aviation or marine NDBs operating in the LW band between 190 535kHz. Like RDF units, most ADF receivers can also receive medium wave (AM) broadcast stations, though as mentioned, these are less reliable for navigational purposes

An instrument landing system (ILS) is a ground-based instrument approach system that provides precision lateral and vertical guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow.

An inertial navigation system (INS) is a navigation aid that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate via dead reckoning the position, orientation, and velocity (direction and speed of movement) of a moving object without the need for external references Aircraft fuel systems:Aircraft fuel systems are highly used to supply proper amount of fuel to the engine to have a proper combustion .To prevent progress of fire from any part of the airplane through fuel pipes to the fuel tank due to some fire accident.An aircraft fuel system allows the crew to pump, manage, and deliver fuel to the propulsion system and Auxilary Power Unit (APU) of an aircraft.To prevent engine from fuel starvation.Each fuel system for a multiengine airplane must be arranged so that, in at least one system configuration, the failure of any one component (other than a fuel tank) does not result in the loss of power of more than one engine or require immediate action by the pilot to prevent the loss of power of more than one engine.

Small Single-Engine Aircraft Fuel SystemsSmall single-engine aircraft fuel systems vary depending on factors, such as tank location and method of metering fuel to the engine. A high-wing aircraft fuel system can bedesigned differently from one on a low-wing aircraft. An aircraft engine with a carburetor has a different fuel system than one with fuel injection.

Gravity Feed SystemsHigh-wing aircraft with a fuel tank in each wing are common. With the tanks above the engine, gravity is used to deliver the fuel. A simple gravity feed fuel system is shown inFigure 14-13. The space above the liquid fuel is vented to maintain atmospheric pressure on the fuel as the tank empties. The two tanks are also vented to each other to ensure equal pressure when both tanks feed the engine. A single screened outlet on each tank feeds lines that connect to either a fuel shutoff valve or multiposition selector valve. The shutoff valve has two positions: fuel ON and fuel OFF. If installedthe selector valve provides four options: fuel shutoff to the engine; fuel feed from the right wing tank only; fuel feed from the left fuel tank only; fuel feed to the engine from bothtanks simultaneously. Downstream of the shutoff valve or selector valve, the fuel passes through a main system strainer. This often has a drain function to remove sediment and water. From there, it flows to the carburetor or to the primer pump for engine starting. Having no fuel pump, the gravity feed system is the simplest aircraft fuel system.

Pump Feed Systems

Low- and mid-wing single reciprocating engine aircraft cannot utilize gravity-feed fuel systems because the fuel tanks are not located above the engine. Instead, one or more pumps are used to move the fuel from the tanks to the engine. A common fuel system of this type is shown in Figure 14-14. Each tank has a line from the screened outlet to a selectorvalve. However, fuel cannot be drawn from both tanks simultaneously; if the fuel is depleted in one tank, the pump would draw air from that tank instead of fuel from the fulltank. Since fuel is not drawn from both tanks at the same time, there is no need to connect the tank vent spaces together. From the selector valve (LEFT, RIGHT, or OFF), fuelflows through the main strainer where it can supply the engine primer. Then, it flows downstream to the fuel pumps. Typically, one electric and one engine-driven fuel pump arearranged in parallel. They draw the fuel from the tank(s) and deliver it to the carburetor. The two pumps provide redundancy. The engine-driven fuel pump acts as the primary pump. The electric pump can supply fuel should the other fail. The electric pump also supplies fuel pressure while starting and is used to prevent vapor lock during flight at high altitude

propeller

Flight control systemsprimary control surfaces:Generally, the primary cockpit flight controls are arranged as follow acontrol yoke(also known as a control column),centre stickorside-stick(the latter two also colloquially known as a control orjoystick), governs the aircraft'srollandpitchby moving theailerons(or activatingwing warpingon some very early aircraft designs) when turned or deflected left and right, and moves theelevatorswhen moved backwards or forwards rudder pedals, or the earlier, pre-1919 "rudder bar", to controlyaw, which move therudder; left foot forward will move the rudder left for instance. throttle controls to control engine speed orthrustfor powered aircraft.The control yokes also vary greatly amongst aircraft. There are yokes where roll is controlled by rotating the yoke clockwise/counterclockwise (like steering a car) and pitch is controlled by tilting the control column towards you or away from you, but in others the pitch is controlled by sliding the yoke into and out of the instrument panel (like most Cessnas, such as the 152 and 172), and in some the roll is controlled by sliding the whole yoke to the left and right (like the Cessna 162). Centre sticks also vary between aircraft. Some are directly connected to the control surfaces using cables,others (fly-by-wire airplanes) have a computer in between which then controls the electrical actuators.secondary control surfaces:In addition to the primary flight controls for roll, pitch, and yaw, there are often secondary controls available to give the pilot finer control over flight or to ease the workload. The most commonly available control is a wheel or other device to controlelevator trim, so that the pilot does not have to maintain constant backward or forward pressure to hold a specific pitchattitude ,(other types of trim, forrudderandailerons, are common on larger aircraft but may also appear on smaller ones). Many aircraft havewing flaps, controlled by a switch or a mechanical lever or in some cases are fully automatic by computer control, which alter the shape of the wing for improved control at the slower speeds used for takeoff and landing. Other secondary flight control systems may be available, includingslats,spoilers,air brakesandvariable-sweep wings.

