Low frequency vibration in the vertical plane which is only apparent in high speed flight is due to a ?
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Other study patent: Telepilote theorique examen 39
Low frequency vibration in a plane parallel to the rotor plane is likely to be associated with ?
Erosion strips fitted to the leading edge of rotor blades are usually manufactured from the following alloys ?
Dynamic balancing of main rotor systems Is usually achieved adding or subtracting weights to either main rotor blade attachment pins or to main rotor head itself. 
During a flight under normal conditions a main rotor blade seen to be flying higher than other blades in disc during cruise this can usually be adjusted Adjusting trim tabs on subject blade. 
Tail rotor blade hinges arranged with a ''delta three'' hinge effect Decrease their pitch angle with flap up. 
Adjusting an outboard blade tab upwards will produce a Nose up moment on blade. Question 39-8
A rotor blade trim tab provides a corrective force Indirectly causing pitch angle to change thus altering blade lift in appropriate sense. Question 39-9
A rotor blade running out of track produces A vertical vibration once per revolution. Question 39-10
Wind gusts have a greater adverse effect on Semi rigid rotors due to their see saw flapping. Question 39-11
The epr engine pressure ratio computed Dividing turbine discharge pressure compressor inlet pressure. it engine thrust in term of epr. Question 39-12
A thermocouple type thermometer consists of Two metal conductors of different type connected at two points. it engine thrust in term of epr. Question 39-13
One of disadvantages of an electronic tachometer the Necessity of a power supply. it engine thrust in term of epr. Question 39-14
The principle of capacity gauges based on capacitance variation of A capacitor with type of dielectric. a capacitance type fuel gauge system consists of a variable capacitor located in fuel tank an amplifier an indicator the complete circuit forms an electrical bridge which continuously being rebalanced as a result of differences between capacitances of tank capacitor a reference capacitor the signal produced due to differences in signals amplified to operate a motor the motor then drives pointer to indicate capacitance change of tank capacitor thus change in fuel quantity indicated we have seen basic construction of this system now let us discuss how electrical capacitance principle utilized the capacitance type fuel gauge system in aircraft the capacitors which are to be installed in fuel tanks the fuel quantity measurement must be different in construction from those normally employed in electrical equipment the plates of capacitors take form of two tubes mounted concentrically with a narrow air space between them these plates extend full depth of a fuel tank capacitance depends on some factors which are area of plates distance between two plates the dielectric constant of material between two plates of capacitors now in this capacitance type fuel gauge system two factors plate area distance between plates are fixed the dielectric here the fuel in tank of aircraft the flow of a momentary current into a capacitor establishes a potential difference across its plates the dielectric i e fuel in aircraft's fuel tanks contains no free electrons so current cannot flow through it but it should be remembered that potential difference sets up a state of stress in atoms comprising it. Question 39-15
A synchroscope used on aircraft to Set several engines to same speed. On a multi engined aircraft a synchronizing system ensures propeller speeds are all same this achieved 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 electrically trimming engine speeds until all signals are equal. Question 39-16
The 'bourdon tube' used to measure Set several engines to same speed. On a multi engined aircraft a synchronizing system ensures propeller speeds are all same this achieved 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 electrically trimming engine speeds until all signals are equal. Question 39-17
If a manifold pressure gauge consistently registers atmospheric pressure cause probably Leak in pressure gauge line. On a multi engined aircraft a synchronizing system ensures propeller speeds are all same this achieved 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 electrically trimming engine speeds until all signals are equal. Question 39-18
A manifold pressure gauge of a piston engine measures Absolute pressure in intake system near inlet valve. On a multi engined aircraft a synchronizing system ensures propeller speeds are all same this achieved 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 electrically trimming engine speeds until all signals are equal. Question 39-19
In an engine vibration monitoring system a turbojet any vibration produced the engine Amplified filtered before being fed to cockpit indicator. vibrations are picked up 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 initial acceleration signal not practical use depending on engine type the bearing location displacement speed (usually noted in inch per second ips) used the vibration frequency filtered the cockpit indication to indicate only vibration in a frequency band corresponding to spool speed n1 n2 n3 that's why engines can have vibrations which are not related to spools rotating speed not being indicated in cockpit. Question 39-20
According to range of pressure to be measured low medium high different types of pressure sensors are used 1 bellows type2 bourdon tube type3 aneroid capsule classify following sensors order of increasing pressure which they are suitable Amplified filtered before being fed to cockpit indicator. vibrations are picked up 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 initial acceleration signal not practical use depending on engine type the bearing location displacement speed (usually noted in inch per second ips) used the vibration frequency filtered the cockpit indication to indicate only vibration in a frequency band corresponding to spool speed n1 n2 n3 that's why engines can have vibrations which are not related to spools rotating speed not being indicated in cockpit. Question 39-21
