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Flight Class 22-13 > Engines > Flashcards

Engines Flashcards

1
Q

Describe the behavior of subsonic airflow in a nozzle and diffuser

A

Airflow at subsonic speeds is considered incompressible.

At subsonic speeds, airflow in a nozzle will increase velocity with a decrease in pressure. The nozzle will be a convergent shape

Subsonic airflow in a diffuser will decrease velocity with an increase in pressure. The shape of the diffuser will be divergent.

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2
Q

Describe the behavior of supersonic airflow in a nozzle and diffuser

A

As airflow approaches supersonic speeds it becomes more compressible.

A Nozzle will always increase velocity and decrease pressure. Its shape will be divergent at supersonic speeds

A diffuser will always decrease velocity and increase pressure. Its shape will be convergent at supersonic speeds

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3
Q

what are the three main sections of a gas generator

A

the three main sections of a gas generator are

compressor

combustion chamber

turbine

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4
Q

Describe the Brayton cycle

A

The four components of the operating cycle (intake, compression, combustion, exhaust) happen SIMULTANEOUSLY in the Brayton Cycle.

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5
Q

Describe the Otto cycle

A

The four events of the operating cycle occur SEQUENTIALLY in the Otto Cycle

(same 4 events- suck, squeeze, bang, blow)

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6
Q

Describe the basic components of the gas generator

A

The basic components of the gas generator

Inlet

Compressor

Diffuser

Combustion

Turbine

Exhaust

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7
Q

Describe:

Gross Thrust

Net Thrust

A

Thrust = mass x acceleration

Gross Thrust: measured on stationary engines or on aircraft groun run-ups. Based on standard day conditions (29.92, 15C). Gross thrust ignores the velocity of the air at the inlet- measures exhaust gas velocity only

Net Thrust: thrust corrected for the effects of inlet airflow. More realistic. Net thrust = mass * (Vfinal - Vinitial)/t

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8
Q

How does atmospheric temperature effect thrust in a gas turbine engine

A

As air increases temperature, its density decreases. Density is related to the mass of air

T= m x a

as temperature increases, density (mass) decreases, thrust decreases

* above 36,000 ft temperature stabilizes and will no longer offset pressure changes

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9
Q

How does altitude effect thrust?

A

Higher altitudes have decreased air density (mass)

T = m x a

as altitude increases, density (mass) decreases, thrust decreases

altitude has a greater impact upon overall thrust than temperature

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10
Q

What is the effect of engine RPM on thrust?

A

Increasing RPM will increase thrust.

HOWEVER, at lower RPM settings there is very little increase in thrust when the throttle is increased.

At higher RPM settings a relatively small increase in throttle will produce a large increase in thrust

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11
Q

Describe the effect of airspeed on thrust

A

airspeed

as the inlet velocity approaches the exhaust velocity thrust is reduced

T = m x a

acceleration is between the inlet and the exhaust, as these get closer to equal, acceleration decreases leading to reduced thrust production

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12
Q

what is the effect of ram effect on thrust

A

Ram effect: at higher speeds more air molecules are rammed into the inlet = increased air mass

The ram effect greatly increases thust at SUPERSONIC speeds

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13
Q

what are the cockpit instruments that measure thrust?

A

The cockpit instruments the measure thrust are

Engine Pressure Ratio (epr)

Torquemeter

Tachometer (Monitor Only)

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14
Q

what is a nozzle?

diffuser?

A

Nozzle: increase velocity, decrease pressure

Diffuser: increase pressure, decrease velocity

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15
Q

What is the function of the Inlet?

A

The Inlet will increase air pressure and decrease velocity.

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16
Q

What is the function of the Compressor:

A

The compressor

increases velocity, temperature, Pressure, Total Pressure

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17
Q

What is the function of the Diffuser

A

The diffuser is part of the compressor. It will increase pressure and decrease velocity.

At SUBSONIC speeds the diffuser will be DIVERGENT

SUPERSONIC = CONVERGENT

The pressure is the highest at the diffuser

18
Q

What is the function of COMBUSTION?

A

Air/Fuel Combusted, increase temperature, increase velocity.

Slight decrease in Pressure

19
Q

What is the function of the turbine?

A

the TURBINE increases velocity, decrease Pressure.

Kinetic energy from the turbine is used to turn the compressor

20
Q

What is the function of the exhaust?

A

The Exhaust has the final velocity increase and pressure decrease

21
Q

What does the EPR indicate?

What type of engines have an EPR?

A

The EPR gauges indicate the pressure ratio between the inlet and exhaust airflow

used in most turbojet and turbofan aircraft

22
Q

What is the torquemeter

A

thetorquemeter indicates

SHAFT HORSEPOWER AVAILABLE

23
Q

What is the Tachometer?

