Students > VFR : The purpose of magnetic chip detectors is to ?

Question 30-1 : Warn of impending failure increase lubricating oil adhesion to main surfaces remove large items of debris from the system perform the function of a micron filter

exemple 130 warn of impending failure. — The most basic type of magnetic filter is a drain plug where a magnet in the shape of a disc or cylinder is attached to its inside surface typically by adhesion periodically the magnetic plug is removed and inspected for ferromagnetic particles which are then wiped from the plug. 663..such plugs are commonly used in engine sumps gearboxes and occasionally in hydraulic reservoirs one useful advantage of mag plugs relates to examining the density of wear particles observed as a visual indication of the wear rate occurring within the machine over a fixed period of running time the appearance of these iron filings on magnets are often described in inspection reports using terms such as peach fuzz whiskers or christmas trees if one normally sees peach fuzz but on one occasion sees a christmas tree instead this would be a reportable condition requiring further inspection and remediation warn of impending failure.

Apart from flight into known icing conditions the intake system of a diesel ?

Question 30-2 : Is never heated because a diesel engine is a injection engine needs to be heated to prevent ice on the air filter needs to be heated at low power settings due to vaporisation heat is never heated because diesel engines operate at very high temperatures

exemple 134 is never heated because a diesel engine is a injection engine. — is never heated because a diesel engine is a injection engine.

The thermal efficiency of a diesel engine is higher than that of a petrol ?

Question 30-3 : The compression ratio is much higher the calorific value of the fuel is higher the egt is higher the air mass flow through the engine is higher

exemple 138 the compression ratio is much higher. — the compression ratio is much higher.

Given the following statements about diesel engines.1 power is regulated by ?

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

exemple 142 2, 3, 5. — There is no mixture control and no throttle valve the power output of a diesel engine is controlled by regulating the quantity of fuel that is injected into the cylinder the amount of air is constant diesel engines are fitted with injectors not with valves 2, 3, 5.

In liquid cooled engines the compostion by volume of coolant mixture is ?

Question 30-5 : 30% ethylene glycol and 70% water 60% ethylene glycol and 40% water 50% ethylene glycol and 50% water 65% ethylene glycol and 35% water

exemple 146 30% ethylene glycol and 70% water. — 30% ethylene glycol and 70% water.

The oil system for a piston engine incorporates an oil cooler that is fitted ?

Question 30-6 : In the return line to the oil tank after the oil has passed through the scavenge pump after the pressure pump but before the oil passes through the engine after the oil has passed through the engine and before it enters the sump between the oil tank and the pressure pump

exemple 150 in the return line to the oil tank after the oil has passed through the scavenge pump. — in the return line to the oil tank after the oil has passed through the scavenge pump.

Diesel engines always produce a certain amount of soot because ?

Question 30-7 : The fuel droplets coming from the atomiser do not burn completely the mixture is always too rich the intake air is too cold the fuel droplets are too small

exemple 154 the fuel droplets coming from the atomiser do not burn completely. — the fuel droplets coming from the atomiser do not burn completely.

What may happen during a continuous climb with a mixture setting fully rich ?

Question 30-8 : Fouling of spark plugs increase of the power available the engine will operate smoother even though fuel consumption is increased the engine will overheat

exemple 158 fouling of spark plugs. — Carburetors are calibrated to operate with the mixture control set to 'full rich' when operating at sea level as the aircraft gains altitude it becomes necessary to reduce the amount of fuel entering the carburetor because the amount of air is automatically decreasing with altitude due to lower atmospheric pressure. if the pilot fails to decrease the amount of fuel as altitude is gained the result will be an overly 'rich' mixture creating problems such as fouled spark plugs and excessive fuel consumption fouling of spark plugs.

Prolonged running at low rpm can have an adverse effect on the functioning of ?

Question 30-9 : Spark plugs carburettor oil pump fuel filter

When leaning the mixture for the most economic cruise fuel flow excessive ?

Question 30-10 : High cylinder head temperature high engine rpm low cylinder head temperature high manifold pressure

exemple 166 high cylinder head temperature. — Egt is relative to the temperature of the charge as it burns within the cylinder cht measures the temperature of the engine cylinder.the highest egt is achieved at a ratio of 15 parts of air to one part of fuel.if the ratio is reduced ie rich the charge temperature reduces due to excess fuel being left in the cylinder if the ratio is greater than 15 1 ie lean or weak the charge is cooled by excess air to appreciate why cht increases with lean mixtures we must consider the speed at which the fuel burns ie its flame rate lean mixtures burn slower than rich mixtures this means more heat is transferred to the engine components with lean mixtures.example if you move a lighted match quickly under your hand no problem but move it slowly and you will burn your hand slow burning lean mixtures will increase cht high cylinder head temperature.