Fly By Wire

Fly-By-Wire In the 70s the fly-by-wire architecture was developed, starting as an analogue technique and later on, in most cases, transformed into digital. It was first developed for military aviation, where it is now a common solution; the supersonic Concorde can be considered a first and isolated civil aircraft equipped with a (analogue) fly-by-wire system, but in the 80s the digital technique was imported from military into civil aviation by Airbus, first with the A320, then followed by A319, A321, A330, A340, Boeing 777 and A380 (scheduled for 2005). This architecture is based on computer signal processing and is schematically shown in fig. 6.5: the pilots demand is first of all transduced into electrical signal in the cabin and sent to a group of independent computers (Airbus architecture substitute the cabin control column with a side stick); the computers sample also data concerning the flight conditions and servo-valves and actuators positions; the pilots demand is then processed and sent to the actuator, properly tailored to the actual flight status. The flight data used by the system mainly depend on the aircraft category; in general the following data are sampled and processed

angle of attack and sideslip; airspeed/mach number, pressure altitude and radio altimeter indications; stick and pedal demands; other cabin commands such as landing gear condition, thrust lever position, etc.

The full system has high redundancy to restore the level of reliability of a mechanical or hydraulic system, in the form of multiple (triplex or quadruplex) parallel and independent lanes to generate and transmit the signals, and independent computers that process them; in many cases both hardware and software are different, to make the generation of a common error extremely remote, increase fault tolerance and isolation; in some cases the multiplexing of the digital computing and signal transmission is supported with an analogue or mechanical back-up system, to achieve adequate system reliability.

For civil fly-by-wire aircraft in normal operation the flight control changes according to the flight mode: ground, take-off, flight and flare. Transition between modes is smooth and the pilot is not affected in its ability to control the aircraft: in ground mode the pilot has control on the nose wheel steering as a function of speed, after lift-off the envelope protection is gradually introduced and in flight mode the aircraft is fully protected by exceeding the maximum negative and positive load factors (with and without high lift devices extracted), angle of attack, stall, airspeed/Mach number, pitch attitude, roll rate, bank angle etc; finally, when the aircraft approaches to ground the control is gradually switched to flare mode, where automatic trim is deactivated and modified flight laws are used for pitch control.

Autopilot

Autopilot is an automatic flight control system that keeps an aircraft in level flight or on a set course. It can be directed by the pilot, or it may be coupled to a radio navigation signal. Autopilot reduces the physical and mental demands on a pilot and increases safety. The common features available on an autopilot are altitude and heading hold. The simplest systems use gyroscopic attitude indicators and magnetic compasses to control servos connected to the flight control system. [Figure 5-24] The number and location of these servos depends on the complexity of the system. For example, a single-axis autopilot controls the aircraft about the longitudinal axis and a servo actuates the ailerons. A threeaxis autopilot controls the aircraft about the longitudinal, lateral, and vertical axes. Three different servos actuate ailerons, elevator, and rudder. More advanced systems often include a vertical speed and/or indicated airspeed hold mode. Advanced autopilot systems are coupled to navigational aids through a flight director.

The autopilot system also incorporates a disconnect safety feature to disengage the system automatically or manually. These autopilots work with inertial navigation systems, global positioning systems (GPS), and flight computers to control the aircraft. In fly-by-wire systems, the autopilot is an integrated component. Additionally, autopilots can be manually overriddenFly by light

A type of flight-control system where input command signals are sent to the actuators through the medium of optical-fiber lines. The feedback from the control surfaces and other systems is routed in a similar way. The inputs from the control column, aircraft control surfaces, and other data, such as static and dynamic pressure and angle of attack, are fed into a computer connected to fiber-optic lines. The computer then provides data for movement of the aircraft control surfaces through these cables.

