TERMINOLOGY Flashcards
(199 cards)
1
Q
A carbon-pile-type voltage regulator
A
A carbon-pile-type voltage regulator uses variable resistance to control DC generator current.
2
Q
AC
A
AC: AC reverses direction. AC power requires less current because of higher voltage and a ground neutral system. This allows the use of smaller aircraft wiring and therefore, less weight.
3
Q
ACCESSORY DRIVE
A
Accessory Drive:
The accessory drive is a gearbox that forms part of a gas turbine engine. Although not part of the engine’s core, it drives the accessories, fuel pumps etc., that are otherwise essential for the operation of the engine or the aircraft on which it is mounted. Accessory drives on large engines handle between 400–500 hp.
Power for the accessory drive is taken from the central shaft linking the turbine and compressor sections of the engine. This requires an internal gearbox that couples the drive to a radial driveshaft or tower shaft that drives an external gearbox.
Some of the accessories that may be driven include:
•Fuel pump
There may be a number of fuel pumps: low pressure, high pressure and also a speed-sensitive governor
•Generators, often one for engine systems and one for the aircraft
•Constant Speed Drive to maintain a constant frequency AC generator
•Lubricating oil pumps
•Hydraulic pump
•High-pressure air compressor (undercarriage actuation, etc.)
•Low-pressure air compressor (cabin air conditioning), where this is not provided by tapping engine compressor bleed air.
•Engine starter
•Tachometer sensor drives
•Auxiliary gearbox drive, to a further gearbox that may be required in some installations.
•Additional facilities are provided for a centrifugal oil breather, to separate the drive lubricating oil from the overboard breather air vent. Also access for hand-turning the engine, during ground maintenance.
4
Q
ACCESSORY SECTION
A
The basic elements of the accessory section are:
1. The accessory case, which has machined mounting pads for the engine-driven accessories, and
2. The gear train, which is housed within the accessory case.
The accessory case may be designed to act as an oil reservoir. If an oil tank is utilized, a sump is usually provided below the front bearing support for the drainage and scavenging of oil used to lubricate bearings and drive gears. The accessory case is also provided with adequate tubing or cored passages for spraying, lubricating oil on the gear train and supporting bearings.
5
Q
Accessory: (may not be considered major section in some applications)
.
A
Accessory: (may not be considered major section in some applications)
Gear assembly, driven by high-pressure rotor shaft, which functions to drive various accessories (oil pump, fuel pump, hydraulic pump, fuel control unit, starter-generator).
6
Q
AFTERBURNER SECTION
A
AFTERBURNER SECTION
Afterburning. or thrust augmentation. is a method used in turbojets and turbofans to increase the maximum thrust available from an engine by 50 percent or more. However, this increase comes at the expense of fuel consumption, which increases some 300 percent. Afterburner is used during instances where added thrust is required for short periods such as takeoff, increasing rate of climb, high speeds, or providing extra performance in a combat situation. A typical afterburner assembly consists of many parts such as the afterburner fuel control unit, pressurizing valve, ignition system, the afterburner duct, etc. At this time, we will concentrate on four parts: the spray bars. the flame holders, the screech liner and the variable exhaust nozzle.
7
Q
AIR PRESSURE
A
As air pressure increases, air molecules tend to move closer together. This results in an increase in density, and therefore, thrust increases (Figure 3.1-10). For example, an aircraft that flies through the low-pressure eye of a hurricane will produce less thrust than an aircraft operating at normal ambient pressures.
8
Q
AIR TEMPERATURE
A
As air temperature increases, air molecules tend to move apart. This results in a density decrease, and a resultant decrease in thrust (Figure 3.1-9). An engine operating in the warm temperatures near the equator will produce less thrust than an engine operating in the cold of Alaska. Thrust may vary as much as 20 percent from standard rated thrust on a hot or cold day.
9
Q
AIRSPEED
A
AIRSPEED
In the thrust equation, the difference between the inlet and exhaust velocities plays a major role in determining thrust available. As the inlet velocity (v initial) approaches the magnitude of the exhaust velocity (v final), thrust is reduced. Therefore, if the mass of air and fuel is held constant, thrust will decrease as airspeed increases (Figure 3.1-12). This decrease in thrust due to an increase in airspeed is theoretical.
10
Q
AL TITUDE
A
AL TITUDE
Figure 3.1-10 Pressure Effect on Thrust
As an aircraft climbs, pressure and temperature will normally drop. From the previous discussion, thrust will decrease with a pressure decrease, and thrust will increase with a temperature decrease. With an increase in altitude, however, the rate of thrust decreases because a pressure drop is greater than the thrust increase resulting from a temperature drop. This means an engine will produce less thrust as it increases in altitude (Figure 3.1-11).
11
Q
Ammeter
A
Ammeter – An Aircraft Ammeter is an instrument installed in series with an electrical load used to measure the amount of current flowing through the load. The unit of measure is the ampere.
An ammeter is used to monitor the performance of the aircraft electrical system. The ammeter shows if the alternator/generator is producing an adequate supply of electrical power. It also indicates whether or not the battery is receiving an electrical charge.
Ammeters are designed with the zero point in the center of the face and a negative or positive indication on either side. When the pointer of the ammeter is on the plus side, it shows the charging rate of the battery.
-A minus indication means more current is being drawn from the battery than is being replaced.
-A full-scale minus deflection indicates a malfunction of the alternator/generator.
-A full-scale positive deflection indicates a malfunction of the regulator.
12
Q
AMMETER
A
An Ammeter measures the flow of the electric current in AMPS. An ammeter is used to monitor the performance of the airplane electrical system. The ammeter shows if the alternator/generator is producing an adequate supply of electrical power. It also indicates whether or not the battery is receiving an electrical charge. **Some gouge references “Kilowatts” as the answer.
13
Q
ANNULAR COMBUSTION CHAMBER
A
ANNULAR COMBUSTION CHAMBER
The liner of the annular combustion chamber (Figure 3.2-17) consists of a continuous, circular, inner and outer shroud around the outside of the compressor drive shaft. The liner is often called a “burner basket” or “basket” because of its shape and the many holes that allow cooling air inside. In this type of chamber, fuel is introduced through a series of nozzles where it is mixed and ignited with the incoming air.
Advantages of the annular combustion chamber include uniform heat distribution across the face of the turbine section, which aids in the prevention of heat warping or turbine blade failure. The configuration allows for better mixing of the air and fuel. It also makes better use of available space.
The disadvantages of the annular combustion chamber include that the unit cannot be removed without first disassembling the engine from the aircraft. Also, structural problems may arise due to the large-diameter, thin-wall cylinder required with this type of chamber. This type of burner is most often found on smaller engines, such as those of helicopters, where engine removal and tear down is not too difficult.
