.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.
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 tank..2. dump the unusable fuel..3. adjust fuel distribution.4. to transfer fuel from one tank to another located in the same wing.the 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 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.
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 = 6000/60 x pole pairs..pole pairs = 4.
Question 39-7 : In an ac power generation system, the constant speed drive csd..1 can be disconnected from the engine shaft.2 can be disconnected from the generator.3 is a hydro mechanical system.4 is an electronic system.5 can not be disconnected in flight.6 can be disconnected in flight..the combination ?
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 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.
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 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.
Question 39-11 : On the ground, the auxiliary power unit apu can provide..1 electricity.2 air for starting system.3 hydraulic pressure.4 air for air conditioning..the 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 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.
Question 39-12 : A thermal circuit breaker ?
Protects the system in the event of overload/overheating.
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 connection.2 high starting torque.3 flexibility in use.4 lighter weight of equipment.5 easy to convert into direct current.6 easy maintenance of machines..the 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 runaway.2 high internal resistance, hence higher power.3 good charging and discharging capability at high rating.4 wider permissible temperature range.5 good storage capability.6 ?
3, 4, 5, 6.
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.
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 ac...dc to ac inverter..ac 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 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.
Question 39-22 : A relay is ?
A magnetically operated switch.
Question 39-23 : The voltage of a fully charged lead acid battery cell is ?
2.2 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 ?
Increase 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.
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 and/or 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 input/output 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°.
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