Aeronautical Engineering Flashcards
nature and scope of the aeronautical engineering profession
study of how things fly, move move through air or move through air into space also:
- what are the human, physical and psychological stresses that affect the performance of pilots?
- what systems and procedures are necessary to design the tools, instruments, wind tunnels or probes that are used to maintain and repair modern aircraft or spacecraft?
- how can aircraft designs be improved in response to environmental concerns regarding noise and emission pollutions?
current projects and innovations
- manufacturing processes that overcome limitations of low metal removal rates and rapid tool wear when working with extremely hard materials
- 3D metal forming process for integrated aero structures, to produce large and intricate, double-curved shapes.
- fuel trials using sustainable alternatives such as biofuels
- fire resistant composite urethane-based components and alumni-trihydrate adhesives
- flight management software and systems that monitor and adjust real-time energy demands to improve efficiency, reduce heat and lower emissions.
health and safety issues
- excessive noise from aircraft in both the field and workshop environments
- exposure to potentially dangerous chemicals and vapours from solvents, surface treatments, fuels etc
- dirt, dust and fibres. they use a wide range of composites that may require sanding or grinding
training for the profession
what do they study?
similar educational foundation of maths and science but also study aerodynamics, aircraft structures, aircraft design and control.
use of flight simulators so student can become familiar principles of flight, the controls and instrumentation
career prospects
military, commercial, general aviation
perform tasks such as:
- investigating aircraft crashes
- overseeing modifications to aircraft
- studying aircraft defects and recommending repairs or modifications
- designing new aircraft or modifications to existing aircraft
- designing equipment or tools to repair or maintain aircraft
- creating instructions on how to use, maintain and calibrate this equipment
- interpreting data and making appropriate recommendations for action
- giving technical and regulatory/legal advice to professionals within the aerospace industry
- discussing designs and data with colleagues, aircraft engineering trades people, aircraft manufacturers and airline owners
- creating paperwork, which is to be kept on file for future reference, for approved data
unique technologies in the profession
advanced composites: metal, polymer and ceramic matrix composites
legal and ethical implications
engineers need to report their findings truthfully and accurately to ensure decisions are properly documented and defensible.
Certification of new aircraft designs, the modification of existing systems and structures and the establishment of repair and maintenance routines.
inflight tests to ensure handling and performance. Maintenance engineers ensure the aircraft is safe and operational. regular inspection, maintenance and servicing. must be licensed.
long term environmental impacts - toxic by-products of manufacturing processes, exposure to dangerous substances, any health and safety issues regarding disposal of aircraft.
engineers as managers
profits, time, prestige
make right decision in the interest of public safety.
relations with the community
traffic problems, flight paths, noise and air pollution, ozone depletion, life cycle impact of aircraft operations and materials.
historical developments in aeronautical engineering
400 BCE: kites used in china
100 BCE: heron developed the aeolipile which helped Newton formulate the 3rd law of motion, explains lift
1783: hot air balloon
1799-1850s: modified gliders.
1903: wright brothers made first sustained flight, 12 seconds and 31 metres
wood and cloth —> steel and aluminium alloys, titanium alloys and carbon fibre.
the effects of aeronautical innovation on people’s lives and living standards
made flying possible. ever increasing power, reliability and fuel consumption. brings people, cultures and commodities close together
environmental implications of flight
- noise pollution
- climate change
- stratospheric ozone reduction, leading to increased surface UV radiation
- local air pollution
aircraft emit carbon dioxide, oxides of nitrogen and sulphur, water vapour, hyrdocarbons and soot particles when flying
solutions to problems
- alternative fuels
- operational improvements through direct routing of smaller aircraft
- higher load factors and optimisation of aircraft speed
- policies and regulations, including more stringent engine emissions certification standards
- intermodal transport networks (Swap short flights with buses and trains)
- technological improvements such as improved engine and airframe designs resulting in great fuel efficeincy
fundamental flight mechanics - lift to drag ratio
during level unpowered flight, the plane will descend rapidly due to the fact that the thrust/drag relationship is unbalanced.
fundamental flight mechanics - effect of angle of attack
angle at which the leading edge of the wing meets the oncoming air. As the angle increases, the lifting force of the wing increases (until stall). the effect is to increase the amount of air redirected downward from both above and below the wing. as the lift increases steadily until the critical angle, it is normally the point where the combined drag is at its lowest that the wing or aircraft is performing at its best.
