03 Systems Revision Feb 08

7/26/2019 03 Systems Revision Feb 08

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Aircraft General Knowledge(Systems)

Revision Notes

February 2008


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AIRCRAFT SYSTEMS REVISION

Notes

Steve Chesher Feb 08 1

PART ONE AIRFRAMES AND SYSTEMS

Section 1. HYDRAULICS

Hydrostatics- The pressure produced at the base ofa column of fluid isdirectly proportional to its height, irrespective of the shape of the container.

Hydraulic power transmissionPascals Law - Pressure is transmitted in all directions, undiminished bydistance, acts at right angles to the container.

A mechanical advantageis gained by moving a small force over a largedistance, to enable a large loadto be moved over a small distance

FluidsProperties - Low viscosity, good lubrication, non-flammable, non toxic, low

freezing point, high boiling point, non foaming, coloured for identification,Effectively incompressible, different types cannot be mixedTypes-Mineral - DTD 585 - Red (flammable, narrow temp range)Synthetic- Skydrol - purple (non flammable, wide temp range)

Basic System

Reservoir - Contains fluidPower Pump - Provides normal pressureHand Pump - Provides emergency pressureFilter - Cleans fluidACOV - Controls system pressure

Accumulator - Contains fluid under pressurePressure relief valve - Relieves excess pressureSelector Valve - Directs pressure and return fluidActuator - Converts hyd press to mechanical movement

Components

1. ReservoirContains fluid, allows for thermal expansion, variations in fluid level due toactuator position, allows for slight leakage. Vented to prevent partial vacuum,pressurised to prevent cavitation of pump in high altitude aircraft. Containsde-aerator and baffles. Stack pipe to feed power pump

2. Power Pumpa) Constant displacement - requires ACOV and accumulator to controlsystem pressure, off loads pump output back to return at low pressure tomaintain lubrication and cooling flow when ACOV has cut out.

b) Constant Pressure (Live Line) - variable angle swash plate, controls itsown pressure to system working value. Pump pistons set for maximum strokewhen pump stationary.

3. Hand PumpProvides emergency source of pressure, takes its supply from the bottom ofthe reservoir, double acting (delivers fluid on both strokes)

4. FilterPressure filter after pump, contains by pass valve and blockage indicator,filter element may be changed if blocked.5. Automatic Cut Out ValveControls system working pressure in a constant delivery system, off loads


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pump back to reservoir when cut out, requires an accumulator to operateproperly

6. AccumulatorHolds a quantity of fluid under pressure when charged, (does not storepressure or fluid), absorbs pressure surges, maintains system pressure when

ACOV cut out, provides instant reaction to a selection, provides limitedemergency pressure, gas press too low hammering in system, gas presstoo high - rapid cycling of ACOV

7. Pressure relief valve, (PRV)or full flow relief valvePrevents damage to components from over pressurising of system byrelieving excess pressure back to return side of reservoir, set to open at avalue above normal system working pressure. Cracking pressure - thepressure at which the valve first begins to pass fluid - somewhere betweenfull flow (fully open) and reseat (closing) pressure.

8. Thermal relief valve, (TRV)Similar to PRV, relieves excess pressure from a line which has trapped fluid

in it, set to open a higher value than the PRV. Responds to increase inpressure caused by an increase in temperature, does not relievetemperature.

9. Selector valve (control valve)Directs pressure fluid to the actuator and opens a path for the return fluid topass back to the reservoir.

10. ActuatorsConverts hydraulic pressure into mechanical movement to operate therequired serviceSingle acting - sprung loaded one way, hydraulic the otherDouble acting - hyd both ways

Balanced - equal areas

11. Shuttle valveAllows an alternate hydraulic supply to power a component while shutting offthe first, sometimes for emergency use. Typically found in hydraulic brakesystems.

12. Pressure reducing valveReduces system pressure to that pressure required by a particular system

13. Hydraulic fusePrevents fluid loss by closing when leakage is sensed down stream, oftenfound in brake systems. Always found in large passenger airliner wheel brakesystems.

14. Pressure Maintaining Valve (Priority Valve)Maintains falling system pressure for essential services by closing off supplyto non essentials

15. Restrictor valves (one way and two way)Restricts flow of fluid to control rate of travel of an actuator, found in landinggear up line to control rate of lowering and flap down line to control rate ofraising with added air loads

16. Sequence valveAllows correct sequencing of different operations, e.g., landing gear door andleg

17. Pressure relay valveAllows transmission of pressure and not fluid, used in pressure gauge andtransmitter lines will prevent fluid loss in the event of gauge breakage


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18. Hydraulic system indicationsAs well as system quantity, pressure and temperature indications mostsystems will have the following warningsa) Low pressure (pump output)b) High temperature (measured in reservoir)

c) Low contents (measured in reservoir)d) Pump failure (pump output)

Light Aircraft Systems

1. Open Centre SystemSelector valves have open centres and are arranged in series to allow thepump to be off loaded unless a service is being operated, only one servicecan be operated at a time.

2. Power PackMost of the system components contained in one easily serviced unit

Al ternate Forms of Pressure

In the event of a main pump failure there is usually an alternate means ofpressurising the system

Engine Driven Pump EDP (normal source of pressure)Electrically Driven Pump - AC PumpPower Transfer Unit PTU (Hyd motor driving a hyd. pump)Air Turbine Driven Motor/Pump - ATMRam Air Turbine Driven Pump RAT or HYRAT.

High Pressure Pneumatic Systems

Older aircraft used pneumatic (high pressure air) systems rather thanhydraulics. The F27 is an example of this type of aircraft. The pneumaticsystem uses air at high pressure to operate the actuators for landing gearretraction etc. The system comprises engine driven compressors to raise thepressure to 3,000 psi. approximately. The system includes accumulators(storage bottles) to store the air under pressure ready for use, filters, reliefvalves, control valves and actuators very similar to hydraulic systems. Theadvantage being that there are no return lines back to the reservoir and thereis an inexhaustible supply of free air. Disadvantage being air is compressibleand is not as powerful as a hydraulic system.

Section 2. LANDING GEAR

The Landing Gear absorbs the landing shock, supports the weight of theaircraft when on the ground and enables the aircraft to be manoeuvred.Contains shock absorbers, wheels, tyres, brakes and some means to steerthe aircraft.

The Main Gear supports the majority of the weight balanced by a Nose wheelor Tail wheel

The most common layout for a passenger aircraft is two main landing gearlegs and a nose landing gear leg (tricycle undercarriage) because it is easierto steer, less likely to nose over in a crosswind gives better forward visionparticularly during taxyingSome light aircraft have a fixed landing gear; larger aircraft have a retractablegear to reduce drag in flight. The gear can be retracted by electrical,pneumatic or, more normally, by a hydraulic actuators.

Retractable landing gear will be locked in the down and up positions by downlocks and uplocks, which are closed by spring action and opened by


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hydraulic action (usually by a single acting actuator)When down and locked the gear is braced by a system of side stays andgeometric locks to prevent collapse on landing. When on the ground the gearis prevented from being retracted by a solenoid lock on the selector lever,which is activated by the air/ground logic circuit. Ground locking devices canalso fitted by the ground crew when the aircraft is parked, which are removed

before flight.

To indicate the position of the gear there are red and green lamps on theflight deck, which are activated by micro switches, or proximity sensors oneach leg.

Green light - down and lockedRed light - unlockedNo light - up and locked

Emergency extension of the landing gear provided by alternate hydraulicsystem or pneumatic system via a shuttle valve, or by gravity (free fall)

Steering

The steering is either by differential braking (tail wheel), or by turning thenose wheel (tricycle) The nose wheel may be connected mechanically to therudder pedals in a light aircraft but usually turned by hydraulic actuators in alarge aircraft operated by a steering tiller on the flight deck

Oleo pneumatic shock absorberTelescopic tube filled with air and oil. The air acts like a spring to support theweight of the aircraft and absorb the landing shock, the oil acts as a damperto prevent recoil in the strutTorque linksconnect the upper and lower parts of the strut to prevent thelower part of the leg rotating around the upper but still allow telescopingaction.

The amount of shock absorber extension gives an indication of the gaspressure in the strutGas pressure too high - too much extension hard rideGas pressure too low - too little extension soft ride and bottoming of thestrut

ShimmyNose wheels suffer from shimmy, which is rapid sinusoidal oscillation of thenose wheel about the track causing unpleasant vibrationIt can be caused by a broken or worn torque link or uneven tyre pressures ona twin wheeled legA shimmy damper, two nosewheels or a twin contact tyre on a single wheelcan reduce shimmy

Turn RadiusThe turn radius or the aircraft is determined by the steering angle of the nosewheels, the distance between the nose and main gear and the main geartrackDuring the push back the steering is deactivated by fitting a steering lockout pin, which must be removed before flight

Section 3 WHEELS AND TYRES

WheelStrong and light usually made of magnesium alloy. Constructed in two partsto allow tyre to be fitted - Split flange, loose flange or divided. Two halvesbolted together. Look out for corrosion and crackingWheel contains valves, anti skid speed sensor, wheel bearings and fusibleplugs.

