15.6 Turbine Section.

61. What is the normal range of turbine efficiency?. A. 90% - 95%. B. 70% - 85%. C. 30% - 40%.

Ans.- 90% - 95%. Explanation. Rolls Royce The Jet Engine page 51 Para 11 refers to 92%.

5. Where do stress rupture cracks usually appear on turbine blades?. A. Across the blade root, parallel to the fir tree. B. Across the leading or trailing edge at a right angle to the edge. C. Along the leading edge, parallel to the edge.

Ans.- Across the leading or trailing edge at a right angle to the edge. Explanation. Jeppesen A&P Powerplant Textbook 4-25.

40. How are turbine disks attached to the shaft in gas turbine engine?. A. Splined. B. Curvic couplings. C. Bolted.

Ans.- Bolted. Explanation. Jeppesen Aircraft gas Turbine Powerplant page 3-41 refers.

63. How is a radial turbine driven?. A. By impulse. B. By change of momentum and angle of airflow. C. By reaction.

Ans.- By change of momentum and angle of airflow. Explanation. Radial turbines are effectively reversed centrifugal compressors.

47. Which of the following is most likely to occur in the turbine section of a gas turbine engine?. A. Pitting. B. Galling. C. Cracking.

Ans.- Cracking. Explanation. A turbine bearing is under great heat stress, cracking is the only possible choice here.

23. Which of the following conditions is usually not acceptable to any extent in turbine blades?. A. Cracks. B. Dents. C. Pits.

Ans.- Cracks. Explanation. NIL.

9. What term is used to describe a permanent and cumulative deformation of turbine blades?. A. Stretch. B. Creep. C. Distortion.

Ans.- Creep. Explanation. NIL.

27. Why are two or more turbine wheels coupled?. A. To keep turbine rotor diameter small. B. So power output is doubled. C. To simplify dynamic balancing.

Ans.- So power output is doubled. Explanation. Rolls Royce The Jet Engine page 45 refers.

2. What are the two main basic components of the turbine section in a gas turbine engine?. A. Stator and rotor. B. Hot and cold. C. Impeller and diffuser.

Ans.- Stator and rotor. Explanation. Jeppesen A&P Powerplant Textbook 3-25.

22. When aircraft turbine blades are subjected to excessive heat stress, what type of failures would you expect?. A. Bending and torsion. B. Stress rupture. C. Torsion and tension.

Ans.- Stress rupture. Explanation. NIL.

10. What is the major function of the turbine assembly in a turbojet engine?. A. Directs the gases in the proper direction to the tailpipe. B. Supplies the power to turn the compressor. C. Increases the temperature of the exhaust gases.

Ans.- Supplies the power to turn the compressor. Explanation. NIL.

6. What is meant by a shrouded turbine?. A. The turbine blades are shaped so that their ends form a band or shroud. B. The turbine wheel has a shroud or duct which provides cooling air to the turbine blades. C. The turbine wheel is enclosed by a protective shroud to contain the blades in case of failure.

Ans.- The turbine blades are shaped so that their ends form a band or shroud. Explanation. Jeppesen A&P Powerplant Textbook 3-28.

51. What are blue and golden deposits evidence of, on a turbine blade?. A. Titanium. B. Aluminium. C. Magnesium.

Ans.- Titanium. Explanation. Aluminium and magnesium leave white powder deposits so by elimination the answer is titanium.

21. Why do some turbine engines have more than one turbine wheel attached to a single shaft?. A. To facilitate balancing of the turbine assembly. B. To extract more power from the exhaust gases than a single wheel can absorb. C. To help stabilize the pressure between the compressor and the turbine.

Ans.- To extract more power from the exhaust gases than a single wheel can absorb. Explanation. NIL.

30. Why are nozzle guide vanes fitted?. A. To decrease velocity of the gas flow. B. To increase velocity of the gas flow. C. To increase velocity of the air flow.

Ans.- To increase velocity of the gas flow. Explanation. Jeppesen Gas Turbine Powerplants Page 3-38 refers.

17. Dirt particles in the air going into the compressor of a turbine engine will form a coating on all but which of the following?. A. Turbine blades. B. Casings. C. Inlet guide vanes.

Ans.- Turbine blades. Explanation. NIL.

31. A turbine disk is. A. a disk at the core of the engine that the blades are attached to. B. a segmented or complete shroud on blade tips that reduces leakage. C. a shroud around the stators of the turbine.

