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Aeronautical Notes
Engineering Studies
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Aeronautical Engineering
Scope of Profession
Nature and scope of the profession
- From purely mechanical view involves the study of how things fly, move through the air or move into space.
- Involves considerations such as: a) Human, physical and psychological stresses pilot performance b) What tools, procedures are necessary to design the tools, instruments etc to maintain and repair modern aircraft or space craft? c) How can aircraft designs be improved? (environmental concerns, noise etc)
- Aeronautical engineers work as part of a very efficient and organised team
- Often work at great speed and under immense pressure
- Main thrust of the profession lies in design, development, maintenance teaching. Also involved in non conventional fields such as air turbine production. Current Projects and innovations
- Constantly engaged in design of new aircraft – improve air travel and defence.
- For many years they have used composites to reduce weight of aircraft (less weight = longer range, more weapon load)
- In civil aviation, recent development = A380 airbus. Its development will depend on increased power, increased lift and reduced weight. Health and Safety Matters
- Risk of – machinery, OHS, design airplane testing.
Career Prospects
- Greatest employment in Defence Forces (need engineers to deal with modifications and upgrades to various aircraft).
- Large companies eg Hawker de Havilland Unique technologies in the profession
- The turbine – developed in late 1930s.
- Aircraft alloys (properties looked for in aeronautics = strength to weight ratio, formability, durability and corrosion resistance, and ultimate property is stability at high temperatures). Such materials include titanium and nimonic alloys.
- Composite and adhesive technologies – offer good specific strengths joined with adhesives. Euro fighter and Saab Gripen. Legal and Ethical Implications
- They must consider the health impacts and safety of their design.
- Ethically engineers have a responsibility to report their findings truthfully and accurately.
- Long term Environmental impact
Engineers as managers 1) They may be manager of their design process, overseeing development of a project. 2) Good managers of companies – skills as engineer Relations with the community 1) They provide fast and safe transport 2) They have to be proactive in considering the complexities inherent in sustainable development and community impacts. 3) Excessive noise pollution of the air, water and land, sustainability, waste disposal and recycling are all issues that can impact on the community, both locally and globally. Historical Development Early Years o Hot air balloons and human gliders (first aerodynamic testing) o December 17 1903, Wilbur and Orville was first to successfully fly with biplane (two wings) Flyer I. Kitty Hawk, North Carolina. o Harry Farman used ailerons first in France. They were a flap mounted on the outboard aft surface of each wing. When moved up, it varied the lift and caused the plane to bank. o Banking: Rolling to a side to turn. Wings were warped to achieve this. o Biplanes, triplanes and monoplane were used. o By WWI, they weren’t looking like gliders but more like planes. o German, British, French and American led the way in air defences. Rapid growth in plane development. Jet Age
Military Jets
o 1938 Frank Whittle developed turbojet engine; improvements in speed and rate of climb. o In WWII, there was a rush to develop the first jet fighter (between Germans and British). First flight made by German Heinkel He178 on 27th August 1939. First operational turbojet fighter with the Gloster Meteor on March 5th 1943 and operational duty July 1944. o First German jet fighter was Messerschmitt Me262 Schwalbe (Swallow) in July 1942 but operational in late 1944. Impressive speed and cannons mounted at nose. o Germany had advanced really fast; developed Arado bomber and small Messerschmitt Me163 Comet rocket plane. o British developed centrifugal turbojet while Germans used axial flow turbojet. Centrifugal was more bulky and eventually everything was axial flow system. o Jet propulsion airplanes overtook the design and development priorities. USA had most money for fighter development. Britain had Vampire twin boom jet.
