COASTIE GOUGE FOR ENGINES

CHAPTER 1: PRINCIPLES OF GAS TURBINE OPERATION Used in turboprop or turboshaft

Pressure: CHAPTER 2: GAS TURBINE ENGINES The sum of the pressure and velocity In a closed system total pressure remains constant Subsonic Inlet Total Pressure = Static Pressure + Dynamic Pressure Divergent: increases airflow pressure while decreasing velocity Total Pressure = Pressure + Velocity Supersonic Inlet Pressure vs. Velocity: Inversely related Convergent – Divergent At supersonic, decreases velocity, increases pressure. (V Bernoulli’s Theorem reduced to subsonic) As any incompressible fluid passes through a convergent At subsonic, changes to divergent, decreases velocity, increases opening, its velocity increases as pressure decreases pressure

Diffusers and Nozzles Variable Geometry Inlet Duct Supersonic nozzle: divergent, V-up P-down Utilizes mechanical devices such as ramps, wedges, or cones to Subsonic nozzle: convergent, V-up P-down change the shape of the inlet duct as the aircraft speed varies Supersonic diffuser: convergent, V-down, P-up between subsonic and supersonic Subsonic diffuser: divergent, V-down, P-up (Total Pressure remains the same in all) Compressor Primary function is to supply enough air to satisfy the Gas Generator minimal components requirements of the combustion section Compressor, Combustion Chamber, Turbine Improves burner efficiency

Brayton Cycle Centrifugal Flow Compressor Four events occur simultaneously Have divergent passages in the diffuser to convert the high Intake, Compression, Combustion, Exhaust velocity airflow to high pressure Advantages: Rugged, low cost, good power output over wide Gross Thrust range of RPM, high pressure increase per stage Measurement of thrust due solely from the velocity of the Disadvantages: Large frontal area required, impractical for exhaust gases. Measured on a static or stationary engine multiple stages on a standard day Axial Flow Compressor Air Density Uses multiple stages As air temp increases, air molecules tend to move apart. The efficient use of multiple stages can produce very high This results in a density decreases, and thus a resultant overall compression ratios decrease in thrust Dual Spool: also referred to as twin or split spool. Order: Altitude Low Pressure Compressor, High Pressure Compressor With an increase in altitude, rate of thrust decreases High Pressure Turbine, Low Pressure Turbine Although pressure and temp. both decrease, the pressure drop is greater thus decreasing thrust Combustion / Burner Section Primary air: 25%mixed with fuel for combustion Ram Effect Secondary air: 75% flows around the chamber to cool and Normally thrust decreases with an increase in airspeed control flame. Unburned air can be used to help cool the turbine However, more and more air is being rammed into the and for afterburner operation inlet as airspeed increases, thus offsetting the decrease in acceleration and resulting in a neutral or increase thrust at Burner Section subsonic airspeeds Contains the combustion chamber At supersonic airspeeds, there is a significant increase in Must delivery the combustion gases to the turbine section at a overall thrust due to ram effect temperature that will not exceed the allowable limit of the turbine blades Pressure Indication Gauges Combustion chamber must add sufficient heat energy to the EPR: Engine Pressure Ration gauge, also referred to as gases passing through the engine to accelerate their mass and TPDI produce the desired thrust for the engine and power of the Used in turbojets and turbofans turbines

