Engines Gouge.txt

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Engines Gouge.txt
2012-04-25 21:59:30
API 12 25

Coastie Engines Gouge
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  1. Pressure:
    • The sum of the pressure and velocity
    • In a closed system total pressure remains constant
    • Total Pressure = Static Pressure + Dynamic Pressure
    • Total Pressure = Pressure + Velocity
  2. Pressure vs. Velocity Relationship
    Inversely related
  3. Bernoulli’s Theorem
    As any incompressible fluid passes through a convergent opening, its velocity increases as pressure decreases
  4. Diffusers and Nozzles
    • Supersonic nozzle: divergent, V-up P-down
    • Subsonic nozzle: convergent, V-up P-down
    • Supersonic diffuser: convergent, V-down, P-up
    • Subsonic diffuser: divergent, V-down, P-up
    • (Total Pressure remains the same in all)
  5. Gas Generator minimal components
    Compressor, Combustion Chamber, Turbine
  6. Brayton Cycle
    • Four events occur simultaneously
    • Intake, Compression, Combustion, Exhaust
  7. Gross Thrust
    Measurement of thrust due solely from the velocity of the exhaust gases. Measured on a static or stationary engine on a standard day
  8. Air Density
    As air temp increases, air molecules tend to move apart. This results in a density decreases, and thus a resultant decrease in thrust
  9. Altitude
    • With an increase in altitude, rate of thrust decreases
    • Although pressure and temp. both decrease, the pressure drop is greater thus decreasing thrust
  10. Ram Effect
    • Normally thrust decreases with an increase in airspeed
    • However, more and more air is being rammed into the inlet as airspeed increases, thus offsetting the decrease in acceleration and resulting in a neutral or increase thrust at subsonic airspeeds
    • At supersonic airspeeds, there is a significant increase in overall thrust due to ram effect
  11. Pressure Indication Gauges
    • EPR: Engine Pressure Ratio gauge, also referred to as TPDI
    • Used in turbojets and turbofans
  12. Torquemeter
    • Indicates shaft horsepower
    • Used in turboprop or turboshaft
  13. Subsonic Inlet
    Divergent: increases airflow pressure while decreasing velocity
  14. Supersonic Inlet
    • Convergent – Divergent
    • At supersonic, decreases velocity, increases pressure. (V reduced to subsonic)
    • At subsonic, changes to divergent, decreases velocity, increases pressure
  15. Variable Geometry Inlet Duct
    Utilizes mechanical devices such as ramps, wedges, or cones to change the shape of the inlet duct as the aircraft speed varies between subsonic and supersonic
  16. Compressor
    • Primary function is to supply enough air to satisfy the requirements of the combustion section
    • Improves burner efficiency
  17. Centrifugal Flow Compressor
    • Have divergent passages in the diffuser to convert the high velocity airflow to high pressure
    • Advantages: Rugged, low cost, good power output over wide range of RPM, high pressure increase per stage
    • Disadvantages: Large frontal area required, impractical for multiple stages
  18. Axial Flow Compressor
    • Uses multiple stages
    • The efficient use of multiple stages can produce very high overall compression ratios
    • Dual Spool: also referred to as twin or split spool.
