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Aircraft Systems > Aircraft Systems Questions > Flashcards

Aircraft Systems Questions Flashcards

1
Q

What is System Thinking?

A
  • System Thinking is the ability to take a holistic or a total systems view of the development or analysis of any system
  • Take into account all influences or factors which may effect the behavior of a system
  • System thinking is a way to understand and manage complex problems
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2
Q

What are the major systems of an aircraft?

A
  • Airframe and structure provides the lift and control surfaces and the passenger cabin
  • Avionics represents the “brain” of the aircraft providing navigation, communications, autopilot and display functions
  • Aircraft systems provides the means and flying the aircraft reliable and safe
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3
Q

What is the definition of Aircraft Systems?

A

A group of components that work together to perform a common aircraft function is generally referred to as an aircraft system.

-> Aircraft systems enable a reliable and safe operation of an aircraft due to a proven system design philosophy

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4
Q

What are the Safety Objectives?

A
  • System hardware has to fulfill strict environmental and safety requirements
  • Software fulfills strict requirements by dissimilating programming (different project teams and program languages)
  • Each system has a self-monitoring function
  • Multiple redundancy is the essential factor for a high level of safety
  • Each redundant (backup) system allows a safe continuation of the flight and landing
  • Automatic backup or separation in the case of a system failure to prevent immediate intervention of the crew (reduces workload)
  • Each single system failure leads to a single failure in the appropriate system/sub-system
  • The combination of the two failures does not lead to a total loss of the superior system
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5
Q

What are the Handling Quality Objectives?

A
  • Keep the workload for the crew as low as possible: If all systems are in normal operation no action by the crew is needed or signals are displayed
  • Instruments and displays using synoptic and visual designs
  • Clear assignment of a visual system indication of the represented system for a good understanding of the current system status
  • Most switches, displays and signals are applied in “flow” of the schematics system diagram
  • Master Warning Panel is visible for all flight crew members
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6
Q

What are the Maintainability Objectives?

A
  • Good accessibility to all system components
  • Commonality of all system components
  • Commonality and replicability within an aircraft and within an aircraft family
  • Maintainability and reliability are considered as major design parameters
  • “Built-In Test Equipment” supports failure reorganization - it has to be independent of the electrical
  • Manual control and test of the integrity of the protective circuits
  • Spatial separated maintenance areas of each larger system allows a faster inspection and simultaneously maintenance, without interfering of maintenance personnel or devices
  • Spatial separation of hydraulic and electrical connections
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7
Q

What are the Flexibility Objectives?

A
  • Space for future instruments, avionics and equipment for the baseline aircraft of an aircraft family
  • The addition of further instruments and equipment is not limited by energy and power system capacities - a power margin (buffer) of +20% should be provided
  • Additional wiring capacities and interfaces are provided in baseline layout
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8
Q

What are the advantages of Fly-By-Wire (FBW)?

A
  • Weight and parts reduction by replacement of heavy mechanical linkages
  • Lower maintenance costs (less complex system)
  • Pilot work reducing (automatic control features)
  • Better and common aircraft handling characteristics on different aircraft types
  • Greater flexibility including new functionality and changes after initial design/production
  • Features of autopilot are in manual control mode available (i.e. attitude control)
  • Safety enhancement by highly reliable flight envelope protection systems
  • Minimizing of structural loads by control design or active load control
  • Common control surfaces for different types
  • Possibility to implement new control laws functions (i.e. adaptive wing, variable camber)
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9
Q

What is Fault Tolerance and which fault classes exist?

A

Fault Tolerance

Fault Tolerance is a term that is used to define the ability of any system to withstand single or multiple failures which results in either no loss of functionality or a known loss of functionality or reduced level of redundancy while maintaining the required level of safety

  • Class 1 fault: A failure which results in some particular component becoming totally inoperative. Example: Loss of power to an electronic component
  • Class 2 fault: A failure which results in some particular component remaining active, but the functionality it provides is in error. Example: False signals by erroneous operation sensor

-> Fault tolerant flight control systems require the principal techniques of redundancy, dissimilarity, and installation segregation

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10
Q

What is Redundancy in Aircraft Systems?

A

Redundancy is the multiplication of flight critical components or functions of the safety-critical system with the intention of increasing reliability of the system (backup/fail-safe)

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11
Q

What is Dissimilarity in Aircraft Systems?

A

Dissimilar implementations increases robustness to common-mode faults for safety critical systems by using dissimilar hardware and/or dissimilar software. The objective is to tolerate a “design error” of the system

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12
Q

Name some examples for hardware redundany

A
  • Multiple flight control computer
  • Different control surface actuation
  • Different power sources/systems)
  • Ram Air Turbine (RAT) as a last power back-up
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13
Q

How can actuators be categorized?