14
Q
APU
A
Auxiliary Power Unit (APU), a small, independent gas turbine engine, provides power through a driveshaft to a gearbox that turns a backup generator. Through this generator, the APU provides electrical power and frees an aircraft from being depend on external power. The APU can also ensure aircraft power when the engine-driven generators are not operating or fail
15
Q
AXIAL FLOW COMPRESSOR
ADVANTAGES 1 2 3 4 5
DIS-ADVANTAGES 1 2 3 4 5
A
Advantages
1. High peak efficiencies 1. 2. Small frontal area reduces drag
3. Straight through-flow, allowing for high
ram efficiency
4. Combustion efficiency is better than
centrifugal compressors (increased 2. pressure rise by increasing the number of stages)
5. With the dual/twin/split spool, starting flexibility is greater and it has improved high-altitude performance
Disadvantages
At low inlet speed, airflow will decrease in the compressor, creating a high angle of attack on the rotor blades that could lead to a compressor stall (compressor stall discussed in later chapter). High-speed aircraft may experience an inlet air temperature of 250 degrees F. because of ram effect. These high compressor inlet air temperatures cause low compression ratios (due to air density changes) and will also reduce the air supply to the rear of the compressor
Axial Flow Compressor
3. Good efficiencies only possible over a narrow rotational-speed
4. Difficulty of manufacture and high cost
5. High starting power requirements
16
Q
AXIAL FLOW COMPRESSORS
ADVANTAGES
DISADVANTAGES
A
The axial-flow compressor’s advantages are:
• High peak efficiencies;
• Small frontal area for given airflow;
• Straight-through flow, allowing high ram efficiency; and
• Increased pressure rise by increasing number of stages, with negligible losses.
The axial-flow compressor’s disadvantages are:
• Good efficiencies over only narrow rotational speed range,
• Difficulty of manufacture and high cost,
• Relatively high weight, and
• High starting power requirements (partially overcome by split compressors).
17
Q
Axial-Centrifugal Flow Compressor-
A
HELICOPTERS AND SMALL AIRCRAFT.
Axial-Centrifugal Flow Compressor- A third type of compressor design utilizes the combination of the axial and centrifugal flow compressor (Figure 3.2-11). The main advantage is the large pressure increase yet small size that is useful on helicopters and small aircraft.
18
Q
Axial-Flow Compressors
A
Axial-flow compressor- forces air along longitudinal axis, into stator vanes. Stator vanes reduce rotational flow, slow velocity, & increase air pressure.
OLDER AIRPLANES.
HIGHER EFFICIENCY, HIGH COMPRESSION RATIO (15:1)
SMALL OPENING. COMPLEX, SMALL BLADES SUSCEPTIBLE TO FOD.
Axial-Flow Compressors- The term axial-flow applies to the axial (straight line) flow of air through the compressor section of the engine. An axial-flow compressor has two main elements: Rotor blades and stator vanes. Rotor blades are rotating, airfoil- shaped blades, while stator vanes are stationary airfoil-shaped blades. Each rotor and stator pair forms a stage (Figure 3.2-9). Unfortunately, the delicate blades, especially toward the rear, make this type of compressor especially susceptible to FOD. Furthermore, the number of compressor blades and vanes (which can exceed 1,000), the close fits, and the narrow range of operating conditions make the axial flow compressor both complex and expensive. For this reason, the axial flow compressor finds its greatest application where the considerations of efficiency and power outweigh cost and simplicity. The small frontal area of this design is also beneficial to high-speed aircraft due to decreased drag.
19
Q
Batteries:
A
Batteries: two 12 volt batts in series will be 24 volt system.
20
Q
BATTERY
A
If you lose the generator and the alternator, how is the AC bus powered?
The Battery, via an inverter (converts DC to AC)
Battery provides DC power, but it’s primarily used as a source of emergency power should the generators fail and also for starting the aircraft
21
Q
Battery:
A
Battery: power reservoir that stores electrical energy in a chemical form. Must have lower voltage than the system to charge. Rated at amp-hours.
22
Q
Bernoulli’s theorem
A
Bernoulli’s theorem states that as any incompressible fluid passes through a convergent opening its velocity increases and pressure decreases. Only Subsonic. It has opposite effect in Super sonic.
23
Q
Bleed Air-
A
Bleed Air- air tapped from compressor section to used for pressurization, heating, air-conditioning, thermal anti-ice, and other systems.
24
Q
BRAYTON CYCLE
A
THE BRAYTON CYCLE
A gas turbine engine follows a cycle of operation known as the Brayton Cycle (Figure 3.1-4). This operating cycle consists of four events which occur simultaneously: intake. compression. combustion and exhaust. It is important to note that this cycle of operation is different than the operating cycle of a reciprocating engine. Different than a reciprocating engine.
25
BREATHER PRESSURIZING SUBSYSTEM:
The breather pressurizing subsystem pressurizes the scavenge subsystem along with the oil tank to sea level pressure. Pressurization is provided by compressor bleed air
26
Burner Can (combustion chamber)-
Burner Can (combustion chamber)- outer casing, with inner liner, which contains fuel injection, ignition, & self-sustaining “fireball.” Combustion chamber ports expanding combustion gases via high-pressure turbine nozzle into high-pressure turbine rotor.
27
Bus ties:
Bus ties: switches or relays used to connect or disconnect buses from one another in order to isolate failed buses
28
Bypass air-
Bypass air- ratio of air flowing through fan to amount of air flowing through gas turbine. Higher bypass ratios yield greater fuel efficiency at low altitude.
29
BYPASS RATIO
The amount of air that bypasses the gas generator in comparison with the amount of air that passes through the gas generator is called the bypass ratio. This ratio ranges from about 1 to 5 or more. For example, a bypass ratio of 2 : 1 means that for every two molecules of air that travels around the gas generator, one molecule goes through the gas generator. A bypass ratio of 6 : 1 has six molecules bypassing the gas generator and one molecule going into the generator.
30
BYPASSED OR DUCTED AIR
This airflow that goes around the gas generator is called bypassed or ducted air.
31
CAN COMBUSTION CHAMBER
CAN COMBUSTION CHAMBER
The can type combustion chamber is used most frequently on older centrifugal compressor engines. The airflow is ducted to individual combustion cans that are arranged around the circumference of the burner section (Figure 3.2-16). Each burner can contains its own fuel nozzle, burner liner and casing. Primary air introduced at the nozzle supports combustion, while secondary air flows through, between, and around the liner and burner case to provide cooling.
Advantages of the can combustion chamber lie in its strength and durability, combined with the ease of maintenance. Individual units can be inspected or replaced without disturbing the rest of the engine.
Disadvantages of the can combustion chamber include poor use of space in the chamber, greater pressure loss, and uneven heat distribution to the turbine section. Since each can directly adjoins the turbine section, a malfunction of one can may lead to turbine damage due to non-uniform temperature distribution at the turbine inlet.
32
CAN-ANNULAR TYPE
CAN-ANNULAR TYPE
Used primarily on larger, high performance engines, the can-annular combustion chamber combines the ease of maintenance of the can type with the excellent thermodynamics of the annular type. The can-annular combustion chamber (Figure 3.2-18) consists of cans at the front where the fuel and air are mixed and burned.Since the frontal area is where most problems occur (fuel nozzle failure or "burn-through"), an engine needs the structural strength of the can along with its ability to be easily inspected or replaced. The hot gases then pass to the annular area of the chamber where they are mixed together. This design provides an even temperature distribution at the turbine inlet and eliminating the possibility of cold spots caused by nozzles clogging. It also has greater structural stability and lower pressure loss than that of the can type. Though this type of design is efficient, its disadvantage is that it is expensive.
33
CENTIFUGAL COMPRESSOR
ADVANTAGES
DIS-ADVANTAGES
```
Advantages
1. Rugged
2. Low cost
3. Good power output over a wide range of
RPMs
4. High pressure increases per stage
Disadvantages
1. Large frontal area required
2. Impractical for multiple stages
```
34
CENTRIFUGAL FLOW COMPRESSOR
Centrifugal-flow compressor- forces air outward, into diffuser. Diffuser slows velocity, & increases air pressure
LOWER COMPRESSION RATIO
Centrifugal flow compressor consists of three main components: an impeller (also known as the rotor inducer), a diffuser, and a manifold (Figure 3.2-8). Air enters this type of compressor near the center of the impeller. The impeller, which is driven at high speeds by the turbine, accelerates the air
outward toward the diffuser. This high
rotational speed increases airflow velocity. As
the air is accelerated outwards, it passes through
divergent passages on the impeller. This
divergence causes a pressure increase. Since the
airflow velocity and pressure is increased by
the impeller, total pressure is increased.