A vibration indicator receives a signal from different sensors accelerometers it indicates Vibration amplitude at a given frequency. vibrations are picked up 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 initial acceleration signal not practical use depending on engine type the bearing location displacement speed (usually noted in inch per second ips) used the vibration frequency filtered the cockpit indication to indicate only vibration in a frequency band corresponding to spool speed n1 n2 n3 that's why engines can have vibrations which are not related to spools rotating speed not being indicated in cockpit. Question 39-22
The transmitter of rpm indicator may consist of 1 a magnetic sensor supplying an induced ac voltage2 a dc generator supplying a dc voltage3 a single phase ac generator supplying an ac voltage4 a three phase ac generator supplying a three phase voltagethe combination of correct statements Vibration amplitude at a given frequency. statement 1 it refers to a permanent magnet that coupled to engine as it rotates within a 3 phase stator 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 indicates rpm statement 2 it refers to a device that converts ac signals into dc that drives a dc motor the output then compared to a dc reference output the difference indicates rpm statement 3 it refers to a device that used on some jet engine aircraft to sense shaft speed of lp compressor during engine start up cycle it uses a single ac phase of a normal tachogenerator to show that shaft rotating is automatically isolated after start cycle has been successfully completed statement 4 it refers to a direct drive 3 phase ac generator that operated in conjunction with a 3 phase ac synchronous motor to indicate rpm. Question 39-23
The indication of a fuel float gauge varies with 1 pitch attitude 2 accelerations 3 fuel temperaturethe combination that regroups all of correct statements Vibration amplitude at a given frequency. in 1904 first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on outside of fuel tank to indicate fuel level idea was taken one step further when vehicles started to get better electrical systems connecting hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in vehicle's dashboard and that's basic operating principle that's still in use today but airplane attitude accelerations will affect accuracy of indication due to movements of fuel in tank temperature will modify volume thus indication. Question 39-24
If tanks of your aircraft only contain water capacitor gauges indicate A mass of water different from zero but inaccurate. in 1904 first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on outside of fuel tank to indicate fuel level idea was taken one step further when vehicles started to get better electrical systems connecting hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in vehicle's dashboard and that's basic operating principle that's still in use today but airplane attitude accelerations will affect accuracy of indication due to movements of fuel in tank temperature will modify volume thus indication. Question 39-25
The float type fuel gauges provide information on Volume whose indication varies with temperature of fuel. in 1904 first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on outside of fuel tank to indicate fuel level idea was taken one step further when vehicles started to get better electrical systems connecting hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in vehicle's dashboard and that's basic operating principle that's still in use today but airplane attitude accelerations will affect accuracy of indication due to movements of fuel in tank temperature will modify volume thus indication. Question 39-26
The sensors used to measure exhaust gas temperature on an aircraft equipped with gas turbine engine are Volume whose indication varies with temperature of fuel. a thermocouple type thermometer consists of two metal conductors of different type connected at two points the operating principle of a thermocouple a conductor that subject to a thermal gradient generates a voltage this voltage measured interpreted a thermocouple thermometer (millivoltmeter). Question 39-27
The measurement of turbine temperature or of tgt turbine gas temperature carried out at High pressure turbine outlet. a thermocouple type thermometer located between hp turbine lp turbine allowing measurement of turbine temperature. Question 39-28
The two main sources of information used to calculate turbojet thrust are Fan rotation speed (or n ) or epr (engine pressure ratio). a thermocouple type thermometer located between hp turbine lp turbine allowing measurement of turbine temperature. Question 39-29
The advantages of an 'electric' fuel float gauge are 1 easy construction2 independence of indications with regard to airplane attitude3 independence of indications with regard to accelerations4 independence of indications with regard to temperature variations5 independence of indications with regard to vibrationsthe combination regrouping all correct statements Fan rotation speed (or n ) or epr (engine pressure ratio). in 1904 first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on outside of fuel tank to indicate fuel level idea was taken one step further when vehicles started to get better electrical systems connecting hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in vehicle's dashboard and that's basic operating principle that's still in use today but airplane attitude accelerations will affect accuracy of indication due to movements of fuel in tank temperature will modify volume thus indication. Question 39-30