During climb with constant throttle and rpm lever setting mixture being ?

Question 30-11 : Manifold absolute pressure map decreases rpm decreases manifold absolute pressure map increases rpm increases

exemple 170 manifold absolute pressure (map) decreases. — The manifold absolute pressure map indicates the power output of a piston engine being a measure of the pressure of the fuel/air mixture in the inlet manifold.in an unsupercharged engine the reading will drop with height for a given throttle setting because there is less atmospheric pressure to push the useful charge into the cylinder manifold absolute pressure (map) decreases.

Both gas turbine and piston engines use a cycle made up of induction ?

Question 30-12 : I is correct ii is incorrect i is incorrect ii is incorrect i is incorrect ii is correct i is correct ii is correct

exemple 174 i is correct, ii is incorrect. — .piston engine the combustion process is intermittent governed by the rythm of the back and forth movements of the piston in a cylinder the combustion occurs at constant volume in the cylinder.turbine engine the combustion process is continuous and occurs at constant pressure i is correct, ii is incorrect.

A piston engine compression ratio is the ratio of the ?

Question 30-13 : Total volume to the clearance volume clearance volume to the swept volume total volume to the swept volume swept volume to the clearance volume

exemple 178 total volume to the clearance volume. — 897.compression ratio = volume at bottom dead total volume / volume at top dead clearance volume.the clearance volume is the volume that is not expelled from the cylinder total volume to the clearance volume.

The purpose of a chip detector in the oil system of an engine/gearbox is to ?

Question 30-14 : There are metal particles in the oil the piston rings are worn the seals are worn the oil temperature is too high

The most basic type of magnetic filter is a drain plug where a magnet in the shape of a disc or cylinder is attached to its inside surface typically by adhesion periodically the magnetic plug is removed and inspected for ferromagnetic particles which are then wiped from the plug..such plugs are commonly used in engine sumps gearboxes and occasionally in hydraulic reservoirs one useful advantage of mag plugs relates to examining the density of wear particles observed as a visual indication of the wear rate occurring within the machine over a fixed period of running time the appearance of these iron filings on magnets are often described in inspection reports using terms such as peach fuzz whiskers or christmas trees if one normally sees peach fuzz but on one occasion sees a christmas tree instead this would be a reportable condition requiring further inspection and remediation

The thermal efficiency of a piston engine is about ?

Question 30-15 : 30% 50% 70% 80%

exemple 186 30%. — Thermal efficiency is the ratio of useful work to the heat put in expressed as a percentage.the first law of thermodynamics states that energy may be changed from one form to another but cannot be destroyed as far as engines are concerned it means that heat and mechanical work are mutually convertible and that the rate of exchande is constant and measurable.however the second law says more or less that 'heat flows from a hot substance to a cold one unaided but energy from an external source is needed for it to flow the other way' that is you might be able to convert most of your work into heat but turning heat into work will incur serious losses which is another way of saying that engines are grossly inefficient if it were otherwise exhausts would be cold.in fact engines waste as much energy in heat as the power they produce the approximate thermal efficiency of a four stroke engine is 30% 30%.

On a normally aspirated engine non turbo charged the manifold pressure gauge ?

Question 30-16 : A lower value than atmospheric pressure when the engine is running a value equal to the qfe when the engine is at full power on the ground a greater value than atmospheric pressure when the engine is running zero on the ground when the engine is stopped

Devidson .if the engine is on full power i e the butterfly valve is fully open the admision pressure would be equal to the atmospheric pressure on a non turbo charged engine no..no matter how wide the butterfly throttle is opened there will always be some restriction hence the manifold pressure will always be lower than atmospheric even if only slightly

The purpose of a distributor in an ignition system is to distribute ?