Air cycle and vapour cycle systems:

Oxygen systems:

Unit 6 (half)Basic Propeller Principles The airplane propeller consists of two or more blades and a central hub to which the blades are attached. Each blade of an airplane propeller is essentially a rotating wing. As a result of their construction, the propeller blades are like airfoils and produce forces that create the thrust to pull, or push, the airplane through the air. The power needed to rotate the propeller blades is furnished by the engine. The engine rotates the airfoils of the blades through the air at high speeds, and the propeller transforms the rotary power of the engine into forward thrust. An airplane moving through the air creates a drag force opposing its forward motion. Consequently, if an airplane is to fly, there must be a force applied to it that is equal to the drag, but acting forward. This force, as we know, is called "thrust." A cross section of a typical propeller blade is shown in Fig 17-38. This section or blade element is an airfoil comparable to a cross section of an airplane wing. One surface of the blade is cambered or curved, similar to the upper surface of an airplane wing, while the other surface is flat like the bottom surface of a wing. The chord line is an imaginary line drawn through the blade from its leading edge to its trailing edge. As in a wing, the leading edge is the thick edge of the blade that meets the air as the propeller rotates.

Blade angle, usually measured in degrees, is the angle between the chord of the blade and the plane of rotation (Fig. 17-39) and is measured at a specific point along the length of the blade. Because most propellers have a flat blade "face," the chord line is often drawn along the face of the propeller blade. Pitch is not the same as blade angle, but because pitch is largely determined by blade angle, the two terms are often used interchangeably. An increase or decrease in one is usually associated with an increase or decrease in the other.

Jet propulsion is thrust produced by passing a jet of matter (typically air or water) in the opposite direction to the direction of motion. By Newton's third law, the moving body is propelled in the opposite direction to the jet. It is most commonly used in the jet engine,A jet engine is an air-breathing internal combustion engine often used to propel high-speed aircraft. Jet engines, like rocket engines, use the reaction principle in that they accelerate a mass in one direction and, from Newton's third law of motion, experience thrust in the opposite direction. However, jet engines use air to burn fuel while rocket engines use stored oxidizer. Air-breathing provides higher performance in terms of thrust per unit of propellant and allows the highest endurance.

Rocket propulsion:

A rocket is a machine that develops thrust by the rapid expulsion of matter. The major components of a chemical rocket assembly are a rocket motor or engine, propellant consisting of fuel and an oxidizer, a frame to hold the components, control systems and a cargo such as a satellite. A rocket differs from other engines in that it carries its fuel and oxidizer internally, therefore it will burn in the vacuum of space as well as within the Earth's atmosphere. The cargo is commonly referred to as the payload. A rocket is called a launch vehicle when it is used to launch a satellite or other payload into space. A rocket becomes a missile when the payload is a warhead and it is used as a weapon. At present, rockets are the only means capable of achieving the altitude and velocity necessary to put a payload into orbit. Thrust is the force generated, measured in pounds or kilograms. Thrust generated by the first stage must be greater than the weight of the complete launch vehicle while standing on the launch pad in order to get it moving. Once moving upward, thrust must continue to be generated to accelerate the launch vehicle against the force of the Earth's gravity. To place a satellite into orbit around the Earth, thrust must continue until the minimum altitude and orbital velocity have been attained or the launch vehicle will fall back to the Earth. Minimum altitude is rarely desirable, therefore thrust must continue to be generated to gain additional orbital altitude. The impulse, sometimes called total impulse, is the product of thrust and the effective firing duration. A shoulder fired rocket such as the LAW has an average thrust of 600 lbs and a firing duration of 0.2 seconds for an impulse of 120 lbsec. The Saturn V rocket, used during the Apollo program, not only generated much more thrust but also for a much longer time. It had an impulse of 1.15 billion lbsec. The efficiency of a rocket engine is measured by its specific impulse (Isp). Specific impulse is defined as the thrust divided by the mass of propellant consumed per second. The result is expressed in seconds. The specific impulse can be thought of as the number of seconds that one pound of propellant will produce one pound of thrust. If thrust is expressed in pounds, a specific impulse of 300 seconds is considered good. Higher values are better. A rocket's mass ratio is defined as the total mass at liftoff divided by the mass remaining after all the propellant has been consumed. A high mass ratio means that more propellant is pushing less launch vehicle and payload mass, resulting in higher velocity. A high mass ratio is necessary to achieve the high velocities needed to put a payload into orbit.