Bernoulli’s principle and its application to - venturi effect
typically demonstrated through the use of a necked-in tube, where the fluid is forced to speed up as it moves through the necked-in area.
The pressure is less at the necked area than the normal area. also a reduction in temperature.
this has important implications for icing of both external and internal components such as leading edges of wings and the formation of ice in carburettors
Bernoulli’s principle and its application to - lift
the velocity of air over the top of the wing is greater than that below the wing, resulting in pressure variation in the air around the wing, this creates lift.
bending stress - airframes
Stresses induced into the aircraft and their structures include:
- vibration
- wind shear
- take off and landing stresses
- temperature stresses (expansion and contraction)
- pressure differentials, internal pressures are higher than external pressures
types of stress
- tension: pulling or stretching e.g. elevator control cables
- compression: squeezing e.g. when on runway aircraft landing struts are in compression
- shear: sliding one part over another, when 2 pieces of fastened material try and separate. e.g. rivets and bolts
- bending: combination of tension and compression e.g. wing spars
propulsion systems including - internal combustion engines
Take place within an enclosed cylinder, inside cylinder is a moving piston which compresses a mixture
of fuel and air before combustion and is the forced back down the cylinder
propulsion systems including - jet including turbofan, ram and scram
Blades bring air into engine where its compressed. This is completed by a series of rotors and stator blades. Rotors push air backwards into engine, stators straighten the flow and force deeper into a combustion chamber.
Travels from low compression set of rotors and stators to high compression set. Combustion chamber received high pressure air, mixes fuel with it and burns mixture. Hot, very high velocity gases are produced striking the blades of the turbine spinning rapidly. Hot gas expelled through the exhaust section both straightening the flow of gas and inducing
propulsion systems including - turboprop
Propeller driven by a gas turbine engine. Thrust produced 90% by propeller and 10% by exhaust gas
- Propellers force air into a series of compressors where they are forced into a combustion chamber, here
they are combined with fuel and ignited to primarily turn the driveshaft in turn rotating the prop and thus
creating thrust.
- Propellers reduce efficiency at high speeds and as such aren’t used on aircrafts travelling over 850km/h.
Only used on smaller, private aircrafts
propulsion systems including - rockets
jhv
fluid mechanics - Pascal’s principle
basis of all hydraulic systems.
in aviation, two prospects of fluid mechanics considered are: the systems of sensors used in the aircrafts instruments, the systems of fluid (liquid and air) pressure used in an aircrafts avionics
hydraulic systems take engine power and convert it to hydraulic power. the power can be distributed throughout the aircraft by tubing.
pressures measured in megapascals.
actuating cylinder converts hydraulic or fluid power into movement or mechanical energy
fluid mechanics - hydrostatic and dynamic pressure
hyrdostatic - static pressure in the atmosphere at any point is exerted equally in all directions. Static pressure does not involve relative movement of the air. It is produced by the weight of all the molecules in the air. Static pressure is measured on the surface of an aircraft by a static vent.
dynamic - is an additional pressure that is generated due to relative movement and is felt by a body that is moving relative to the air. Just how strong this is depends on the: density of the air, and the speed of the body relative to the air.
fluid mechanics - applications to aircraft components and instruments
altimeters, airspeed indicators, vertical speed indicators.
each of these basic instruments are measures of air pressure outside the aircraft. need to take in to account dynamic and hydrostatic pressure.
specialised testing of aircraft materials - dye penetrant
oldest methods of non destructive testing, used on non-magnetic materials.
involves wetting a surface with fluro dye, on for a sufficient time and allowed to seep into surface discontinuities. excess dye is removed before a light coloured developer is applied to reveal any cracks, voids or flaws in surface. cracks visible to naked eye.
used on aircraft wheels, landing gear and braking systems
specialised testing of aircraft materials - X-ray, gamma ray
use of radiation projected through the component to be tested and onto a film. the image varies in contrast based on variations in the density and thickness of the component. Internal cracks, porosity, shrinkage, delaminations and corrosion appear darker than sound material.
