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Aeronautic Propulsion Systems > Special Systems and Aspects > Flashcards

Special Systems and Aspects Flashcards

1
Q

What are 5 considerations for engine installation?

A
  • Center of Gravity
  • Different Thrust categories, affected aerodynamics
  • Noise
  • Safety Aspects
  • Structural Aspects
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2
Q

What are 6 engine placement options for sub- / transsonic flight?

A
  • Under the wings
  • Integrated in fuselage
  • On tailplane
  • Over the wings
  • On fuselage
  • At wing tips
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3
Q

What are 3 engine placement options for supersonic flight?

A
  • Under the wings
  • In tail (single engine)
  • In tail (twin-engine)
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4
Q

What are 3 purposes of the cowl (hull)?

A
  • Encloses engine
  • Encloses secondary systems
  • Drag reduction
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5
Q

How is the load of the engine transfered to the aircraft?

A
  • Thrust links
  • Forward and backward mounts
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6
Q

What are the 3 design stages?

A
  • Conceptual
  • Preliminary
  • Detailed
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7
Q

What is done between conceptual and preliminary design?

A

Rapid models based on knowledge, data, and physics model

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8
Q

What is done between preliminary and detailed design?

A
  • Increased accuracy
  • All disciplines are considered
  • Prediction of life cycle
  • Various tests are conducted
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9
Q

What is important during the first stages of design?

A

Accurate predictions, as very high percentage of costs defined in this phase

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10
Q

How to start an engine?

A

Rotating the shaft until combustion chamber can maintain operation

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11
Q

What are 2 ways of starting an engine?

A
  • Air/Pneumatic starting (With built-in auxiliary power unit or external air compressor)
  • Gear box that drives the engine shaft providing torque
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12
Q

According to what can turbofan engines be classified?

A
  • Bypass ratio
  • Number of spools
  • Flow type
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13
Q

According to what bypass ratios can engines be classified?

A
  • Low bypass
  • Medium bypass
  • High bypass
  • Ultra-high bypass
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14
Q

According to what number of spools can engines be classified?

A
  • Single spool
  • Two spool
  • Three spool
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15
Q

According to what flow types can engines be classified?

A
  • Mixed flow
  • Separate flow
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16
Q

What is the advantage of high bypass ratio?

A
  • Increases efficiency
  • Lower thrust specific fuel consumption
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17
Q

What are 6 primary design impacts of a propulsion system?

A
  • Air flow distortion
  • Weight
  • Physical envelope
  • Thrust output
  • Fuel consumption
  • Cost
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18
Q

What are advantages and disadvantages of a larger engine?

A

+ More thrust
- More fuel consumed
- Useless excess power
- More complex
- Higher cost
- Increased drag
- Landing gear needs to be larger
- Increased weight

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19
Q

How is noise generated and what measures have been taken against it?

A
  • Noise generated in both cold bypass and hot core
    stream
  • Late recognition that fan/compressor noise may be as
    disturbing as jet noise
  • Advent of high-bypass ratio fans allowed to consider
    noise from design inception
  • New type of noise introduced by transonic fan design → Supersonic blade portion
  • Took time to realize that fan noise from the rear as
    important as from the front
  • Strong design objectives emerge from future low-noise
    requirements
20
Q

What is the difference between a geared turbofan (GTF) and a direct drive turbofan (DDTF)?

A
  • GTF uses reduction gearbox
  • Minimum block fuel consumption at higher BPR for GTF
  • GTF may save weight
  • GTF leads to reduced fan pressure ratio and fan tip speed
21
Q

Where is the gearbox located and what is its use?

A
  • Between fan and low pressure compressor (LPC)
  • Provide optimum speed for Fan and LP shaft
    • To prevent efficiency losses
    • To achieve lower SFC with lower noise levels
22
Q

What are the components of a planetary gearbox?

A
  • Ring gear
  • Sun gear
  • Planet gear
23
Q

What is a secondary air system?

A

Allows small amounts of air to travel off-line the hot gas path and through engine components

24
Q

What is a seconary air system used for?

A
  • Ensuring smooth temperature distribution in the engine
  • Controlling leakages
25
Q

What are bleeds used for?

A
  • Handling bleeds: Manage compressor surge margin
  • Customer bleed extraction: Required for functions such as cooling of systems or aircraft cabin pressurization
26
Q

What is the purpose of a fuel system?

A

Provide the engine with fuel in the right flow, quantity and form

27
Q

What do fuel pumps do?

A

Deliver to fuel spray nozzles to inject it into combustion system

28
Q

Where can fuel be stored in an A340?

A
  • Main wings
  • Rear wings
  • Center section
29
Q

What does an afterburner do?

A

Improves basic thrust of an engine

30
Q

How does an afterburner work?

A
  • Supplies fuel downstream of the turbine and burns it
  • Increases the temperature of the exhaust gas and therefor gas velocity in the nozzle
31
Q

What is a variable nozzle used for?

A

To match inside and outside pressure

32
Q

What are thrust reversers used for?

A
  • Decelerate the aircraft
  • Less wear on landing gear brakes
  • More safety on wet, icy, or snowcovered runways
33
Q

How is the thrust reversed on high bypass ratio engines and propeller-powered aircraft?

A
  • HBR: Fan flow can be reversed
  • Propeller: Blade pitch is changed to negative values
34
Q

What is thrust vectoring used for?

A
  • Enable aircraft to take off / land vertically or on short runways
  • Additional maneuverability
  • High angle of attack
  • Low-speed flight control
35
Q

What is the heat management system used for?

A

Collect and transport heat from heat-generating sources and redirect this heat into suitable sink (e.g. fuel)
–> minimize heat losses

36
Q

What can be recognized as heat management systems?

A
  • Nacelle ventilation
  • Powerplant anti-icing
  • Secondary air system
  • Cabin bleed systems
37
Q

What are advantages and disadvantages of transfering exhaust heat back to the combustion chamber?

A

+ Improve thermodynamic efficiency
- Total weight
- Complexity
- Cost

38
Q

What are 3 types of turbine blades?

A
  • Conventionally cast turbine blade
  • Directionally solidified turbine blade
  • Single crystal turbine blade
39
Q

What are properties of conventionally cast turbine blades?

A
  • Good mechanical properties in all
    directions
  • Equiaxed crystal structure
40
Q

What are properties of directionally solidified turbine blades?

A
  • Improved mechanical properties in
    longitudinal axis
  • Columnar crystal structure
41
Q

What are properties of single crystal turbine blades?

A
  • Excellent mechanical properties in
    longitudinal axis
  • Improved heat resistance
42
Q

How is safety of passengers ensured?

A
  • Engine is equipped with containment structures made out of steel or aramid fiber materials like Kevlar
  • Engine placement
43
Q

When do bird strikes often happen and what can result from them?

A
  • Takeoff and landing
  • Minor dents to severe deformation
  • Especially critical during takeoff, as engines at full speed
44
Q

What is a compressor surge?

A

Unpredictable phenomenon leading to high pressure pulsation

45
Q

When does surge happen in axial flow compressors?

A

During high angles of incidence of incoming air (maneuvers, sudden acceleration/deceleration)

46
Q

What indicates a compressor surge?

A
  • Drop in rotor speed
  • Increase in jet pipe temperature
  • BANG
47
Q

How does a compressor recover after a surge?

A

Engine pressure ratio is reduced to sustainable level, else it will repeat

Aeronautic Propulsion Systems (9 decks)

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