The disadvantages of an 'electric' fuel float gauge are 1 design complex 2 indications are influenced the airplane attitude variations 3 indications are influenced the accelerations 4 indications are influenced temperature variations 5 that an alternative current supply necessary the combination regrouping all correct statements Fan rotation speed (or n ) or epr (engine pressure ratio). in 1904 first float arm gas gauge appeared a float mounted on a hinged arm moved a mechanical pointer on gauge on outside of fuel tank to indicate fuel level idea was taken one step further when vehicles started to get better electrical systems connecting hinged float arm to a rheostat this allows an electrically operated fuel gauge to be mounted in vehicle's dashboard and that's basic operating principle that's still in use today but airplane attitude accelerations will affect accuracy of indication due to movements of fuel in tank temperature will modify volume thus indication. Question 39-31
On an electronic flight instrument system efis following fuel flow parameters may be displayed 1 present fuel flow of each engine2 mean fuel flow over 1 minute3 maximum admission fuel flowthe combination regrouping all correct statements Fan rotation speed (or n ) or epr (engine pressure ratio). An efis displays fuel flow to engine it displays also fuel used since last reset fuel flow usually shown in kilograms per hour. Question 39-32
The aircraft outside air temperature 'probe' measures 'tota air temperature minus kinetic heating effects in order to obtain static temperature. this question has been seen in july 2022 with this correct answer total air temperature this must be corrected ram rise recovery factor to obtain static air temperature the other wrong answers remain unchanged. Question 39-33
A millivoltmeter measuring electromotive force between 'hot junction' and 'cold junction' of a thermocouple can be directly graduated in temperature values provided that temperature of Cold junction maintained constant. this question has been seen in july 2022 with this correct answer total air temperature this must be corrected ram rise recovery factor to obtain static air temperature the other wrong answers remain unchanged. Question 39-34
The gauge indicating quantity of fuel measured a capacity gauging system can be graduated directly in weight units because dielectric constant of fuel Twice that of air varies directly with density. the dielectric constant (or permittivity) of fuel determined establishing ratio of electrical capacitance of a tank filled with fuel as compared with electrical capacitance of tank when filled with air measurements of dielectric constant of a fuel at various temperatures show that dielectric constant a linear function of temperature decreasing with increasing temperature varying with applied frequency dielectric of air (at 70°f) = 0 85 dielectric of jet fuel (at 70°f) = 1 7. Question 39-35
When compared with volumetric fuel flowmeter mass fuel flowmeter takes into account fuel Twice that of air varies directly with density. the mass fuel flow meter allows measurement of mass consumption of fuel the mass fuel flowmeter takes into account fuel density. Question 39-36
The electronic tachometer sensor composed of A notched wheel rotating in front of an electro magnet. the mass fuel flow meter allows measurement of mass consumption of fuel the mass fuel flowmeter takes into account fuel density. Question 39-37
The advantages of a d c generator tachometer are 1 easy transmission of information 2 independence of information relative to airborne electrical power supply3 freedom from any spurious current due to commutatorthe combination regrouping all correct statements A notched wheel rotating in front of an electro magnet. d c generator tachometer consists of a small armature which coupled to machine whose speed to be measured this armature revolves in field of a permanent magnet the electro magnetic force (emf) generated proportational to product of flux speed since flux of permanent magnet constant voltage generated proportational to speed the polarity of output voltage indicates direction of rotation this electro magnetic force (emf) measured with help of moving coil voltmeter having a uniform scale calibrated directly in terms of speed but d c generator tachometer has a dc commutator ring which causes spurious signals. Question 39-38
The advantages of single phase a c generator tachometer are 1 suppression of spurious signals due to a d c generator commutator2 importance of line resistance on information value3 independence of information in relation to airborne electrical power supply4 ease of transmission of informationthe combination regrouping all correct statements A notched wheel rotating in front of an electro magnet. the single phase ac generator tachometer doesn't have a dc commutator ring thus no spurious signals the measurement independent of aircraft power supply. Question 39-39
The disadvantages of a single phase a c generator tachometer are 1 presence of spurious signals due to a d c generator commutator 2 importance of line resistance on information value 3 influence of temperature on tachometer information the combination regrouping all correct statements A notched wheel rotating in front of an electro magnet. the single phase ac generator tachometer brushless thus no spurious signals the measurement independent of aircraft power supply but one disadvantage of a single phase ac generator the possibility of values transmitted being affected line resistance. Question 39-40
Torque can be determined measuring Oil pressure at fixed crown of an epicycloidal reducer of main engine gearbox. operating principle of a epicyclic reducer with fixed crown input drive applied to a central or sun gear (1) which three or more pinions or planet gears (2) are set in rotation these in turn rotate in mesh with internal teeth of a fixed crown (fixed ring gear) (3) the shafts of planet gears (4) mounted to a planet carrier (5) are translated along a circumferential trajectory made thus to revolve around sun gear the result that planet carrier (5) to which output assembly mounted (shaft bearings seals etc ) rotates at a lower speed than that of sun gear (1) torque can be determined measuring oil pressure at fixed crown of an epicycloidal reducer of main engine gearbox.
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