Engines

=AIRCRAFT ENGINES AND SYSTEMS ELO's=

ELO 3.1 Pressure Explain the relationship between static pressure, dynamic pressure and total pressure.
ELO 3.2 State Bernoulli’s theorem. BERNOULLI’S THEOREM ELO 3.3 Describe the behavior of subsonic airflow in a nozzle and diffuser. ELO 3.4 Describe the behavior of supersonic airflow in a nozzle and diffuser. ELO 3.5 Identify the three main sections of a gas generator. ELO 3.6 Describe the Brayton Cycle. ELO 3.7 Describe the basic components and operation of the gas generator. ELO 3.8 Describe how pressure, temperature, and velocity changes through each section of a gas turbine engine. PRESSURE TEMPERATURE VELOCITY ELO 3.9 Describe gross thrust and net thrust. GROSS THRUST NET THRUST
 * Total pressure is equal to the static pressure plus the dynamic pressure
 * Bernoulli’s theorem states that as any incompressible fluid passes through a convergent opening its velocity increases and pressure decreases
 * A subsonic nozzle is convergent, it increases velocity and decreases pressure
 * A subsonic diffuser is divergent, it decreases velocity and increases pressure
 * A supersonic nozzle is divergent, it increases velocity and decreases pressure
 * A supersonic diffuser is convergent, it decreases velocity and increases pressure
 * A gas generator has a compressor, combustion chamber, and a turbine
 * The Brayton Cycle consists of four events occurring simultaneously: intake, compression, combustion, and exhaust
 * The gas generator has the Brayton Cycle which occurs simultaneously throughout the gas turbine engine
 * Compression takes place in the compressor, combustion in the combustion chamber, and exhaust through the turbine producing thrust
 * Pressure increases from the inlet, through the compressor into the diffuser, and it decreases from the burner through the turbine into the exhaust
 * Temperature increases from the inlet, through the compressor and the diffuser into the burner, and decreases through the turbine into the exhaust
 * Velocity remains virtually constant through the inlet and compressor, into the diffuser and increases through the burner and turbine and peaks in the exhaust
 * Gross thrust is a measurement of thrust due solely from the velocity of the exhaust gases
 * Equation is given as Gross thrust = m x (V final) / t
 * Net thrust is thrust that is corrected for the effect of inlet airflow velocity
 * Equation is given as Net thrust = m x (Vfinal – Vinitial) / t

ELO 3.10 Temperature Describe how atmospheric temperature effects thrust in a gas turbine engine.
ELO 3.11 Describe how atmospheric pressure effects thrust in a gas turbine engine. ELO 3.12 Describe how altitude effects thrust. ELO 3.13 Describe the effect of airspeed on thrust. ELO 3.14 Describe the effect of ram effect on thrust. ELO 3.15 Identify the cockpit instrument that measures thrust in a typical turbojet, turbofan, turboprop, and turboshaft. GAS TURBINE ENGINES ELO 3.16 Describe purpose and the types of inlet ducts. ELO 3.17 State the operation and shape of subsonic and supersonic inlet ducts. SUBSONIC INLETS SUPERSONIC INLETS ELO 3.18 State the function of a variable geometry inlet duct. ELO 3.19 State the function of the compressor section.
 * As temperature increases thrust decreases
 * As pressure increases thrust increases
 * As altitude increases thrust decreases
 * As airspeed increases thrust decreases
 * Ram effect has a neutral effect on thrust at low airspeed but a slight increase in thrust at subsonic airspeeds
 * The turbine pressure discharge indicator (TPDI) or the engine pressure ratio (EPR) gauge are used to measure thrust for turbojets and turbofans
 * Propeller or rotor driven aircraft use a torquemeter gauge to indicate power available
 * The inlet duct is designed to provide the proper amount of high pressure, turbulence-free air to the compressor
 * Single-entrance inlet ducts are the simplest and most effective inlet design
 * Has very smooth airflow characteristics
 * Engine is mounted midship
 * Divided-entrance inlet ducts are split ducts that can cause some distortion of air flow
 * Allows pilot to sit lower in the fuselage
 * Reduces friction loss due to length
 * Skin friction may distort air flow
 * Subsonic inlets are divergent
 * Because of the relative incompressibility of subsonic airflow, the shape of the subsonic inlet will increase airflow pressure while reducing its velocity
 * Supersonic inlets are convergent – divergent inlet ducts
 * Supersonic airflow is highly compressible
 * At supersonic speeds, sonic shock waves are developed and if these are not controlled high duct losses will result and could create inlet buzz
 * The 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
 * The primary function of the compressor section is to supply enough air to satisfy the requirements of the combustion section
 * Specifically, the compressor increases the pressure of the airflow from the air inlet duct and directs it to the burners in the quantity and at the pressures required

ELO 3.20 Describe the three types of compressors used in gas turbine engines, including their advantages and disadvantages.
CENTRIFUGAL FLOW COMPRESSOR AXIAL-FLOW COMPRESSOR DUAL SPOOL AXIAL FLOW COMPRESSORS AXIAL-CENTRIFUGAL FLOW COMPRESSOR ELO 3.21 State the function of the burner section. ELO 3.22 Describe the three types of combustion chambers used in gas turbine engines, including their advantages and disadvantages. CAN COMBUSTION CHAMBER ANNULAR COMBUSTION CHAMBER CAN-ANNULAR TYPE ELO 3.23 State the function of the turbine section. ELO 3.24 State the effects of thermal stress on turbine components. ELO 3.25 Define "fir tree" and "creep". FIR TREE CREEP ELO 3.26 Explain how heat and potential energy are converted into mechanical energy in the turbine section. ELO 3.27 State the function of the exhaust section. ELO 3.28 Describe subsonic and supersonic exhaust nozzles. SUBSONIC EXHAUST NOZZLE SUPERSONIC EXHAUST NOZZLE ELO 3.29 State the function of the afterburner.
 * Centrifugal flow compressors consist of three main components; an impeller, a diffuser, and a manifold
 * Advantages are good power output over a wide range of RPM’s, low cost, ruggedness, and it produces the best pressure increase per stage
 * Disadvantages are a large frontal area is required and it is impractical for multiple stages
 * Axial flow compressors have to main elements; rotor blades and stator vanes
 * Advantages are efficient use of multiple stages producing very high overall compression ratios
 * Disadvantages include being susceptible to foreign object damage, and it is very expensive and complex
 * Dual spool axial flow compressors are divided into two completely independent rotor spools, each driven by its own turbine and drive shaft; one is the high pressure compressor and one is the low pressure compressor
 * Advantages are greater flexibility, power, small frontal area reducing drag, high peak efficiencies, straight through flow, allowing for high ram efficiency, and increased combustion efficiency
 * Disadvantages are possible stalls at slow speeds, ram effect may increase inlet temperatures, good efficiencies only possible over a narrow rotational speed, difficult to manufacture and costly, and they have high starting power requirements
 * Axial-centrifugal flow compressors utilizes the combination of the centrifugal and axial flow compressors
 * Advantage is the large pressure increase yet small size which is useful on helicopters and small aircraft
 * Disadvantage is that it is only capable on small aircraft
 * The burner section contains the combustion chamber, and provides the means for proper mixing of the fuel and air to assure good combustion
 * The can combustion chamber is used mainly on older centrifugal compressor engines
 * Airflow is ducted to individual combustion cans that are arranged around the circumference of the burner section
 * Each can contains its own fuel nozzle, burner liner, and casing
 * Advantages include its strength and durability, combined with the ease of maintenance
 * Disadvantages include poor use of space in the chamber, greater pressure loss, and uneven heat distribution to the turbine section
 * Annular combustion chambers consist of a circular, continuous, inner and outer shroud around the outside of the compressor drive shaft
 * Fuel is introduced through a series of nozzles where it is mixed and ignited with the incoming air
 * Advantages include providing a uniform heat distribution across the face of the turbine section which aids in the prevention of heat warping or turbine blade failure, and for better mixing of air and fuel along with better use of space
 * Disadvantages include not being able to be removed without complete disassembly of the engine from the aircraft, and possible structural problems may arise due to the large-diameter, thin-wall cylinder required with this type of chamber
 * Often found in helicopters
 * Can-annular type chambers combine the ease of maintenance of the can type with the outstanding thermodynamics of the annular type
 * Contains cans at the front where the fuel and air are mixed and burned
 * Advantages are even temperature distribution, and eliminates the possibility of cold spots by nozzles clogging, it also has greater structural stability and lower pressure loss than that of the can type
 * Disadvantage is that it is expensive
 * The turbine section drives the compressor and the accessories and is also designed to increase airflow velocity
 * Thermal stress on turbine components causes "creep", or blade elongation, which is caused by excessive temperatures over long periods causing permanent deformation
 * Fir tree is an attachment method preventing the thin metal blades from cracking at the attachments points by allowing them to expand when heated
 * Creep is elongation of blades under extreme heating
 * The increasing turbine inlet temperature results in an increase in specific thrust with a corresponding decrease in fuel consumption
 * The exhaust section must direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence
 * Subsonic exhaust nozzles are convergent because as the gas velocity increases, the ability of pressure to push the molecules from behind decreases
 * Supersonic exhaust nozzles are convergent / divergent because the divergent section allows for pressure buildup to propel the gases forward to supersonic speeds
 * The afterburner is used in turbojets and turbofans to increase maximum thrust available from an engine by 50% or more

