Chapter 3 - Turbine Engines

Question 1

What are the four types of Jet Propulsion?

Answer 1

Rocket

Ramjet

Pulsejet

Gas Turbine Engine

Question 2

What are the four types of Gas Turbine Engines?

Answer 2

Turbojet

Turbopropeller

Turboshaft

Turbofan

Question 3

With Turbojet engines, the difference in velocity between the air entering and the air exiting the engine produces what?

Answer 3

Thrust

Question 4

What is EPR?

What is it dependent on?

Answer 4

Engine Pressure Ratio

An engine’s EPR is the ratio of the turbine discharge pressure to the engine inlet pressure. EPR gauge readings are an indication of the amount of thrust being produced for a given power lever setting. They are often used to verify power settings for takeoff, climb, and cruise.

EPR readings are affected by and are dependent on pressure altitude and outside air temperature (OAT).

Question 5

Air entering an inlet duct and proceeds to the compressor, ignited with fuel at the combustor section, moves past the turbine section and exits the engine at a much higher velocity than when it entered is what type of engine?

Answer 5

Turbinejet Engine

Question 6

A gas turbine engine that delivers power to a propeller is referred to as what?

Answer 6

Turbopropeller Engine

Question 7

What is the biggest difference between a turbojet and a turboshaft engine?

Answer 7

With a turboshaft engine, most of the energy produced by the expanding gases is used to drive a turbine rather than produce thrust.

Question 8

The output of a turboprop or turboshaft engine is measured in ____ rather than thrust.

Answer 8

The output of a turboprop or turboshaft engine is measured in shaft horsepower rather than thrust.

Question 9

Turbofans were developed to provide a compromise between the best features of what two engines?

Answer 9

Turbojet and turboprop

Question 10

What is the difference between

Thrust ratio

Bypass ratio

Fan pressure ratio

Aspect Ratio

Answer 10

Thrust ratio - a comparison of the thrust produced by the fan to the thrust produced by the engines core exhaust

Bypass ratio - the ratio of incoming air that bypasses the core to the amount of air that passes through the engine’s core.

Fan pressure ratio - ratio of air pressure leaving the fan to the air pressure entering the fan

Aspect ratio - the ratio of a blade’s length to it’s width, or chord

Question 11

What are the three classifications for bypass ratio and what is it determined by?

Answer 11

Low bypass (1:1)

Medium bypass (2:1 or 3:1)

High bypass (4:1 or greater)

Fan diameter determines a fan’s bypass ratio and thrust ratio

Question 12

What are ducted fans?

Answer 12

The bypass air is ducted along the entire length of the engine. Full fan ducts reduce aerodynamic drag and noise emissions.

Question 13

Weight savings in low aspect ratio blads have been achieved with what type of materials?

Answer 13

Hollow titanium blades with inner reinforcements made of composite materials.

Question 14

Name the seven basic sections within every gas turbine engine.

Answer 14

Air inlet duct

Compressor section

Combustion section

Turbine section

Exhaust section

Accessory section

Question 15

The air inlet to a turbine engine is designed to recover as much of the total pressure of the free airstream as possible and diliver it to the compressor. What is this known as?

Answer 15

Ram recovery

Question 16

An air inlet that consists of a fixed geometry duct with a diameter that progressively increases from front to back is called what?

Answer 16

Divergent

The divergent shape works like a venturi; as the intake air spreads out, the velocity of the air decreases and the pressure increases

Question 17

An air inlet that consists of a fixed geometry duct with a diameter that progressively decreases, then increases from front to back is called what?

Answer 17

Convergent-divergent

This shape is used to slow the incoming airflow to subsonic speed before it reaches the compressor.

Question 18

Engines that use a _____direct high-pressure bleed air from the compressor to prevent formation of a low-pressure vortex that can pull debris into the engine.

Answer 18

Vortex dissipater

Question 19

Name and explain the parts of this compressor

Answer 19

Centrifugal Flow Compressor

Impeller - Draws in air and accelerates it outward by centrifugal force.

Diffuser - The air becomes dispersed, velocity is decreased and its pressure is increased.

Compressor Manifold - Distributes the air in a smooth flow to the combustion section

Question 20

Describe the Axial Flow Compresser’s two main elements.

Answer 20

Rotor - rows of blades fixed on a rotating spindle. The angle and airfoil contour of the blades force air rearward, much like a propeller

Stator vanes - arranged in fixed rows between the rows of the rotor blades and act as a diffuser

At each stage, air velocity decreases and pressure increases. Each consecutive row of rotor blades and stator vanes comprises a pressure stage.

