Module 15a, Gas Turbine Engine

Module 15a, GAS TURBINE ENGINE. Paper 1 15.1 GAS TURBINE ENGINE Fundamentals. 1. On an axial flow, dual compressor forward fan engine, the fan turns the same speed as the. A. Low pressure turbine. B. High pressure compressor. C. Forward turbine wheel. 2. Which of the following might be used to identify turbine discharge pressure? A. Pt7. B. Pt2. C. Tt7. 3. Which statements are true regarding aircraft engine propulsion? A. Turbojet and turbofan engines impart a relatively large amount of acceleration to a smaller mass of air. B. In modern turboprop engines, nearly 50 percent of the exhaust gas energy is extracted by turbines to drive the propeller and compressor with the rest providing exhaust thrust. C. An engine driven propeller imparts a relatively small amount of acceleration to a large mass of air. 4. Which of the following units are generally used to measure aircraft noise? A. Effective perceived noise decibels (E P N d B). B. Decibels (dB). C. Sound pressure. 5. What section provides proper mixing of the fuel and efficient burning of the gases?. A. Diffuser section and combustion section. B. Combustion section and compressor section. C. Combustion section only. 6. A turbojet engine is smoother running than a piston engine because. A. The lubrication is better. B. It runs at a lower temperature. C. It has no reciprocating parts. 7. In what section of a turbojet engine is the jet nozzle located? A. Exhaust. B. Turbine. C. Combustion. 8. The Brayton cycle is known as the constant. A. Temperature cycle. B. Mass cycle. C. Pressure cycle. 9. The highest pressure in a gas turbine is. A. At the nozzle exit. B. At the burner exit. C. Just after the last compressor stage but before the burner. 10. In a ducted fan engine, the fan is driven by the. A. Turbine. B. Air passing over the compressor. C. Accessory gearbox. 11. Which law relates to the kinetic, pressure, and potential energy in a fluid flow? A. Bernoulli's theorem. B. Newton's laws. C. Charles's law. 12. The Brayton cycle is. A. The name given to the intermittent cycling of an electrical de-icing system. B. The continuous combustion cycle taking place in a gas turbine engine. C. The constant velocity cycle taking place in a gas turbine engine. 13. Which of the following statements is true on a high bypass ratio turbofan? A. Both the compressor and combustion system are larger than their turbojet equivalent. B. The compressor assembly is larger and combustion chamber smaller than their turbojet equivalent. C. Both the compressor and combustion chamber are smaller than the turbojet equivalent. 14. The principle of jet propulsion is. A. The calorific value of fuel burnt is equal to aircraft. B. The interaction of fluids and gases. C. Every action has an equal and opposite reaction. 7. 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. 8. With an increase in forward speed, the engine thrust. A. Decreases slightly but recover due to ram effect. B. Increases. C. Decreases. 15.2 Engine Performance. 1. Ram effect' due to aircraft forward speed will cause the efficiency of the engine to. A. Remain constant. B. Decrease. C. Increase. 2. Ram effect' due to aircraft forward speed will cause the thrust of the engine to. A. Remain constant. B. Decrease. C. Increase. 9. Thrust will. A. Increase at high temperatures. B. Decrease at low temperatures. C. Increase at low temperatures. 10. 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. 3. The highest heat to metal contact in a jet engine is the. A. Burner cans. B. Turbine inlet guide vanes. C. Turbine blades. 11. 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. 4. Thrust. A. Increases with high temperature. B. Increases with low temperature. C. Decreases with low temperature. 12. Ram Recovery' is a measure of. A. Intake efficiency. B. Net thrust. C. Forward air speed. 5. A method of comparing engine efficiencies is by comparing. A. Fuel consumption. B. Thrust to weight ratio. C. Specific fuel consumption. 13. The efficiency of a gas turbine would be greatest at. A. Cold temperatures. B. Low pressure. C. Hot temperatures 6. The efficiency of conversion of kinetic energy into propulsive work is a measure of. A. Mechanical efficiency. B. Propulsive efficiency. C. Thermal efficiency. 15.3 Engine Inlet. 1. If an electrical de-icing system is operating, thrust will. A. Decrease. B. Remain constant. C. Increase. C. Anti-icing. 15.4 Engine Compressors. 2. A pitot intake is divergent from front to rear because it. A. Reduces ram compression. B. Produces the maximum amount of ram compression. C. Speeds up the air before it hits the compressor face. 3. Inlet guide vanes are anti-iced with. A. Rubber boots. B. Thermal blankets. C. Engine bleed air. 4. A divergent intake is. A. Divergent from front to rear. B. Convergent/divergent from front to rear. C. Divergent/convergent from front to rear. 5. The variable inlet guide vanes are operated. A. By fuel pressure. B. Electrically from cockpit. C. Using N1 fan speed. 