Fusible plugreleases tyre pressure to prevent explosion if the wheel and


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tyre assembly reaches a critical temperature.TyresStrong - to take landing shocks and flexing during taxying. Divided into fourzones: Crown, Shoulder, Sidewall, and Bead. Normally tubeless and crossply for large aircraft, (however some radial ply tyres are used)

Tyre markings include size, speed limitations, part number, balance markingsand awl vents

The correct tyre pressure is important to enable the tyre to wear evenly. Lowpressure wears on shoulder high pressure wears on crown.

Aquaplaning - a layer of water lifting the tyre from the runway reducing thebraking effect occurs at 9 times the square root of the tyre pressure (in psi.)speed in knots. Occurs when tread depth is completely filled with water.

Section 4 BRAKES

Brake UnitsBrakes convert Kinetic Energy into Heat energy by friction, clampingstationary pads to the rotating disc, reducing the speed of the aircraft

Light aircraft - single disc, hydraulic - more pressure on brake pedals, morebraking effect

Heavy aircraft - multiple disc brakes to cope with the extra kinetic energy

Automatic brake adjusters compensate for brake wear by maintaining aconstant running clearance between disc and pads

Brake wear can be determined by brake wear indicators or by applying thebrakes and by measuring the gap between the disc and the piston housing.

Brake fade - loss of braking effect, as the brakes get hot

Dragging - failure of brakes to release properly - broken return springs, air inhydraulic line, distorted disc - causes brake to overheat

Squealing - glazed or warped disc

Parking brake - applies all main wheel brakes equally as long as hydraulicpressure is available. Indicator to show parking brake on

Anti - SkidTo maximise braking effect by preventing wheel skidding

A wheel speed sensor on each wheel sends signals to an electronic controlunit, which monitors the rate of deceleration of each wheel. A brakemodulator valve controls the hydraulic pressure to prevent skid

Armed during approach when gear is down does 3 things

1. Prevents landing with brakes applied

2. After landing the wheels spin up to activate the system, with the brakesapplied will sense an impending skid on any wheel and will reduce pressureto that wheel

3. If a locked wheel is detected it will release the pressure to that wheel onlyuntil it spins up again and then will re - apply brake pressureDeactivated below 5 -10 knots to allow aircraft to be brought to a halt


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Warning light on flight deck to indicate failure of system or component

Auto BrakesAutomatically applies brakes and controls to achieve a selected decelerationrate, either on landing or on rejected take off (RTO). The anti skid must beserviceable and switched on to allow auto-brake system to work.

Aircraft must be on the ground with throttles at idle to select RTO

For RTO system is armed before commencing take off run, brakes will beapplied if after an airspeed of 60 - 80kts is reached and allthe throttles aremoved to idle, deactivated by applying manual braking.

Brake IndicationsHydraulic pressure available, brake accumulator pressure, parking brake on,anti -skid and auto brake failure, brake temperatures, may have tyrepressures on modern glass cockpit displays

Section 5 FUELS - REFUELLING

Piston engine - AVGAS or MOGASAVGAS 100LL - blue SG 0.72 (low lead)AVGAS 100 - green SG 0.72Turbine engine - AVTUR or AVTAGAVTUR JET A1 sg 0.8

JET A sg 0.8AVTAG JET B sg 0.77

Jet fuels colourless to straw yellow

When using Jet B adjustment of the fuel control unit may be required

Colour Coding of Pipelines

AVGAS - White lettering on RED background

AVTUR/AVTAG - White lettering on BLACK background

SamplingCheck for: - Sediment

Bulk waterCloudiness (suspended water)Water content (water detector)

Refuelling/DefuellingCheck correct grade of fuelOverwing refuelling - Open lineUnderwing refuelling - Pressure refuelling - closed lineFuel is pumped in by fuel truck or hydrant NOT sucked in using aircraftpumps.Ensure correct grounding, bonding or earthing to equalise electrical potentialbefore removing fuel caps. Do not bond refueller to hydrant pitEstablish refuelling Zone - 6m radially from filling and venting points andensure safety precautions are observed. Do not

i) Transmit on radiosii) Switch on and off electricsiii) Replenish oxygeniv) Switch on weather radarv) Smoke within 50 ft of the aircraft

APU can be used for electrical power but must be started before refuellingand not stopped until after refuelling finishedRefuelling with passengers on board is ok if: -Aircraft has more than 20 seats


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Refuelling with AVTUR only2 exits are available, manned by cabin crewUsing loading bridge one exit may be automatic escape slide, manned bycabin crewNOT WHENusing AVGAS or JET B without anti - static additiveWhen defuelling same precautions must be observed, disposal of the

defuelled fuel remains the responsibility of the aircraft operator. It cannot beput into another aircraft or mixed with fuel in a refueller until its quality hasbeen confirmed.Defuelling can be achieved by pumping fuel out with aircraft pumps or bysucking fuel out using fuel truck pumps.Filling tanks full at night helps to reduce condensation in the tanks, but if thetemperature increases the fuel may expand and vent, or the aircraft may betoo heavy to take off the next morning

Fuel SystemsStorageTanks: - Rigid

Flexible

Integral

All tanks have:Vent system - prevents vacuum forming when fuel is usedFeed systemFiller systemBooster pumps - prevent cavitation and vapour locking, 3 phase AC

induction motor driving centrifugal impeller (20 50psi)Feeder box to mount pumps, prevents cavitationFuel drainGaugingBaffles - prevents surging or sloshingBaffle check valves - prevent fuel moving outboard from root to tip

Multiple fuel tanks - allow even distribution between wings. Selectiveswitching allows fuel to be used evenly or transferred from tank to tank toallow even usage or to cater for failure. It may not be possible to pump fuelfrom tank to tank in a modern airliner so to keep the lateral balance correct itmay be necessary to selectively burn the fuel.

DumpingLarge a/c may have the ability to dump fuel in an emergency in order toreduce the landing weight if MLM is significantly less then MTOM.Must be carried out under the control of ATC and within the correct flightenvelope and configuration for the a/cSafety switching prevents dumping all the fuel - JAA min requirement toremain

GaugingCan be resistive or capacitiveResistive- for small aircraft, measures volume - subject to manoeuvre error,variable resistance/DC powered

Capacitive- For larger a/c, measures weight (kgs or lbs) Accurate at allattitudes, failure drives indicator to zero. Variable capacitance/AC powered.

Dipsticks, drip sticks or drop sticks allow for manually determining the level offuel in the tank to cross check gauge accuracy, or if the gauge has failed.

Section 6. AIR DRIVEN SYSTEMS

Compressed airUses: - Air Conditioning

Pressurisation


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Emergency Flap/slat operationEngine startingHot air anti-icingHyd reservoir pressurisation

Sources of compressed air

Engine driven compressor - for piston engine and small gas turbine /turboprop a/c (cabin blower, cabin supercharger)Engine bleed air- For larger gas turbine engine a/c that can afford to havesome air taken from the engine compressor without too much loss of thrust -bleed air can also be supplied by the APUNormally taken from two places on the compressor (a low and high pressurestage of the compressor) low is sufficient for high power operation, low andhigh for low power operation. Typical pressure requirement 30 - 40 psiAll of the bleed air can be closed off if required by a shut off valve, whichopens slowly and shuts quickly.

Stored compressed airA limited emergency source of compressed air can be supplied by high-

pressure air from storage bottles. Recharged on the ground (these areunusual in modern airliners)

Section 7 AIR CONDITIONING

Minimum requirements are laid down in BCAR and JARi) Fresh air - 1 lb / seat / minii) Temp - +18

0C to 24

0C

iii) Humidity - approx 30%iv) Contamination - level of Co - 1 part in 20,000v) Ventilation - must be adequate when unpressurisedDuplication of components - so that no single failure causes less than 0.5lb /seat / min

These requirements are met by:1. Adequate supply constant mass flow to achieve correct ventilationand fresh airExternally dr iven compressor. - The excess air is dumped overboard by aspill valve, which is controlled by a mass flow controller, maintaining thecorrect flow for minimum fresh air requirements i.e. Constant mass flowirrespective of engine RPM.Engine bleed air systems- Air bled from the engine compressor andcontrolled by a bleed air shut off valve. Mass flow controlled by a variableorifice Mass Flow Controller (no spill valve required in this type of system)Both systems will have protection devices to prevent overpressure orovertemp using sensors to automatically close the shut off valve.2. Mixing hot and cold air to achieve the temperature requirement3. Humidity - atomised water added or excess water removed(humidifier and water extractor)Light aircraft systems. - Unpressurised: -Ram air heated by exhaust muff or combustion heater, used air exhaustedoverboard. Combustion heater must have safeguards against high outlettemp, including fire protection and auto fuel shut off in the event of anovertempRam air ventilation directly to cockpitPressurised aircraftPiston engine and small gas turbine or turbo prop a/c may be supplied by anengine driven compressor (cabin blower or cabin supercharger) Some turbocharged engines use turbo compressor discharge air.

