1. To ensure high compressor efficiency, the velocity of the airflow at the compressor inlet is normally not in excess of:-
(a) Mach 0.5.
(b) Mach 0.75.
(c) Mach 1.
2. A supersonic diffuser takes the form of a:~
(a) convergent/divergent duct.
(b) divergent duct.
(c) convergent duct.
3. In the vaneless space, the pressure, velocity and temperature of air leaving the impeller will:-
(a) increase.
(b) remain unchanged, (c) decrease.
4. The maximum pressure ratio obtained by a single stage centrifugal compressor is relatively low, being in the region of:~
(a) 1:1.
(b) 4:1.
(c) 6.25:1.
3. The rotating guide vanes of a centrifugal impeller are normally manufactured from:-
(a) steel, as the leading edges are more prone to impact damage.
(b) aluminium alloy, because lightness of structure is important.
(c) titanium, because of its good resistance to high temperature.
1 . (a ) 2 . (c ) 3 . (b ) 4 . (b ) 5 . (a )
1. When considering the rotating assembly, the complete disc assembly including spacer rings is secured on the shaft by:-
(a) splines.
(b) a retaining ring nut.
(c) a bolted flanged plate.
2. Stagger angle is the term applicable to the:- (a) angle of twist on a rotor blade.
(b) misalignment permissible between rotor blades and stator blades.
(c) tangential disposition of inlet guide vanes.
3. The passage formed between individual rotor blades is :- (a) convergent.
(b) convergent/divergent.
(c) divergent.
4. The pressure rise across one stage of the axial flow compressor is:-
(a) not more than 1.3:1.
(b) 4:1 maximum.
(c) greater than that attained by a single stage centrifugal compressor.
5. Stop plates are fitted in an axial compressor in order to prevent:-
(a) axial movement of the rotor spacer rings.
(b) circumferential movement of the stator blades.
(c) axial movement of the compressor shaft at high rpm.
1 . (b ) 2 . (a ) 3 . (c) 4 . (a ) 5 . (b )
1. Air used for combustion is termed:- (a) primary and secondary.
(b) primary.
(c) tertiary.
2. The ratio of kerosine to air for efficient combustion is :- (a) 1:45
(b) 1:130.
(c) 1:15.
3. What is a can-annular combustion system?
(a) A set of flame tubes each mounted in a separate air casing.
(b) A set of flame tubes enclosed in a common air casing.
(c) One common tube enclosed in a common air casing.
4. What is the purpose of the tertiary airflow created in the
(c) To ensure the complete combustion of the fuel.
5. An advantage of an annular combustion chamber is that:- (a) the diameter of the engine is reduced.
(b) there is unrestricted airflow at maximum rpm.
(c) there is a decrease in engine length.
The approximate amount of mass airflow taken in by the combustor snout is:-
(a) 18%.
(b) 82%.
(c) 25%.
The overall air/fuel ratio of a combustion chamber can vary between:-
(a) 10:1 to 45:1.
(b) 45:1 to 130:1.
(c) 130:1 to 200:1.
Combustion chamber flame temperatures can be as high as:- (a) 500°C.
(b) 2000°C (c) 1400°C
1 . (b ) 2 . (c ) 3 . (b ) 4 . (a ) 5 . (c ) 6 . (a ) 7 . (b ) 8 . (b )
1. On an exhaust unit there is a convergent orifice. This is located on the exhaust unit:-
(a) inlet.
(b) outlet.
(c) in the centre of the exhaust duct.
2. What is the purpose of the propelling nozzle?
(a) To increase the velocity and decrease the of th e «jas stfearai teavtn the exhaust .
(b) To decrease the velocity and increase the pressure of the gas stream leaving the exhaust.
(c) To increase the velocity and pressure of the gas stream leaving the exhaust.
3. What is the reason for shrouding turbine blades?
(a) To Whic h way tw the blades.
(b) To reduce air losses and increase efficiency.
(c) To enable thinner blades to be used.
