Aircraft Powerplant

Powerplant

Refers to a complete system that develops power for an aircraft, which provides thrust.

First law of motion

A body at rest will remain at rest and a body in motion will tend to remain in motion; unless acted upon by an outside force.

Second law of motion

When a body's velocity changes under an impressed force, the force is equal to the product of the mass of the body and the resulting acceleration.

Third law of motion

For every action, there is an equal and opposite reaction.

False

True or false? The jet of gasses pushes on the atmosphere behind a gas turbine engine to thrust the aircraft forward.

Accelerating the air through the engine

A gas turbine engine produces to thrust by:

Otto cycle

An aircraft reciprocating engine uses four piston strokes in its operating cycle called the:

Brayton Cycle

The operating cycle of a gas turbine engine consisting of the following 4 simultaneous events: intake, compression, combustion, exhaust.

Intake

Compression

Combustion

Exhaust

What are the four stages of the Brayton cycle?

Intake

Which cycle draws air into the engine and directs it into the compressor?

Compression

Which cycle compresses and directs air into the combustion section?

Combustion

Which cycle introduces fuel and ignites it, creating hot gasses that are directed into the turbine?

Exhaust

Which cycle expels the hot gasses out of the engine?

Inlet

Compressor

Combustion

Turbine

Exhaust

Accessory

What are the six major sections of a gas turbine engine?

Cold and Hot sections

What are the two areas of a gas turbine engine (not to be confused with the six sections)?

Intake section

Compressor section

Accessory section

Which sections are included in the cold section?

600 degrees F

What temperature can be reached in the cold section due to the action of compressing the air?

Combustion section

Turbine

Exhaust section

Which sections are included in the hot section?

1800 degrees F

What temperature may be exceeded in the hot section?

Inlet section

Provides a uniform, turbulence-free supply of air to the compressor throughout all operating conditions.

Compressor speed (RPM)

Forward speed of the airframe (ram effect)

Density of the ambient (surrounding) air

What three factors affect the amount of air passing through the inlet?

Compressor section

Which section's primary function is to increase the pressure of the mass of air entering the engine inlet and to discharge it to the combustion section at the correct velocity, temperature, and pressure?

To supply engine bleed air

What is the secondary function of the compressor section?

Bernoulli's Principle

As the velocity of a fluid (or air) is increased, a corresponding drop in pressure will occur.

Rotor

Which component accelerates the air that is drawn into the compressor?

Stator

Which component decelerates the air in the compressor, producing an increase in air pressure?

Reducing the length of the stator and rotor blades

Increasing the diameter of the disk that the blades are attached to

What two methods are used to restrict the area of each following stage of compression and maintain velocity of airflow?

Axial

Centrifugal

What are the two types of compressors used in turbine engines?

Axial-Flow Compressor

Which compressor type allows air to move in a relatively straight path along the engine axis?

Rotor assembly

Stator vanes

Compressor casing

What parts make up an axial-flow compressor?

Fixed and variable

What are the two types of stator vanes?

Inlet Guide vanes

Mounted forward of the first rotor, they direct the air from the inlet into the first rotor blades at the proper angle.

Compressor Casing

Forms the outer housing of the compressor section, supports the stator vanes, and encloses the rotor assembly.

One set of rotor blades and on set of stator blades

What makes up a single stage of compression?

Axial-flow compressor

The following are advantages of what compressor type?

-High peak efficiencies from ram air, created by its straight through design

-High peak pressures attained by additional stages of compression

-small frontal area, resulting in low drag

Axial-flow compressor

The following are disadvantages of what compressor type?

-Difficult to manufacture

-High cost

-Relatively high weight

-high starting power requirements

-Low pressure rise per compressor stage

-Compressor stall

1.27:1

What is the pressure rise ratio per compressor stage in an axial-flow compressor?

Centrifugal compressor

Uses centrifugal force to compress the air.

Centrifugal compressor

The following are advantages of what compressor type?

-High pressure rise per stage, up to 8:1

-Good efficiency of compression over a wide range of rotational speeds

-Simple to manufacture

-Low cost

-Low weight

-Low starting power requirements

Centrifugal compressor

The following are disadvantages of what compressor type?

-Large frontal area

-Use of more than two stages is not practical because of energy loss between stages

Impeller

What part in a centrifugal compressor rotates at a high rate of speed producing the centrifugal force to accelerate the air?

Diffuser

What part in a centrifugal compressor is an annular chamber that has a number of vanes forming a series of divergent passages into the manifold?

Compressor Manifold

What part in a centrifugal compressor directs the flow of high-pressure air from the diffuser into the combustion chambers?

Combustion section

Which section adds heat energy to the gasses flowing from the compressor, expanding an accelerating them?

Outer casing

Inner casing

Perforated combustion liner or can(s)

What is the combustion section made of?

Primary air

Secondary air

The air flowing from the compressor separates into what two flows?

Primary air

One of two flows from the compressor, it supports combustion of the fuel.

25%

Approximately how much of the total air from the compressor is used for primary air?

Secondary air

One of two flows from the compressor, it provides a cooling air blanket between the flame and the liner to prevent the flame from contacting any metal.

75%

Approximately how much of the total air from the compressor is used for secondary air?

Combustion liner

A metal structure that directs primary air, secondary air, and combustion gasses (heat energy) through the cobusation section and directs these gasses into the turbine.

