Engines Ch.1-10 questions

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Engines Ch.1-10 questions
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2012-04-24 20:25:18
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API 12 25
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API Engines Book Questions All
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  1. What is the start sequence?
    Compressor RPM, ignition, fuel
  2. What are the different types of starters?
    DC electric motor and air turbine
  3. Which starter is commonly used on smaller gas generator engines?
    DC electric motor
  4. What are some uses for compressor discharge air?
    drive accessories, air conditioning and cabin pressurization.
  5. Where would you find the hottest air: the high or low pressure compressor?
    High pressure compressor
  6. In a dual spool axial flow engine, which compressor would provide bleed air for anti-ice protection?
    High pressure compressor
  7. What are some mechanically-driven accessories?
    generators, alternators, pumps
  8. Why do you want the starter to remain engaged after you've reached self-accelerating speed?
    To decrease the potential for an abnormal start by reaching normal idle rapidly.
  9. What is the most common type of large gas generator starter?
    Air turbine starter
  10. How does an air turbine starter work?
    A small geared air turbine motor attached to the accessory drive gearbox that turns the accessory drive shaft and rotates the compressor.
  11. What type of ignitor plugs are used in gas turnbine engine ignition systems?
    Annular gap and constrained gap
  12. What causes the flame to spread between combustion chambers in can or can-annular designs?
    flame propagation tubes
  13. How many ignitor plugs does each engine utilize?
    two
  14. Why do gas turbine engines use a synthetic oil?
    It is better suited for high temperatures.
  15. Why are liquid lubricants the best type for use in gas turbine engines?
    They effectively dissipate heat
  16. What is the designation of the most common synthetic oil used by the military?
    MIL-L-23699
  17. What are the advantages of a synthetic oil over a petroleum base oil?
    • (1) Stability at high temperatures
    • (2) less coke/lacquer deposits.
  18. Are synthetic base and petroleum base oils compatible with each other?
    No, cuases a sticky mass when mixed and poor lubricating qualities.
  19. List the various types of oil contamination. What is the most common type of contamination?
    Metallic particles, carbon, sand, fuel, over age synthetic oil.

    Metallic particles from engine wear.
  20. How does the shelf life of synthetic oil compare to that of petroleum oil?
    Six months vs indefinite
  21. What is the purpose of a lubrication system?
    To provide an adequate supply of clean oil to bearings and gears at the proper temperature and pressure.
  22. Define viscosity.
    Resistance to flow
  23. What is the relationship between temperature and viscosity?
    Temperature increases, viscosity decreases, and vice versa.
  24. What is the difference between a wet and dry sump system?
    • Wet sump-oil stored internally
    • Dry sump- external oil tank
  25. What does an oil reservoir contain to ensure a constant oil supply during all flight attitudes and G loads?
    a weighted swivel outlet assembly
  26. What are the two functions of pumps used in the lubrication system?
    to supply oil under pressure and scavenge oil
  27. What is the main advantage of a dry sump system?
    the temperature/viscosity can be better regulated.
  28. What does oil pressure system use a relief valve for?
    To vent off excess fluid pressure.
  29. Where is oil pressure monitored? Why?
    After the oil pump. It can indicate a pump malfunction.
  30. What does the filter bypass valve do?
    Ensures continuous oil supply to the engine in the event the filter becomes clogged.
  31. What are the two types of oil coolers?
    Fuel-oil heat exchanger and air-oil cooler
  32. What is the fuel-oil heat exchanger designed to do?
    Heat the fuel and cool the oil
  33. Does fuel always go through the fuel-oil heat exchanger?
    Yes, if the aircraft is designed with that component.
  34. Does oil always go through the fuel-oil heat exchanger?
    No
  35. Does airflow always go through the air-oil cooler?
    No
  36. What are the three subsystems of the engine lubrication system?
    Pressure, Scavenge, and Breather Pressurizing
  37. What does the pressure subsystem do?
    Supplies oil under pressure to the engine main bearings and accessory drive gear.