ELO 3.30 Describe the components and operation of the afterburner.
COMPRESSOR STALLS ELO 3.31 Name two vector components that make up the relative wind in the compressor. ELO 3.32 Describe a compressor stall. ELO 3.33 Describe the angle of attack of compressor blades and the two factors that determine it. ELO 3.34 Identify the indications of a compressor stall. ELO 3.35 Identify the two main causes of a compressor stall. ELO 3.36 Describe how airflow distortions can cause compressor stalls. ELO 3.37 Describe the four possible mechanical malfunctions that can lead to compressor stall. VARIABLE INLET GUIDE VANE (IGV) AND STATOR VANE FAILURE FUEL CONTROL UNIT (FCU) FAILURE FOREIGN OBJECT DAMAGE (FOD) VARIABLE EXHAUST NOZZLE FAILURE ELO 3.38 Describe what a pilot can do to minimize the potential of a compressor stall. ELO 3.39 Describe the four components that can be incorporated into an engine design to minimize the potential of a compressor stall. VARIABLE INLET GUIDES AND STATORS SPLIT SPOOL BLEED VALVES VARIABLE EXHAUST NOZZLE
 * The afterburner has four main components; fuel spray bars which introduce fuel to the afterburner, the flame holders which is located downstream of the fuel spray bars and is where turbulent eddies are formed allowing for the proper mixture of fuel and air combustion, the screech liner controls screech which is characterized by loud noise and vibration, and the variable exhaust nozzle which can be convergent or divergent and prevents a back pressure which could cause a stall
 * Two vector components that make up the relative wind in the compressor are the compressor rotation (RPM) and the inlet airflow
 * A stall occurs when the airflow over the airfoil breaks away causing the airflow to lose lift due to excessive angle of attack
 * Angle of attack is defined as the angle formed between the chordline of the airfoil and the airfoil’s relative wind
 * The angle of attack of the compressor blades is changed by changing the rotation speed of the rotors during engine operation and/or changing the velocity of the inlet airflow
 * A low angle of attack will result in a low compression ratio and the compressor will be inefficient
 * A high angle of attack will result in a possible stall
 * Indications of a compressor stall can range from mild pulsation with minimum indications to aircraft vibration and loud bangs or noises
 * With constant PCL / throttle position, indications of a compressor stall include RPM decay, and/or interstage turbine temperature (ITT) rise, along with possible loud noises
 * Compressor stalls are mainly the result of airflow distortions or mechanical malfunctions
 * Airflow distortions can cause compressor stalls by the breakdown of the airflow through a few stages of the compressor
 * Airflow distortion to the compressor can be a result of the aircraft attitude and airspeed
 * The compressor blade angle of attack is affected by the velocity and direction of the airflow entering the compressor and the rotational velocity of the compressor rotor blades
 * The instances when airflow distortions may induce compressor stall include:
 * Abrupt changes in aircraft attitude
 * Encountering air turbulence
 * Deficiency of air volume, caused by atmospheric conditions
 * Rapid throttle movement
 * Failure to change the angle of attack will cause too much or too little airflow at low engine speeds
 * The FCU determines the correct amount of fuel to be introduced into the combustion chamber
 * If the FCU fails too much or too little fuel could added
 * FOD is caused when an object damages the delicate blades of the compressor
 * If the variable exhaust nozzle fails to open, an excessive back pressure will be produced which could lead to a compressor stall
 * Erratic or abrupt power control lever (PCL) movements should be avoided, especially at low airspeeds or high angles of attack
 * The PCL should be advanced or retarded in a smooth fashion
 * The pilot should maintain at least the prescribed minimum airspeed and avoid abrupt changes in aircraft attitude to allow the proper amounts of smooth air to enter the inlets
 * Variable inlet guides and variable stator vanes are installed so the angle of attack is changed at low engine speed
 * They are automatically positioned by the stator vane actuator (SVA) using fuel pressure via the fuel control unit
 * This action maintains the velocity of the air within acceptable limits for low airflow conditions and permits high airflow with a minimum of restrictions
 * Dual spool axial flow compressors may be incorporated which allows the front rotor to turn at a slower RPM than the rear rotor
 * This allows the front rotor to turn without being choked by the low airflow
 * Bleed valves are installed near the middle or rear of the compressor to "bleed" air into the atmosphere and increase airflow in the front of the compressor at low speeds
 * Variable exhaust nozzle is used to unload the pressure during afterburner operation

ELO 3.40 State the steps to be taken if a compressor stall occurs.
TURBOJET AND TURBOFAN ENGINES ELO 3.41 Identify the components of a turbojet engine. ELO 3.42 Define thrust specific fuel consumption (TSFC). THRUST SPECIFIC FUEL CONSUMPTION (TSFC) ELO 3.43 Describe the operation of a turbojet. ELO 3.44 Compare the propulsive efficiencies of a turbojet, turbofan, and a turboprop. ELO 3.45 Compare TSFC of a turbojet with a turbofan. ELO 3.46 Describe the characteristics of a turbojet engine. ELO 3.47 Identify the components of a turbofan engine. ELO 3.48 Describe the basic operation of the turbofan engine. ELO 3.49 Describe the characteristics of a turbofan engine.
 * The first step if a stall occurs is to reduce the attitude of the aircraft which will reduce the inlet’s angle of attack
 * The PCL should be retarded to just below stall threshold to allow the engine to "catch up" with the inlet airflow
 * The components of a turbojet engine are the inlet, compressor, burner, turbine, and exhaust
 * TSFC is the amount of fuel required to produce one pound of thrust
 * The total energy of the airflow within the gas generator is altered as it passes through each section
 * Altering the airflow causes an imbalance of forces within the engine which provides the propulsive means to the turbojet engine
 * As speed increases the turbojet engine becomes increasingly more efficient
 * Efficiency of the turboprop increases with speed to a maximum efficiency and decreases efficiency with increasing speeds beyond the maximum efficiency speed
 * A turbofan engine increases in efficiency with the increase in speed, but is more efficient that the turbojet engine at every stage
 * The TSFC of a turbojet is relatively high at low velocity and low altitude
 * The TSFC of a turbofan is lower than that of a turbojet
 * Low propulsive efficiency at low forward airspeeds
 * Relatively high TSFC at low altitude and low airspeeds
 * Long takeoff roll required
 * Lightest specific weight (weight per pound of thrust produced)
 * The components of a turbofan engine are a duct-enclosed fan, gas generator, inlet, compressor, burner, turbine, and exhaust
 * The duct-enclosed fan is driven by the gas generator providing additional thrust by accelerating a fairly large mass of air around the gas generator
 * The increased airflow helps to cool the engine without altering the percentages for the secondary airflow in the combustion chamber
 * Higher thrust at low airspeeds
 * Lower TSFC due to less fuel to produce the same thrust
 * Considerable noise reduction
 * Heavier takeoff weights and shorter takeoff distances
 * Increased performance at operational altitudes when compared to the turbojet

ELO 3.50 State the average percentage of total thrust produced by the fan.
ELO 3.51 State the average percentage of total thrust produced by the exhaust gases of the gas generator on a turbofan engine. ELO 3.52 Explain how the fan is driven by the turbine section. ELO 3.53 Define bypass ratio. BYPASS RATIO ELO 3.54 Explain how bypass ratio effects a turbofan engine’s TSFC. TURBOPROP AND TURBOSHAFT ENGINES ELO 3.55 Describe the basic construction of a turboprop engine. ELO 3.56 Explain how a turboprop produces thrust. ELO 3.57 Define the major components of the propeller assembly. BLADES HUB PITCH CHANGE/DOME ASSEMBLY ELO 3.58 Describe the purpose and operation of the reduction gear box used on a turboprop engine. ELO 3.59 Describe the major components and their operation of the torquemeter assembly.
 * The fan produces 30 to 60 percent of the total thrust of a turbofan engine
 * The gas generator produces between 40 and 70 percent of the total thrust
 * The fan is driven by a free or power turbine, which is a turbine aft of the gas generator turbines and is not connected to the gas generator
 * Another way to drive the fan is with the gas generator turbine which is done by attaching the fan directly to the compressor
 * Bypass ratio is a ratio of the amount of air that bypasses the gas generator in comparison with the amount of air that passes through the gas generator
 * A higher bypass ratio results in a lower TSFC as the efficiency of the engine is increased
 * The turboprop engine couples a gas generator with a propeller, which is driven by the turbine section
 * A turboprop uses a propeller to provide the majority of the thrust and imparts a small amount of acceleration to a large mass of air
 * The blades are installed into the hub
 * The hub is the barrel assembly and is then attached to the propeller shaft
 * The pitch change/dome assembly is the mechanism that changes the blade angle of the propeller
 * The reduction gear box is located between the propeller assembly and the gas generator and is basically a one speed transmission
 * This assembly prevents the propeller blades from reaching supersonic speeds
 * It converts the high RPM and low torque of the gas generator to low RPM, high torque necessary for efficient propeller operation
 * The torquemeter assembly is a set of shafts (the torque shaft and the reference shaft) located between the gas generator and reduction gear box
 * It is used on some turboprop engines to transmit and measure the power output from the gas generator to the reduction gear box
 * The torquemeter operates on the principle of accurately measuring the torsional deflection that occurs in any power transmitting shaft, commonly called the torque shaft