800km/h). US tried to match with turboprop airliners, but waited for a new fast jet airliner. o De Havilland Comet entered service in May 1952. One incident saw the Comet run off the runway because its nose was too high and wings didn’t give enough lift. Then March 1953 at Karachi airport over rotated (nose too high) and eleven were killed. It ran the entire runway and struck a culvert and swung into a gully and burst into flames. o March 1953, a Comet was lost at altitude of 32,000 ft when turbulence caused tailplane to fail. 37 passengers and 6 crew perished. o On 10th January 1954 a BOAC (British Overseas Airline Corporation) Comet left Rome en route to London. At 26,000 ft it exploded in the middle of radio transmission. This happened again when BOAC Comet left Rome en route to Cairo exploded over the Mediterranean Sea at 35,000 ft. Both were climbing to operating altitude. Testing of the Comet was underway. It was discovered that two small fibreglass antenna windows at the top of fuselage had ruptured the fuselage. The rivet pattern and window design promoted propagation of fatigue cracks. The fuselage cracking meant explosive decompression. 2 million pounds were spent on investigation and was later fixed by de Havilland and released Comet 4, holding 81 passengers and made regular transatlantic flights. o The Boeing 707 was to become the most utilised aircraft of its time. It used 4 turbojet engines beneath the wings. It carried about 180 passengers, more than any typical load. Similar looking McDonnell Douglas DC-8 was also leading the world commercial jet industry. o BOAC created Vickers VC10 to cope with shorter runways in Africa and the Middle East. It has four low bypass turbofan engines on either side of the T tail, with high efficient wings using leading edge slats, outboard ailerons, upper wing spoilers and larger fowler flaps. However, most airports were willing to lengthen runways for American planes so VC10 were not necessary. o It was upgraded to VC10 Super. It could carry 187 passengers and had a longer range. Quiet operations were quite appealing. It had split control system driven by separate power units, managed by two autopilots that monitored each other. High level of system reliability, which was the first for ‘hands-off’ automatic landing in nil visibility conditions. However, technical design meant very costly to operate (more than 707). American planes dominated so VC10 was not used much. o Boeing 747 or ‘Jumbo Jet’ was a major step and originally for US Air Force transportation. The passenger jet had 4 high bypass turbofan engines, advanced wing design and complex high lift devices. Original 747-100 carried 397 passengers and was only outclassed in 2001 with Airbus A380 holding 555 passengers. o Passenger jets were designed to operate at supersonics speeds. The first was Soviet Tupovlev Tu144. It was similar to concord but withdrawn after crash at air show. o British Aerospace/Aerospatiale Concorde first flew in 1969 and is only supersonic transport in regular service. Uses military technology to produce fast speeds. Cabin was cramped but time saving. However, in 2000 after a fatal crash were Concords removed from service. The fuel tank was hit by debris, causing a fuel leak that ignited the rear of the plane. o McDonnell Douglas DC-10 released after Boeing 747 with three-engine arrangement (one at each wing and one in the tail). Third engine was requirement to operate from existing runways. This had fewer problems as one engine out, not all
thrust was away from centreline. Still used today and also by US military as in-flight tanker. o Boeing is dominating the aircraft industry with it only main competitor of Airbus. Airbus is owned by a European consortium EADS (80%) and BAE Systems (20%). The Effects of Engineering Innovation on peoples lives
- Made travel more accessible
- Faster, luxurious and longer travel
- Military – so advanced, can be used instead of ground troops
- Acting as ambulances, save lives, fight bushfires
- Boosted tourism (esp. isolated Australia) Environmental Implications of flight
- Pollution – from piston and turbine engines
- pollute environment with exhaust gases
- fuel dumping
- noise pollution
- Insect spraying – became easier and more large scale using conventional aircrafts and helicopters, protect crops but affects food chain
- Destruction – aerial bombing, destruction far away from base.
