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Knowledge > EASA : Low frequency vibration in the vertical plane which is only apparent in high ?

Question 39-1 : Badly adjusted tab on the main rotor blade badly adjusted rod on the main rotor blade mass imbalance of the main rotor mass imbalance of the tail rotor

exemple 139 badly adjusted tab on the main rotor blade.badly adjusted tab on the main rotor blade.

Low frequency vibration in a plane parallel to the rotor plane is likely to be ?

Question 39-2 : An out of balance main rotor an out of balance tail rotor an engine problem a transmission problem

exemple 143 an out-of-balance main rotor.an out-of-balance main rotor.

Erosion strips fitted to the leading edge of rotor blades are usually ?

Question 39-3 : Nickel titanium or stainless steel aluminium titanium or stainless steel aluminium nickel or titanium tungsten nickel or stainless steel

exemple 147 nickel, titanium or stainless steel.nickel, titanium or stainless steel.

Dynamic balancing of main rotor systems ?

Question 39-4 : Is usually achieved by adding or subtracting weights to either the main rotor blade attachment pins or to the main rotor head itself is usually achieved by adding weights to certain nominated rotor blades only is usually achieved by adding or subtracting weights to the main rotor blade tips is not necessary as the hub and blades are statically balanced at manufacture

exemple 151 is usually achieved by adding or subtracting weights to either the main rotor blade attachment pins or to the main rotor head itself.is usually achieved by adding or subtracting weights to either the main rotor blade attachment pins or to the main rotor head itself.

During a flight under normal conditions a main rotor blade is seen to be flying ?

Question 39-5 : Adjusting the trim tabs on the subject blade lengthening the pitch change rod on the subject blade shortening the pitch change rod on the subject blade adjusting the weights on the blade tip

exemple 155 adjusting the trim tabs on the subject blade.adjusting the trim tabs on the subject blade.

Tail rotor blade hinges arranged with a ''delta three'' hinge effect ?

Question 39-6 : Decrease their pitch angle with flap up increase the lift of the blade with flap up decrease their pitch angle with blade dragging increase their pitch angle with flap up

exemple 159 decrease their pitch angle with flap up.decrease their pitch angle with flap up.

Adjusting an outboard blade tab upwards will produce a ?

Question 39-7 : Nose up moment on the blade nose down moment on the blade medium frequency vibration in flight high frequency vibration in flight

exemple 163 nose up moment on the blade.nose up moment on the blade.

A rotor blade trim tab provides a corrective force ?

Question 39-8 : Indirectly by causing the pitch angle to change thus altering blade lift in the appropriate sense by varying blade drag so repositioning the blade in azimuth relative to other blade s directly by its displacement causing the blade to track in the correct plane indirectly by adjusting the centre of gravity of the blade longitudinally thus causing the blade to track in the correct plane

exemple 167 indirectly, by causing the pitch angle to change, thus altering blade lift in the appropriate sense.indirectly, by causing the pitch angle to change, thus altering blade lift in the appropriate sense.

A rotor blade running out of track produces ?

Question 39-9 : A vertical vibration once per revolution a lateral vibration once per revolution a vertical vibration four times per revolution in a four bladed rotor system a lateral vibration three and five times per revolution in a four bladed rotor system

exemple 171 a vertical vibration once per revolution.a vertical vibration once per revolution.

Wind gusts have a greater adverse effect on ?

Question 39-10 : Semi rigid rotors due to their see saw flapping rigid rotors due to the lack of a flapping hinge fully articulated rotors as the gust will cause the blade to flap thus altering the pitch angle fully articulated rotors as the flapping blades will induce vibration

exemple 175 semi-rigid rotors due to their see-saw flapping.semi-rigid rotors due to their see-saw flapping.

The epr engine pressure ratio is computed by ?

Question 39-11 : Dividing turbine discharge pressure by compressor inlet pressure dividing compressor discharge pressure by turbine discharge pressure multiplying compressor inlet pressure by turbine discharge pressure multiplying compressor discharge pressure by turbine inlet pressure

911.it is engine thrust in term of epr exemple 179 dividing turbine discharge pressure by compressor inlet pressure.dividing turbine discharge pressure by compressor inlet pressure.

A thermocouple type thermometer consists of ?

Question 39-12 : Two metal conductors of different type connected at two points two metal conductors of the same type connected at two points a single wire coil a wheatstone bridge connected to a voltage indicator

exemple 183 two metal conductors of different type connected at two points.two metal conductors of different type connected at two points.

One of the disadvantages of an electronic tachometer is the ?