ELO 3.60 State the two main ways the propeller assembly may be connected to the gas generator.
ELO 3.61 Describe the operation and characteristics of a turboprop engine. ELO 3.62 Describe the alpha range and beta range operations of the propeller. ALPHA RANGE BETA RANGE ELO 3.63 Describe the construction of a turboshaft engine. ELO 3.64 Describe the operation of the free/power turbine section. ELO 3.65 Explain how the turboshaft produces thrust. HYDRAULIC SYSTEMS ELO 3.66 Explain Pascal’s Law. ELO 3.67 Define force, pressure, and area. FORCE PRESSURE AREA ELO 3.68 Explain how force, pressure, and area relate to the hydraulic theory. ELO 3.69 Explain the relationship between linear displacement and the change of force between the input and output pistons of a closed hydraulic system.
 * The propeller assembly may be connected to the gas generator by being attached to the front of the compressor drive shaft or attached to the free/power turbine
 * The turboprop accelerates a large amount of air to a moderate speed
 * The propeller assembly maintains the propeller at a constant 100 percent RPM
 * The propeller adjusts the angle of its blades to accommodate the fluctuations of fuel flow resulting in increased and decreased power in order to maintain constant propeller RPM
 * In the alpha range, also known as the flight range, the PCL can be positioned from flight idle to full power
 * The PCL send signals to the FCU for fuel flow
 * The FCU works with the prop governor to maintain constant propeller RPM by adjusting the blade angle
 * The beta range is only used during ground operations
 * This range is from flight idle to max reverse
 * Allows the pilot direct control of blade angle
 * Reversing blade angle results in decreased landing distances and greater ground mobility
 * The turboshaft engine consists of a gas generator and a free/power turbine section
 * The free/power turbine section is mechanically independent from the gas generator
 * Exhaust gases from the gas generator turbine drive the power turbine
 * In the turboshaft, 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
 * In the turboshaft engine, virtually all of the pressure energy is converted into shaft horsepower
 * Pascal’s Law states that pressure applies to a confined liquid is transmitted equally in all directions without the loss of pressure and acts with equal force on equal surfaces
 * The shape of the container has no effect on the pressure or force relationships
 * Force is simply a push or pull
 * Pressure is the amount of force per unit area
 * Area, for hydraulic systems, is given in square inches
 * Pressure is equal to the amount of force per unit area
 * Equation is given as P = F / A
 * Linear displacement or distance traveled is exchanged for the change in force
 * Linear displacement is inversely proportional to the multiplied force

ELO 3.70 Explain why hydraulic systems are required on aircraft.
ELO 3.71 Describe the function of the basic hydraulic components used on aircraft. RESERVOIR PUMPS PRESSURE REGULATOR / UNLOADER VALVE CHECK VALVE ACCUMULATOR FILTERS RELIEF VALVES PRESSURE GAUGE PRESSURE SWITCHES HYDRAULIC FUSES SELECTOR CONTROL VALVES ACTUATORS ELO 3.72 Describe the operation of a basic aircraft hydraulic system. ELECTRICAL SYSTEMS ELO 3.73 Describe the two forms of electricity. AC DC ELO 3.74 Explain why AC electrical systems are preferred over DC systems. ELO 3.75 Explain the function of several aircraft electrical system components. GENERATORS INVERTER TRANSFORMER RECTIFIER (TR) BATTERY ELO 3.76 Describe the electrical distribution network. ELO 3.77 Describe the operation of a basic aircraft electrical system. FUEL SYSTEMS ELO 3.78 Define volatility and flashpoint. VOLATILITY FLASHPOINT ELO 3.79 Describe the relationship between temperature, volatility, and flashpoint.
 * Hydraulic systems are required on aircraft because they are used to operate flight controls as well as up to a dozen other systems on the aircraft
 * The reservoir functions as a storage tank for the hydraulic fluid required in the system
 * It also serves as an overflow basin for excess hydraulic fluid forced out of the system by thermal expansion, heat dissipation, allow air bubbles to be purged, and separate some foreign matter from the system
 * Pressurized reservoirs exist on high altitude aircraft
 * Hand pumps are used in hydraulic systems to supply fluid under pressure to subsystems such as landing gear, flaps, canopy, cargo doors, bomb bay doors, and to charge brake accumulators
 * Hand pump systems are referred to as emergency systems
 * Power pumps are normally driven by the engine but may be electric-motor driven
 * They displace a constant or a variable amount of fluid
 * The pressure regulator or unloader valve always works in conjunction with the constant displacement pump
 * Pressure regulator maintains a set pressure in the system
 * The unloading valve diverts all pump flow back to the reservoir when the preset system pressure is met
 * The check valve allows for one way flow in a hydraulic system
 * Allows free flow from the pumps but prevents a back flow
 * The accumulator serves as a cushion or shock absorber by absorbing pressure surges in the system
 * Supplements the pump’s output when the pump is under peak load by storing energy in the form of fluid under pressure
 * Filters ensure delivery of contaminant free hydraulic fluid by preventing dust, grit, and undesirable impurities from entering the system
 * Relief valves are simply a pressure limiting device
 * The valves prevent seals from bursting or becoming damaged due to pressure build-up
 * The pressure gauge indicates the amount of pressure in the hydraulic system
 * Pressure switches are used to indicate a hydraulic drop that falls below allowable limits
 * Located in the lines leading from the pump
 * Hydraulic fuses are safety devices that are installed at strategic locations throughout a hydraulic system
 * They are designed to detect or gauge ruptures, failed fittings, or other leak-producing failures or damage
 * Selector control valves are used in a hydraulic system to direct the flow of fluid
 * Directs fluid under pressure to the desired working port of an actuating unit
 * At the same time it directs the return fluid from the opposite working port of the actuator to the reservoir
 * Actuators convert fluid under pressure into linear or reciprocating mechanical motion
 * Usually installed with the piston shaft end attached to the mechanism and the other end to the aircraft structure
 * Fluid is pumped out of the reservoir through the check valve past the pressure regulator
 * Pressure is then released to the actuating cylinder allowing function of the piston
 * Fluid is returned through the selector valve and the filter to the reservoir
 * AC is a form of electricity that reverses its direction
 * AC is used in our homes
 * DC is a form of electricity that only flows in one direction
 * DC is used in our boats, cars, and even small electrical devices such as watches
 * DC units are heavy compared to their power output capabilities
 * DC units are often not reliable and they increase maintenance
 * DC units also use an inverter for conversion to alternating current for AC powered equipment
 * AC power requires less current because of higher voltage and a ground neutral system
 * AC components are lightweight, simple, and reliable
 * Generators are often used as the main source for AC and DC power
 * DC generators are called generators while AC generators are called alternators
 * Generators require a constant rotational input speed regardless of engine RPM
 * A constant speed drive is a hydro-mechanical linkage between the engine and the generator
 * An inverter is an electro-mechanical device that transforms direct current into alternating current
 * On DC electrical systems, inverters are used to power AC equipment
 * A transformer rectifier is an electrical device which transforms AC power into DC power
 * The rectifier’s DC current capability is high and is largely dependent on the cooling ability of its fan
 * The battery provides direct current power
 * This DC voltage is primarily used as a source of emergency power should the generators fail and also for starting the aircraft’s engines
 * Nickel cadmium is the preferred battery over the lead-acid battery
 * Nickel cadmium batteries recharge in a short amount of time
 * They hold charge for long periods
 * Worn cells can be replaced
 * Delivers a large amount of power
 * The electrical distribution network in an aircraft provide the various electrical components with their power requirements through several buses
 * The essential bus routes power to equipment required for flight safety
 * The primary bus routs power to equipment devoted to the aircraft’s intended mission
 * The monitor or secondary bus routes power to convenience circuits
 * The starter bus routes power to start the aircraft’s engine(s)
 * Manual or automatic control over the flow of electrical power comes from fuses, switches, and circuit breakers
 * The main generators are powered from the aircraft engine’s accessory drive section via the constant speed drive
 * Warning lights are designed to alert the crew to any system malfunction
 * A series of buses is incorporated to provide the electrical distribution based on equipment type and current required
 * Emergency power is available to energize the essential busses in the event of generator failure
 * Electrical power for the starter bus is obtained from either an external source, the battery, or the auxiliary power unit (APU)
 * Volatility is the measurement of a liquid’s ability to convert to a vaporous state
 * Flash point is the lowest temperature of a combustible substance that would ignite with a momentarily application of a flame
 * A fuel’s flashpoint and volatility rating are inversely related
 * As the flash point increases, the temperature at which fuel would ignite decreases