Engineering Mechanics and Hydraulics
Flight mechanics Part Definition Fuselage Houses flight crew passengers and freight. Pressurised to allow people to survive at high temps, where turbine aircraft are most efficient Wing Provides most of the lift to support aircrafts weight. Ailerons Outboard trailing edge sections of the wing used to control roll Flaps Inboard trailing edge sections, used to generate additional lift during low speed manoeuvring and landing Horizontal stabiliser (tail plane) In level flight it provides downward force to keep aircraft level and stable Elevator Trailing edge sections of the horizontal stabiliser, used for pitch control (force and aft rotation). Fin (vertical stabiliser) Used to provide left/right stability. Together with the rudder it provides yaw (left right) control Rudder Trailing edge section of the fin
Newton’s 3rd law: 1. lift is produced as a reaction to the action of the wing in changing the direction of air downward 2. This change in direction occurs both below the wing due ti oncoming air hitting the underside of the wing and above the wing by the “coanda effect”. 3. “Coanda Effect” described the way in which a fluid tends to follow a curved surface. 4. The wing creates an action force on the air redirecting it downwards and the air creates a reaction to the force pushing the wing up. Drag:
A force resisting movement of the aircraft through the air.
mechanical force generated by the interaction between a solid body and a fluid (aeroplane and atmosphere)
Generated by difference in velocity between the solid object and the fluid.
Induced drag – drag developed as a result of lift production
Parasitic drag = drag resulting from moving the aircraft shape through the air. Thrust:
forward force caused by the power plant (engine)
In propeller driven aircraft thrust is generated by the movement of the blades through the air.
When rotating the propeller blades cause the air to flow such that the static pressure ahead of the blade is less than that directly behind the blade = forward thrust on propeller blade (pulling aircraft through atmosphere)
When thrust = drag we get constant airspeed
When lift = weight we maintain level flight. Basic Aerodynamics Stalling is produced when:
low airspeed below a certain point
angle of attack above a certain angle
when wing can’t make lift
can occur during landing (increase of drag, nose up, angle of attack)
To avoid this flaps are placed on plane wings to increase lift at a given angle of attack and airspeed – produce required lift at low speed (also produce additional drag to assist slowing down). Bernoulli’s Principle Venturi effect Think of fluid through a pipe with a constricted section where there is no difference between height, then Bernoulli’s equation = P+1/2pv
This effect allows the aerofoil to provide lift
As air passes over the aerofoil, the air on the upper surface must travel faster than the lower surface.
If velocity has increased then pressure must decrease to keep the equation constant
Thus the pressure on the top of the wing is lower than the pressure below the wing – lift because of different pressure.
As velocity increases, temp decreases (ice on wing = de icing systems) There are three basic methods an aircraft can use to increase the lift force over its wings: Angle of attack, increasing the camber of the wing (wing section) and increasing the speed of the relative airflow over the wing. o Increasing the wings’ angle of attack – the angle at which the leading edge of the wing meets the oncoming relative airflow. o Because of AOA the air below the plate will be compressed by the lower surface of the plate – air above the plate experiences reduced pressure. o Static pressure below plate is higher than above the plate causing net upwards reaction o Glide angle Lift Glide Angle
Rivets and bolts of aircraft experience both shear and tensile stresses Bending Wing spars in an aircraft in flight undergo bending stresses Torsion Produced in engine and turbine crankshafts while the engine is running Forces causing torsional stresses produce torque or turning moments. (Page 226 Excel) Propulsion Systems Turbojet contains
- Inlet – air enters and is compressed slightly
- Compressor – sets of turning blades which compress the air, hence heating it.
- Combustor/burner – fuel is injected into the combustion chambers where it is mixed with the compressed air and burned.
- Turbine – burnt gases expand through the turbine stages, which are rotated by the gas flow. The turbine is connected to the same shaft as the compressor and provides the energy to drive the compressor
- Nozzle – the gas is expanded through the nozzle and exits the engine as very hot, very fast gas, providing the thrust. Turboprop
- Same operation as the turbojet but a turbine is used to power compressor and drive the propeller.
- Majority of the energy of the gas is used to drive the turbine leaving only a very small amount of exhaust energy to provide thrust. Advantages of turboprop
- control is simple because one lever controls speed and power
- with large airflow cooling is less complicated
- well suited to middle-distance aircraft
- Suitable on short runways. Disadvantages of turboprop
- poor performance at low power setting, low speeds and low altitudes
- the large gear box has many moving parts (that could malfunction and impede the air stream)
- High level of fuel consumption.