    • Order:
    • Low Pressure Compressor, High Pressure Compressor
    • High Pressure Turbine, Low Pressure Turbine
  19. Combustion / Burner Section
    • Primary air: 25% mixed with fuel for combustion
    • Secondary air: 75% flows around the chamber to cool and control flame. Unburned air can be used to help cool the turbine and for afterburner operation
  20. Burner Section
    • Contains the combustion chamber
    • Must delivery the combustion gases to the turbine section at a temperature that will not exceed the allowable limit of the turbine blades
    • Combustion chamber must add sufficient heat energy to the gases passing through the engine to accelerate their mass and produce the desired thrust for the engine and power of the turbines
  21. Can Combustion Chamber
    • Advantages: strength, durability, ease of maintenance
    • Disadvantages:
    • Poor use of space
    • Greater pressure loss
    • Uneven heat distribution
    • Malfunction of one can lead to turbine damage
  22. Annular Combustion Chamber
    • Main advantage: uniform heat distribution
    • Main disadvantage: unit cannot be removed without major overhaul
    • Turbine Section
    • Comprised of stators and rotors
    • Turbine section drives the compressor and the accessories
    • Unlike compressor, designed to increase airflow velocity
    • Turbines rotor converts the heat energy of the hot expanding gases from the burner chamber into mechanical energy
    • 75% of the total pressure energy from the exhaust gases is converted
    • 25% is used for thrust
  23. Turbine Blades
    • Attached to the shaft by a method call Fir Tree
    • Blades are not welded onto the rotor shaft
  24. Exhaust Section
    Must direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence
  25. Exhaust Nozzles
    Convergent, Fixed area, takes relatively slow subsonic gases from the turbine section and gradually accelerates them through the convergent section
  26. Afterburner Section
    • Used in turbojets and turbofans for a short period of time
    • Increases max thrust available from an engine by 50% or more
    • Spray Bars-inject fuel into the afterburner
    • Flame holder: provides a region in which airflow velocity is reduced and turbulent eddies are formed
    • Screech: violent pressure fluctuations caused by cyclic vibrations that reduce efficiency. Characterized by loud noise and vibration
    • Screech Liners: reduce pressure fluctuations and vibrations by acting as a form of shock absorber
  27. Relative Wind
    Formed by combining the compressor rotation and inlet airflow
  28. Angle of Attack
    • Relative wind and rotor blade chordline (angle between)
    • Main cause for compressor stall is excessive angle of attack
  29. Indications of Compressor Stall
    • Mild pulsation with minimum indications to aircraft vibration and loud bangs and noises
    • With constant PCL position, RPM decay, ITT rise, and possible loud noises also indicate stall
  30. Airflow distortion
    Airflow distortion is the most common cause of compressor stall, however, excessive AOA is what causes a compressor stall
  31. Mechanical Malfunctions 4 Types
    • Variable inlet guide vane and stator vane failure
    • FCU failure
    • FOD
    • Variable exhaust nozzle failure
  32. FCU
    • Provides proper amounts of fuel to combustion chamber
    • An over rich mixture (too much fuel) causes excessive chamber burner pressure and a back flow of air into the compressor that leads to a compressor stall
    • A lean mixture (to little fuel) may cause the engine to flame out which can be just as hazardous depending on the situation
  33. Avoidance of Compressor Stalls
    • Avoid erratic or abrupt PCL movements, esp. at low airspeed and high AOA
    • Maintain the minimum prescribed airspeed and avoid abrupt changes in aircraft attitude to allow the proper amounts of smooth air to enter the inlets
    • Avoid flight through severe weather and turbulence
  34. Turbojet Engine
    • Constructed by the addition of an inlet and an exhaust section to the basic gas generator
    • Derives thrust by highly accelerating a small mass of air through the engine
    • Advantages:
    • Lightest specific weight
    • Higher and faster than any other engine
    • Best high end performance engine
    • Disadvantages:
    • Low propulsive efficiency at low forward speeds
    • High TSFC and low altitude and low airspeeds
    • Long takeoff roll required
  35. Turbofan Engine
    • Fan provides thrust by accelerating a large air mass around the gas generator
    • Combined with the exhaust gases of the gas generator, the overall thrust is greater than the thrust of a turbojet at the same fuel consumption rate
    • Main advantage: Lower TSFC
    • Main disadvantage: Inefficient at higher altitudes
  36. Thrust Specific Fuel Consumption (TSFC)
    Amount of Fuel required to produce one pound of thrust
  37. Bypass ratio
    • Higher bypass ratio yields lower TSFC
    • Cargo aircraft, airliners
    • Lower bypass ratio turbofan engines resemble turbojet but are more efficient
    • Modern fighters and interceptor
  38. Turboprop Engine
    • The actual percentage of thrust will vary with a host of factors such as speed, altitude, and temperature. The turboprop will deliver more thrust, up to medium speeds, than either the turbojet or turbofan. Also, as the turboprop climbs to higher altitudes, the mass of air being accelerated by the propeller decreases due to the decrease in air density.