Annular

Can annular

Reverse flow annular

What are the three different types of combustion chambers used in Coast Guard powerplants?

Annular cobustion chamber

Made up of a number of smaller assemblies welded together to form a cylindrical, one-piece liner. Used primarily with the axial compressor.

Structural problems due to thermal expansion and contraction in larger liners

What is one major disadvantage of an annular combustion chamber?

Can annular combustion chamber

Consists of a number of individual combustion can liners mounted around an inner casing and surrounded by an outer casing.

Greater structural stability and lower pressure loss

What two advantages does the can annular combustion chamber have over the annular and can type?

Reverse flow annular combustion chamber

Reverses the direction of the airflow through the engine in the combustion section.

Smaller footprint

What is the advantage of the reverse flow annular combustion chamber?

Turbine

Extracts heat energy from the expanding gasses to drive the compressor.

Rotors and stators

The turbine assembly is made up of:

Gas Generator (NG or N1)

The forward turbine which connects to the compressor by a shaft and extracts power to turn the compressor.

Free turbine/Power turbine (NP or N2)

Used to drive the powertrain system. Works independently from the gas generator section.

Gas generator

Which turbine will fluctuate in speed to meet power demands?

Exhaust Section

Which section directs the flow of hot gasses from the turbine rearward in a manner to prevent turbulence and to increase the exit velocity of the gasses?

Outer duct

Inner cone

What are the two components of the exhaust section?

Accessory section

Which section provides space for mounting and driving the accessories necessary for the operation and control of the engine?

Fuel control

Fuel pump

Oil pressure pump

Oil scavenge pump(s)

Starter

Tachometer generator

Which components mount on most engine accessory stations?

Rotating the compressor

How do gas turbine engines start?

Direct Current (DC) electric motor

Starter/Generators

Air turbine type starters

What basic types of starters are currently used for gas turbine engines?

Direct current electric starter

Mostly used on small turbine engines, such as Auxiliary Power Units (APUs) and some small turboshaft engines.

Starter Generator

Similar to a DC electric starter, except they can be used as a generator after the engine has reached a self-sustaining speed.

Air turbine starters

Designed to provide high starting torque from a small, lightweight source.

Ground-operated air cart

Auxiliary Power Unit (APU)

Cross-bleed start from an engine already operating

What are three ways that an air turbine starter can be supplied with air?

Fuel syste

Provides a metered flow of fuel under pressure for engine combustion regardless of aircraft altitude or attitude.

Fuel pump

Delivers a continuous supply of fuel to the fuel control via the fuel filter(s) at a quantity in excess of the engine demands.

The engine

What drives the fuel pump?

Fuel filter(s)

Provides protection from contaminates (particles) in your fuel.

Fuel control

A fuel-metering device that meters the proper quantity of fuel fed to the fuel nozzles in the combustion section.

Fuel nozzles

Inject fuel into the combustion chamber in a precise spray pattern for rapid mixing with the air for combustion.

Flow Divider

Found within duplex fuel nozzles, it creates a primary and secondary/main fuel supply. It does this by using a spring and valve system.

Fuel manifold

Carries fuel from the fuel control to the flow divider and the fuel nozzles.

Combustion drain valve

Drains residual fuel from the combustion section to prevent an accumulation of fuel.

"Hot start"

The resulting over temperature that occurs during the following start attempt when fuel has been allowed to accumulate in the combustion section is commonly referred to as a:

Prevent metal to metal contact

Remove heat from high temperature areas

Helps to remove impurities fro the engine as the oil circulates through the engine

What are three functions of the oil system?

Dry sump

Wet sump

What are the two types of basic oil systems?

Dry sump

Which oil system is common in gas turbine engines?

Dry sump oil system

The oil supply in this type of system is stored in a tank separate from the engine.

Oil is removed fro the heat of the engine when in the tank

Oil passes through an oil cooler on the way back to the tank for increased cooling

Large quantity of oil is possible in the tank

Positive oil supply from tank during unusual flight attitudes

What are some advantages of the dry-sump oil system?

Oil pressure pump

Supplies a continuous flow of oil under pressure to the engine bearings, seals, and gears for lubrication and cooling.

Oil scavenge pump(s)

Picks up oil from the engine and returns it to the oil tank.

Magnetic plugs

Removes ferrous metals from the oil stream, but does not provide a means of indicating excess metal.

Chip detectors

Completes a circuit with ferrous metals picked up from the oil stream which turns on an indicator light for aircrew notification.

Carbon rubbing seal

Used in a bearing cavity to seal oil against a rotating shaft.

Labyrinth seal

Uses bleed air from the engine compressor to form a positive oil seal.

Turboshaft

Turboprop

Turbofan

What three types of gas turbine engines are used as powerplants on Cost Guard aircraft?

Turbojet

Which type of gas turbine engine is not used in Coast Guard aircraft?

Turboshaft engine

A gas turbine engine that delivers power through the shaft to operate something other than a propeller.

Turboprop engine

An application of the gas turbine engine driving a propeller through a reduction gear assembly.

High takeoff thrust for short field takeoffs

Subsonic cruising fuel economy

Short landing distance

What are some of the advantages of the turboprop engine?

Turbofan engine

A ducted multi-bladed propeller driven by a gas turbine.