Question 30-17 : Secondary current to the sparking plugs primary current to the condenser secondary current to the condenser primary current to the sparking plugs

exemple 194 secondary current to the sparking plugs. — .the purpose of the ignition system is to provide an ignition spark to the proper cylinder at the correct time in order to burn the compressed air/fuel mixture .it consists of two separate but closely related electrical circuits . low voltage primary circuit battery voltage . high voltage secondary circuit over 20000 volts.the ignition coil is the unit that takes your relatively weak battery power and turns it into a spark powerful enough to ignite fuel vapor inside a a traditional ignition coil are two coils of wire on top of each other these coils are called windings one winding is called the primary winding the other is the secondary the primary winding gets the juice together to make a spark and the secondary sends it out the door to the distributor.the distributor 'distributes' the secondary current to the sparking plugs secondary current to the sparking plugs.

Viscosity is ?

Question 30-18 : The tendency of a liquid or gas to resist flow the temperature dependence of an oil the pressure resistance of an oil the flow velocity inside the oil lines

exemple 198 the tendency of a liquid or gas to resist flow. — the tendency of a liquid or gas to resist flow.

With which instrument s do you monitor the power output of an aeroplane fitted ?

Question 30-19 : Rpm indicator fuel flow indicator rpm and map indicator cylinder head temperature indicator

exemple 202 rpm indicator. — rpm indicator.

In a piston engine turbocharger boost pressure may be monitored by ?

Question 30-20 : A manifold pressure gauge only a cylinder head temperature gauge cht a manifold pressure gauge and engine rpm readings both a cht gauge and manifold pressure gauge both engine rpm readings and a manifold pressure gauge

exemple 206 a manifold pressure gauge only. — a manifold pressure gauge only.

Fixed pitch propellers are usually designed for maximum efficiency at ?

Question 30-21 : Cruising speed idling full throttle take off

exemple 210 cruising speed — cruising speed

Overheating of a piston engine is likely to result from an excessively ?

Question 30-22 : Weak mixture rich mixture low barometric pressure high barometric pressure

exemple 214 weak mixture. — Jaredleto .egt is relative to the temperature of the charge as it burns within the cylinder cht measures the temperature of the engine cylinder .the highest egt is achieved at a ratio of 15 parts of air to one part of fuel .if the ratio is reduced ie rich the charge temperature reduces due to excess fuel being left in the cylinder if the ratio is greater than 15 1 ie lean or weak the charge is cooled by excess air to appreciate why cht increases with lean mixtures we must consider the speed at which the fuel burns ie its flame rate lean mixtures burn slower than rich mixtures this means more heat is transferred to the engine components with lean mixtures .example if you move a lighted match quickly under your hand no problem but move it slowly and you will burn your hand slow burning lean mixtures will increase cht weak mixture.

In an engine equipped with a float type carburettor the low temperature that ?

Question 30-23 : Vaporization of fuel and expansion of the air in the carburettor freezing temperature of the air entering the carburettor compression of air at the carburettor venturi low volatility of aviation fuel

exemple 218 vaporization of fuel and expansion of the air in the carburettor. — One disadvantage of the float type carburetor is its icing tendency the vaporization of fuel combined with the expansion of air as it flows through the carburetor causes a sudden cooling of the mixture the temperature of the air passing through the carburetor may drop significantly within a fraction of a second water vapor in the air is 'squeezed out' by this cooling and if the temperature in the carburetor reaches 0°c or below the moisture will be deposited as frost or ice inside the carburetor passages even a slight accumulation of this deposit will reduce power and may lead to complete engine failure particularly when the throttle is partly or fully closed . 1048.the formation of carburetor ice may reduce or block fuel/air flow to the engine vaporization of fuel and expansion of the air in the carburettor.

In addition to the fire hazard introduced excessive priming should be avoided ?

Question 30-24 : It fouls the spark plugs it washes the lubricant of cylinder walls it drains the carburettor float chamber the gasoline dilutes the oil and necessitates changing oil

exemple 222 it fouls the spark plugs. — it fouls the spark plugs.

With respect to a piston engine aircraft ice in the carburettor ?

Question 30-25 : May form at oat's higher than +10°c will only form at oat's below +10°c will only form at outside air temperatures oat's below the freezing point of water will only form at oat's below the freezing point of fuel

exemple 226 may form at oat's higher than +10°c. — may form at oat's higher than +10°c.

As the flight altitude increases if no leaning is made with the mixture control ?

