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Terms in this set (203)
the propeller assembly, reduction gear box, and torque meter can be connected in what two ways
2 types of power pump
states that as any incompressible fluid passes through a convergent opening its velocity increases and pressure decreases. (divergent opening is vise versa).
which one is compressible?
diffusers do what?
increase pressure and decrease velocity
heart beat of engine
Can, annular, can annular
primary air is what precent and used for what?
25% and combustion
secondary air used for
cooling, flame control, may be used for afterburner ops.
Which aircrafts use epr
turbojet and turbofan
gross thrust 3 conditions
amount of fuel used to produce on pound of thrust
Turbojets are efficient?
NO. very inefficient.
propeller section is made up of what 3 sections?
Hub assembly(holds everything in), blade assembly, pitch assembly (changes pitch of blade)
T-6 does not have beta
Centrifugal flow compressor
impeller (divergent design), diffuser, manifold, incr compression ratio with just one stage, lots of drag, multi stage so it's not practical.
AGB accessory gear box
drive mechanically driven accessories . (pumps, tachometer, generator, starter connected there)
spark always there, fuel introduced at designated point- 50% rpm starter will shutoff
wet start- most dangerous, no ignition
convergent-divergent opening on airframe
low turbulent, high pressure with ---- entrance inlet duct
creates a lot of turbulence, feeding one engine, not desirable
divided inlet duct
factors affecting thrust
hand pump requires a
2 types of power pump
constant (pressure regulator valve)
fluid pressure to mechanical work
detect large loss of fluid
blade elongation/deformation due to high heat. combatted by fir tree method
signs of compressor stall
fuel flow increase
what is bypass air that is used by after burner called?
turboprop reduction gear box-
convert high rpm and low torque into low rpm high torque. can sometimes act like the accessory gear box.
bleed valves from compressor section
interstage and provide compressor stability
convergent- convergent at subsonic. turkey feathers open and (ecomes divergen) at supersonic.
best heat distribution and good thermodynamics in annular construction. gas generator and free power turbine. exhaust gasses are NEGLIGABLE.
Dual/split spool .
low pressure compressor driven by low pressure turbine and vice versa. can annular. low pressure bleed air from after low pressure compressor.
afterburner 4 main parts
variable exhaust nozzle
variable flight inlet duct
allows all flight regimes. is convergent to divergent from fore to aft
diffuser in supersonic airflow is a what opening
2 types of igniter
constrained is cooler
annular is inside
potential energy of fluid molecules at rest.
also called pressure
kinetic energy of fluid molecules at rest
also called velocity
Bernoulis theorem states
that as any incompressible fluid passes through a convergent opening its velocity increases and pressure decreases
what happens to super sonic airflow as it goes through a super sonic nozzle and what happens to subsonic airflow as it goes through a subsonic nozzle
V increases and P decreases
V increase and P decreases
Brayton cycle consist of
ICCE- happens simulataneously: intake, compression, combustion, exhaust
Otto cycle events occur
is a measurement of thrust due soley from velocity of exit gas
gross thrust 3 things
exhaust only (does not account for Velocity)
accounts for velocity
when does net thrust = gross thrust
when inlet airflow velocity is zero
with an increase in rpm there is an
icrease in thrust,
however at low rpm there is very little increase in thrust with an increase in throttle.
at high rate of revolution an increase in throttle will produce a lot more thrust
which aircraft utilize EPR and rely on the propulsive power of exhaust gases
turbojets and turbofans
propeller or rotor driven aircraft rely on what to indicate power available?
torque meter gauge
what does torque meter indicate
shaft horse power available to drive a propeller or rotor.