Temperature ControlUsually achieved by mixing of hot air with cooled air. Air from a cabin blowermay need heating or cooling. Bleed air will always need cooling at loweraltitudes. There are many ways to cool the air.1. Ram Air Bleed air or Blower air is passed through a heat exchanger


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where some of the heat is removed by cold ram air2. Vapour Cycle Cooling System Works on the same principle as thedomestic fridge, using the Latent Heat of Vaporisation to remove heat fromthe incoming cabin air supply.The refrigerant used is FREON 12, chosen for its low boiling point (about 3

0C

at atmospheric pressure)

The refrigerant is circulated around a sealed system where it removes heatfrom the cabin supply in a heat exchanger called the evaporator (where theliquid refrigerant turns into a gas), it is then pressurised and cooled in thecondenser (turning back into a liquid) The greater the cooling required themore refrigerant is allowed into the evaporator through an expansion valve.The cooled air is then mixed with hot air to suit the cabin requirements.3. Air Cycle MachineThe Air Cycle Machine (ACM) cools the airsupply by expansion through a turbine. The more work the turbine has to dothe more the air is cooled. (Adiabatic Cooling). Temperatures just abovefreezing point are typically achievable.

There are two major configurations for ACMsa) Brake Turbine

b) Bootstrap

a) Brake Turbine (old airc raft)Is used where there is a fairly high pressure supply - the turbine is loaded bya brake which may be a compressor, or a fan (turbo fan). This system canbe easily identified by having only one heat exchanger. The compressor orfan provides work for the turbine to do. The jet pump induces airflow acrossthe heat exchanger to enable the system to cool when the a/c is on theground.b) Bootstrap (Most Popular in modern aircraft)Used in aircraft having lower pressure bleed air supply.The lower pressure bleed air is boosted by passing it through a compressorto raise its pressure sufficiently to achieve a good temperature drop across

the turbine.Recognised by having two heat exchangers. A ground cooling fan induces acooling airflow across the heat exchanger when the a/c is on the ground.These units are generally referred to asAi r Condit ioning Packs (ACS) orEnvironmental Control System Packs (ECS Packs)and comprise heatexchangers, cooling components, water extractors, humidifiers andsometimes the mass flow controller. There is a shut off valve to allow air intothe packs called a pack valve, pack inlet valve or pack flow control valve.

Automatic temperature control is achieved by comparing a temperatureselection made by the pilot with the temperature of the mixed air inlet to thecabin. The Hot Air Bypass Valve modulates to allow more or less air to passthrough the cooling components to obtain the correct temperature at the pointof mixing. A manual control is also provided which allows the hot air valve tobe moved open or closed directly.

Water ExtractorRemoves excess moisture fitted at the turbine outlet - water is thrownaway, sometimes over the heat exchanger to increase cooling effect byevaporation. It is notused for the humidifier

HumidifierAdds water to cabin supply to increase humidity at high altitude - downstreamof water extractor - uses water from the domestic supply. Switched off at lowaltitude.

ECS Packs are usually duplicated in twin engine a/c and triplicated in 3 & 4engine a/c. Layout of pack valves and cross feed valves allow any pack to befed from any supply.In the event of contamination entering the aircraft distribution systemselective operation of these valves can isolate the source of the


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contamination.The ECS packs can be operated on the ground to condition the a/c whenparked by using APU bleed air.

Section 8 PRESSURISATION

As pressure and density decrease with altitude the effects of hypoxiaincrease (lack of oxygen)Below 10,000 ft there is sufficient oxygen content in the reduced density airfor efficient human performanceAbove this altitude the body requires additional oxygen

Alternatively, by keeping a higher pressure in the cabin than outside theaircraft an artificially lower altitude can be maintained in the cabin where theoxygen content will now be sufficient. A typical normal maximum CabinAl ti tudewould be 8,000 ft although anything below 10,000ft would beacceptable.The fuselage of the aircraft must be strengthened to withstand considerablyhigher pressures inside than outside (Differential Pressure). The greater the

differential press the stronger the fuselage must be.Every time the aircraft flies the diff press will rise from zero, when the a/c ison the ground, to a maximum value at maximum cruise alt, and then reduceto zero again when the a/c descends and lands.This pressurisation Cyclecauses repetitive stress on the structure of the a/cas it is continually being blown up and let down.This cyclic stress is called Hoop Stresswhich is cumulative and willultimately limit the structural life of the a/c. Keeping the maximum allowablediff press to its lowest practical value reduces the hoop stress.(Some oldaircraft may have their max diff reduced to reduce the fatigue stress on thehull. I would avoid going on holiday in such an aircraft!) Hence keeping thecabin altitude at 8,000 ft instead of sea level reduces the fatigue on thepressure hull. Typical Max Diff 8 - 9psi.To prevent structural damage

occurring if max diff is exceeded there is a Safety Valve, which will open torelieve excess pressure if the pressure rises to Max Diff plus 0.25psi.If thepressure outsidethe a/c exceeds the pressure insidestructural damagemay also occur. To prevent this negative pressan Inward Relief Valve isfitted to open at a negative diff of 0.5psi.Both of these valves are duplicated

ControlPressurisation is achieved by having a constant mass flow of air into thecabin (remember the mass flow controller from the aircon system) andcontrolling the rate at which it allowed to escape to atmosphere

The components that accomplish this are Pressure cont rollersand OutflowValves(Discharge valves) these are also duplicated although the controllermay be one box but with duplicated circuits.The pressure controller is the brains of the system and is set before flight bythe pilot for the required flight profile.The outflow valves are biased fully open on the groundAt take off and climb the controller senses ambient pressure and cabinpressure and positions the outflow valves to control the rate of change ofcabin altitude (within 300 - 500 ft/min) in proportion to the rate of climb of thea/c to achieve the desired cabin altitude when the cruising alt has beenreached (Proportional control).In cruise the controller maintains the desired cabin alt by maintaining aconstant diff press (Isobaric Control). If Max Diff has been reached then thecontroller will not allow any further increase in Diff Press (Max Diff Control)During descent the controller is once again in proportional control to controlthe rate of descent of the cabin to ensure the diff press is reduced to zero bythe time the a/c has descended to its landing altitude (Proportional Control)The controller has Automatic and Standby modes of operation.In the event of a failure there must be a manual method of reducing the cabin


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pressure to zero (dump valve)

NB. Aircraft climbing - outflow valve closing - diff press increasingAircraft descending - outflow valve opening - diff press reducing

Minimum Indications Required

1. Cabin Altimeter2. Cabin VSI3. Differential Pressure Gauge4. Cabin Altitude Warning when Cabin Alt exceeds 10,000ft

(aural and visual)

Section 9 OXYGEN SYSTEMS

The flight deck crew will require oxygen if cabin alt rises above 10,000ft.Passengers are given oxygen automatically at 14,000ft cabin alt or whenselected manually by the pilot.

Types of systemGaseous - Continuous flow (crew or passengers)Diluter demand (crew only)Portable sets (therapeutic or emergency use)Chemical - Self contained units provides pax oxygen only for limitedperiod (15 mins)

1. Continuous Flow1800 psi storage cylinder - pressure reduced to useable level HP and LPindications, plug in or drop out masks crew or passenger use. Passengermasks activated by releasing the door for the drop down maskspneumatically.

2. Diluter Demand- Crew use only1800 psi storage cylinder - regulator meters oxygen on demand, mixed withcabin air in proportion to cabin alt when normal is selected, not mixed when100% is selected.4-position selectorNormal- diluted with cabin air up to 32,000ft cab alt100%- neat oxy supplied on demandEmergency- 100% oxy supplied at greater than cabin pressureTest- Oxy provided at higher press than emergency to test the mask

3. Portable SetsGaseous 1800 psi 120 litres - typical set has two settingsHigh 4 litres/minLow 2 litres/minTo ensure correct volume, gaseous cylinders are charged to 1800 psi at21

oC - if the ambient temp is higher charge to a higher press and vice-versa

in accordance with a press/temp gradient

4. Chemical Oxy GeneratorsGenerates oxygen by controlled burning of Sodium Chlorate and Iron powderIgnited by electrical firing mechanism. Masks are deployed manually or bybarometric switch at 14000ft. Drop down mask doors released electrically forchemical systems..Minimum duration 15 mins - Shelf life 10 years - heat sensitive paint or tapeto ascertain serviceability - oxy supplied at low press and temp - continuousflow.

Section 10 ICE & RAIN PROTECTION

Ice accretion (build up) during flight or on the ground must be removed, addsweight destroys lift characteristics of wing.


