Systems Engineering Flashcards
Definitions of system and Systems Engineering:
System: A set of elements that when combined have a “quality” that is notpresent in any of the individual elements themselves.
Systems Engineering: A holistic, interdisciplinary management process, aimedat evolving a lifecycle balanced set of systems solutions which satisfyuser/customer needs.
Pyramid of Systems Hierarchy (reverse order):
Components
Subsystems
System
System of systems
Enterprise
Factors influencing development of systems engineering?
Advancement in technology
Competition
Specialisation
Name any two principle of systems thinking
Hierarchy
Viability
Completeness
Emergence
Boundary
Holism
Name any two systems engineering problem solving “STEPS”
Understand the problem context
Identify and understand the problem
Generate potential solution options
Implement the chosen solution
Review the success of the solution
Name all four elements that make “Structure of systems engineering”
SE Management
Requirement and architecture definition
Development of sub-systems
System integration and verification
What is the lifecycle, lifecycle stage, lifecycle process?
Lifecycle: The evolution with time of system from idea/concept to disposal
Lifecycle Stage: An identified objective in the life of a system
Lifecycle Process: A sequence of tasks needed to achieve a defined goal
Name any generic process model
Waterfall Model
Spiral Model
V-Model
Spiral to circle Model
What are the process interdependencies contained within the “V” model?
User tests (Stakeholder requirements, Validation and Transition)
System tests (Requirement analysis, Verification)
Integration tests (Architectural design, Integration)
Sub System tests (Sub system design, Build and Test, Verification
What is system design methodology?
The path which needs to be followed to achieve three primary objectives in system design:
Initiation of the creative process
Envisage all elements necessary
Ensure design has appropriate consequences on environment and society
Name any two types of customer needs?
Direct
Latent
Constant
Variable
General
Niche
What represents the house of quality?
A method of benchmarking Quality Function Deployment, represented by a house
What types of system architecture we recognize?
Integral: Each tool only performs one task
Modular: Substructure that correspond to the subsets of the system function model
Name any two methods used for concept design? Two from:
Brainstorming
Brain Ball Method
C-Sketch/ 6-3-5 Method
Theory of Inventive Problem Solving (TRIZ)
Morphological Analysis
Name any four on-board Aerospace systems? Four from:
Hydraulic
Pneumatic
Electrical
Fuel
Landing gear
Air con and Pressure
Environmental
Emergency
Flight controls
Navigation and Avionics
On board electronics
From perspective of safety, and the success of the mission, how do we classify aerospace systems?
Primary, eg. Flight Controls
Secondary, eg. Air Conditioning
Auxiliary, eg. Passenger Entertainment
What are the design specifications for an aerospace system?
Qualitative and quantitative definition of system functions
Definition of environmental characteristics:
Pressure, temperature, density, humidity, microgravity, radiation, acceleration, vibration.
What are the most important design constraints for an aerospace system?
Relations to the other systems or structure or propulsion of the aircraft, eg.
Available volume
Weight, eg. COG of aircraft
What do the functional diagrams of the system represent?
Also known as block diagrams, represent the functions performed by system components
Name any type of technical drawings:
Parts
Components
Sub-assemblies
Installation and assembling
Interfaces
Other on board systems
What is viscosity of fluid?
Resistance of a fluid to flow
What is dynamic viscosity and what is kinematic viscosity? Unit for both dimensions?
Dynamic: μ=Fh/AV (Pa.s) in Poise where 1P=0.1Pa.s
Kinematic: υ=μ/ρ (m^2/s) in Stokes where 1St=1cm^2/s
What is vapour pressure?
A way to define the volatility of a liquid, its tendency to evaporate
What represents flash point of hydraulic fluid or fuel?
Flammability
What is auto-ignition point?
The lowest temperature when a flame is generated in the presence of air with no external ignition
What is compressibility of fluid?
The ability of a fluid to change volume when subjected to a changing pressure
What represents β and what is the unit of β?
Bulk Modulus, a measure of compressibility
Units Psi or N/m^2
What is “effective bulk modulus”?
In real hydraulic systems small amounts of air enter the system, increasing compressibility
Define the pascal’s principle?
Pressure is transmitted over the entire volume of the fluid, if it is in static conditions
What represents “pressure drop” phenomenon?
Also known as head loss
Despite constant pipe diameter and height and no energy exchange, pressure will decrease
Caused by internal friction
Represented by α, the pressure drop coefficient
What is Reynolds number?
A measure of the turbulence of a flow
What represents hydraulic diameter?