  38. What does the scavenge subsystem do?
    Returns oil to the tank from the bearings and accessory section. Provides cooling for the oil.
  39. Where is the oil temperature regulator valve located and what does it do?
    1. At the entrance of the fuel-oil heat exchanger. 2. Thermostatically operated to direct flow of oil either through or past the heat exchanger.
  40. Where is oil temperature monitored?
    Prior to entering the engine bearing compartments.
  41. Where is the fuel temperature sensing switch located and what does it do?
    On the fuel exit of the fuel-oil cooler. It controls the operation of the air-oil cooler doors.
  42. What is the function of the breather pressurizing subsystem?
    Ensures sea level pressure is maintained in the oil tank and scavenge subsystem to prevent oil leaks.
  43. The tendency of a fuel to vaporize refers to its ________
    volatility
  44. Define flashpoint
    The minimum temperature at which a combustible liquid emits a sufficient quantity of vapor that ignition will occur during a momentary application of a flame.
  45. What type of fuel is used during shipboard operations? Why?
    JP-5, less volatile, higher flashpoint.
  46. An increase in temperature will cause what change, if any, in volatility? In flashpoint?
    Increase the volatility. Flashpoint always remains constant.
  47. What are the major considerations in designing a fuel system?
    • Operation at low atmospheric pressures.
    • Complexity of the piping system.
    • Cold weather starting
    • High fuel flow pressure
  48. What controls the amount of fuel delivered to the combustion chamber?
    the FCU
  49. How does the pilot communicate with the FCU?
    Through the PCL
  50. List the various operational parameters the FCU must process to deliver the proper fuel flow to the engine.
    • PCL inputs
    • Compressor inlet temperature
    • Compressor rpm (high pressure RPM in dual spool)
    • Turbine inlet temperature
  51. Why is a boost pump included in the aircraft fuel system?
    Pilot controls amount of fuel supplied to the burner and the rate of application. Pilot must monitor the engines critical limits.
  52. Why is a boost pump included in the aircraft fuel system?
    To avoid vapor lock or engine fuel pump cavitation.
  53. What part does the FCU play during engine starts?
    Sends a pressure signal to close the dump valve. Schedules fuel flow for start.
  54. What is the position of the pressurizing and dump valve during an engine start? During normal engine operation? During engine shutdown?
    • dump valve closed
    • dump valve closed
    • open
  55. What cuts off fuel flow during engine shutdown?
    the FCU
  56. Where does metered fuel begin in the aircraft fuel system?
    After the FCU
  57. What is military rated thrust?
    The maximum thrust for a specified limited period of time (30 minutes)
  58. What component measures the proper amount of fuel flow to the afterburner?
    Afterburner FCU
  59. What are the two types of electric current?
    AC and DC
  60. What components supply AC power?
    AC generators and inverters
  61. Transformer rectifiers produce what type of electric current?
    DC from an AC input
  62. What provides a constant rotational input to the generator regardless of engine rpm?
    CSD (constant speed drive)
  63. Generators can provide what type(s) of power?
    AC or DC depending on generator type.
  64. If equipped, what does an APU provide?
    Emergency power or power during ground operations.
  65. What bus provides power to safety of flight components?
    essential bus
  66. Distribution of electrical energy is accomplished by a __________ system.
    bus
  67. Name the four types of busses and the type of equipment that is supplied power.
    • Essential Bus: safety of flight;
    • Primary Bus: mission equipment;
    • Monitor/Secondary bus: convenience items
    • Starter Bus: starting circuits
  68. What provides an automatic means of interrupting electrical power? A manual method?
    Circuit breakers. Circuit breakers and switches.
  69. What signals a system malfunction?
    Warning lights
  70. What is the main provider of power to the AC busses?
    AC generator
  71. With the main generator failure, what bus or busses will stay on the line?
    DC and AC essential buses.
  72. What provides power to the start bus?
    External DC power, internal battery or APU
  73. What bus charges the battery?
    DC essential bus.