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Anti Icing - Prevention of ice build upDe icing - Removal of ice which has formed

In flight warning ice warning detectorsVisual - hot rodPressure operated- Differential pressure

Mechanical- Rotating spline knife edge cutterElectronic- Vibrating rodThe last three will show ice warning on the flight deck, switch on yourprotection systems.Ai rcraft ice protection systemsAirf rame1. Mechanical- De icing boots, inflatable to break the ice from wings, fin andstabiliser. Needs a pressure and vacuum source, allow build up of ice beforeactivating, cycles between wings tail and fin, may have timer for automaticoperation. Typically on piston and turbo prop aircraft.

2. Thermal- Hot air, hot oil or electrically heated elements, prevents ice buildup or removes already formed ice - it is always better to prevent build up in

the first place. Electrical elements may use frequency wild supply. Hot airtypically on modern jet transports.

3. Fluid- Applied from storage tank under pressure to porous leading edgepanels to prevent or remove ice. Limited storage capacity.

PropellerAnti icing - FluidDe icing - Electrical - Frequency wild AC cycled to allow only one propeller tobe de iced at a time as vibration may occur when ice is shed from blades

WindscreensFluid

Electrical - Maintains screen at a constant temp to prevent ice build up andincrease impact resistance of forward facing screensRain repellent - Applied to screens to encourage rain to clear screen, do notapply to a dry screen, as it will smear. Use on wet screen in conjunction withwipers

Ground De icing (unlikely to be examined in the Systems paper)

Remove snow, ice with brush, hot air, scraper, fluid or put a/c into hangerPrevent refreezing with fluidFluid can be used for de icing or anti icingThree types of fluidType 1 not used much because it has a very short holdover timeType 2 - thickened to remain on the a/c longer can be applied hot and dilutedfor de icing, cold undiluted for anti icingType 4 can be applied hot and diluted for de icing, cold undiluted for anti icingType 4 when applied 100% cold has the longest holdover time

De icing with engines/APU running can be carried out but switch off airbleeds to air conditioning system

Hot Water de icing can be carried out but not below -7oC and must be

followed within 3 mins by an application of de icing fluid to prevent refreezing.Be aware of general information in the holdover chart i.e. holdover time isdependent on Temp of fluid, strength of mixture, ambient temp and prevailingweather conditions.

E.g. freezing rain - best holdover time with 100% cold - 20 mins.

Section 11 FIRE PROTECTION


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Aircraft installation for engine, cargo bay, radio electrics bay, wheel well etc.Detection and protection.

Portable extinguishers for cabin use.

Engine System

Detection and protection1. DetectionFire warning systems comprise a common aural warning and a steady redlight for each engine to indicate the location of the fire. The red light typicallyilluminates the fire handle or fire switch. Operating the fire handle or switchwill isolate the affected engine from the aircraft systems (fuel, electrics, bleedair, hydraulics)Each engine has its own detection system, often duplicated (dual loop) and isprovided with an extinguishing system, which typically allows the pilot twoattempts (shots) to extinguish the fire

2. ProtectionThe fire extinguishers (bottles) are discharged from the flight deck by the

pilot. A typical system will have a fire handle, which as well as isolating thesystems as above will also arm the fire extinguisher firing circuits (squibs)allowing the bottle to be fired by either turning the handle left or right or byactivating a firing switch to fire the first or second shot.Pressure sensors on the bottle tell the pilot that the extinguishant has beendischarged by illuminating a warning light on the flight deck.

Similar systems can be installed in cargo compartments

Detection systemsEngine compartments are usually split into fire Zones. Detectors andextinguishers protect those zones most at riskCargo compartments can be similarly equipped but are usually fitted with

smoke detectors rather than overheat detectorsToilet and electric compartments are also fitted with smoke detectorsOverheat detectors are also fitted alongside hot air ducting for airconditioning and anti icing.

Types of detector Overheat DetectorsUnit Type- detects in its immediate vicinity only, about the size of a pen,may be bi-metallic switch or thermocouple. An increase in temp past itsthreshold value will activate the system. May be many connected in parallelto protect a large area. Has a time delay in the circuit to prevent vibrationfrom setting it off.

Continuous wire type- Narrow stainless steel wire (2mm dia) up to 15 ftlong can be connected in series to form a longer circuit.Will detect anywhere along its length, is routed and supported around theengine or along a hot air pipe. More commonly called firewire.3 Types:Resistive- Co-axial wire element having a central electrode insulated froman outer sheath fed with a DC supply. An increase in temperature causes areduction in the resistance of the insulator until current flows between thecentral electrode and outer sheath. This activates the fire warning system(bell and light) on the flight deck. (Negative coefficient of resistance).Disadvantage - short circuit causes a fire warning.

Capacitive- Same construction as the resistive but fed with AC supply. Anincrease in temperature causes an increase in the value of the capacitanceuntil the fire warning activates (positive coeffic ient of capacitance).Doesnot give a fire warning when short-circuited.

Pneumatic- The element is filled with a material, which expands whenheated activating the alarm


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All of these detectors can be tested from the flight deck and are self re-setting when the overheat condition has gone away

Smoke DetectorsPhoto - electric cell, alpha particle ionisation detector, visual detector, carbonmonoxide detector. Fitted in toilets, equipment bays, and cargo bays.

ExtinguishersAircraft instal led - contains Freon, BCF, BTM, MB in a pressurisedcontainer (fire bottle)Discharged by pilot, discharge indicator on flight deck If pressure in bottleincreases to a dangerous level protection against fracture is provided byallowing the contents to be discharged overboard. Indication that this hashappened is by an externally mounted mechanical indicator (Pressure ReliefDischarge Indicator) showing a red circle.Fire bottle squibs are fired electrically taking their power from the vital busbar.

Portable Extinguishers

Aircraft useWater/gas - red - domestic type firesCO2 - black - electrical firesBCF - green - all typesToilet fire ext.Self-contained unit activated by high temp in its vicinity, discharges intowaste bin and under sink. Nozzle changes colour from black to silver whendischarged

Ground use extinguishersWater/gas - red - domestic firesCO2 - black - electrical firesBCF - green - all types

Foam - cream - liquid firesPowder - blue Wheel brakesSand magnesium

Section 12 EMERGENCY EQUIPMENT

JAR subpart K (read very carefully)defines the scale and position ofemergency equipment eg. Life jackets for passengers and crew Smokehoods - for paxEmergency lighting - inside and outside aircraft must be capable of remainingilluminated for a minimum of 10 mins, powered from vital busInflatable escape slides - can be used as a life raft in certain cases. Deployedfrom inside the aircraft only. Inflated with CO2.Cut in Areas - marked on the outside of the fuselage, shows an area that canbe cut through without too much obstruction. It is NOTa weakened area ofthe fuselageEmergency torches - powered by battery, automatically switched on whenremoved from their stowage. Small LED lamp shows serviceability of torch.Not flashing - U/S. Flashing at frequency of 3 - 4 secs - battery and bulb ok.

APUCan provide electrical power and air for air conditioning/engine starting, usedon the ground and in the airNormally a self contained, constant speed gas turbine engine situated in anunpressurised compartment in the tail of the a/cIt has its own oil system but it is fed with fuel from one of the main fuel tanksStarted by a DC starter motor powered by the aircraft battery enables the a/cto be non reliant on major ground support equipmentThe APU is generally a one button operated engine controlled by anElectronic Control Unit (ECU) which controls the start and stop cycles andmonitors during running for High EGT, Over speed, Low oil pressure, High oil


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temp and fire warning.Any of these conditions will cause the ECU to automatically shut down theAPU.


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PART 2 PROPULSION

GENERAL

1. A thrust force has to be produced to push or pull the aircraft through the air fast enough to

enable the aircraft wing to generate sufficient lift force to initiate and maintain airborne

flight.

2. The propulsion system must be such that the propulsive force can be varied to cater for all

flight conditions that the aircraft is designed for.

3. An aircraft propulsion system may be one of three types, piston engine driving a propeller,

gas turbine engine driving a propeller or gas turbine engine directly producing jet thrust.

4. In each type the engine is a heat engine, converting heat energy to mechanical energy

by burning liquid fuel internally and causing a rapid expansion of gas.

5. The energy released is then converted into propulsion either by turning a propeller or

providing jet thrust.

6. The propeller pushes a large mass of air backwards at a relatively low velocity. The jet

engine pushes a small mass of air backwards with a relatively high velocity.

In either case pushing air backwards causes forward thrust in accordance with Newtons third law ofmotion. Force = Mass x Acceleration. The greater the mass or acceleration the greater the thrust.

PISTON ENGINES and PROPELLERS

GENERAL

1. The engine most common in use in aircraft is the four-stroke engine

2. The number of revolutions to complete a full cycle (four strokes) in a multi-cylinder engineis TWO.

3. The order in which the four strokes occur is:- induction, compression, power and exhaust.

4. During the four stroke cycle, the spark is timed to occur before TDC towards the end of the

compression stroke.

