Term
| Thrust reversers do they make the engine spin backwards? |
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Definition
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Term
| Do turbo props have thrust reversers? |
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Definition
| No, but they can produce reverse thrust by changing the prop blade angle |
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Term
| Pre-exit thrust reversers work how? |
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Definition
reverse the thrust of the
engine by diverting (redirecting) the airflow prior to its leaving
the exhaust or fan nozzle. |
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Term
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Definition
extend into the exhaust
stream after the exhaust gases leave the nozzle. |
|
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Term
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Definition
redirect the fan discharge air,
and are primarily used on High Bypass Ratio
Turbofan Engines. |
|
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Term
|
Definition
redirect the exhaust gases
leaving the gas generator. Turbine Reversers are
used primarily on Turbojet Engines but they are
also used in combination with Fan Reversers on
High Bypass Ratio Turbofan Engines. |
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Term
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Definition
| The design is usually a Post-exit Reverser. During operation, two large deflectors are deployed into the exhaust stream The exhaust gases are redirected either vertically or horizontally based upon the installation |
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Term
| Explain the 737-300 thrust reverse system |
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Definition
| The 737-300 reverser system is a Pre-exit, Fan type system utilizing two translating sleeves on each engine. During reverser operation, the sleeves move aft exposing fixed cascade vanes and pulling (mechanically connected) blocker doors into place.the blocker doors redirect air forward through the fixed cascading vanes |
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Term
| What do blocker doors do? |
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Definition
| Redirect the exhaust air forward through the cascade vanes |
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Term
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Definition
| "Ice cube trays" fixed and angle discharged air forward to produce reverse thrust |
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Term
| 2 types of thrust augmentation |
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Definition
| Water injected, afterburner |
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Term
| How does water injection increase thrust? |
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Definition
( increases air density)
restore the thrust (power) that would normally be lost during high density altitude operations.
Replace "Wa" losses, due to decreases in air density in relation to high altitudes or high temperatures. |
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Term
| How does afterburner increase thrust? |
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Definition
(Up to 400%more fuel to inc thrust 60%)
Operation - because 75% of the air processed by the gas generator is not used in the combustion process, large amounts of oxygen remain in the exhaust gas stream. Therefore, large amounts of fuel can be injected into the exhaust gases and burned. This increases the temperature of the exhaust gas stream and results in an increase in velocity of the exhaust gases (V2), thus increasing thrust. |
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Term
| Advantages / disadvantages if water injection thrust augmentation |
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Definition
Adv.- Restores (or increases 10-30%) power for approximately 2 minutes for takeoff
Dis.-Heavy - 1200 gallons of water, plus tanks, pumps,controls, etc.
-Compressor blade erosion.
-Thermal shock.
- De-mineralized (distilled) water is required to minimize deposits on compressor blades. |
|
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Term
| Advantages / disadvantages of afterburners |
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Definition
Adv.- No TIT Limits. The temperature is only limited by the amount of air that is available to burn the fuel.
-Provides extra thrust for takeoff, climb, and short duration bursts of speed without the need to install larger (heavier) engines with larger frontal areas.
Dis.- VERY HIGH SFC! |
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Term
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Definition
| Kerosene type, gasoline type |
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Term
| What is kerosene type gas and gasoline type made of? What makes them differ? |
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Definition
Turbine engine fuels are blended from hydrocarbon
fuels, derived from refined crude oil. They differ by the different boiling points, kerosene is "more refined" |
|
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Term
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Definition
| have lower flash points (-35oF) and low freezing points (-65oF) They provide good cold weather and inflight starting characteristics but are more dangerous to store and handle. |
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Term
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Definition
| have a higher flash point (100oF) and higher freezing points (-40oF). (Starting characteristics are less critical with modern high energy ignition systems) |
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Term
| Can you use any fuel in any engine? |
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Definition
| "Can use av gas in a jet engine in emergency but will need to overhaul the engine, can't use jet fuel in a piston engine will clog every thing " |
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Term
| Military designations if fuel |
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Definition
JP-4 Same as Jet B with a military
additive package*
JP-5 Very high flash point 140oF
designed to be carried on aircraft
carriers and mixed with avgas
to provide JP-4 characteristics
JP-7 SR-71 Very low freezing point
below -65oF
JP-8 Same as Jet A-1 with a military
additive package |
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Term
| Civilian designation of fuel |
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Definition
Jet A Kerosene type with freezing
point -40oF
Jet A-1 Kerosene type with freezing
point -58oF
Jet B Gasoline type with a freezing point
well below kerosene |
|
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Term
| Fuel system name for opening and closing the main fuel valves. |
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Definition
The “Start Levers” are
actually fuel valve “open/
close” levers. They open
and close the same valve as
the fire handles.
