15.2 Engine Performance.

51. Full reverse power is approximately. A. 95% of forward thrust. B. 75% of forward thrust. C. 50% of forward thrust.

Ans.- 50% of forward thrust. Explanation. Jeppesen Aircraft Gas Turbine Powerplants page 3-52 refers.

14. Which of the following variables affect the inlet air density of a turbine engine?. A. Altitude of the aircraft, Ambient temperature. B. Compression ratio, Turbine inlet temperature, Altitude of the aircraft, Ambient temperature. C. Speed of the aircraft, Compression ratio, Turbine inlet temperature,Altitude of the aircraft.

Ans.- Altitude of the aircraft, Ambient temperature. Explanation. NIL.

3. Which statement is true regarding jet engines?. A. At the higher engine speeds, thrust increases rapidly with small increases in RPM. B. At the lower engine speeds, thrust increases rapidly with small increases in RPM. C. The thrust delivered per pound of air consumed is less at high altitude.

Ans.- At the higher engine speeds, thrust increases rapidly with small increases in RPM. Explanation. Jeppesen A&P Powerplant Textbook 3-43.

7. At what stage in a gas turbine engine are gas pressures the greatest? A. Compressor outlet. B. Turbine outlet. C. Compressor inlet.

Ans.- Compressor outlet. Explanation. NIL.

30. The total power in a turboprop engine is the. A. SHP. B. BHP. C. E S HP

Ans.- E S HP . Explanation. E S HP = shaft horse power plus residual gas exhaust thrust.

6. With a fixed throttle, and with increased mass airflow, what happens to EPR?. A. EPR goes up. B. EPR remains constant. C. EPR goes down.

Ans.- EPR goes down. Explanation. With increasing mass airflow with throttles fixed Ram pressure (Pt2) increases but the P7 pressure remains the same. Jeppesen Aircraft Gas Turbines page 12-18 refers.

24. What effect does high atmospheric humidity have in the operation of a jet engine?. A. Decreases compressor and turbine RPM. B. Decreases engine pressure ratio. C. Has little or no effect.

Ans.- Has little or no effect. Explanation. Jeppesen A&P Technician Propulsion Textbook 7-70.

46. Which of the following is not an engine rating?. A. Maximum Continuous. B. Idle. C. Maximum Take Off.

Ans.- Idle. Explanation. NIL.

54. As air density changes the RPM of a gas turbine engine will change. How is RPM kept at a constant speed?. A. It is not. B. Automatically by a simple engine device. C. Manually by the pilot.

Ans.- It is not. Explanation. Whilst maximum RPM's are limited by various devices RPM is free to wander with changing density. eg As you climb higher minimum idle will increase.

17. How does engine thrust vary with temperature?. A. Increase in temperature gives greater thrust because of low friction in compressors. B. Low temperatures give low thrust. C. Low temperature gives greater mass flow and therefore greater thrust.

Ans.- Low temperature gives greater mass flow and therefore greater thrust. Explanation. Jeppesen Aircraft Gas Turbine Power plant Page 2-33 Refers.

19. With a fixed throttle in a climb. A. RPM will increase. B. RPM will remain constant. C. RPM will decrease.

Ans.- RPM will increase. Explanation. Jeppesen Gas Turbine Powerplants Page 3-15 refers.

10. Which compressor type gives the greatest advantages for both starting flexibility and improved high altitude performance?. A. Single spool, axial flow. B. Dual stage, centrifugal flow. C. Split spool, axial flow.

Ans.- Split spool, axial flow. Explanation. NIL.

11. Which of the following is the ultimate limiting factor of turbine engine operation?. A. Compressor inlet air temperature. B. Burner can pressure. C. Turbine inlet temperature.

Ans.- Turbine inlet temperature. Explanation. NIL.

37. Across the turbines, there is. A. a general temperature rise. B. a general temperature drop. C. an isometric expansion.

Ans.- a general temperature drop. Explanation. Rolls Royce the Jet Engine Page 15 shows a temperature decrease across the turbines due to energy extraction.