Question 21

In a basic axial flow compressor, the compressor and turbine are connected by a shaft and rotate as a single unit. If there is only one compressor unit, what would it commonly be called?

What if it has two or three compressors?

Answer 21

Single-spool compressor - For only one compressor

Dual-spool compressors - For two compressors.

• The front section of a dual-spool compressor is called the low pressure or N1 compressor.
• The second compresor is called the high-speed or N2 compressor.

Triple-spool compressor - For three compressors

• The compressor in the middle is called the intermediate or N2 compressor

Question 22

What is a compressor stall?

Answer 22

An imbalance between two vector quantities: inlet velocity and compressor rotational speed. Compressor stalls occur when the compressor blade angle of attack exceeds the critical angle of attack. At this point, smooth airflow is interrupted creating turbulence and pressure fluctuations

Question 23

Compressor air that is used for cabin pressurization, heating, and cooling is called____and it is supplied from the______.

Answer 23

Compressor bleed air

Bleed port

Question 24

Name three types of compressor rotor blades root

Answer 24

Bulb

Fir tree

dovetail

Question 25

The only way to overcome a compressor stall is to reduce the angle of attack on the rotor blades. This can be accomplished by ______ as well as stator vanes that change the direction of air contacting the rotor blades.

Answer 25

Variable inlet guides

Question 26

What are the basic elements of a combustion section?

Answer 26

One or more combustion chamber Fuel injection system Fuel drain system

Question 27

What is Newton's 1st law of motion?

Answer 27

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This is often called the Law of Inertia

Question 28

What is Newton's 2nd Law of Motion

Answer 28

The force is proportional to the product of mass times acceleration. Furthermore, the acceleration produced when a force acts on a mass is directly proportional to the force and is inversly proportional to the mass. This relationship is expressed by the formula: F = M x A F= force M= mass A= acceleration

Question 29

What is Newton's 3rd Law of Motion?

Answer 29

For every action there is an equal and opposite reaction.

Question 30

What are the three main components of a centrifugal flow compressor?

Answer 30

Impeller - Draws in and accelerates the air Diffuser - Divergence duct Compressor manifold - Distributes the air in a smooth flow.

Question 31

What is the purpose of swirl vanes?

Answer 31

They slow down air in a vortex motion and helps mix the air/fuel for better combustion.

Question 32

Is the air inlet duct on a turbojet engine normally considered part of the airframe or the powerplant section?

Answer 32

Airframe Section

Question 33

What is the difference between a subsonic and a supersonic inlet?

Answer 33

Subsonic inlet - divergent shape Supersonic inlet - convergent-divergent shape

Question 34

Name a few applications for compressor bleed air. Where does it come from?

Answer 34

Bleed air is supplied by bleed ports anywhere along the compressor or along the difusser and can be used for: * Cabin pressurization * Air conditioning * Deicing and anti-icing * Pneumatic starting of the engine

Question 35

What are the two basic types of compressors?

Answer 35

Centrifugal flow compressors * Impeller * Diffuser * Compressor Manifold Axial flow compressors * Rotor * Stator

Question 36

What are the two types of flameouts?

Answer 36

Lean die-out Usually occurs at high altitudes where low engine speeds and low fuel pressure form a waek flame that is extinguished in a normal airflow Rich blowout Typically occurs during rapid engine acceleration with an overly rich mixture, in which either the fuel temperature drops below the temperature necessary for combustion or there is insufficient airflow to support combustion.

Question 37

Which section of a turbine engine forces air into the engine?

Answer 37

The compressor section

Question 38

Which components make up the hot and cold sections of a turbine engine?

Answer 38

Hot section * Combustors * Turbine * Exhaust Cold Section * Air inlet ducts * Compressor * Accessories

Question 39

What is an APU?

Answer 39

Auxiliary Power Unit Meets the demand for ground electrical and pneumatic power when the aircraft engine is not running.

Question 40

Which ATA chapter covers APU?

Answer 40

Air Transport Association of America (ATA) Chapter 49 - Auxillary Power Units

Question 41

What two components does the APU engine need to start?

Answer 41

1. Its own electric starter motor 2. Aircraft battery power With fuel supplied from one of the aircraft's main fuel tanks, an APU can start up, provide electric power, heat or cool the cabin, and start the main engines without the need for a ground power source

Question 42

What three main components are included in a high-energy capacitor discharge system?

Answer 42

1. Exciter unit 2. Two high-tension cables 3. Two spark igniters

Question 43

When year did the world's first successful powered jet flight occur?

Answer 43

August 27, 1939 Heinkel He-178 Aircraft

Question 44

What is the purpose of the turbine nozzle?