What is the Gauge most commonly used by pilot to determine ENGINE PERFORMANCE (not thrust)
in a gas turbine engine the--- ----- and --- build up potential energy. and ---- ---- and --- turn this into dynamic energy
inlet, compressor and diffuser
burner, turbine, and exhaust
inlet ducts are designed to
provide the proper amount of high pressure, turbulence free air to compressor.
inlet ducts are designed to act as a --- but never a ---
2 basic designs for inlet ducts
single and divided
single entrance inlet duct is---
the simplest and most efficient inlet duct design
divided inlet duct design allows it's pilots to
sit lower in fuselage and reduces friction
inlet ducts can be divided into --- and are designed to act as a ----
subsonic and supersonic
the design of the subsonic inlet duct is what shape
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
supply enough air to satisfy the requirements of the combustion section. specifically the compressor increases the airflow from the inlet ducts and directs it to the burners in the quantity and pressure required
centrifugal flow is made up of what 3 main components
impeller, diffuser, and manifold
increases total pressure
inefficient and not used by large aircraft since higher compression ratios means increased fuel consumption.
centrifugal flow compressor find its greatest application on
small engine. because:
are more important than the ability to handle high rates of airflow
typical centrifugal ratios can only attain
dual spool axial flow compressor
greater flexibility and power can be achieved in the axial flow compressor through what is known as dual spool. also known as twin or split spool
dual spool is used to
each spool is divided into its own rotor spools each driven by its own turbine and shaft
low pressure compressor is located at the
front of the compressor section. it will provide intial pressure increase
high pressure compressor is located
after the low pressure compressor ovides further increase to airflow pressure. turned by the high pressure turbine
the high pressure turbine will receive more energy from the combustion section and therefore
it will turn the high pressure compressor at a faster rate.
the blades of a high pressure compressor are ----- than a low pressure compressor?
shorter and turn faster
when a dual axial compressor is used in an engine, higher consumption ratios can be attained with
minimum total compressor weight and frontal areas.
axial flow compressor
advantages and disadvantages
axial centrifugal flow compressor and its main advantage
utilizes the combination of the axial and centrifugal flow compressor. the main adv is the large pressure increase yet small size that is useful on helicopters and other aircraft.
in addition to the rotors and stators it utilizes inlet and exit guide vanes.
inlet guide vanes impart a
swirling motion to air entering.
where is the diffuser located and what does it do?
located after the compressor and prepares airflow for the burner section.
airflow from compressor entering burner section
adds sufficient heat energy to accelerate gases to produce desired thrust.
25% used for combustion
75% used for cooling and flame control.
what contains the combustion chamber
the chamber must allow within limited space
sufficient heat energy to gases passing through the engine to accelerate their mass and produce desired thrust for the engine and power for the turbines.
3 tpes of combustion chambers
can- durable, easy maintenance
disadv- poor use of space, uneven heat distrib, and press loss
annular- uniform heat, better use of spaces, mixing of fuel
disadv- difficult to remove, found in small engine like helos
can annular- even temp distribu, great strength, low press loss
what percent of hot gas is converted from turbine
remaining 25% used for thrust
turbine can be either
single or multistage.
turbine wheels may be operated independently
dual spool compressor will require?
dual turbine driving the compressor via separate shafts.
most highly stressed part of the engine
pic on page 528\
turbine blades are not welded to the rotor shaft but connected with a method called
fir tree, allows them to expand when heated
exhaust section is directly behind the
2 types of exhaust nozzles
convergent- fixed area used in subsonic aircraft
convergent-divergent- supersonic aircraft use a variable feometry convergent-divergent nozzle
what must fighter ac have becvause not efficient enough to produce supersonic flow?
afterburner is used in what types of aircraft?
turbo jet and turbofan
afterburners increase a maximum thrust by
secondary air from the burner section is used for ----- in the after burner section of turbojets
after burner ignition
spark ignition, torch ignition, and -----???
when only a single engine is in use the exhaust nozzle must be --- to allow for the acceleration of gases
compressor is designed to provide
optimum compression ratio
compressor stall indications
rise in ITT
loud noise or bang
2 causes of stall
airflow distortion (most common cause of compressor stall)
the instances when airflow distortion may induce compressor stall include
abrupt change in ac attitude
deficiency of ac veloc because atmosphere
rapid throttle movement
4 mechanical malfunctions that can cause compressor stall
variable inlet guide vane failure
fuel control unit failure
variable exhaust nozzle
purpose of the fuel control unit
determines proper amount of fuel to be introduced in combustion chamber
when are variable exhaust nozzles needed?