ELO 3.80 State the characteristics of common military aviation fuels.
JP-4 (NATO CODE F-40) JP-5 (NATO CODE F-44) JP-8 (NATO CODE F-34) ELO 3.81 Describe the function of the aircraft fuel system components. FUEL TANK BOOST PUMP CROSSFEED EMERGENCY SHUTOFF VALVE FUEL PRESSURE GAUGE LOW PRESSURE FUEL FILTER ENGINE-DRIVEN PUMP FUEL CONTROL UNIT (FCU) ELO 3.82 Describe the three types of thrust ratings. NORMAL RATED THRUST (NRT) MILITARY RATED THRUST (MRT) COMBAT RELATED THRUST (CRT) ELO 3.83 Explain the operation of an afterburner fuel system. ELO 3.84 Explain the operation of an afterburner fuel control unit. LUBRICANTS AND LUBRICATION SYSTEMS ELO 3.85 Describe the characteristics of synthetic lubricants. ELO 3.86 Define viscosity. VISCOSITY ELO 3.87 Describe the functions of lubricants. LUBRICATION COOLING CLEANING ELO 3.88 Describe the operation of a basic aircraft lubrication system. ELO 3.89 Describe the functions of the three subsystems of the aircraft lubrication system. WET SUMP SYSTEM DRY SUMP SYSTEM PRESSURE SUBSYSTEM
 * JP-4 is a wide cut blend of kerosene with some naphtha fractions and gasoline
 * Highly volatile with a flashpoint of –35 degrees farenheight
 * Easier starting, slower acceleration, lower operating temperatures, higher tendency to vapor lock, and shorter range compared to JP-5
 * The Navy, Marine Corps, and Coast Guards primary jet fuel
 * JP-5 is a heavy kerosene to be blended with gasoline
 * Thermally stable with a high heat content per gallon
 * Low volatility and a flashpoint of 140 degrees farenheight permits storage aboard ships
 * Similar to JP-5 except for the flashpoint, which is 100 degrees farenheight and permits storage aboard ships
 * Air force’s primary jet fuel
 * Advantages include fuel handling and operational safety
 * The fuel tank is the starting point for fuel
 * The tank is a reservoir, or holding cell, for the jet propellant
 * The boost pump is an integral unit composed of a centrifugal pump and electric motor
 * Submerged in fuel tanks, they insure adequate supply of fuel to the engine-driven fuel pump
 * A critical function of the boost pump is to prevent aeration of the fuel supply which may result from a rapid pressure change incurred during a climb
 * Used to regulate stability of the fuel load by transferring fuel to even out the load
 * When the pilot pulls the emergency handle, the emergency shutoff valve shuts off fuel to the engine electrically and mechanically
 * Located in the cockpit, the fuel pressure gauge receives signals from a pressure sensor at the boost pump outlet
 * The low pressure fuel filter is usually a paper cartridge type filter, located downstream of the boost pump to strain impurities from the fuel
 * The minute openings make this type of filter susceptible to clogging, therefore, a bypass valve is a necessary safety factor to ensure a positive supply of fuel to the engine
 * The engine-driven pump is a high pressure pump designed to deliver fuel to the control unit in excess amounts
 * The fuel control unit is the "brain" of the engine fuel system
 * The FCU is a hydromechanical or electrical device that consists of fuel computing and fuel metering systems
 * To ensure proper fuel flow the system incorporates various inputs to include:
 * PCL position – inputs from the aviator
 * Compressor inlet temperature (CIT) – measures ambient air density
 * RPM’s - compressor speed
 * Turbine temperature – prevent turbine damage
 * NRT is the thrust produced at the maximum continuous turbine temperature with no time limitation
 * This rating is for cruising
 * MRT is the thrust produced at the maximum turbine temperature for a limited time, normally 30 minutes
 * The maximum temperature for MRT is higher than for NRT, however, the time constraints ensure blades are not damaged
 * This rating is for takeoff or when additional thrust is needed
 * CRT is thrust produced with the afterburner in operation, and is not based on turbine temperature limitations
 * The fuel transfer valve, which is mounted on the body of the engine driven fuel pump, supplies fuel to the afterburner fuel control unit
 * The afterburner fuel control unit meters fuel to the afterburner spray bars and excess fuel is returned to the fuel pump inlet
 * Synthetic lubricants are less volatile, has a stronger chemical stability, and a lower tendency to leave cooking deposits
 * Multiple synthetics may not be derived from the same base and therefore cannot be mixed
 * Synthetic oils are never to be mixed with petroleum based lubricants
 * Viscosity is the property of a fluid that resists the force tending to cause the fluid to flow
 * Viscosity is inversely related to temperature
 * Oils should have the following characteristics to lubricate properly:
 * It must be low enough viscosity to flow, yet high enough to protect
 * Must not break down under high heat or pressure
 * Must flow readily when starting under extremely low temperatures
 * Must have a high flashpoint so it does not burn or vaporize
 * Should not form or deposit excessive amounts of gum, carbon, or varnish
 * Lubricants must cool moving parts by carrying heat away from gears and bearings
 * Temperatures in excess of 1700 degrees farenheight so this is important
 * Lubricants must carry dirt, metal, and carbon away from moving parts to the filter
 * This is a vital function
 * The lubrication system pumps oil around moving parts of the engine
 * As the oil is pumped through the engine it removes heat, dirt, carbon, and metal from moving parts while lubricating at the same time
 * The wet sump system is used on aircraft that require a limited supply of oil and limited cooling
 * Oil is stored in a sump which limits the amount of oil carried
 * Oil is difficult to cool in this system and it is not adaptable for unusual flight attitudes for extended periods of time
 * Oil is carried in a dry sump mounted to the engine or in the airframe
 * More oil can be stored and temperature is readily controlled
 * Three subsystems of the dry sump system are:
 * Pressure subsystem supplies lubricating oil from the tank to the main engine bearings and the accessory drives
 * Scavenge subsystem removes the oil from the main bearings and accessory drives through the oil coolers and returns it to the tank, completing the flow cycle
 * The breather pressurizing subsystem connects the individual bearing components and the oil tank with the breather pressurizing valve to help minimize oil leakage
 * Pressure subsystems normally employ an engine driven, gear type, pressure pump
 * Oil is sprayed at a constant pressure despite engine speed

ELO 3.90 Describe the function of basic lubrication system components used on aircraft.
OIL PUMP GAUGES FILTERS SCAVENGE SUBSYSTEM BREATHER PRESSURIZING SUBSYSTEM ACCESSORY, STARTER AND IGNITION SYSTEMS ELO 3.91 Describe the types of accessories used on aircraft. ELO 3.92 Describe how the accessories are driven. BLEED AIR-DRIVEN MECHANICALLY-DRIVEN ELO 3.93 Define interstage bleed air. INTERSTAGE BLEED AIR ELO 3.94 Describe the starting sequence for a gas turbine. ELO 3.95 Describe the four types of abdominal starts. HOT START HUNG START FALSE START WET START ELO 3.96 Describe a DC Electric starter. ELO 3.97 Describe an Air Turbine Starter. ELO 3.98 Describe a basic aircraft ignition system. ELO 3.99 Describe the two types of igniters. ANNULAR-GAP CONSTRAINED-GAP
 * The oil pump supplies oil under pressure to the parts of the engine that must have lubrication
 * The oil pressure gauge displays oil pump discharge pressure
 * The oil temperature gauge displays the temperature of the oil prior to entering the engine bearing compartments
 * Filters remove any foreign particles that may be present in the oil
 * The filter bypass valve allows oil to flow around the filter in the event the filter gets clogged
 * The magnetic-chip detector is a metal plug with magnetized contacts, and is placed in the scavenged oil path
 * The oil pressure relief valve is the pressure oil line to limit the maximum pressure within the system
 * The relief valve is preset to relieve pressure by bypassing oil back to the pump inlet whenever the pressure exceeds safe limits
 * The scavenge subsystem removes oil from the main bearing compartments and accessory gear drives
 * The breather pressurizing subsystem provides the following functions
 * Minimizes internal oil leakage by encasing the oil sumps
 * Ensures proper spray patterns of oil across the bearing by mixing pressurized air with the oil to form a fine oil mist for the bearings
 * Accessories for gas turbine engines can be divided into two categories: those driven by bleed air and those driven mechanically
 * Compressor discharge air at high pressure is bled from the engine through ports or valves at intervals along the compressor case and at the end of the diffuser
 * It is used as a source of power for operating air conditioning units, cockpit pressurization, and engine anti-icing to name a few
 * Driven by a geared drive taken directly from the main shaft connecting the turbine to the compressor
 * This is used for tachometers, hydraulic pumps, generators, alternators, and other accessories
 * Interstage bleed air is required to maintain and ensure compressor stability
 * As soon as the starter has accelerated the compressor sufficiently to establish airflow through the engine, the ignition is activated and then the fuel is added
 * A hot start is defined as exceeding the maximum allowable temperature for the turbine section during start
 * A hung start describes a situation where the temperature within the turbine section continues to rise, and the compressor RPM stabilizes below normal
 * A false start occurs when compressor RPM stabilizes below normal, and the turbine temperature remains within limits
 * A wet start is a situation in which the fuel-air mixture does not light off initially, but has the capability to ignite
 * The wet start is an ignition problem and is the most dangerous abdominal start
 * The electric starter is mechanically connected to the compressor and is mounted on either the engine accessory gear box or the front frame of the engine
 * A battery, auxiliary power unit, or external electrical source may be used to supply electric current to the start motor
 * An air turbine starter is a small, geared, air turbine motor attached to the engine
 * Air is directed to the air turbine which accelerates the compressor
 * A basic aircraft ignition system is a high energy, capacitor-type ignition system that provides both high voltage and an exceptionally hot spark which gives an excellent chance of lighting the fuel-air mixture at reasonably high altitudes
 * The annular-gap plug protrudes slightly into the combustion chamber line to provide an effective spark
 * The constrained-gap does not closely follow the face of the plug, it jumps in an arc which carries it beyond the face of the chamber liner

=Engines Q&A=

Chapter 1 - Principles of Gas Turbine Operation
Total Pressure = Static Pressure (Pressure) + Dynamic Pressure (Velocity) Bernoulli’s Theorem * as any incompressible fluid passes through a convergent opening its velocity increase and pressure decreases Convergent Passages Divergent Passages Gas Generator The Brayton Cycle Gross Thrust Air Temperature Air Pressure Altitude Ram Effect Engine Pressure Ratio (EPR) gauge - TPDI Torquemeter
 * Subsonic Nozzle - P decreases/V increase
 * Supersonic Diffuser - P increases/V decrease
 * Supersonic Nozzle - P decreases/V increases
 * Subsonic Diffuser - P increases/V decrease
 * Produces the high energy airflow necessary for creating thrust and includes compressor, combustion chamber, and turbine
 * Operating cycle that consists of four events simultaneously: intake, compression, combustion, exhaust
 * Measurement of thrust due solely from the velocity of the exhaust gases
 * Produced by a stationary or static engine in standard conditions
 * As Temperature increases, density decreases, therefore Thrust decreases
 * As Pressure increases, density increases, therefore Thrust increases
 * Rate of thrust decreases because a pressure drop is greater than the thrust increase resulting from a temperature drop
 * Offsets the decrease in acceleration and results in a neutral effect in thrust at subsonic airspeeds
 * Due tot he compressibility of airflow as velocity increases toward supersonic
 * Significant increase in overall thrust at supersonic speeds
 * Indicates the pressure ratio between the inlet and exhaust airflow
 * Used on aircraft that rely on the propulsive power of the exhaust gases of a gas turbine engine(turbojets/turbofans)
 * Indicates shaft horsepower available to drive a propeller or rotor
 * Used on propeller or rotor driven aircraft to indicate power available