  74. What is Pascal's law?
    Pressure applied to an enclosed or confined liquid is transmitted equally in all directions without loss and acts with equal force on equal surfaces.
  75. What is the output pressure of most aircraft hydraulic systems?
    3,000 psi
  76. What do hydraulic systems multiply?
    Force
  77. The force multiplication achieved in a hydraulic system is accomplished by a decrease in _________ movement.
    linear
  78. What are the two types of power pumps used to generate fluid pressure in hydraulic systems?
    Constant displacement and variable displacement pumps.
  79. What are the functions of the reservoir?
    Store fluid, trap impurities, dissipate heat, purge air bubbles.
  80. What does the pressure regulator or unloader valve do during normal operation?
    Used with the constant displacement pump. Regulates the system pressure to normal limits.
  81. What is the purpose of the accumulator?
    System shock absorber, supplements system pressure during peak operations, one time emergency use.
  82. What is the function of the check valve?
    Ensure one way fluid flow.
  83. What is the purpose of the selector valve?
    Redirects the flow of fluid for system operation
  84. Why is a relief valve included in a hydraulic system?
    As a safety backup in case of over-pressurization of the hydraulic system.
  85. Changing the position of the selector valve will have what effect on the movement of fluid in the system?
    Reverse the flow of hydraulic fluid, changing the direction of travel to the actuator.
  86. What is the purpose of the hydraulic fuse?
    Helps guard against leaks by isolating a part of the system.
  87. What is the purpose of the actuating cylinder?
    Converts fluid energy into mechanical motion.
  88. Describe the basic construction of a turboprop engine.
    Gas generator with a reduction gearbox, torque-meter assembly, and a propeller assembly.
  89. What component produces the majority of thrust in a turboprop?
    Prop (90% of total thrust)
  90. Why are reduction gears required in a turboprop?
    To keep the blade tips subsonic. Converts high RPM / low torque to low RPM/high torque.
  91. How much trust is produced from the exhaust gases of a turboprop?
    10%
  92. What are the advantages and disadvantages of a turboprop in comparison with a turbojet?
    • +: low TSFC, high thrust at low airspeed, able to carry more load requiring short runways.
    • -: heavier and more complicated, limited to 450 knots
  93. How is a turboshaft constructed?
    Gas turbine with a free air/power turbine.
  94. What is a free turbine?
    A turbine that is not mechanically connected to the compressor and aft of the gas generator turbines.
  95. Describe the sections of a turboshaft and its function.
    • Gas gen: provides exhaust gas to drive the free/power turbine.
    • Free/power turbine: connected to the main transmission, it converts the heat energy to mechanical energy to drive the rotors.
  96. What percentage of a turboshaft's thrust comes from the exhaust?
    negligible
  97. What does the term "gas generator" mean?
    An engine which is operated by converting the energy of expanding gases into propulsive force
  98. How does a turbojet produce thrust?
    By greatly accelerating a small mass of air and expanding the gases leaving the exhaust nozzle.
  99. How is a turbojet constructed?
    Inlet, compressor, burner, turbine, exhaust nozzle.
  100. What are the + - of the turbojet?
    Best high speed and high altitude performance. Highest TSFC. Longest takeoff rolls.
  101. How is a turbofan constructed?
    Fan, compressor, burner, turbine, exhaust nozzle.
  102. How does a turbofan produce thrust?
    Fan pushes a large mass of air and provides 30-60% of the total thrust.
  103. How much thrust is produced by the fan on a turbofan?
    • 30-60% from the fan.
    • 40-70% from the gas generator exhaust gases.
  104. What is meant by "bypass air?"
    Airflow from the fan "bypassed around the gas generator."
  105. What are the +- of the turbofan?
    • Better TSFC than a turbojet
    • shorter takeoff distance
    • can lift larger weights

    Large frontal area, slower, and can not fly as high as turbojet.
  106. 1. What is the purpose of the engine inlet?
    Acts as a diffuser and provides a turbulent-free supply of air to the face of the compressor.