A

The Tachometer provides an indication of engine rotation speed (RPM)

CALIBRATED IN % RPM

*does not measure thrust. provides for a quick assessment of the amount of energy being used by the engine

24
Q

Describe inlet ducts:

A

inlet ducts provide the proper amount of high pressure, turbulent free air that is steady and uniform to the first stage of the compressor

act as diffusers. the subsonic inlet is divergent in shape (increase airflow pressure and decreases airflow velocity)

Supersonic inlet is CONVERGENT/DIVERGENT: it must first slow down the airflow to subsonic speeds, then it acts like a subsonic inlet duct

25
Q

Describe compressors

A

The compressors main function is to supply enough high pressure air to satisfy conduction

driven by energy from teh turbine

airflow pressure and velocity increase

26
Q

Describe the burner section of a gas turbine engine

what types of airflow happen in this section?

A

the combuston/burner section provides the proper mixing of the fuel and air to ensure proper combustion

air is divided into two types;

primary air (25%) which is mixed with fuel for combustion

secondary air (75%) flows around the chamber and is used for cooling the chamber walls, turbine, and controls the flame within the chamber itself. This air can also be used in the after burner section

27
Q

Describe the turbine section of a gas turbine engine

A

transforms 75% of the heat energy of the expanding gases from the combustion chamber into mechanical energy to drive the compressor and accessory gear box

25% of energy used for thrust

28
Q

describe the phenomenon of creep in a gas turbine engine

A

Creep is an abnormal elongation of the turbine blades due to overheating and it can result in permanent blade deformation

prevent it with “Fir Tree” attachments

29
Q

Describe the exhaust section of a gas turbine engine

A

The exhaust section directs the flow of hot gasses rearward causing a high exit velocity of the gasses while preventing turbulence

2 kinds of exhaust nozzles

Convergent: direct gasses to a focal point and accelerates gasses from the turbine leading to increased velocity

Convergent/Divergent: SUPERSONIC aircraft. convergent section accelerates gasses to the speed of sound, divergent section increases the supersonic air even faster

30
Q

describe the afterburner section of a gas turbine engine

A

increase the maximum thrust available from an engine for short periods of time

increase thrust by 50% at a cost of using 300% more fuel

31
Q

Describe the components of a reciprocating engine

A

the basic components of a reciprocating engine are

crankcase

cylinders

pistons

connecting rods

valves

valve-operating mechanism

crankshaft

32
Q

Single entrance ducts

location

disadvantages

A

single entrance ducts

location: directly in front of engine
disadvantages: short single ducts can cause stall at slow airspeed or high AOA

33
Q

Divided entrance ducts

pros:

cons:

A

Divided entrance ducts

less friction loss

cons: more air turbulence, larger and shorter inlets

34
Q

What is the variable geometry inlet duct?

A

The variable geometry inlet duct can change shape.

at subsonic speeds it is divergent. At supersonic speeds it becomes CONVERGENT/DIVERGENT

35
Q

What are the three types of compressor

A

The three types of compressors are:

centrifugal

axial

axial- centrifugal

36
Q

what are the components of a centrifugal flow compressor?

A

the three components of a centrifugal flow compressor are:

impeller- accelerates the airflow toward the diffuser.

diffuser-converts high velocity to high pressure airflow (total pressure remains the same) point of highest compression

manifold- directs airflow to the combustion chambers

*highest pressure increase per stage

**large, lots of drag, single stage

37
Q

What are the elements of an axial-flow compressor

A

The 2 main elements of the axial-flow compressor are

rotor- increases air pressure

stator- reduces the airflow velocity produces an increase in airflow pressure

*one rotor blad and one stator form a SINGLE STAGE

GREATEST OVERALL COMPRESSOR RATIOS (they are multi-staged compressors)

Higher combustion efficiency due to multiple stages

38
Q

Where is the point of highest compression?

A

The point of highest compression is the diffuser (just before the air goes into the combustion section)

divergent design

39
Q

What are the three types of combustion chambers used?

A

The three types of combustion chambers are:

can- greater pressure loss, cold spots on turbine. Strong, easily maintained

annular- continuous inner and outer shroud that surrounds the compressor drive shaft- uniform heat distribution, smaller, maintenance is a bitch

can-annular- efficient, lower pressure loss but pricy

40
Q

What are the parts of the turbine

A

The turbine consists of

stationary stator

rotor

41
Q

What are the parts of the exhaust section

A

Outer Duct

Inner Cone

Radial struts

42
Q

What are the components of the afterburner?

A

The afterburner consists of

Spray bars- introduce fuel

flameholders- help mix fuel and air, keep flame in the duct

screech liner- shock absorber

variable exhaust nozzle- allos for the acceleration of the subsonic gasses (its the iris)

Flight Class 22-13 (11 decks)

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