4. Why are nozzle guide vanes fitted?
(a) To increase velocity of the cooling air flow.
(b)
(c) To increase velocity of the gas flow.
5. Cooling air for turbine blades and nozzle guide vanes is normally tapped from the:-
(a) compressor.
(b)
(c) exhaust gases
1. (b) 2. (a) 3. (b) 4 . (c) 5. (a)
1. Cooling air cleansing is achieved by using a:
(a) centrifugal filter.
(b) micronic filter.
(c) felt filter element.
2. Which stage of cooling air is used for oil sump pressurisation?
(a) Intermediate air.
(b) HP air.
(c) LP air.
3. Which type of air/oil seal is machine ground and finally lapped to a micro finish?
(a) Rubber micronic seal.
(b) Carbon seal.
(b) By an increase of air pressure across the knife edge seal.
(c) By application of springs on the carbon seal.
5. Once air cleansing has taken place, where is the dirty air directed?
(a) Into the turbine disc.
(b) Into the turbine exhaust.
(c) Overboard from the engine through side vents.
1. (a) 2. (c) 3. (b) 4. (a) 5. (c)
External Cooling
1. The cooling air that is used to cool the bleed air passing through the heat exchanger is from the:-
(a) turbine stream.
(b) fan stream.
(c) bleed air ducts.
2. Pressurising air to the hydraulic tank:-
(a) prevents the oil from boiling at altitude.
(b) provides cooling of the oil.
(c) provides a head of pressure in the tank.
3. Turbine case cooling:-
(a) prevents the turbine case from expanding.
(b) prevents the turbine case from contracting.
(c) ensures that compressors run efficiently.
4. The bleed air valve can be electrically closed in an over temperature situation by the:-
(a) overheat switch.
(b) duct temperature sensor.
(c) fan air valve.
1. (b) 2. (c) 3. (a) 4. (a)
LUBRICATION
1. A bearing which can accept radial and axial loads in one direction is a:-
(a) needle roller bearing.
(b) angular contact bearing.
(c) plain bearing.
2. A cylindrical roller bearing is:-
(a) used where there is a large radial load.
(b) used where there is a large axial load.
(c) only used where the motion of the bearing is oscillatory.
3. Tapered roller bearings which are fitted in pairs are :- (a) fitted with the cone ends towards each other.
(b) fitted with the cone ends away from each other.
(c) fitted with the cone ends both facing in the same direction.
4. Fluid damped bearings :- (a) dampen out noise.
(b) dampen out vibration.
(c) are always ball bearings.
5. Bearings which are to be stored should be stored:- (a) flat.
(b) on their edges.
(c) in either condition.
Which gear would be quietest in operation?
(a) spur.
(b) straight bevel.
(c) helical. Backlash in gears:-
(a) will only occur with wear.
(b} is necessary.
(c) should be eliminated on installation. Helical gears:-
(a) produce an axial load.
(b) produce a radial load.
(c) are only used to change direction. Plain bearings:-
(a) are made from hard alloys, (b) are made from soft metals.
(c) can be made from either.
1. (b) 2. (a) 3. (a) 4. (b) 5. (a) 6. (c) 7. (b) 8. (a) 9. (b)
1. The part of the engine in which surge occurs is the:- (a) front fan.
(b) turbine.
(c) compressor.
2. Compressor stall can be caused by the blades being subjected tor-
(a) sonic vibration, (b) a low angle of attack.
(c) an excessively high angle of attack.
3. What should a ground run engineer do when he discovers the first indication of surge?
(a) Reduce the throttle setting.
(b) Close the fuel valve.
(c) Carry out shut down procedure.
4. The value of the airflow and pressure ratio at which a surge occurs is termed the:-
(a) surge margin.
(b) working line.
(c) surge point.
5. What must a variable geometry intake system do to supersonic airflow?
(a) Slow it down.
(b) Compress it.
(c) Keep it at sonic speeds.
1 (c) 2 (c) 3 (a)
4 (c) 5 (a)