α=λ(L/D), where λ is the friction coefficient
λ= λ(Re)
For fully turbulent flow, friction coefficient is a function of which parameters?
Reynolds number and internal roughness
What represents loss coefficient?
P1 = P2+ 0.5αρ*V^2
Describe the phenomenon of “water hammer”?
Over pressurisation due to rapid closure of valves
What is the purpose of hydraulic system?
Transformation, distribution, and utilisation of mechanical energy through use of incompressible fluid at high pressure
What type of hydraulic device generates and maintains pressure inside hydraulic system?
Hydraulic motors and pumps
What are the main positive aspects of hydraulic systems?
Low weight per unit of installed power
High efficiency of the power transmission
Great flexibility in installation
Ability to withstand overloads without damage
High reliability
Reduced maintenance requirements
Low inertia of system, therefore high frequency response
Ease of control
Which aircraft systems are powered by hydraulics?
Landing gear movements
Airbrakes
Wheel brakes
Nose wheel steering system
Flight controls
Control surfaces
Thrust reversers
Doors
What are the advantages of high pressure hydraulic instillations?
Small size actuators/cylinders for same level of required force
Components are smaller, therefore weigh less
Flow required and fluid velocity in pipes lower, and tubing is smaller
Which types of pump works on fluid-dynamic principle?
Centrifugal
Hydraulic shock
Axial
Magneto fluid-dynamics
Which type of volumetric – positive displacement pumps you know?
Reciprocating, eg. Piston
Rotary, eg. Rotary valve, gear
What is the required number of pistons for smooth operation of piston pump?
Seven to Nine
How operating pressure affects the flow capacity of positive displacement pumps?
Flow rate decreases due to loss of volumetric efficiency as pressure increases
Why should we keep pressure constant in hydraulic systems?
Sizing of actuators is based on constant pressure and calculated external loads
Prevent interference between multiple consumers
What are the methods of flow regulation for volumetric pumps?
Pump with constant delivery with regulator valve in a hydraulic pipeline downstream of a pump to control required flow
Pump with variable flow delivery
What is the purpose of piping in on-board aerospace hydraulic systems?
Distribution of pressure between generator and consumers
What is the role of hydraulic accumulator?
Pressurised storage of fluid for:
Short emergency operation of branches or single components
Damping of pressure fluctuations
Name any two types of hydraulic accumulator
Spring
Direct gas fluid
Gas piston
Gas diaphragm
Gas bladder
Name any two types of hydraulic cylinders-actuator
Unidirectional:
Single acting
Bidirectional:
Double acting
Double rod
Dual feed
What is purpose of heat exchanger in hydraulic system?
Maintain temperature of a system
What is function of relief valve?
Release pressure should it raise above a certain point
What is function of check valve?
Allow fluid to flow in only one direction
What is purpose of hydraulic distributor?
Distribute hydraulic fluid, hence hydraulic pressure
What is the purpose of environmental control system on board of the aircraft?
Ensures the environment of cockpit/cabin is safe and without hazard in all flight conditions
What is the use of ECS on board aircraft?
Supplied by air from pneumatic systems
Control thermodynamic processes to ensure temperature, pressure, and humidity requirements
Mixing recycled and external air
Air filtering
Uniform air and pressure distribution
What is “equivalent altitude” for cabin pressure?
Comfortable at 8000ft or 2400m (>750mBar)
What is source of cabin air?
Aircraft pneumatic systems
Name one type of thermodynamic cycle for supply of cabin air? One from:
Simple inverted joule cycle
Boot strap
How can we control the oxygen supply in passenger cabin?
Normal Conditions:
Computer monitor environmental parameters, air flow regulated through valve and in flow depending on environmental conditions and change in pressure
Emergency Conditions:
Emergency oxygen for cabin crew and passengers, landing gear doors opened to regulate pressure
Name all types of hazardous weather conditions:
Wind Gusts
Hail
Ice
Atmospheric Electrical Discharge
What are the effects of ice-build up on an aircraft?
Deteriorated aerodynamic characteristics of the aircraft
Damage to controls and control surfaces
What types of anti-icing and de-icing systems on-board of the aircraft you know?
Heat exchanger
Fluid injection
Electric
Pneumo-mechanical de-icing (boots)
What is the basic solution to prevent the damage to an aircraft when the lightning strikes?
Make the Whole structure a good conductor, with no gaps in the conductive path which may cause overheating or localised melting
What is the purpose of the fuel system?
Carry required amount of fuel
Distribute fuel to engines and maintain required fuel levels
What we need to know in order to size an aircraft fuel system?