    • Components
    • Propeller Assembly
    • Majority of thrust (90%) is a result of the large mass being accelerated by the propeller
    • Blades are installed into the hub
    • The hub (barrel assembly) is then attached to the propeller shaft
    • The pitch change/dome assembly is the mechanism that changes the blade angle of the propeller
  39. Reduction Gear Box
    • Prevents the propeller blades from reach supersonic speeds
    • Converts high rpm and low torque of the gas generator to low rpm, high torque necessary for efficient propeller operation
  40. Torquemeter Assembly
    Used to transmit and measure the power output from the gas generator to the reduction gear box
  41. ** The propeller assembly, the reduction gear box and the torquemeter may be connected to the gas generator in two possible configurations:
    • 1] Attached to the front of the compressor drive shaft
    • 2] Attached to the free / power turbine
  42. Turboshaft Engine
    • The propulsive energy from the exhaust is negligible; that is, all of the remaining energy is extracted by the free or power turbine to drive the rotor assembly
    • Free/Power Turbine: exhaust gases from the gas generator turbine drive the power turbine
  43. Hydraulics Basics
    • Used in military aircraft to provide extra power and mechanical advantage
    • Pascal’s Law: pressure applied to a confined liquid is transmitted equally in all directions without the loss of pressure and acts with equal force on equal surfaces
  44. Force and Pressure
    Pressure is the force acting upon one square inch of area (PSI)
  45. Power Control Systems
    Supply pressure only for flight controls
  46. System Components
    • Reservoir
    • Storage tank for hydraulic fluid
    • Also serves as an overflow basin for excess hydraulic fluid forced out of the system by thermal expansion, allow air bubbles to be purged, and separate some foreign matter from the system
  47. Variable displacement Pumps
    Regulates volume delivery in accordance with system flow demands
  48. Check Valve
    • Prevents back flow. Allows flow in only one direction
    • Works in conjunction with accumulator to maintain system pressure during shutdown
  49. Accumulator
    • Acts as a shock absorber
    • Stores enough fluid under pressure to provide for emergency operation of certain actuating units
  50. Relief Valve
    • Pressure limiting device
    • Safety valve that is installed in the system to prevent pressure from building up to a point where seals might burst or damage may occur to the system
  51. Hydraulic fuses
    • Safety devices
    • Designed to detect or gauge ruptures, failed fittings, or other leak producing failures of damage
    • Prevents excessive loss of fluid
  52. Selector Control Valves
    Used to direct the flow of fluids to actuators
  53. Actuators
    Convert fluid under pressure into linear or reciprocating mechanical motion
  54. Alternating Current Sources
    • A/C Generator
    • Alternator Inverter
  55. Direct Current
    • D/C Generator
    • Transformer Rectifier
    • Battery
    • Constant Speed Drive
    • Ensures constant input rpm. Hydro mechanical linkage between the engine and the generator
    • Ensures a steady voltage output to supplied equipment. The electric generator is mechanically coupled to the gas turbine engine’s accessory drive section
  56. Inverter
    On DC electrical systems, inverters are used to power AC equipment
  57. Transformer Rectifier
    Transforms AC to DC
  58. Electrical bus
    • Common distribution point for electricity
    • Essential bus: powers equipment required for flight safety (gyro)
    • Primary bus: powers equipment devoted to aircraft mission (radar)
    • Monitor/Secondary: powers convenience circuits (cabin lighting)
    • Starter bus: routes power to start the aircraft engines
  60. JP-5
    • Low volatility
    • High flash point (140 deg F)
    • Only fuel that can be stored on ships
  61. JP-8
    Flash point 100 deg F
  62. Basic Fuel System
    • When designing take these factors into account in rank order
    • 1] High rates of fuel flow
    • 2] Low atmospheric pressure
    • 3] Piping system complexity
    • 4] Weight and size constraints
    • 5] Vapor loss with consequent reductions in range and cold weather starting
  63. Boost Pump
    • Submerged and installed in fuel tanks
    • Ensure adequate supply of vapor free fuel to the engine driven fuel pump
    • Critical function  prevent aeration of the fuel supply which may result from a rapid pressure change incurred during a climb
  64. Fuel Pressure Gauge
    • Pressure sensor at the boost pump outlet
    • Drop in fuel pressure may indicate a failed boost pump or absence of fuel which could lead to cavitation of the main fuel pump
  65. Low Pressure Filter
    Located downstream of the boost pump to strain impurities from the fuel
  66. Engine Driven Pump
    • Provides fuel in excess of engine requirements
    • Excess fuel ensures that a sufficient supply of high pressure fuel is available to meet engine requirements and if available, afterburner requirements
