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Apu fuel can be provided by ? [ Knowledge EASA ]

Question 39-1 : Any ac fuel pump supplying fuel to the left fuel manifold or by the left main tank dc fuel pump the dc fuel pump the left forward ac fuel pump only by ac fuel pumps in the left main tank

Cqb 15 september 2011 exemple 139 Any ac fuel pump supplying fuel to the left fuel manifold or by the left main tank dc fuel pump.Any ac fuel pump supplying fuel to the left fuel manifold or by the left main tank dc fuel pump.

The primary input signals for a hydro mechanical gas turbine engine fuel ?

Question 39-2 : N2 compressor discharge pressure compressor inlet temperature fuel shut off thrust lever angle n1 n2 bypass ratio fuel shut off thrust lever angle n2 bypass ratio epr fuel shut off thrust lever angle n2 turbine inlet temperature fuel shut off generator thrust lever angle

.fitted within the hp fuel pump is a 'hydro mechanical governor' which uses hydraulic pressure proportional to engine speed as its controlling parameter .this system uses n2 compressor discharge pressure compressor inlet temperature fuel shut off thrust lever angle as primary input signals exemple 143 N2, compressor discharge pressure, compressor inlet temperature, fuel shut-off, thrust lever angle.N2, compressor discharge pressure, compressor inlet temperature, fuel shut-off, thrust lever angle.

The primary reason for venting an engine oil tank is to ?

Question 39-3 : Prevent excessive pressure in the tank prevent overflow allow for expansion of hot oil cool the oil

exemple 147 Prevent excessive pressure in the tank.Prevent excessive pressure in the tank.

The cross feed fuel system can be used to .1 feed any engine from any fuel tank ?

Question 39-4 : 1 3 1 4 2 3 2 4

.using crossfeed an engine can draw fuel from a fuel tank located in the opposite wing .on most multi engine airplanes operation in the crossfeed mode is an emergency procedure used to extend airplane range and endurance in one engine inoperative flight there are a few models that permit crossfeed as a normal fuel balancing technique in normal operation fuel distribution adjustment exemple 151 1, 3.1, 3.

If one of the 12 cells of a lead acid battery is dead the battery ?

Question 39-5 : Is unserviceable has 1/12 less voltage but can still be used has 1/12 less capacity but can still be used has 1/12 less voltage and less capacity but can still be used

exemple 155 Is unserviceable.Is unserviceable.

When the ac generators are connected in parallel the reactive loads are ?

Question 39-6 : Energizing current frequency voltage torque of the constant speed drive csd

The energising current is the current that controls the voltage regulator so it will control the voltage to balance the reactive loads exemple 159 Energizing current.Energizing current.

In order to produce an alternating voltage of 400 hz the number of pairs of ?

Question 39-7 : 4 pairs 8 pairs 12 pairs 24 pairs

400 = 6000/60 x pole pairs.pole pairs = 4 exemple 163 4 pairs.4 pairs.

In an ac power generation system the constant speed drive csd .1 can be ?

Question 39-8 : 1 3 6 2 3 4 1 4 5 1 2 5

The csd unit is normally integral with the generator therefore the disconnect is between the csd and the engine gearbox not between the csd and the generator therefore it's only the csd that can be disconnected from the engine gearbox .the disconnect is there for the purpose of isolating a hydromechanical unit i e it might either be leaking oil overheating or causing the load sharing system to do oddball things .if you operate the disconnect it will dump the generator via the csd i e the rotational input from the engine gearbox is removed and resolves the oil leak/problem exemple 167 1, 3, 6.1, 3, 6.

An inverter is a ?

Question 39-9 : Unit used to convert dc into ac device for reversing the polarity of the static charge static discharger filter against radio interference

exemple 171 Unit used to convert dc into ac.Unit used to convert dc into ac.

In an aircraft electrical system where ac generators are not paralleled mounted ?

