Aircraft General Knowledge - Electrics, Systems & Engines Flashcards

Question

What is a semi conductor and some of its properties?

Answer 1

A semi conductor in its natural state is an insulator. however, have unique properties such as their temp rises their resistance falls - NTC opposite to that of metals. Likewise, they may only allow conduction in one direction and insulation in another. Some of these materials are silicon.

Answer 2

Law one: the total current flow into a point of a circuit equals the current flow out of that point Law two: if all the voltage drops are added together in a closed circuit, they will equate to the total voltage applied to the closed circuit.

Answer 3

Ammeter is always connected in series and has low resistance Voltmeter is always connected in parallel and has high resistance Both work by detecting current, using a coil in a magnetic field. The ammeter in an aircraft is connected between the busbar and the battery in series. This allows measurements of current drawn from the battery which will be negative.

Answer 4

Zero centre and zero left ammeters Zero centre - shows positive and negative charge (negative indicates battery discharging) Zero left - only shows positive charge

Answer 5

To ensure that bending forces at the wing root do not exceed maximum designed loads in flight (g)

Answer 6

Stringers are used to reinforce the aircraft skin to prevent buckling and support against tensile forces. They also give the fuselage its shape.

Answer 7

Lines of flux

Answer 8

When a positive and negative charge attract an electrical field is produced. It is caused by voltage and creates static electricity.

Answer 9

The proximity of poles that attract I.e. Positive and negative the closer together the greater the charge The amount of charge (Coloumb) or an increasing amount of electrons will increase the charge

Answer 10

Direct current is a form of electricity which flows in one direction. It is simple to setup and can be stored in batteries for future use. Batteries, DC generators, AC generators (alternators) via a rectifier (converts AC to DC)

Answer 11

Starting the engines and APU In emergency situations such as electrical failure ( by law an aircraft must have 30minutes battery power) To stabilise voltage during the switching of loads

Answer 12

Anode (-) Cathode (+) Electrolyte (insulating solution that prevents electrons flowing from the anode to the cathode the shortest way I.e. Inside the battery)

Answer 13

Primary cell is the most basic form of battery and is non-rechargeable. 1.5v and not used in aircraft. A secondary cell is a battery, made up of numerous cells in series, that is rechargeable. In a light aircraft the terminal voltage of a lead acid battery is 13.2v with each cell producing 2.2v. The nominal voltage is 12v under load. In a turbine aircraft a 24v battery is used.

Answer 14

Lead acid battery Advantages: Cheaper Predictable life expectancy Disadvantages Heavier Corrosive electrolyte inside that can cause damage if battery split Slow charge rate Cannot be left for a long period after being discharged as this may caused sulphation rendering the battery useless Voltage reduces over time Nickel cadmium (NiCad) Advantages: Lighter than lead acid Maintain charge even if discharged and left for a period of time Fast charge rate Have a wider range in operating temperature (operates better in colder conditions) Disadvantages: Susceptible to thermal runaway upon quick recharge, that can cause the battery to catch fire as the battery materials have a negative thermal coefficient Expensive When a NiCad battery fails it is unpredictable as it maintains voltage all the way until it fails.

Answer 15

Given a lead acid battery loses charge as the sulphuric acid corrodes the lead plates turning them into lead sulphate the voltage will drop throughout its life. To measure this a hygrometer is used to measure the specific gravity of the sulphuric acid. Therefore: a brand new lead acid battery fully charged should have - 1.25 to 1.30 A discharged battery at low charge - 1.20 to 1.24 A fully discharged battery - 1.17

Answer 16

``` Lead acid: Anode - lead Cathode- lead peroxide Electrolyte -sulphuric acid Cells - 6 Nominal voltage - 12v(13v) ``` ``` NiCad: Anode - iron Cathode - nickel cadmium Electrolyte - potassium hydroxide gel Cells - 10 Nominal voltage - 12v(13v) ```

Answer 17

Alloy - 2 or more metals with desirable properties to produce a new material Composite - 2 or more materials brought together to give new properties you didn't have before.

Answer 18

Composite - matrix and fibre Constructs: honeycomb and sandwich structure e.g. Fibreglass, carbon fibre, Kevlar Advantages: lightweight, good rigidity and strength Disadvantages: susceptible to core damage under concentrated loads

Answer 19

Hard time maintenance - paced urge under which an item must be removed from service before its scheduled maintenace period for inspection or repair. Labour intensive due to detailed inspections and likely un-utilised aircraft time On-condition maintenance - procedure whereby upon inspection or functional check of items performance may result in item removed from service before potential fail. This include visual inspection, tests or other means without disassembly or overhaul.

Answer 20

A cantilever is a structure that is self supporting and supported at one end only. Therefore, a cantilever wing has no external bracing or support.

Answer 21

They are either fabricated taking many components to make one I-beam or extruded using a malleable metal and pushed through a hole or model to shape it. If extruded it is called a girder.

Answer 22

The plug type - the open inside and when pressurised are pushed into their seals causing a tighter seal.

Answer 23

Nose wheel: Damage to the nose wheel assembly specifically the drag struct which holds the nose undercarriage vertical Damage to the forward pressure bulkhead Tail strike: Damage to the rear pressure bulkhead Damage to the empennage I.e. Tailplane and rear control surfaces etc.

Answer 24

Three layers of glass with a vinyl (polycarbonate) inter layer. Within the layer is also a heating element Impact loads specifically air flow/resistance, bird/insect strikes and precipitation. It must also pressurisation/ compression loads.

Answer 25

It's the pressure of a fluid as an effect of its height. The higher the fluid the higher the pressure. It acts at 90 degrees to a surface. Pressure =force/area

Answer 26

A hydraulic system is one which allows a fluid to be compressed that applies a small input and a large output therefore a mechanical advantage. A passive system is one without a pump and pressure is applied when a force is applied. These systems are reminiscent of braking systems and tend to be confined to small aircraft and cars. An active system is one that utilises a pump and is continually doing work whilst a system is active. These systems are categorised as high and low pressure systems.

Answer 27

``` Properties: Virtually incompressible Chemically inert Stable or has good storage properties Non-corrosive Lubricant Reasonably priced and readily available Non-sludging/foaming ``` Hydraulic fluid is stored in a reservoir ``` Mineral oil (oil based so flammable) - DTD580/OM15 (to be replaced by def stan a1-48) Skydrol (synthetic oil which is phosphate ester based) ```

Answer 28

O-ring - cheap and bi directional seal but susceptible to extrusion Square- cheap and bi directional seal but susceptible to extrusion Chevron - can only be used in the direction of the 'v' U-ring Seals are paired with backing rings to prevent extrusion(rolling out) of the seal. These tend to be only for dynamic seals I.e. Those used to seal moving frictions surfaces

Answer 29

When air is present in the hydraulic fluid systems for example in a braking system, when the force is applied it will feel spongy. This is because a gas is very compressible and therefore, makes the fluid more compressible. As such, the hydraulic system must be bled normally whilst simultaneously adding the correct hydraulic fluid in the reservoir until you get air free oil.

Answer 30

An open centred system can only provide hydraulic pressure to one system at a time. The closed system is therefore found in more modern jet transport aircraft which often have many pumps allowing multiple systems to be operated at the same time. These systems tend to operate to 3000psi

Answer 31

Series: Voltage is the sum of all batteries Same capacity (Amp/hr) Parallel: The nominal voltage of 1 battery and current of 1. The capacity is the sum of all batteries

Answer 32

There must be emergency power from batteries to last 30minutes and 10minutes for emergency lighting

Answer 33

A dipole system is one that is a closed circuit using conductive wiring often used in an aircraft that is made not of a conductive skin e.g. Wood. In a modern jet airliner, a uni pole system is used whereby electrical components are wiring to the positive terminal but the circuit is completed by conductivity being carried out via the outer skin of the aircraft. The primary advantage of this is saving on weight by cutting out half the wiring required. The primary disadvantage is that damaged wiring connecting the skin to the negative terminal can cause a short to the earth disabling systems and become a fire risk.