They are referred to as
start levers because they
are used by the crew to
open the fuel valve during
engine start. |
|
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Term
|
Definition
Centrifugal Boost Pumps
Gear Type High Pressure Pumps |
|
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Term
|
Definition
| Fuel nozzles are located in the combustion chamber and provide atomization of the fuel. The nozzles can be relatively simple, and simply spray fuel into the burner. Most are complex and vary the spray pattern based upon rpm (fuel pressure) in order to help control the flame pattern. Require 800psi or greater provided by the fuel pumps |
|
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Term
|
Definition
Simplex- point and spray
Duplex- controls the shape of the out put(primary and main) two cones of spray |
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Term
|
Definition
| The fuel manifold is drained automatically during the shutdown cycle to prevent any fuel from leaking into the burner section and causing a fire. The manifold drain valve is combined with the fuel pressurization valve and referred to as the P&D valve (pressurization and dump valve). Some manufacturers utilize an electric valve referred to as a drip valve. |
|
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Term
| Fuel pressurized valve or P&D valve |
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Definition
| Fuel pressurization valves prevent fuel flow to the nozzles until sufficient fuel pressure is available to properly atomize the fuel. The valves can be located in the nozzle or in the fuel manifold. |
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Term
|
Definition
- Contaminates in fuel can clog the small passages and orifices in fuel controls. Contaminates can take the form of rust, scale, sand, dust, metal, and rubber particles.
-In addition, microorganisms can clog filters and controls.
- Several filters are usually employed throughout the system. |
|
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Term
| Fuel filter micron ratings |
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Definition
| The lower the rating the better! About 40micron for low pressure systems and about 5 micron rating for a high pressure system |
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Term
|
Definition
Compressor bleed air is used in some systems to heat the fuel and prevent ice crystals from forming due to the water in the fuel.
Fuel/oil heat exchangers can be utilized to accomplish the same task. Many installations take advantage of the heat exchangers to cool the engine oil. |
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Term
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Definition
| In order to measure fuel flow in pounds per hour and display this information in the cockpit, most systems incorporate a transducer between the fuel control and the manifold. |
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Term
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Definition
| The lubrication system carries oil to-and-from the components of the engine that require lubrication and oil cooling. |
|
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Term
|
Definition
Dry sump-All modern turbine engines use a
Wet sump- where recip. Engines use a wet sump |
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Term
| Lubricating pressure pumps |
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Definition
Gear type
Gerotor type
-Pressure pumps force the oil from the tank, through the lubrication lines and cord passages to the bearings and gears that require lubrication and cooling.
-Nominal operating pressures are between 50 and 100 psi.
-The pump is turned by a spline drive from the accessory section of the engine.
- Most bearings are lubricated by a "jet" of oil sprayed on the bearing. |
|
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Term
|
Definition
| The scavenge pump(s) drain oil from the bearing and gear areas, and returns the oil to the tank. This action provides positive flow of the heated oil away from the lubricated areas and insures a continuous "closed loop" system. |
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Term
|
Definition
| Labyrinth oil seals function by a differential in pressure…bleed air pressure vs. oil pressure. (more in a minute). Because of the entrained air, scavenge pumps must have a much higher capacity (volume) than pressure pumps. |
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Term
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Definition
Filters capture small foreign particles that are suspended in the oil. Most filters are rated at approximately 50 microns.
Also integrated bypass valve invade it becomes clogged |
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Term
| Lubricating oil types / mil spec/ types |
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Definition
Type 1 -
Mil-L-7808
Aeroshell 300
Mobil Jet Oil I
Type 2-Mil-L-23699
Aeroshell 500
Castrol 5000
Mobil Jet Oil II
Exxon (Chevron) 2380 |
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Term
| Type 2 oil specs compared to type 1 |
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Definition
1. Higher Viscosity and Viscosity Index
2. Higher load-carrying characteristics
3. Better high-temperature-oxidation stability
4. Better thermal stability |
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Term
| What is synthetic lubricants (oil) made of? |
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Definition
All modern turbine engine oils are synthetic.
Synthetic lubricants are formulated from animal tallow or vegetable oils (castor bean) or from hydrocarbon synthesis.
Current lubricants are classified as Type I or Type II oils.