  107. 2. Why should the inlet duct be constructed with a straight section?
    smooth out turbulent airflow
  108. 3. What are the advantages of a single-entrance duct?
    Simplest and most effective at providing smooth airflow.
  109. 4. What is the shape of a subsonic inlet duct? Why?
    Divergent. Decrease V increase P
  110. 5. What is the shape of a supersonic inlet duct? Why?
    >< (c/d) decrease V increase P
  111. 6. What is the purpose of a variable geometry inlet duct?
    To allow a supersonic aircraft to fly in all flight regimes (ss and subsonic)
  112. 7. What are the advantages and disadvantages of a centrifugal compressor? Of an axial flow compressor?
    • Centrifugal:
    • +: Rugged, low cost, good power output over wide range of RPMs, High pressure increases per stage
    • -: Large frontal area required, impractical for multiple stages
    • Axial Flow:
    • + High peak efficiencies, small frontal area reduces drag, straight through flow allowing for high ram eff, combustion efff is better than centrifugal, with dual/twin/split starting flex is greater, improved high alt performance.
    • - Low inlet speed=>compressor stall, narrow rotational speed for good eff, high cost, difficult to manufacture, high starting power requirements.
  113. 8. What are the parts of a centrifugal compressor and what is the function of each?
    • Impeller: +V, P, Pt
    • Diffuser: -V,+P
    • Manifold: route air mass to burner
  114. 9. What are the components of an axial flow compressor?
    Rotors, stators
  115. 10. Why do rotor and stator vanes within an axial compressor decrease in length from the front to rear of the compressor?
    The cross sectional area decreases within the compressor from fore to aft to allow the velocity to remain fairly constant as pressure increases. Therefore, the rotor and stator length requirements will decrease.
  116. 11. What do inlet and exit guide vanes do?
    Redirect the flow
  117. 12. What is the function of the diffuser?
    • final -V
    • and +P
    • before combustion.
  118. 13. Describe a dual-spool axial flow compressor. Why is it used?
    Two separate compressors, driven by its own turbine, to obtain higher compressor ratios.
  119. 14. Where is fuel introduced within a gas turbine engine?
    In the burner.
  120. 15. What is the criteria for a good burner section?
    • MInimum pressure loss.
    • High combustion efficiency
    • Flame must not blow out
    • Contain the total combustion process
  121. 16. What are the three types of combustion chambers? What are the advantages and disadvantages of each?
    • Can- ease of maintenance, cause cold spots on engine.
    • Annular- even heat, complicated maintenance.
    • Can-Annular- even heat, ease of maintenance, expensive
  122. 17. What is primary and secondary air?
    • Primary air = 25% mixes fuel for combustion
    • Secondary air=75% cooling and flame control
  123. 18. What is the purpose of the turbine section?
    To turn the compressor and accessories.
  124. 19. How much of the energy produced is used to turn the compressor and accessories?
    75% of the total heat energy produced prior to the turbine section.
  125. 20. What are the main parts of the turbine?
    Stators and rotors
  126. 21. What is creep?
    Turbine blade elongation and deformation
  127. 22. What is the purpose of the exhaust duct?
    To increase velocity and decrease turbulence.
  128. 23. Describe a subsonic and supersonic exhaust duct and how each operates.
    • Subsonic- convergent>, supersonic c/d ><
    • Both will maximize the increase in velocity at the expense of pressure.
  129. 24. Describe the four parts of an afterburner.
    Spray bars, flame holder, screech liner, variable exhaust nozzle.
  130. 25. Describe how an afterburner operates.
    Secondary air from burner section along with bypassed air (turbofan) is mixed with fuel and ignited in the afterburner duct to augment thrust.
  131. 26. What controls the amount of thrust augmentation an afterburner will produce?
    The more fuel introduced, the more thrust produced.
  132. 27. What is the function of the spray bars? The flame holder?
    Spray bars spray fuel. Flame holders hold the flame and they create local turbulence (eddies) to enable a better fuel/air mixture for combustion.