Turbojets are efficient at high speeds and high altitudes while turboprop aircraft are more efficient at speeds below 840 kph and altitudes below 10000m. Turbofan
- Same operation as the turbojet but with additional fan stage mounted inside the nacelle, forward of the compressor (i. aft the inlet)
- an additional turbine stage drives the fan
- known as bypass engine nacelle passes around, not through the engine (approx 5:1 by weight)
- the fan cuts as a ducted propeller producing thrust from the bypass air while the engine still produces thrust as per the turbojet
- Majority of net thrust produces by the fan.
- The advantages of turbofan are that the bypass air shields the hot engine core gases reducing noise significantly and they are more efficient than turbojets. Ramjet
- has no moving parts
- shape of engine compresses the entering air
- This compressed and hence heated air has fuel injected and then a flame holder ignites the fuel air mix.
- the expanding gases are forced out the mozzle to produce thrust
- The disadvantage – needs to reach high speeds to work – makes it useless for take off, landing or low speed work. Fluid mechanics Relative Speed – the rise in dynamic pressure due to relative speed occurs because of the fact that as an object travels faster, more molecules of air will impact upon the object per second. Air density - at sea level a body in movement would thus register bum nay more particles and thus registers a much high Pd. At higher altitudes dynamic pressure will be lower even though relative speed will be the same
The three non destructive tests that are used to ensure the airframe is in good order are: o X-ray o Ultrasonic o Dye penetrant. These are discussed in previous topics. Advantages of NDT:
- The same test may be repeated over and over again
- Tests may be performed on parts in service
- Equipment is often portable for field use Limitations of NDT:
- Some NDT requires some large capital investment
- without correlation different observers may disagree on the meaning and significance of some results Magnetic Particle testing piece of metal is placed across 2 magnetic poles or a magnetic field is induced in it or sprinkled with magnetic powder the excess powder is removed and cracks are revealed by magnetic powder striking to the area each side of the crack major limitation is only works in magnetic materials (useless with aluminium and titanium) Eddy Current testing: Inducing small eddy currents into a conductive article with a probe and observing the interaction between the article and the currents on a display. Allows the detection of second or third layer cracking invisible form surface as well as revealing thinning of any different layers making up structure. Applications = inspection of rivet and bolt holes, tubular components and undercarriage wheel hubs.
Materials One prime consideration in material selection is low weight and optimum strength. Steel Has high density compared to aluminium and titanium Can be alloys and heat treated to produce desirable mechanical properties. Material finds application as the landing gear which must be very strong yet cannot take up too much space. Aluminium and its Alloys The use of dural Unum (aluminium and copper) enabled some of the aerodynamic forces to be carried by stressed skin of the wings and fuselage. Aluminium and its alloys posses the following properties:
Composites Composite materials offer good specific strength, high resistance to cyclic stresses and weather resistance. Types Carbon Fibre Composite of carbon fibres embedded in a matrix epoxy resin. This combination produces desirable strength and toughness. Lightweight, very high specific strength and high modulus of elasticity. Fighters such as Saab Gripen and Euro fighter Typhoon use them as well as Boeing 737 and Airbus control surfaces and wingtips. Disadvantage is that failure is often sudden and catastrophic and complex damage detection and repair. Aramid Fibre Similar to carbon fibre but Aramid fibre are used in lieu of the carbon fibres in a epoxy resin matrix. A.k. Kevlar. More resistant to impact relative to carbon fibre. Metal Matrix Composites (MMC) Similar to carbon fibre except the matrix is not a polymer but a metal eg boron fibre aluminium.
This improves tensile strength MMS’s are capable of withstanding higher temperatures as the metal matrix can withstand elevated temperatures better than epoxy matrix. They are however heavier than polymer matrix composites. Adhesives Epoxy adhesives are used to join composite aircraft surfaces to the base structure eg Euro fighter Typhoon uses them. Corrosion
Aeronautical Notes
Subject: Engineering Studies
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