MOD 3-4 Flashcards
what is modular designed
The ability to replace parts of the engine.
where we convert the ram pressure to static pressure without loss of total pressure
Divergent duct
ram recovery point is?
when the pressure rise due to ram effect is going to increase the pressure at the face of the compressor is equal to the ambient pressure
what is duct pressure efficiency ratio?
ability of the duct to convert kinetic energy to potential energy (velocity to static pressure) whit out loss in total pressure.
which is considered the cold section of the engine ?
inlet and compressor
which is considered the hot section of the engine
when gases leave the diffuser combustion
purpose of the combustion section ?
place for mixing fuel and air for combustion, as well as mixing and expansion gases, full energy is converted to heat and velocity. Pressure held constant
performance requirements
-high combustion efficiency -stable -uniform temp distribution -easy starting -small -low smoke -low carbon
why the air velocity most be slow at the combustion section?
So that the flame is not moved toward the turbine (high ITT) or blown out completely (flame out)
what is flame out ?
is when the air is moving so fast that it blows out the flame
why the pressure must be constant on the combustion section ?
high pressure flows to low pressure so if there was a pressure rise it would cause a surge which would cause a stall
combustion section components
-case -perforated inner liner -fuel metering orifice -ignition source -drain
3 .types of combustion sections
- Can 2.Annular 3. Can-annular
what means reverse flow ?
air flow changes direction 2 times on the combustion section
can type advantages ?
-Each can, may be removed without separating the engine cases - Each can has it’s own fuel/air pattern control.
what is primary air
-25%-33% of air trough the engine -swirls upstream -low velocity (stabilization zone) -turbulence(just at the head of the combustion liner )
what is secondary air
67% to 75% of the air going through the engine • Dilution air – big holes • Cooling air – small holes • Film cooling • Cools the flame – is heated (energy transfer) • Presents a uniform flame front (temp. and press.) to the first stage turbine nozzle
What is an advantage of the modular design on a gas turbine engine?
Modules can be replaced individually. The engine is not required to be removed and sent to an overhaul shop for repair
What is the cross-sectional shape of an inlet duct?
Divergent
The inlet duct converts energy in the gas, causing the _____to decrease and the _____to increase
velocity, static pressure
One function of an inlet duct is to deliver and even ______ and _____ to the face of the compressor
pressure, velocity
The air pressure in the inlet duct at ram recovery point is the same as _____
Ambient pressure
If the duct pressure efficiency ratio is1:1 or 100%, the _____ will be the same at the inlet as it is at the outlet.
total pressure
The manufacturing and repair instructions for an inlet duct will is the responsibility of the _____ manufacturer
airframe
The bell mouth inlet duct is used primarily for _____
testing engines in a test cell
The air coming into the bell mouth inlet duct sees _____ % of the orifice/inlet size
100
In addition to having the same function as a sub-sonic inlet duct, the supersonic inlet duct has the additional function of _____.
Slowing the velocity of the air to sub-sonic speeds
The compressor is considered part of the _____ section
cold
On the Brayton Cycle graph, the compressor is described by line from point _____ to _____
A-B
If the engine has a low pressure compressor (N1) and a high pressure compressor (N2), which one is shown on the Brayton Cycle graph?
Line A to B represents all the compressors if there is more than one rotating group (N1 and N2)
List the 3 types of compressors
axial centrifugal axial-centrifugal
mayor parts of the compressor
impeller ,diffuser, manifold (The impeller is what puts energy (velocity) into the gas)
What are the 3 major parts of a centrifugal compressor?
Impeller•Diffuser•Manifold
List 2 advantages of a centrifugal compressor
Simplicity –easy to manufacture•Rugged (compared to axial compressor)•Low cost (relative)•Less FO
List 1 disadvantage of a centrifugal compressor
About 80% efficient•Limited stages (2)•Large frontal area
Why is there a limit of 2 stages of compression when using a centrifugal compressor?
Limited to 2 stages by the law of diminishing returns with more than 2 stages the loses will equal the gain
Why does the static pressure rise as the gasses travel through the centrifugal compressor impeller?
add velocity at the same time that is converting the velocity in static pressure
Indications of Stall
Vibration•Slow power lever response•Mild stall –no loud noises, maybe a rumbling sound•Explosive stall (loud bang) –can cause extensive damage
What are the 2 major parts of an axial compressor?
rotor(add energy and converts it) and stators (converts energy)
AoA is affected by ?
engine RPM air flow velocity FCU acceleration rate
The axial compressor is limited to a_____ compression ratio per stage. This happens when the compressor is running at the most efficient RPM it was designed to run. This is close to 100% RPM.