  67. FCU Manual / Emergency Operation
    • PCL functions as a throttle and fuel flow is now regulated exclusively by its movement
    • Most monitor temps, pressures closely to ensure critical limits are not exceeded
  68. Fuel Flow Gauge
    A fuel flow transmitter is located at the outlet f the FCU just before the fuel-oil heat exchanger. This transmitter measures the fuel flow rate coming out of the FCU and converts it to electrical signals. The electrical signal is sent to the fuel flow gauge in the cockpit indicating fuel consumption/usage in pounds per hour (PPH)
  69. Fuel –Oil Cooler / Heat Exchanger
    Preheating fuel removes any ice crystals and increases its volatility, facilitating fuel ignition
  70. P&D Valve
    • During engine starts, the dump valve is closed by an electrical signal from the FCU
    • During shutdown it opens up to allow fuel to drain to manifolds
  71. Afterburner Fuel Control Unit
    Meters fuel to the afterburner spray bars
  72. Normal Rated Thrust
    Thrust produced at maximum continuous turbine temperature with no time limitation
  73. Military Rated Thrust
    Thrust produced at the maximum turbine temperature for a limited time; normally 30 minutes
  74. Combat Rated Thrust
    Thrust produced with the afterburner operation, not based on temp. limitations rather based on fuel limitations
  75. Viscosity
    • Property of fluid that resists the force tending to cause the fluid to flow
    • Inversely related with temperature
  76. Oil Tank
    • Stores system supply oil
    • Designed to furnish a constant supply of oil to the engine in any aircraft attitude to include inverted flight or during negative G maneuvers
    • Gravity, acting on the weighted end, ensures the pickup end is constantly immersed in the oil supply
    • Provide an expansion space and venting to ensure proper operation. This space is required to allow for both expansion of the oil due to heat absorption and foaming due to circulation through the system
  77. Instrumentation
    gauges that indicate current operations and possible future failures of the lubrication components
  78. Oil Pump
    • Consists of a pressure supply element to supply oil and scavenge element to remove oil from an area
    • Scavenge elements have a greater pumping capacity than the pressure element to prevent back pressure in the system and/or accumulation of oil in the bearing sumps.
  79. Filter Bypass Valve
    • Allows oil to flow around the filter element should the filter become clogged
    • Dirty oil is better than no oil
  80. Oil Pressure Relief Valve
    • Limits maximum pressure within the system
    • Preset to relieve pressure by bypassing oil back to the pump inlet whenever the pressure exceeds a safe limit
  81. Magnetic Chip Detector
    Metal plug with magnetized contacts, placed in scavenged oil path. Advises pilot of metal contamination which is an indication of possible failure of one of the engine gears, bearings, or other metal parts
  82. Air Cooler
    Controlled by the fuel temperature sensing switch
  83. Fuel Oil Cooler / Heat Exchanger
    • Controlled by the oil temperature regulator valve
    • Main purpose is to heat fuel
    • Takes hot oil from the bearings and preheats fuel for combustion
  84. Breather Pressurizing Subsystem
    Pressurization is provided by compressor bleed air. At sea level pressure, the breather pressurizing valve is open to the atmosphere
  85. Bleed Air
    • High and low pressure systems are used to drive aircraft and engine components or accessories, while the interstage bleed valves are required to ensure compressor stability
    • Low pressure bleed air is taken from the back end of the low pressure compressor
    • High pressure bleed air is taken from the back end of the high pressure compressor
    • Interstage bleed air is taken in between stages
  86. Starting Systems
    Purpose is to accelerate the engine until the turbine is producing enough power to continue the engine acceleration itself
  87. Abnormal Starts
    • Hot Start: exceeds max temps
    • Hung Start: temp continues to rise, compressor stabilizes below normal
    • False Start: temp remains within limits, compressor stabilizes below normal
    • Wet Start: fuel is present but light-off doesn’t take place (most dangerous)
    • Trick Question: If you are using an air turbine starter do you still need electricity?
    • Yes, for ignition system
  88. Ignition Systems
    • We normally use high energy capacitor-type ignition systems
    • This provides both high voltage and an exceptionally hot spark, which gives an excellent chance of igniting the fuel-air mixture at reasonably high altitudes
    • Another benefit of this high energy igniting system is that fouling of the igniter plugs is minimal
  89. Annular –gap
    Protrudes slightly into the combustion chamber liner to provide an effective spark
  90. Constrained- gap
    • Does not closely follow the face of the plug
    • Tends to jump in an arc which carries it beyond the face of the chamber liner