Chapter 2 - Gas Turbine Engines
Subsonic Inlet Supersonic Inlet Variable Geometry Inlet Duct Compressor Centrifugal Flow Compressor Advantages Axial*Flow Compressor Dual Spool - twin or split spool Axial Flow Advantages Axial Flow Disadvantages Turbine Section Exhaust Section Afterburner Section
 * Divergent Shaped
 * Convergent-Divergent Shaped
 * 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.
 * Main function of the compressor is to supply enough air to satisfy the requirements of the combustion section and improve burner efficiency
 * Another function is to supply compressor bleed air to operate various components throughout the engine aircraft
 * Impeller, diffuser, and manifold
 * Divergent passages in the diffuser convert the high velocity airflow to high pressure
 * Thus, velocity decreases, pressure increases, and total pressure remains the same
 * Airflow passes through the compressor manifold, which directs it to the combustion chamber
 * Rugged, low cost, good power output over a wide range or RPMs, High pressure increases per stage
 * Rotor blades and Stator vanes
 * Efficient use of multiple stages can produce very high overall compression ratios
 * Higher compression ratios can be attained with minimum total compressor weight and frontal area
 * Compressor is divided into two completely independent rotor spools, each driven by its own turbine and drive shaft
 * Low Pressure Compressor
 * High Pressure Compressor
 * High Pressure Turbine
 * Low Pressure Turbine
 * High peak efficiencies
 * Small frontal area reduces drag
 * Straight through-flow, allowing for high ram efficiency
 * Combustion efficiency is better than centrifugal compressors
 * Starting flexibility is greater and it has improved high-altitude performance
 * Low inlet speed, airflow will decrease in the compressor, creating a high AOA on the rotor blades that could lead to a compressor stall
 * High Cost
 * High starting power requirements
 * Stators/Rotors
 * Creep
 * Single/Multistage
 * Convergent Nozzles
 * Convergent-Divergent Nozzles
 * Spray Bars
 * Flame Holder
 * Screech Liners
 * Variable Exhaust Nozzle

Chapter 3 - Compressor Stalls
Characteristics Indications Causes Avoidance Prevention Remedy and Recovery
 * Relative Wind
 * Angle of Attack
 * Airflow Distortion
 * Mechanical Malfunctions
 * Variable Inlet Guide Vanes (IGV) and Stator Vanes
 * Fuel Control Unit (FCU)
 * Foreign Object Damage (FOD)
 * Variable Exhaust Nozzle
 * Variable IGV
 * Dual/Twin/Split*Spool Axial Flow Compressors
 * Bleed Valves
 * Variable Exhaust Nozzle

Chapter 4 - Turbojet and Turbofan Engines
Turbojet Engine Turbofan Engine
 * Thrust Specific Fuel Consumption (TSFC)
 * Advantages/Disadvantages
 * Bypassed/Ducted Air
 * Bypass ratio
 * Free/Power Turbine
 * Advantages/Disadvantages

Chapter 5 - Turboprop and Turboshaft Engines
Turboprop Engine Propeller Assembly Reduction Gear Box (RGB) Torquemeter Assembly Turboshaft Engine
 * Construction
 * Components
 * Blades
 * Hub
 * Pitch Change/Dome Assembly
 * Operation
 * Alpha Range
 * Beta Range
 * Advantages/Disadvantages
 * Construction
 * Free/Power Turbine
 * Operation

Chapter 6 - Hydraulic Systems
Basics Force and Pressure Aircraft Hydraulic Systems System Components
 * Pascal’s Law
 * Pressure and Force in Fluid Power Systems
 * Reservoir
 * Nonpressurized Reservoirs
 * Pressurized Reservoirs
 * Pumps
 * Hand Pumps
 * Power Pumps
 * Variable Displacement Pumps
 * Constant Displacement Pump
 * Pressure Regulator/Unloader Valve
 * Check Valve
 * Accumulator
 * Filters
 * Relief Valves
 * Pressure Gauge
 * Pressure Switch
 * Hydraulic Fuses
 * Selector Control Valves
 * Actuators

Chapter 7 - Electrical Systems
Electrical Engery Electrical Source Components Electrical System Breakers Fuses Other Power Sources Ground Support Equipment
 * AC
 * DC
 * Generators
 * Constant Speed Drive (CSD)
 * Inverter
 * Transformer Rectifier
 * Battery
 * Distribution Networks (Buses)
 * Essential Bus
 * Primary Bus
 * Monitor or Secondary Bus
 * Starter Bus
 * Switches Circuit
 * Warning Lights
 * Auxiliary Power Unit (APU)

Chapter 8 Fuel Systems
Fuel Characteristics Military Fuels Basic Fuel System Afterburner Fuel System Rated Thrust
 * Volatility
 * Flash Point
 * JP-4 * (NATO Code F-40)
 * JP-5 * (NATO Code F-44)
 * JP-8 * (NATO Code F-34)
 * Fuel Tank
 * Boost Pump
 * Emergency Shutoff Valve
 * Fuel Pressure Gauge
 * Low Pressure Fuel Filter
 * Engine*Driven Pump
 * Fuel Control Unit (FCU)
 * FCU Modes of Operations
 * Normal (Automatic) Operation
 * Manual/Emergency Operation
 * Fuel*Flow Gauge
 * Fuel*Oil Cooler/Heat Exchanger
 * Fuel Manifolds
 * Pressurizing and Dump (P&D) Valve
 * Fuel Transfer Valve
 * Afterburner fuel control unit*
 * Normal Rated Thrust (NRT)
 * Military Rated Thrust (MRT)
 * Combat Rated Thrust (CRT)

Chapter 9 - Lubricants and Lubrication System
Lubricants Contamination Lubrication Systems
 * Mineral Lubricants
 * Synthetic Oil
 * Designations of Lubricating Oils
 * Oil Grade Utilization
 * Viscosity
 * Squeeze Film
 * PON*6/Bowser
 * Wet Sump System
 * Dry Sump System
 * Pressure Sub System
 * Operation
 * Components
 * Oil Tank
 * Oil Pump
 * Oil Pressure Gauge
 * Oil Temperature Gauge
 * Filters
 * Filter Bypass Valve
 * Oil Pressure Relief Valve
 * Scavenge Subsystem
 * Magnetic Chip Detector
 * Oil Coolers
 * Air*Oil Cooler
 * Fuel*Oil Cooler/Heat Exchanger
 * Oil Temperature Regulating Valve
 * Fuel Temperature Sensing Switch
 * Breather Pressurizing Subsystem

Chapter 10 - Accessory, Starter, and Ignition System
Accessories Starting Systems Starters Ignition System
 * Air-Driven Accessories
 * Mechanically-Driven Accessories
 * Starting Cycle
 * Abnormal Starts
 * Hot Start
 * Hung Start
 * False Start
 * Wet Start
 * DC Electric Motor
 * Air Turbine Starter (ATS)
 * Ignition Plugs
 * Annular gap
 * Constrained gap

=Coastie Gouge for Engines!!=

Chapter 1 : Principles of Gas Turbine Operation
Total 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

Pressure vs. Velocity
 * Inversely related

Bernoulli’s Theorem
 * As any incompressible fluid passes through a convergent opening, its velocity increases as pressure decreases

Diffusers and Nozzles
 * Supersonic nozzle : 	divergent	V increases	P decreases
 * Subsonic nozzle : 	convergent	V increases	P decreases
 * Supersonic diffuser :	convergent	V decreases	P increases
 * Subsonic diffuser :	divergent	V decreases	P increases
 * Total Pressure remains the same in all, do not be confused by this question

Gas Generator minimal components
 * Compressor
 * Combustion Chamber
 * Turbine

Brayton Cycle
 * Four events occur simultaneously
 * Intake
 * Compression
 * Combustion
 * Exhaust

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

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

Altitude Ram Effect
 * With an increase in altitude, rate of thrust decreases
 * Although pressure and temp. both decrease, the pressure drop is greater thus decreasing thrust
 * 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

Pressure Indication Gauges
 * EPR : Engine Pressure Ration gauge, also referred to as TPDI
 * Used in turbojets and turbofans

Torquemeter
 * Indicates shaft horsepower
 * Used in turboprop or turboshaft

Chapter 2 : Gas Turbine Engines
Subsonic Inlet
 * Divergent : increases airflow pressure while decreasing velocity

Supersonic Inlet
 * Convergent – Divergent
 * At supersonic, decreases velocity, increases pressure. (V reduced to subsonic)
 * At subsonic, changes to divergent, decreases velocity, increases pressure

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

Compressor
 * Primary function is to supply enough air to satisfy the requirements of the combustion section
 * Improves burner efficiency

Centrifugal Flow Compressor
 * Has 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

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

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

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

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

Annular Combustion Chamber Turbine Section
 * Main advantage : uniform heat distribution
 * Main disadvantage : unit cannot be removed without major overhaul
 * 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

Turbine Blades
 * Attached to the shaft by a method call Fir Tree
 * Blades are not welded onto the rotor shaft

Exhaust Section
 * Must direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence

Exhaust Nozzles Convergent:
 * fixed area
 * takes relatively slow subsonic gases from the turbine section and gradually accelerates them through the convergent section

Afterburner Section
 * Used in turbojets and turbofans for a short period of time
 * Increases max thrust available from an engine by 50% or more
 * 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

Chapter 3 Compressor Stalls
Relative Wind
 * Formed by combining the compressor rotation and inlet airflow

Angle of Attack
 * Relative wind and rotor blade chordline (angle between)
 * Main cause for compressor stall is excessive angle of attack

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

Airflow distortion
 * Airflow distortion is the most common cause of compressor stall, however, excessive AOA is what causes a compressor stall

Mechanical Malfunctions 4 Types
 * Variable inlet guide vane and stator vane failure
 * FCU failure
 * FOD
 * Variable exhaust nozzle failure

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

Avoidance
 * 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

Chapter 4 Turbojet and Turbofan Engines
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

Thrust Specific Fuel Consumption (TSFC) Turbofan Engine
 * Amount of Fuel required to produce one pound of thrust
 * 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

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

Chapter 5 Turboprop and Turboshaft
Turboprop Engine Components Propeller Assembly
 * 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.
 * 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

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

Torquemeter Assembly
 * Used to transmit and measure the power output from the gas generator to the reduction gear box

1] Attached to the front of the compressor drive shaft 2] Attached to the free / power turbine
 * The propeller assembly, the reduction gear box and the torquemeter may be connected to the gas generator in two possible configurations:

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

Chapter 6 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

Force and Pressure
 * Pressure is the force acting upon one square inch of area (PSI)

Power Control Systems
 * Supply pressure only for flight controls

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

Variable displacement Pumps
 * Regulates volume delivery in accordance with system flow demands

Check Valve
 * Prevents back flow. Allows flow in only one direction
 * Works in conjunction with accumulator to maintain system pressure during shutdown

Accumulator
 * Acts as a shock absorber
 * Stores enough fluid under pressure to provide for emergency operation of certain actuating units

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

Hydraulic fuses
 * Safety devices
 * Designed to detect or gauge ruptures, failed fittings, or other leak producing failures of damage
 * Prevents excessive loss of fluid

Selector Control Valves
 * Used to direct the flow of fluids to actuators

Actuators
 * Convert fluid under pressure into linear or reciprocating mechanical motion

Chapter 7 Electrical Systems
Alternating Current Sources
 * A/C Generator
 * Alternator Inverter

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

Inverter
 * On DC electrical systems, inverters are used to power AC equipment

Transformer Rectifier
 * Transforms AC to DC

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

Chapter 8 Fuel Systems
JP-5
 * Low volatility
 * High flash point (140 deg F)
 * Only fuel that can be stored on ships

JP-8
 * Flash point 100 deg F

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

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

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

Low Pressure Filter
 * Located downstream of the boost pump to strain impurities from the fuel

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

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

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)

Fuel –Oil Cooler / Heat Exchanger
 * Preheating fuel removes any ice crystals and increases its volatility, facilitating fuel ignition

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

Afterburner Fuel Control Unit
 * Meters fuel to the afterburner spray bars

Normal Rated Thrust
 * Thrust produced at maximum continuous turbine temperature with no time limitation

Military Rated Thrust
 * Thrust produced at the maximum turbine temperature for a limited time; normally 30 minutes

Combat Rated Thrust
 * Thrust produced with the afterburner operation, not based on temp. limitations rather based on fuel limitations

Chapter 9 Lubrication
Viscosity
 * Property of fluid that resists the force tending to cause the fluid to flow
 * Inversely related with temperature

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

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.
 * Instrumentation: gauges that indicate current operations and possible future failures of the lubrication components

Filter Bypass Valve
 * Allows oil to flow around the filter element should the filter become clogged
 * Dirty oil is better than no oil

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

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

Air Cooler
 * Controlled by the fuel temperature sensing switch

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

Breather Pressurizing Subsystem
 * Pressurization is provided by compressor bleed air
 * At sea level pressure, the breather pressurizing valve is open to the atmosphere

Chapter 10 Accessory, Ignition, and Starter Systems
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

Starting Systems
 * Purpose is to accelerate the engine until the turbine is producing enough power to continue the engine acceleration itself

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

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 ignitor plugs is minimal

Ignitor Plug Types Annular –gap
 * Protrudes slightly into the combustion chamber liner to provide an effective spark

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

=Class Notes=  Engines 

  Total Pressure = Static Pressure + Dynamic Pressure  

Total Pressure = Velocity + Pressure

  Bernoullis Theorem states that as a subsonic fluid passes through a converging opening, its velocity increases and its pressure decreases while the total pressure does not change   Subsonic Airflow in a nozzle increases in velocity and decreases in pressure. In a    diffuser, the pressure increases and the velocity decreases. The nozzle is    convergent and the diffuser is divergent at subsonic speeds   Supersonic Airflow in a nozzle increase velocity and decrease pressure. In a    diffuser, pressure increases and velocity decreases. With supersonic airflow, a nozzle is divergent and a diffuser is convergent.   All gas generators have compressors, combustion chambers and turbines. </li>  The Brayton cycle for a jet engine consist of the simultaneous firing of the Intake, Compression, Combustion and exhaust cycles. <span style='font-size: 9.0pt;font-family:"Comic Sans MS"'> </li>  The compressor, compresses the air by decreasing the volume of the unit. +P, +V, +T The diffuser than effects the air. +P, -V The combustion chamber ignites gas which expands and further increases the air’s volume. -P, +V The Turbine extracts energy to run the compressor. -P, +V The exhaust extracts the air and moves the engine. -P, +V </li> </ol>

<ol style='margin-top:0in' start=8 type=1>  Gross thrust does not take into account inlet airflow produced by the engine moving through the air. Net thrust takes the initial airflow into account and give a more realistic synonymous with thrust </li>  As the temperature increase, density decrease, and the thrust decreases. Air Temp is inverse to Thrust. </li>  If pressure increases, density increase and thrust will increase. </li>  As altitude increases, P and T will drop. The rate thrust decrease due to pressure drop is greater than the increase in thrust from T dropping. The engine produces less thrust as altitude increases. After 36,000’ the T stabilizes and the thrust will drop dramatically. 36,000 is the optimum cruise altitude because thrust available, plus low fuel flow and diminished drag provide optimum performance! </li>  As inlet velocity approaches the exhaust velocity thrust is reduced. If mass and air are held constant thrust will decrease as airspeed increases. </li>  The ram air effect forces more and more air into the inlet as airspeeds increase. This increases the mass and pressure of the air. This offsets the decrease in    acceleration and produces a neutral or slight gain in thrust at subsonic speeds. </li>  Thrust is    measured in the following ways: Jet: EPR (TPDI) Fan: EPR Prop: Torquemeter (SHP) Shaft: Torquemeter </li>  Inlet ducts act as diffuser by always decreasing velocity and increasing pressure. Velocity is decreased to stabilize airflow before it reaches the diffuser or compressor. This will provide the proper amount of high pressure, turbulence free air to the compressor. It must operate efficiently from ground idle to supersonic speeds at high altitude. Single Entrance is the simplest and most effective. It has smooth airflow. Divided entrance allows the pilot to sit lower and reduce friction due to    shorter duct length. Must be offset from the fuselage so as not to upset the boundary layer. It also curves which can cause turbulence. </li>  Subsonic and Supersonic Airflow inlet ducts always act as diffusers by increasing pressure and decreasing velocity. Subsonic air has a divergent opening while supersonic air has a convergent/divergent opening. </li>  Variable Geometry inlet ducts use ramps, wedges or cones to change the shape of the inlet as the aircraft speed varies between sub/supersonic. </li>  The compressor section must supply enough air to satisfy the requirements of    the combustion section. The pressure and velocity is increased with this air being directed to the burner section. A secondary purpose is to supply compressor bleed air to operate various components throughout the aircraft and engine. </li>  Centrifugal Flow uses a impeller, diffuser and manifold to compress the air. Air is    ingested near the center and accelerated outward toward the diffuser adding potential and kinetic energy. This is done by passing the air through the divergent passages of the impeller; which increase both velocity and pressure. The high pressure air then enters the diffuser which is stationary and converts the velocity into more pressure. The air then goes to the compressor manifold which directs the air into the combustion chamber. Axial Flow uses rotor blades and stator veins. Each pair of rotor-stators form a stage. Turbine drives the rotors which increases the pressure and the velocity of the air. Then the air is pushed through the static stator vanes which act as diffuser (increase pressure, and decrease velocity). This continues through each stage of the compressor. Compressors are set up as velocity remains about constant throughout. As pressure increases, the air becomes more compressed. The cross sectional area of each stage decreases so that velocity remains constant as the pressure increases. Axial-Centrifugal uses a compressor inlet case, compressor and a diffuser. The compressor directs air to the outside air compressor. The air is    compressed 7:1 by a three stage axial and single stage centrifugal compressor that is run as one integral unit by the turbine. The air leaves the compressor via diffuser pipes and enters the diffuser where P is    further increased. </li>  The burner section is the combustion chamber and provides the means for proper mixing of the fuel and air. It must deliver combustion gases to the turbine section at the appropriate temperature. It must also add sufficient heat energy to the gases to accelerate their mass and produce the desired thrust for the engine and power the turbines. It must minimize the pressure decrease to allow the pressure to turn the turbines, keep combustion efficiency high, not blow out the flame and complete the burning before the gases enter the turbine stage. </li>  The can burner has individual cans around the circumference of burner section. Each has its own fuel nozzle, liner and casing. Primary air is burned with the secondary air cooling the liner and casing. Strong and durable, easy to maintain, and individual units can be replaced. It provides a poor use of space, pressure loss, and uneven turbine heating. The annular burner provides continuous, circular, inner and outer shroud around the outside of the compressor drive shaft. The liner has holes to    cool the inside. Fuel is introduced through a series of nozzles where it    is mixed with air and ignited. It provides uniform heat, better air mixing and great use of space, but is difficult to repair, has structural problems with its large diameter and thin wall design. The can-annular burner is used on larger high performance engines. Cans at    the front mix and burn the air and fuel. The hot gases then pass to the annular chamber where they are further mixed. It is easy to maintain, has great uniform heat, is structurally sound, lower pressure loss, efficient, but is considerably more expensive. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The turbine section is comprised of stators and rotors. The turbine section drives the compressor and accessories. It is designed to increase velocity. Converts the heat of the expanding gases to mechanical energy. Approximately 75% of    the total P is converted to mechanical energy, while the remaining 25% is     used for thrust. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The components of a turbine engine are effected by thermal stress. The repeated heating and cooling results in creep. The turbine uses an EGT Exhaust Gas Temp gauge and an ITT Interstage Turbine Temp gauge to measure thermal changes. The turbine section is exposed to the greatest amount of thermal stress. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Creep is    the gradual elongation of blades as they are heated and can lead to     catastrophic failures. The fir tree method is used to cool turbine blades and prevent them from deforming. Blades are attached to the turbine shaft to improve ability to    withstand high heat and repeated heating and cooling. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Heat is a    result of the combustion of the fuel air mixture. High pressure is a    result and used to turn the turbine. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The exhaust section is used to vent the gases rearward at a high exit velocity with minimized turbulence. It is usually composed of an outer duct, inner core and radial hollow struts. The struts support the inner core and straighten out the whirling gasses. The cone converts the gases to a solid jet. The initial divergent shape between the outer duct and the inner core allow for smooth expansion of the gases. Toward the rear, the exhaust section becomes progressively narrower converting pressure to velocity. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Subsonic uses a convergent nozzle and is usually fixed. Supersonic turbine air is high sonic not supersonic. Convergent/Divergent nozzles are sued to decrease pressure and increase velocity. Air speed is    very high sonic and makes air compressible. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The afterburner is used by turbofans and jets to increases thrust available by    50% or more. Fuel consumption increase by 300%. Secondary air from the burner is used in the turbojets. Secondary air and bypass air is used in    turbofans. Two methods are used to ignite the afterburner. Hot streak and Spark/Torch. Hot streak uses an extra quantity of fuel which is injected into one of the combustion chamber. Thus streaks of hot gases ignite the afterburner fuel. The spark/torch method uses a pilot light or igniter plug located near the spray bars and flameholder to ignite the afterburner fuel/air mixture. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The afterburner is comprised of spray bars, flameholder, screech liners, and variable exhaust nozzles. The spray bars spray fuel into the stream of hot gasses. The flameholder provides a region of turbulent eddies to reduce the gas V. The screech line is a sleeve with holes that reduces the violent pressure fluctuations. The variable exhaust nozzle provides the convergent shape for subsonic flows and convergent divergent for supersonic afterburner flows. This prevents a pressure buildup which will stall the engine. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The relative wind is formed by the inlet airflow and the compressor rotation vectors </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> A    compressor is designed to provide an optimum compression ratio. If the AOA of the compressor blades is too low, the compression is inefficient. If it    is too high, then a compressor stall may result. A stall occurs when airflow over an airfoil brakes away causing the airfoil to lose lift due to excesssive AOA. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The rotors are fixed to the rotor disk, the change in AOA occurs when the RBM changes or the inlet airflow V changes. A decrease in inlet airflow or decrease in    RPM will increase the AOA of the rotor blades. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> A    compressor stall is characterized by a surge. This surge results in a    reduction of airflow to the turbines which means the more fuel is needed to maintain current thrust. This will increase burner and turbine temperatures. If PCL is constant, RPM decay and ITT rise along with possible noises will be present. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Compressor stalls are caused by airflow distortions and mechanical failures. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Mechanical problems that can lead to compressor stalls include variable inlet guide vane and strator vane failures which result in too much or too little airflow at low engine speeds. Fuel Control Unit failure which cause rich blow outs (too much fuel with combustion reaching back into the    compressor) or lean die outs (airflow is too high to allow fuel to ignite     in compressor). FOD causes damage to the blades and alters their aerodynamic properties. And Variable exhaust nozzle failure if it fails open at supersonic speeds could cause back pressure which will result in a    compressor stall. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> To avoid compressor stalls avoid erratic or abrupt PCL changes, especially at slow speeds or high angles of attack. Maintain a prescribed minimum airspeed and avoid abrupt changes in altitude. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> To minimize compressor stalls, use the following: Variable inlet guide vanes and stator vanes so that AOA is changed at low speeds. These are controlled by    the stator vane actuator using fuel pressure via the FCU. Dual/Twin/Split Spool Axial flow compressors allow the front rotor to turn at a lower speed than the rear rotor so that the front rotor wont be choked by low airflow. Bleed valves near the middle or rear of the compressor vent air and increase airflow in the front compressor at low engine speeds. Variable exhaust nozzle is used to unload the pressure after the afterburner. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> If a stall occurs, reduce attitude of aircraft so AOA is less, retard the PCL just below the stall threshold to let the engine catch up with inlet airflow, and once engine returns to normal, slowly advance the PCL to desired setting. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> The turbojet consist of a Inlet, Compressor, Burner, Turbine and Exhaust. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Thrust Specific Fuel Consumption is the amount of fuel required to produce one pound of thrust. The propulsive force of the turbojet relies on the amount of fuel added to the air mass. More air requires more fuel. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Turbojets rely on the thrust to produce 25% of the total energy for its propulsion while the other 75% goes into mechanical force required to power the compressor. They are not efficient </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> More air require more fuel. Since density of air decreases with altitude, less fuel is required at higher altitudes. Turbojets are inefficient at producing thrust at low speeds. Low-mass coupled with high velocity exhaust is    wasteful compared to high mass, low V airflow from turboprop. This changes as speed increases. At high speeds, the difference between V of the exhaust and the surrounding atmosphere is lessened so it is more efficient than when a turbojet is at low speeds </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Turbojets have higher TSFC than Turbofans because it is inefficient at producing thrust at low speeds and requires more fuel. </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Turbojets have low propulsive efficiency at low forward airspeeds, relatively high TSFC at low altitudes and low airspeeds, long takeoff roll is required and they have the lightest specific weight (wt per pound of thrust produced) </li> <li class=MsoNormal style='mso-outline-level:1;mso-list:l0 level1 lfo1; tab-stops:list .5in'> Turbofans have a gas generator (compressor, burner and turbine) and a duct enclosed fan. It is like a turbojet with a fan surrounding it. </li> </ol>