Question 39-13 : Necessity of a power supply generation of spurious signals at the commutator influence of temperature on the indication high influence of line resistance on the indication

exemple 187 necessity of a power supply.necessity of a power supply.

The principle of capacity gauges is based on the capacitance variation of ?

Question 39-14 : A capacitor with the type of dielectric two dissimilar metals joined together at their ends two dissimilar metals joined together at one end only liquids with the variations in temperature

.a capacitance type fuel gauge system consists of a variable capacitor located in the fuel tank an amplifier and an indicator. the complete circuit forms an electrical bridge which is continuously being rebalanced as a result of the differences between the capacitances of the tank capacitor and a reference capacitor. the signal produced due to the differences in the signals is amplified to operate a motor. the motor then drives the pointer to indicate the capacitance change of the tank capacitor and thus change in the fuel quantity is indicated..we have seen the basic construction of this system now let us discuss how the electrical capacitance principle is utilized for the capacitance type fuel gauge system in aircraft. the capacitors which are to be installed in the fuel tanks for the fuel quantity measurement must be different in construction from those normally employed in electrical equipment. the plates of the capacitors take the form of two tubes mounted concentrically with a narrow air space between them these plates extend the full depth of a fuel tank..capacitance depends on some factors which are area of the plates distance between the two plates and the dielectric constant of the material between the two plates of the capacitors .now in this capacitance type fuel gauge system the two factors plate area and distance between plates are fixed and the dielectric here is the fuel in the tank of the aircraft. the flow of a momentary current into a capacitor establishes a potential difference across its plates. the dielectric i e fuel in the aircraft's fuel tanks contains no free electrons so the current cannot flow through it but it should be remembered that potential difference sets up a state of stress in the atoms comprising it exemple 191 a capacitor with the type of dielectric.a capacitor with the type of dielectric.

A synchroscope is used on aircraft to ?

Question 39-15 : Set several engines to the same speed reduce the vibration of each engine reduce the rpm of each engine achieve optimum control of on board voltages

On a multi engined aircraft a synchronizing system ensures the propeller speeds are all the same this is achieved by an electrical system that compares speed signals from engine mounted generators out of balance signals using one engine as a master signal are automatically corrected by electrically trimming the engine speeds until all signals are equal exemple 195 set several engines to the same speed.set several engines to the same speed.

The 'bourdon tube' is used to measure ?

Question 39-16 : Pressure temperature quantity a flow rate

exemple 199 pressure.pressure.

If a manifold pressure gauge consistently registers atmospheric pressure the ?

Question 39-17 : Leak in pressure gauge line too high float level fuel of too low volatility ice in induction system

exemple 203 leak in pressure gauge line.leak in pressure gauge line.

A manifold pressure gauge of a piston engine measures ?

Question 39-18 : Absolute pressure in intake system near the inlet valve vacuum in the carburettor fuel pressure leaving the carburettor absolute airpressure entering the carburettor

exemple 207 absolute pressure in intake system near the inlet valve.absolute pressure in intake system near the inlet valve.

In an engine vibration monitoring system for a turbojet any vibration produced ?

Question 39-19 : Amplified and filtered before being fed to the cockpit indicator inversely proportional to engine speed directly proportional to engine speed fed directly to the cockpit indicator without amplification or filtering

.vibrations are picked up by accelerometers so you measure accelerations piezzo electric or capacity type pickups giving after conversion displacement / square second .a first integration will give displacement speed displacement per second a second integration will give displacement .each integration may introduce or amplify measurement errors but the initial acceleration signal is not practical for use depending on the engine type and the bearing location the displacement speed usually noted in inch per second ips is used .the vibration frequency is filtered for the cockpit indication to indicate only vibration in a frequency band corresponding to the spool speed n1 n2 n3 that's why engines can have vibrations which are not related to spools rotating speed not being indicated in the cockpit exemple 211 amplified and filtered before being fed to the cockpit indicator.amplified and filtered before being fed to the cockpit indicator.

According to the range of pressure to be measured low medium high different ?

Question 39-20 : 3 1 and 2 2 1 and 3 1 2 and 3 3 2 and 1

exemple 215 3, 1 and 2.3, 1 and 2.

A vibration indicator receives a signal from different sensors accelerometers ?

Question 39-21 : Vibration amplitude at a given frequency vibration frequency expressed in hz vibration period expressed in seconds acceleration measured by the sensors expressed in g

exemple 219 vibration amplitude at a given frequency.vibration amplitude at a given frequency.

The transmitter of rpm indicator may consist of.1 a magnetic sensor supplying ?