6. A well designed intake will take advantage of forward speed by. A. Converting kinetic energy into pressure energy. B. Converting velocity energy into kinetic energy. C. Converting pressure energy of the air into kinetic energy. 7. Intakes are designed to. A. Decrease the intake air pressure. B. Decelerate the free air stream flow. C. Accelerate the free air stream flow. 8. What is the system that breaks up ice formations on a turboprop engine nose cowl called? A. Nose cowl heating. B. De-icing. 1. A bypass engine LP compressor. A. Supplies less air than is required for combustion. B. Supplies more air than is required for combustion. C. Supplies only the required quantity for combustion. 2. A bypass ratio of 5:1 indicates that the bypass flow is. A. Equal to 1/5 of the hot stream. B. Five times the hot stream. C. Five times the cold stream. 3. During the high RPM range on an axial flow gas turbine engine, in what position are the variable intake guide vanes and bleed valves? A. At maximum swirl position, bleed valves open. B. At minimum swirl position, bleed valves closed. C. At maximum swirl position, bleed valves closed. 4. What is the function of the stator vane assembly at the discharge end of a typical axial flow compressor? A. To increase air swirling motion into the combustion chambers. B. To direct the flow of gases into the combustion chambers. C. To straighten airflow to eliminate turbulence. 5. What is used to aid in stabilization of compressor airflow? A. Variable guide vanes and/or compressor bleed valves. B. Pressurization and dump valves. C. Stator vanes and rotor vanes. 6. During the low RPM range on an axial flow gas turbine engine, in what position are the variable intake guide vanes and bleed valves? A. At maximum swirl position, bleed valves open. B. At maximum swirl position, bleed valves closed. C. At minimum swirl position, bleed valves closed. 7. Which of the following can cause fan blade shingling in a turbofan engine? A. Large, rapid throttle movements and FOD. B. Engine over temperature, large, rapid throttle movements and FOD. C. Engine overspeed and large, rapid throttle movements. 8. An advantage of the centrifugal flow compressor is its high. A. Ram efficiency. B. Pressure rise per stage. C. Peak efficiency. 9. The two types of centrifugal compressor impellers are. A. Impeller and diffuser. B. Single entry and double entry. C. Rotor and stator. 10. As a consequence of tapping air from the compressor, the TGT will. A. Fall. B. Remain constant. C. Rise. 11. What purpose do the diffuser vanes of a centrifugal compressor serve? A. To convert pressure energy into kinetic energy. B. To increase the air velocity. C. To convert kinetic energy into pressure energy. 12. Variable inlet guide vanes help to prevent. A. Compressor runaway. B. Ice build up on compressor blades. C. Compressor stalling. 13. If a compressor has a compression ratio of 9:1 and an intake compression of 2:1, what is the overall compression ratio? A. 9:1. B. 11:1. C. 18:1. 14. An abradable lining around the fan is to. A. Provide less leakage for anti-icing. B. Prevent fan blade tip rub. C. Strengthen the EPR value. 15. What is a compressor stage? A. One compressor rotor and one nozzle guide vane. B. One rotor plus one stator. C. One Nozzle Guide Vane and one rotor. 16. What is the result of deposit build-up on compressor blades. A. Airflow is too fast for deposits to build up. B. Will not decrease efficiency but may cause corrosion. C. Can decrease compressor efficiency and cause corrosion. 17. What is the purpose of pressure balance seal?. A. To ensure the location bearing is adequately loaded throughout the engine thrust range. B. To ensure LP compressor is statically balanced. C. To ensure HP compressor is dynamically balanced. 18. Air bleed valves are. A. Closed at low RPM. B. Open at high RPM. C. Open at low RPM. 19. Nozzle Guide Vane bow is an indication of. A. Engine overspeed. B. Engine overheat. C. Engine shock loading. 15.5 Combustion Section. 1. In a turbojet engine, combustion occurs at. A. Constant velocity. B. Constant volume. C. Constant pressure. 2. The primary air passing through the combustion chamber is. A. Entirely combined with fuel and burned. B. Used to support combustion and to cool the engine. C. Speeded up and heated by the action of the turbines. 3. The primary purpose of secondary air flow to a combustion can is to? A. Aid combustion. B. Provide cooling. C. Increase pressure. 4. Which of the following types of combustion sections are used in aircraft turbine engines? A. Annular, variable, and cascade vane. B. Multiple can, annular, and canannular. C. Can, multiple can, and variable. C. By the pattern of holes and louvers cut in the diffuser section. 9. Flame stabilization in a combustion chamber is achieved by. A. The correct burner pressure. B. The airflow pattern. C. The correct air/fuel ratio. 10. Carbon forming on fuel spray nozzles will have the effect of. A. Increasing the combustion chamber pressure ratio. B. Producing turbulent air flow. C. Changing the fuel spray angle. 