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Deepen > EASA : The alternators when connected are usually connected ?

Question 27-1 : In parallel mode in series mode dependant on the type of generator dependant on the type of engine

exemple 127 in parallel mode.in parallel mode.

The capacity of an accumulator is ?

Question 27-2 : The quantity of electricity that the battery can supply during discharge the number of cycles charging and discharging that a battery can withstand without deterioration of its cells the no load voltage of the battery multiplied by its rated output current the intensity withstood by the battery during charging

.a battery's capacity is the quantity of electricity that it can supply during discharge the more electrolyte and electrode material there is in the cell the greater the capacity of the cell .a small cell has less capacity than a larger cell with the same chemistry and they develop the same open circuit voltage.because of the chemical reactions within the cells the capacity of a battery depends on the discharge conditions such as the magnitude of the current which may vary with time the allowable terminal voltage of the battery temperature and other factors the available capacity of a battery depends upon the rate at which it is discharged if a battery is discharged at a relatively high rate the available capacity will be lower than expected exemple 131 the quantity of electricity that the battery can supply during discharge.the quantity of electricity that the battery can supply during discharge.

The moving part in an ac generator is usually referred to as the ?

Question 27-3 : Rotor slip ring stator oscillator

exemple 135 rotor.rotor.

The purpose of bonding the metallic parts of an aircraft is to ?

Question 27-4 : Provide safe distribution of electrical charges and currents prevent electrolytic corrosion between mating surfaces of similar metals isolate all components electrically and thus make the static potential constant provide a single earth for electrical devices

.the single earth return uses the aircraft structure as a return path if the component is not electrical it does not need a return path but still requires bonding to equalise potential difference in the event of static build up this is why the answer provide a single earth for electrical devices is false exemple 139 provide safe distribution of electrical charges and currents.provide safe distribution of electrical charges and currents.

A constant speed drive aims at ensuring ?

Question 27-5 : That the electric generator produces a constant frequency that the starter motor maintains a constant rpm not withstanding the acceleration of the engine that the csd remains at a constant rpm not withstanding the generator rpm equal ac voltage from all generators

exemple 143 that the electric generator produces a constant frequency.that the electric generator produces a constant frequency.

When a persistent underexcitation fault is detected on an ac generator ?

Question 27-6 : The exciter control relay the generator breaker and the tie breaker the generator breaker and the tie breaker the generator control relay and the generator breaker the tie breaker

A control relay is a 'magnetic switch' which can isolate a circuit so is in effect the same as a 'breaker' an 'exciter breaker' and an 'exciter control relay' are in effect the same thing .an exciter breaker exciter control relay will isolate the power to the voltage regulator .the generator breaker will isolate the generator from the bus bar .the tie breaker will isolate two different bus bars from each other or can connect two generators to the same bus bar .in most cases you will want to keep bus bars connected so that you can use all your services so you will trip the generator breaker to isolate the generator from the bus bar and the exciter breaker so you effectively shut down that generator .if you have 2 generators supplying the same single bus bar then you will trip the tie breaker to isolate generator and the generator and exciter breakers to isolate and shut down the generator exemple 147 the exciter control relay, the generator breaker and the tie breaker.the exciter control relay, the generator breaker and the tie breaker.

A test to assess the state of charge of a lead acid battery would involve ?

Question 27-7 : Comparing the 'on load' and 'off load' battery voltages checking the level of the electrolyte checking the discharge current of the battery 'on load' checking the battery voltage 'off load'

exemple 151 comparing the 'on-load' and 'off-load' battery voltages.comparing the 'on-load' and 'off-load' battery voltages.

The advantages of grounding the negative pole of the aircraft structure are . 1 ?

Question 27-8 : 1 2 4 1 2 3 2 3 5 1 3 5

.the fuselage is used as an earth return for electrical components on an aircraft which means that you only need one length of cable the battery will be connected by its negative pole this saves weight and space as you don't need two cables to complete a circuit .statement 3 increase of short circuit risk is not an advantage and statement 5 circuits are not single wired lines is wrong .correct answer '1 2 4' is the most correct one even if we are not totally agree with exemple 155 1, 2, 4.1, 2, 4.

When an 'open circuit' occurs in an electrical supply system the ?

Question 27-9 : Loss of continuity will prevent its working components from functioning load as indicated by the ammeter will increase fuse or cb should isolate the circuit due to excess current drawn component will operate normally but will not switch off

.short circuit open circuit fault as the most common failure of aircraft electrical power supply system when an 'open circuit' occurs the components connected on the circuit cease to operate exemple 159 loss of continuity will prevent its working components from functioning.loss of continuity will prevent its working components from functioning.

An ac generator driven by a csd unit ?