45. The term Pb means. A. burner pressure measured at the diffuser case. B. burner pressure measured at the NGV. C. burner pressure measured at the combustion chamber.

Ans.- burner pressure measured at the combustion chamber. Explanation. Burner pressure is the static pressure in the combustor can, used in some systems to regulate fuel flow.

28. Thrust rating on an FADEC controlled engine can be changed by. A. varying the ballast resistor in the EGT system. B. changing the engine rating plug. C. varying the EPR datum plug.

Ans.- changing the engine rating plug. Explanation. Jeppesen Aircraft Powerplant Page 7- 21 refers.

52. The efficiency of a gas turbine would be greatest at. A. cold temperatures. B. low pressure. C. hot temperatures

Ans.- cold temperatures Explanation. Maximum thermal efficiency is achieved at the tropopause due to that being the coldest ambient temperature achievable.

31. In a dive, with the throttles fixed, the EPR will. A. not change. B. increase. C. decrease.

Ans.- decrease. Explanation. Jeppesen Aircraft Gas Turbines page 12-18 refers.

32. With an increase in forward speed, the engine thrust. A. decreases slightly but recover due to ram effect. B. increases. C. decreases.

Ans.- decreases slightly but recover due to ram effect. Explanation. Jeppesen Aircraft Gas Turbine Powerplant Page 2-35 refers.

56. Through turbine rotor blades, the pressure. A. increases, temperature increases, velocity decreases. B. decreases, temperature and velocity decreases. C. remains constant, temperature increases.

Ans.- decreases, temperature and velocity decreases. Explanation. RR The Jet Engine (4th edition) fig 2-5- 1 page 15 (working cycle and airflow).

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

Ans.- exhaust exit nozzle. Explanation. Rolls Royce The Jet Engine page 15 refers.

15. The propulsive efficiency is. A. low, with a low mass flow acceleration. B. high, with a low mass flow acceleration. C. high, with a high mass flow acceleration.

Ans.- high, with a low mass flow acceleration. Explanation. Jeppesen Gas Turbine Powerplants Page 2-37 Refers - a large mass of air moved slowly!.

12. At altitude, idling RPM is. A. same as at sea level. B. higher than at sea level. C. lower than at sea level.

Ans.- higher than at sea level. Explanation. Due to decreased density there is less resistance to rotation.

47. At higher then standard day ambient temperatures, compressor speed will be. A. lower than standard day speed. B. no different. C. higher than standard day speed.

Ans.- higher than standard day speed. Explanation. The air is thinner at higher temperatures, therefore the compressor has less load to work against and goes faster. RR Jet Engine Fig 2-18 refers. Note that due to the max allowable EGT the engine will reach a limiting 'corner-point thrust' and fuel will be trimmed off to prevent any over boost or over temperature

34. To ensure an engine maintains self sustaining speed. A. idle remains same for any density. B. idle increases with density decrease. C. idle increases with density increase.

Ans.- idle increases with density decrease. Explanation. Rolls Royce The Jet Engine page 103 para 15 refers.

55. With fixed throttle and increasing altitude, the fan on a high by-pass engine will. A. decrease RPM. B. increase RPM. C. stay the same RPM.

Ans.- increase RPM. Explanation. NIL.

36. Thrust will. A. increase at high temperatures. B. decrease at low temperatures. C. increase at low temperatures.

Ans.- increase at low temperatures. Explanation. Higher density gives higher mass flow hence higher thrust.

1. Ram effect' due to aircraft forward speed will cause the efficiency of the engine to. A. remain constant. B. decrease. C. increase.

Ans.- increase. Explanation. Ram effect improves compression ratio which improves thrust without using extra fuel Rolls Royce The Jet engine Page 219 refers.

57. Temperature of the mass airflow through a Gas Turbine Engine. A. increases from the inlet, through the compressor and the diffuser into the burner, and decreases through the turbine into the exhaust. B. increases from the inlet, through the compressor and remains constant through the diffuser and increases at the burner, and decreases through the turbine into the exhaust. C. remains constant at the inlet, increases from the compressor and the diffuser into the burner, and decreases through the turbine into the exhaust.

