Engines 2 Flashcards

1
Q

Describe the AOA of compressor blades

A

AOA is the angle between rotor blades chordline and the relative wind of the compressor

*relative wind is formed within the compressor by combining the inlet airflow with the compressor RPM. Increasing the compressor RPM increases the rw, which increases the AOA

*AOA can also be increased by decreasing the inlet airflow while the compressor RPM remains constant

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2
Q

Describe a compressor stall

A

A stall occurs when airflow over an airfoil breaks away causing the airfoil to lose lift due to excessive angle of attack.

It happens when anything increases the RPM or decreases the inlet airflow

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3
Q

Describe four mechanical malfunctions that can lead to a compressor stall

A
  1. Variable inlet gide vanes failure
    1. insufficient airflow at lower engine RPMs
  2. fuel control unit failure
    1. too much fuel leads to excessive back pressure
  3. Foreign Object Damage (FOD)
    1. can damage compressor blades
  4. Variable Exhaust Nozzle Failure
    1. excessive back pressure
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4
Q

Describe appropriate actions a pilot can take to avoid compressor stalls in the first place

A
  1. avoid erratic or abrupt power control lever (PCL) movement
  2. Maintain prescribed minimums
  3. avoid abrupt changes in aircraft attitude
  4. avoid flight through severe weather or air turbulence
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5
Q

Describe four engine design features that can be incorporated into a gas turbine engine design to minimize the potential for a compressor stall

A

Engine design features:

  1. variable inlet guide vanes
  2. dual/twin/split-spool Axial Flow Compressor
  3. Bleed Valves
  4. Variable exhaust nozzle
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6
Q

What are the two ways to increase the AOA of compressor blades?

A

increase the compressor blade AOA by

decreasing inlet airflow

increasing the compressor RPM

*an increased AOA increases the posibility of a compressor stall

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7
Q

What causes a compressor to stall?

(2 general ways that the AOA can be increased)

A
  1. Airflow distortions- most common cause
    1. abrupt change in attitude
    2. air turbulence
    3. atmospheric conditions
    4. rapid throttle movement
  2. Mechanical malfunctions- there is a whole flash card on this topic, do don’t worry about it just yet.
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8
Q

what actions should a pilot take if a compressor stall occurs

A

if a compressor stall occurs

reduce aircraft attitude (reduce inlet air AOA)

slowly retard to power control lever to adjust below stall threshold- this allows the engine to catch up with the inlet airflow and “clear” the stall

bleed valves to increase airflow

once normal you can advance the PCL slowly

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9
Q

Define thrust specific fuel consumption (TSFC)

A

the amount of fuel required to produce one pound of thrust

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10
Q

Describe a turbojet engine

How is thrust produced?

A
  1. gas generator with the addition of
    1. inlet section
    2. exhaust section

thrust is derived exclusively from the expanding gasses leaving the exhaust section. it is dependent on amount of fuel mixed with airflow

the propulsive efficiency of turbojets exhaust is not as efficient as work using a turbine (mechanical work)

high TSFC

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11
Q

Describe a turbofan engine

A
  1. gas generator +
    1. duct-enclosed fan driven by the turbine section connected to the front of the compressor of gg

A turbofan provides the propulsive thrust of the exhaust from the gg with additional thrust provided by the duct-enclosed fan

total thrust:

gg: 40%- 70%

ducted fan: 30%- 60%

*Turbofan as a lower TSFC than a turbojet

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12
Q

Describe a turboprop engine

What are the basic componants of the turboprop engine?

A

gas generator + a propeller which is driven by the turbine section

  1. Parts:
    1. Reduction gear assembly: converts high RPM and low torque of turbine into low RPM with high torque for propeller
    2. Torquemeter Assembly- connects the RGB to the gas generator. Measures and transmits the power output from the gg to the RGB
    3. Gas generator

* high thrust at low speed, good for lifting heavy loads on short runways.

Turboprop have the lowest TSFC of any gas turbine engine

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13
Q

What are the two ways that the propeller can be connected to the generator?

A

The propeller is attached to the gg in one of two ways.

1) attached to the front of the compressor or
2) attached to a free turbine/power turbine

90% of thrust is produced from the propeller

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14
Q

Describe the major components of the torquemeter assembly

A

The major components of the torquemeter assembly

  1. torque shaft (inner shaft)
    1. carries load from propeller and produces the measured twist
  2. reference shaft (outer shaft)
    1. proveides referene to the torque shaft. Does not move
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15
Q

Describe a turboshaft engine

A

similar to the turboprop: uses free turbine to drive the rotor

  1. 2 basic sections
    1. gas Generator
    2. Free/Power Turbine (PT)

Exhaust gases that come from the gas generator turbine drive the PT

propulsive energy from the exhaust gases is negligible. Virtually all of the pressure energy is converted to SHAFT HORSEPOWER

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16
Q

Describe the operation of the free/power turbine section

A

This is a turbine that is not mechanically connected to the compressor.