Answer 34

A busbar is a heavy copper bar that is used to extend electrical power and connect multiple loads. There maybe many busbars in an aircraft and can be connected together much like an extension cable in a home. Loads are connected to a busbar in parallel which means if a load fails, other components still receive electrical power.

Answer 35

Pressure x velocity/ temp = constant When flowing through a convergent duct: velocity increases, temp and pressure decrease When flowing through a divergent duct: velocity decreases, pressure and temp increase

Answer 36

An engine where the working fluid expanded in a cylinder against a reciprocating piston.

Answer 37

Induction - mixture added to the combustion chamber Compression - the mixture is compressed and ignited Power - pressure energy pushes the piston downwards to produce mechanical energy Exhaust - exhaust gases are expelled via an inlet valve as the piston comes back up

Answer 38

Top dead centre - the point at which the piston in a cylinder is at maximum linear travel Bottom dead centre - the point at which the piston in a cylinder is at minus linear travel The volume between the two is defined as swept volume. Swept volume is the piston cross sectional area multiplied by the stroke

Answer 39

720 degrees and 2 crankshaft rotations

Answer 40

A petrol engine requires a spark plug to initiate combustion whereas a Diesel engine uses high compression to initiate compression therefore, no spark plugs.

Answer 41

The theoretical otto cycle has all events occurring at TDC and BDC I.e. Valves opening/closing and all strokes. However, in reality this is very inefficient due to inefficient crank angle and doesn't optimise the finite volume to optimise peak pressure I.e. Volumetric efficiency The practical cycle optimises these inefficiencies by using valve lag and lead to optimise volume of air in the cylinder and the expelling of exhaust gases. It also advances/ retards ignition to maximise peak pressure and exploit ineffective crank angle between compression and power strokes

Answer 42

Isochoric processes are those that have a pressure change with no change in volume. E.g combustion post spark adiabatic process is one that has a change in pressure with no heat energy added or removed. E.g. Mechanical work post combustion expanding volume of cylinder.

Answer 43

A single acting actuator has one jack ram acting on a piston with an empty volume the other side. There maybe a spring on the jack ram side to operate the actuator in the opposite direction The double acting actuator works in both ways often used with a 4 port selector valve to allow hydraulic fluid to be pumped in the higher volume side There are balanced and unbalanced double acting actuators - balanced ones have 2 jack Rams attached to a single equal area piston. These give the same force either side due to the same volumes. An unbalanced variant is where there is a larger volume on the other side of the piston to where the jack ram is.

Answer 44

An active hydraulic system is one that is powered and doesn't rely on an input to work. They have pumps. A passive system relies on a force being applied to work and therefore have no pump. Standard pressures for a low pressure hydraulic system are up to 2000psi but can be as low as 1000psi. For a high pressure hydraulic system standard pressures are 3000psi but can be as high as 5000psi

Answer 45

An EDP is a gear type pump found in most light aircraft and can be used as backup pumps in larger aircraft. The EDP is also known as the constant volume pump and by this it means that a constant amount of hydraulic fluid fed to the teeth is consistent not same volume in/out A rotary actuator is another form of actuator that can provide mechanical advantage to services requiring a rotary motion. These are made up of a number of small Pistons attached to an angled swash plate that is immovable and as such the force causes a rotary motion. These actuators are often used for flaps and undercarriage. They also can be used to drive backup electrical generators

Answer 46

Rotary Selector valves - 2 ror 4 port selector valves that have multiple fluid paths. Spool/pilot valves - sliding valve type that has land and grooves that blocks and allows oils flow respectively Non-return valves - made up of a ball and Spring and have many variants e.g. PRV, TRV and check valves that are construction ally the same but serve different purposes. They all do not allow fluid to flow in its opposite direction unless they are pressure or temperature calibrate (PRV/TRV) Shuttle valves - often used as redundancy if one hydraulic flow to a system fails shuttle valves engage upon one failing due to the pressure difference ensuring hydraulic fluid is supplied to the system. Pressure maintain/priority valves - in the event of hydraulic failure these valves prioritise primary flight controls and wheel brakes ensuring that there is sufficient pressure to maintain priority services. Restrictor valves - restrict flow in either one or both directions with the aim of reducing the speed of an operation e.g. Retraction flaps or undercarriage Flow control valves more sophisticate form of restrictors that tend to be positioned upstream of hydraulic motors Throttling valves - another more sophisticated restrictors Sequencing valves - ensure that one hydraulic operation is completed before another commences. They can be hydraulic or mechanical and are fitted to the pressure supply circuit. Hydraulic fuses - valves that are flow rate sensitive and are used to isolate a leak. Modulators are valves with a piston inside that contains a very small opening through the middle that is often used in anti skid systems to provide fine control of brake pressure.

Answer 47

Indicated horse power or the theoretical power of a piston engine: ``` Pressure Length of stroke Area of piston Number of cylinders RPM/2 ```

Answer 48

Mechanical is the indicated horsepower the frictional horse power Volumetric is the ratio of mass of air induced into the cylinder by comparison to the mass of air in ISA conditions Thermal efficiency is the ratio of work done by the propeller crankshaft by comparison to the heat lost in combusting the fuel

Answer 49

The total volume = swept + clearance Swept = TDC-BDC volume Clearance =TDC - remainder Compression ratio = total volume: clearance or (swept -clearance)/clearance

Answer 50

Detonation is when the mixture reaches it auto ignition point changing the steady burn 60-80ft per second to in excess of 1000ft per second closer to an explosion. This can produce severe engine and piston damage The reason petrol engines cannot reach a higher compression ration is because there is minimal way of stopping the fuel detonating at higher compression ratios. Diesels avoid this because fuel as it is injected in auto ignites under the extreme pressure and temperature of the compressed air in the cylinder. Detonation is impossible as detonation requires a large mixture to all be at the auto ignition point, instead the fuel is injected at its auto ignition point causing an immediate burn.

Answer 51

Crankcase - magnesium Piston - aluminium alloy Crankshaft - steel alloy Cylinder head and barrel - aluminium alloy and steel respectively

Answer 52

Poppet valves Inlet valve tends to be larger to allow as much air into the system (LP Inside vs out), the exhaust valve tends to get hotter than the inlet as it vents hot exhaust gases therefore tends to be made hollow and filled with sodium to absorb some of the heat up the valve stem.

Answer 53

Tappet clearance is important in the appropriate operation of the inlet and exhaust valves to ensure they are not late or early in their opening or closing. Likewise it allows for thermal expansion of metals at high temps Most modern engines have hydraulic tappets that allow hydraulic fluid to set the best tappet clearance automatically rather than relying upon manual calibration

Answer 54

Pressure relief valves and their variants that are pressure sensitive will be cracked or their ball unseated at a specific pressure, when the system pressure drops and the ball is re seated by the string this is the feasting pressure A pressure refile if valve that can support the full flow rate of the pump are called full flow pressure relief valves.

Answer 55

It is the process whereby very low pressure is produced in the hydraulic system causing high temps and 'hammering' of services and their uneven movement.

Answer 56

An ACOV valve is used with a constant volume/displacement pump as it cannot regulate its out put and therefore system pressure. Therefore, there must be protection mechanisms in place to protect against over or under pressurisation to prevent cavitation An accumulator is also used alongside an ACOV and a full flow relief valve that exceeds the ACOV pressure setting.

Answer 57

System pressure. This is once hydraulic fluid exceeds the charge pressure of 1500psi.

Answer 58

Maximum stroke by spring pressure

Answer 59

As an emergency means of keeping hydraulic pressure to the primary flight controls.

