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A PROJECT ABOUT COMMERCIAL AIRLINERS
Air transportation is carrying passengers to their destinations by airplanes and this has become a very important type of transport in the modern world. This is due to people demanding travel between cities and countries with the minimal amount of time. The group that has pushed aviation travel is the business trade group where time is money and they need to travel to another place (often different countries) for meetings. The travel time is preferred to be minimised for efficiency. As for Sydney, inter-state travel is crucial between Sydney and Melbourne, Sydney and Brisbane, Sydney and Canberra as well as Sydney and Perth. The use of aircraft to carry passengers between cities will significantly reduce travel time comparing to travels by coach or rail. Below is a table showing a comparison between travel means between the cities mentioned above. Note- All travel times, frequency and Price are subject to change. Frequency is tabulated from direct routes. Sydney - Melbourne
Melbourne - Sydney
Sydney - Brisbane
Brisbane - Sydney
Sydney - Canberra
Canberra - Sydney
Sydney - Perth
* Effective until 31MAR03 ** Effective from 01APR03 # No direct service is available Perth - Sydney
* Effective until 31MAR03 ** Effective from 01APR03 # No direct service is available * Note: The range in the Price column reflects in different class of service. From the tables above, there is a clear trend that travel by air requires the shortest travel time and has the most frequency. This is again, most important for the business sector travel as short travel time as well as flexibility in travel time is most crucial. In fact, many leisure travellers will prefer to fly to their destination as it will allow maximum usage of their holiday time. Also, since the cost between travelling by air and by rail does not differ too much in most cases for the lowest fares, travellers will be attracted to fly to their destinations. Apart from travelling between cities within Australia, airplanes can transport passengers to other countries. Again, the reasons for passengers travelling international are for business and leisure. The only other alternative for people travelling internationally is by sea due to the geographical location of Australia. During the year 2001-2002, Sydney Kingsford Smith Airport handled 23.9 million passengers, continuing a trend of growing passenger since 1996 of 20.5 million passengers. The figure includes both international and domestic passengers arriving and departing Sydney. International air travel recorded 8.4 million passengers representing 35% of the total passenger movements. International flight movements were 45,795 flights (18% of total flight movements). Domestic passenger movements were 15.5million passengers (65% of total). Flight movements for the domestic routes held at 201,405 (79% of total). The remaining 3% of flight movements were in the nature of freight.
HISTORY OF AIRLINERS The history of airliners began with The Wright Brothers. At 10:35 on 17 December 1903, Orville Wright flew the first ever powered biplane at Kitty Hawk which he and his brother Wilbur built. This marked the birth event of the aviation industry. Due to the lack of technology as well as low demand of air travel at that time, airliners did not prosper in development until after WWII. However, airlines had already operated during the 1920s using biplanes to carry a few passengers at a time. Following WWII, many of the undamaged aircraft used in the war were converted into airliners to carry passengers. These included the DC2 and DC3 which were one of the first aircraft to carry passengers on a scheduled service provided by various airlines. Then gradually over the years, both Britain and the US manufactured larger airliners to carry more passengers. Many turbulent years were experienced before success was finally achieved. Airliners companies such as the de Havilland Comet preceded the renowned Boeing and Airbus nowadays. Boeing first introduced the B707-367-80 on 15 July 1954 which marked the beginning of success from the US in this industry. The success Boeing achieved with the B707 led to the production of further types of airliners, namely the B717, B727, B737, B747, B757, B767 and B777. Currently, Boeing is one of the key companies in the aviation industry along with the European Airbus Industrie. Airbus flown its first airliner, the A300, in 1972 and has developed the A310, A318/319/320/321, A330/340 and A380 since then. The growth of airliners was only possible with the development of the engines used for powering the aircraft. Current airliners use the Turbine Engines as its power unit. History dates the concept of this type of engine from the discoveries of the Egyptians at around 200BCE. The Egyptians invented a device which could convert steam pressure into mechanical power. Then at around 1200AD, the Chinese developed rockets based on the same concept of reaction. The first gas turbine device was used in 1629 by an Italian engineer who produced a steam-driven impulse turbine. Turbine engines are classified into four groups; Turbojet and Turbofan which produce thrust where as the Turboshaft and Turboprop which produce torque. Depending on the aircraft, different engines would be used. Generally, smaller aircraft travelling at below 450mph will use the Turboshaft or the Turboprop engine while