5. The inlet valve closes after BDC as the piston begins to rise on the compression stroke, toallow the maximum amount of mixture to enter the cylinder. (Valve lag)

6. The exhaust valve closes after TDC as the piston begins to descend on the inductionstroke, to assist with complete scavenging and to help draw in the fresh mixture. (Valvelag)

7. The inlet valve opens before TDC on the exhaust stroke, to ensure the valve is fully openat TDC. (Valve lead)

8. The exhaust valve opens before BDC on the power stroke, to make use of the residual

gas pressure to assist in scavenging. (Valve lead)

9. VALVE OVERLAP is the period of time when both valves are open at the same time.

10. Valve overlap increases volumetric efficiency.


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11. Valve overlap remains the same, whatever the engine RPM

12. VOLUMETRIC EFFICIENCY is the ratio by weight of a cylinders total capacity with thepiston at BDC, to the actual weight of mixture drawn into the cylinder during the inductionstroke. It is usually expressed as a percentage.

13. An increase in air temperature will reduce the weight of the mixture entering the cylinder.

14. The COMPRESSION RATIO is the ratio of the total volume of the cylinder when the pistonis at BDC, to the volume of the cylinder with the piston at TDC.

15. The STROKE is the distance the piston moves from TDC to BDC. This distance is equal totwice the crank throw.

16. The compression ratio = Total Volume/Clearance Volume

17. The compression ratio for a particular engine remains constant at all engine rpm.

18. The ratio of the power produced by an engine to the power available in the fuel is knownas THERMAL EFFICIENCY and is 28 30% at best.

19. The thermal efficiency of an engine increases with an increase of compression ratio.

20. The SPECIFIC FUEL CONSUMPTION (SFC) is the weight of fuel burnt per unithorsepower per unit time.

21. INDICATED HORSE POWER (IHP) is the theoretical power developed by the engine.(PxLxAxNxE)

22. BRAKE HORSE POWER (BHP) is the actual power measured at the propeller shaft and isRPM x torque

23. FRICTIONAL HORSEPOWER (FHP) is the amount of power lost in overcoming theinternal resistance of the engine

24. INDICATED MEAN EFFECTIVE PRESSURE (IMEP) is the average pressure exerted onthe piston during the power stroke. (This value is used to calculate the IHP).

25. The weight of charge remains the same during the compression stroke.

26. The temperature of the charge during the compression stroke will increase.

27. The volume of the charge will decrease during the compression stroke

28. Engine power depends upon: rpm and pressure achieved during combustion.

29. MECHANICAL EFFICIENCY is the ratio between the power developed in the cylindersand the power available at the propeller shaft it is usually expressed as a percentage.

30. The firing order of a four-cylinder in-line engine is: 1.3.4.2.

31. The camshaft of an engine a1ways rotates at half engine speed.

32. As an aircraft climbs, volumetric efficiency will increase because exhaust back pressuredecreases.

33. A normally aspirated engine is one that has no supercharger.

34. When a spark plug ignites the correct air/fuel mixture, the mixture will burn and thetemperature and pressure will rapidly increase.

35. Ignition is advanced as engine speed increases or as fuel/air mixture weakens, to ensure


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that maximum pressure is developed in the cylinder 8 to 10 degrees after TDC on thepower stroke.

CONSTRUCTION

1. The purpose of the crankcase breather is to prevent the build up of pressure inside thecrankcase.

2. The reason for a tappet clearance is to allow for thermal expansion when the engine isrunning. Hydraulic tappets save constant adjustment.

3. Tappet clearance is measured between the tip of the valve stem and the rocker pad.

4. If the valve has insufficient tappet clearance, the valve would open early and close lateand for an inlet valve may cause popping back in the induction manifold.

5. If the valve has too much tappet clearance the valve would open late and close early

6. The valves are closed by springs, opened by the camshaft-pushrod rocker arm.

7. To improve safety and to reduce valve bounce, two or more springs are fitted to eachvalve, coiled in opposite directions.

7. Piston rings are made of cast iron, the oil control rings are positioned below thecompression rings.

8. Excessive valve clearance can reduce Volumetric efficiency.

9. A square engine is one in which the bore and stroke measurements are equal.

COOLING AND LUBRICATION

1. The cylinder head temperature of an air cooled engine can be controlled by cowling flaps.

2. Air cooled engines have fins on the cylinder head and barrel to increase the surface areaand thereby the cooling effect.

3. Cylinder head temperature is measured by a therocouple attached to the hottest cylinder

4. The scavenge pump in the dry sump oil system is of a greater capacity than the pressurepump to keep the sump dry.

5. A relief valve is fitted to the outlet side of the pressure pump, to prevent excessivepressure being delivered to the engine.

6. The most probable cause of small fluctuations, or low oil pressure, would be the reliefvalve sticking open.

7. The oil temperature gauge records the temperature of the oil being delivered to theengine.

8. The viscosity of a lubricating oil will increase with a drop in temperature and lower the flowrate.

9. A wet sump engine is one where the oil is collected in the engine sump.

10. Engine oil contents should be checked a short time after the engine has stopped in a wetsump engine and immediately after shut down in a dry sump system.


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CARBURATION

1. The chemically correct mixture strength is 15lbs of air to 1 lb of fuel by WEIGHT.(ie: 15:1)

2. The mixture strength varies in piston engines between 8:1 (rich) and 20:1. (weak), to suitengine requirements.

3. Lead is added to aviation fuel, to decrease the risk of detonation, and is essential toengines with high compression ratios.

4. The octane rating is the ability of a fuel to resist detonation, the higher the number thegreater the resistance.

5. Pre-ignition is caused by the ignition of the fuel/air mixture due to hot spots in the cylinder,and will occur before the spark.

6. Detonation occurs after the spark has ignited the mixture and is caused by unstable

combustion.

7. The purpose of the choke tube (throat of the venturi) in a carburettor is to create adepression at the dishcharge tube to allow fuel to be metered in proportion to the airflow.

8. The pressure in a carburettor choke tube will decrease with an increase in engine speed,as the velocity of the airflow increases.

9. The mixture control on a carburettor varies the fuel flow to the main jet to compensate fora reduction in air density as the aircraft climbs

10. The fuel flow to the engine will be affected by: the r.p.m., throttle position and mixturesetting,

11. The slow running jet is located in the choke tube, where the throttle valve closes and thedepression is at its greatest across the throttle

12. The purpose of a diffuser is to meter the fuel correctly for all engine speeds and to improvethe vaporisation.

13. To compensate for poor scavenging at slow running, the mixture is enriched.

14. At high power the mixture is enriched to ensure satisfactory cylinder head cooling, and soprevent detonation.

15. An accelerator pump is fitted to prevent a weak cut on rapid opening of the throttle.Temporarily enriches the mixture during engine acceleration

16. The fuel pump in the fuel system ensures a positive supply of fuel to the float chamber.

17. When fuel priming is used to assist starting, a quantity of fuel is supplied directly to theinduction manifold.

18. Should the manual priming pump not be locked in after start, a rich mixture will result.

19. A booster pump prevents vapour locks which occur due to a decrease in pressure withincreasing altitude.

20. In a normally aspirated engine the manifold pressure increases when the throttle isopened.

FUEL INJECTION

1. In a fuel injected engine, the fuel enters the inlet manifold continuously immediately


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upstream of the inlet valves.

2. The fuel pump pumps the fuel to the injector nozzles.

3. Fuel is metered by the fuel control unit.

4. A separate priming system is not required

5. The fuel pressure gauge indicates the pressure being delivered to the nozzles and can beused as an indication of fuel flow to enable accurate leaning during cruise.

6. There will be a throttle valve but no venturi.

IGNITION SYSTEMS

1. The magneto produces a spark by utilising a self contained generator and transformer. It isrotated mechanically by the engine and requires no input from the aircraft electrical system

2. The primary circuit of a magneto has a voltage induced into it by the rotation of a magnet(generator theory).

3. The primary circuit creates a magnetic field in proportion to the current flow

4. The electrical current flowing in a magneto is transformed from low to high tension(voltage) by the rapid collapse of the magnetic field across the secondary coil(transformer).

5. The rapid collapse of the magnetic field is caused by interrupting the primary current by acontact breaker

6. A capacitor fitted in parallel prevents arcing across the contact breaker points and assists

with the rapid collapse of the magnetic field.

7. The spark occurs at the spark plug as the contact breaker points just begin to open.

8. The distributor of a magneto distributes the secondary voltage and current to the correctplug at the correct time.

9. The engine speed falls when one magneto is switched off, due to an increase in the timefor complete combustion to occur.

10. When the magneto switch is placed to off, the primary circuit is earthed or grounded.

11. The ignition switch is in the primary circuit an is in parallel with the contact breaker and thecondenser

12. If a magneto ignition switch becomes open circuited, the magneto will remain live whenswitched OFF.

13. An ignition switch which becomes shorted circuited on one magneto would cause a deadcut when the other magneto was switched off.