Answer 60

The outlet to the EDP

Answer 61

In a light aircraft generally using one hydraulic service namely undercarriage deployment and retraction will use a hydraulic power pack. It is made up of a self contained: reservoir, linear actuators (3 - rear and nose gear), shuttle, non-return valves and pressure relief valves (and TRVs) as well as a single electrical motor. In case of electrical failure free fall control is provided to deploy the undercarriage. In larger aircraft, extensive closed centred systems are used to run multiple hydraulic systems often comprising of 4 or more services. These are often duplicated and triplicated using PTUs, have numerous hydraulic EDPs per system as well as back up electrical pumps. Emergency pumps such as RATs are also present. Numerous pressure maintaining, NRVs and other valves make up the system. The systems are finely interlinked and therefore each hydraulic system is often colour coded to identify it

Answer 62

Liquid cooled is more efficient as you have greatest temperature control. This is due to increasing/ decreasing flow of liquid to the amount of heat generated in a specific state of flight. An air cooled engine has no such control and Cylinder Head temperature varies with 4 factors (of which 3 are in the pilots control): - power produced by engine - mass flow flowing over the engine - mixture ratio - cooling air temperature

Answer 63

Dry - immediately after shutdown Wet - after at least 20 minutes post shutdown In a wet sump, the oil cools and lubricates using splash lubrication. As the dipstick takes a measure from the sump, gravity needs time to work the oil back into the sump. In a dry sump, because oil is stored in a tank, the most oil is in that tank during operation hence the 'dry sump' therefore, checking immediately after shutdown will be most accurate

Answer 64

Primary properties: Lubrication Cooling Secondary properties: Corrosion protection Cleaning And hydraulic operations

Answer 65

The dry sump system contains the pressure pump and the scavenge pump. To maintain a dry sump, the scavenge pump must output more volume than the pressure pump otherwise oil will begin to pool in the sump. Precisely, the scavenge pump is approximately double the capacity of the pressure pump

Answer 66

Each magneto is controlled by its own ignition switch. The switch Isolates the magnetos ignition circuit by connecting the primary circuit to earth. The magneto is turned off by earthing the primary circuit and therefore, turned on by removing the earth connection. This is fail safe in the air as a broken wire does not affect the ignition but means that a broken wire on the ground leaves the mags live.

Answer 67

A spark plug with too large a gap may not spark at all whereas, a small gap may produce a weaker spark and therefore, effect engine output

Answer 68

Impulse magneto - a spring is wound, which upon release dramatically increases the spin of the magnet inducing a larger voltage therefore, larger spark. High tension booster coil - commonly used on larger engines, the HT booster coil induces a large current in the secondary winding while the battery powers the primary winding. A trembler interrupter is used to interrupt the primary winding circuit to produce high voltage pulses in the secondary winding Low tension booster coil- requires the battery to work and feeds boosted battery power to the primary winding to improve slow speed power generation

Answer 69

A magneto is an AC generator, transformer and distribution system providing high voltage current to spark plugs. It Rotates a permanent magnet within a ferro-magnetic core

Answer 70

Fouling of the spark plug occurs when deposits like carbon, lead and oil clog the gap between the spark plug electrodes inhibiting or delaying a spark.

Answer 71

A selector because it provides fluid to an actuator and simultaneously allows fluid to return from the actuator

Answer 72

A control piston because it is a constant pressure/variable volume pump, it is self regulating not requiring an ACOV. Therefore, the output of constant pressure pumps is regulated by an internal control piston which alters the stroke of the piston.

Answer 73

The depressurising solenoid is energised by the selection from the cockpit to offload the engine driven hydraulic pump on engine start

Answer 74

Flash point - the point at which there is enough vapour to support a momentary flame Flame point - the lowest temperature at which there is enough vapour to support a continuous flame Therefore, a hydraulic fluid must have high of each. It cannot have a high viscosity at all temp ranges due to excessive pressures. Therefore, it muse have low viscosity at all temps

Answer 75

When input pressure is less that output pressure

Answer 76

To separate gas and liquid inside of an accumulator

Answer 77

The effects for both tend to be the ACOV operating more often and rapid pressure fluctuations.

Answer 78

Light aircraft: - spur gear constant volume pumps Larger aircraft - constant pressure piston pumps (with constant volume pumps sometimes used as backup)

Answer 79

A hydraulic fuse is a one time operated device which remains open until system is reset. It is a flow rate sensitive device which tend to be used to stop leaks and are often used in exposed pipes and brake systems. They are always placed upstream side of the hydraulic actuator I.e. On the supply side.

Answer 80

The primary purpose of the springs is to close the valve which are opened by the rocker arm. The tappet clearance is measured between the valve stem and rocker pad

Answer 81

Slightly less that atmospheric pressure

Answer 82

The inlet valve closes before top dead centre on the exhaust phase and exhaust closes after top dead centre on the induction phase

Answer 83

A condenser is a capacitor. It stores a brief amount of electrical potential to assist in the breakdown of primary current and prevent arcing at the contact breaker points.

Answer 84

The magneto primary circuit normally derives its voltage by induction, it needs no battery to start.

Answer 85

It is advanced so that peak ignition comes close to the start of the power stroke.

Answer 86

After the pressure pump (and micronic filter) but before the engine

Answer 87

Displacement = piston area x no cylinders x stroke length

Answer 88

A reversible control system is a power assisted system in which the pilot is connected directly to the controls but control movements can be hydraulically assisted in larger aircraft A non-reversible control system is one in which the pilot is not connected to the control system, but instead is connected to a power control unit and an artificial feel unit either by cable runs or electronically in fly by wire systems.

Answer 89

Fly by wire removes any connection from a control column to the PCU. It is placed in a powered control system in which pilot control column actions are sent in analogue form to actuator control electronics. The ACE computes the control deflection sends it in digital format to another ACE which then converts it to an analogue signal to be issued to the PCU.

Answer 90

A gear change system is in an effort to match large control deflections at low speed whilst safe guarding against over stress at high speed. This type of system is most used on the rudder.

Answer 91

Leading edge devices are retracted after trailing edge devices. Therefore, trailing edge devices first.

Answer 92

Over weak mixture Low RPM and high power settings Applying heat when engine config. Is in high power situations Fuel usage with low anti-knock qualities Detonation causes auto ignition of the fuel vapour with air and as such sounds like a knocking in the engine. The best solution is to increase RPM and ensure fuel mixture is rich in an attempt to bring the temperature down. If climbing, a shallower angle of attack to allow more airflow over the cylinders

Answer 93

LL - low lead (tetra ethyl lead added to aviation gasoline to lessen chance of detonation) 100 is the octane of the fuel at lean mixture 100/130 - the 130 refers to the octane of the fuel when fully rich

Answer 94

Due to the slower burn cylinder head temp will increase as there is more time for the burn to transfer its heat energy to the engine body. Conversely as mixture weakens the burn temperature decreases therefore, exhaust gas temp decreases.

Answer 95

This is also known as the chemically correct mixture or ideal ratio. Is optimal combustion ration is 15 parts air 1 part fuel. It represents maximum power and heat released from combustion. This is not used in Normal operations because it is a relatively weak mixture by carburettor and piston engine requirements. This mixture runs very close to high temps and as such detonation risk. Hence, why in piston engines it tends to be 12 parts to 1.

Answer 96

To ensure that mixture ratio is appropriate across all flight conditions and range of air speeds. It pipes the throat to the carb. Chamber. This ensures the pressure in the throat equals the carb chamber therefore, ensuring that mixture doesn't get progressively weaker. At high forward speed, pressures in the intake can rise above atmospheric meaning a lower pressure in the fuel chamber and as such lack of fuel flow.