  133. 28. What is a screech liner and how does it operate?
    It acts as a shock absorber to guard against pressure fluctuations or cyclic vibrations sometimes associated with AB.
  134. 29. What type of exhaust nozzle is used on an afterburner equipped aircraft?
    Exhaust nozzle.
  135. 1. Describe the relationship between pressure and velocity in a closed system.
    Together the make up total pressure.
  136. 2. How does subsonic airflow react through a convergent opening? Divergent opening?
    • Convergent: V increase and P decreases
    • Divergent: V decreases and P increases
  137. 3. How does supersonic airflow react through a convergent opening? Divergent opening?
    • Divergent: V increases P decreases
    • Convergent: V decreases P increases
  138. 4. What happens to the airflow as it passes through a nozzle? Diffuser?
    • Nozzle: velocity increases and pressure decreases.
    • Diffuser: velocity decreases and pressure increases.
  139. 5. What are the three sections of a gas turbine engine?
    Compressor, burner, turbine
  140. 6. How does a gas turbine engine produce thrust?
    By rapidly compressing, heating and accelerating a large quantity of air (mass) and fuel
  141. 7. What cycle explains the movement of air through a gas turbine engine?
    Brayton Cycle
  142. 8. What happens to the velocity of the gases as they pass through the compressor section? The burner section? The turbines?
    • Compresor: Remains fairly constant.
    • Burner and turbine: increases
  143. 9. What is gross thrust?
    Thrust measured at exhaust at standard day conditions 29.92 and 15 degrees Celsius
  144. 10. What is net thrust?
    Thrust measured under normal flight conditions
  145. 11. When are gross thrust and net thrust equal?
    When aircraft is in a static position and standard day conditions.
  146. 12. What affects the density of the air mass?
    Temperature, pressure, and altitude.
  147. 13. What happens to thrust when air density decreases?
    Thrust decreases
  148. 14. What happens to thrust when air temperature increases?
    Thrust decreases
  149. 15. What happens to thrust when air pressure decreases?
    Thrust decreases.
  150. 16. What is the relationship between pressure and temperature as altitude increases?
    Temperature and pressure both decrease with an overall decrease in thrust.
  151. 17. What is the optimum cruise altitude and why?
    Approximately 36,000 ft. temperature remains isothermal.
  152. 18. How does airspeed and the ram effect change the amount of thrust produced at subsonic and supersonic airspeeds?
    • Airspeed increase without ram effect causes thrust to decrease.
    • Airspeed increase with ram effect causes thrust to remain relatively constant at subsonic speeds and increased greatly at supersonic speeds.
  153. What are some indications of a compressor stall?
    Mild pulsations, engine vibration, loud bangs, drop in RPMs, rise in turbine temperature.
  154. What causes a compressor stall?
    Excessive compressor blade AOA
  155. Other than compressor stall resulting from mechanical malfunctions, what causes most stalls?
    Airflow distortions
  156. What determines the angle of attack on a compressor blade?
    The angle between the chord line of the rotors and the relative wind. The relative wind is comprised of the inlet airflow and the compressor RPM
  157. List some flight conditions that could cause a compressor stall.
    Abrupt attitude change or flight through turbulent air.
  158. How can FOD affect compressor performance?
    Adversely due to compressor blade deformation.
  159. What automatically compensates for acceleration and deceleration schedules to help prevent stalls?
    Fuel Control Unit (FCU)
  160. How can an exhaust nozzle cause a compressor stall?
    (Only applies to variable exhaust nozzle) it could fail to open, causing a back pressure and reverse flow back through the compressor.
  161. What are some of the ways manufactures decrease the possibility of stalls?
    Incorporating split-spool compressor, bleed air valves, variable inlet guide vanes, and variable exhaust nozzle.
  162. What should a pilot do to avoid compressor stalls?
    Avoid rapid and unnecessary PCL movements. Maintain at least minimum prescribed airspeeds.
  163. What should be done if a stall cannot be controlled?
    Execute engine failure procedures.

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