Capable of operating from about 60-450 degrees F |
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Term
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Definition
| Viscosity - The ability to flow at a given temperature. |
|
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Term
|
Definition
Viscosity Index - The affects of temperature on viscosity
(high index = low rate of change). |
|
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Term
|
Definition
| Pour Point - The effect of temperature on the ability to pour. |
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Term
|
Definition
| Flash Point - The lowest temperature at which the vapors given off, will ignite. |
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Term
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Definition
| Fire Point - The lowest temperature that the oil will ignite and burn for a minimum of 5seconds. |
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Term
|
Definition
| Volatility - The ease with which the liquid is converted to a vapor state. |
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Term
|
Definition
| Acidity - A measure of corrosiveness. |
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Term
|
Definition
| Oil Foaming - A measure of the resistance of the oil to separate from entrained air. |
|
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Term
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Definition
| Rubber Swell - A measure of how much the oil will cause swelling in a particular rubber compound. |
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Term
| Oxidation and thermal stability |
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Definition
| Oxidation and Thermal Stability - Measures of how well an oil can resist the formation of hard carbon and sludge at high temperatures |
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Term
|
Definition
| Corrosivity to Metals - The corrosivity of the oil on a strip of polished copper (or other specified metal). |
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Term
|
Definition
| Gear and Pressure Tests - The ability of the oil to carry a load. |
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Term
| Carbon or residual coking |
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Definition
| Carbon Residue or Coking - A measure of the amount of carbon residue remaining in an oil after subjecting it to extreme heating in the absence of air. |
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Term
| Why do modern turbine engines need a different ignition system than a recip. Engine? |
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Definition
The air/fuel mixture in a turbine engine is very cold and considerably over-lean (too much air in relation to fuel). The mixture is rushing by the igniter plug at high velocity. These difficult conditions are amplified at high altitudes.
The ignition system must bring the air/fuel mixture to a high temperature during the brief instant that it passes by the igniter plug. |
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Term
| How does a modern turbine ignition work? |
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Definition
Capacitor-type Systems
Modern Gas Turbine Engines utilize High Energy Capacitor-type ignition systems.
The capacitor type ignition system provides a high voltage and exceptionally hot spark that covers a large gap. |
|
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Term
| How do you increase the temp of the spark from the ignition system? |
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Definition
| The temperature of a spark can be increased either by increasing the energy level (J) or shortening the duration (t). |
|
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Term
| What formula relates temp of spark from the ignition and the system |
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Definition
|
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Term
| Capacitor types in ignition systems |
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Definition
1. High-voltage - 5000v
2. Low-voltage - 1000v
Utilize a special "self-ionizing" igniter plug. |
|
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Term
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Definition
| Igniter Plugs must accommodate a very high current and are subject to rapid igniter-electrode erosion. This is not a major problem since igniters are only used for starting. However, this can lead to frequent igniter failure if the ignition system is left on any longer than necessary. |
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Term
| Function of the starter system |
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Definition
| The function of any starting system is to accelerate the engine to the point where the turbine is producing enough power to continue the engine's acceleration. This point is called the self-accelerating speed. |
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Term
|
Definition
-Electric Motor Starters
-Starter-Generators
-Pneumatic (air-turbine) Starters
Air-impingement Starter
-Gas Turbine Starters
-Hydraulic Starters
-Cartridge (solid-propellant) Starters
- Form of Pneumatic (15s) |
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Term
| Can starters turn the engine? |
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Definition
NO!
- The starter turns the engine “backwards” via the
accessory drive gears to the turbine shaft. The starter is not
really turning the engine “backwards” - by backwards, I mean
that the accessory drive is turning the engine, instead of the
engine turning the accessory drive.
- The exception is the air impingement starter that directs air
directly onto the turbine blades. |
|
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Term
|
Definition
Starter-Generators can function as either a starter or a generator
but, it can not do both simultaneously. |
|
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Term
|
Definition
-No Start
-Hot Start
-Hung Start
Starting problems may be caused by abnormal fuel flow, starter valve malfunction, low duct pressure - high density altitude, high tailwinds, or no ignition. |
|
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Term
| Starter duty cycle / cold weather starting |
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Definition
•First attempt: 2mins on, 20sec off.
•Second and subsequent attempts: 2mins on, 3mins off.
Do not re-engage engine start switch until N2 is below 20%.
-During cold weather starts, oil pressure may temporarily exceed the green band or may not show any increase until oil temperature rises. No indication of oil pressure by the time idle RPM is achieved requires an immediate engine shutdown.
-At low ambient temperatures, a temporary high oil pressure above the green band may be tolerated. |
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Term
| Aborted engine start criteria |
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Definition
•No N1 (before start lever is raised to idle).
•No oil pressure (by the time the engine is stable).
•No EGT (within 10 secs of start lever being raised to idle).
•No increase, or very slow increase, in N1 or N2 (after EGT indication).
•EGT rapidly approaching or exceeding 725˚C.
An abnormal start advisory does not by itself mean that you have to abort the engine start. |
|
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Term
|
Definition
Follow all steps / checklists
Monitor systems to make sure everything is working properly |
|
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Term
| What significance does turning on the rotating beacon have with ground crew? |
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Definition
| Shows them you are about to start the engine |
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