Answer 97

Ensures that at all engine speeds the mixture ratio is correct. An increase in mass flow of air entering the Venturi, will have a four fold drop in pressure. Therefore, this represents a LP in the intake vs the float chamber. This means the greater the mass flow the richer the mixture. The diffuser is a perforated tube fed by air from the pressure balanced duct, which lets a specific amount of fuel into the mixture. It also AIDS the atomisation of the fuel as the air is added to the fuel at the perforations.

Answer 98

Up to plus 30 degrees centigrade and 30% humidity. In the induction system the large draw back of the carburettor system and the Venturi throat is that with a large pressure drop also induces a large temp drop as much as 25-30 degrees centigrade. Therefore, at low RPMs (throttle closed) is when icing is most prevalent

Answer 99

``` MAIN METERING - diffuser/main jet IDLE - idle jet STOPPING - idle cut off HALTITUDE - mixture control ACCELERATION - throttle pump POWER ENRICHMENT - economiser ```

Answer 100

The indirect injection system is also the continuous flow injection system. It delivers pressurised fuel of a set ratio to a manifold valve that distributes it to the injectors in the cylinders. A direct or common rail system delivers a precisely metered quantity of fuel injected into the cylinders. This is used in Diesel engines

Answer 101

- large reduction in icing risk: no need for a Venturi or other restrictions within induction system. - quicker throttle response: no lag in waiting for a differential in pressure to deliver correct fuel mixture from carb/intake to engine - even and reliable fuel delivery: an even amount of fuel is delivered to each cylinder via dedicated injectors. With a carb. Metering done using a differential in pressure wasn't precise per cylinder. Allows the aircraft to fly in more varied flying conditions e.g. Inverted flight.

Answer 102

Power - lean mixture back until peak EGT then add a little more mixture till it drops slightly (approx 12:1) Economy - lean mixture back till peak EGT and then lean further by a set amount till EGT drops slightly (due to colder burn, approx 17:1 but watch CHT)

Answer 103

1. Shut off fuel flow with mixture at ICO | 2. Divide metered fuel between all cylinders

Answer 104

It is done by varying the speed of the turbocharger impeller. This is done by varying the exhaust gas flow to the turbine via the use of a wastegate.

Answer 105

The pressure differential controller measures the difference in deck pressure either side of the butterfly throttle valve and tries to maintain a constant pressure difference. This works at all throttle settings other than fully open (full throttle) The density controller is sensitive to deck pressure and temperature. Its job is to measure top temp and pressure in the pipe and ensure these thresholds are not breached. As such, this is only pertinent at throttle open (full throttle)

Answer 106

The internal supercharger is an engine mounted turbine attached to the crankshaft and therefore is downstream of the carb. Compressing the total mixture The turbo charger or external supercharger is not affixed to the engine, uses exhaust gases to spin the turbine and as such is not dependent on the crankshaft and due to its high operating RPMs and temps it ONLY compresses air hence its placement upstream of the carb.

Answer 107

An FTH is dependent upon power setting but it is the height/altitude achieved when that power setting is at full throttle A critical altitude is a FTH equivalent but for turbo/supercharged engines. It is the altitude or height at which the turbo/supercharger can provide sustained pressure from the compressor before power begins to fall like a naturally aspirated engine.

Answer 108

A rated power is a manufacturers designated power output in which the rated altitude can be achieved giving continuous power. After rated altitude power begins to decrease at approximately 3.5% per 1000ft in a naturally aspirated engine. The rated boost is the pressure in the manifold required to achieve rated power and therefore rated altitude.

Answer 109

Atmospheric pressure

Answer 110

The gauge is the same other than its face and units. An MAP reads manifold pressure in inches of mercury. A boost gauge is a zero centred gauge which reads PSI

Answer 111

The Diesel engine operates naturally lean because of the less risk of detonation and as the fuel is operated right at the last minute. This is also why there's no mixture control lever.

Answer 112

The weight of fuel used to produced 1 bhp per hour

Answer 113

The power jet uses a throttle operated cam to open an extra enrichment jet at high power settings only.

Answer 114

Carbs work in the pressure difference produced by the Venturi principle to the pressure in the float chamber which is the same as the air inlet pressure.

Answer 115

Fuel is continuously delivered into the inlet manifold

Answer 116

The manifold pressure would drop. This is because in a normal climb, air density will decrease and the wastegate would in normal operation progressively close to direct more exhaust gases to maintain turbine RPM. Therefore, if seized, MAP would drop and turbine RPM would drop.

Answer 117

Full throttle height will decrease. The boost is controlled by engine RPM and the throttle butterfly. Therefore, if rated boost is maintained at lower RPM, the throttle butterfly must be more open than normal meaning FTH is achieved earlier.

Answer 118

High MAP at low RPM can cause detonation. When increasing power it is: mixture, RPM and then throttle. Rev up, throttle down

Answer 119

The oleo pneumatic struts are piston rods inside of a cylinder. Charged gas, nitrogen, is placed between a free floating separator with mineral oil (DTD 585) the other side. The gas is used to support the aircraft on the ground and absorb landing shocks - it is akin to a spring. The oil is used to control the speed of compression and expansion. It's use is the dampening of landing load and recoil action.

Answer 120

Oleo pneumatic shock absorbing strut tends to be used on larger retractable undercarriage aircraft. These systems can only absorb vertical loads

Answer 121

Gravity free-fall

Answer 122

Uplocks are used to secure the retraction. These are also known as hook locks and require hydraulic force to dislodge them. Down locks are used to secure the gear upon deployment and these are usually over centre or geometric locks

Answer 123

Shimmy is the sinusoidal motion of the nose wheel whilst taxiing in the ground

Answer 124

VLE - maximum speed for landing gear extended VLO - maximum speed in which to operate the landing gear VLE is usually greater than VLO

Answer 125

During heavy loads and tight turns

Answer 126

Torque links ensure that there is no rotation of the inner piston (which is what causes shimmy) and that it is inline with the aircraft centre. There are other bracing mechanisms that ensure side loads and the gear remains in positions: - side stays: side load bracing - fore stays: ensure the gear doesn't collapse rear wards (rearward retracting gear) - drag stays: ensure that the gear doesn't collapse forwards (foreword retracting gear)

Answer 127

Body gear is automatically activated beyond 20 degrees of nosewheel deflection and will steer in the opposite direction to the nose to reduce turning radius

Answer 128

Auto braking delivers constant g deceleration based on pilot selection. Therefore, if a further lift dumping device is activated to slow the aircraft down the auto braking force will be reduced to maintain selected deceleration rate.

Answer 129

When an emergency brake selection is made the anti skid system is made inoperative

Answer 130

Increases it by up to 50%

Answer 131

Locked wheel protection - will dump all pressure to the wheels if they have stopped spinning Touch down and bounce protection- if brakes applied by the pilot before touchdown, touch down protection will ensure these aren't applied. Bounce protection ensures that if a bounce occurs that all pressure from the affected wheels is released. Normal skid control

Answer 132

A fusible plug is fitted to wheel rims that house a small piston under gas pressure. These are sensitive to temperature and when temp exceeded in tubeless tyres then it creates a hole in the tyre to vent excess pressure - stoping them from exploding When one fusible plug is discovered to be spent the rest are replaced as well.

Answer 133

The tyre carcass is made of a lattice or layered ply of nylon or rayon material that is either cross layered (cross ply) or layered on top of each other in the direction of travel (radial ply). The more layers the stronger the tyre. A radial tyre which is tubeless is used in most large aviation safety transport aircraft. Whereas, radial tubed tyres tend to me used for lighter aircraft

Answer 134

Greater tyre pressure

Answer 135

To castoring nose wheels to counteract shimmy.

Answer 136

Crossing threshold at correct speed and height, applying maximum braking from the anti skid system up in touchdown and by applying the reverse thrust and extending the speed brakes or lift dumping devices asap.

Answer 137

Ensure the doors close after the main strut is extended. These valves ensure that the undercarriage doors (D doors) open and close at the appropriate times.

