GAS TURBINE COMPRESSOR – Air – DGCA Question Bank For Politics

#1. The pressure ratio of a gas turbine engine compressor is:

The ratio between compressor outlet and compressor inlet pressure.

Equal to the number of compression stages.

The ratio between exhaust inlet and exhaust outlet pressure.

Never greater than 5 to 1.

#2. The compressor idling speed of a gas turbine engine will increase:

At higher ambient temperature.

With higher than sea level density.

At altitudes lower than sea level.

At lower ambient temperature.

#3. One stage of an axial flow compressor consists of:

One rotor assembly and one row of stator vanes.

One stator assembly and one row of guide vanes.

One rotor and one impeller assembly.

One impeller and one diffuser assembly.

#4. The pressure rise across each stage of an axial flow compressor is:

Greater than that of a centrifugal compressor.

Between 3 and 5 to one.

Twice the inlet pressure.

Between 1.1 and 1.2 to one.

#5. The ring of blades which sometimes precede the first rotor stage of an axial flow compressor are called:

The first stage stator blades.

The inlet guides vanes.

First stage diffuser blades.

Nozzle guide vanes.

#6. As air passes through an axial flow compressor, a pressure rise takes place in:

The impeller and the diffuser.

The rotor blades only.

Both the rotor blades and the stator vanes.

The stator vanes only.

#7. In the event of a surge occurring the correct action to be taken is:

To close the throttle quickly.

To close the throttle slowly.

To open the throttle fully.

To close the LP fuel valve.

#8. Shrouding of stator blade tips is designed to:

Prevent tip turbulence.

Ensure adequate cooling.

Minimise vibration.

Prevent tip losses.

#9. The cross sectional area of the air annulus is reduced as it approaches the combustion chamber:

To maintain the volume of the air under rising pressure.

To prevent an increase of the velocity of the air under rising pressure.

To maintain the speed of the air entering the engine.

To allow longer blades to be used in the latter stages of the compressor.

#10. The attachment of blades to the compressor disc:

Allows slight movement to relieve stress concentration.

Is rigid.

Prevents them being contaminated by the atmosphere.

Allows slight movement because of the different expansion rates of the blades and the disc, which would otherwise cause center line closure.

#11. Compressor blades are designed to produce:

A given pressure and velocity rise.

A constant flow over the engine speed range.

A steady velocity with a pressure rise over the engine speed range.

Turbulent flow into the combustion chamber.

#12. A compressor blade will stall when:

The air axial velocity and rotational speed relationship is disturbed.

The mass air flow and speed relationship is constant.

The speed of the gas flow through the turbine falls below 0.4 Mach.

The compression ratio exceeds 10 to 1.

#13. Compressor surge will occur when:

All stages are at maximum efficiency.

All stages are at maximum RPM.

There is a partial breakdown of airflow through the compressor.

All stages have stalled.

#14. Cascade vanes are fitted in which part of the centrifugal compressor?

The air inlet

The outlet elbow

The impeller

The diffuser

#15. The purpose of the diffuser vanes in a centrifugal compressor is to:

Increase the charge temperature.

Convert pressure energy into kinetic energy.

Increase the air velocity.

Convert kinetic energy into pressure energy.

#16. The pressure rise across a centrifugal compressor:

Occurs in the impeller only.

Occurs in the diffuser only.

Is shared almost equally by the impeller and the diffuser.

Is always greater in the diffuser than in the impeller.

#17. To gain a greater pressure ratio than 4:1:

Two centrifugal compressors can be placed in parallel.

The compressor diameter must be reduced.

Two centrifugal compressors can be placed in series with each other.

The cascade vanes must be convergent.

#18. The major disadvantage of a centrifugal compressor is that:

It cannot cope with a large mass flow of air.

It cannot be used for a turbo jet engine.

A larger turbine must be used.

It is more prone to damage than the axial flow compressor

#19. The purpose of cascade vanes is to:

Increase the velocity of the airflow prior to it entering the combustion chambers.

Turn the air smoothly through 90 degrees and complete diffusion.

Remove swirl from the airflow.

Swirl the air, ready for the next compression stage.

#20. The type of compressor used to create radial airflow would be:

Positive displacement.

Axial.

Centrifugal.

Constant volume.

#21. Under ideal conditions the pressure rise across a centrifugal compressor can be:

1.1 or 1.2 to 1.