1.2:1
preventing stalls
lower angle of attack (derating the engine) use a bleed valve employ a two spool rotor variable IGV and variable vanes vary the exhaust nozzle size
what is flat rate ?
engine performance limit by thrust, the manufacture will determine that , because we don’t want to exceed ITT or RPM
what kind of performance limitations an engine has and must never exceed
-wheels speeds -Turbine temperature -torque or thrust for which the AC was certified (flat rate, airframe limitations)
What is Standard Day Barometric Pressure: _____ OAT: _____ Altitude: _____
29.92 inches of mercury 15 degrees Celsius at sea level
As temperature increases, density __________
decreases
As pressure decreases, density
decreases
In the stratosphere the temperature stabilizes at____ so even as altitude_____, the temperature does not change (assuming Standard Day)
-69.7˚F - increases
The profile of the exhaust nozzle is a convergent duct so static pressure_____________________________
decreases and velocity increases
As the subsonic gases exit the nozzle (convergent duct), the static pressure will___________________________ until sonic velocity is reached in the throat of the nozzle.
decrease and the velocity will increase
As the subsonic gases exit the nozzle (convergent duct), the static pressure will___________________________ until sonic velocity is reached in the throat of the nozzle.
decrease and the velocity will increase
on the thrust formula is the aircraft is not moving, nozzle not ___________
choked
on the thrust formula is the aircraft is moving, nozzle is ___________
choked
When is a nozzle considered a choked nozzle
As the subsonic gases exit the nozzle (convergent duct), the static pressure will decrease and the velocity will increase until sonic velocity is reached in the throat of the nozzle.
How does atmospheric temperature affect thrust?
Higher density = higher mass airflow Lower density = lower mass airflow
How does atmospheric pressure affect thrust?
As the pressure increases, the temperature increases reducing the density of air entering into the engine thrust decreases
Ram pressure_______ thrust, ram temperature _______ thrust
increases, decreases
If the result of ram pressure rise is added to the ram temperature rise, the resultant is called the
ram effect
Increase in altitude results in a decrease in ______________
temperature and pressure
Why does the thrust decrease at a faster rate as aircraft altitude increases above 36, 089 ft?
because less density less drag
Fg = Fr = Fn =
-gross thrust -ram drag - net thrust
what is a RPM speed indication
eddy current, probe produces a magnetic field using aircraft electrical power, passing blade gear tooth disrupts the field magnetic lines of flux (phonetic wheel)
how a monopole indicator works?
similar to eddy current has a permanent magnet instead to used the power of the aircraft
what is a phonic wheel
is a gear that does not drive anything but gives us the pulse to a speed indication
tachometer generator parts ?
-generator -driven from accessory drive -indicator -synchronous motor and flux coupling
What is EPR ?
engine pressure ratio or tail pipe ratio is the ratio between Pt2 ( face of the compressor ) and Pt7 (pressure total tail pipe)
what is IEPR
Integrated EPR average of fan exhaust pressure and gas generator gas pressure , divide by the Pt2
exhaust section purpose
• Imparts a high exit velocity to the exhaust gases as they exit the engine • TF and TJ engines – Choked nozzle at high RPMs
A convergent-divergent exhaust nozzle causes an increase in ______by increased acceleration of the exhaust gases.
Thrust
Forces acting 90° to the walls of the duct resulting in the increase __________-
Thrust
purpose of the nozzles of the Vectored Thrust
the four controlable nozzles allow the thrust produce by the turbo fan engine to vectored downward to takeoff and aft for forward flight
name the parts of the exhaust
A.Exhaust cone
B. exhaust collector
C.strut
The exhaust collector bolts to the engine housing just aft of the turbine. The tail pipe bolts to the ring around the collector
A convergent-divergent exhaust nozzle causes an increase in thrust by increased acceleration of the exhaust gases.
what is A, B and C
A. Subsonic convergent section
B.Supersonic Divergent Section
C. gas attains sonic velocity
Characteristics of thrust reverses
- For use on turbo jet and turbo fan engines
- Deployed on the ground
- Slow aircraft
- Reduces wear on the brakes
- Not always made by the engine manufacturer. Can be a 3rd party manufacturer but fitted to specific engines
Thrust reversers types?
Pre-Exist
Post-Exist
what kind of thrust reverser is this one ?
Pre- Exist
what kind of trust reverse is this ?
Post-Exist
Target type
what kind of thrust reverse is this?
A clamshell-type thrust reverser.
what Reverser deploiment conditions have to be met in order to deploy thrust reversers?
- Weight on landing gear (squat switch)
- Power lever – idle
Thrust Augmentation types
- Afterburner – re-heat, Take-off or increased thrust requirement
- Water or Water/methanol injection • Take-off only
Characteristics Thrust augmentation afterburner
Add fuel after the last turbine • 300% increase in fuel burn – 50% increase in thrust • Works like a ram jet • Usually has a variable geometry exhaust nozzle • Open when accelerating to full power, then restricts to choke the nozzle after A/B initiated
Thrust augmentation Water or Water/Methanol Injection characteristics
-Used for take-off only
- Injected in the inlet, compressor, or diffuser
- Methanol keeps water from freezing (if stored during flight)
- Water only (consumed on take-off then remainder is jettisoned)
On the Brayton Cycle graph, the exhaust section of a turbofan or turbojet engine is represented by a line that goes from point _____ to point _____
D TO E
when we use Thrust augmentation ?
when we need a lot of performance and performance recovery (like hot day, not enough, density air is really low orwhen need to get to sonic velocity )
Noise comes from the _____ and the ____
noise suppresion is done by ?