35
CENTRIFUGAL FLOW COMPRESSOR
ADVANTAGES
DISADVANTAGES
The centrifugal-flow compressor’s advantages are:Screen
• High pressure rise per stage,
• Efficiency over wide rotational speed range,
• Simplicity of manufacture and low cost,
• Low weight, and
• Low starting power requirements.
The centrifugal-flow compressor’s disadvantages are:
• Its large frontal area for a given airflow and
• Losses in turns between stages.
36
CIRCUIT BREAKERS
Circuit breakers provide a means to manually or automatically interrupt power. In an abnormal electrical situation such as an ‘overload’ or a short in the circuit (wires), circuit breakers automatically open (“pop out”), de-energizing the circuit which prevents damage to the component or the electrical system. It can also provide a manual control of electrical power to various components in case of troubleshooting, or replacement of components
37
Circuit breakers:
Circuit breakers: disconnect individual components that are drawing too much current
38
Circuit Breakers:
Circuit Breakers:
Electromagnetic-type may be reset immediately and rated in amperes Only trip-free circuit breakers (impossible to hold manually closed) are used in aircraft. Automatic-reset breakers are not used.
39
COMBUSTION/BURNER SECTION
Airflow from the compressor entering the burner section will be divided into two types: primary and secondary air. Twenty-five percent is primary air, and it is mixed with fuel for combustion. The remaining 75 percent is secondary air, it flows around the chamber and through the small holes and louvers to cool the thin walls and control the flame. This unburned air can also be used to help cool the turbine and for afterburner operation.
The burner section (Figure 3.2-15) contains the combustion chamber, and provides the means for proper mixing of the fuel and air to assure good combustion. The development of burner systems presents many challenges in the areas of thermodynamics, fluid mechanics and metallurgy. It must deliver the combustion gases to the turbine section at a temperature that will not exceed the allowable limit of the turbine blades. The chamber must also, within a limited space, 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 for the turbines.
40
COMPRESSOR SECTION
COMPRESSOR SECTION
The primary function of the compressor 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. A secondary function is to supply compressor bleed air to operate various components throughout the engine and aircraft
41
Compressor stall-
distorted inlet air exceeds the fixed pitch compressor blade’s critical angle of attack. Airflow to compressor slows or stagnates, resulting in flow reversal. Indicated with loud “bang.” Reduce power setting, reduce angle of attack, & increase airspeed to correct.
42
CONSTANT SPEED DRIVE CSD
Generators frequently use a Constant Speed Drive (CSD) to maintain a constant rotational input speed regardless of engine RPM. This ensures a steady voltage output.
43
CONSTANT SPEED DRIVES (CSDs)
CSDs are mainly used on airliner and military aircraft jet engines to drive the alternating current (AC) electrical generator. In order to produce the proper voltage at a constant AC frequency, usually 3-phase 115 VAC at 400 Hz, a generator needs to spin at a constant specific RPM (typically 6,000 RPM for air-cooled generators).Since the jet engine gearbox speed varies from idle to full power, this creates the need for the Constant Speed Drive (CSD). The CSD takes the variable speed output of the accessory drive gearbox and hydro-mechanically produces a constant output RPM.The CSD holds the speed of the generator, and the frequency of the AC constant as the engine speed varies through its normal operating range. CSDs prevent power surges or breaks.
44
CONVERGENT
THIS CONVERT IS VERY NARROW MINDED
The tube narrows and velocity increases and pressure decreases. At supersonic airspeeds, the airflow has an opposite effect when encountering convergent or divergent openings. As airflow approaches/reaches supersonic speeds, the airflow becomes more compressible. Since the airflow is compressible, it doesn't follow Bernoulli's Theorem but actually acts opposite to it. Therefore, when supersonic airflow passes through a convergent opening, the velocity decreases and the pressure increases (Figure 3.1- 2b). Conversely, when supersonic airflow encounters a divergent opening, its velocity will increase and its pressure will decrease
45
CREEP
Blades undergo elongation, or "creep", as they are heated. This is a cumulative process, and excessive temperatures over long periods may result in permanent blade deformation. Deformed blades will not operate efficiently and may fail catastrophically causing severe damage and possible injury or death to personnel.
46
Current
Current = output volume or flow (measured in amps).
47
DC
DC: DC is a form of electricity that flows in one direction (we originally thought from positive to negative, hence why negative is ground). The components of a DC system are very heavy compared to their relative power outputs.
48
Density
Density is the mass of a substance per unit of its volume. According to the thrust equation, if the mass of airflow increases, thrust will increase. If the density of air increases, mass will increase, and therefore thrust will increase. As an aircraft operates at various altitudes and climates, the ambient air temperature and pressure will vary. These factors will affect the density of the air entering the engine, and as a result, will affect thrust.
49
DIFFUSER
DIFFUSER = When velocity is decreased then the pressure is increased.
When the pressure is increased and velocity is decreased, the opening is a diffuser.Only Subsonic. It has opposite effect in Supersonic.
50
DIFFUSER
In addition to critical aerodynamic functions, the diffuser also provides:
• Engine structural support, including engine mounting to the nacelle
• Support for the rear compressor bearings and seals
7
• Bleed air ports, which provide pressurized air for:
• airframe "customer" requirements (air conditioning, etc.)
• engine inlet anti-icing
• control of acceleration bleed air valves
• Pressure and scavenge oil passages for the rear compressor and front turbine bearings.
• Mounting for the fuel nozzles.
51
DIFFUSER
CONVERT HIGH VELOCITY OF AIRFLOW TO HIGH PRESSURE.
As the air is thrown from the outer rim of the impeller, it is forced through divergent passages in the diffuser. The diffuser is stationary and therefore it does not add energy to the airflow. The divergent passages in the diffuser convert the high velocity airflow to high pressure. Thus, velocity decreases, pressure increases, and total pressure remains the same. The airflow then passes through the compressor manifold. which directs it to the combustion chamberThe diffuser (Figure 3.2-14) is located after the compressor, and it prepares the airflow for the burner chamber. The diffuser decreases the velocity, which gives the airflow a final pressure increase. The airflow velocity must decrease slightly to avoid blowing out the burner flame, and the increase in pressure helps combustion and fuel efficiency.
52
DIFFUSER
The diffuser is located after the compressor, and it prepares the airflow for the burner chamber. The diffuser decreases the velocity, which gives the airflow a final pressure increase. The airflow velocity must decrease slightly to avoid blowing out the burner flame, and the increase in pressure helps combustion and fuel efficiency
53
Diode is a two-element device
Diode is a two-element device that allows current to travel in one direction.
54
Diodes:
Diodes: one-way check valves
55
DIVERGENT
THIS DIVERT IS LEAVING AND OPENING UP TO NEW CONCEPTS.
| The tube opens up and velocity decreases so pressure increases.
56
DIVIDED ENTRANCE INLETS
DIVIDED ENTRANCE INLETS
The divided-entrance inlet duct can be found in a variety of aircraft, including the AV-8 (Figure 3.2-4). While it allows the pilot to sit lower in the fuselage and reduces friction losses due to length, the divided-entrance inlet duct does present some problems.