Answer 138

When the brakes are applied and between the brake housing to the disc. This maybe coupled with an automatic brake wear adjuster which in which the pun is visually inspected to see how much is present.

Answer 139

The torque links. Torque links prevent piston rotation but also keep the wheel in line with aircraft centre and prevent the wheel castoring

Answer 140

Counteract the force of gravity in which it would normally bring down the gear too fast.

Answer 141

Mechanical inputs are converted to electrical signals which are integrated with electrical inputs from the flight control computers and then turned into mechanical outputs to deflect the control surfaces. Pilot input ->mechanical converted to electrical digital in an ACE ->other flight computers take input from other systems to compute a digital demand and electrical signal sent to second ACE -> analogue conversion sent to PCU which converts it to hydraulic force -> control surface movement

Answer 142

Ground system logic A safety lick physically prevents the gear selector from being moved when the air/ground logic system senses ground. Additionally many systems use geometric locks and bracing struts.

Answer 143

Weakest: square Middle: double bubble Strongest: circular

Answer 144

Torsion and bending Bending, torsion and shear are loads imposed on the wings during flight. But torsion and bending can combine to cause flutter

Answer 145

Skin, frames and stringers

Answer 146

When The aileron deflects The effects can be reduced by up rigging the ailerons in order to produce less lift in their at rest position

Answer 147

Upwards because the location of the aileron CoG lies behind the hinge line If the wing bends up and the control bends and twists down, then this can eco cyclic and flutter can occur.

Answer 148

A shuttle valve is used to allow one service to be operated by 2 independent supplied at different times for instance a normal and an emergency supply

Answer 149

To damp the fluid pressure variations ``` Accumulators are fitted to: Store fluid under pressure provide a limited supply in an emergency Dampen out pressure fluctuations Allow for thermal expansion Cater for small internal leaks ```

Answer 150

ACOV Fixed volume, constant displacement pump controlled by an automatic cut out valve.

Answer 151

They cannot be used in primary flight control systems because pneumatics cannot provide rapid response or precise movement. However, can be used in secondary flight controls like flaps.

Answer 152

Low pressure comparatively and available at high volume

Answer 153

- leaks are harder to trace | - cannot provide rapid response of precise movement of control surfaces

Answer 154

The risk of CO poisoning from exhaust leaks.

Answer 155

Describes the outlet pressure of a piston engine turbo charger. Larger turbo charged piston engine aircraft can make use of some of the deck pressure air from the turbo compressor for cabin heating

Answer 156

A compressor and turbine This is the cold air unit it an air cycle machine

Answer 157

Outflow or discharge valve The pressure is controlled by a large valve fitted in the outside skin of the pressure hull called the outflow or discharge valve.

Answer 158

Pressurisation is achieved by feeding air through the air conditioning packs and restricting its flow out.

Answer 159

Audible and visual warning at 10000ft, at 13000ft outflow valves automatically close and at 14000ft passenger oxygen masks are automatically donned. There is a legal limit of 15000ft

Answer 160

7-9PSi As the pressure in the cabin increases the difference between the cabin pressure and ambient pressure will increase. This difference is called the differential pressure.

Answer 161

In the pressure controller, the altitude selector maintains isobaric range which involves continually opening and closing the outflow valve to maintain cabin altitude

Answer 162

Explosive - 0-3 seconds Rapid - 4-6 seconds Normal - 6-10 seconds

Answer 163

V=IR The current in a circuit is directly proportional to voltage

Answer 164

Dissipate static charge of the aircraft in flight thus avoiding radio interference as a result of static electricity Static is discharged to the atmosphere through static wicks on the trailing edges of control surfaces

Answer 165

A force will be exerted on the conductor A coil of wire with a current passing through it has a magnetic field. When it is placed between the poles of a permanent magnet the attraction and repel cause torque to be produced. Lorenz force is produced which is perpendicular to the current and perpendicular to the magnetic field.

Answer 166

Electrical bonding is an effort to ensure that the aircraft skin is all one voltage which deters sparking/lightning effects due to Voltage differences between surfaces. It also provides a single earth for all devices. This is done by bonding or electrically connecting all aircraft parts with a conductor. Inadequate bonding can be seen by the presence of corrosion at joints in the aircraft skin, or static noise on the radio.

Answer 167

Fuses and circuit breakers are used as over current protection in an aircraft. A fuse is a small tube which contains a thin metal wire that melts at a specific current (stated on the fuse) breaking the circuit. A circuit breaker does the same thing as a fuse but works differently. A bimetallic circuit breaker utilises the thermal expansion properties of 2 different metals to break an electrical circuit by popping switches which have expanded due to over current. You can only reset a circuit breaker once You can only replace a fuse once By law, 10% of each fuse must be carried or 3 which ever is greater

Answer 168

Bi-metallic Adv: Cheap Disadvantages: Slow tripping response time Tend to be non-trip free I.e. They can be replaced more than once and their service will continue working regardless of danger posed Magnetic Adv: Quick tripping response time as it works on the principle of magnetism not thermal properties of metals Tends to be trip- free I.e. If you reset more than once the service is still disabled and not reactivated

Answer 169

Rectifier - AC to DC conversion | Inverter - DC to AC conversion

Answer 170

To control the output voltage of the generator at varying loads and speeds. If the output voltage of generators is not controlled it would vary with RPM and system loads. Constant Voltage is optimal running of electrical services.

Answer 171

By varying the strength of the magnetic field. Varying the field strength is best achieved by altering the current flowing through the field coils. The larger the current, the greater the output voltage and the greater the magnetic field.

Answer 172

The difference is in the constructor specifically around the rotor or armature and the stator. Alternator - AC output - the armature is the magnet and the stator is the field coils. DC generator - DC output - the armature are the rotating field coils with the stator being a stationary magnet.

Answer 173

Generators are connected in parallel to a busbar which ensure that if one fails the other does not. They are voltage regulated by such devices like a carbon pile regulator or on large aircraft electronically. The generators need to load share and therefore, an equalising circuit is connected between the return lines to the generators. If any part of the equalising circuit fails, it will mean that one generator may work harder than the other and as such load shedding should occur to limit stress on the generator.

Answer 174

Voltage regulators are always connected in series with the shunt field coil windings

Answer 175

To provide maximum power

Answer 176

Parallel: same voltage, same current, sum of all battery capacities (Amp/hr) Series: sum of all battery voltages, same current and same battery capacity

Answer 177

Field flashing is when the residual magnetism in a self exciting generator is depleted and as such current is used to replenish it.

Answer 178

A self exciting generator relies upon residual magnetism in the iron core to provide a small magnetic field upon startup. Once current begins to be generated this can be directed through the field coils to increase output.

Answer 179

Parallel/shunt - current split between loads and therefore, decreasing output voltage. The more services turned on the more output current in the main circuit. Series - maximum voltage/current through coils therefore more loads increases output current. As max output goes through coils, smaller amount of field windings but of heavier wire. Hard to control and not used in aircraft Compound - mixture between the 2, at a constant speed output voltage remains the same as services are turned on. Aircraft use either shunt or compound generators

Answer 180

Ohms law: V=IR I=V/R R=V/I Power=VI or I(I)R or V(V)/R Series Resistance = R1+R2+R3 Parallel Resistance = 1/R1+1/R2+1/R3

Answer 181

Would be normal and is only cause for concern if the high charge rate persists

Answer 182

A load should be applied to the battery in order to give a better indication if condition

Answer 183