14. An impulse coupling in a magneto flicks over the magneto to give a large retarded sparkfor starting.

15. The impulse coupling is deactivated by centrifugal action after the engine has started andthereafter acts as a normal magneto

16. The spark occurs before TDC on the compression stroke during normal engine operation.

17. The spark occurs after TDC for starting and then is advanced to before TDC after starting.


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HANDLING

1. Before starting an engine, the propeller should be rotated by hand, with the ignitionswitched off, through two complete revolutions in tits normal direction of rotation to checkfor hydraulicing.

2. Hydraulicing refers to an accumulation of liquid in a cylinder, which could cause damageon start up.

3. Black smoke from the exhaust would indicate too rich a mixture.

4. Blue smoke from the exhaust would indicate oil burning, which could be caused by brokenor sticking piston rings.

5. Magnetos should be checked at slow running (dead cut), to ensure that the ignition systemis serviceable before a high power check is carried out.

7. The magneto drop check is carried out during the power check where a specific drop in

RPM is established.

7. During take off with a fixed pitch propeller, the RPM will show an increase because of themore efficient angle of attack of the propeller due to increased forward speed.

8. On a normally aspirated engine fitted with a fixed pitch propeller, the manifold pressure willdecrease with an increase in altitude at fixed throttle setting.

9. Excessive cylinder head temperatures could be caused by prolonged use of a weakmixture, especially at high altitude.

10. Carburettor hot air is used in flight to overcome carburettor icing.

11. Carburettor heat should be off whilst on the ground, as the hot air is un-filtered and maycause engine wear.

12. On a normally aspirated engine with a fixed pitch propeller, carburettor icing may beindicated by a drop in RPM for no apparent reason.

13. An engine should be run at the specified run down RPM after flight, to allow enginecomponents to cool to a uniform temperature before shut down.

14. After starting, if the STARTER ENGAGED warning light stays on, the starter is stillengaged and the engine must be shut down immediately.

15. After starting if the oil pressure has not risen after the prescribed time the engine must beshut down an the fault investigated

SUPERCHARGERS

1. Boost pressure is the pressure in the induction manifold, measured in lb/sq.in above orbelow ISA sea level standard pressure.

2. Manifold Absolute Pressure (MAP) is the absolute pressure in the induction manifoldmeasured in inches of mercury.

3. Manifold pressure can be indicated as either of the above.

4. Manifold or boost pressure is measured between the throttle valve and the engine inletvalve.

5. If the throttle is opened manifold pressure increases. More manifold pressure means morepower.


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Notes


6. A supercharger will always be used in conjunction with a variable pitch propeller

7. Supercharging is the term given to increasing the manifold pressure above ambientpressure to increase the power. (Improves Volumetric Efficiency)

8. A supercharger is a compressor used to raise the pressure in the manifold

9. The compressor used is a centrifugal compressor for its simplicity.

10. The compressor can be driven by the engine crankshaft (internally driven) or by anexhaust turbine (turbo-charger)

11. The centrifugal compressor has two parts, the impeller, which rotates and the diffuser.

12. Through the impeller the velocity pressure and the temperature all increase.

13. In the diffuser the velocity decreases and the pressure and temperature increase

14. The impeller and diffuser equally contribute to the pressure rise.

15. The air enters the eye of the impeller axially, is radially accelerated and leaves the tip ofthe impeller tangentially.

16. The pressure ratio across the compressor depends on the diameter of the impeller, theshape of the vanes and its speed of rotation.

17. The impeller can rotate at speeds of 120,000 RPM and achieve a pressure ratio of about3:1.

18. Rated power is the maximum power at which the engine can be operated continuouslyand is a specific RPM and Manifold pressure for any particular engine

19. Rated boost is the maximum manifold pressure for continuous use

20. Take off power for any engine may be higher than rated power, but only used for a limitedperiod of time after which the power setting must be reduced to at least rated power.

21. An engine can be Altitude Boosted where sea level power is maintained up to a specificaltitude, or Ground Boosted where the power at sea level is increased by allowing themanifold pressure to be increased above sea level values.

22. Modern engines may allow a combination of the two, where modest increases of sea levelpower are allowed and can be maintained up to a specified altitude.

INTERNAL SUPERCHARGER (Supercharger)

1. An internally driven supercharger is driven by the engine crankshaft, and rotates ata speed proportional to crankshaft speed. If the engine speed (crankshaft speed) isincreased there is a corresponding increase if impeller speed and therefore an increase inthe pressure ratio

2. The normal positioning of a supercharger is between the carburettor and the inletmanifold. (The throttle is upstream of the compressor).

3. The supercharger compresses fuel/air mixture.

4. At full power on the runway for take off the throttle is only partially open.

5. As the aircraft climbs the throttle must be progressively opened to maintain rated power asthe ambient pressure falls.


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6. When the throttle is fully open the aircraft has reached full throttle height. Climb abovethis height will cause the manifold pressure to reduce.

7. Full throttle height at rated power is called rated altitude

8. An Automatic Boost Control (ABC) is a device which maintains selected boost by

progressively opening the throttle butterfly as the aircraft climbs, and vice versa on thedescent.

9. The automatic boost capsule is sensitive to manifold pressure.

10. To reduce the risk of detonation, an inter-cooler may be fitted between the compressorand the inlet valve.

11. The inter-cooler is cooled by ram air.

12. The compressor outlet pressure of a supercharger is the same as manifold pressure.

13. To prevent over boosting when increasing the power setting, the RPM is increased first,

followed by the manifold pressure.

14. When decreasing power the manifold pressure is reduced first followed by the RPM

15. Static boost is the indication on the MAP or boost gauge with the aircraft on the groundand the engine stopped. It will indicate the ambient pressure.

EXTERNALLY DRIVEN SUPERCHARGER (Turbo-Supercharger or Turbo-Charger)

1. A turbocharger is a compressor driven by a turbine, mounted on the same shaft, andlubricated by engine oil. The turbine is driven by exhaust gases, utilizing energy that wouldotherwise have been directed overboard.

2. The compressor is fitted upstream of the throttle and the compressor outlet pressure isalways greater than manifold pressure.

3. The turbocharger compressor compresses air.

4. The exhaust is diverted into the turbine by a Waste Gate.

5. The waste gate is fitted in the exhaust manifold in parallel with the turbine, it regulates thequantity of exhaust gases by-passing, the turbine.

6. The waste gate is operated by a single acting actuator sprung loaded to the openposition.

7. The turbine speed and therefore the compressor speed are determined by the amount ofexhaust gas passing through the turbine.

8. The further closed the waste gate is the more exhaust passes through the turbine and thefaster it rotates, the further open the waste gate is the slower the turbine rotates as moreexhaust is allowed directly to atmosphere

9. The waste gate position is determined by an automatic controller that is sensitive toturbocharger discharge pressure.

10. The Absolute Pressure Controller is designed to prevent turbocharger output pressureexceeding the design maximum pressure under any condition. Therefore preventinginadvertent over boosting.

11. At idle or low manifold pressure conditions, the turbocharger waste gate is almost closed.

12. At sea level with rated power set, the throttle is likely to be fully open with the waste gatealmost fully open.


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13. As the aircraft climbs and the ambient pressure decreases the waste gate progressively

closes to speed up the turbocharger and maintain the rated MAP.

14. When the waste gate is fully closed the aircraft has reached critical altitude and climbinghigher will cause the manifold pressure to reduce.

15. If the waste gate seizes in the climb critical altitude will be lower.

16. If the waste gate seizes in the cruise, the engine could over boost on the descent.

17. As a turbocharged engine climbs, the cylinder head temperature will increase, due to theincreased compression of the air.

18. To reduce the likelihood of detonation an intercooler may be fitted at the outlet of thecompressor.

19. In place of the APC there may be a pair of controllers to give better turbo charger control.These are called the Density Controller (DC) and the Differential Pressure Controller

(DPC).

20. The waste gate is controlled by the density controller at full throttle and the diff pressurecontroller at less than full throttle.

21. The DC and DPC help to reduce bootstrapping, a condition where the manifold pressureoscillates around the selected value.

22. Turbo lag is a condition where there is a lag between the selection of a higher manifoldpressure and its value being achieved because of the time taken for the turbine andcompressor to increase their speed. Does not occur in a supercharger.

PROPELLERS

1. Blade twist is the reducing blade angle from root to tip.

2. The angle of attack of the blade remains constant, because of blade twist.

3. The region of greatest stress occurs at the blade root.

4. Plane of Rotation is the plane at right angles to the propeller axis.

5. Blade angle is measured between the Plane of Rotation and Chord Line.

6. Pitch is a linear measurement, it is the distance the blade moves forward in onerevolution.

7. Geometric Pitch is the theoretical distance a blade moves forward in one revolution.

8. Effective Pitch is the actual distance a blade moves forward in flight in one revolution.

9. The difference between Geometric Pitch and Effective Pitch is Slip.

10. Propeller Efficiency = Thrust Horse Power x 100Brake Horse Power

11. Centrifugal Twisting Moment is a force tending to turn the blades to fine pitch.

12. Aerodynamic Twisting Moment is a force tending to turn the blades to coarse pitch with thepropeller producing thrust and to fine pitch with the propeller windmilling.