Ans.- increases from the inlet, through the compressor and the diffuser into the burner, and decreases through. Explanation. NIL.

8. Increasing ram effect with increased speed. A. reduces thrust due to reduced compressor efficiency. B. increases thrust due to increased maximum airflow. C. reduces thrust due to reduced turbine temperature.

Ans.- increases thrust due to increased maximum airflow. Explanation. Jepperson Gas Turbine Powerplants Page 2-35 refers.

13. Thrust. A. increases with high temperature. B. increases with low temperature. C. decreases with low temperature.

Ans.- increases with low temperature. Explanation. Jeppesen Gas Turbine Powerplants Page 2-33 Refers.

2. The efficiency of a gas turbine engine at altitude. A. decreases. B. remains constant. C. increases.

Ans.- increases. Explanation. The compressor performs better at lower air temperatures(see Jeppersen Gas Turbines Page 2-33) thus improving thermal efficiency. Also lower air temperatures up to the tropopause assist in maintaining Propulsive Efficiency(whilst accepting that decreasing density decreases mass flow). Also note that operators fly at the tropopause whenever possible even for short flights for the best SFC.

25. Power is adjusted in a gas turbine engine by. A. increasing fuel flow. B. increasing air and fuel flow. C. increasing airflow to the combustion chamber.

Ans.- increasing air and fuel flow. Explanation. You cannot have extra fuel without extra air.

48. Ram Recovery' is a measure of. A. intake efficiency. B. net thrust. C. forward air speed.

Ans.- intake efficiency. Explanation. Ram Recovery is the ability of an intake to convert kinetic energy into useful pressure energy.

22. With the aircraft stationary, propulsive efficiency. A. depends on RPM. B. is minimum. C. is maximum.

Ans.- is minimum. Explanation. Jeppesen Gas Turbine Powerplants Page 2-29 refers.

26. The engine rating plug. A. is permanently connected to the E E C. B. is connected to the EPR transmitter. C. is permanently connected to the Engine casing.

Ans.- is permanently connected to the Engine casing. Explanation. Jeppesen Aircraft Powerplant Page 7- 21.

4. Some turboprop and turbojet engines are equipped with two spool or split compressors. When these engines are operated at high altitudes, the. A. low pressure rotor will increase in speed as the compressor load decreases in the lower density air. B. low pressure rotor will decrease in speed as the compressor load decreases in the lower density air. C. throttle must be retarded to prevent overspeeding of the high pressure rotor due to the lower density air.

Ans.- low pressure rotor will increase in speed as the compressor load decreases in the lower density air. Explanation. Jeppesen A&P Powerplant Textbook 3-18.

16. The RPM for maximum power would be. A. lower on a colder day. B. lower on a hotter day. C. greater on a colder day.

Ans.- lower on a colder day. Explanation. Jeppesen Gas Turbine Powerplant Page 3-16 refers.

40. Ram pressure recovery will generally take effect at aircraft speeds of. A. mach 1. B. mach 0.1 - 0.2. C. only when the aircraft is stationary with engines running.

Ans.- mach 0.1 - 0.2. Explanation. Jeppesen Gas turbine Powerplant page 3-2 refers. With the aircraft stationary and engines running intake pressure is negative. As the aircraft begins its take off run the pressure recovers to above ambient (ram recovery.

33. The main factor considered when designing an engine is. A. maximum fuel consumption. B. maximum turbine temperature. C. maximum tip speed.

Ans.- maximum turbine temperature. Explanation. The turbine is the most highly stressed component in the engine.

49. most likely parameter limiting the height at which a jet engine powered aircraft can operate would be insufficient. A. lift to support the aircraft weight. B. mass airflow to maintain 15:1 air/fuel ratio. C. oxygen to support combustion.

Ans.- oxygen to support combustion. Explanation. The engine will flame out with insufficient oxygen.

41. As the air is passed through the turbine, due to the convergent shape formed between adjacent blades. A. pressure decreases, velocity increases, temperature increases. B. pressure increases, velocity increases, temperature constant. C. pressure decreases, velocity increases, temperature decreases.