aircraft larger than those and travelling faster, use the Turbojet and Turbofan engines. Both the Turboshaft and Turboprop engines do not power the aircraft directly as the power produced are transmitted to the gearbox which then produce the thrust for the aircraft movement. Turboshaft engines consist of a gas generator which produces the energy needed to function the power turbine system. This function requires about two-thirds of the combustion energy produced by the engine. The remaining one-third is used to drive the power turbine that drives the aircraft transmission. The Turboprop engines are an improvement on the Turboshaft engines. Turboprop engines have a propeller which is driven by either a fixed or free turbine. The free turbine is superior to the fixed turbine as the free turbine allows propeller to run at a very low rpm during taxi causing less noise and low blade erosion. Free turbine also makes the engine easier to start in cold weather and the rotor brake can stop the propeller movement without shutting down the engines. However, the disadvantage is that the engine does not have instantaneous power of the reciprocating engines. As for thrust producing turbine engines, there are not power transmission devices as the engines are ‘direct drive’ where the power generated is used directly to move the aircraft. The Turbojet engines operate by air entering the inlet (front of the engine) then passing through the compressor, pressure is increased. When the air is met with the combustor where fuel is present, heat force is created to rotate the turbine wheel. As a chain reaction, the turbine wheel’s rotation will run the compressor. The reaction of this flow of hot gases provides the propulsive power to move the aircraft in a forward motion as the induced air produces energy that goes out at the back of the engine. Thus according to Newton’s third law, for very action, there’s an equal and opposite reaction. Turbofan engines are an improvement of the turbojet engines and are currently the most efficient, low fuel consumption and reliable engine. These engines run on the same principle of the turbojet engines except that there’s an extra set of fan stage in the engine, this is located in the nacelle (which is forward of the compressor just after the inlet). The advantage of these engines is that the bypass ratio is higher than the other types of engines. Bypass ratio will be discussed in section 4 of the report. The turbofan engines is currently the most efficient and quiet engine used by airliners nowadays. Passenger comfort in airliners has revolutionised since the introduction of the DC2. At that time, there was only one class of service and the type of seat was no where as comfortable as any current Economy Class seats. The seats are also unable to recline presents poorly to a passenger’s comfort. The steel frame support of the seats show the simplicity of the seat. There is also no Inflight Entertainment such as movies onboard these aircraft which does not meet the norm of current standards provided by most airlines. On most international airlines nowadays, there are choices between the classes of travel. Namely, First, Business, Premium Economy* and Economy Class. There are variations between the names of the classes as well as the degree of comfort provided by each airline. This is a result of competition to attract customers. First Class is the best class of service onboard each flight and the seats nowadays boast in a seat which can be converted into a flat bed for sleeping inflight. This type of product is mainly available on long haul routes with large international airlines such as British Airways, Cathay Pacific, Singapore Airlines and Qantas as well as other large airlines. Business Class is recline angle, better inflight entertainment and more personalised service comparing to Economy Class. The more premium Business Class service is again, available through large international airlines as well. The difference comparing to standard business class is that passenger can also enjoy the seat being reclined to 180° inflight, however, not as comfortable as first class seats. Finally, Economy Class has also improved through out the years. In normal airlines, the improvements include reclinable seats and having movies shown on the main-screen. In premium airlines such as those mention above for first class, improvements include a better cushioning system on the seat itself, adjustable headrest, footrest, seat pitch of around 32” to 34” and the introduction of Personal TVs as improvements of the inflight entertainment. In some airlines the better Economy Class could be termed as Premium Economy Class.*
The above 2 photos shows the Economy Class onboard Cathay Pacific, these seats include the better cushioning systems, adjustable headrest and the Personal TV. The improvement in passenger comfort is the result of passengers demanding more comfortable seats and services as well as airlines need to provide outstanding comfort and service to keep in competition. More information about passenger comfort and comparisons between different airlines is available at http://www.airlinequality.com/index.htm. Details about classes of service provided by Cathay Pacific are available at the following 2 websites. 1) http://members.optusnet.com.au/cx346/CX%20Product.htm 2) http://www.cathaypacific.com/intl/inflight/class/0,,,00.html *Premium Economy Class is not widely available.