Torquemeter Indicates shaft horsepower 1 of 5 Can Combustion Chamber Indications of Compressor Stall Advantages: strength, durability, ease of maintenance Mild pulsation with minimum indications to aircraft vibration Disadvantages: and loud bangs and noises Poor use of space With constant PCL position, RPM decay, ITT rise, and possible Greater pressure loss loud noises also indicate stall Uneven heat distribution Malfunction of one can lead to turbine damage Airflow distortion Airflow distortion is the most common cause of compressor Annular Combustion Chamber stall, however, excessive AOA is what causes a compressor stall Main advantage: uniform heat distribution Main disadvantage: unit cannot be removed without major Mechanical Malfunctions 4 Types overhaul Variable inlet guide vane and stator vane failure Turbine Section FCU failure Comprised of stators and rotors FOD Turbine section drives the compressor and the accessories Variable exhaust nozzle failure Unlike compressor, designed to increase airflow velocity Turbines rotor converts the heat energy of the hot FCU expanding gases from the burner chamber into Provides proper amounts of fuel to combustion chamber mechanical energy An over rich mixture (too much fuel) causes excessive chamber 75% of the total pressure energy from the exhaust gases burner pressure and a back flow of air into the compressor that is converted leads to a compressor stall 25% is used for thrust A lean mixture (to little fuel) may cause the engine to flame out which can be just as hazardous depending on the situation Turbine Blades Attached to the shaft by a method call Fir Tree Avoidance Blades are not welded onto the rotor shaft Avoid erratic or abrupt PCL movements, esp. at low airspeed and high AOA Exhaust Section Maintain the minimum prescribed airspeed and avoid abrupt Must direct the flow of hot gases rearward to cause a high changes in aircraft attitude to allow the proper amounts of exit velocity to the gases while preventing turbulence smooth air to enter the inlets Avoid flight through severe weather and turbulence Exhaust Nozzles Convergent, Fixed area, takes relatively slow subsonic CHAPTER 4 TURBOJET AND TURBOFAN ENGINES gases from the turbine section and gradually accelerates them through the convergent section Turbojet Engine Constructed by the addition of an inlet and an exhaust section Afterburner Section to the basic gas generator Used in turbojets and turbofans for a short period of time Derives thrust by highly accelerating a small mass of air Increases max thrust available from an engine by 50% or through the engine more Advantages: Flame holder: provides a region in which airflow velocity is Lightest specific weight reduced and turbulent eddies are formed Higher and faster than any other engine Screech: violent pressure fluctuations caused by cyclic Best high end performance engine vibrations that reduce efficiency. Characterized by loud Disadvantages: noise and vibration Low propulsive efficiency at low forward speeds Screech Liners: reduce pressure fluctuations and High TSFC and low altitude and low airspeeds vibrations by acting as a form of shock absorber Long takeoff roll required

CHAPTER 3 COMPRESSOR STALLS Thrust Specific Fuel Consumption (TSFC) Amount of Fuel required to produce one pound of thrust Relative Wind Turbofan Engine Formed by combining the compressor rotation and inlet Fan provides thrust by accelerating a large air mass around the airflow gas generator Combined with the exhaust gases of the gas generator, the Angle of Attack overall thrust is greater than the thrust of a turbojet at the Relative wind and rotor blade chordline (angle between) same fuel consumption rate Main cause for compressor stall is excessive angle of Main advantage: Lower TSFC attack Main disadvantage: Inefficient at higher altitudes

2 of 5 Bypass ratio Force and Pressure Higher bypass ratio yields lower TSFC Pressure is the force acting upon one square inch of area (PSI) Cargo aircraft, airliners Lower bypass ratio turbofan engines resemble turbojet but Power Control Systems are more efficient Supply pressure only for flight controls Modern fighters and interceptor System Components CHAPTER 5 TURBOPROP AND TURBOSHAFT Reservoir Storage tank for hydraulic fluid Turboprop Engine Also serves as an overflow basin for excess hydraulic fluid The actual percentage of thrust will vary with a host of forced out of the system by thermal expansion, allow air factors such as speed, altitude, and temperature. The bubbles to be purged, and separate some foreign matter from turboprop will deliver more thrust, up to medium the system speeds, than either the turbojet or turbofan. Also, as the turboprop climbs to higher altitudes, the mass of Variable displacement Pumps air being accelerated by the propeller decreases due Regulates volume delivery in accordance with system flow to the decrease in air density. demands Components Propeller Assembly Check Valve Majority of thrust (90%) is a result of the large mass being Prevents back flow. Allows flow in only one direction accelerated by the propeller Works in conjunction with accumulator to maintain system Blades are installed into the hub pressure during shutdown The hub (barrel assembly) is then attached to the propeller shaft Accumulator The pitch change/dome assembly is the mechanism that Acts as a shock absorber changes the blade angle of the propeller Stores enough fluid under pressure to provide for emergency operation of certain actuating units Reduction Gear Box Prevents the propeller blades from reach supersonic Relief Valve speeds Pressure limiting device Converts high rpm and low torque of the gas generator to Safety valve that is installed in the system to prevent pressure low rpm, high torque necessary for efficient propeller from building up to a point where seals might burst or damage operation may occur to the system