Ans.- a disk at the core of the engine that the blades are attached to. Explanation. The turbine blades are mounted to the disc which absorbs the centrifugal force.

12. A condition known as 'hot streaking' in turbine engines is caused by A. a partially clogged fuel nozzle. B. excessive fuel flow. C. a misaligned combustion liner.

Ans.- a partially clogged fuel nozzle. Explanation. NIL.

64. Turbine disk growth is due to. A. a permanent change in disk diameter. B. an overall increase in blade length. C. a build up of carbon deposits.

Ans.- a permanent change in disk diameter. Explanation. The turbine disc does not include the blades.

38. Creep is. A. not found in turbines. B. a temporary deformation of turbine. C. a permanent deformation of turbine.

Ans.- a permanent deformation of turbine. Explanation. Jeppesen Aircraft Gas Turbine Powerplant Page 5-28 refers.

41. Fir tree turbine blade attachment locates the blade. A. allows slight movement. B. radially. C. axially.

Ans.- allows slight movement. Explanation. Rolls Royce The Jet Engine page 52 Para 19 refers.

54. During a borescope check of the H.P turbine blades. A. dry motor the engine at minimum speed. B. hand turn the turbine wheel. C. attach a device to the accessory gearbox and rotate slowly.

Ans.- attach a device to the accessory gearbox and rotate slowly. Explanation. All large GTE have a hand turning tool adaptor fitted to the accessory or high speed gearbox.

58. A fir tree root. A. allows compressor cooling air to alleviate thermal stress. B. attaches turbine blades to the turbine disk. C. allows individual turbine blades to be changed without engine disassembly.

Ans.- attaches turbine blades to the turbine disk. Explanation. Rolls Royce the Jet Engine Page 52 para 19 refers.

3. Turbine impulse blading forms a. A. constant area duct. B. divergent duct. C. convergent duct.

Ans.- constant area duct. Explanation. Rolls Royce - The Jet Engine (New) Page 135 diagram.

59. The passage between adjacent nozzle guide vanes forms a. A. convergent duct. B. divergent duct. C. parallel duct.

Ans.- convergent duct. Explanation. Rolls Royce The Jet Engine page 51 paragraph 13 refers.

16. N.G.V's form. A. convergent ducts. B. parallel ducts. C. divergent ducts.

Ans.- convergent ducts. Explanation. Jepperson Gas Turbine Powerplants Page 3-38 refers.

55. The turbine section of a jet engine. A. converts dynamic pressure into mechanical energy. B. circulates air to cool the engine. C. extracts heat energy to drive the compressor.

Ans.- converts dynamic pressure into mechanical energy. Explanation. The shape and size of the turbine blades determines the amount of energy extracted from the dynamic pressure of the airflow.

56. The temperature and centrifugal loads which the turbine is subjected to during normal engine operation causes. A. fatigue failure. B. elastic stretching. C. creep loading.

Ans.- creep loading. Explanation. Creep is a permanent deformation caused by high centrifugal loads at continuous high temperature.

15. Continued and/or excessive heat and centrifugal force on turbine engine rotor blades is likely to cause. A. galling. B. creep. C. profile.

Ans.- creep. Explanation. Jeppesen A&P Powerplant Textbook 4-22.

11. Gas pressure through the turbine section will generally. A. increase. B. remain the same. C. decrease.

Ans.- decrease. Explanation. NIL.

13. Temperature through the turbine stages generally. A. remains the same. B. decreases. C. increases.

Ans.- decreases. Explanation. NIL.

7. Turbine nozzle diaphragms located on the upstream side of each turbine wheel, are used to. A. decrease the velocity of the heated gases flowing past this point. B. direct the flow of gases parallel to the vertical line of the turbine blades. C. increase the velocity of the heated gases flowing past this point.

Ans.- direct the flow of gases parallel to the vertical line of the turbine blades. Explanation. Jeppesen A&P Powerplant Textbook 3-25.

4. The turbine section. A. increases air velocity to create thrust. B. uses heat energy to expand and accelerate the gas flow. C. drives the compressor section.

Ans.- drives the compressor section. Explanation. Jeppesen A&P Powerplant Textbook 3-25.

33. The active clearance control system aids turbine engine efficiency by. A. automatically adjusting engine speed to maintain a desired EPR. B. adjusting stator vane position according to operating conditions and power requirements. C. ensuring turbine blade to engine case clearances are kept to a minimum by controlling case temperatures.