MATERIALS USED ON AIRLINERS Polymer There’s a wide usage of polymers material, especially thermosetting polymer in an airliner due to the light weight, good resistance to chemical reaction and the ease of production and formation. Polymers replaced many of the materials previously used such as metals. A good example is the overhead luggage bins. At first, passenger aircraft’s overhead bins were either made of a wooden material or metal material. These include the frame and the body itself. The use of these materials proved to be inefficient and dangerous. Wood is prone to burning which creates a hazard both inflight and on the ground. Also there’s a weight limit imposed on the wooden bins, in fact, on any type of bins, but wooden bins would not have the ability to carry excessive weights comparing to metal and polymer. Metal overhead bins were an improvement over the wooden bins. However, metal is still inefficient and dangerous as it is quite heavy and is prone to corrosion due to chemical reaction. Metal also burns furiously. But indeed, metal bins can carry the most weight. To overcome all these problems, polymers such as Reinforced Plastics are used on aircraft widely nowadays. A common type is the Fibreglass (Glass reinforced plastic) which has glass strands placed randomly on the base polymer and treated so that a liquid layer of plastic is used to cover the glass strands to set it in place. The result of this treatment is a polymer with greatly increased strength while the weight is still significantly less than materials such as metal. This is one of the main reasons for overhead luggage bins to be made of reinforced plastics. The advantage is light weight while the strength remains high. This is a great substitution for metal bins as the polymer has better wear resistance and if further treated, it may withstand fire for a certain amount of time, thus a safer material to be used. Current overhead bins on all new commercial aircraft are made of reinforced polymers because of these advantages. Metal The aircraft body has an abundance use of metal and the main type is the aluminium alloy. The properties of this will be discussed in detail in later parts. Metal has succeed the use of wooden material on the aircraft body as were the case in early aircraft such as the biplane the Wright Brothers invented. The usage of wood was dangerous as it’s prone to burning easily and once initiated, hard to stop. The aircraft body being made from wood can only sustain certain amount of force. Thus when aircraft was made to fly faster, a new material was imperative so that the body of the aircraft would not fail under stress. Therefore, metals such as aluminium alloys are used in the structure of the aircraft nowadays. Ceramics The most noticeable ceramics material used on an aircraft is the glass used as the windows. Historically, the windows of an aircraft were made of normal glass in the beginning of aircraft production. But when aircraft had the ability to fly at a high speed, normal glass could not handle the amount of stress imposed on it, thus advanced treatment was the only solution. This is because glass and polymer are the only material which can provide a protection and enclose and area while it may still be see-through. Polymer cannot be used on the flight deck windows or the most exterior layer of passengers windows because of the stress imposed on it. The treatment of the glass to make it useable was to heat it to toughen its strength. The outcome of these glasses is similar to the glass found on ovenware glass which has very strong strength. Thus heat treated toughen glass are used nowadays.