Torquemeter Assembly Hydraulic fuses Used to transmit and measure the power output from the Safety devices gas generator to the reduction gear box Designed to detect or gauge ruptures, failed fittings, or other leak producing failures of damage ** The propeller assembly, the reduction gear box and the Prevents excessive loss of fluid torquemeter may be connected to the gas generator in two possible configurations: Selector Control Valves 1] Attached to the front of the compressor drive shaft Used to direct the flow of fluids to actuators 2] Attached to the free / power turbine Actuators Turboshaft Engine Convert fluid under pressure into linear or reciprocating The propulsive energy from the exhaust is negligible; that mechanical motion is, all of the remaining energy is extracted by the free or power turbine to drive the rotor assembly CHAPTER 7 ELECTRICAL SYSTEMS Free/Power Turbine: exhaust gases from the gas generator turbine drive the power turbine Alternating Current Sources A/C Generator CHAPTER 6 HYDRAULICS Alternator Inverter

Basics Direct Current Used in military aircraft to provide extra power and D/C Generator mechanical advantage Transformer Rectifier Pascal’s Law: pressure applied to a confined liquid is Battery transmitted equally in all directions without the loss of pressure and acts with equal force on equal surfaces

3 of 5 Constant Speed Drive Engine Driven Pump Ensures constant input rpm. Hydro mechanical linkage Provides fuel in excess of engine requirements between the engine and the generator Excess fuel ensures that a sufficient supply of high pressure Ensures a steady voltage output to supplied equipment. fuel is available to meet engine requirements and if available, The electric generator is mechanically coupled to the gas afterburner requirements turbine engine’s accessory drive section FCU Manual / Emergency Operation Inverter PCL functions as a throttle and fuel flow is now regulated On DC electrical systems, inverters are used to power AC exclusively by its movement equipment Most monitor temps, pressures closely to ensure critical limits are not exceeded Transformer Rectifier Transforms AC to DC Fuel Flow Gauge A fuel flow transmitter is located at the outlet f the FCU just Electrical bus before the fuel-oil heat exchanger. This transmitter measures Common distribution point for electricity the fuel flow rate coming out of the FCU and converts it to Essential bus: powers equipment required for flight safety electrical signals. The electrical signal is sent to the fuel flow (gyro) gauge in the cockpit indicating fuel consumption/usage in Primary bus: powers equipment devoted to aircraft pounds per hour (PPH) mission (radar) Monitor/Secondary: powers convenience circuits (cabin Fuel –Oil Cooler / Heat Exchanger lighting) Preheating fuel removes any ice crystals and increases its Starter bus: routes power to start the aircraft engines volatility, facilitating fuel ignition