=The T34C table.=

=Practice Exams= You can download a zip file. of the exams. It would be nice if somone felt like typing them up on here so people don't have to download and try to read these scans. How about you?

Engines Exam 1

1) What is potential energy?

a) The energy associated with position	b) The ability to do work as a function of motion c) The speed of doing work	d) Dynamic pressure

2) What is the shape of a supersonic nozzle?

a) Parallel	b) Convergent from fore to aft c) Divergent from fore to aft	d) Divergent/convergent

3) What components are common to all gas turbine engines?

a) Inlet, compressor, burner, turbine, afterburner	b) Inlet, fan, compressor, burner, exhaust c) Compressor, burner, turbine	d) Fan, compressor, burner, turbine

4) An increase in ______ will cause an increase in thrust.

a) Altitude	b) Temperature c) Pressure	d) Humidity

5) What four events are occurring simultaneously in the Brayton cycle?

a) Intake, compression, power, ignition	b) Intake, power, combustion, exhaust c) Intake, combustion, compression, exhaust	d) Intake, ignition, combustion, exhaust

6) What makes up a single stage of an axial flow compressor?

a) Rotors and guide vanes	b) Impellers and rotors c) Rotors and stators	d) Impellers and diffusers

7) Primary air in a gas turbine engine is used for:

a) Cooling the burner section	b) To turn the compressor c) Combustion in the afterburner	d) Combustion in the burner

8) What can the pilot do to prevent a compressor stall?

a) Avoid clouds and rain showers	b) Avoid smooth throttle movements c) Directly adjust variable guide vanes	d) Avoid abrupt changes in aircraft attitude

9) How do manufacturers minimize compressor stall susceptibility?

a) Variable pitch rotor blades	b) Constant pitch rotor blades c) Variable pitch stators	d) Variable rotor blade failure

10) What percentage of total thrust is generated by the fan section of a turbofan engine?

a) 75%	b) 30%-60% c) 40%-70%	d) 90%-100%

11) What is the advantage of a turbofan engine over a turbojet engine?

a) Turbofans are more efficient at high altitudes	b) Turbofans are lighter and less complicated c) Turbofans have lower thrust specific fuel consumption	d) Turbofans accelerate a smaller mass of air, but to a greater velocity

12) In a turbo-shaft engine, what will the expanding gases from the burner section drive first?

a) Free/power turbine	b) Accessories c) Gas generator turbine	d) Lower pressure compressor

13) Why does a turboprop utilize a reduction gear box?

a) To vary the propeller blade pitch angle	b) To reduce thrust specific fuel consumption rate c) To keep propeller blade tips at subsonic velocity	d) To ensure propeller RPM is greater than compressor RPM

14) What is the purpose of the actuator in a hydraulic system?

a) It acts as a shock absorber for system pressure fluctuations	b) It prevents excessive system pressure c) It determines where the fluid pressure will go	d) It converts fluid motion into mechanical motion

15) The two types of hydraulic systems used on Navy aircraft are constant _____ and variable _____.

a) Pressure; pressure	b) Displacement; displacement c) Pressure; displacement	d) Displacement; pressure

16) Hydraulic systems multiply what?

a) Force	b) Work c) Distance	d) Power

17) What is a source of DC power in an aircraft electrical system?

a) Transformer rectifier	b) Engine driven alternator c) Inverter	d) Constant speed drive

18) What components supply AC power?

a) Generators and alternators	b) Inverters and alternators c) Batteries and inverters	d) Alternators and transformer rectifiers

19) What controls the amount of both fuel and air delivered to an engine?

a) Throttle	b) Fuel control unit c) Fuel spray nozzles	d) Compressor RPM

20) A lean die-out can occur during a (n):

a) Acceleration when the fuel control unit fails	b) Deceleration when the fuel control unit fails c) Deceleration when too much fuel is introduced into the burner	d) Acceleration when not enough fuel is available due to a faulty fuel pump

21) How is thrust controlled in a turboprop?

a) The fuel control unit adjusts fuel and air flow to increase thrust	b) The PCL signals the prop governor to adjust thrust c) The fuel control unit and prop governor jointly control the thrust	d) The prop governor adjustment valves control thrust

22) The two purposes for oil in the gas turbine engine are:

a) Cleaning and cooling	b) Cooling and lubrication c) Lubrication and cleaning	d) Lubrication and viscosity control

23) What is the advantage of a synthetic oil over a petroleum based oil?

a) Low flash point	b) Permits coking and lacquer deposits c) Long shelf life	d) Better stability at high temperatures

24) Compressor bleed air that is ducted overboard to prevent stalls and is not suitable for driving accessories is called _____ bleed air.

a) High pressure	b) Inter stage c) Low pressure	d) Compressor accessory

25) What helps a gas turbine engine to rapidly reach idle RPM?