DETAILS OF TURBOFAN ENGINES As mentioned above, the turbofan engines are most widely used on large airliners to power the aircraft due to its efficiency, low fuel usage and reliability. The advantage of these engines is that the bypass ratio is higher than the other types of engines. Bypass ratio is the ratio of the mass airflow which flows through the fan duct over the mass airflow which flows through the core portion of the engine. It is the airflow passing through the core portion of the engine that will experience combustion and compressed hot air being produced. Higher bypass ratio has better efficiency and lower fuel consumption because the thrust of the engine is a mixture of the bypass air and the gas produced by the core, thus higher bypass ratio means more thrust will be produced by less core effort. Generally speaking, the engine will run efficiently with a bypass ratio up to about 9:1, because high bypass ratio is achieved by increasing the diameter of the engine. Therefore the high bypass ratio will only be beneficial up to a certain point because the weight of the engine, up to a certain point, will exceed the advantageous of the high bypass ratio efficiency. The result of this is drag on the aircraft. The high bypass ratio will also reduce the noise produced by the engine. The operation of the turbofan engine to provide the thrust is similar to the turbojet engines. The turbofan engine creates the thrust (the force which moves the aircraft), which is generated by the propulsion system. The engine consist of a core engine which is surrounded by 2 fan systems, one in front of the core engine and one behind it which is the fan turbine. Some turbofan engines may have more fans (called spools) for higher efficiency. The turbine and the compressor are connected on shaft so that the turbine could provide the energy for the compressor to function.
Source: Engineering Studies The Definitive Guide Volume 2 The diagram shown above is a simplified diagram of a turbofan engine. Starting from left to right, the fan is the component that induces the air. This is also where the inlet is. At this point, the entering air has been slightly compressed. Then immediately after the fan/inlet, is the Compressor which is connected on the same shaft as the Turbine at the back. Both the Compressor and the Turbine are composed of many rows of small airfoil shaped blades (similar to the shape of the cross section of the wing). These rows are classified into 2 categories, rotors and stators. The rotors are rows that spin and stators are rows that are fixed. Between the compressor and the turbine is also where fuel and air are mixed together known as the combustion section or the burner. This is where the rows of rotors and stators interact to mix the air and the fuel together. The air mixed with fuel is now very hot and very fast moving gas exit the engine through the nozzle which is immediately past the Turbine. The Turbine (not shown) is shaped so that it will accelerate the passing gas and set the mass flow rate through the engine. The output of this gas is the thrust. Air that had been induced by the inlet and not passed through the core is passed through bypasses or around the engine. The advantage of this has already been discussed in the opening paragraph. The high bypass ratio also lower the noise produced by the engines as the noise is a result of quite mixture of very hot with colder air. With the high bypass ration engine, there are more cold air to be mixed with the hot gas produced in the core and after the mixture of the air and gas inside the engine cowling which has moderated the gas temperature to an extent. So when the gas leaves the engine cowling, the noise produced would be lessened. Power produced from a turbofan engine purely depends on the size of the engine. Below is a table comparing various turbofan engines and its power.
The fuel consumption of the turbofan engines, again differ between each type of engines. Due to lack of technical information available, only one type of engine will be described, the Rolls Royce Trent 772 which is considered for the use on the Airbus A330-300. *Note fuel consumption discussed below is the total fuel require for both engines. Since the fuel consumption is depended on the thrust required and the load of the aircraft, the fuel consumption rate is broken down into several stages. The first stage is the first hour of flight. This is the aircraft having taken off and climbs to an altitude of 10000ft at 250KIAS (Knots), then climbing from 10000ft to 27000ft (FL270) at 2000ft/min. Then finally at a climb rate of 500-1000ft/min to cruising altitude. The fuel consumption is 18000 litres of aviation fuel. Below is a chart showing the fuel consumption (burn rate) of the A330-300 with the specific loadings Cruise, Aircraft Fuel on board 57000kgs (77% fuel load). Chart is calculated for Litres per hour, standard sea level temperatures.
Cruise, Aircraft Fuel on board 31000kgs (40% fuel load). Chart is calculated for Litres per hour, standard sea level temperatures.