A
  • Simple Mechanical/Hydraulic Actuation
  • Fly-By-Wire Hydraulic Actuator (HA)
  • Electro Hydrostatic Actuator (EHA)
  • Electro-Mechanical Actuator (EMA)
  • Electrical Backup Hydraulic Actuator (EBHA)
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14
Q

What are the benefits of electric powered actuation?

A
  • Reduced Weight: Fewer hydraulic components: Weight reduction of approx. 450kg for the Airbus A380
  • Improved Performance and Optimization: Hydraulic pump/system is a continuous load on the engine -> electric load is on demand/when needed.
  • Improved Maintainability and Robustness: Elimination of hydraulic system improves reliability -> higher Mean Time Between Failure (MTBF) for electrical system compared to hydraulic system. Efficient Segregation & Independence of the Actuation Power provides robustness
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15
Q

What functions are fulfilled by the Flight Management System (FMS)?

A
  • Navigation
  • Flight planning
  • Trajectory prediction
  • Performance computations (e.g. fuel consumption)
  • Guidance
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16
Q

The definition of an Interface Control Document (ICD) enables the major project contractor to declare and agree their interfaces. What are typical interface categories?

A
  • Installation
  • System Connections
  • Power Offtakes
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17
Q

What is the advantage of a “no-bleed engine”?

A

Eliminating the pneumatic bleed results in a more efficient engine operation due to reduced overall airplane level power requirements

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18
Q

What is the propulsion control problem?

A

The basic control problem is to control fuel flow and air flow to the engine to operate at its optimum efficiency within the aircraft flight envelope (speeds, altitudes, temperatures). The major design aspects are reliable, economical and long-term operation under defined predictable conditions

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19
Q

What are the goals of Engine Air Management?

A
  • Ensure efficient operation
  • Maintain safety margin to engine surge line
  • Optimum acceleration without surge
  • Variable intake area/shock control for high Mach
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20
Q

What is FADEC, what are the principal functions and main benefits?

A

Principles of Engine Control - Full Authority Digital Engine Control

The FADEC also called Engine Control Unit is a fully redundant digital control system which provides complete engine management and control. The FADEC is mounted on the fan casing

Principal Functions

  • Optimized engine efficiency
  • Protection from operation outside engine limits
  • Coordination of engine/aircraft control functions
  • Saves weight, reduces pilot workload and reduces maintenance costs

Main Benefits

  • Enhance basic control functions: Engine start, idle acceleration etc.
  • Optimized engine control: air management, bleed-air control (anti-surge), cooling
  • Enhanced engine protection: thrust limitation, critical speed and pressure
  • Improved pilot/engine interface
  • Improved reliability and safety
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21
Q

What are major subsystems of the propulsion system?

A
  • Fuel jettison (dumping) system
  • Fuel heating system
  • Cross feeding fuel system
  • Fuel tank ventilation
  • Central refueling
22
Q

What´s a “dry bay”?

A
  • The potential failure mode of an unconfined rotor burst of an engine has to be considered in fuel storage design
  • The zone normal to the engines axis called rotor burst zone is not suitable for tanks, fuel, hydraulic and electric lines
23
Q

What´s special about the Engine and APU feed?

A

Engine and APU feed is by far the most critical element of the fuel control system

  • Each engine is typically supplied by two fuel pumps with independent power supply
  • The cross-feed valve allows the supply of an engine by the opposite side pumps (in case of failure)
  • In cruise conditions, a single booster pump is able to supply flow to both engines
  • The engine Low Pressure (LP) valves shut off the fuel supply in case of an engine fire
24
Q

Which forms of energy exist on planes, what components do they power and what are current trends?

A

4 forms of energy:

  • Hydraulic power: flight control, landing gear, braking, thrust reverser, doors
  • Pneumatic power: air conditioning, pressurization, anti-ice, engine start
  • Electrical power: avionics, commercial, pumps, de-icing, lights
  • Mechanical power: fuel pump, oil pump, engine start
  • > Trend: power demand is increasing
  • > Trend and tendency to more electric aircraft: reduce number of energy forms by innovative and highly-integrated electrical systems
25
Q

How does hydrostatic power transmission work?