Question 30-26 : The density of air entering the carburettor decreases and the amount of fuel remains constant the volume of air entering the carburettor remains constant and the amount of fuel decreases the volume of air entering the carburettor decreases and the amount of fuel decreases the density of air entering the carburettor decreases and the amount of fuel increases

exemple 230 the density of air entering the carburettor decreases and the amount of fuel remains constant. — .density decreases as we gain altitude but volume of air entering in the carburettor does not change as for the volume of fuel fuel density does not change with altitude the density of air entering the carburettor decreases and the amount of fuel remains constant.

Cooling air for a reciprocating engine can be obtained by means of ?

Question 30-27 : Ram air a supercharger a turbocharger a pneumatic system

The main advantage of a constant speed propeller as compared to a fixed pitch ?

Question 30-28 : High efficiency in a much wider speed range of the aeroplane constant efficiency in the whole speed range of the aeroplane lower propeller blade stress higher efficiency in cruising range

exemple 238 high efficiency in a much wider speed range of the aeroplane. — .advantages of a constant speed propeller compared to a fixed pitch propeller .the power setting of a piston engine is defined by a combination of manifold pressure boost and rpm where separate power lever and rpm lever control is provided it is possible to vary one while leaving the other constant so optimising the operation of the engine/propeller combination to give best efficiency/fuel economy and least engine wear and tear in order to achieve this a 'variable pitch' propeller must be used enabling the pilot to select a propeller pitch and thus to vary rpm independently of manifold pressure provided that the propeller is operating between its internal fine and coarse pitch stops once an rpm has been selected a control unit csu constant speed unit or pcu propeller control unit will automatically vary the propeller pitch angle and therefore its angle of attack to the prevailing relative airflow in order to maintain the selected rpm despite airspeed and manifold pressure variations a constant speed propeller has a high efficiency in a much wider speed range than a fixed pitch propeller high efficiency in a much wider speed range of the aeroplane.

From the cruise with all the parameters correctly set if the altitude is ?

Question 30-29 : Increase decrease remain the same increase or decrease depending on the engine type

.when altitude increases air density decreases .to maintain a correct mixture ratio of 1 to 15 fuel mass / air mass if the altitude is reduced we need to increase the fuel flow to maintain a constant ratio air volume entering the carburettor will not change but the air mass will increase

A turbocharger in a reciprocating engine consists of a ?

Question 30-30 : Compressor and turbine mounted on a common shaft compressor and turbine on individual shafts compressor driving a turbine via a reduction gear turbine driving a compressor via a reduction gear

exemple 246 compressor and turbine mounted on a common shaft. — compressor and turbine mounted on a common shaft.

An impulse coupling is inhibited at higher than normal rotational starting ?

Question 30-31 : Centrifugal force engine oil pressure a coil spring electro magnetic action of operating magneto

exemple 250 centrifugal force. — .impulse coupling magneto .the impulse coupling is a spring loaded mechanical coupling which delays rotation of the magneto during an engine start after a short period of rotation the device allows the magneto to catch up in effect spinning the magneto shaft faster than the engine is turning it the faster it turns the hotter the spark and the bigger the voltage impulse making for easier starting after the engine is running centrifugal forces move the spring loaded arms which make the impulse coupling work at low speeds out of the way the impulse coupling only works at very low engine speeds centrifugal force.

The very rapid magnetic field changes flux changes in the primary coil of a ?

Question 30-32 : Contact breaker points opening distributor arm aligning with one of the high voltage segments contact breaker points closing rotor turning past the position of maximum flux in the armature

exemple 254 contact breaker points opening. — .inside the primary circuit is a set of contact points that make the flux reversals more abrupt when they open and close at critical moments .when the points are closed current flows in the primary coil and a flux field builds up around it when a spark is needed they open which causes the field in the primary to collapse and induce a current in the secondary winding as the field moves across it which is fed to the spark plugs through the distributor.the more suddent the breaking of the primary circuit is the more current will be induced in the secondary coil contact breaker points opening.

In a compressor stage of a jet engine the sequence is ?

Question 30-33 : Rotor stator stator rotor rotor rotor stator stator stator rotor

exemple 258 rotor - stator — Comp r e s sor highlighted rs means correct order so rotor stator.turbine stage the opposite rotor - stator

The accessory units driven by the accessory gearbox of a turbo jet engine are ?