57
DRY SUMP
Most aircraft employ a dry sump configuration for oil storage. In a dry sump system, the oil supply is carried in a tank located in the airframe or mounted on (but not an integral part of) the engine. With this type of system a larger oil supply can be carried and the temperature of the oil can be readily controlled. The dry sump system allows axial flow engines to retain their comparatively small diameter by arranging the oil tank and oil cooler in a manner consistent with the streamlined design of the engine
Three Subsystems of the Dry Sump System:
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 oil flow cycle.
Breather pressurizing subsystem: connects the individual bearing compartments and the oil tank with the breather pressurizing valve to help minimize oil leakage
58
DUAL SPOOL AXIAL FLOW COMPRESSOR
Dual spool axial flow compressor- Greater flexibility and power can be achieved in the axial flow compressor through what is known as a dual spool (also known as twin or split spool) compressor. In this configuration, the compressor is divided into two completely independent rotor spools, each driven by its own turbine and drive shaft
(Figure 3.2-10). One spool is known as the low-pressure compressor, while the other is known as the high-pressure compressor.
59
Dynamic pressure
Dynamic pressure is the kinetic energy of fluid molecules in motion. It is a measure of the force of the fluid molecules as they move through a system. Sometimes called Velocity.
60
EGT- Exhaust Gas Temperature.
EGT- Exhaust Gas Temperature. Usually, main engine temperature gauge used to prevent heat damage to turbine blades or other systems. EGT (Exhaust Gas Temperature): Measured aft of the turbine section
61
Electric relay
A purpose of a electric relay (magnetically operated switch) is to control high-current equipment items with a small switch.
62
Electrical bonding
Electrical bonding is process of connecting various parts of the aircraft to prevent static electricity discharges within the aircraft structure. Also to decrease the probability of lightning damage to control hinges.
63
Electrical bus bar system:
Electrical bus bar system: aircraft’s electrical system is carefully organized into separate but interconnected circuits. Important circuits can be isolated from one another and supplied by alternate power sources. Redundancy is also provided.
64
Engine driven generators
Engine driven generators supply electric current to the electrical system and maintain a sufficient electrical charge in the battery.
Generators: engine driven, generate electricity by moving permanent magnets around a coil of wire, thereby motivating electron flow in the coil
Normally generate AC current and must produce adequate amperage to power all of the components on its circuit(s) (or load shedding)
65
ENGINE PRESSURE RATIO (EPR)
EPR gauge indicates the pressure ratio between the inlet and exhaust airflow.
For aircraft that rely on the propulsive power of the exhaust gases of a gas turbine engine. such as turbojets and turbofans. use a Engine Pressure Ratio (EPR) gauge (Figure 3.1-15). The EPR gauge indicates the pressure ratio between the inlet and exhaust airflow. The EPR gauge is more widely used because it automatically accounts for some of the airflow variations at the inlet.
66
ENGINE REVOLUTIONS PER MINUTE (RPM)
ENGINE REVOLUTIONS PER MINUTE (RPM)
One of the most obvious factors that affects the thrust output is the rotational speed of the engine. With an increase in RPM, there is an increase in thrust. However, at low RPM there is very little increase in thrust with an increase in throttle. At higher rates of revolution, a small increase in throttle setting will produce a large increase in thrust. At the lower settings, fuel consumption is high for the amount of thrust produced. normally operated at near their maximum RPM.
67
EPR- Engine Pressure Ratio “eeper.”
EPR- Engine Pressure Ratio “eeper.” Ratio of turbine discharge (exhaust) to engine inlet pressure (intake). EPR used to measure thrust produced, especially for takeoff, of “pressure-rated” engine.
68
Essential bus:
routes power to equipment required for flight safety (i.e., primary attitude gyro).
69
Exhaust
Exhaust
After the gas has passed through the turbine, it is discharged through the exhaust. Though most of the gaseous energy is converted to mechanical energy by the turbine, a significant amount of power remains in the exhaust gas. This gas energy is accelerated through the convergent duct shape of the exhaust to make it more useful as jet thrust - the principle of equal and opposite reaction means that the force of the exhausted air drives the airplane forward.
70
EXHAUST SECTION
EXHAUST SECTION
The exhaust section of the turbojet engine is constructed of several parts, each of which has its individual functions. Although the parts have individual purposes, they have one common function. They must direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence. If a majority of the gas expansion takes place in the turbine section, as in a turboprop and turboshaft, the exhaust section merely acts to conduct the exhaust stream towards the rear.
71
Exhaust:
Exhaust:
Accelerated exhaust gasses provide thrust. Turbojet exhaust- hot exhaust gases rip into cool atmosphere, resulting in loud wind shear. Turbofan exhaust- tapered cone & struts mix hot primary exhaust with cool bypass airflow to produce total thrust. Cool bypass air mixing with hot exhaust air, insulates/disperses hot exhaust gasses & muffles loud wind shear.
72
EXIT GUIDE VANES
Exit guide vanes, also known as straightening vanes, are located at the discharge end of the compressor. They are the last set of stator vanes which prepares the airflow for the diffuser by straightening the airflow to reduce the airflow turbulence as it comes off the rotational movement of the compressor
73
FALSE START
A “false start” occurs when compressor rpm stabilizes below normal, and the turbine temperature remains within limits
74
FILTER BYPASS VALVE (OIL)
The filter bypass valve allows oil to flow around the filter element, should this filter become clogged. If this occurs, the filtering action is lost, allowing unfiltered oil to be pumped to the bearings
75
FILTERS
Filters ensure delivery of contaminant free hydraulic fluid by preventing dust, grit and undesirable impurities from entering the system
A red differential pressure indicator button raises when differential pressure is exceeded indicating a clogged filter element
76
FLAME HOLDER / afterburner
flame holder (Figure 3-2.29) that is located downstream of the fuel spray bars. The flame holder provides a region in which airflow velocity is reduced and turbulent eddies are formed. This allows the proper mixing of fuel and air for combustion. These flame holders usually take the form of several concentric rings with a V cross-sectional shape.
77
Flameout-
Flameout- fuel/air mixture is not sufficient to sustain combustion.
78
FLASH POINT
The lowest temperature of a combustible substance (fuel) that would ignite with a momentarily application of a flame is its flash point. A fuel’s flash point and volatility rating are inversely related. As the fuel’s volatility rating increases, the flash point of the fuel decreases
79
FREE POWER TURBINE
The fan is driven by the turbine section. A free or power turbine (Figure 3.4-4), which is a turbine aft of the gas generator turbines and is not connected to the gas generator, may drive the fan. In this configuration, the fan is also separate from the
gas generator.
80
FUEL BOOST PUMPS
The boost pump is an integral unit composed of a centrifugal pump and electric motor. Submerged and installed in the fuel tanks. they ensure an adequate supply of fuel to the engine-driven fuel pump
It may also be used to transfer fuel from one tank to another tank for proper weight and balance
Boost pumps are needed to supply fuel pressure for starting engines and to supply fuel to the primer system
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
In extreme cases these bubbles may induce vapor lock or cavitation of the engine-driven pump.
