Question 39-1 : The primary input signals for a hydro mechanical gas turbine engine fuel control system include ? [ Knowledge EASA ]

Question 39-2 : The primary reason for venting an engine oil tank is to ?

Prevent excessive pressure in the tank.

Question 39-3 : The cross feed fuel system can be used to 1 feed any engine from any fuel tank2 dump the unusable fuel3 adjust fuel distribution4 to transfer fuel from one tank to another located in the same wingthe combination that regroups all of the correct statements is ?

1 3.

Using crossfeed an engine can draw fuel from a fuel tank located in the opposite wingon 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

Question 39-4 : If one of the 12 cells of a lead acid battery is dead the battery ?

Is unserviceable.

Question 39-5 : When the ac generators are connected in parallel the reactive loads are balanced by means of the ?

Energizing current.

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

Question 39-6 : In order to produce an alternating voltage of 400 hz the number of pairs of poles required in an ac generator running at 6000 rpm is ?

4 pairs.

400 = 600060 x pole pairspole pairs = 4

Question 39-7 : In an ac power generation system the constant speed drive csd 1 can be disconnected from the engine shaft2 can be disconnected from the generator3 is a hydro mechanical system4 is an electronic system5 can not be disconnected in flight6 can be disconnected in flightthe combination regrouping ?

1 3 6.

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 gearboxthe disconnect is there for the purpose of isolating a hydromechanical unit ie it might either be leaking oil overheating or causing the load sharing system to do oddball thingsif you operate the disconnect it will dump the generator via the csd ie the rotational input from the engine gearbox is removed and resolves the oil leakproblem

Question 39-8 : An inverter is a ?

Unit used to convert dc into ac.

Question 39-9 : In an aircraft electrical system where ac generators are not paralleled mounted the changeover relay allows ?

Power supply to the faulty ac generators 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

Question 39-10 : Pulling the fire shutoff handle causes a number of devices to disconnect in respect of the ac generator it can be said that the ?

Exciter control relay and the generator breaker open.

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 thingan exciter breaker exciter control relay will isolate the power to the voltage regulatorthe generator breaker will isolate the generator from the bus barthe tie breaker will isolate two different bus bars from each other or can connect two generators to the same bus barin 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 generatorif 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

Question 39-11 : On the ground the auxiliary power unit apu can provide 1 electricity2 air for starting system3 hydraulic pressure4 air for air conditioningthe combination which regroups all of the correct statements is ?

1 2 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 enginesapus 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 checksfor 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

Question 39-12 : A thermal circuit breaker ?

Protects the system in the event of overloadoverheating.

Question 39-13 : The auxiliary power unit apu has its own ac generator that ?

Supplies the aircraft with three phase 115 200 v 400 hz ac.

Question 39-14 : A magnetic circuit breaker is ?

A protection system that has a quick tripping response.

Question 39-15 : The advantages of alternating current on board an aircraft are 1 simple connection2 high starting torque3 flexibility in use4 lighter weight of equipment5 easy to convert into direct current6 easy maintenance of machinesthe combination of correct statements is ?

3 4 5 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

Question 39-16 : On board present aircraft the batteries used are mainly cadmium nickel their advantages are 1 low risk of thermal runaway2 high internal resistance hence higher power3 good charging and discharging capability at high rating4 wider permissible temperature range5 good storage capability6 ?

3 4 5 6.

The terminal voltage remains substantially constant at about 12 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 voltagenicad batteries have a low thermal capacity the heat generated in certain conditions is faster than it can dissipate so causing rapid increase in temperaturethis 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

Question 39-17 : A static inverter is powered by ?

Direct current on input alternating current output.

An inverter is a unit used to convert dc into acdc to ac inverterac to dc rectifier

Question 39-18 : The voltage regulator of a dc generator is connected in ?

Series with the shunt field coil.

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

Question 39-19 : During start of an engine fitted with a brushless ac generator with no commutator rings the generator is activated by ?

A set of permanent magnets.

Question 39-20 : The type of windings commonly used in dc starter motors are ?

Series 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

Question 39-21 : The power output of a generator is controlled by ?

Varying the field strength.

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 regulatorthe 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

Question 39-22 : A relay is ?

A magnetically operated switch.

Question 39-23 : The voltage of a fully charged lead acid battery cell is ?

22 volts.

Question 39-24 : The capacity of a battery is given in ?

Ampere hours.

Question 39-25 : A relay is ?

An electromagnetically operated switch.

Question 39-26 : The most widely used electrical frequency in aircraft is ?

400 hz.

Question 39-27 : If the electrical load of an ac generator providing a constant output voltage increases the voltage regulator will ?

Question 39-28 : The so called 'hot buses' or 'direct buses' are ?

Directly connected to the battery.

Question 39-29 : The reason for using inverters in an electrical system is ?

To change dc into ac.

Question 39-30 : The function of a constant speed drive csd is to ensure ?

That the generator produces a constant frequency.

Question 39-31 : A bus bar is ?

A distribution point for electrical power.

Question 39-32 : A csd of an ac generator may be disconnected in flight the primary reason s for disconnection are ?

Low oil pressure andor high oil temperature of the generator drive.

Question 39-33 : A csd unit which has been disconnected in flight ?

May be reset on the ground only after engine shut down.

Question 39-34 : Because of the inputoutput relationship of an or gate it is often referred to as the ?

'any' or 'all' gate.

Question 39-35 : Connecting two 12 volt 40 ampere hour capacity batteries in series will result in a total voltage and capacity respectively of ?

24 volts 40 ampere hours.

Question 39-36 : When a conductor cuts the flux of a magnetic field ?

An electromotive force emf is induced in the conductor.

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

Question 39-37 : In order that dc generators will achieve equal load sharing when operating in parallel it is necessary to ensure that ?

Their voltages are almost equal.

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

Question 39-38 : The purpose of a voltage regulator is to control the output voltage of the ?

Generator at varying loads and speeds.

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

Question 39-39 : A current limiter fuse in a dc generation system is used to ?

Allow a short term overload before rupturing.

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

Question 39-40 : A 3 phase ac generator has 3 separate stator windings spaced at ?

120°.