Question 39-10 : Power supply to the faulty ac generators busbar connection of the ac generator to its distribution busbar connection of the ground power truck to its distribution busbar connection of the auxiliary power unit apu to its main busbar

In an ac electrical power system where the generators are not paralleled a split busbar system only one generator can supply a busbar at any given moment however one generator may supply two or more busbars should a generator fail then its busbar would not be powered the changeover relays allow a different generator to supply that busbar in addition to its own exemple 175 Power supply to the faulty ac generators busbar.Power supply to the faulty ac generators busbar.

Pulling the fire shutoff handle causes a number of devices to disconnect in ?

Question 39-11 : Exciter control relay and the generator breaker open generator breaker opens exciter control relay the generator breaker and the tie breaker open exciter control relay opens

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 179 Exciter control relay and the generator breaker open.Exciter control relay and the generator breaker open.

On the ground the auxiliary power unit apu can provide .1 electricity.2 air ?

Question 39-12 : 1 2 4 1 2 3 4 1 only 2 3 4

The primary purpose of an aircraft apu is to provide power to start the main engines turbine engines must be accelerated to a high rotational speed in order to provide sufficient air compression for self sustaining operation smaller jet engines are usually started by an electric motor while larger engines are usually started by an air turbine motor before engines are to be turned the apu is started generally by a battery once the apu is running it provides power electric or pneumatic depending on the design to start the aircraft's main engines .apus are also used to run accessories while the engines are shut down this allows the cabin to be comfortable while the passengers are boarding before the aircraft's engines are started electrical power is used to run systems for preflight checks .for information some apus are also connected to a hydraulic pump allowing crews to operate hydraulic equipment but for the learning objectives apu is not considered as a power source for hydraulic pressure exemple 183 1, 2, 4.1, 2, 4.

A thermal circuit breaker ?

Question 39-13 : Protects the system in the event of overload/overheating uses electromagnetic trip system to prevent over heating limits any overcurrent can be re engaged without any danger even if the fault remains

exemple 187 Protects the system in the event of overload/overheating.Protects the system in the event of overload/overheating.

The auxiliary power unit apu has its own ac generator that ?

Question 39-14 : Supplies the aircraft with three phase 115 200 v 400 hz ac is driven at constant speed through a constant speed drive csd in the same way as the main ac generator is excited by its generator control unit gcu as soon as the apu starts up must have the same characteristics as the main ac generator so that it can be easily coupled with the latter

exemple 191 Supplies the aircraft with three-phase 115-200 v, 400 hz ac.Supplies the aircraft with three-phase 115-200 v, 400 hz ac.

A magnetic circuit breaker is ?

Question 39-15 : A protection system that has a quick tripping response permits an overcurrent limited in time can be reset without any danger even when fault remains is a system with a slow response time

exemple 195 A protection system that has a quick tripping response.A protection system that has a quick tripping response.

The advantages of alternating current on board an aircraft are .1 simple ?

Question 39-16 : 3 4 5 6 1 2 3 4 5 6 1 2 3 5 6 1 4 6

Alternating current ac is extremely versatile and has the following advantages over direct current ac can be simply and efficiently changed from one voltage to another using a transformer ac generators are simpler in construction and lighter for the equivalent power output of a dc machine ac can be easily and efficiently changed into dc using a rectifier exemple 199 3, 4, 5, 6.3, 4, 5, 6.

On board present aircraft the batteries used are mainly cadmium nickel their ?

Question 39-17 : 3 4 5 6 3 4 6 7 2 3 4 5 6 1 2 5 6 7

The terminal voltage remains substantially constant at about 1 2 volts throughout most of the discharge due to its low internal resistance it is also capable of supply high current during its discharge cycle and low current during recharging without violent fluctuations of terminal voltage .nicad batteries have a low thermal capacity the heat generated in certain conditions is faster than it can dissipate so causing rapid increase in temperature .this has the effect of lowering the effective internal resistance thus allowing an ever increasing charging current which unless checked leads to the total destruction of the battery exemple 203 3, 4, 5, 6.3, 4, 5, 6.

A static inverter is powered by ?