The boost pump supplies the fuel under pressure to the main fuel pump, reducing or eliminating the effects of aeration
81
FUEL CONTROL UNIT FCU
The fuel control unit (FCU) 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. It is designed to send ‘metered fuel’ (measured fuel) to satisfy fuel-flow requirements for starting, acceleration, deceleration, and stabilized (steady state) operation
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FUEL FLOW
From the fuel tank to the boost pump through the emergency fuel shutoff through the filter to the engine driven fuel pump through the fuel control unit to the flowmeter to the fuel-oil heat exchanger into the manifolds and into the engine
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FUEL MANIFOLD
The fuel manifold delivers fuel to the engine burner section through a series of fuel nozzles
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FUEL OIL COOLER (HEAT EXCHANGE)
The fuel-oil cooler is a heat exchanger designed to preheat metered fuel and cool the engine lubricant as it flows from the engine. Preheating fuel removes any ice crystals and increases its volatility. facilitating efficient fuel ignition
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FUEL OIL COOLER/HEAR EXCHANGE
The fuel-oil cooler/heat exchanger is designed to cool the hot oil taken from the bearings and to preheat the fuel for combustion. Fuel flow to the engine must pass through the fuel-oil cooler/heat exchanger; however, a thermostatic valve allows the oil to bypass the cooler if no cooling is needed.
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FUEL PUMP ENGINE DRIVEN
The engine-driven pump is a high pressure pump. It is designed to deliver fuel to the fuel control unit. This pump provides fuel in excess of engine requirements. The excess fuel ensures that a sufficient supply of high pressure fuel is available to meet engine requirements
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FUEL TANK RESERVOIR
The tank is a reservoir, or holding cell, for the jet propellant. Fuel tanks, as well as any fuel system, are normally made of materials that will not react chemically with any fuel. Most fuel tanks are made of synthetic rubber with self-sealing cells called bladders that fit into cavities in the wing or fuselage of the aircraft
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Fuse-type current limiter
The purpose of a fuse-type current limiter is to permit short periods of overload before the fuse link melts.
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FUSES
Fuses provide automatic circuit protection should an over-load or an excessive amount of current is flowing through the system or to a component
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Fuses:
Fuses: open circuits that are drawing too much current
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gas generator
A gas generator produces the high-energy airflow necessary for creating thrust. I think that's what they call the whole Turbine Engine.
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Generating systems
Generating systems are operated in parallel to obtain equal loads, a paralleling or equalizing circuit distributes the load equally.
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GENERATOR
Generator output is normally 115-120V/400HZ AC, 28V DCGenerators are used as the main source for either AC or DC power. A generator transforms mechanical energy into electrical energy.
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GENERATOR CONTROL UNIT GCU
OVER VOLTAGE PROTECTION
The generator control unit (GCU) is more commonly found on turbine power aircraft. The most basic generator control units perform a number of functions related to the regulation, sensing, and protection of the DC generation system.
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Generator Control Units (GCU):
Overvoltage, current limiting, and generator overspeed.
Generator Control Units (GCU): voltage regulators, direct generator current to the battery when necessary for recharging, provide circuit and generator protection by disconnecting the generator from the system when electrical abnormalities occur.
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Generator Control Units (GCUs)
AC Generator Control Units (GCUs) provide generator field controls and indication and protective functions, open phase, under-excitation, and over-voltage.
If a AC generator is being driven but there is no field excitation, residual voltage will be produced.
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Generators
Generators are rate in amperes at rated voltage. Convert mechanical energy into electrical energy by electromagnetic induction. AC gen. in KVA.
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Gross thrust
ENGINE NOT MOVING THRUST
Gross thrust is a measurement of thrust due solely from the velocity of the exhaust gases. Gross thrust (Figure 3.1-7) will be produced by a stationary engine; perhaps while mounted on a test stand, or on an aircraft while completing a 'ground run-up'. This measurement ignores the velocity of the air at the inlet. In addition, the test must have standard conditions or parameters that serve as a baseline to ensure consistent measurements. These conditions include atmospheric pressures and temperatures. Therefore, engineers or maintenance personnel use standard day (29.92" hg and 15oC at sea level) as their baseline for measuring gross thrust. When an engine manufacturer provides the thrust rating of an engine, it is typically the amount of gross thrust it produces. It is often used to compare the thrust produced to another.
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GUIDE VANES
Guide Vanes – In addition to the rotors and stators, the compressor utilizes inlet and exit guide vanes
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HIGH PRESSURE COMPRESSOR
AFT OF LOW PRESSURE COMPRESSOR SO IT CAN GO FASTER.
The high-pressure compressor is located after the low-pressure compressor, and provides a further increase to airflow pressure. This compressor is turned by the high- pressure turbine. Located forward of the low-pressure turbine, the high-pressure turbine will receive more energy from the combustion section. Therefore, it will turn the high- pressure compressor at a faster rate The high-pressure spool is turned at higher speeds by the high-pressure turbine, both because it is smaller and lighter weight, and because the high-pressure turbine is located directly after the burner chamber. This higher speed helps to produce a vacuum, which eases the transition from the low to the high pressure compressor
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High-pressure compressor-
High-pressure compressor- second or intermediate compressor. Driven by the high-pressure turbine. Rotational speed of high-pressure compressor shaft, read in % design RPM, known as N2. N2 shaft counter-rotates concentrically around the N1 shaft. Triple spool engines have an additional high-pressure compressor
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High-pressure turbine-
High-pressure turbine- extracts sufficient energy from expanding combustion gases to drive high-pressure compressor (& accessory section). High-pressure spool % design RPM indicated with N2.
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HOT START
A “hot start” is defined as exceeding the maximum allowable temperature for the turbine section during start. If the engine experiences more than the usual difficulty accelerating (due to such problems as early starter cut-out, fuel mis-scheduling, or strong tailwinds), the engine may spend a considerable time at very low RPM (sub-idle). Normal engine cooling flows will not be effective during sub-idle operation, and turbine temperatures may appear relatively high. This is known as a hot start
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HUNG START
A “hung start” describes a situation where the temperature within the turbine section continues to rise, and the compressor rpm stabilizes below normal
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HUNG START
What start abnormality is indicated by a slight rise in EGT with RPM stabilizing below limit?
Hung Start
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HYDDRUALIC RESERVOIR
The reservoir is a tank in which an adequate supply of fluid for the system is stored. Fluid flows from the reservoir to the pump, where it is forced through the system and eventually returned to the reservoir. The reservoir not only supplies the operating needs of the system, but it also replenishes fluid lost through leakage. Furthermore, the reservoir serves as an overflow basin for excess fluid forced out of the system by thermal expansion (the increase of fluid volume caused by temperature changes), the accumulators, and by piston and rod displacement.
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HYDRAULIC ACCUMULATORS
What are the uses of a hydraulic accumulator? Accumulators maintain hydraulic fluid under pressure and system shock absorption during periods of high demand
It serves as a cushion, or shock absorber, by absorbing pressure surges in the system (such as engine shut-down or actuator operation)
It supplements the pump’s output when the pump is under peak load by storing energy in the form of fluid under pressure.
It stores enough fluid under pressure to provide for emergency operation of certain actuating units
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HYDRAULIC ACTUATORS
Actuators convert fluid under pressure into linear or reciprocating mechanical motion
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HYDRAULIC FUSES:
| I WISH WE HAD THESE
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. If a leak develops in a subsystem while the aircraft is flying, a fuse prevents excessive loss of fluid yet it permits the operation of the remaining subsystem.
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HYDRAULIC SYSTEM
The main purpose of a hydraulic system is to multiple force. MAKE IT SO LITTLE FORCE CAN MOVE BIG FLIGHT CONTROLS.