* Information obtained from http://www.cpavirtual.org/files/Manuals/CPV%20A330%20Pilots%20Operating%20Handbook * The first column refers to the altitude of the cruising aircraft in the unit of Flight Level (FL) * From second column onwards, it refers to the cruise speed in the unit of Mach (M) * N/A means the aircraft is unable to achieve the condition due to unstable flight conditions. From the above charts, it can be clearly seen that there’s a trade off point between flight altitude and speed. Thus, depending on the weight of the flight (including passengers and cargo), an optimum altitude and speed will be chosen to be the target to conserve fuel. Environmental impacts of the turbofan engines include producing pollution whilst the engines are running because the exhaust is produced. Also the noise of the engines could impact on the environment and humans’ lives. Therefore, more environmental friendly and efficient engines are the key goal of new developments of aircraft engines. However, due the lower fuel consumption of the turbofan engine, which directly means that it is more environmental friendly, and the lower noise emission, turbofan engines are most widely used in large airliners since the production of the Boeing 747.
ALUMINIUM ALLOYS Aluminium alloys are used extensively on the aircraft structure. Aluminium Alloys used on aircraft generally have a composition of the following; over 90% aluminium, 4% copper, ½% silicon, ½% magnesium and small traves of manganese, iron and chromium. This mixture of allow has a significant increase to the strength as opposed to pure aluminium. The strength improvement could be as great as 6-8 times its original strength. This increased strength can be as strong as steel. Other advantages of using an aluminium alloy are its low specific gravity and it’s the most abundant metal in the Earth’s crust. Properties required in the structure of the aircraft are strong in strength to withstand the great pressure and load experienced inflight. The material also needs to be light weight to reduce the overall weight so that fuel can be conserved in the engine. Also the material needs to be as corrosion resistance as possible as atmospheric substance corrodes normal metal very easily, therefore, the material is required to withstand such problems. To satisfy the requirements above, the Aluminium Alloys is the best choice currently as it is light in weight, strong in strength and able to resist corrosion when treated to be “Alclad”. Corrosion prevention is also done by painting the aircraft with special protective chemical and paint which will protect corrosion of up to 13 years. Other metals such as steel are not suitable as it is heavy and prone to corrosion even though it has very strong strength. Titanium is also not used extensively on the aircraft due to its weigh. To form and shape an aluminium alloy into sheets as panels for used on the aircraft body requires several processes. Firstly Aluminium is extracted from bauxite material which is then crushed and under high temperature, mixed with other alloying materials. Then the molten metal is cooled to form into sheets. To treat this alloy into alclad, a very thin layer of non-vulnerable low strength pure aluminium is melted onto the alloys to form as a protective coating. Then to shape this alloy, which may include cutting the alloy as well, a few machines are used. To cut the alloy, a computerized laser cutting machine is used where specific data of the cutting required is entered into the computer and exact cutting dimensions can be performed. The to shape the alloy into a shape other than flat sheets for the aircraft body, a folding machine, bending roller and presses are deployed into shaping the alloy. Then having shaped the alloy, joining different pieces of alloys requires fusion arc welding. Two types of fusion arc welding is used; Tungsten-Inert-Gas (TIG0 and Metal-Inert-Gas (MIG). The TIG process is used for welding aluminium alloys less than 3mm in thickness while MIG is used for thicker alloys as it has a higher welding speed and uses a wire filler metal. As the name suggested, TIG uses Tungsten as the electrode while the MIG uses a metal (aluminium) as the electrode. For sheets from 1.5mm to 3mm in thickness, square butt welding is performed while sheets thicker than 3, a single or double-vee bevel is used.