Ans.- ensuring turbine blade to engine case clearances are kept to a minimum by controlling case temperatures. Explanation. NIL.

62. Turbine engine components are never manufactured by. A. electrical resistance welding. B. argon arc welding. C. gas welding.

Ans.- gas welding. Explanation. Both Argon arc and Electron beam welding are referred to in RR the Jet Engine so we assume gas welding is not used, this is probably due to carburisation of the weld.

65. A nozzle guide vane is. A. hollow in construction to allow for thermal expansion. B. hollow in construction to allow for flow of cooling air. C. solid in construction to support the guide vane.

Ans.- hollow in construction to allow for flow of cooling air. Explanation. Air is tapped from the H.P compressor and passed through the N.G.V to cool it.

24. The forces driving a turbine round are due to. A. impulse only. B. reaction only. C. impulse and reaction.

Ans.- impulse and reaction. Explanation. Rolls Royce The Jet Engine Page 50 Refers.

36. On an impulse-reaction turbine blade it is. A. impulse at the root and reaction at the tip. B. reaction at the root and impulse at the tip. C. impulse and reaction all the away along the blade.

Ans.- impulse at the root and reaction at the tip. Explanation. Jeppesen Aircraft Gas Turbine Powerplant page 3-40 refers. Rolls Royce pg.50 para.10 and figure5.6 stagger angle.

1. The three main types of turbine blades are. A. impulse, vector, and impulse-vector. B. reaction, converging, and diverging. C. impulse, reaction, and impulse-reaction.

Ans.- impulse, reaction, and impulse-reaction. Explanation. Jeppesen A&P Powerplant Textbook 3-27.

39. Creep, overall. A. has no effect on turbine diameter. B. increases turbine diameter. C. decreases turbine diameter.

Ans.- increases turbine diameter. Explanation. Jeppesen Aircraft Gas Turbine Powerplant Page 5-28 refers.

52. Necking and mottling of turbine blades. A. is due to thermal stress. B. is formed during manufacture. C. is due to bending when the gas hits the blades.

Ans.- is due to thermal stress. Explanation. Necking could occur due to creep which is a function of thermal stress and centrifugal loads, and turbine blades do show signs of discolouration after use, the latter is not normally a defect.

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

Ans.- minimise vibration. Explanation. Jeppesen Gas Turbine Powerplant Page 3-43 refers.

44. Forces driving the turbine are due to. A. aerodynamic lift imposing impulse on blades. B. momentum and directional acceleration of gases. C. expansion of gases.

Ans.- momentum and directional acceleration of gases. Explanation. Rolls Royce The Jet Engine Page 49-50 refers.

20. Hot section inspections for many modern turbine engines are required. A. on a time or cycle basis. B. only when an over temperature or overspeed has occurred. C. only at engine overhaul.

Ans.- on a time or cycle basis. Explanation. NIL.

42. Creep may occur to turbine blades due to. A. prolonged low RPM use. B. over-temp with excessive centrifugal loads. C. high back pressures.

Ans.- over-temp with excessive centrifugal loads. Explanation. Creep is irreversible Rolls Royce the Jet Engine Page 56 refers.

43. Creep may occur to turbine blades due to. A. prolonged low RPM use. B. over-temp with excessive centrifugal loads. C. high back pressures.

Ans.- over-temp with excessive centrifugal loads. Explanation. Creep is irreversible Rolls Royce the Jet Engine Page 56 refers.

35. Bowing of turbine blades indicates an. A. over-temperature condition. B. over-speed condition. C. under-temperature condition.

Ans.- over-temperature condition. Explanation. Jeppesen Aircraft Gas Turbine Powerplant page 5-30 refers to bowing as part of the ageing process. Over temp is the only answer relevant to aging (temperature creep).

25. Nozzle guide vanes give a. A. pressure increase, velocity decrease. B. pressure increase, velocity increase. C. pressure decrease, velocity increase.

Ans.- pressure decrease, velocity increase. Explanation. Jeppesen Gas Turbine Powerplant Page 3-35 refers.

46. An increase in turbine diameter is caused by. A. prolonged high temperatures and centrifugal loads. B. products of combustion. C. over speed.

Ans.- prolonged high temperatures and centrifugal loads. Explanation. This is known as creep.

29. Two basic types of turbine blades are. A. impulse and vector. B. reaction and impulse. C. tangential and reaction.

Ans.- reaction and impulse. Explanation. Jeppesen Gas Turbine Powerplants Page 3-40 refers.