This works because hydraulic fluid is incompressible
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HYDRUALIC PRESSURIZED RESRVOIR
Reservoirs on aircraft designed for high-altitude flight are
usually pressurized. Pressurizing assures a positive flow of
fluid to the pump at high altitudes when low atmospheric
pressures are encountered and it also keeps the fluid from foaming.
On some aircraft, the reservoir is
pressurized by bleed air taken from the compressor section
of the engine. On others, the reservoir may be pressurized
by hydraulic system pressure
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IMPACT PRESSURE
Impact pressure, on the other hand, is the force per unit area exerted by fluids in motion. Impact pressure is a function of the velocity of the fluid. An example of impact pressure is the pressure exerted on one's hand held outside a moving car’s window. Total pressure is the sum of static and impact pressures.
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INLET DUCT
INLET DUCT
Opening of the engine.
Although technically part of the airframe, inlet ducts (Figure 3.2-2) are essential to the efficient operation of a gas turbine engine. It is designed to provide the proper amount of high pressure, turbulence-free air to the compressor. It must operate with high efficiency
from ground idle to possible supersonic speeds at a variety of altitudes and attitudes.
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INLET GUIED VANES
Inlet guide vanes impart a swirling motion to the air entering the compressor in the direction of engine rotation. This motion improves the aerodynamic characteristics of the compressor by reducing the drag on the first-stage rotor blades
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INVERTER
Inverter transforms DC to AC
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Inverters
Inverters convert DC to 115 volt AC power
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Inverters:
Inverters: convert DC power to AC power
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ITT- Inter-stage Turbine Temperature.
ITT- Inter-stage Turbine Temperature. Measured between compressor & power turbines.
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KEROSENE
Kerosene’s use as a fuel additive, why?
Reduce freeze potential.
flash point for kerosene is higher than gasoline, making it more stable
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KW meter
KVAR meter
measures work performed
measures how hard the generator is working.
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Lead-acid batt:
Lead-acid batt: sulfuric acid and water.
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LOAD METER
Load meters will tell you to amperage load on a bus, usually in a fraction of the maximum load. Reference: Aviation Maintenance Technician Handbook – Airframe (Vol 2), Aircraft Electrical System.
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LOW PRESSURE COMPRESSOR
IN FRONT OF HIGH PRESSURE COMPRESSOR
The low-pressure compressor is located at the front of the compressor section. It will provide the initial pressure increase to airflow arriving from the inlet. As such, this compressor spool must spin slow enough to provide an initial pressure increase without creating an excessive velocity increase.
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Low-pressure compressor-
Low-pressure compressor- forward most compressor. Driven by rearmost low-pressure turbine. Rotational speed of low-pressure compressor shaft, read in % design RPM, known as N1. N1 shaft turns freely inside of N2 shaft. N1 is primary means of setting power on “speed rated” engine.
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Low-pressure turbine-N1.
Low-pressure turbine- extracts sufficient energy from combustion gases to drive low-pressure compressor & fan. Low-pressure spool % design RPM indicated with N1.
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MAGNETIC CHIP DETECTOR (OIL)
The magnetic-chip detector is a metal plug with magnetized contacts, and is placed in the scavenged oil path. These detectors are normally located at the lower part of the accessory gearbox and/or reduction gearbox.
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Monitor or secondary bus: (UTILITY BUS)
In an electrical malfunction, which bus do you lose first?
Utility bus
routes power to convenience circuits, e.g., cabin lighting.
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NET THRUST
ENGINE MOVING THRUST
Under normal flight conditions, an aircraft engine will seldom be stationary. The measurement of inlet airflow velocity must be included for the calculation of this thrust. Thrust that corrects for the effect of inlet airflow velocity is known as net thrust (Figure 3.1-8).Net thrust and gross thrust will be equal when inlet airflow velocity is zero
and the atmospheric conditions are
standard. Because net thrust is a more
realistic measurement of an engine's thrust, the terms thrust and net thrust are often used interchangeably.
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Ni-cad:
Ni-cad: put out sustained voltage over a longer period of time, subject to memory characteristic (low use limits ability to handle high demand) and thermal runaway (excessive current is drawn from and then replaced to the battery causing it to overheat)
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Nickel-cadmium (NICAD) batt:
Nickel-cadmium (NICAD) batt: potassium hydroxide and water.
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NOZZLE
NOZZLE = When the shape decreases the velocity increases and the pressure decreases.
If the shape of the opening increases the airflow's velocity and decreases the airflow's pressure, it is a nozzle. Only Subsonic. It has opposite effect in Supersonic.
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OIL COOLERS
Oil Coolers are often used in lubrication systems to reduce the temperature of the oil for re-circulation through the system. Dry sump lubrication systems require coolers because air entering the axial-flow engine does not flow around the oil reservoir like it does on wet sump systems.
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OPTIMUM CRUIS LEVEL
At approximately 36,000 feet (beginning of the isothermal layer), temperature stabilizes. As a result, temperature will no longer offset the density decrease due to pressure. Therefore, thrust decreases more rapidly. This altitude is also known as the optimum cruise level. At this altitude, thrust available plus low fuel flow and diminished drag combine to provide optimum performance for many engines.
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OTTO CYCLE
A reciprocating engine's cycle, like that of an automobile, is called the Otto cycle (Figure 3.1-5). While the events in the Brayton cycle and Otto cycle are similar, the events in the Otto cycle occur sequentially rather than simultaneously. In addition, the events in the Otto cycle will generally take place within a single piston, while the Brayton cycle takes place throughout the gas turbine engine (F
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PARALLEL BUS SYSTEM
What increases or decreases the voltage of a generator so it carries its share of the load? Paralleling circuit.
advantage of the parallel bus system is electrical load is automatically redistributed when one generator fails. Bus tie provides a means of isolating a power bus from one that has failed.
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PASCALS LAW STATES
Pascal’s Law states: 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. The shape of the container holding the liquid has no effect on the pressure or force relationships
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PITOT/STATIC
| Blocked pitot tube and blocked drain hole.
```
Blocked tube and blocked drain hole
•Pressure is trapped and no changes will be indicated on the airspeed indicator unless there is a change of altitude which means a change of static pressure.
Acts as an Altimeter.
Descend = decrease in speed
Climb = Increase in speed.
```
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PITOT/STATIC
| Blocked pitot tube and clear drain hole
•Airspeed indicator will go to zero because of the lack of ram air pressure. The static pressure has equalized and there is no longer a pressure differential being sensed by the diaphragm.
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PITOT/STATIC
| Blocked static but Pitot tube remains clear.
Blocked static port
•If the static system becomes blocked but the pitot tube remains clear, the ASI continues to operate; however, it is inaccurate.
•The airspeed indicates lower than the actual airspeed when the aircraft is operated above the altitude where the static ports became blocked, because the trapped static pressure is higher than normal for that altitude. When operating at a lower altitude, a faster than actual airspeed is displayed due to the relatively low static pressure trapped in the system.
•If the aircraft descends, the static pressure increases on the pitot side showing an increase on the ASI. This assumes that the aircraft does not actually increase its speed. The increase in static pressure on the pitot side is equivalent to an increase in dynamic pressure since the pressure can not change on the static side.
•If an aircraft begins to climb after a static port becomes blocked, the airspeed begins to show a decrease as the aircraft continues to climb. This is due to the decrease in static pressure on the pitot side, while the pressure on the static side is held constant.
•A blockage of the static system also affects the altimeter and VSI. Trapped static pressure causes the altimeter to freeze at the altitude where the blockage occurred. In the case of the VSI, a blocked static system produces a continuous zero indication.