Not more than 4 to 1.

1.5 to 1.

30 to 1.

#22. An advantage of a centrifugal compressor is that it is:

Dynamically balanced.

More robust and is easier to develop and manufacture.

Unaffected by turbulence.

Able to handle a larger mass of air than an axial flow compressor.

#23. A compressor stall causes:

The vibration level to increase with a decrease in the turbine gas temperature.

An increase in the turbine gas temperature and the vibration level.

The airflow through the engine to stop suddenly.

The rotation of the engine to stop suddenly.

#24. Air passing through a convergent duct experiences:

A decrease in temperature and pressure with an increase in velocity.

An increase in temperature and velocity with a decrease in pressure.

An increase in temperature and pressure with a velocity decrease.

Adiabatic expansion.

#25. Fuel is regulated on rapid engine acceleration:

To prevent detonation in the combustion chambers.

Because the rapid response of the compressor might cause a flame out.

Because the cooling effect of too much fuel would cause a drop in pressure in the combustion chamber.

To prevent inducing a compressor stall and surge.

#26. A compressor stall:

Is overcome by increasing the fuel flow.

Is a complete breakdown of the airflow through the compressor.

May only affect one stage or several stages of a compressor.

Is mechanical failure of the compressor.

#27. Compressor blades increase in size:

From the root to the tip to increase the temperature.

From the high pressure section of the compressor to the low-pressure section

From the low-pressure section of the compressor to the high-pressure section to maintain a constant airflow velocity.

From the tip to the root to decrease the temperature.

#28. The occurrence of compressor stalls is limited by:

Bleed valves.

Nozzle guide vanes.

Swirl vanes.

Cascade vanes.

#29. Bleed valves are automatically opened:

At maximum R.P.M. to prevent compressor stall.

At low R.P.M. to prevent the turbine stalling.

During engine acceleration to prevent turbine surge.

At low engine R.P.M to prevent the compressor stalling.

#30. To prevent compressor stall at the rear of the compressor, bleed valves must be positioned:

At the rear stages of the compressor.

At the front stages of the compressor.

At the mid stages of the compressor.

At the intake of the engine.

#31. A complete breakdown of airflow through a compressor is known as:

Compressor turbulence.

Compressor buffet.

Compressor surge.

Compressor seizure.

#32. One indication that a compressor bleed valve has stuck closed at low R.P.M. is:

Possible compressor stall.

An inability to achieve full power.

That bleed air is reduced.

That the engine will stop.

#33. Within the compressor:

Bleed valves are set to open at high R.P.M.

Pressure decreases.

Temperature decreases.

Temperature increases.

#34. Bleeding compressor air for anti-icing will cause:

An increase in T.G.T., a decrease in thrust and an increase in S.F.C.

A decrease in T.G.T., an increase in thrust and a decrease in S.F.C.

An increase in R.P.M. and fuel flow.

An increase in R.P.M. and a decrease in fuel flow.

#35. Variable inlet guide vanes:

Deflect air past the compressor.

Prevent compressor stall.

Deflect air past the turbine.

Induce air into a centrifugal compressor.

#36. Compressor blades are twisted from root to tip:

To decrease the pressure.

To maintain a correct angle of attack.

To reduce the relative airflow.

To give added rigidity to the blade structure.

#37. In a compressor:

The air temperature is steady with a pressure rise.

The air temperature falls with a pressure rise.

The drop in air temperature is inversely proportional to the pressure rise.

The air temperature rises with a pressure rise.

#38. A stall in a gas turbine engine is most likely to occur with:

Pressure ratio: High, Location in compressor: Front

Pressure ratio: High, Location in compressor: Back

Pressure ratio: Low. Location in compressor: Back

Pressure ratio: Low, Location in compressor: Front

#39. The low pressure compressor of a high ratio by-pass engine:

Is driven by the high pressure turbine.

Rotates faster than the high-pressure compressor.

Is always a centrifugal compressor.

Is driven by the rearmost turbine.

#40. Contamination of the compressor:

Is not likely to prove a problem if the aircraft is not flown at low level over the sea.

Will not decrease the performance of the engine if the fuel sulphur content does not exceed .001%.

Can seriously reduce the efficiency of the engine.

Can be reduced by periodically flying through thunderstorms.

Dgca Question Bank For Pilots

Results