Required fuel volume
COG shifting limitations
Minimum and maximum flow rates
Limitations in pressure differences
How much percentage of the MTOW is fuel for the passenger aircraft?
30-45%
What types of fuel tanks you know?
Rigid
Flexible
Integral
What is the purpose of ”tip-tanks” and where are the tip-tanks located?
Located at wing tip
Extended range/endurance of aircraft
Which of these three aircraft angular motions, is most affected by the location of the tip tanks – pitch, yaw and roll?
Roll
What are the advantages and the disadvantages of the integral fuel tanks in the airplane wings?
Advantages:
Utilises free volume
COG of system close to COG of aircraft
Acts as a counterweight, reduces load on wings
Disadvantages:
Increased moment of inertia in roll axis
Little volume in supersonic aircrafts
Vulnerable area exposed to projectiles
How can we refuel the airplane?
Loaded from the outside under pressure though central inlet valve and on board fuel distribution network, controlled by fuel control panel
In case of emergency landing, what should be done with the excess amount of fuel on-board of the aircraft, which is not required/allowed for landing? Which aircraft sub-system should be engaged to “handle” he fuel surplus?
The jettison system is a convenient way to rapidly discharge fuel and minimise risk of fire
How we can measure the quantity of fuel in the airplane reservoirs?
By checking the volume of fuel in reservoirs, inclusive of temperature effect correction
Describe the working principle of any type of fuel level probe:
Potentiometer:
Measure linear displacement of probe floating in fuel, using linear variable differential transformer
Name all components of the landing gear that are able to absorb and dissipate aircraft impact energy on touch-down during landing?
Shock absorbers
Tires
What are the values (limits) for permissible vertical component of landing speed?
Approximate maximum limitation of 3m/s vertically
Descried the working principle of landing gear shock absorber?
Reversibly deformable object capable of dissipating kinetic energy
What type of shock absorber you know?
Deformable leg leaf spring
Coil spring
Rubber pads
Spring/Ring spring
Hydro-pneumatic
Name the flight control surfaces required to move aircraft about the principal axes of inertia, i.e. pitch, yaw and roll?
Normal axis (yaw): Rudder
Longitudinal axis (roll): Ailerons
Lateral axis (pitch): Elevators
What are the primary flight control and what are the secondary flight controls?
Primary:
Rudders
Ailerons
Elevators
Secondary:
Flaps
Spoilers
Airbrake
Engine control
Thrust reversers
Landing gear extraction/retraction
What combination of control surfaces represents the following: elevon, flaperon, taileron, and ruddevator?
Elevon: Delta wings for pitch and roll, if no horizontal tail is present
Flaperon: Trailing edge flaps/ ailerons across whole span
Taileron: Stabilisers/ ailerons
Ruddevator: Rudder
Name all four methods for actuating flying controls?
Manual
Electric
Pneumatic
Hydraulic
What is the purpose of balance tab on control surface?
Provides aerodynamic balance and makes it easier for the pilot to move the controls
What is the difference between power assisted and power operated flight controls?
Assisted:
Moves both flying control and pilot valve
Reversible controls
Operated:
Moves only the pilot valve
Irreversible controls
What are the main characteristics of fly-by-wire flight control systems?
Replaces manual flight control with an electronic interface
Reduces weight and pilot workload
Commands input without pilot knowledge
What are the advantages of fly-by-wire flight control systems?
Flight envelope protection
Increase in stability and handling qualities
Turbulence suppression, hence reduction in fatigue and passenger discomfort
Thrust vectoring to reduce need for aerodynamic controls
Drag reduction by optimising trim
Higher stability during release of fuel tanks and weapons
Weight and maintenance reduction
Reduction in pilot training costs
What is the weak point of fly-by-wire flight control system?
If the control software fails loss of life may occur
Which types of aircraft cannot fly without fly-by-wire flight control systems by default? Name at least one type of airplane in each category?
Inherently unstable aircraft, eg. F117 Stealth Bomber, B-2 Bomber
Forward swept wing aircraft, eg. Sukohoi SU-47, Grumman X-29
Thrust vector control, eg. Sukohoi T-50, Rockwell MBB X-31
Aircraft with manoeuvring difficulties, eg. Harrier Jump Jet, Osprey
Name all helicopter’s flight controls? Which flight controls we are using to move helicopter left – right? Forward-back? Up-down?
Cyclic (lateral): Varies main rotor blade pitch, induces roll
Cyclic (longitudinal): Varies main rotor blade pitch, induces nose pitch
Collective: Collective angle of attack for main blades, up and down
Anti-torque pedals: Collective pitch of rear blades, yaw rate
