Low frequency vibration in the vertical plane which is only apparent in high speed flight is due to a ?
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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, is usually achieved adding weights to certain nominated rotor blades only, is usually achieved adding or subtracting weights to main rotor blade tips, is not necessary as hub blades are statically balanced at manufacture. 
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, lengthening pitch change rod on subject blade, shortening pitch change rod on subject blade, adjusting weights on blade tip. 
Tail rotor blade hinges arranged with a ''delta three'' hinge effect Decrease their pitch angle with flap up, increase lift of blade with flap up, decrease their pitch angle with blade dragging, increase their pitch angle with flap up. 
Adjusting an outboard blade tab upwards will produce a Nose up moment on blade, nose down moment on blade, medium frequency vibration in flight, high frequency vibration in flight. Question Sensors and Instruments 39 Answer 8
A rotor blade trim tab provides a corrective force Indirectly, causing pitch angle to change, thus altering blade lift in appropriate sense, varying blade drag so repositioning blade in azimuth relative to other blade(s), directly, its displacement causing blade to track in correct plane, indirectly, adjusting centre of gravity of blade longitudinally, thus causing blade to track in correct plane. Question Sensors and Instruments 39 Answer 9
A rotor blade running out of track produces 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 five times per revolution in a four bladed rotor system. Question Sensors and Instruments 39 Answer 10
Wind gusts have a greater adverse effect on Semi rigid rotors due to their see saw flapping, rigid rotors due to lack of a flapping hinge, fully articulated rotors as gust will cause blade to flap thus altering pitch angle, fully articulated rotors as flapping blades will induce vibration. Question Sensors and Instruments 39 Answer 11
The epr engine pressure ratio computed Dividing turbine discharge pressure compressor inlet pressure, dividing compressor discharge pressure turbine discharge pressure, multiplying compressor inlet pressure turbine discharge pressure, multiplying compressor discharge pressure turbine inlet pressure. it engine thrust in term of epr. Question Sensors and Instruments 39 Answer 12
A thermocouple type thermometer consists of Two metal conductors of different type connected at two points, two metal conductors of same type connected at two points, a single wire coil, a wheatstone bridge connected to a voltage indicator. Question Sensors and Instruments 39 Answer 13
One of disadvantages of an electronic tachometer the Necessity of a power supply, generation of spurious signals at commutator, influence of temperature on indication, high influence of line resistance on indication. Question Sensors and Instruments 39 Answer 14
The principle of capacity gauges based on capacitance variation of A capacitor with type of dielectric, two dissimilar metals joined together at their ends, two dissimilar metals joined together at one end only, liquids with variations in temperature. 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 Sensors and Instruments 39 Answer 15
A synchroscope used on aircraft to Set several engines to same speed, reduce vibration of each engine, reduce rpm of each engine, achieve optimum control of on board voltages. 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 Sensors and Instruments 39 Answer 16
The 'bourdon tube' used to measure Pressure, temperature, quantity, a flow rate. Question Sensors and Instruments 39 Answer 17
If a manifold pressure gauge consistently registers atmospheric pressure cause probably Leak in pressure gauge line, too high float level, fuel of too low volatility, ice in induction system. Question Sensors and Instruments 39 Answer 18
A manifold pressure gauge of a piston engine measures Absolute pressure in intake system near inlet valve, vacuum in carburettor, fuel pressure leaving carburettor, absolute airpressure entering carburettor. Question Sensors and Instruments 39 Answer 19
In an engine vibration monitoring system a turbojet any vibration produced the engine Amplified filtered before being fed to cockpit indicator, inversely proportional to engine speed, directly proportional to engine speed, fed directly to cockpit indicator without amplification or filtering. 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 Sensors and Instruments 39 Answer 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 3, 2, 2, 3,, 2 3, 3, 2. Question Sensors and Instruments 39 Answer 21