19. A purpose of the shrouds on the turbine blades of an axial flow engine is to. A. reduce air entrance. B. increase tip speed. C. reduce vibration.

Ans.- reduce vibration. Explanation. NIL.

60. As the hot gasses flow through an impulse turbine blading, the velocity. A. will decrease. B. remains constant. C. will increase.

Ans.- remains constant. Explanation. In an 'Impulse bladed turbine' the turbine blades form parallel ducts therefore the velocity will remain constant figure 5-5 of RR the Jet Engine shows the contour of impulse turbine blades.

66. A slow constant growth in a turbine blade is known as. A. primary creep. B. secondary creep. C. tertiary creep.

Ans.- secondary creep. Explanation. NIL.

18. Reduced blade vibration and improved airflow characteristics in gas turbines are brought about by. A. shrouded turbine rotor blades. B. fir tree blade attachment. C. impulse type blades.

Ans.- shrouded turbine rotor blades. Explanation. NIL.

8. Reduced blade vibration and improved airflow characteristics in turbines are brought by. A. shrouded turbine rotor blades. B. impulse type blades. C. fir tree blade attachment.

Ans.- shrouded turbine rotor blades. Explanation. NIL.

34. Turbine rear struts. A. straighten the gas flow. B. increase the velocity of the gas flow. C. increase the pressure of the gas flow.

Ans.- straighten the gas flow. Explanation. Jeppesen Aircraft Gas Turbine Powerplant page 3-34 refers.

45. Impulse turbine blades run cooler than reaction blades because. A. impulse spin faster radially. B. temperature drop across N.G.V is greater. C. converging rotors increase velocity.

Ans.- temperature drop across N.G.V is greater. Explanation. Impulse blades have total pressure drop in N.G.V's hence air is colder as it enters turbine RR Page51 refers.

53. Impulse blades operate cooler than reaction blades because. A. impulse blades rotate at higher speeds. B. the N.G.V's cool the air. C. the airflow has a higher velocity through a impulse turbine N.G.V.

Ans.- the airflow has a higher velocity through a impulse turbine N.G.V. Explanation. Impulse turbine N.G.Vs accelerate gases faster than their reaction counterparts therefore the pressure and temperature is reduced more in the impulse turbine.

14. Shrouded blades allow. A. smaller inlets to be used. B. higher turbine inlet temperatures. C. thinner more efficient blade sections to be used.

Ans.- thinner more efficient blade sections to be used. Explanation. Jepperson Gas Turbine Powerplants Page 3-42 refers.

32. .When carrying out a borescope the damage on turbine blades that would indicate a failure is. A. speckling. B. tip curl. C. colour changes.

Ans.- tip curl. Explanation. Jeppesen Gas Turbine Powerplants figure 5-23 page 178 and figure 5-26 page 185 refers.

57. Impulse-reaction turbine blades form. A. tip half reaction, root half Impulse. B. 1 stage impulse, 1 stage reaction. C. tip half Impulse, root half reaction.

Ans.- tip half reaction, root half Impulse. Explanation. Turbine blades move from impulse at the root to reaction at the tip.

28. Running clearance on a turbine disk is kept to a minimum to reduce. A. temperature loss. B. aerodynamic buffeting. C. tip losses.

Ans.- tip losses. Explanation. Jeppesen Gas Turbine Powerplants Page 3-18 refers.

50. Excessive turbine temperatures can lead to. A. turbine blade creep and an increase in the diameter of the turbine. B. not a serious problem as long as engine oil pressure is within limits. C. a serious fire risk in the engine.

Ans.- turbine blade creep and an increase in the diameter of the turbine. Explanation. Jeppesen gas turbine Powerplant Page 5-28 discusses the causes of creep.

37. Turbine creep effects. A. turbine blades. B. turbine disks. C. N.G.Vs.

Ans.- turbine blades. Explanation. Jeppesen Aircraft Gas Turbine Powerplant Page 5-28 refers.

49. An impulse/reaction turbine is designed to ensure. A. greater axial velocity at the blade root. B. uniform axial velocity from blade root to tip. C. greater axial velocity at the blade tip.

Ans.- uniform axial velocity from blade root to tip. Explanation. Jeppesen Gas turbine Powerplant page 3-40 refers.

48. Aluminium deposits on the turbine show up as. A. white or silver speckles. B. white powder traces. C. black stains.

Ans.- white or silver speckles. Explanation. CAIPs E L/3-10 refers. It also says titanium speckles are blue or gold.