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PRESSURE SUBSYSTEMS OF THE DRY SUMB SYSTEM:
Pressure subsystems normally employ an engine driven, gear type, pressure pump. The pump receives oil at its inlet side through gravity flow from the oil tank and discharges oil to a spacers-and-screens type oil filter. From the oil filter, oil is transmitted downstream to the pressure relief valve. The pressure relief valve regulates system pressure and returns unwanted oil to the pump inlet. From the pressure relief valve, the oil is sent via tubing to lubricate the main engine bearings and accessory drive housing. The pressurized oil is sprayed through fixed orifice nozzles, providing a relatively constant oil flow at all engine speeds
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PRIMARY AIR
SECONDARY AIR
Primary air (amounting to about one fourth of the total engine’s total airflow) is used to support the combustion process.
Secondary or dilution air, is admitted into the liners in a controlled manner. The secondary air controls the flame pattern, cools the liner walls, dilutes the temperature of the core gasses, and provides mass.
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Primary bus:
routes power to equipment devoted to the aircraft’s intended mission (i.e., radar).
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RAIM
Receiver autonomous integrity monitoring.
Correct
RAIM stands for receiver autonomous integrity monitoring. It is a receiver internal process that evaluates the performance of the GPS receiver. Reference: Pilot’s Handbook of Aeronautical Knowledge, Navigation.
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RAM EFFECT
RAM EFFECT
For many high-performance fighter aircraft, ram effect allows excellent high altitude performance, although air density is low.
If we only consider the change in airflow velocity in the thrust equation, then thrust decreases with an increase in airspeed. Remember, that the thrust equation consists of two variables: mass (m) and acceleration (vfinal - Vinitial). As mentioned, the difference between inlet and exhaust velocities decreases as the aircraft increases speed. However, more and more air is being rammed into the inlet, increasing the mass and pressure of inlet air. This offsets the decrease in acceleration and results in a neutral effect or slight increase in thrust at subsonic airspeedsThis is due to the compressibility of airflow as velocity increases toward supersonic. As airflow becomes compressible, mass due to ram effect increases at an increasing rate. Ram effect is especially important to high performance aircraft due to the exceptionally high- mass airflow that occur at supersonic speeds. This results in a significant increase in overall thrust due to ram effect at supersonic speeds (Figure 3.1-13).
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Relays:
Relays: remotely control electric circuits carrying large amounts of current
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RELIEF VALVES
Relief valves are simply a pressure limiting device. It is a 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.
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RESERVOIR
```
Fluid supply (reservoir)
A reservoir can also serve 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
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Reverse-current relay
A reverse-current relay disconnects gen. from bus when gen. voltage is less than Battery voltage. Relays are electrical switches used for remote control of circuits.
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Rotor blades
Rotor blades are rotating, airfoil- shaped blades
The rotors are driven by the turbine at high speeds (near 15,000 RPM), which increases the velocity and pressure of the incoming airflow, thus, increasing total pressure. This high velocity airflow is then pushed through the stator vanes which act like diffusers (the airflow velocity decreases with a proportional increase in pressure). The airflow then passes on to the next rotor/stator stage and the process continues.
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ROTOR SECTION
The turbine's rotor section converts the heat energy (potential and kinetic) of the hot expanding gases from the burner chamber into mechanical energy. Approximately
75 percent of that total pressure energy from the exhaust gases is converted. The exact amount of absorption in the turbine is determined by the load the turbine is driving. The load on the turbine is affected by the compressor size, compressor type, and accessories. The remaining 25 percent of the available energy is used for thrust. That 25 percent is utilized differently by the four types of gas turbine engines that will be discussed in later topics.
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Rotor Section
Rotor Section
1) Converts the heat energy (potential and kinetic) of the hot expanding gases from the burner chamber into mechanical energy
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SCAVENGER SUBSYSTEM (OIL)
The scavenge subsystem removes oil from the main bearing compartments and accessory gear drives. Under certain temperature conditions, this subsystem circulates the oil through the oil cooler(s) and back to the tank
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SECTOR VALVES
All other components leading up to, but not including, the selector valves. The selector valves direct the flow of fluid to various actuating units
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SINGLE ENTRANCE INLET DUCT
THE RJ
The single-entrance inlet duct (Figure 3.2-3) is the simplest and most effective inlet duct design. Located directly in front of the engine, it is positioned to collect generally undisturbed air. In single engine aircraft, the engine is usually mounted amidship (as in the F-16), and a single entrance duct is necessarily long. While the length of the inlet duct may result in a slight pressure loss, it is offset by smooth airflow characteristics.
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Soldered terminals
Soldered terminals are considered unsat for aircraft.
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Solenoid
A solenoid is an electromagnetic switch with a movable core.
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Solenoid:
Solenoid: electrically powered remote control device, moves a shaft over a short distance (hydraulic and pneumatic valves)
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SPECIFIC FUEL CONSUMPTION
Define specific fuel consumption.
Fuel flow in lbs. per hour at a given power setting.
Specific fuel consumption is the amount of fuel burned per hour per unit of thrust (lbs of fuel per hour/pounds of thrust). Reference: Aerodynamics for Naval Aviators, Turbojet Operating Characteristics.
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Spool-
combination of compressor, shaft, & turbine.
ONE COMPRESSOR CONNECTED BY A SHAFT TO ONE TURBINE IS A SINGLE SPOOL.
NEW AIRPLANES HAVE MULTI SPOOL ENGINES LOW PRESSURE COMPRESSOR CONNECTING TO LOW PRESSURE TURBINE AND HIGH PRESSURE COMPRESSOR CONNECTING TO HIGH PRESSURE TURBINE. N1 AND N2.
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Spray bars / afterburner
Spray bars (Figure 3.2-28) introduce fuel to the afterburner and they are located in the forward section of the duct. In some engines, the afterburner can vary the amount of fuel being introduced to determine the degree or zones of afterburning. Other engines can only engage or disengage afterburner operations.
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Starter bus:
routes power to start the aircraft’s engines.
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STARTER SYSTEM
The purpose of any starter system is to accelerate the engine until the turbine is producing enough power to continue the engine acceleration itself. This is called the self-accelerating speed
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Starter-generator unit
Starter-generator unit combines both systems in turbine aircraft.
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Starter:
Starter: driven electrically by a battery
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Static dischargers (wicks)
Static dischargers (wicks) dissipate static charges from control surfaces into the air to prevent radio interference.
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Static pressure
Static pressure is the potential energy of fluid molecules at rest. Again, most engineers along with many other professions refer to static pressure simply as pressure.
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STATIC PRESSURE
Static pressure is the force per unit area exerted on the walls of a container by a stationary fluid. An example is the air pressure within a car tire.
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STATOR
The function of the stator is twofold.
1) It prepares the airflow from the combustion chamber for harnessing of power by the turbine rotor.
2) The stator deflects the gases at a specific angle in the direction of the turbine wheel rotation.
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Stator Element
Stator Element
| •Sometimes called the stationary stator vanes, turbine, nozzle guide vanes, turbine guide vanes or just nozzles
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Stator vanes
stator vanes are stationary airfoil-shaped blades.
The rotors are driven by the turbine at high speeds (near 15,000 RPM), which increases the velocity and pressure of the incoming airflow, thus, increasing total pressure. This high velocity airflow is then pushed through the stator vanes which act like diffusers (the airflow velocity decreases with a proportional increase in pressure). The airflow then passes on to the next rotor/stator stage and the process continues.