Answer 44

To collect the high-energy airflow from the combustors and direct the flow to strike the turbine rotor at the appropriate angle It is located directly aft of the combustion section and immediately ahead of the turbine wheel.

Question 45

What attachment is most common for the base of turbine blades?

Answer 45

Fir Tree The loose fit of a fir tree base permits the base of a turbine blade to expand as it heats to operating temperatures.

Question 46

What type of air inlet is used on helicopters?

Answer 46

Bellmouth Inlets Bellmouth inlet ducts have convergent profile that is designed for obtaining high aerodynamic efficiency when in stationary or in slow flight.

Question 47

What is a Vortex Dissipater?

Answer 47

A high-velocy stream of compressor bleed air blown from a nozzle onto the ground to prevent a vortex from forming and sucking in debris such as sand, stones, and water.

Question 48

Which is the low speed and high speed compressor?

Answer 48

Low Speed Compressor - N1 Compressor High Speed Compressor - N2 Compressor

Question 49

Name the 3 sections.

Answer 49

Question 50

What two common types of bearings are used to support the main compressor & turbine shaft? What are the three common type of oil lubrication is used? What is the main purpose of the bearings?

Answer 50

Two Common types of bearings: * Ball * Rotor Three Common types of oil lubrication: * Labyrinth seal * Helical Seal * Carbon Seal Main purpose: Keeps shaft aligned

Question 51

What are the different types of combustion chambers?

Answer 51

Muliple-Can Combustors (flame propagation tubing) Annular Combustors (fuel nozzle at several locations) Can-Annular (flame propagation tubing and most efficient)

Question 52

What is a flame propagation tube?

Answer 52

Tubes that connect individual combustors to allow flames to travel through and ignite the air/fuel mixture.

Question 53

What is the purpose of a turbine and what are the four main sections of a jet engine's turbine?

Answer 53

A turbine transform a portion of the kinetic energy in the hot exhaust gases into mechanical energy to drive the compressor and accessories Case - * Encloses stator & rotor Stator - * Vanes that do not rotate * Used to increase velocity and direct flow of air to rotor ar proper angle * A.K.A - Turbine Nozzle Shroud - Encloses the vanes (stator) and holds them in place * Inner shroud * Outter Shroud Rotor * Rotes from the exhaust gases

Question 54

What are the three types of turbine blades?

Answer 54

Impulse - Produces minimum change in pressure or velocity Reaction - Produces a turning force based on aerodynamic action. Acts like a wing on a plane. Impulse-reaction - Impulse shaped at the base, reaction shaped at the tip for uniform pressure and velocity

Question 55

What two types of cooling is used for turbine blades?

Answer 55

Convection cooling (film cooling) - * bleed air is routed to the tip leading edge and trailing edge. Transpiration cooling - * bleed air is ducted into the vanes and exits through the porous material

Question 56

What are the different sections of an exhaust assembly?

Answer 56

Cone Assembly - Attached to turbine case and further directs the exhaust gases in a streamline Tailpipe (duct) - used to protect the fuselage from the exhaust gases, not always needed Exhaust Nozzle - Final boost in velocity

Question 57

What is the four stroke cycle of a reciprocating engine? What is the name of this cycle?

Answer 57

Four-Stroke Otto Cycle 1. Air/fuel Intake 2. Compression 3. Combustion 4. Exhaust

Question 58

What is a Brayton Cycle (constant pressure cycle) ?

Answer 58

Energy transformation for a gas turbine engine similar to a four-stroke Otto Cycle. The Brayton cycle has intake, compression, combustion, and exhaust that occur SIMULTANEOUSLY and CONTINUOUSLY.

Question 59

What three factors effect thrust?

Answer 59

Temperature Altitude Airspeed

Question 60

When the variables of Teperature, Airspeed, and Altitude (factors that effect thrust) is represented as a SINGLE variable is called?

Answer 60

Stagnation Density

Question 61

What three primary factors determine the thermal efficiency of a gas turbine engine?

Answer 61

Turbine inlet temperature Compression ratio Compressor and turbine component efficiencies

Question 62

What is the standard temperature and air pressure according to the ISA?

Answer 62

Internation Standard Atmosphere (ISA) Temperature : 15 degrees C (59 degrees F) Pressure : 29.92 in.Hg, or 14.69 psi, or 1013 millibars

Question 63

What is a VIGV?

Answer 63

Variable Inlet Guide Vanes * Automatically controlled by the fuel control unit * Used to change the angle of attack of the stator vanes to prevent compressor stalls.