There is a placard indicating flap load relief trigger speeds. The speed is sensed electrically and when the speed exceeds the threshold its retracted. Remember that flap load limiter ONLY activates when exceeded.

Answer 184

With jack operation and temperature

Answer 185

It will decrease slightly because accumulators will fill with hydraulic fluid

Answer 186

An electrical control system (air-ground sensing logic) detects weight via the compressed landing gear switches and therefore, disconnects an electrical circuit that prevents the gear switch from being active. There are also gear lever locks to stop accidental retraction of the Undercarriage

Answer 187

Turbo prop - at medium alts at about 300kts Turbojet - most efficient at very high airspeeds High bypass turbofan - at higher altitudes at high subsonic Mach numbers as they accelerate a larger mass of air more slowly than a turbojet

Answer 188

Highest temp during combustion Highest pressure upon exit of the diffuser Highest velocity upon entering the turbine

Answer 189

Constant pressure engine - fuel is burnt at constant pressure The brayton cycle - forms an elongated trapezium equivalent to the otto cycle for piston. Gas turbines continuously combust and go through compression, combustion, expansion and exhaust.

Answer 190

A spool is the assembly that comprises of a compressor and turbine connected by a shaft. Multi spool gas turbine engines have multiple compressor-turbine assemblies each running at their optimum RPM making them more inherently efficient than a single spool. They tend to comprise of a Low pressure and High pressure spool and in the case of a triple spool a fan (LP), intermediate pressure compressor-turbine and HP compressor turbine. Multi spools also tend to be low bypass and turbo fans which have triple spools are high by pass engines. This is in an effort to increase mass flow and take in a larger volume of air at slower acceleration thereby increasing propulsive efficiency

Answer 191

How efficiently is kinetic energy turned into propulsive force or how well am I using the thrust produced

Answer 192

Thrust =mass(air) x (velocity of jet - velocity of flight)

Answer 193

Pressure thrust is generated when the exhaust propelling nozzle is choked as the air exits supersonic. Due to the pressure difference from the inside of the nozzle vs the outside it produces a thrust force in the direction of travel - pressure thrust Can be calculated by PT= area of nozzle(nozzle static pressure - atmospheric pressure)

Answer 194

When the armature coils are at 0 degrees to the magnetic field or when the coil lay parallel with the magnetic field

Answer 195

Series - high torque used in starter motors but hard to control, prone to overspeed with no loads and speed reduces as mechanical load increases. Parallel/shunt wound - constant speed motors, low torque and current flow but much more controllable Compound - a mixture of the 2. 60-70% of the magnetic field created by the shunt windings whereas the remainder by the series.

Answer 196

Carbon pile regulator - most common regulator Vibrating contact - used in low current systems normal light aircraft using a contact breaker switch opening/closing 50-200times a second. Transistorised/ electrical - most modern and used in commercial aircraft. Uses a network of transistors and diodes to sense output voltage. The carbon pile regulator works by altering the resistance of a set of carbon discs using compression. The more the compression the lesser the resistance and vice versa. It is always wired in series with the field coil.

Answer 197

By changing the direction of current flow in the field coil

Answer 198

To save weight but to also stiffen the structure

Answer 199

O2 generated from a chemical generator which feed drop down masks located above the passenger heads. This feeds a continuous flow system which is not activated in the risk/event of a fire/fumes

Answer 200

The crew utilise a supplemental/ gaseous oxygen system fed by a diluted demand system which legally must work for 2hours constant use. Control 1 - ON/OFF Control 2 - 3 position switch: Normal, emergency and test Control 3 - 100% ON/OFF 100% O2 is fed either by manual selection or automatically at and above 32000' cabin altitude (in which the air metering valve will fully close)

Answer 201

Smoke hoods used with a 15minute O2 reserve from a small gas bottle

Answer 202

2 minimum and enough oxygen for 2% of the passengers for the time above 8000'

Answer 203

The high pressure is detected by a valve that directs the contents of the bottle overboard; thus bursts the green safety disc leaving a red hole in the aircraft skin

Answer 204

Chemical generator used in passenger O2 and gaseous used in crew O2 Chemical generator: - low maintenance and 5 year self life - lightweight and inexpensive - one charge and if set off, cannot be stopped Gaseous - refillable externally - self contained and larger capacity - flow of O2 can be regulated - Heavy!!

Answer 205

Variable inlet guide vanes and variable stator vanes - vanes set to optimum angle (which are variable depending on engine conditions) to guide air towards the first stage of the compressor Inter stage bleed valves - release pressure in later stages of the compressor to preserve axial flow Acceleration control unit - rapid throttle movements can cause fuel flow surge and possibly a reversal sending flames through the intake. Therefore, this control unit slowly increases power output on application of the throttle

Answer 206

Compressor stall - when a single stage of the compressor cannot accelerate air rearward a due to a too high angle of attack of air hitting the compressor blade Surge - multiple or all stages are stalled and a deep surge is a reversal of air often leading to a flame through the inlet

Answer 207

1 stage of a compressor forms a rotor followed by a stator. There are multiple stages in a compressor A rotor is a twisted blade from root to tip. A stator is a stationary vane used to direct air at the optimum angle to the next set of rotors. The rotor accelerates air, pressure increases and as does temperature. At the stator, it forms a divergent duct and therefore, velocity decreases but pressure and temperature increase. One stage represents an increase of approximately 1.1-1.2 (10-20%) pressure and about 25 degrees Celsius

Answer 208

The pressure ratio is a measure of compressor delivery pressure to the diffuser vs. Inlet pressure. Latest axial flows can produce upwards of 35:1.

Answer 209

Remember that the compressor is a continuous cycle of increasing pressure and temperature. Given that high pressure flows to low pressure, it would want to flow back to the inlet - to stop this the whole compressor assembly is a convergent duct - air annulus . Being a convergent duct allows this increasing pressure to continually flow through the compressor without reversal.

Answer 210

Flight deck and passenger compartments do not require fire of smoke detection systems - Class A compartments

Answer 211

Pulling the handle cuts off the fuel and twisting fires the extinguishant

Answer 212

- optical - utilise the principle of smoke refracting light onto a light sensitive cell to set off an alarm - ionisation - a small quantity of radioactive material is used that generates an electrical current. Smoke interrupts this elegiacally current and therefore an alarm sounds

Answer 213

Always approach head or behind on as there is a risk of tyreexplosion which emanates debris sideways. Spray water mist to cool the brakes at a slow pace

Answer 214

Resistive/ capacitative FireWire (FFFD) - uses 2 or duplicated loops of FireWire which has a central conductive core surrounded by an insulating layer in a capillary tube. Fire heats up the FireWire insulating material which has a negative temp coefficient reducing the resistance with greater heat and at a point a current can be transferred to earth sounding an alarm. A capacitative circuit contains a charging and measuring unit which reduces the chance for false alarm by measuring the capacitance of the electrical charge against a reference threshold. The capacitative circuit prevents false readings if for example FireWire is crushed. Systron Donner - a gas pressure activated system in which a core of titanium hydride is surrounded by pressurised helium gas stopped by 2 switches. As heat is applied, the core releases hydrogen gas increase gas pressure by which the alarm switch is tripped at 40 PSI

Answer 215

Overheat detectors are little gas tubes containing 2 sides of a spring like metal holding 2 contacts. As heat is applied and the gas expands it pulls the metal bringing the contacts closer together and when they touch an electrical circuit is made showing a light on the flight deck They tend to be found in the Engine bay, APU bay and wheel bay

Answer 216

Class B-E compartments, galleys and toilets

Answer 217

Automated suppression systems are found in unmanned compartments and engine bays. These areas require 2 shots of an extinguishant system. These systems tend to be controlled by the fire handle for engines in which a pill shuts off fuel and arms extinguishers and a rotation let and right fires both shots. Extinguishers use squibs, small gunpowder charges, which gives a temporary spike in pressure against an actuator allowing extinguishant to release via an open pipe.