A vibration indicator receives a signal from different sensors accelerometers it indicates Vibration amplitude at a given frequency, vibration frequency expressed in hz, vibration period expressed in seconds, acceleration measured the sensors, expressed in g. Question Sensors and Instruments 39 Answer 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 , 2, 3, 4,, 2, 3, 2, 3, 4,, 4. 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 Sensors and Instruments 39 Answer 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 , 2, 3,, 3,, 2, 2, 3. 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 Sensors and Instruments 39 Answer 24
If tanks of your aircraft only contain water capacitor gauges indicate A mass of water different from zero, but inaccurate, exact mass of water contained in tanks, a mass equal to zero, a mass equal to mass of a same volume of fuel. Question Sensors and Instruments 39 Answer 25
The float type fuel gauges provide information on Volume whose indication varies with temperature of fuel, volume whose indication independent of temperature of fuel, mass whose indication varies with temperature of fuel, mass whose indication independent of temperature of fuel. Question Sensors and Instruments 39 Answer 26
The sensors used to measure exhaust gas temperature on an aircraft equipped with gas turbine engine are Thermocouples, based on metallic parts whose expansion/contraction 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 a conductor that subject to a thermal gradient generates a voltage. this voltage measured interpreted a thermocouple thermometer (millivoltmeter). Question Sensors and Instruments 39 Answer 27
The measurement of turbine temperature or of tgt turbine gas temperature carried out at High pressure turbine outlet, combustion chamber outlet, combustion chamber intake, high pressure chamber intake. a thermocouple type thermometer located between hp turbine lp turbine allowing measurement of turbine temperature. Question Sensors and Instruments 39 Answer 28
The two main sources of information used to calculate turbojet thrust are Fan rotation speed (or n ) or epr (engine pressure ratio), high pressure turbine rotation speed or epr (engine pressure ratio), fan rotation speed (or n ) or total pressure at high pressure compressor outlet, fan rotation speed (or n ) or total pressure at low pressure turbine outlet. Question Sensors and Instruments 39 Answer 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 ,, 2, 3, 4, 5, 2, 3, 4, 5, 2, 3, 4. 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 Sensors and Instruments 39 Answer 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 2, 3, 4,,, 2, 3, 4, 2, 3, 4, 5. Question Sensors and Instruments 39 Answer 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 An efis displays fuel flow to engine. it displays also fuel used since last reset. fuel flow usually shown in kilograms per hour. Question Sensors and Instruments 39 Answer 32
The aircraft outside air temperature 'probe' measures 'tota air temperature minus kinetic heating effects in order to obtain static temperature, 'static' air temperature minus kinetic heating effects in order to obtain total temperature, 'tota air temperature minus compressibility effects in order to obtain static temperature, 'static' air temperature minus compressibility effects in order to obtain total 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 Sensors and Instruments 39 Answer 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, hot junction maintained constant, cold junction maintained at5 °c, hot junction maintained at5 °c. Question Sensors and Instruments 39 Answer 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, same as that of air varies directly with density, twice that of air varies inversely with density, same as that of air varies inversely 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 Sensors and Instruments 39 Answer 35
When compared with volumetric fuel flowmeter mass fuel flowmeter takes into account fuel Density, temperature, pressure, turbulent flow in line. the mass fuel flow meter allows measurement of mass consumption of fuel. the mass fuel flowmeter takes into account fuel density. Question Sensors and Instruments 39 Answer 36
The electronic tachometer sensor composed of A notched wheel rotating in front of an electro magnet, a circular magnet with four poles, rotor of a single phase a.c. generator, rotor of a three phase a.c. generator. Question Sensors and Instruments 39 Answer 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 , 2, 2, 3,, 2, 3,, 3. 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 Sensors and Instruments 39 Answer 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 , 3,, 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 independent of aircraft power supply. Question Sensors and Instruments 39 Answer 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 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 Sensors and Instruments 39 Answer 40
Torque can be determined measuring Oil pressure at fixed crown of an epicycloidal reducer of 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 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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