Question 27-10 : Requires a voltage controller to maintain constant voltage under load does not need a voltage controller since the csd will ensure constant voltage does not need a voltage controller since an ac generator voltage cannot alter under load requires a voltage controller to maintain constant frequency

The csd constant speed drive is a hydro mechanical unit fitted between the engine gearbox and the generator its function is to maintain a constant generator speed regardless of engine speed. for a three phase generator to maintain 400hz this would be 8000 rpm although generator speed remains constant the electrical load will vary according to services selected to maintain a steady output voltage the strength of the field excitation is controlled by the voltage regulator exemple 163 requires a voltage controller to maintain constant voltage under load.requires a voltage controller to maintain constant voltage under load.

Consider the variable pitch propeller of a turbo prop during deceleration ?

Question 27-11 : When braking the propeller supplies negative thrust and absorbs engine power at zero power the propeller thrust is zero and the engine power absorbed is nil when feathered the propeller produces thrust and absorbs no engine power with propeller windmilling the thrust is zero and the propeller supplies engine power

When braking it means when you move the power lever in the reverse or beta range.in the 'reverse' pitch position the engine/propeller turns in the same direction as in the normal forward pitch position but the propeller blade angle is positioned to the other side of flat pitch in reverse pitch air is pushed away from the airplane rather than being drawn over it reverse pitch results in braking action rather than forward thrust of the airplane exemple 167 when braking, the propeller supplies negative thrust and absorbs engine power.when braking, the propeller supplies negative thrust and absorbs engine power.

The correct formula to calculate the total displacement of a multi cylinder ?

Question 27-12 : Piston area x piston stroke x number of cylinders piston area x piston stroke cylinder volume x number of cylinders cylinder length x cylinder diameter

exemple 171 piston area x piston stroke x number of cylinderspiston area x piston stroke x number of cylinders

When changing power on engines equipped with constant speed propeller engine ?

Question 27-13 : Increasing the rpm before increasing the manifold pressure reducing the rpm before reducing the manifold pressure adjusting fuel flow before the manifold pressure increasing the manifold pressure before increasing the rpm

A small trick .propeller´s control is the bravest .the first to enter increase the rpm before increase the map and the last to leave decrease the map before decrease the rpm exemple 175 increasing the rpm before increasing the manifold pressure.increasing the rpm before increasing the manifold pressure.

The blade angle of a constant speed propeller ?

Question 27-14 : Increases with increasing true air speed only varies with engine rpm decreases with increasing true air speed is independent of the true air speed

When it refers to blade angle it refers to the angle between the chord line and the direction of propeller rotation .the important bit in this question is that it is a constant speed prop you are correct in that the angle of attack does decrease as forward speed increases and so the thrust decreases as well .therefore the rpm would increase the csu would sense the increase in rpm and would then increase the blade angle to reduce the rpm down to the correct speed and restore the lost thrust exemple 179 increases with increasing true air speed.increases with increasing true air speed.

A propeller blade is twisted so as to ?

Question 27-15 : Keep the local angle of attack constant along the blade avoid the appearance of sonic phenomena decrease the blade tangential velocity from the blade root to the tip allow a higher mechanical stress

The angle of attack is the angle between the blade chord line and the relative airflow trouble is the relative airflow is different along the blade the blade is rotating so the bit nearest the hub has a small speed at right angles to the way the aircraft is going but the bit near the tip is moving rapidly across the aircraft flight path.to put real numbers on to this a 10 ft blade doing 3000rpm will have a tip speed of about 300mph so if the aircraft is going forward at 300mph the relative airflow is hitting the tip at 45deg off the aircraft centre line.thus if you want the tip to have the same angle of attack as the root you have to twist the blade by 45deg along its length.the speed past the tip will now be more like 440mph in total so if the angle of attack and the chord length were the same you would get a lot more lift thrust out toward the tip.but the only reason why you might not want the extra thrust is because it might bend the blade and if that worries you you can taper the blade reducing the chord length.blade design is always a compromise but if you want best efficiency least fuel consumption in the cruise you will twist the blade so all sections reach their most efficient angle of attack at the same time exemple 183 keep the local angle of attack constant along the blade.keep the local angle of attack constant along the blade.

A pilot can actuate the feathering system by ?

Question 27-16 : Pulling the propeller control lever rearwards pushing the propeller control lever forwards pulling the power levers rearwards pushing the power lever forwards

884.by pulling the propeller control lever fully rearwards you will feather the propeller to minimize drag in the event of an engine failure for example in normal flight you will pull or push the propeller control lever to adjust the blade pitch for the different phases of the flight climb cruise and descent . 885 exemple 187 pulling the propeller control lever rearwards.pulling the propeller control lever rearwards.

