MOD. 15 (PARTE 2)

If the LP compressor shaft severed. the LP turbine will speed up and the LP compressor will slow down. the HP compressor will slow down. the LP compressor of cruise thrust.

The bearings of a compressor rotor are usually. sintered. ball and roller. plain.

A jet engine derives its thrust by. drawing air into the compressor. impingement of the propelling gases on the outside air. reaction of the propelling gases.

The forces driving a turbine round are due to. impulse and reaction. impulse only. reaction only.

Run down time is indicative of. compressor malfunction. the freedom of rotation of the compressor. an FCU malfunction.

The propulsive efficiency is. high, with a high mass flow acceleration. low, with a low mass flow acceleration. high, with a low mass flow acceleration.

A hung start or false start is one in which. there is no ’light up’. the engine does not rotate. ‘light up’ occurs, but the RPM does not increase.

The maximum RPM of a turbine engine is limited by. a temperature sensitive device which reduces the fuel pump speed. diversion of some of the fuel pump outlet flow by a spill valve sensitive to burner fuel pressure. reduction of the fuel pump stroke by a spill valve sensitive to centrifugally generated fuel pressure.

The function of a labyrinth seal is to create. an airtight seal between fixed and rotation components. a restricted leakage of air between fixed and rotating components. an airtight seal between fixed adjacent casing surfaces.

Intake air turbulence. has little effect on the efficiency of the compressor. increases the efficiency of the compressor. decreases the efficiency of the compressor.

To what condition does the fuel flow respond during aircraft acceleration. the change in pressure at the compressor intake. the effect of ‘ram-air’ at altitude. mass airflow rate through the engine.

An ignitor plug for a large gas turbine takes the form of a. surface discharge plug. sparking plug. ‘glow’ plug.

What will be the effect of operating the intake anti-icing system of a gas turbine engine?. A decrease in power. Increased power at altitude. Increased power for take off.

An advantage of a centrifugal compressor is. it is dynamically balanced. it is robust and can stand some shock from ‘icing up’. it is unaffected by turbulence.

Variable inlet guide vanes prevent. compressor runaway. compressor stalling. engine flame out at high speed.

During acceleration, the fuel flow is increased at a controlled rate in order to. increase s.f.c. prevent fuel pump damage. prevent surge and the risk of flame-out.

Which of the following is the least likely indication of a main bearing failure?. High oil temperature. High oil consumption. High oil pressure.

An axial flow compressor surges when. all stages are stalled. early stages are stalled. later stages are stalled.

As a consequence of tapping air from the compressor, the TGT will. rise. remain constant. fall.

Compressor air bleeds promote the flow of air through the early stages by. opening to allow air in. opening to allow air out. closing.

Compressor blades have reduced angle of attack at the tips. to allow uniform axial velocity. to prevent turbine stall. to increase the velocity.

The chip detector in the oil system is a. magnetic plug in the return line. window in the oil pump. window in the pump casing.

Nozzle guide vanes give. pressure increase, velocity decrease. pressure decrease, velocity increase. pressure increase, velocity increase.

After shutdown, flames are present in the exhaust pipe. The probable cause is. a defective fuel control unit (FCU). a defective HP cock. a defective pressurizing and dump valve.

The BPC controls the FCU by: pressure sensing. temperature sensing. density sensing.

If the LP cock is used to shutdown an engine. the fuel pump will run dry. the FCU will continue to function. flames will appear in the exhaust.

Compressor surge is caused by. over fuelling. rapid closing of the throttle. prolonged engine running at high RPM.

Shrouding of stator blade tips is to. prevent tip turbulence. ensure adequate cooling. minimise vibration.

The RPM for maximum power would be. lower on a colder day. lower on a hotter day. greater on a colder day.

The spark in the HE igniter is supplied by. a capacitor. the AC busbar. a contact circuit breaker.

If the swash plate of a positive displacement swash plate pump is perpendicular to the axis of the pump, the flow will be. reversed. zero. maximum.

What is DERD 2494?. Kerosene. Oil. Wide cut gasoline.

The burner fuel flow is at maximum at. altitude. I.S.A. sea level. 10oC above I.S.A. sea level.

Engine thrust varies with temperature. low temperatures give low thrust. increase in temperature gives greater thrust because of low friction in compressors. low temperature gives greater mass flow and therefore greater thrust.

A Pitot intake is divergent from front to rear because it. reduces ram compression and turbulence. speeds up the air before it hits the compressor face. produces the maximum amount of ram compression.

A method of comparing engine efficiencies is by comparing. thrust to weight ratio. specific fuel consumption. fuel consumption.