Question 39-22 : 1 2 3 4 1 2 3 2 3 4 1 4

.statement 1 it refers to a permanent magnet that is coupled to the engine and as it rotates within a 3 phase stator the resulting 3 phase ac supply drives a 3 phase ac synchronous motor that rotates a drag cup around a permanent magnet the magnet rotates against a hairspring and indicates the rpm.statement 2 it refers to a device that converts ac signals into dc that drives a dc motor the output is then compared to a dc reference output and the difference indicates the rpm.statement 3 it refers to a device that is used on some jet engine aircraft to sense the shaft speed of the lp compressor during the engine start up cycle it uses a single ac phase of a normal tachogenerator to show that the shaft is rotating and is automatically isolated after the start cycle has been successfully completed.statement 4 it refers to a direct drive 3 phase ac generator that is operated in conjunction with a 3 phase ac synchronous motor to indicate the rpm exemple 223 1, 2, 3, 4.1, 2, 3, 4.

The indication of a fuel float gauge varies with. 1 pitch attitude. 2 ?

Question 39-23 : 1 2 3 1 3 1 2 2 3

.in 1904 the first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on the outside of the fuel tank to indicate the fuel level .idea was taken one step further when vehicles started to get better electrical systems by connecting the hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in the vehicle's dashboard and that's the basic operating principle that's still in use today.but airplane attitude and accelerations will affect the accuracy of the indication due to the movements of the fuel in the tank temperature will modify the volume thus the indication exemple 227 1, 2, 3.1, 2, 3.

If the tanks of your aircraft only contain water the capacitor gauges indicate ?

Question 39-24 : A mass of water different from zero but inaccurate the exact mass of water contained in the tanks a mass equal to zero a mass equal to the mass of a same volume of fuel

exemple 231 a mass of water different from zero, but inaccurate.a mass of water different from zero, but inaccurate.

The float type fuel gauges provide information on ?

Question 39-25 : Volume whose indication varies with the temperature of the fuel volume whose indication is independent of the temperature of the fuel mass whose indication varies with the temperature of the fuel mass whose indication is independent of the temperature of the fuel

exemple 235 volume whose indication varies with the temperature of the fuel.volume whose indication varies with the temperature of the fuel.

The sensors used to measure the exhaust gas temperature on an aircraft equipped ?

Question 39-26 : Thermocouples based on metallic parts whose expansion/contraction is measured based on metallic conductors whose resistance increases linearly with temperature capacitors whose capacity varies proportionally with temperature

.a thermocouple type thermometer consists of two metal conductors of different type connected at two points the operating principle of a thermocouple is a conductor that is subject to a thermal gradient generates a voltage.this voltage is measured and interpreted by a thermocouple thermometer millivoltmeter exemple 239 thermocouples.thermocouples.

The measurement of the turbine temperature or of the tgt turbine gas ?

Question 39-27 : High pressure turbine outlet combustion chamber outlet combustion chamber intake high pressure chamber intake

.a thermocouple type thermometer is located between the hp turbine and lp turbine allowing the measurement of the turbine temperature

The two main sources of information used to calculate turbojet thrust are the ?

Question 39-28 : Fan rotation speed or n1 or the epr engine pressure ratio high pressure turbine rotation speed or the epr engine pressure ratio fan rotation speed or n1 or the total pressure at the high pressure compressor outlet fan rotation speed or n1 or the total pressure at the low pressure turbine outlet

exemple 247 fan rotation speed (or n1) or the epr (engine pressure ratio).fan rotation speed (or n1) or the epr (engine pressure ratio).

The advantages of an 'electric' fuel float gauge are.1 easy construction.2 ?

Question 39-29 : 1 1 2 3 4 5 2 3 4 5 2 3 4

.in 1904 the first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on the outside of the fuel tank to indicate the fuel level .idea was taken one step further when vehicles started to get better electrical systems by connecting the hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in the vehicle's dashboard and that's the basic operating principle that's still in use today.but airplane attitude and accelerations will affect the accuracy of the indication due to the movements of the fuel in the tank temperature will modify the volume thus the indication exemple 251 1.1.

The disadvantages of an 'electric' fuel float gauge are. 1 the design is ?

Question 39-30 : 2 3 4 1 1 2 3 4 2 3 4 5

exemple 255 2, 3, 4.2, 3, 4.

On an electronic flight instrument system efis the following fuel flow ?

Question 39-31 : 1 1 2 1 2 3 1 3

An efis displays fuel flow to engine it displays also fuel used since last reset fuel flow is usually shown in kilograms per hour exemple 259 1.1.

The aircraft outside air temperature 'probe' measures the ?