11. A vaporising burner injects fuel vapour. A. With the airflow. B. Across the airflow. C. Against the airflow. 5. When light-up takes place. A. The nozzle guide vanes spread the heat to adjacent flame tubes. B. Interconnectors spread the heat to adjacent flame tubes. C. Each combustion can is isolated from its neighbours. 15.6 Turbine Section. 6. Why is it necessary to have a combustion drain system? A. To prevent pressure build up in the combustion chamber. B. To prevent initial over-fuelling on start up or hot start. C. To allow water in the combustor to drain away. 2. Where do stress rupture cracks usually appear on turbine blades? A. Across the blade root, parallel to the fir tree. 7. Fuel entering the combustion chamber from an atomizer spray nozzle enters as. A. Fuel in air pulses. B. A fuel/air mixture. C. Fuel continuously. 3. 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. 8. How are combustion liner walls cooled in a gas turbine engine? A. By secondary air flowing through the combustion chamber. B. By bleed air vented from the engine air inlet. 1. The three main types of turbine blades are. A. Impulse, vector, and impulse-vector. B. Reaction, converging, and diverging. C. Impulse, reaction, and impulsereaction. B. Across the leading or trailing edge at a right angle to the edge. C. Along the leading edge, parallel to the edge. 4. Shrouded blades allow. A. Smaller inlets to be used. B. Higher turbine inlet temperatures. C. Thinner more efficient blade sections to be used. 5. 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. 6. 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. 7. Shrouding of rotor blade tips is to. A. Minimise vibration. B. Ensure adequate cooling. C. Prevent tip turbulence. C. Cracking. 13. 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. 14. The passage between adjacent nozzle guide vanes of an impulse-reaction turbine forms a. A. Convergent duct. B. Divergent duct. C. Parallel duct. 15. A slow constant growth in a turbine blade is known as. A. Primary creep. B. Secondary creep. C. Tertiary creep. 15.7 Engine Exhaust. 8. 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 pressure of the gas flow. 9. Turbine rear struts. A. Straighten the gas flow. B. Increase the velocity of the gas flow. C. Increase the pressure of the gas flow. 10. Creep is. A. Not found in turbines. B. A temporary deformation of turbine. C. A permanent deformation of turbine. 11. Creep may occur to turbine blades due to. A. Prolonged low RPM use. B. Over-temp with excessive centrifugal loads. C. High back pressures. 12. Which of the following is most likely to occur in the turbine section of a gas turbine engine?. A. Pitting. B. Galling. 1. The function of the exhaust cone assembly of a turbine engine is to. A. Swirl and collect the exhaust gases into a single exhaust jet. B. Collect the exhaust gases and act as a noise suppressor. C. Straighten and collect the exhaust gases into a solid exhaust jet. 2. What is the maximum practical angle through which the gas flow can be turned during thrust reversal? A. 180°. B. 50°. C. 135°. 3. An exhaust cone placed aft of the turbine in a jet engine will cause the pressure in the first part of the exhaust duct to. A. Increase and the velocity to decrease. B. Decrease and the velocity to increase. C. Increase and the velocity to increase. 4. If the exit area of the nozzle was too large, the effect is. A. Exit velocity lower causing loss of thrust. B. Will choke at a lower gas temperature. C. Exit velocity lower, negligible effect on thrust. 5. Exhaust noise can be reduced by. A. Lowering the vibration frequency. B. Increasing the mixing rate. C. Increasing the jet velocity. 6. If damage is found to the reverse thrust cascade vanes and they need replacing, you can. A. Replace damaged vanes with 45 degree vanes. B. Only replace vanes with new ones that have the correct part as the originals removed. C. Interchange the cascade vanes as they are interchangeable. 7. What angle are the exhaust gasses turned through in a clamshell type thrust reverser? A. 180 degrees. B. 135 degrees. C. 45 degrees. 8. On a Clamshell door type thrust reverser. The Clamshell doors redirect the exhaust gas stream. A. 0 degrees to the thrust line. B. 45 degrees to the thrust line. C. 90 degrees to the thrust line. 15.8 Bearings and Seals. 1. Main bearing oil seals used with turbine engines are usually what type(s)? A. Teflon and synthetic rubber. B. Labyrinth and/or carbon rubbing. C. Labyrinth and/or silicone rubber. 2. Indentations on bearing races caused by high static loads are known as. A. Fretting. B. Galling. C. Brinelling. 3. Why are oil seals pressurised? A. To ensure minimum oil loss. B. To ensure oil is forced into the bearings. C. To ensure that the oil is prevented from leaving the bearing housing. 4. Some labyrinth seals. A. Control the outflow of air at the turbine. B. Are self lubricating. C. Are spring loaded.