When increasing true airspeed with a constant engine rpm the angle of attack of ?

Question 27-17 : Reduces increases stays constant stays constant because it only varies with engine rpm

With fixed propellers the throttle controls rpm .variations in forward speed affect the angle of attack which varies in line with the amount of airflow into the propeller disc if you increase speed the angle of attack reduces and if you slow down it increases affecting the lift/drag ratio meaning that a fixed pitch propeller gets less efficient as you move away from its optimum speed which is usually set for cruise exemple 191 reduces.reduces.

A pressure relief valve in an oil system that does not seat correctly could ?

Question 27-18 : Low oil pressure high oil pressure low oil temperature excessive oil consumption

To prevent too high a pressure a pressure release valve prv is fitted it comprises a stainless steel ball bearing and a spring .the ball is forced by the spring against an oil port when the oil pressure is sufficiently high the ball if forced off its seat and oil is allowed to bypass this restriction thus making sure that the pressure never gets too high .if the pressure relief valve is not hermetic there will be a leak and the pressure decreases exemple 195 low oil pressure.low oil pressure.

In case of engine failure during flight the blades of a constant speed ?

Question 27-19 : Move in the lowest pitch position by the centrifugal force and/or the spring force move in low pitch position by oil pressure created by the windmilling propeller move in a certain pitch position depending on windmilling rpm move in the highest pitch position by the aerodynamic force

In the event of a problem causing the engine to stop the propeller goes to minimum pitch in order to reduce drag and permits the pilot to try to restart the engine if possible with less drag you will have less propeller torque allowing a windmilling start a constant speed propeller system will make use of the centrifugal force oil or gas pressure or a spring to reduce the pitch exemple 199 move in the lowest pitch position by the centrifugal force and/or the spring force.move in the lowest pitch position by the centrifugal force and/or the spring force.

For take off the correct combination of propeller pitch 1 and propeller lever ?

Question 27-20 : 1 low 2 forward 1 high 2 forward 1 low 2 aft 1 high 2 aft

Pushing the propeller control lever fully forward selects max rpm in order to achieve this the propeller goes to a fine pitch this is also called low pitch high pitch would be a coarse pitch position . 884 exemple 203 (1) low (2) forward.(1) low (2) forward.

For piston engines mixture ratio is the ratio between the ?

Question 27-21 : Mass of fuel and mass of air entering the cylinder volume of fuel and volume of air entering the cylinder volume of fuel and volume of air entering the carburettor mass of fuel and volume of air entering the carburettor

exemple 207 mass of fuel and mass of air entering the cylinder.mass of fuel and mass of air entering the cylinder.

Variations in mixture ratios for carburettors are achieved by the adjustment of ?

Question 27-22 : Fuel flow air flow fuel flow air flow and temperature fuel flow and air flow

exemple 211 fuel flow.fuel flow.

As altitude increases the mixture ratio of a piston engine should be adjusted to ?

Question 27-23 : Reduce the fuel flow in order to compensate for the decreasing air density reduce the fuel flow in order to compensate for the increasing air density increase the mixture ratio increase the fuel flow in order to compensate for the decreasing air pressure and density

exemple 215 reduce the fuel flow in order to compensate for the decreasing air density.reduce the fuel flow in order to compensate for the decreasing air density.

When applying carburettor heating ?

Question 27-24 : The mixture becomes richer the mixture becomes leaner a decrease in rpm results from the lean mixture no change occurs in the mixture ratio

When you apply carburettor heating the air which will mix with fuel in the carburettor passes around the muffler or exhaust pipe in order to be heated and to avoid the risks of icing the air's density decreases as the air is heated what generates a mixture mixture richer exemple 219 the mixture becomes richer.the mixture becomes richer.

When the pilot moves the mixture lever of a piston engine towards a lean ?

Question 27-25 : Amount of fuel entering the combustion chamber is reduced volume of air entering the carburettor is reduced amount of fuel entering the combustion chamber is increased volume of air entering the carburettor is increased

exemple 223 amount of fuel entering the combustion chamber is reduced.amount of fuel entering the combustion chamber is reduced.

When altitude increases without adjustment of the mixture ratio the piston ?

Question 27-26 : A decrease of air density with a fuel flow which becomes too high an increase of air density with a fuel flow which becomes too high an increase of air density with a fuel flow which becomes too low a decrease of air density with a fuel flow which becomes too low

exemple 227 a decrease of air density with a fuel flow which becomes too high.a decrease of air density with a fuel flow which becomes too high.

A rich mixture setting has to be used during climb segments this results in a ?

Question 27-27 : Lower cylinder head temperature higher efficiency increase of power higher torque

To obtain the best torque during climb you will have to decrease fuel entering in the carburettor in order to compensate the decreasing of the air density.a rich mixture will not permit to deliver the best available power but it permits a lower cylinder head temperature exemple 231 lower cylinder head temperature.lower cylinder head temperature.