Question 39-32 : 'total' air temperature minus kinetic heating effects in order to obtain the static temperature 'static' air temperature minus kinetic heating effects in order to obtain the total temperature 'total' air temperature minus compressibility effects in order to obtain the static temperature 'static' air temperature minus compressibility effects in order to obtain the total temperature

.this question has been seen in july 2022 with this correct answer . total air temperature this must be corrected for ram rise and recovery factor to obtain the static air temperature .the other wrong answers remain unchanged exemple 263 'total' air temperature minus kinetic heating effects in order to obtain the static temperature.'total' air temperature minus kinetic heating effects in order to obtain the static temperature.

A millivoltmeter measuring the electromotive force between the 'hot junction' ?

Question 39-33 : Cold junction is maintained constant hot junction is maintained constant cold junction is maintained at 15 °c hot junction is maintained at 15 °c

exemple 267 cold junction is maintained constant.cold junction is maintained constant.

The gauge indicating the quantity of fuel measured by a capacity gauging system ?

Question 39-34 : Twice that of air and varies directly with density the same as that of air and varies directly with density twice that of air and varies inversely with density the same as that of air and varies inversely with density

.the dielectric constant or permittivity of fuel is determined by establishing the ratio of the electrical capacitance of a tank filled with fuel as compared with the electrical capacitance of the tank when filled with air measurements of the dielectric constant of a fuel at various temperatures show that the dielectric constant is a linear function of temperature decreasing with increasing temperature and varying with the applied frequency .dielectric of air at 70°f = 0 85 .dielectric of jet fuel at 70°f = 1 7 exemple 271 twice that of air and varies directly with density.twice that of air and varies directly with density.

When compared with the volumetric fuel flowmeter the mass fuel flowmeter takes ?

Question 39-35 : Density temperature pressure turbulent flow in the line

.the mass fuel flow meter allows the measurement of the mass consumption of fuel the mass fuel flowmeter takes into account the fuel density exemple 275 density.density.

The electronic tachometer sensor is composed of ?

Question 39-36 : A notched wheel rotating in front of an electro magnet a circular magnet with four poles the rotor of a single phase a c generator the rotor of a three phase a c generator

exemple 279 a notched wheel rotating in front of an electro-magnet.a notched wheel rotating in front of an electro-magnet.

The advantages of a d c generator tachometer are . 1 easy transmission of the ?

Question 39-37 : 1 2 2 3 1 2 3 1 3

.d c generator tachometer consists of a small armature which is coupled to the machine whose speed is to be measured this armature revolves in the field of a permanent magnet the electro magnetic force emf generated is proportational to the product of flux and speed since the flux of the permanent magnet is constant the voltage generated is proportational to speed .the polarity of output voltage indicates the direction of rotation this electro magnetic force emf is measured with the help of moving coil voltmeter having a uniform scale and calibrated directly in terms of speed .but d c generator tachometer has a dc commutator ring which causes spurious signals exemple 283 1, 2.1, 2.

The advantages of single phase a c generator tachometer are.1 the suppression ?

Question 39-38 : 1 3 1 2 3 4 2 3 4 2 4

.the single phase ac generator tachometer doesn't have a dc commutator ring thus no spurious signals .the measurement is independent of aircraft power supply exemple 287 1, 3.1, 3.

The disadvantages of a single phase a c generator tachometer are . 1 the ?

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

.the single phase ac generator tachometer is brushless thus no spurious signals .the measurement is independent of aircraft power supply but one disadvantage of a single phase ac generator is the possibility of the values transmitted being affected by line resistance exemple 291 2.2.

Torque can be determined by measuring the ?

Question 39-40 : Oil pressure at the fixed crown of an epicycloidal reducer of the main engine gearbox frequency of an impulse tachometer attached to a transmission shaft quantity of light passing through a rack wheel attached to a transmission shaft phase difference between 2 impulse tachometers attached to a transmission shaft

.operating principle of a epicyclic reducer with fixed crown . 994.input drive is applied to a central or sun gear 1 by which three or more pinions or planet gears 2 are set in rotation these in turn rotate in mesh with the internal teeth of a fixed crown fixed ring gear 3 .the shafts of the planet gears 4 mounted to a planet carrier 5 are translated along a circumferential trajectory and made thus to revolve around the sun gear the result is that the planet carrier 5 to which the output assembly is mounted shaft bearings seals etc rotates at a lower speed than that of the sun gear 1 .torque can be determined by measuring the oil pressure at the fixed crown of an epicycloidal reducer of the main engine gearbox exemple 295 oil pressure at the fixed crown of an epicycloidal reducer of the main engine gearbox.oil pressure at the fixed crown of an epicycloidal reducer of the main engine gearbox.

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