Question 39-18 : Direct current on input alternating current output alternating current on input direct current on output alternating current on input alternating current on output direct current on input direct current on output

.an inverter is a unit used to convert dc into ac .dc to ac inverter .ac to dc rectifier exemple 207 Direct current on input, alternating current output.Direct current on input, alternating current output.

The voltage regulator of a dc generator is connected in ?

Question 39-19 : Series with the shunt field coil series with the armature parallel with the shunt field coil parallel with the armature

On a dc generator voltage regulation is achieved by changing the voltage in the voltage coil which changes the carbon pile pressure which changes the current in the shunt field the voltage regulator is connected in series with the shunt field coil exemple 211 Series with the shunt field coil.Series with the shunt field coil.

During start of an engine fitted with a brushless ac generator with no ?

Question 39-20 : A set of permanent magnets the main field winding the stabiliser winding jointly with the voltage regulator the auxiliary winding

exemple 215 A set of permanent magnets.A set of permanent magnets.

The type of windings commonly used in dc starter motors are ?

Question 39-21 : Series wound shunt wound series shunt wound compound wound

Dc motors are classified as to the ways in wich their field excitation circuits are arranged series wound shunt wound compound wound the series wound motors have their field and armature windings in series with each other so the same current flows through both adding them together . these motors have a high starting torque especially as in the initial stages there is little back emf so all the current is used in them they are commonly used as starter motors exemple 219 Series wound.Series wound.

The power output of a generator is controlled by ?

Question 39-22 : Varying the field strength varying the speed of the engine the reverse current relay circuit breaker varying the length of wire in the armature windings

The only practical method of controlling the output voltage of a generator is to control the strength of the magnetic field by controlling the current flow in a coil wound around the magnetic pole pieces field coil or field winding control of the current flow is achieved by a voltage regulator .the voltage regulator senses the output voltage of the generator or alternator and adjusts the field current to maintain the correct output voltage irrespective of generator speed or electrical load exemple 223 Varying the field strength.Varying the field strength.

A relay is ?

Question 39-23 : A magnetically operated switch another name for a solenoid valve a unit that is used to convert electrical energy to heat energy a device that is used to increase electrical power

exemple 227 A magnetically operated switch.A magnetically operated switch.

The voltage of a fully charged lead acid battery cell is ?

Question 39-24 : 2 2 volts 1 4 volts 1 8 volts 1 2 volts

exemple 231 2.2 volts.2.2 volts.

The capacity of a battery is given in ?

Question 39-25 : Ampere hours amperes/volts watts ohms

exemple 235 Ampere hours.Ampere hours.

A relay is ?

Question 39-26 : An electromagnetically operated switch an electrical security switch a switch specially designed for ac circuits an electrical energy conversion unit

exemple 239 An electromagnetically operated switch.An electromagnetically operated switch.

The most widely used electrical frequency in aircraft is ?

Question 39-27 : 400 hz 200 hz 50 hz 60 hz

If the electrical load of an ac generator providing a constant output voltage ?

Question 39-28 : Increase the intensity of the excitation current change the direction of the excitation current maintain the intensity of the excitation current constant decrease the intensity of the excitation current

The output is regulated by varying the current to the field windings the voltage regulator senses the alternator output and adjusts the field current when a voltage rises above a set value typically 115 5 v the current is cut off around 2000 times a second the voltage regulator is there to stop the battery being overcharged or the system being overloaded exemple 247 Increase the intensity of the excitation current.Increase the intensity of the excitation current.

The so called 'hot buses' or 'direct buses' are ?

Question 39-29 : Directly connected to the battery kept in operating conditions by an electrical resistance in the case of energy failure automatically connected to the battery if generators have failed providing an alternative current

exemple 251 Directly connected to the battery.Directly connected to the battery.

The reason for using inverters in an electrical system is ?

Question 39-30 : To change dc into ac to change the dc voltage to change ac into dc to avoid a short circuit

exemple 255 To change dc into ac.To change dc into ac.