CHAPTER 8 FUEL SYSTEMS P&D Valve During engine starts, the dump valve is closed by an electrical JP-5 signal from the FCU Low volatility During shutdown it opens up to allow fuel to drain to manifolds High flash point (140 deg F) Only fuel that can be stored on ships Afterburner Fuel Control Unit Meters fuel to the afterburner spray bars JP-8 Flash point 100 deg F Normal Rated Thrust Thrust produced at maximum continuous turbine temperature Basic Fuel System with no time limitation When designing take these factors into account in rank order Military Rated Thrust 1] High rates of fuel flow Thrust produced at the maximum turbine temperature for a 2] Low atmospheric pressure limited time; normally 30 minutes 3] Piping system complexity 4] Weight and size constraints Combat Rated Thrust 5] Vapor loss with consequent reductions in range and Thrust produced with the afterburner operation, not based on cold weather starting temp. limitations rather based on fuel limitations

Boost Pump CHAPTER 9 LUBRICATION Submerged and installed in fuel tanks Ensure adequate supply of vapor free fuel to the engine Viscosity driven fuel pump Property of fluid that resists the force tending to cause the fluid Critical function  prevent aeration of the fuel supply to flow which may result from a rapid pressure change incurred Inversely related with temperature during a climb Oil Tank Fuel Pressure Gauge Stores system supply oil Pressure sensor at the boost pump outlet Designed to furnish a constant supply of oil to the engine in any Drop in fuel pressure may indicate a failed boost pump or aircraft attitude to include inverted flight or during negative G absence of fuel which could lead to cavitation of the main maneuvers fuel pump Gravity, acting on the weighted end, ensures the pickup end is constantly immersed in the oil supply Low Pressure Filter Provide an expansion space and venting to ensure proper Located downstream of the boost pump to strain operation. This space is required to allow for both expansion of impurities from the fuel the oil due to heat absorption and foaming due to circulation through the system 4 of 5 Bleed Air Oil Pump High and low pressure systems are used to drive aircraft and Consists of a pressure supply element to supply oil and engine components or accessories, while the interstage bleed scavenge element to remove oil from an area valves are required to ensure compressor stability Scavenge elements have a greater pumping capacity than Low pressure bleed air is taken from the back end of the low the pressure element to prevent back pressure in the pressure compressor system and/or accumulation of oil in the bearing sumps. High pressure bleed air is taken from the back end of the high Instrumentation: gauges that indicate current operations pressure compressor and possible future failures of the lubrication components Interstage bleed air is taken in between stages

Filter Bypass Valve Starting Systems Allows oil to flow around the filter element should the filter Purpose is to accelerate the engine until the turbine is become clogged producing enough power to continue the engine acceleration Dirty oil is better than no oil itself

Oil Pressure Relief Valve Abnormal Starts Limits maximum pressure within the system Hot Start: exceeds max temps Preset to relieve pressure by bypassing oil back to the Hung Start: temp continues to rise, compressor stabilizes below pump inlet whenever the pressure exceeds a safe limit normal False Start: temp remains within limits, compressor stabilizes Magnetic Chip Detector below normal Metal plug with magnetized contacts, placed in scavenged Wet Start: fuel is present but light-off doesn’t take place (most oil path. Advises pilot of metal contamination which is an dangerous) indication of possible failure of one of the engine gears, Trick Question: If you are using an air turbine starter do you still bearings, or other metal parts need electricity? Yes, for ignition system Air Cooler Controlled by the fuel temperature sensing switch Ignition Systems We normally use high energy capacitor-type ignition systems Fuel Oil Cooler / Heat Exchanger This provides both high voltage and an exceptionally hot spark, Controlled by the oil temperature regulator valve which gives an excellent chance of igniting the fuel-air mixture Main purpose is to heat fuel at reasonably high altitudes Takes hot oil from the bearings and preheats fuel for Another benefit of this high energy igniting system is that combustion fouling of the igniter plugs is minimal

Breather Pressurizing Subsystem Igniter Plug Types Pressurization is provided by compressor bleed air. At sea Annular –gap level pressure, the breather pressurizing valve is open to Protrudes slightly into the combustion chamber liner to provide the atmosphere an effective spark

CHAPTER 10 ACCESSORY, IGNITION, AND STARTER Constrained- gap SYSTEMS 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

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