Ans.- pressure decreases, velocity increases, temperature decreases. Explanation. Rolls Royce The Jet Engine Fig 2-5-1 refers.

50. With increasing ram effect. A. turbine temperatures decreases. B. propulsive efficiency decreases. C. propulsive efficiency increases.

Ans.- propulsive efficiency increases. Explanation. Increasing Ram Effect increases the overall system pressure ratio, hence increasing propulsive efficiency.

23. The efficiency of conversion of kinetic energy into propulsive work is a measure of. A. mechanical efficiency. B. propulsive efficiency. C. thermal efficiency.

Ans.- propulsive efficiency. Explanation. Jeppesen Gas Turbine Powerplants Page 2-29 refers.

5. Ram effect' due to aircraft forward speed will cause the thrust of the engine to. A. remain constant. B. decrease. C. increase.

Ans.- remain constant. Explanation. Thrust is constant, but efficiency will increase.

21. At constant RPM, the pressure ratio of the compressor and the temperature rise across the compressor. A. increases with height. B. remains constant irrespective of height. C. decrease with height.

Ans.- remains constant irrespective of height. Explanation. Jeppesen Aircraft Gas Turbine Powerplant Page 3-20 refers.

29. Propeller torque is analogous to. A. engine RPM. B. shaft horsepower. C. propeller RPM.

Ans.- shaft horsepower. Explanation. Propeller torque is equal and opposite to SHP under steady state conditions.

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

Ans.- specific fuel consumption. Explanation. Jeppesen Aircraft Gas Turbine Power plant Page7-3 Refers.

42. The hottest component in a gas turbine engine is. A. the nozzle guide vanes. B. the turbines. C. the combustion chamber.

Ans.- the combustion chamber. Explanation. Combustors have to withstand flame temperatures of 2000 degrees C.

44. To maintain the selected RPM of a gas turbine at altitude. A. the pilot will have to throttle back. B. more fuel will automatically be added. C. the fuel will automatically be reduced as the aircraft climbs.

Ans.- the fuel will automatically be reduced as the aircraft climbs. Explanation. In a hydro mechanical engine the P1 capsule will sense increasing altitude and trim off the fuel.

27. Flat Rated thrust is defined as. A. the thrust at the ambient temperature point above which thrust drops below 100%. B. that power achieved at idle RPM. C. that power achieved at maximum EGT.

Ans.- the thrust at the ambient temperature point above which thrust drops below 100%. Explanation. Jeppesen Aircraft Powerplant Page 7- 34.

43. The basic equation for thrust is. A. thrust = force * acceleration. B. thrust = mass * velocity. C. thrust = mass * acceleration.

Ans.- thrust = mass * acceleration. Explanation. Newtons second Law.

39. If an aircraft climbs with a fixed throttle position. A. thrust decreases and RPM increases. B. thrust and RPM remain the same. C. thrust increases and RPM remains the same.

Ans.- thrust decreases and RPM increases. Explanation. Thinner air causes thrust to decrease and the compressor to speed up.

9. The highest heat to metal contact in a jet engine is the. A. burner cans. B. turbine inlet guide vanes. C. turbine blades.

Ans.- turbine inlet guide vanes. Explanation. NIL.

35. A factor that limits EGT is the. A. jet pipe. B. compressors. C. turbine.

Ans.- turbine. Explanation. Rolls Royce the Jet Engine Page 13 refers.

53. In a gas turbine engine, turbine section. A. temperature decreases along with pressure and velocity. B. velocity decreases and pressure increases. C. velocity increases and pressure decreases.

Ans.- velocity increases and pressure decreases. Explanation. Pressure and temperature always go down in the turbine as velocity goes up.

38. If the throttle position remains constant. A. with increasing OAT, RPM and TGT will increase. B. with decreasing OAT, RPM will increase. C. with increasing OAT, TGT will increase.

Ans.- with increasing OAT, RPM and TGT will increase. Explanation. As OAT increases the air is thinner RPM increases but thrust decreases due to the thin air. Extra fuel is required to increase thrust therefore TGT increases.