The function of a constant speed drive csd is to ensure ?

Question 39-31 : That the generator produces a constant frequency that the starter motor maintains a constant rpm irrespective of engine acceleration/deceleration that the csd output remains at a constant rpm irrespective of generator rpm an equal ac voltage output from all generators

exemple 259 That the generator produces a constant frequency.That the generator produces a constant frequency.

A bus bar is ?

Question 39-32 : A distribution point for electrical power a device which may only be used in dc circuits the stator of a moving coil instrument a device permitting operation of two or more switches together

exemple 263 A distribution point for electrical power.A distribution point for electrical power.

A csd of an ac generator may be disconnected in flight the primary reason s for ?

Question 39-33 : Low oil pressure and/or high oil temperature of the generator drive slight variation about the normal operating frequency excessive variation of voltage and kvar illumination of the csd disconnect warning light

exemple 267 Low oil pressure and/or high oil temperature of the generator drive.Low oil pressure and/or high oil temperature of the generator drive.

A csd unit which has been disconnected in flight ?

Question 39-34 : May be reset on the ground only after engine shut down automatically resets at engine shut down automatically resets in flight providing engine rpm is below a given value may be reset in flight using the reset mechanism

exemple 271 May be reset on the ground only, after engine shut-down.May be reset on the ground only, after engine shut-down.

Because of the input/output relationship of an or gate it is often referred to ?

Question 39-35 : 'any' or 'all' gate 'all or nothing' gate 'state indicator' gate 'inhibited' or 'negated' gate

exemple 275 'any' or 'all' gate.'any' or 'all' gate.

Connecting two 12 volt 40 ampere hour capacity batteries in series will result ?

Question 39-36 : 24 volts 40 ampere hours 12 volts 80 ampere hours 12 volts 40 ampere hours 24 volts 80 ampere hours

exemple 279 24 volts, 40 ampere-hours.24 volts, 40 ampere-hours.

When a conductor cuts the flux of a magnetic field ?

Question 39-37 : An electromotive force emf is induced in the conductor there will be no effect on the conductor current will flow in accordance with flemings left hand rule the field will collapse

.when a current is passed through the wire wrapped around a conductor its magnetic field penetrates the conductor and causes the domains to turn aligning parallel to the magnetic field so their tiny magnetic fields add to the wire's field creating a large magnetic field that extends into the space around the magnet . the larger the current passed through the wire coil the more the domains align and the stronger the magnetic field is exemple 283 An electromotive force (emf) is induced in the conductor.An electromotive force (emf) is induced in the conductor.

In order that dc generators will achieve equal load sharing when operating in ?

Question 39-38 : Their voltages are almost equal equal loads are connected to each generator busbar before paralleling adequate voltage differences exist the synchronising bus bar is disconnected from the busbar system

When two dc generators are operating in parallel control of load sharing is achieved by an equalising circuit which in conjunction with the voltage regulators varies the field excitation current of the generators exemple 287 Their voltages are almost equal.Their voltages are almost equal.

The purpose of a voltage regulator is to control the output voltage of the ?

Question 39-39 : Generator at varying loads and speeds batteries at varying loads generators at varying speeds and the batteries at varying loads tru

For dc generators the voltage regulation is achieved by changing the voltage in the voltage coil which changes the carbon pile pressure which changes the current in the shunt field this then is the reactive load wasted power that adjusts the energising current the same principle applies in ac generators alternators but they use solid state circuitry exemple 291 Generator at varying loads and speeds.Generator at varying loads and speeds.

A current limiter fuse in a dc generation system is used to ?

Question 39-40 : Allow a short term overload before rupturing limit the current in the field circuit allow no overload before rupturing limit the current in the armature

A fuse is a deliberately weak part of a circuit that is designed to fail if a problems occurs current limiters are like fuses but with a much higher melting point so that a higher overload current can be carried they allow a short term overload they will limit the current to a predetermined value and are used for heavy duty circuits exemple 295 Allow a short term overload before rupturing.Allow a short term overload before rupturing.

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