a) Reaching the self-sustaining RPM	b) Engaging afterburners c) Allowing starter to increase compressor RPM after light-off	d) Utilizing the igniters after the fuel flow has been initiated

KEY

1) a 2) c 3) c 4) c 5) c 6) c 7) d 8) d 9) c 10) b 11) c 12) c 13) c 14) d 15) b 16) a 17) a 18) b 19) b 20) d 21) c 22) b 23) d 24) b 25) c

Engines Exam 2

1) Basically, hydraulic systems are used to multiply:

a) Force	b) Pressure c) Work	d) Power

2) In a closed hydraulic system a force of 40 pounds applied to a 4 square inch piston will produce ____ pounds of force on a 100 square inch piston.

a) 1,000	b) 50 c) 2,000	d) 5

3) What component in the hydraulic system converts fluid pressure into mechanical movement?

a) Selector valve	b) Actuator c) Accumulator	d) Pressure/dump valve

4) How is the main hydraulic pump powered?

a) Electrically	b) Hydraulically c) By the engine	d) By the RAT

5) What does the pressure regulator do?

a) Adjusts the pump output	b) Regulates system pressure c) Controls the unloader	d) Controls pressure valves

6) What does the selector valve do?

a) Adjust system pressure	b) Select system pressure c) Direct pump output	d) Change direction of fluid flow

7) A hydraulic system that contains a constant displacement pump must also contain:

a) Unloader valve	b) Constant actuating valve c) Variable displacement valve	d) Pressure regulating unit

8) The hydraulic system component that acts as a safety valve to vent excess system pressure is the:

a) Selector valve	b) Regulator valve c) Relief valve	d) Unloader valve

9) What components supply AC power?

a) Transformer rectifiers and inverters 	b) Constant speed drives c) Generators and rectifiers	d) Inverters and alternators

10) Which one of the following is not a source of DC power?

a) Transformer rectifier	b) DC generator c) Ni-Cad battery	d) Alternator

11) Which one of the following buses provides the power to safely fly an aircraft?

a) Instrument bus	b) Primary bus c) Essential bus	d) Secondary bus

12) The start bus is used to power the:

a) Starter for an aircraft	b) Essential bus in emergencies c) APU	d) Battery

13) Which AC buses will be powered in the event of an AC generator failure?

a) All AC buses are powered	b) Only the primary bus is powered c) Only the essential bus is powered	d) Primary and secondary buses are powered

14) What are the sources of emergency AC power?

a) Transformer rectifier and DC generator	b) Inverter and emergency power package c) Inverter and the DC alternator	d) The essential and primary buses

15) Which bus or buses provide for the two-way flow of energy with the battery?

a) The essential and start buses	b) The start bus only c) The essential bus only	d) The essential and primary buses

16) What is the function of the constant speed drive in the typical electrical system?

a) To keep the accessory gear case rotating at a constant RPM	b) To keep the generators and alternators rotating at a constant RPM c) To ensure the aircraft maintains a predetermined TAS	d) To ensure the tachometer does not exceed 100% RPM

17) Which bus powers mission equipment?

a) The mission bus	b) The essential bus c) The secondary bus	d) The monitored bus

18) Which bus or buses will not be powered in the event of a DC generator failure?

a) The primary bus	b) The essential bus c) The essential and primary buses	d) The primary and secondary buses

19) What is the effect of rising temperatures on a fuel's volatility?

a) There is no change	b) Volatility goes down c) Volatility rises	d) Volatility will not change but density will rise

20) When JP-4 is compared to JP-5:

a) JP-5 is more volatile	b) JP-4 is a safer fuel c) JP-5 is easier to ignite	d) JP-4 is easier to ignite

21) Which one of the following is not a consideration in the design of an aircraft's fuel system?

a) The chemical composition of the fuel	b) The complexity of the piping system c) Cold weather starting	d) System operation at low atmospheric pressure

22) The amount of fuel and air delivered to the engine is controlled by the:

a) Power condition lever	b) Throttle c) Pressurizing and dump valve	d) Fuel control unit

23) What is the major difference between the normal and manual fuel control systems?

a) The manual control system automatically adjusts fuel and air to the engine	b) The normal fuel system requires constant monitoring c) The manual fuel control system bypasses the normal fuel control system	d) The normal fuel control system is also called the emergency control system

24) What is the position of the overboard drain in the pressurizing and dump valve when the engine is shut down?

a) The drain is closed allowing fuel to the engine	b) The drain is open allowing fuel to flow onto the ground c) The drain is closed returning fuel to the tank	d) The drain is open allowing fuel to the engine

25) What cuts off fuel flow when the engine is secured?

a) A valve in the pressurizing and dump valve	b) A pressure signal from the FCU the to flow meter c) A pressure signal to the FCU from the throttle	d) A valve in the FCU

26) What are the limits on military thrust?

a) Time only	b) Temperature only c) Time and temperature	d) There are no limits

27) What happens to fuel flow with a constant throttle setting and increasing altitude?

a) Fuel flow increases	b) Fuel flow decreases c) Fuel flow remains constant	d) Fuel flow is a function of temperature, not altitude

28) How is thrust controlled in a turbojet engine?

a) Thrust increases with an increase in airflow	b) Thrust decreases with an increase in throttle position c) The FCU controls thrust based on throttle position	d) The PCL regulates fuel flow directly and thus controls thrust

29) How is thrust controlled in a turboprop engine?

a) The FCU adjusts fuel and airflow to increase thrust	b) The FCU and propeller governor control thrust c) The PCL signals the propeller governor to control thrust	d) The pressurizing dump valve controls fuel flow and thrust

30) Which lubricants are used in a gas turbine engine?

a) Liquids	b) Semi-solids c) Solids	d) Greases

31) Why are semi- solids not used as lubricants in gas turbine engines?

a) They are prone to chip contamination	b) They must be changed too often c) They do not work well in low temperature conditions	d) They do not work well in high temperature conditions

32) What is the most common synthetic lubricant used, by designation?

a) MILL-23699	b) MIL-L-23669 c) MIL-L-23699	d) MILL-23699

33) What is one advantage of synthetic oils over petroleum based oils?

a) Synthetic oil has a shorter shelf life	b) Synthetic oil is more stable at high temperatures c) Synthetic oils leave more coke deposits to lubricate the engines	d) Synthetic oil cost less

34) What two purposes does oil serve in a gas turbine engine?

a) Lubrication and viscosity control	b) Cooling and contamination control c) Cooling and lubrication	d) Viscosity and contamination control

35) What is the main advantage of a dry sump lubrication system?

a) Temperature/viscosity can be regulated	b) Temperature and pressure can be regulated c) The oil is cleaner	d) Distribution is easier to control

36) What are three subsystems of the engine lubrication system?

a) Pressure, breather pressurizing and oil return	b) Delivery, breather pressurizing and scavenge c) Delivery, breather pressurizing and return	d) Pressure, breather pressurizing and scavenge

37) What is the function of the weighted swivel outlet assembly?

a) Provides constant oil flow regardless of altitude	b) Provides continuous oil supply during flight in low pressure conditions c) Insures constant oil supply during flight in low pressure conditions	d) Keeps oil stirred up to ensure correct viscosity

38) What sections of the gas turbine engine are lubricated by the oil supply?

a) Engine main bearings	b) Accessory gear drive c) The turbine shaft	d) Both a and b

39) What is the function of the oil temperature regulating valve?

a) Directs oil to the air/oil cooler if its temperature is too high	b) Directs oil to the fuel/oil cooler if its temperature is too high c) Restricts oil the bearings if its temperature is too low	d) Directs oil to the fuel/oil heater if its temperature is too low

40) What is the function of the fuel temperature sensing switch?

a) Indicates fuel temperature in the cockpit	b) Works in conjunction with the pressurizing/dump valve during engine start c) Causes the air/oil cooler to function if fuel temperatures are too high	d) Inhibits engine start if fuel temperature is too low

41) When is the breather pressurizing valve closed?

a) It is closed on the ground	b) It is closed to the atmosphere on the ground c) It is closed to the atmosphere at altitude	d) It is closed to the engine at altitude

42) What are the steps in the typical starting sequence?

a) Turn on fuel, start airflow and light igniters	b) Start airflow, turn on fuel and light igniters c) Turn on igniters, start airflow, turn on fuel	d) Start airflow, light igniters and add fuel*

43) What are three types of start systems used in gas turbine engines?

a) Air turbine starter, DC electric motor starter, turbine impingement	b) Gas generator turbine starter, DC electric motor starter, air turbine starter c) DC battery starter, air turbine starter, turbine generator starter	d) CSD/S, compressor impingement, GPU/APU

44) What is the importance of the engine's self accelerating speed?

a) At this RPM, extra fuel flow can be cut off	b) At this RPM, the engine will continue to run if the start system fails c) At this RPM the aircraft can taxi under its own power	d) At this RPM, the pilot does not have to advance the PCL any farther

45) How many igniters are there on a gas turbine engine?

a) Two per system	b) One per engine c) Four per engine	d) Two per engine

46) How many igniter are there in a can design combustion chamber?

a) One 	b) Two c) Three	d) None

47) What are the most common uses for compressor discharge air?

a) Cockpit pressurization, inlet anti-ice and air conditioning	b) Inlet anti-ice, VEN actuation and boundary layer control c) Cockpit pressurization, gear actuation and air conditioning	d) Cockpit pressurization, air conditioning and APU start power

KEY

1) a 2) a 3) b 4) c 5) b 6) d 7) d 8) c 9) d 10) d 11) c 12) a 13) c 14) b 15) c 16) b 17) a 18) d 19) c 20) d 21) a 22) d 23) c 24) b 25) a 26) c 27) b 28) c 29) b 30) a 31) d 32) c 33) b 34) c 35) a 36) d 37) a 38) d 39) b 40) c 41) c 42) d 43) a 44) b 45) d 46) b 47) a