13. A Constant Speed Propeller is fitted with a constant speed unit, which maintains the RPMselected by the pilot, within the constraints of power applied and forward speed.

14. Fine pitch is selected for take-off, to enable maximum RPM to be attained.


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15. During cruising flight conditions the blades will be in a coarse pitch setting.

16. Feathering is when the blade leading edge is in-line with the direction of flight.

17. Feathering is necessary to reduce drag and engine damage on a failed engine.

18. Constant Speed Double acting propeller means oil is fed to both sides of the piston.

19. Single acting propeller means, oil only to one side of the piston.

20. The maximum CSU oil pressure is controlled by a pressure relief valve.

21. The CSU control valve directs oil to or from the propeller.

22. The speeder spring always attempts to force the control valve down.

23. The centrifugal force acting on the flyweight attempts to raise the control valve.

24. Maximum RPM adjustments is carried out on the CSU.

25. The Centrifugal latches (feathering stops) is a device which prevents the blades turning tothe feathered position when the engine is stopped (on the ground), or at low RPM in flight.

26. When adjusting engine power, adjust manifold pressure first, then RPM when reducingpower.

27. When increasing power, adjust RPM first then manifold pressure.

28. "ON-SPEED" condition means spring pressure and flyweight centrifugal force balanced.Hyd lock achieved by control valve in neutral position.

29. "OVERSPEED" condition means flyweight force greater than speeder spring pressure, oildraining from the propeller, (single acting) the blades will be coarsening.

30. "UNDERSPEED" condition means, speeder spring pressure greater than flyweightcentrifugal force, oil being passed to the propeller, blades are going to fine pitch.

31. "BETA" control is used for ground operations only.

32. "SYNCHRONISATION" means the RPM of the propeller are being automaticallymaintained to that of the master engine.

33. "SYNCHROPHASING" means the blades of the propellers are adjusted relative to oneanother to provide the lowest possible noise level.

34. The unfeathering accumulator is for unfeathering a single acting propeller.

35. Double acting propellers use an electrically driven pump for feathering and unfeatheringgenerally called a feathering pump.

36. AUTO-FEATHER is a system which senses engine torque, if below a certain value willautomatically feather the propeller. It is normally armed for take-off and landing only.

37. When unfeathering coarse pitch is selected to prevent engine overspeed.

38. Electrical power for propeller de-icing is transferred from the engine to the bladesby slip rings and brushes.

39. With a fixed pitch propeller increasing the propeller RPM will increase the blade angle ofattack.

40. With a fixed pitch propeller increasing the aircraft speed will decrease the blade angle of


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Notes


attack.

41. The CSU senses engine RPM and RPM lever position.

42. Oil used for feathering in a double-acting propeller is taken from the engine oil tank.

43. Blade stations are measured from the centre of the hub.

44. Propeller torque is the resistance offered by the propeller to being rotated.

45. The thrust face or pressure face is the flat surface (back) in forward thrust.

46. The thrust face or pressure face is the curved surface (front) when the propeller is in thereverse thrust mode of operation.

47. Beta range operation is for ground use only, and includes: reverse - dwell - ground fine orsuper fine.

48. Alpha range operation is for both in flight and ground use.

49. Engine shut down due to fire, the fire extinguisher is not operated until feathering iscompleted.

50. Ground fine or super fine are blade angles in the beta range, which allows a gas turbineengine to achieve any given RPM for a lower fuel flow and hence a lower turbinetemperature. Reduces starting torque.

GAS TURBINE ENGINES

1. A modular construction of the engine allows major sections to be replaced individually ie.

LP compressor, gearbox, turbine, exhaust.

2. The thrust developed by an engine is limited by the temperature that the turbine can

withstand.

3. The working cycle of the engine is:- induction, compression, expansion and exhaust.

4. The combustion process is continuous and therefore continuous thrust is supplied.

5. The compressor may be CentrifugalorAxialand is responsible for inducing air into the

engine and increasing the mass flow by raising the pressure.

6. Centrifugal compressors are more robust but cannot cope with large mass flows of air and

so are used on smaller jet or turboprop engines. Centrifugal compressors are less liable to

rupture.

7. Axial compressors can process large mass flows of air and so are used on larger turbojet

and turbofan engines.

8. Axial compressors may be split into two or three separate compressors, designated LowPressure (LP) and High Pressure (HP) or LP, Intermediate Pressure (IP) and HP

respectively.

9. The LP compressor is mechanically connected to and driven by the LP turbine, they rotate


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Notes


at the same speed, but at a lower speed than the HP compressor/turbine.

10. The HP compressor is mechanically connected to and driven by the HP turbine, they

rotate at the same speed, but at a higher speed than the LP compressor/turbine

11. A compressor/turbine assembly is referred to as a spool i.e. LP spool, HP spool.

12. The highest pressure in the engine occurs at the outlet of the high-pressure compressor

before the air enters the combustion chamber.

13. Through the compressor the pressure and temperature of the air increase, the axial

velocity remains essentially the same.

14. A centrifugal compressor is made up of a rotating impeller and a stationary diffuser. In the

impeller the velocity, pressure and temperature of the air increase, in the diffuser the

velocity reduces and the pressure and temperature increase.

15. An axial compressor is made up of alternate rows of rotor blades (rotor disc) and stator

blades (diffusers). In the rotors the velocity pressure and temperature increase and in the

stators the velocity decreases and the pressure and temperature increase.

16. In an axial compressor one stage comprises one set of rotors and one set of stator

blades.

17. Many stages are used to achieve the required increase in pressure.

18. The increase in pressure is referred to as the pressure ratioand is determined by the

number of stages and the speed of rotation.

19. A mismatch between the rotational velocity of the compressor and the axial velocity of the

air can cause the compressor to stall or surge.

20. A stall is a disruption of the airflow over one or more stages of the compressor.

21. A surge is a complete breakdown and even reversal of the airflow through the compressor.

22. To help prevent stalling and surging, particularly at low engine RPM, Variable Inlet Guide

Vanes (VIGVs), Variable Stator Vanes (VSVs), surge bleed valves (blow off valves) and

Multi Spool Compressors may be used.

23. To prevent inducing a stall or surge during rapid acceleration the Fuel Control Unit (FCU)

limits the rate at which fuel flow is increased thereby limiting the rate of acceleration of the

compressor.

24. A By pass engine is one where not all of the air that enters the LP compressor goes

through the HP compressor and combustion chamber. The by pass air or cold stream

recombines with the turbine exhaust gas or hot stream after the turbine section.

25. A low by pass engine (1:1 to 2:1) has a relatively high exhaust velocity.

26. A high by pass engine (4:1, 5:1) has a relatively low exhaust velocity and a better

propulsive efficiency at high subsonic speed than the low by pass engine.

27. In the combustion chamber 20% of the air is mixed with the fuel and burnt the remaining


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Notes


80% is used for flame shaping, dilution of the burnt gasses and cooling the flame tube and

combustion casing.

28. By pass air is notused for cooling the combustion chamber.

29. The highest temperature of the engine is the combustion chamber.

30. Combustion occurs at relatively constant pressure.

31. The chemically correct air fuel ratio is 15:1

32. The addition of heat energy at constant pressure cause the velocity of the gasses to

increase.

33. The gas velocity is at its highest when leaving the HP nozzle guide vanes.

34. The turbine takes energy from the gas flow to drive the compressor or fan.

35. The turbine is effectively the opposite of the compressor and is made up of alternating

stators (nozzle guide vanes) and rotors (turbine wheel or disc).

36. Turbines are typically one two or three stages.

37. There are two types of turbine design, IMPULSE and REACTION turbines.

38. Modern engine turbine blades are part impulse and part reaction and change shape from

the root to the tip of the blade to allow an even velocity into the exhaust.

39. An IMPULSE turbine uses the velocity of the gas built up by the nozzle guide vanes to

spin the turbine.

40. Nozzle guide vanes for an impulse turbine form a convergent duct, increasing gas velocity

and reducing pressure before entering the turbine rotor.

41. A REACTION turbine comprises turbine blades which are designed to be convergent,

increasing the velocity and reducing the pressure of the gas flow.

42. The engine pressure ratio(EPR) is the ratio of the exhaust gas pressure (turbine outlet) to

the compressor inlet pressure.

43. Exhaust temperature(EGT) is measured by thermocouples fitted in the exhaust.

44. A fuel cooled oil cooler cools the oil and heats the fuel.

45. A fuel heater uses bleed air to heat the fuel.

46. Bleed air is taken from the engine compressor to operate various aircraft systems, the

operating pressure is 40psi-60psi.