When rotating, the gear type oil pump. draws oil into the pump and carries it round between the gear teeth and casing. oil is drawn into the pump and through the intermeshing gears to the outlet. oil is drawn into the pump, half being carried around between pump and casing, the other half passing between the gears to the outlet.

A high viscosity index means the oil viscosity. will vary greatly with temperature change. will not vary greatly with temperature change. has a large index number.

The type of fuel control unit most commonly used in modern jet engines is. electrical. mechanical. hydro-mechanical.

Self sustaining speed is. the RPM at which the engine continues without external assistance. V1 speed. take off velocity.

Pressure rise across a single spool axial flow compressor is. two to one. four to one. up to fifteen to one.

What purpose do the diffuser vanes of a centrifugal compressor serve?. To increase the air velocity. To convert pressure energy into kinetic energy. To convert kinetic energy into pressure energy.

The main reason for adding methanol to the water is to. supply the additional heat required. temper the cooling effect of the water to prevent distortion. prevent mixture freezing.

In a reverse flow system the last stage of an axial flow compressor is often centrifugal, this is to. increase the temperature rise. prevent compressor surge. provide initial turning of the airflow.

Reverse thrust can only be selected when the throttle is. 75% power position. open. closed.

The overall air/fuel ratio of a combustion chamber can vary between. 10:1 and 45:1. 45:1 and 130:1. 130:1 and 200:1.

During normal running conditions. combustion is continuously supported by ignition. combustion is intermittently supported by ignition. combustion is self supporting.

How is servo pressure, which is used to control fuel pump swash plate angle, obtained?. From pump inlet pressure through fixed restrictions. From pump delivery pressure through fixed restrictions. From pump delivery pressure through variable restrictions.

Why is the Barometric Pressure Control fitted in a gas turbine engine fuel system. To decrease the fuel flow to the burners with increased air intake pressure. To proportion the fuel flow between primary and main burner lines. To vary pressure pump output in relation to the pressure variation at the intake.

When light-up takes place. the nozzle guide vanes spread the heat to adjacent flame tubes. Interconnectors spread the heat to adjacent flame tubes. each flame tube is isolated from its neighbours.

During any stabilised running condition the spill or half ball valve is. open fully. closed fully. lightly seated.

The swash plate in a fuel pump (static) is. in the minimum position. in the maximum position. at some intermediate position.

Bearing seal failure would most probably cause. high oil temperature. low oil pressure. high oil consumption.

The purpose of the rotating guide vanes on a centrifugal compressor is to. prevent damage by solid objects. direct the air smoothly into the impeller. provide initial diffusing of the air.

With fixed throttle in a climb. RPM will increase. RPM will decrease. RPM will remain constant.

A kinetic valve is a device used to control HP pump output. This is achieved by movement of a. needle valve. diaphragm and half ball valve. knife blade.

What is the surge margin of an axial flow compressor?. The margin between minimum and maximum pressure ratio obtained at constant RPM. The margin between the compressor working line and the surge line. The margin between the stall condition and the surge condition.

High energy ignition is required because of the. high flash point of the fuel. low flash point of the fuel. absorbed moisture content.

The point of maximum velocity in the engine is in the. exhaust exit nozzle. combustion chamber. nozzle guide vanes.

The minimum bend radius for a continuous loop type fire wire is. 1/8". 1/2". 1".

The compression ratio of a jet engine is. the compressor outlet pressure divided by the number of compressor stages. the ratio between turbine pressure and compressor outlet pressure. the ratio between compressor inlet pressure and compressor outlet pressure.

In the H.E.I.U. the discharge resistors. allows sufficient voltage to be stored to provide relight facilities up to 55,000 ft. protects the unit from excessive voltages. allows the capacitors to discharge when the unit is switched off.

A free turbine is. connected directly to the propeller. not directly connected to the power output shaft. connected directly to the power output shaft.

Why do the holes in the body of the duple burner provide air to the shroud around the burner head?. To reduce burner temperature. To minimise carbon formation on the burner face. To assist atomisation of the fuel at slow running.

Variable inlet guide vanes prevent. compressor runaway. compressor stalling. ice build up on compressor blades.

The air passing through the combustion chamber of a jet engine is. used to support combustion and to cool the engine. entirely combined with fuel and burned. speeded up and heated by the action of the turbines.

Water used in a thrust augmentation system should be demineralised to prevent. blocking the jet. fouling the blades and vanes. carbon formation.

A Convergent-Divergent nozzle. produces a type of thrust known as kinetic thrust. makes maximum use of Pressure thrust. requires the aircraft to be travelling at supersonic speeds.

A toroidal vortex is. a bull-nosed cowling for deflecting air from the static. a vapour trail visible in moist air conditions. a region in the combustion chamber of low velocity re-circulation.