ALTERNATIVE MATERIALS For the component named in the previous section, aircraft body panels, alternative materials could be considered for use, but are less suitable. Titanium could be used as a substitution for the aluminium alloy as titanium has the advantage of very strong strength which would provide a safer body for the aircraft to overcome metal fatigue in a short period of time. However, titanium is far less widely available on Earth comparing to Aluminium. Also the weight of titanium has prevents the industry from building an aircraft using titanium as the main material. Carbon fibre can also be an alternative material for the aircraft body and could possibly be a future alternative if the strength and mechanical properties can be further improved. Due to the light weight of the carbon fibre (as it’s a form of polymer) there will be significant weight reduction. Carbon fibre will also overcome the problem of corrosion which is ideal. However, the reliability and the consistency in strength is preventing full usage at current times. Further research is required before it maybe safe to use on aircraft. Therefore, the most suitable potential
material to replace the use of aluminium alloy is the carbon fibre as it has
advantages superior to the aluminium alloy. FORCE REQUIREMENT TO POWER THE AIRCRAFT Since the Airbus A330-300 engines have been discussed in the previous sections, it is convenient to discuss the force required to power this aircraft. Incidentally, this is the most efficient aircraft currently. Airbus A330-300 Weight Data Empty Operational Weight- 124.5 tonnes Maximum Take-off Weight- 230.0 tonnes
1) Force required to propel the A330-300 at a constant velocity up a plane inclined at 10° to the horizontal if μ=0.3 Empty Operational Weight- 572.3kN Maximum Take-off Weight- 1.06GN
2) Force required to propel the A330-300 at a constant velocity down a plane inclined at 10° to the horizontal if μ=0.3 Empty Operational Weight- 148.6kN Maximum Take-off Weight- 274.5kN
ENGINEER’S ROLE IN DESIGINING THE AIRCRAFT Within the designing of any aircraft, an Aeronautical Engineer along with engineers from fields such as chemical, materials, mechanical and environmental are crucial. The main role of the Aeronautical Engineer is to design and assess possible plans which could be used in designing an aircraft. This may include designing the shape of the aircraft that will satisfy all aerodynamic laws, designing how the aircraft will be powered and by what means. Furthermore, the aeronautical engineer will need to choose the materials, having consulted the materials engineer, for the aircraft. Same applies to choosing the power plants for the aircraft as well as designing the layout of the interior of the aircraft that may provide a balance load. The Engineer is seen as a co-ordinator for his part of the work and design. Ethical considerations such as environmental impacts and impacts on human lives are imperative to be considered. The engineers are to design an environmental friendly aircraft which will run of efficient engines producing less pollution. This is important for the future world as pollution could prove to be a problem if care has not been taken. Human impact must also be considered by reducing the noise produced by the aircraft. This is an ethical issue as it may interfere with other people’s life and lifestyle. An Aeronautical Engineer is required to have completed Tertiary education in the field of aeronautical engineering. In Sydney, this course may be taken at University of Sydney. The 2003 First round UAI cut-off for HECS students for the Aeronautical Engineering course at USYD is 92.80. Apart from studying the course, work experience is also required has many aspects of engineering are only learnt with on hand experience.
POSSIBLE PROPULSION SYSTEM Since the turbofan engines are the most efficient and environmentally friendly engines currently available, there have been no plans of creating a new concept for aircraft engines. However, improvements are being investigated for the turbofan engines. This includes investigation in producing a turbofan engine with very high bypass ratio while it will still run efficiently as it is hoped that the advantages of the high bypass ratio will out rule the disadvantages due to the large size of the engines. If this type of engines could be produced, it’ll be able to provide a huge magnitude of thrust with a relatively small amount of fuel as the bypass ratio is so high. Improving on the aviation fuel might also help because having aviation fuel with very long chian strand will result in longer burning time for each strand of chemical, thus producing less pollution caused by unburnt fuel. This will also allow the engine to run more economically because it will use relatively less fuel as well has having greater power. This means that further non-stop routes can be travelled.
REFERENCE Charles, E., Aircraft Gas Turbine Powerplants, 1997, Jeppesen Copeland, P. L., Engineering Studies The Definitive Guide, 2001, Anno Domini 2000 Pty Ltd, Sydney Cutler. J., Understanding aircraft structure, 1981, Granada Publishing Limited, Great Britain Edwards. E , M, The aircraft cabin, 1990, Gower Technical, Great Britain Horne, D.F., Aircraft production technology, 1986, Cambridge University Press, Melbourne, Australia
http://www.grc.nasa.gov/WWW/K-12/airplane/aturbf.html http://www.grc.nasa.gov/WWW/K-12/airplane/turbparts.html http://www.regionalexpress.com.au http://www.sydneyairport.com.au
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