Answer 218

- steady red light and an audible warning bell/noise | - overheat detection shown as a red flashing light

Answer 219

Compressed gas leaves the diffuser at approximately 110m/sec and 20% enters flame tube and 80% goes through the outer air casing. The 20% needs to be slowed down and enters through swirl vanes into the primary zone which recirculates it into a doughnut shape and this is what fuel is sprayed into and burnt. The air in the outer air casing is then reintroduced into the secondary and dilution zones to cool the air from 2100 degrees to temperatures that the turbine can handle approximately 1000-1500 degrees

Answer 220

Multi combustion chamber - ultimate combustion chambers surrounding engine connected via interconnections to allow the flame to propagate and equalise the pressure. Tuboannular or canannular - multiple flame tubes surrounded by an outer casing Annular - single circular flame tube making it shorter and more even distribution of thermal loads on the turbine

Answer 221

Gas turbine combustion is done at constant pressure and therefore there is no sudden spike of pressure as you get in the piston engine as fuel is ignited close to TDC.

Answer 222

Pressure, spray and atomiser nozzles The spray uses compressed air from the LP compressor and takes fuel into an annular nozzle and ejects into amongst the turbulent air atomising it. Vaporiser (pressure) nozzles simply eject atomised fuel into the air and use the heat to atomise - not good at low RPMs were heat is low and in conditions were atomisation is poor Atomiser burner (pressure) - uses a check valve and a fixed size orofice to eject atomised fuel (duplex)

Answer 223

Stage in a turbine is Stator (nozzle guide vane) and rotor The blade in a turbine is called an impulse - reactive blade because the stagger angle of the blade increases to its max at the tip and therefore is twisted along its length which accomplishes equal work done along the length of the blade. Impulse blading is found at the bottom of the blade and reaction at the tip with 50% of both found in the middle. Pure Impulse - produces a convergent duct increasing gas velocity and decreasing static pressure and temperature - this enacts a force onto the rotor making it spin Pure Reaction - nozzle guide vanes form a parallel duct to change the direction of airflow only therefore pressure, velocity and temp the same.

Answer 224

Nickel alloy and sometimes have a thermal ceramic coating Convection - cooling voids inside blade promote heat transfer by convection Impingement - jets of cooling air played onto internal blade faces which are ejected holes on the trailing edge Film - internal air passages are fed with high pressure cooling air. This exits through fine drilled holes into the faces and forms a protective film of cooling air across the surface

Answer 225

Current and voltage are constantly change in magnitude and polarity

Answer 226

RMS = 0.707 x peak voltage Frequency = RPM x pole pairs / 60 Line voltage (VL) = 1.73 x phase voltage

Answer 227

In a capacitor (C), (I) current leads (V) voltage and voltage lead (I) current in and inductor (L) Xc is capacitive reactance(ohms) = 1/ (2pieFC) therefore it can be seen that with increasing frequency Xc reduces and therefore less current opposing flow XL is inductive reactance = 2pieFL

Answer 228

Exhaust waste gases | Suppress noise

Answer 229

Used in reverse thrust systems. This allows for less strain to be placed on the aircraft braking systems. It uses the exhaust gases from the hot or cold stream (engine dependent) to provide a retarding force.

Answer 230

Bucket doors - an external thrust reverser that is hydraulically operated using 2 sheathes to redirect hot gases which provided approximately 10-20% reverse thrust Clamshell doors - internal system used to open cascade vanes from inside the hot section of the exhaust stream. These are pneumatic ally operated Colder stream reverser - high bypass reverses use cold stream reversal as a large proportion of the thrust is produced from the greatest mass flow. therefore, pneumatic ally operated jack Rams move the nacelle backwards opening cascade vanes for the cold air to exit.

Answer 231

1 cockpit operated and 2 engine interlocks 1. Air/ground sensing logic senses weight on wheels therefore in the ground 2. Engine RPM idle 3. Full Thrust reverse not available till control mechanism at full travel.

Answer 232

The rapidly exiting gases cause violent turbulence and rapid shearing. This causes high amplitude vibrations. The best mitigation is the use of a high bypass engine in which large amount of energy is absorbed from the hot engine core but is also sheathed with a vastly superior mass flow around the engine core dampening it. This means gases exit considerably slowly and therefore, produce less noise. Low bypass engines use mixer chutes in an attempt to quieten exhaust gases and turbojets are retrofitted with hush kits which lengthen the exhaust pipe

Answer 233

As the gases leave the last stage of the turbine, it enters a divergent duct between the exhaust cone and exhaust casing releasing kinetic energy to static pressure. The supports trust and cone remove any residual turbulence. As it travels to the propelling nozzle it enters a convergent duct which speeds up the velocity of the air trading static pressure for dynamic.

Answer 234

The gas turbine operates at close to maximum power in most stages of flight and therefore, exceedences of temperature can be detrimental to the lifespan of turbine discs, and blades (typically highest stress areas). Therefore, these must be logged - this is why short haul aircraft experience much more high cycle fatigue than long haul.

Answer 235

The ancillary or accessory gear box. This contains a number of gears and linkages to oil, fuel, pumps, starter motor and other ancillary devices. Non essential devices maybe attached using a quill shaft that may shear at a threshold to prevent loads on the gear box.

Answer 236

The most common system is the full flow system which superseded the relief valve system as it had disadvantages of over oiling at low engine RPMs. The main components requiring oil are the main ball and roller bearings in the main drive shafts. Oil temperature is measured on the return to the oil tank and pressure is measured before entering engine before the bearings

Answer 237

Low viscosity oils tend to be used that can support wide operating range of temperatures. This means fully synthetic is used. Low viscosity oils can be used as compression forces like that seen in the reciprocating engine are not present in a gas turbine (only rotational loads) so they aren't required to be as viscous

Answer 238

A hydro-mechanical fuel control unit is the precursor to FADEC (full authority digital engine control). The FCU would have a governor which would provide fuel to the engine in all flight conditions. FADEC is an electronic system that releases the pilot from engine monitoring and control. FADEC utilises an electronic engine control couple with a fuel management unit and protects the engine from compressor surge, stall, overheat and temperature, manages ACC and VSVs. There are always 2 FADEC controllers per engine for redundancy and cross checking of information.

Answer 239

Internal engine and accessory cooling Bearing chamber sealing Prevention of hot gas ingestion into turbine disc cavities Engine anti icing

Answer 240

Main bearings are cooled using oil. They also utilise high pressure air from the compressor along with groove and thread seals to prevent oil leakage. These are known as labyrinth seals - these are used in lieu of ordinary rubber seals because of the intense temperatures.

Answer 241

1. AC 115v, 3 phase, 400hz electricity 2. They feed fuel to the high pressure (HP) pump 3. They are electrical centrifugal pumps (constant pressure - typical operating range 20-30 psi)

Answer 242

In the event of a fuel imbalance to equalise wing tanks or in the event of engine failure, to enable all fuel tanks to feed remaining engine

Answer 243

The jet pump tends to keep the feeder box full of fuel to ensure adequate supply to the low pressure (LP) pumps. It works on the principle of increased fuel pressure flowing through a venturi. As fuel is pushed into the Venturi it sucks in surrounding fuel whilst not letting any out.

Answer 244

-Rigid tanks are standard shape tanks made of aluminium alloy often used in light aircraft and in some larger aircraft fuselages. They do not make use of all available space. Flexible tanks are rubber bags fastened with chord and buttons. They are very light and used in situations where integral tanks are not possible. However, they can be punctured and form folds which can trap water and fuel. Integral tanks utilise the wing as a sealed fuel tank. This is used in most commercial aircraft. They utilise baffles and baffle check valves to control fuel movement in manoeuvres and fuel pooling in the wing tips. If over pressures do occur this can cause structural damage to the wing.

Answer 245

