Special Systems and Aspects Flashcards
What are 5 considerations for engine installation?
- Center of Gravity
- Different Thrust categories, affected aerodynamics
- Noise
- Safety Aspects
- Structural Aspects
What are 6 engine placement options for sub- / transsonic flight?
- Under the wings
- Integrated in fuselage
- On tailplane
- Over the wings
- On fuselage
- At wing tips
What are 3 engine placement options for supersonic flight?
- Under the wings
- In tail (single engine)
- In tail (twin-engine)
What are 3 purposes of the cowl (hull)?
- Encloses engine
- Encloses secondary systems
- Drag reduction
How is the load of the engine transfered to the aircraft?
- Thrust links
- Forward and backward mounts
What are the 3 design stages?
- Conceptual
- Preliminary
- Detailed
What is done between conceptual and preliminary design?
Rapid models based on knowledge, data, and physics model
What is done between preliminary and detailed design?
- Increased accuracy
- All disciplines are considered
- Prediction of life cycle
- Various tests are conducted
What is important during the first stages of design?
Accurate predictions, as very high percentage of costs defined in this phase
How to start an engine?
Rotating the shaft until combustion chamber can maintain operation
What are 2 ways of starting an engine?
- Air/Pneumatic starting (With built-in auxiliary power unit or external air compressor)
- Gear box that drives the engine shaft providing torque
According to what can turbofan engines be classified?
- Bypass ratio
- Number of spools
- Flow type
According to what bypass ratios can engines be classified?
- Low bypass
- Medium bypass
- High bypass
- Ultra-high bypass
According to what number of spools can engines be classified?
- Single spool
- Two spool
- Three spool
According to what flow types can engines be classified?
- Mixed flow
- Separate flow
What is the advantage of high bypass ratio?
- Increases efficiency
- Lower thrust specific fuel consumption
What are 6 primary design impacts of a propulsion system?
- Air flow distortion
- Weight
- Physical envelope
- Thrust output
- Fuel consumption
- Cost
What are advantages and disadvantages of a larger engine?
+ More thrust
- More fuel consumed
- Useless excess power
- More complex
- Higher cost
- Increased drag
- Landing gear needs to be larger
- Increased weight
How is noise generated and what measures have been taken against it?
- 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
What is the difference between a geared turbofan (GTF) and a direct drive turbofan (DDTF)?
- 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
Where is the gearbox located and what is its use?
- 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
What are the components of a planetary gearbox?
- Ring gear
- Sun gear
- Planet gear
What is a secondary air system?
Allows small amounts of air to travel off-line the hot gas path and through engine components
What is a seconary air system used for?
- Ensuring smooth temperature distribution in the engine
- Controlling leakages
What are bleeds used for?
- Handling bleeds: Manage compressor surge margin
- Customer bleed extraction: Required for functions such as cooling of systems or aircraft cabin pressurization
What is the purpose of a fuel system?
Provide the engine with fuel in the right flow, quantity and form
What do fuel pumps do?
Deliver to fuel spray nozzles to inject it into combustion system
Where can fuel be stored in an A340?
- Main wings
- Rear wings
- Center section
What does an afterburner do?
Improves basic thrust of an engine
How does an afterburner work?
- Supplies fuel downstream of the turbine and burns it
- Increases the temperature of the exhaust gas and therefor gas velocity in the nozzle
What is a variable nozzle used for?
To match inside and outside pressure
What are thrust reversers used for?
- Decelerate the aircraft
- Less wear on landing gear brakes
- More safety on wet, icy, or snowcovered runways
How is the thrust reversed on high bypass ratio engines and propeller-powered aircraft?
- HBR: Fan flow can be reversed
- Propeller: Blade pitch is changed to negative values
What is thrust vectoring used for?
- Enable aircraft to take off / land vertically or on short runways
- Additional maneuverability
- High angle of attack
- Low-speed flight control
What is the heat management system used for?
Collect and transport heat from heat-generating sources and redirect this heat into suitable sink (e.g. fuel)
–> minimize heat losses
What can be recognized as heat management systems?
- Nacelle ventilation
- Powerplant anti-icing
- Secondary air system
- Cabin bleed systems
What are advantages and disadvantages of transfering exhaust heat back to the combustion chamber?
+ Improve thermodynamic efficiency
- Total weight
- Complexity
- Cost
What are 3 types of turbine blades?
- Conventionally cast turbine blade
- Directionally solidified turbine blade
- Single crystal turbine blade
What are properties of conventionally cast turbine blades?
- Good mechanical properties in all
directions - Equiaxed crystal structure
What are properties of directionally solidified turbine blades?
- Improved mechanical properties in
longitudinal axis - Columnar crystal structure
What are properties of single crystal turbine blades?
- Excellent mechanical properties in
longitudinal axis - Improved heat resistance
How is safety of passengers ensured?
- Engine is equipped with containment structures made out of steel or aramid fiber materials like Kevlar
- Engine placement
When do bird strikes often happen and what can result from them?
- Takeoff and landing
- Minor dents to severe deformation
- Especially critical during takeoff, as engines at full speed
What is a compressor surge?
Unpredictable phenomenon leading to high pressure pulsation
When does surge happen in axial flow compressors?
During high angles of incidence of incoming air (maneuvers, sudden acceleration/deceleration)
What indicates a compressor surge?
- Drop in rotor speed
- Increase in jet pipe temperature
- BANG
How does a compressor recover after a surge?
Engine pressure ratio is reduced to sustainable level, else it will repeat