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STATOR VANES
The stator element is sometimes called stationary stator vanes, turbine, nozzle guide vanes, turbine guide vanes, or just plain nozzles. Stator vanes come before the rotors in the turbine section. The function of the stator vanes is two fold. First, it prepares the airflow from the combustion chamber for the harnessing of power by the turbine rotor. Second, the stators deflect the gases at a specific angle in the direction of turbine wheel rotation.
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TACHOMETER
TACHOMETER
The gauge most commonly used by a pilot to determine engine performance is the tachometer (Figure 3.1-17). This gauge provides the crew with an indication of engine speed. Although it does not actually measure thrust, this instrument provides the pilot with a quick assessment of the amount of energy being produced by the engine, much like a tachometer in an automobile. Gas turbine engine tachometers are calibrated in percent rpm. On many engines, 100% represents full power. Therefore, using percentages on a tachometer
as a comparative basis, the aviator will not be bogged down by the high numbers that would be necessary on an actual RPM indicator.
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TGT- Turbine Gas Temperature.
TGT- Turbine Gas Temperature.
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Thermal Runaway
Thermal Runaway is continuous rising current and battery temperature.
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THRUST
THRUST
Thrust that a gas turbine engine develops is essentially the result of many pressure, temperature and velocity changes as airflow passes through an engine.
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Thrust Specific Fuel Consumption (TSFC)
Thrust Specific Fuel Consumption (TSFC) is the amount of fuel required to produce one pound of thrust. The propulsive force behind the turbojet is dependent upon the amount of fuel added to the air mass. This is a proportional relationship: more air requires more fuel. Since the density of the air decreases with an increase in altitude, the requirement for fuel is less at higher altitudes.
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TIT- Turbine Inlet Temperature.
TIT- Turbine Inlet Temperature. Highest temperature in a turbine engineTIT (Turbine Inlet Temperature): Temperature of the gases from the combustion section of the engine as they enter the first stage of the turbine
TIT is the highest temperature inside a turbine engine and is difficult to measure which is why EGT is often measured instead.
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TORQUEMETER
TORQUEMETER
Figure 3.1-15 Pressure Indication Gauges
Propeller or rotor driven aircraft use a torguemeter gauge to indicate power available. The torquemeter gauge (Figure 3.1-16) indicates shaft horsepower available to drive a propeller or rotor. This is where most of the thrust is derived. The thrust produced at the exhaust section of the engine of a propeller or rotor driven aircraft is comparatively small.
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TOT- Turbine Outlet Temperature.
TOT- Turbine Outlet Temperature.
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Total pressure
Total pressure is the sum of pressure and velocity. In a closed system, total pressure remains constant.
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TOTAL PRESSURE
Total pressure is the sum of static and impact pressures.
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TRANSFORMER RECTIFIER TRU
Transformer Rectifier, they change the frequency and the rectifier changes AC to DC Transformer Rectifier transforms AC power to DC (AC/DC Totally Rocks)
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Transformer Rectifier Units (TRUs)
Transformer Rectifier Units (TRUs) convert AC to 28 volt DC power. The transformer can change the voltage.
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Transformer-rectifier units (TRU)
Transformer-rectifier units (TRU) convert AC to DC power
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Transformers:
Transformers: used to step aircraft voltage (usually down)
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Turbine
Turbine
This example engine has a four-stage turbine. The turbine converts the gaseous energy of the air/burned fuel mixture out of the combustor into mechanical energy to drive the compressor, driven accessories, and, through a reduction gear, the propeller. The turbine converts gaseous energy into mechanical energy by expanding the hot, high-pressure gases to a lower temperature and pressure.
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TURBINE SECTION
TURBINE SECTION
Like the compressor, the turbine section is comprised of stators and rotors. However. the turbine section drives the compressor and the accessories. It is also designed to increase airflow velocity. This acceleration occurs through the stators, rotors, or both (Figure 3.2-19 and Figure 3.2-20).
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Turbine section
The turbine section
•Drives the compressor
•The compressor drives the engine accessories
•Is designed to increase airflow velocity
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Turbine Section Acceleration
Turbine Section Acceleration
| •Acceleration is produced through the stators, rotors or a combination of both
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Turbine:
Turbine:
Combustion chamber ports expanding combustion gases via high-pressure turbine nozzle into high-pressure turbine rotor, then into low-pressure turbine rotor.
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TURBO FAN ENGINE
On a forward-fan design, the fan blades look similar to rotor blades of the compressor that have been enlarged. The cross section of these fans are larger than the front area of the compressor. This allows a relatively large mass of air to bypass the gas generator. On average. this large mass of bypassed air can produce between
30 to 60 percent of the total thrust of a turbofan engine. Some engines have been designed with an even greater amount of thrust from the fans. These percentages depend upon the size of the fan, the turbine arrangements, and atmospheric conditions. Since the fans provide 30- 60 percent of the total thrust. the gas generator exhaust gases will provide the remaining thrust. which is between 40 and 70 percent of that total thrust.
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TURBO JET ENGINE
OLDER AIRPLANES
GOOD AT HIGH AND FAST PERFORMANCE BUT NOT GOOD AT LOW AND SLOW PERFORMANCE.
INEFFICIENT AT LOW ALTITUDES AND LOW AIRSPEEDS.
LOAD ENGINES
LESS FUEL EFFICIENT
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TURBOFAN ENGINE
TURBOFAN ENGINE
The turbofan engine can be considered a cross between the turbojet and the turboprop engine (turboprop will be discussed in the next lesson topic). The turbofan design combines the propulsive thrust of the exhaust gases from the gas generator with additional thrust that is generated by utilizing a duct-enclosed fan. This fan, which is driven by the gas generator, provides additional thrust by accelerating a fairly large mass of air around the gas generator (Figure 3.4-3). This airflow that goes around the gas generator is called bypassed or ducted air.
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Turbofan-
ACCELERATES MORE AIR WITH THE FAN THAN A TURBO JET ENGINE. INCORPORATES BYPASS IAR AND AIR GOING INTO ENGINE. BYPASS AIR CREATES THRUST AT LOW ALT. 80% THRUST COMES FROM BYPASS AIR AT LOW ALT WHICH GIVES GREATER FUEL ECONOMY. LOWT QUIETER WITH THE MIX OF COOLER BYPASS AIR WITH CORE AIR.
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Turbofan- turbojet w/ shrouded fan prior to compressor.
Turbofan- turbojet w/ shrouded fan prior to compressor. Fan driven by low pressure compressor shaft. Intake air divided into bypass air or inlet air to gas turbine. Large volume of bypass air provides moderate acceleration, good takeoff performance, low-altitude/speed efficiency, & quieter operation.
Turbojet core provides large acceleration & high cruise speed, with relatively
small volume of air.
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Velocity,
Velocity, however, is magnitude (speed) with direction. Since the direction of the airflow within an engine is constant, to simplify terminology, engineers often refer to dynamic pressure as velocity. Sometimes called Dynamic Pressure.
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VOLATILITY
Volatility is the measurement of a liquid’s ability to convert to a vaporous state. Fuel must vaporize and be mixed with a given percentage of air for it to burn or explode. The volatility of a fuel effects engine starting, range, and safety.
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Voltage
Voltage = output of electrical pressure,
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WET START
A “wet start” is a situation in which the fuel-air mixture does not light off initially, but has the capability to eventually ignite. BIG FIRE BALL GOES OUT THE BACK DO TO FUEL BUILD UP.