Advantages:
- creation of a permanent image of inspection
- the ability to inspect without the need for disassembly of components.
although portable, the size of x-ray equipment can restrict its application..
aviation applications include:
- inspection of welds, rivets, composite bond integrity, nozzle guide, vanes, retention lugs and burner cans.
specialised testing of aircraft materials - magnetic particle
fine magnetic particles such as iron fillings are attracted to the lines of magnetic flux produced by a magnet and will be most strongly attracted where this flux is strongest.
A magnet is placed on the part to be tested. in so doing, the magnetic lines of force flow from north pole of the magnet through the test piece to the south pole. A crack lying along this path disrupts the magnetic flux and effectively creates a local north and south pole on either side of the crack.
a mixture of magnetic particles such as iron fillings in a suspension medium is sprayed onto the surface. the particles subsequently accumulate in any crack in the test area.
specialised testing of aircraft materials - ultrasonic
principle of sending ultra-high frequencies into a material and analysing the result signals. a probe sends pulses into a sample through a coupling medium (gel, oil or water). An ultrasonic signal is transmitted into the component under test and a receiver picks up echoes from opposing surfaces and any flaws. the echoes are turned back into an electrical signal through a transducer, which is then registered on a screen.
Pitch and catch, through transmission, transmit-receive
Advantages - test equipment is highly portable, versatility : access to only one side of the part is required, rapid and automated inspection systems are available, penetrating power of pulses allows thicker sections to be examined, highly sensitive and accurate in the measurement of small flaws of both size and positions
disadvantages - signal transmission into other components such as bearings can complicate transmission, differentiation problems where multiple defects occur close to each other or near the surface, can be affected by metal grain size or second phases such as graphite in cast iron, noise discrimination
aluminium and aluminium alloys used in aircraft including aluminium silicon, aluminium silicon magnesium, aluminium copper
Silumin (aluminium silicon)- lightweight, high strength
structure/property relationship and alloy applications - changes in properties
Aluminium and copper = duralumin
- excellent corrosion resistance
- good electrical and heat conductor
- good machining and welding properties
- lightweight almost 3x lighter than steel
- fatigue strength low, especially in precipitation-hardened alloys
- precipitation hardened alloys can suffer stress-corrosion cracking
- structure is FCC, so ductile at all temperatures
Either wrought, worked into form by rolling or extruding, and cast, formed by pouring molten aluminium into a mould.
heat treatment of applicable alloys
Precipitation hardening involves the following
Solution treatment: the alloy is heated to a point where a homogenous single phase is present. This temperature is held until all of the copper is taken into a solid solution.
Quenching: by rapidly cooling the alloy in cold water, the copper is trapped in solution thus preventing segregation. The alloy is now in a soft, readily-machinable condition. The solid solution is supersaturated, however, is an unstable state. Precipitation of the copper is the slowness of diffusion at room temperature.
Precipitation: the alloy is heated to a temperature where the two-phase structure will be stable. For Al-Cu alloys this temperature is normally in the region of 200°C. At this temperature, diffusion can occur and the result is a uniform distribution of fine particles appearing throughout the matrix.
Hardness increases, ductility decreases
thermosetting polymers - structure/property relationships and their application
Examples?
Properties?
Uses?
Polymers are large organic compounds. can be natural or synthetic.
natural - silk, wool, cotton, starch, cellulose, rubber, DNA and RNA.
synthetic - polyethylene, nylon, neoprene, teflon and rayon.
Thermosets bonding between molecular chains is very strong and thus resists melting.
Mechanical properties:
- flame resistance
- optical properties
- impact toughness
- chemical resistance
- strength and stiffness
- environmental durability
- high thermal and mechanical properties
Uses - canopies, windscreens, windows, structural members, tyres, coatings, wall sections and interior linings.
Methods - injection moulding, transfer moulding and compression moulding
thermosetting polymers - manufacturing processes
Thermosetting materials are heated to a plastic state under pressure. Under these conditions of elevated temperature and pressure they are said to set, forming 3D structures linked by covalent bonds.
They therefore form a single large 3D network rather than the mass of molecular chains linked by secondary bonds, as is the case for the thermoplastics
thermosetting polymers - compression moulding
application of pressure with an elevated temperature to distribute a polymer over a mould.
-two metal platens, one fixed one movable, can be internally heated or cooled.
-a sheet or granular form of polymer is placed in the open mould and the plug or movable platen is positioned on top.