Inlet , exhaust
Fan Noise • Fan design can reduce noise • Inlet can be lined with sound absorbing material
• Exhaust noise • Reduce shear zone differential
The cone that follows the last turbine, makes a _____ duct inside the exhaust duct.
divergent
When is water or water/methanol used?
take off
An afterburner thrust augmentation systems injects extra fuel. Where in the engine is the fuel added?
Add fuel after the last turbine
How does a turbofan engine reduce the noise produced by the exhaust of the engine?
- Fan design can reduce noise
- Inlet can be lined with sound absorbing material
- Reduce shear zone differential (exhaust)
The turbine section of the engine is represented by a line from point _____ to point _____ of the Brayton Cycle graph.
C to D
The profile shape of the turbine vane is a _____ duct.
convergent
The purpose of the turbine vane is to increase _____ and decrease _____
velocity ,pressure
The purpose of the turbine is to _____
extract energy to drive the compresor or in turbo prop/shaft to run the gearbox
The combination type turbine blade has the _____ section at the tip and the _____ section at the root
reaction,impulse
reactio= extract velocity and pressure
Impulse = extracts velocity only
If a turbine disk has 50 blades, and extracts 750 Hp out of the gasses, how much does each blade extract?
15 hp= (750/50)
If there are 3 turbine disks, and they extract a total of 750 Hp out of the gasses, how much does each disk extract?
same amount each disk
The _____ type of turbine shroud has the least amount of losses due to clearances
rotating (more mass, less losses)
.Refer to the vector diagram that describes the velocity of the gasses at the root and the tip of the turbine blade, why is U for the root of the blade, less than U for the tip of the blade?
vane assembly converts more pressure to velocity at the root of the blade than at the tip.
Turbine Engine Pneumatic Systems • Provide a source of air for:
– Cabin pressurization – Cabin heating and cooling – Engine and airframe anti-ice systems – Labyrinth seals – Internal cooling – Fuel control (FCU)
Pneumatic System Operation
Shut-off valves control the extraction of bleed air from the compressor (this is a different valve from the compressor bleed valve that is used to prevent compressor stall.
Oil Systems Purpose:
Supply oil under pressure to - clean - cool - lubricate
Typical Oil System
Tank/sump/reservoir • Pump • Relief valve • Filter • Oil pressure indication • Nozzles and jets • Scavenge pump • Chip detector • Oil cooler • Tank/sump/reservoir
purpouse Chip Detectors
Indicate when ferrous metal is present in the oil • Impending failure indicators - ΔP indicators – Button (usually red) pops out when a differential pressure across a filter exceeds a threshold pressure
Starting Systems Purpose:
To accelerate the engine to the point where the turbine is producing enough power to continue the engine’s acceleration up to idle speed
whats the Length of Start Cycle
Starter continues to accelerate the engine even after light off, until the engine has selfsustaining acceleration to idle • A “hot start” or a “hung start” could result if the starter is disengaged too soon or if the battery voltage is low (electric starter)
Types of Starters
Electric motor • Electric motor/generator – Starter/generator • Pneumatic or air turbine • Gas turbine starter (small turboshaft that is used to start the bigger engine) • Hydraulic motor starter
What is the purpose of a gearboxon a gas turbine engine?
Provide a place for mounting accessories for operation and control of the engine and airframe systems
List 4 things that the pneumatic system provides air for.
Cabin pressurization – Cabin heating and cooling – Engine and airframe anti-ice systems – Labyrinth seals – Internal cooling – Fuel control (FCU)
List the 2 types of spark igniters used in turbine engines
spark type
glow plug type
What is the purpose of the engine oil system?
lubricate
cool down
clean
In a typical engine oil system, what is the component that follows next in line to the scavenge pump(s)?
What component protects the engine from oil starvation, if the oil filter completely plugs?
bypass valve
A labyrinth seal has oil pressure on one side and air pressure on the other. Which pressure is higher? Why?
air pressure is higher and hight pressure follows low pressure keeping the oil on the other side
What is the purpose of a chip detector in an engine oil system?
detect any ferrous material
.What could cause a “hung” start?
if we turn off the starter too soon before gets to the sustaineble acceleration we can get a hung start, fire addinf fuel but the engine is not acceleration
.What does self-sustaining acceleration mean?
when the engine is capable to mantain idle accelation
.What is the difference in the drive mechanism for a starter motor, and a starter/generator?
3.How many amps of power would a pneumatic starter draw when it is initially engaged?
1500 amps