when after burners are used
4 system components a pilot can use to reduce the possibility of a compressor stall
variable inlet gu8ide van and stator vane
dual/twin/split spool compressor
variable exhaust nozzle
bleed air valves
installed in middle of compressor and bleed to atmosphere. they provide airflow infront of compressor at low rpm settings
thrust specific fuel consumption TSFC
amount of fuel required to produce one pound of thrust
requirement for fuel is-- at higher alt
adv and disadv of turbojet
lightest specific weight
higher and faster than any othe rengine
disadv- low propulsive eff at low speeds,
relatively high TSFC
long takeoff and roll requirement
simplest form of gas turbine engine.
constructed by air inlet and echuast to basic gas gen.
uses 75% of heat to drive compressor and asseories. other remaining energy is used for thrust by accelerating gases out of exhaust section
cross between turbojet and turboprop.
accelerates large mass of air around gas generator (bypass or ducted air).
fan is connected to front of compressor or ____????
dump sheet exhaust thrust mechanical thrust chart on pg 556
turbofan allows a small or large airmass to bypass gas generator? fan is driven by
relatively large mass which increases thrust
a turbine aft of gas generator turbine is not connected to the gas generator may drive the fan
free or power turbine
another way to drive the fan is through the
gas power turbine
at the same fuel consumption rate which produces more thrust a turbojet or turbofan?
the amount of air that bypasses the gas generator in comparison with the amount of air that passes through the gas generator is called
most fuel efficient engines are those with
a high bypass ratio (this typically yield a lower TSFC)
turbo jet engine bypass ratio
very low, close to 1:1
on a turboprop engine what provides most of the thrust
it imparts a small amount of acceleration to a large mass of air.
90% result of large air mass being accelerated by propeller
3 parts of prop assembly
reduction gear box is located between
the prop assembly and gas generator
reduction gear box assembly converts
high rpm low torque into low rpm high torque.
used on some turboprop engines to transmit and measure the power output from the gas generator to the reduction gear box
torque meter assembly
torque meter assembly components
inner shaft or torque shaft
outer shaft or reference shaft
the prop assembly, redut\ction gear box and torque meter can be attached in what two ways?
front of compressor drive shaft
attached to free power turbine
turbojet accelerates a relative small mass to high speed a turboprop accelerates a large air mass to a
moderate speed. prop assembly maintains propeller at 100% rpm
turboshaft engine is similar to
the turboprop engine.
the difference is the shaft of the free or power turbine is used to drive something other than a propeller such as the rotor of a helicopter. turboshaft engines with a transmission/ reduction gear assembly are used to pwer ships, tanks, trains
turboshaft engine is comprised of 2 basic sections
gas generator and the free power turbine section. Free power turb is mechanically independent of gas generator.
exhaust gases from the gas turbine drive the
power turbine. power turbine is connected to the main transmission (reduction gear box) through a coxial main drive shaft.
where is the main drive shaft located
the front or rear of engines
in a turboshaft the propulsive energy from exhaust is
in other words in order to drive the rotor assembly the free power turbine extarcts all the remaining energy. in a turboshaft engine, all of the pressure energy is converted to SHP
Pascals law states
pressure applied to a confined liquid is transmitted equally in all direction without a law of pressure and acts with equal force on equal surfaces
amount of force per sq inch
push or pull
multiply force to gain mechanical advantage.
main purpose is to multiply force
what is the tradeoff of multiplying force?
linear displacement is what to multiplying force?
the power system includes
fluid supply (reservoir), power supply (pump) and all other components leading up to but not including the selector valve.