Question 30-34 : 2 3 4 5 1 2 3 4 5 2 3 4 1 2 3 4

exemple 262 2, 3, 4, 5. — 908.. 909..the accessory gearbox is driven by a radial shaft that meshes with a bevel gear driven by the n2 or gas producer rotor and is used to drive essential engine components such as the fuel pump oil pump fuel control unit generators and hydraulic pumps the accessory gear box is also used to drive engine rpm feedback tacho generators and is the means by which the starter drives the engine these are systems which must operate as soon as the engine starts .structure containing the gearbox can be utilised as a support as well .each component that attaches to the accesssory gearbox has its own mounting pad with its unique gear reduction for speed and rotational direction 2, 3, 4, 5.

Consider a jet engine whose control is based on the engine pressure ratio epr.1 ?

Question 30-35 : 1 3 3 4 5 1 5 2 3 4

exemple 266 1, 3. — Engine pressure ratio epr is a measure of the thrust of a jet engine obtained by dividing the pressure at the back of the engine by the pressure at the front .epr settings vary with altitude and temperature when the altitude increases the thrust decreases .answer 4 the epr is determined by the impact pressure difference between the turbine outlet and the compressor inlet is wrong this is a ratio not a difference 1, 3.

In the axial flow compressor of a turbo jet engine the flow duct is tapered its ?

Question 30-36 : Maintain a constant axial speed in cruising flight maintain a constant axial speed whatever the engine rating reduce the axial speed in cruising flight reduce the axial speed whatever the engine rating

exemple 270 maintain a constant axial speed in cruising flight. — The duct in question is the convergent duct formed between the compressor and engine compressor casing.the airflow through a jet engine varies dependant on thrust selection since the engine runs for most of the time at cruise the engine is designed to give correct flow rates at this thrust setting maintain a constant axial speed in cruising flight.

In the stator of a turbine the gas velocity v and static pressure ps vary as ?

Question 30-37 : V increases ps decreases v increases ps increases v decreases ps increases v decreases ps decreases

exemple 274 v increases, ps decreases. — If you have multiple stage turbines there is a set of guide vanes between each turbine disc to redirect the flow again before the next turbine blade they are stationary so are sometimes called stators .with the turbine you want a high velocity so turbine blades are designed to extract power from the hot expanding gasses to turn the compressor by using the high velocity hitting the turbine blade the guide vanes straighten the flow before the next set of turbine blades but in effect it decreases the pressure and increases the velocity this also prevents excessive backpressure which could work its way forward and affect the combustion process .the compressor on the other hand is designed to increase the pressure through each of the stages so you can deliver a good mass flow to the combustion chambers however the increasing pressure will try to reverse the flow so the convergent duct is designed to keep the velocity constant through the whole compressor so that the momentum of the airflow prevents reverse flow in effect the velocity is therefore increased in each rotor section.velocity increases and decreases through each set of rotors and stators and by using a convergent duct the velocity therefore stays constant but the pressure is steadily increasing through each stage v increases, ps decreases.

Epr can be defined as the ratio of ?

Question 30-38 : The total turbine outlet pressure to the total compressor inlet pressure the total turbine outlet pressure to the total compressor outlet pressure the total turbine inlet pressure to the total compressor outlet pressure the total turbine inlet pressure to the total compressor inlet pressure

exemple 278 the total turbine outlet pressure to the total compressor inlet pressure. — 911 the total turbine outlet pressure to the total compressor inlet pressure.

A gas turbine engine turbine section may employ active clearance control ?

Question 30-39 : To provide enhanced clearances between the blade tips and the casing in order to cool the disc in order to reduce 'creep' in the blades as a method of attaching the stators and rotors to the hub of the disc

exemple 282 to provide enhanced clearances between the blade tips and the casing. — .active clearance control acc is a method used in gas turbines to improve fuel efficiency this is achieved by controlling the tip clearance it is particularly effective on turbofans since they are required to respond quickly to changes of the thrust setting.the active clearance control consists of the acc valve which receives the air from the bypass duct and routes the air to flow over the pipes surrounding the turbine casing which in turn reduces the thermal expansion of the turbine case and maintains the accurate clearance between the turbine case and the blade tip this clearance should be maintained accurately which is essential for the engine efficiency and its performance the acc valve opening is adjusted automatically by the fadec system depending on the throttle position to provide enhanced clearances between the blade tips and the casing.

In a gas turbine engine the maximum gas temperature is attained ?

Question 30-40 : Within the combustion chamber at the turbine entrance in the cooling airflow around the flame tube at the entry to the exhaust unit

exemple 286 within the combustion chamber. — within the combustion chamber.

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