Fuel tanks are pressurised to prevent vapour locking. As the aircraft climbs pressure drops and can boil the fuel meaning the pumps stop working and provide no fuel flow. Therefore to stop this occurring, the tank is pressurised. pressurisation can be done via the bleed air system pressurising the tank up to 5psi. The B737 and others use the ram air supplied by the vent system to pressurise the fuel tank.

Answer 246

Resonant circuit were impedance is totally resistive.

Answer 247

Reactive power (KVAR - kilovolt amps reactance) is also known as watt less power - it's the wasted power required for a generator to balance/ make the circuit resonant True power (KW) is the power remaining post reactive power Apparent power (KVA) is the total power true + reactive The power factor is a direct relation of AC circuit efficiency. I.e. Power factor = useful or true power / total power.

Answer 248

The use of a hydro-mechanical constant speed drive unit (CSDU) is connected between the engine and the generator via a dog clutch that adjusts torque and thus its RPM to output a constant frequency. A CSDU is often coupled with a generator in modern systems and these are called integrated drive units

Answer 249

Synchronous and induction motors A synchronous motor is a constant speed motor which is construction ally identical to a 3 phase alternator. The reason it is a motor is because current is fed to the stator coils to turn a magnet instead of vice versa (magnet turning to produce current). Used for constant speed applications e.g. A tachometer. An induction motor uses field coils as its rotor instead of a magnet. Therefore, as the stator coils generate an electromagnetic field, it produces a field in the rotor coils. The rotor chases the stator field and never quite is fast enough. This is spill speed. Induction motors are self starting but as load increases they slow down. Used for fuel and hydraulic pumps, AC actuators and gyros.

Answer 250

AC wild generators do not have RPM control and as such their frequency and output isn't controlled. They tend to be fitted to simpler aircraft but can be used in commercial aircraft to power non-inductive devices such as: engine and prop anti icing, heating and non-fluorescent lighting. They typically provide 22 KVA at a frequency range of 280-400hz (but this varies per aircraft e.g. ATR wild gen is 343-488hz).

Answer 251

- low oil level - low oil pressure - high oil temp These may indicate a CSDU that is about to fail. Warning lights in the cockpit will light if at least oil pressure and temp is low or high respectively. If the CSD disconnect is operated, a warning light will also display in the cockpit. It can be operated at any time during flight or when engines are running on the ground. It cannot be reset unless on the ground with engines off and only then by an engineer

Answer 252

A wet start or a failure to light. Fuel is being injected into the exhaust which means upon next start torching may occur. Therefore, a dry run must be done prior to restarting

Answer 253

It is the ratio of compressor inlet pressure to exhaust outlet pressure. EPR may over read in icing conditions.

Answer 254

Engine starting is done either by an electric starter motor (in smaller gas turbines which also double as a generator) or by a pneumatic or air starter motor. The air starter unit is able to take the engine to approximately 20% RPM. It does this by turning the HP compressor via the drive shaft. Because of the huge RPMs this motor attains (120k) it gets very hot and therefore, it must only be used sparingly. After every attempt, it must be allowed to cool down to a maximum of three starts whereby it will require at least an hour.

Answer 255

A step up transformer has more coil windings around its output that on its input. It uses the principle of EM induction, if power is assumed constant, a current will create a magnetic field in the primary windings and the core will magnetise to produce another EM field in the secondary field windings. Double the coils in the secondary windings, double the voltage but half the current. The principle is opposite for a step down

Answer 256

In a split busbar system, each generator is connected to its own AC busbar. In normal operations, each the BTB joining the busbars is open. This is because the generators cannot be paralleled unless of a failure in one were the BTB would close so as the remaining generator can power the rest of the system. A parallel system works of the principle that a synchronising busbar joins each generator AC busbar. For this to work each generator must be operating on the same voltage, frequency and be in phase. These systems tend to be used more in more than 2 engined aircraft or large 2 engined aircraft. The BTBs in normal operation here are closed to allow power to be synchronised.

Answer 257

They use transformer rectifier units (TRUs) usually one for each DC busbar. The TRUs also charge the batteries.

Answer 258

The generator control unit forms a number of sensitive relays that protect the generator from: Over/under voltage Over/under frequency Excess current If any of these occur the GCU will operate the excitation control breaker (ECB) to stop the generator from producing electricity and operate the generator control breaker (GCB) to stop it supplying electricity to the AC busbar. BTB operation also occurs but this is dependent upon the AC distribution system (split or parallel).

Answer 259

AND as both inputs are required - I.e. Positive logic - there is only one outcome that allows for 1 - 1:1 all other outcomes are zero. Other operators: - OR: 3 outcomes provide 1 and 0:0 provides zero - NOT: inverter gate which changes its input to the opposite - NAND: inverts the AND into opposite/negative logic - NOR: inverts the NOT into opposite/negative logic with only 1 outcome producing 1 and the rest zeros

Answer 260

Resistive circuit float or electric float gauges. These indicate volume not mass

Answer 261

Capable of jettisoning in 15 mins fuel from MTOM to MLM Have stops in place that allow the aircraft to retain fuel enough to climb to 10000ft, cruise for 45 minutes Jettisoning is done via the LP booster pumps

Answer 262

50 psi and a -5 psi for defueling. It uses the same refuelling pipe work and connection to fuel and de-fuel

Answer 263

The volume of the fuel will increase as due to thermal expansion and some vaporisation. Therefore, the volume will increase. However, the reference capacitor is at the bottom of the tank and will read the actual capacitance of the fuel and in doing so keep the quantity the same of the fuel gauge.

Answer 264

Flow meter fitted after the HP cock, between the fuel control unit and the engine

Answer 265

TAT +10 degrees Celsius and with visible moisture of visibility less than 1500m Airframe icing tends to be at temps of about +5 degrees

Answer 266

The first third and at most half is de/anti iced. Usually electrically. The remainder is not due to the centrifugal forces stopping ice from settling.

Answer 267

The bleed air system is used for leading edges and engine jet engine intakes as well as the first stage of the compressor inlet guide vanes. Turboprop intake lips are usually electrically heated. All engine icing protection is anti ice to prevent ingestion of ice.

Answer 268

- vibrating rod - pressure operate - rotary serrated rod - visual: heated rod on pilot side screen and ice detection lights for leading edges of wings

Answer 269

As forward speed increases, the blade coarsens. Therefore, the AoA decreases as the chord line comes closer to the relative airflow. The opposite occurs at slower speeds and therefore, AoA increases

Answer 270

ATM - aerodynamic twisting moment CTM - centrifugal twisting moment CTM is the dominant of the 2 and naturally sends the blade to fine with noting stopping it. ATM is the opposite and acts to coarsen the blade due to the thrust acting displaced from the pivot point of the blade

Answer 271

Alpha - the flight ranges | Beta - ground and reverse thrust ranges

Answer 272

SEP - the blade would not feather but allow CTM to take it to fine - this is intentional as it will cause windmilling which will enable better restart ability even though higher drag is present MEP - the increase prop drag of a windmilling prop in asymmetric flight can cause drastic handling difficulties therefore, they are set to fail feathered.

Answer 273

PCM - pitch change mechanisms A single uses oil pressure alters the pitch of the propeller in one direction whereas an opposing spring adjusts it in the other. A double uses oil pressure to adjust it both ways.

Answer 274

Unsynchronised propeller engines I.e. The props have a minorly different RPM from one another

Answer 275

Synchronising - synchroniser control unit using a master engine sets the RPM of all prop engines to be the same Synchro phasing - sets each engine propeller blade angle slightly different whilst maintaining the same RPM to reduce prop noise. Synchronising the props must occur first before synchro phasing

Answer 276

Power lever With prop control set to Max RPM, the power lever is used to select the beta range. Within this range the power lever overrides the CSU and removes the alpha range flight fine pitch stops. Within Beta power lever operates prop blade angle and engine power

Aircraft General Knowledge - Electrics, Systems & Engines Flashcards

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