Maximum exhaust gas temperature egt of a piston engine is theoretically ?

Question 27-28 : Fuel to air ratio of 1 15 cruising mixture setting full rich setting mixture ratio very close to idle cut out

Egt is relative to the temperature of the charge as it burns within the cylinder cht measures the temperature of the engine cylinder.the highest egt is achieved at a ratio of 15 parts of air to one part of fuel.if the ratio is reduced ie rich the charge temperature reduces due to excess fuel being left in the cylinder if the ratio is greater than 15 1 ie lean or weak the charge is cooled by excess air to appreciate why cht increases with lean mixtures we must consider the speed at which the fuel burns ie its flame rate lean mixtures burn slower than rich mixtures this means more heat is transferred to the engine components with lean mixtures.example if you move a lighted match quickly under you hand no problem but move it slowly and you will burn your hand slow burning lean mixtures will increase cht exemple 235 fuel to air ratio of 1:15.fuel to air ratio of 1:15.

For a given type of oil the oil viscosity depends on the ?

Question 27-29 : Oil temperature outside pressure oil pressure quantity of oil

exemple 239 oil temperature.oil temperature.

The fuel temperature at which under standard conditions the vapour ignites in ?

Question 27-30 : Flash point fire point combustion point self ignition point

Pre ignition refers to the condition that may arise when ?

Question 27-31 : The mixture is ignited by abnormal conditions within the cylinder before the spark occurs at the plug the mixture is ignited before the piston has reached top dead centre a rich mixture is ignited by the sparking plugs the sparking plug ignites the mixture too early

exemple 247 the mixture is ignited by abnormal conditions within the cylinder before the spark occurs at the plugthe mixture is ignited by abnormal conditions within the cylinder before the spark occurs at the plug

A fuel strainer fuel filter when fitted to a carburettor will be positioned ?

Question 27-32 : Upstream of the needle valve between the needle valve and the metering jet between the metering jet and the discharge nozzle downstream of the discharge nozzle

A fuel strainer is a fuel filter .the fuel need to be filtered before entering the carburettor . 887 exemple 251 upstream of the needle valve.upstream of the needle valve.

The working cycle of a four stroke engine is ?

Question 27-33 : Induction compression power exhaust induction power compression exhaust induction compression expansion power compression induction power exhaust

exemple 255 induction, compression, power, exhaust.induction, compression, power, exhaust.

Specific fuel consumption is defined as the ?

Question 27-34 : Mass of fuel required to produce unit power for unit time maximum fuel consumption of the aircraft designed fuel consumption for a given rpm quantity of fuel required to run the engine for one minute at maximum operating conditions

exemple 259 mass of fuel required to produce unit power for unit time.mass of fuel required to produce unit power for unit time.

The purpose of the contact breaker is to ?

Question 27-35 : Control the primary circuit of the magneto connect the secondary coil to the distributor connect the battery to the magneto connect the contact breaker and condenser in series with the primary coil

exemple 263 control the primary circuit of the magneto.control the primary circuit of the magneto.

Under normal running conditions a magneto draws primary current ?

Question 27-36 : From a self contained electro magnetic induction system from the booster coil from the aircraft batteries via an inverter directly from the aircraft batteries

exemple 267 from a self-contained electro-magnetic induction system.from a self-contained electro-magnetic induction system.

The air in a piston engine turbo supercharger centrifugal compressor ?

Question 27-37 : Enters the eye of the impeller and leaves at a tangent to the periphery enters via the diffuser and is fed to the impeller at the optimum angle of attack enters at the periphery and leaves via the eye of the impeller enters at a tangent to the rotor and leaves via the stator

889.. 890.the air in a piston engine turbo supercharger centrifugal compressor enters the eye of the impeller and leaves at a tangent to the periphery exemple 271 enters the eye of the impeller and leaves at a tangent to the periphery.enters the eye of the impeller and leaves at a tangent to the periphery.

The power of a piston engine which will be measured by a friction brake is ?

Question 27-38 : Brake horse power frictional horse power heat loss power indicated horse power

exemple 275 brake horse power.brake horse power.

The power output of a piston engine can be calculated by ?

Question 27-39 : Torque times rpm work times velocity force times distance pressure times arm

exemple 279 torque times rpm.torque times rpm.

The power of a piston engine decreases during a climb with a constant power ?

Question 27-40 : Air density engine temperature humidity temperature

Howarthson .note in this question 'with a constant power lever setting' so as you climb the power will be decreasing because the air is becoming less dense so manifold absolute pressure will be decreasing exemple 283 air density.air density.

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