47. If bleed air is used for anti-icing, the EGT will increase and thrust decrease.

48. The control of rpm in a gas turbine engine is accomplished by varying the fuel flow.

49. A convergent duct increases velocity and decreases pressure.

50. A divergent duct decreases velocity and increases pressure and temperature.

51. Diffuser vanes act in the same manner as a divergent duct


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Notes


52. Run down time is the time taken for the engine to stop rotating from the time the fuel HP

valve is closed.

53. Bearing oil seals are pressurised with air using labyrinth seals.

54. Engine over-heat will be indicated by a RED light (internal cooling air overheat).

55. The high energy igniter units work on the principal of capacitor discharge.

56. Igniters use two different energy levels, high energy for starting and high altitude relighting,

low energy for continuousoperation during take of landing and flight during inclement

weather.

57. Reverse thrust can be applied by reversing the cold stream only, the hot stream only, or by

reversing hot and cold stream.

58. The engine primary instruments are:- EGT, N1, and EPR..

59. Engines are started by using DC electrical or air turbine starter motors.

60. A HOT start is one where the EGT reaches too high a reading during the start cycle.

61. A wet start does not achieve a light up and will require a dry motoring cycle with igniters off

prior to a further start attempt.

62. A HUNG start is one where the engine lights up but will not accelerate to self sustaining

speed.


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Notes


PART 3 ELECTRICS AND ELECTRONICS - GLOSSARY

accelerate To change velocity; increase or decrease speed.

accelerometerA device for sensing or measuring acceleration and converting it to an electric

signal.actuator A hydraulic, electric, or pneumatic device used to operate a mechanism by remote

control.

alternating current An electric current which alternates around a mean point and constantly

changes in magnitude.

alternator An electric generator designed to produce alternating current having a rotating

field and stationary armature.

ammeter An instrument used to measure current flow.

ampere (A) The basic unit of current flow. One ampere is the amount of current which flows

when an EMF of 1 volt is applied to a circuit with a resistance of 1 ohm.

ampere-hour (Ah) Quantity of electricity which has passed through a circuit. Current (inamperes) x time (in hours) = ampere-hours. Unit of measurement for battery

capacity.

amplification The increase of power, current, or voltage in an electronic circuit.

amplifier An electronic circuit that produces amplification. eg. of power

amplitude modulation (AM) Modulation of a carrier wave in which the modulating signal

changes the amplitude of the carrier in proportion to the strength of the modulating

signal.

analogue Infinitely variable, or an electrical circuit which operates with infinite possible input

or output signals.

angular velocity Time rate of change of an angle rotated around an axis in degrees per

second or degrees per minute.

anode Positive electrode of a battery; the electrode of an electron tube, diode, or

electroplating cell to which a positive voltage is applied.

antenna A device designed to radiate or intercept electromagnetic waves.

apparent power The power consumed by the resistance, inductance, and capacitance in

an ac circuit.

armature In a dc generator or motor, the rotating member. In an ac generator the armature

is stationary and is acted upon by the rotating field produced by the rotor. The

moving element acted upon by the magnetic field in a relay is also called the

armature.

armature reaction The interaction of the armature field upon the main field of a generator ormotor, resulting in distortion of the main field.

atom The smallest possible particle of an element.

attenuation A reduction in the strength of a signal, the flow of current, flux, or other energy in

an electronic system.

audio frequency A frequency in the audible range, from about 35 to 20 000 Hz.

automatic direction finder (ADF) A radio receiver utilizing a directional loop antenna which

enables the receiver to indicate the direction from which a radio signal is being

received.

automatic frequency contro l (AFC) A circuit arrangement which maintains the frequency of

the system within specified limits.azimuth Angular distance measured on a horizontal circle in a clockwise direction from

either north or south.

back EMF A voltage developed in the armature of a motor which opposes the applied EMF.

The same principle applied to any inductance through which an alternating current


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Notes


fCX

C2

1=

is flowing.

band A range of frequencies.

bandpass f ilter A filter circuit which passes frequencies within a specific band and

attenuates all frequencies outside that band.

bandwidth The difference between the maximum and minimum frequencies in a band.base The terminal of a transistor to which the control current is applied.

battery A group of cells connected together to produce desired voltage and capacity.

bias A voltage applied to the control grid of an electron tube or the base element of a

transistor to control the switching action.

binary system A numbering system using only two symbols 0 and 1 and having 2 as a base.

BITE Built-in test equipment designed to monitor and test aircraft systems.

black box A slang term used to refer to a modular component containing electrical

equipment. Slang term for Flight Data Recorder.

bonding The connecting together of metal structures and components with electric

conductors, thus establishing a uniform electric potential among all the partsbonded together.

brush A device usually made of carbon designed to provide an electrical contact be-

tween a stationary conductor and a rotating element.

buffer amplifier An amplifier in a transmitter circuit designed to isolate the oscillator

section from the power section, thus preventing a frequency shift.

bus bar A power distribution point to which a number of circuits may be connected. It often

consists of a solid metal strip in which a number of terminals are installed.

bus t ie breaker (BTB) An electrical solenoid used to connect two bus bars.

byte A group of binary digits handled as a group or word.

cable A group of insulated electric conductors, usually covered with rubber or plastic toform a flexible transmission line.

capacitance The property enabling two adjacent conductors (plates) separated by an insulating

medium (dielectric) to store an electric charge. The unit of capacitance is the

farad.

capacitive reactance The reaction effect of capacitance in an ac circuit. The formula is

where XC, is capacitive reactance in ohms, fis frequency in hertz,

and Cis the capacitance in farads.

Capacitor A device consisting of conducting plates separated by a dielectric and used to

introduce capacitance into a circuit.

capacity A battery or cells total available current. Typically measured in ampere-hours for

aircraft batteries.

carrier wave A radio-frequency electromagnetic wave used to convey intelligence impressed

upon it by modulation.

cathode The negative electrode of a battery; the negative terminal of a diode or

electroplating cell.

cathode-ray tube (CRT)A special type of electron tube in which a stream of electrons from anelectron gun impinges upon a fluorescent screen, thus producing a bright

spot on the screen. The electron beam is deflected electrically or mag-

netically to produce patterns on the screen.

cell A combination of two electrodes (positive and negative plates) surrounded by an


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Notes


electrolyte for the purpose of producing voltage.

charge A quantity of electricity. A charge is negative when it consists of a number of

electrons greater than the number normally held by the charged material in a

neutral condition. The charge is positive when there is a deficiency of electrons.

choke coil An inductance coil designed to provide a high reactance to certain frequencies

and generally used to block or reduce currents at these frequencies.

Circuit Conductors connected together to provide one or more complete electrical paths.

circui t breakerA device which automatically opens a circuit if the current flow increases beyond a

safe value.

circuit protection The provision of devices in an electric circuit to prevent excessive current

flow. These devices may be fuses, circuit breakers, current limiters, or sensing

relays.

clutch A mechanical device used to connect or disconnect a motor or other driving unit

from the driven device.

coaxial cablesA pair of concentric conductors. The inner conductor is supported by insulation

which holds it in the center of the outer conductor. A coaxial cable is normally

used to conduct HF currents.

coil One or more turns of a conductor designed for use in a circuit to produce

inductance or an electromagnetic field.

collector A section of a transistor.

commutator A rotating contact device in the armature of a dc generator or motor, which in

effect changes the ac current flowing in the armature windings to a dc current in

the external circuit.

compass A device used to determine direction on the earths surface. A magnetic compass

utilizes the earths magnetic field to establish direction.compound winding A combination of series and parallel or shunt windings to provide the

magnetic field for a generator or motor.

conductor A material through which an electric current can pass easily.

conduit A metallic tubular sheath through which insulated conductors are run. The conduit

provides mechanical protection and electric or magnetic shielding for the

conductors.

constant-speed drive (CSD) A hydro-mechanical unit used in conjunction with ac alternators to

produce a constant frequency ac voltage.

continuity tester A device designed to test the electrical continuity of a conductor or circuit.

A battery and light, or other indicating unit, connected in series, or an ohmmeter

may serve as continuity testers.

continuous wave (CW) An RF carrier wave whose successive oscillations are identical in

magnitude and frequency.

control circuit Any one of a variety of circuits designed to exercise control of an operating device,

to perform counting, timing, switching, and other operations.

cosine The ratio of the side adjacent to an acute angle of a right triangle to the

hypotenuse.

coulomb (C) The coulomb is a unit of electric charge consisting of approximately 6.28 x 1018

electrons.

current The movement of electrons through a conductor.

current limiter A device installed in a circuit to prevent current from increasing above a specified

limit.

cycle A complete sequence of events in a recurrent series of similar periods, one

complete AC sinewave.


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Notes


damping The decay in amplitude or strength of an oscillatory current when energy is not

introduced to replace that lost through circuit resistance.

decimal system A numbering system using ten symbols to represent quantity.

delta connection A method of connecting three components to form a three-sided circuit,

usually drawn as a triangle,

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