The quantity of water usually carried by an aircraft equipped with water injection is enough for. one take-off. two take-offs. three take-offs.

A fuel system icing inhibitor is a fuel additive which. prevents the fuel from freezing. prevents the water in the fuel freezing. prevents both the water and the fuel freezing.

Why are two or more turbine wheels coupled. so power output is doubled. to keep turbine rotor diameter small. to simplify dynamic balancing.

On front fan engines, to obtain thrust reversal, the. hot stream is reversed. cold stream is reversed. hot and cold streams are reversed.

Why is it necessary to have a combustion drain system?. To prevent pressure build up in the combustion chamber. To allow moisture content to drain away. To prevent initial over-fuelling on start up or wet start.

How are extinguisher spray rings checked for freedom from obstruction?. Blowing through with compressed air. Firing the system. Pumping water through the system.

What is a ‘cannular’ combustion system. One common flame tube closed in a common air casing. A set of flame tubes, enclosed in a common air casing. A set of flame tubes, each mounted in a separate air casing.

Exhaust noise can be reduced by. lowering the vibration frequency. increasing the jet velocity. increasing the mixing rate.

The flame temperature is approximately. 500°C. 2000°C. 1400°C.

The rate of discharge of a H.E.I.U. is. 4 discharges per revolution. 60 - 100 per minute. 60 - 100 per second.

Fuel entering the combustion chamber from an atomizer spray nozzle enters as. a fuel/air mixture. fuel in air pulses. fuel continuously.

When accelerating from "light-up" to ground idling speed, the EGT wil. increase above idle value then decrease to normal. decrease below idle value then increase to normal. remain constant.

Air through the compressor, before entering the combustion chamber passes. through nozzles to increase the velocity. through divergent passage to increase the pressure. through divergent passage to decrease the pressure.

Why is it necessary to control fuel supply to the engine during rapid acceleration?. To control maximum RPM. To prevent excessively high EGT and possible compressor surge. To prevent compressor stall above cruise RPM.

An advantage of an annular combustion system is. decrease in combustor length compared to a tubo-annular combustor of the same output. unrestricted airflow at maximum RPM. diameter of engine is reduced due to the cans being smaller.

Which component corrects for air density effects on fuel/air mixture in a gas turbine engine?. The adjustable throttle valve. The pressurising valve. The barometric pressure control unit.

How is the combustion chamber drain valve closed?. By 12th stage compressor air pressure. By a return spring. By combustion chamber gas pressure.

A gas turbine engine is stopped by closing. HP cock. LP cock. throttle valve.

Low mass airflow through a compressor will produce. have no effect. stalling of rear stages. stalling of early stages.

Why is the low pressure fuel pump fitted in a gas turbine engine aircraft?. To maintain a vapour free pressure from the aircraft fuel tanks to the HP fuel pump. As an emergency in case of failure of the HP pump. As a booster to the HP pump for excess fuel required during sudden throttle openings.

If compressor surge occurs it is recognized by. fluctuating RPM and fuel flow. fluctuating EGT and oil temperature. coughing in compressor and vibration.

Why are oil seals pressurised?. To ensure minimum oil loss. To ensure oil is forced into the bearings. To ensure that the oil is prevented from leaving the bearing housing.

A bleed valve. relieves compressor choking at low RPM. bleeds air from compressor for intake de-icing. controls air intake pressure.

If a compressor has a compression ratio of 9:1 and an intake compression of 2:1 what is the overall compression ratio?. 11:1. 18:1. 9:1 intake compression does not add to the overall compression ratio of the system.

A compressor stage stalls when. compression ratio is too high. adiabatic temperature rise is too high. smooth airflow is disrupted.

What action is taken to protect integral fuel tanks from corrosion due to micro biological contamination?. A biocidal additive is added to the fuel. The inside of the tank is coated with yellow chromate. Rubber liners are installed in the tank.

Inlet guide vanes are fitted to. guide the airflow. control the angle of airflow into the compressor. control the quantity of air entering the intake.

Why in an axial flow compressor is the cross sectional area of the compressor air duct reduced at each stage. to decrease the velocity of the air rising under pressure. to maintain the velocity of the air under rising pressure. to permit stronger, shorter blades to be used in the later stages.

Why do the holes in the body of the duple burner provide air to shroud around the burner head?. to reduce burner temperature. to minimise carbon formation. to assist atomisation of the fuel at slow running.

At constant RPM the pressure ratio of the compressor and the temperature rise across the compressor. remains constant irrespective of height. decrease with height. increases with height.

With an electrical ice protection system, the heating elements operate. continuously. intermittently. part continuous - part intermittent.