2 hydraulic systems
power- operates flight controls only
utility operates flight controls and everything else
eac system has it's own
pump, reservoir pump distribution lines
primary use of resevoir
reservoirs on high performance ac are
power pumps are normall engine driven but may also be electrically driven
pressure regulator valve always works in conjunction with
constant displacement pump
allows one way fluid and prevents back flow. works in conjunction with accumulator
stores enough fluid for 1 time emergency use
ensure delivery of contaminent free hydraulic fluid by preventing dust, grit, and undesirable purities.
pressure limiting device
indicate the amount of pressure in the hydraulic system
pressure switches indicate drop of hydraulic fluid below allowable limits
selector control valves
direct flow of fluid to the actuator and then reservoir once done
convert fluid under pressure into mechanical motion
fuse is used to
limit fluid loss by shutting down the actuator
filter is a
filter and has a bypass
electricity in an airplane is used to
form of electricity that flows in one direction
form of electricity that reverses its current
ac components have 2 parts
has ac generator
generator is a device that
transforms electrical energy input into mechanical energy output
constant speed drive
mechanical linkage between the engine and generator
dc to ac
tranforms ac to dc
DC volatage is primarily used for (battery)
emergency power if genrators fail and for starting aircraft engines.
get 10-12 min of use
an electrical bus is a common
distribution point for electricity
starting acs engines
signal system malfunction to aircrew. the master caution panel provides the pilot with a centralized warning system. immediate attention to warning lights is paramount to flight
aux power unit
small independent gas turbine engine. provides power through the drive shaft and gear box.
dc power is
heavier and requires more maintenance
ability of a fluid to evaporate
fuels volatility rating is
fuel must vaporize and be mixed with a certain percentage of air for it to explode
flash point is inversely related with
the lowest temp of a combustable substance (fuel) that would ignite with a momentary application of a flame is its
flash points for
140F meets naval requi for ship storage (low volatility)
the ac fuel system
must supply clean fuel free from vapor at the proper pressure and flow rates to the engine under all operating conditions.
what is the staring point for fuel
Fuel tank. the tank is a reservoir or holding cell for JP
boost pump is
electrical and submerged in the fuel tank
boost pump purpose
ensures an adequate supply of fuel to engine driven fuel pump which reduces the effects of aeration
critical function of the boost pump is
to prevent aeration of the fuel supply which may result from a rapid pressure change in climb
what is the main pump and what is it's purpose
engine driven pump and provides fuel in excess for the engine and if still available after burner requirements
FCU is the
brain of the engine.it's a hydro-mechanical or electric device that consist of fuel computing or measuring.
PCL position - inputs from aviatior
compressor inlet temp- measures ambient air dense
rpms- compressor speed
turbine temp- prevent turbine damge
fcu takes into account
how much fuel to send to the engine
normal (automatic) operations
fcu should maintain engine stability and within normal ops.
pcl controls fuel flow because the fcu is bypassed
fuel flow gauge is measure in
pounds per hour. measure fuel flow rate
fuel oil cooler/heat exchanger
removes any ice crystals and increases volatility, facilitating efficient fuel ignition. if an engine has fuel oil cooler- fuel will always flow through it
fuel manifold delivers fuel to
the burner section through a series of fuel nozzles
pressurizing and dump valve 2 purposes
drain combustion manifold upon engine shutdown (expect valve to be open) then an electrical system will close valve and pressure keeps it closed. then decides which manifold to go to and how to adjust fuel flow.
which valve is mounted on the body of the engine driven fuel pump?
fuel transfer valve. it opens and permits fuel flow to the afterburner and FCU. the afterburner fcu then meters fuel to the afterburner spray bars. excess fuel is returned to the fuel pump inlet.
normal rated thrust
thrust produced at max continuous turbine temp with no time limits
military rated thrust
thrust produced at max turbine temp for 30 min. limited time
combat rated thrust
thrust produced with the afterburner in operation and not based on turbine temp
primary function of any lubricant
reduce friction caused by metal to metal contact
what type of oil does the military use
important to ensure synthetic oils from different manufacturers are not mixed or used indiscriminately. additionally synthetic oils are not compatible with mineral or petroleum base oils and must never be mixed (the result is a stick mass with poor lube qualkities
we use synthetic because
lower tendency of coking
has strong chem stabilities at higher temp
synthetic oil disadv
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