-mould is heated while top plug applies pressure
polymer is heated above its glass transition temp where it softens and flows to fill the cavity
-heat and pressure are applied until polymer has cured
mould is cooled before pressure is released and plug removed to allow removal of the product.
can use thermosets and thermoplastics.
advantages - ability to mould small - large parts in intricate detail.
used in aircraft parts such as fairings and components like brackets, clips and window frames etc
thermosetting polymers - hand lay-up
hand lay up is an open mould GRP laminating process used for low volume production and/or large complex components.
Spray deposition is another open mould laminating process where a resin and glass strand mix is sprayed directly onto the mould surface. it is used for producing higher volume products and large complex components, where product thickness tolerances are less critical.
thermosetting polymers - vacuum lay-up
closed moulding process. vacuum assistance is required to close two halves of the mould and to evacuate the mould cavity of any trapped air.
Transparent moulds allow for visual monitoring of the process, resin flow and the removal of porosity. This total elimination of air voids improves material homogeneity and consistency of mechanical properties. semi-automated, this process is significantly faster than either hand or spray lay-up processes
thermosetting polymers - modifying materials for aircraft applications
The use of natural materials such as wood, metal and natural fibre fabrics has disappeared from aviation industry and replaced with highly modified materials, synthetics and advanced composites
composites - types including reinforced glass fibre, Kevlar, carbon fibre and fibre metal laminate (FML) as used in aircraft construction
used to lighten and strengthen aircraft. fuel economies were improved and speeds increased.
properties such as strength, stiffness, fatigue resistance, corrosion resistance and weight benefits are enhanced. longevity
can be made thinner and can be fabricated into more complex shapes when compared to aluminium.
uses of materials include: nose, and main landing gear, doors, engine nacelles, spoilers, flaps and much of he tail.
used to patch cracks or corroded areas.
Kevlar: uses extrusion process (spinning), strength, lightweight, high modulus aramid fibres with superior toughness. meet guidelines in regards to flammability and highly corrosion resistant. engine cowlings made from kevlar are quieter and less sensitive to engine vibrations.
GLARE: significant weight savings and improved mechanical properties
composites - structure/property relationships and their application in aircraft
combining different materials with very different properties into a single until to create a new material
properties:
- high strength
- exceptionally low density
- lower tooling cost alternatives
- outstanding corrosion resistance
- lower thermal expansion properties
- excellent fatigue and fracture resistance
- ability to be easily formed into complex shapes
- ability to fabricate directional mechanical properties
- ability to meet stringent dimensional stability requirements
used for vertical and horizontal stabilisers, rudders, ailerons, and engine fairings.
corrosion - common corrosion mechanisms in aircraft structures
requires 3 conditions to exist
- the presence of an electrolyte such as water
- the presence of an anode and a cathode: this occurs when two dissimilar metals or two regions of differential electrolyte concentration create a difference in electrical potential
- an electrical contact between the anode and the cathode
corrosion - pit and crevice corrosion
crevice - when water is trapped between two surfaces forming stagnant or shielded areas such as under loose paint, beneath washers or fasteners, or within a delaminated bond-line or unsealed joint. corrosion occurs because oxygen cannot easily be replenished within the crevice and the lower oxygen content forms and anode at the metal surface. The metal surface in contact with the portion of the moisture film exposed to air forms a cathode.
can be very aggressive and because it forms within a narrow gap it can be difficult to detect. contact metals are identical.
pitting - similar to concentration or cell corrosion. generally scattered indications over a surface. It produces cavities or holes that perforate the material surface.
Small, narrow pits with minimal surface exposure can still lead to part failure due to depth of penetration . because of the difficulties in detection, prediction and prevention, the presence of pitting corrosion can present a greater danger to components than uniform corrosion damage
corrosion - stress corrosion/cracking
SCC needs all of these 3 things to happen:
- a corrosive environment
- material must be susceptible to attack
- a static residual or applied stress must be present
can be either intergranular (between grains) or trans-granular (through the grains) depending on environment and corrosive species of environment
commonly occurs on aircraft body and wings.
austenite stainless steel is susceptible
corrosion - corrosion prevention in aircraft
Appropriate design and materials selection for corrosion control is imperative but other factors also play a part including:
- sealants
- drainage
- finish selection
- galvanic grouping of materials
- keeping aircraft surfaces clean
- access for maintenance and inspection
- application of corrosion-inhibiting compunds