A
  • A pressure is applied to the fluid by a pump or a piston
  • The force depends on the pressure in the cylinder and the cross section of the cylinder
  • Due to the moving of the piston, the cylinder needs a specific amount of hydraulic fluid flow rate
  • The pumps of the hydraulic system generate the hydraulic power
  • The power can be varied by varying the fluid flow rate at a preferably constant system pressure

-> The hydraulic system acts as a transmission between the power source (engine) and several different loads (e.g. control surfaces actuators)

26
Q

Why use hydraulics?

A
  • Effective and efficient method of power amplification
  • Precise control of load rate, position and magnitude
  • Ability to handle multiple loads simultaneously
  • Smooth, vibration free power output
  • Hydraulic fluid transmission medium for heat transfer/lubricant
27
Q

What are the Design Challenges for hydraulic systems?

A
  • hydraulic system complexity
  • High level of redundancy
  • Leakages
  • Contamination
  • Bad heat dissipation
  • Flow losses
  • Temperature-sensitive fluid properties
  • Heavy

-> High requirements on hydraulic system fluids, architecture design and system components

28
Q

What are key design parameter for hydraulic systems?

A
  • Pressure
  • Integrity
  • Flow rate
  • Emergency or reversionary use
  • Heat load and power dissipation
  • Duty cycle

-> scope and scale of a hydraulic system must be determined by analyzing the different demands of integrity and power

29
Q

What are the electric power sources onboard an aircraft?

A
  • Engine Driven AC Generators
  • APU
  • External Power
  • Ram Air Turbine
  • Batteries
30
Q

What are the Design Challenges for electric systems?

A
  • No single failure should be catastrophic
  • Several independent systems and power sources
  • Wiring and wiring segregation
  • High resistance against aging, smoke and fire
  • Lightning protection
  • Circuit breaker melt, before overheated wires cause further damage
  • Generator cooling (heat exchanger)
  • Fault detection and display warnings
  • In-flight and ground tests possible
  • Modular system concept for easy component and subsystem replacement (LRUs)
31
Q

What are the key design drivers for electrical systems?

A
  • Total electrical load
  • Electrical power quality
  • Safety
  • Reliability
32
Q

What are the back-up systems for electrical power?

A
  • Ram Air Turbine (RAT)
  • Backup Generators and Converters
  • Permanent Magnet Generators (PMG)
33
Q

What are the primary functions of an electrical system?

A
  • Power generation and control
  • Power conversion and regulation
  • Power distribution and protection
34
Q

Why 400 Hz?

A

400 Hz frequency represents a good trade-off between electrical system efficiency and generator compactness (weight)

35
Q

What are the possibilites for pressurized air supply?

A
  • Engine Bleed Air from the Intermediate Pressure (IP) stage of the engine compressor or from the High Pressure (HP) stage of the compressor
  • Auxiliary Power Unit (APU) Bleed Air Supply: The APU can supply the bleed air system via the APU bleed valve. The APU can be used for a pneumatical engine start
  • Ground Air Supply: The APU or ground source would supply the pneumatic system prior to the engine start
36
Q

What are the pneumatic system loads?

A
  • Air conditioning and pressurization: Main air source for environmental temperature control and cooling
  • Wing and engine anti-ice: Hot air for anti-icing of engine nacelles and the wing, tail-plane or fin leading edges
  • Engine start
  • Thrust reverser actuating
  • Hydraulic reservoir pressurization
  • Air-diven hydraulic pumps (ADP)
  • Active Flow Control (AFC)
37
Q

What are the Design Challenges for pneumatic systems?

A
  • System integrity, e.g. bleed air leakages cause
    • Damage to electrical wiring
    • Components to overheat and
    • Damage to aircraft structures
  • Bleed ducts prone to cracking
  • Cross-feed if one engine inoperative
  • Shut-off if systems/functions are not required
  • Bleed air system indications (display status data to flight crew)
  • -> Trend: More electrical aircraft with no-bleed system
38
Q

How does the bleed air system work?

A
  1. Air is taken from an intermediate pressure stage (IP) or high pressure stage (HP) depending on the engine power setting:
  2. Low power: air is extracted from the HP section of the compressor
  3. High power: air is extracted from the IP compressor stage
  4. The High Pressure Valve (HPV) regulates the pressure of air in the engine manifold and controls the supply of bleed air from the engine
  5. The IP check valve prevents reverse flow of the HP bleed air from entering the IP stage
  6. Downstream of the IP and HP ducting the PRSOV regulates the supply of the engine air -> Key element of the bleed air system
  7. Cooling air is directed from the fan stage of the engine through a pre-cooler (air-to-air heat exchanger) to regulate the pre-cooling of the hot bleed air
  8. Pressure and temperature sensors allow the monitoring and controlling of the engine bleed air temperature and pressure
39
Q

What is the APU?