It is driven by the exhaust gasses from the gas generator

*in a turboshaft engine, all pressure energy is converted into shaft horsepower

17
Q

Compare the thrust specific fuel consumption of turbojet, turbofan, and turboprop engine

A

Turbojet > Turbofan > Turboprop

18
Q

compare the propulsive efficiencies of turbojet, turbofan, turboprop, and turboshaft engines

A

Propulsive efficiency of an engine is determined by the efficient conversion of kinetic energy to propulsive force by its propelling mechanism

Turboprop: most efficient at lower air speeds. Efficiency decreases at higher airspeeds (> ~300 mph)

Turbofan: generally more efficient at any speed than the turbo jet

19
Q

What is the difference between High Bypass Engines and Low Bypass Engines?

A

Bypass air: the air that bypasses the gas generator

Bypass ratio: the amount of bypas air in comparison with the amount of air that passes through the gas generator

High Bypass engines are more fuel efficient. Can take off with heavy loads and travel a very long ways without need to refuel

Low bypass ratio: design that resembles a turbojet but is more efficient. preferable for fighter aircraft

20
Q

What are the components of the propeller

A

The main components of the propeller are:

  1. Pitch Change/dome assembly
  2. blade assembly
  3. hub assembly
21
Q

What are the two ranges of propeller operation in a turboprop engine?

A

The propellers have 2 ranges of operation:

  1. alpha: PCL is positioned from flight idle to full power
    1. PCL sends fuel flow signals to FCU
    2. FCU controls the fuel flow
    3. blad angle is controlled by the propeller governor
  2. beta (groud range): PCL is flight idle to Max Reverse
    1. PCL is mechanically connected to FCU and pitch change assembly
22
Q

what is pascal’s law?

how does it govern the forces and pressures associated with a confined liquid?

A

Pascal’s Law states: pressure applied to a confined liquid is transmitted equally in all directions without loss of pressure and acts with equal force on equal surfaces

F = P x A

23
Q

What is the relationship between linear displacement and the change in foce between the input and output pistons of a closed hydraulic system?

A

if the pressure remains constant and the input piston is smaller than the output piston, the original force will be multiplied by the factor of the increase in surface area

P = F/A

However, linear displacement is inversely proportional to the multiplied force

24
Q

What 2 types of hydraulic power systems are on an aircraft?

A

2 hydraulic power systems:

  1. Power Control System
    1. suppplies fluid pressure to flight controls only
  2. Utility Control System
    1. supplies fluid pressure to the utility systems and acts as a backup for the flight controls
25
Q

Hydraulic Systems:

What are the functions of the Reservoir?

A

provides storage space for the hydraulic fluid

heat dissipation

separates air from the system

Trapping of foreign matter

Thermal expansion

Pressurized reservoirs are designed for high altitude. The pressurization ensures a positive flow of fluid and helps to prevent foaming of fluid at high altitude

26
Q

Hydraulic Systems:

What are the two types of Pump?

What is the function of a pump?

A

Two types:

  1. Hand Pump: back up. Normally classified as an emergency system
  2. Power Pump
    1. Variable displacement: regulated fluid volume delivery as the system demands
    2. Constant displacement: delivers a steady flow regardless of demands
      1. MUST INCORPORATE A PRESSURE REGULATOR/UNLOADER VALVE

Function: provides the flow of fluid to the system

27
Q

Hydraulic Systems:

Check Valve

A

allows for one-way flow of hydraulic fluid within the system. This prevents backflow.

Also works with the accumulator to maintain system pressure during shutdown

28
Q

Hydraulic Systems:

Accumulator

A

Functions:

  1. Shock absorber
  2. provides pressure for one time emergency use
  3. helps maintain pressure during peak operation
  4. works with the checkvalves to maintain system pressure during shutdown
29
Q

Hydraulic Systems:

Filters

A

what do you think this does? It filters the hydraulic fluid.

includes a bypass valve in case the filter becomes clogged. Dirty fluid is better than no fluid

30
Q

Pressure Relief Valve

A

Functions

  1. safety- prevents pressure from building up which may eventually cause the system to be damaged (seals, etc)

If excessive pressure builds up, the valve opens and allows fluid to travel back to the reservoir

31
Q

Pressure Gauge

A

Measures pressure in PSI

32
Q

Hydraulic Systems:

Fuses

A

Monitors for fluid leak

33
Q

Hydraulic Systems:

Actuator

A

Function:

  1. Converts fluid power into mechanical force and motion

a piston rod (shaft) of the actuator is attached to the mechanism to be moved and other end attached to the aircraft structure