A

The APU is a compact, self-contained unit that provides electrical power and compressed air during periods of aircraft ground activity or in flight if needed

40
Q

What are the main functions of the APU?

A

On Ground Operation

  • Due to the APU the aircraft is independent from Ground Power Supply
  • APU bleed air is used for pneumatically starting of the main engines
  • Electrical power is generated by one or two generators driven by the load gearbox

In-Flight Operation

  • Pressurized Air for environmental control system (ECS) packs and engine restarting
  • Electrical power supply has priority over pressurized air supply
  • Unloading of main engine as power source
41
Q

What are the Design Challenges for the APU?

A
  • Low development and unit costs
  • High reliability and maintainability
  • Low volume and weight
  • Low emissions and low noise
  • In-flight APU start
  • Fault detection and display warnings
  • Air inlet is an aerodynamic challenge
  • Firewalls, fire detection and warning systems
  • Clearly defined exhaust velocities and temperature during ground operation
42
Q

What is the RAT and what is its purpose?

A

The RAT deployed from the aircraft’s wing or fuselage and rotates to generate sufficient power from the airstream to control and land the aircraft

The RAT are generally used only in emergency situations

  • All engines inoperative
  • Power generators failure
  • Hydraulic pressure drop in all hydraulic circuits

The RAT provides the aircraft with

  • Hydraulic Power for powered actuation of flight control surfaces and/or
  • Electric Power for flight control computers, essential instruments, radio, cockpit lighting, windshield and pitot tube de-icing
43
Q

What is the purpose of the environmental control system?

A

Commercial transport aircraft conditioning is provided to maintain a comfortable environment for passengers and cabin crew throughout the flight, including the time required for boarding and taxying to the runway.

  • Safe and comfortable environment for passengers and crew inside the aircraft cabin
  • Control and monitor the cabin temperature and significant amounts of fresh air
  • Ensure avionics and electronics ventilation and/or cooling
44
Q

What are the main heat loads for the ECS?

A
  • Aerodynamic Heating
  • Solar Heating
  • Avionics Heat Loads
  • Airframe Systems
  • Heat Dissipation by Passengers and Crew
45
Q

What are the main functions of the Landing Gear?

A
  • Support the aircraft at the required height and altitude while on ground
  • Absorb energy of landing and taxiing shocks
  • Braking system for deceleration
  • Handling of the aircraft on ground: Retractable in flight (low drag)
  • Provide mounting for runway and taxi turn-off lights, towing and jacking attachments, aerodynamic fairings
46
Q

What are the Design Challenges for the Landing Gear?

A
  • Absorb landing & taxiing shocks
  • Allowing ground maneuvering
  • Retractable in flight
  • Fault detection and display warnings
  • Provide necessary braking performance
  • Low cost, weight and complexity
  • Long-life and minimum maintenance effort
  • Limited installation space
  • Provide required ground clearance
  • Comply with maximum runway surface pressure
47
Q

How does the Angle-of-Attack (AOA) sensor work?

A
  • The AOA vane aligns itself with the prevailing airstream
  • The vane rotates a shaft inside the housing, which is connected to a synchro that provides an electrical output proportional to the AOA
  • A viscous damper connected to the AOA vane stabilizes vane movements and reduced the effects of turbulence
  • The AOA sensor contains a heater that provides continuous de-icing/anti-icing, prevents condensation and reduces changes in damper fluid viscosity
48
Q

What are the Design Challenges for Avionics?

A
  • Electromagnetic compatibility (EMC) of the system components and antennas
  • Cooling of the devices
  • No or only minor vibrations at the installation locations
  • Lightning protection
  • Good accessibility
  • High power supply stability
  • Consider human engineering factors and ergonomic aspects for displays and control unit (“synoptic displays”)
  • Built-In Test (BITE) capability
  • Keep number of interfaces between the devices as low as possible
49
Q

What is the purpose of the Ice Protection System?

A

The main function of the Ice Protection System (IPS) is to avoid ice accumulation at certain surfaces and components:

  • Wing leading edges
  • Engine inlet cowlings
  • Air data probes
  • Cockpit windows
50
Q

What are the design requirements for smoke detectors?

A
  • No false warnings
  • Rapid, accurate and perceptible indication of a fire and its location
  • Accurate indication of conclusion of hazardous situation causing the alert
  • Capability of detection of a subsequent fire
  • Means for testing the detector system during flight
  • Robustness against physical influences

Aircraft Systems (1 decks)

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