De Havilland Comet - Assignment Example

De Havilland Comet - the First Produced Commercial Jetliner The De Havilland Comet was the first produced commercial jetliner. It was designed, developed and manufactured by De Havilland at the Hertfordshire headquarters in the United Kingdom. De Havilland Comet 1 prototype flew on 27 July 1949 for the first time. The flight was a great advancement in aerodynamics, performance and materials. It could fly much faster and higher than the previously existing airlines given its highly pressurized cabin. The first challenge for the design of the airline was its weight. De Havilland Ghost engines lacked the required power to carry the weights required for the passenger jets. BOAC accepted the Ghost as a temporary measure as it developed more appropriate Rolls Royce Avon. At that time, De Havilland Comet overcame the problem of weight by extensive use of metal bonding instead of the traditional reverts. In addition, the manufacturers used thin aluminums gauge on the fuselage. Design Requirements and Property of Materials The design requirement of the aircraft included a few things that were not present prior to its development. Foremost, there was the requirement of a swept-wing principal edge. BOAC also needed integral wings fuel tanks. In addition, there was the need for a four-wheel bogie major undercarriage unit. Given the high weight that the jet required to ferry as a passenger jet, it needed powerful engines that would propel the weight. The liner needed a streamlined shape that would allow it move through air currents like those that the earlier jets did. It, therefore, needed space for four jet engines that would power the low-wing cantilever. Considering the design size, the De Havilland Comet was almost the size of the soon after Boeing 737-100. It carried less people than the later design in a appreciably more spacious environment. Its design required that BOAC install thirty-six reclining slumber-seats with 1100 mm (45 inch) centers. This allowed for enough legroom both in the front and behind the seat. The airliner had eleven rows of seats and with 4 seats on each row. There were large picture window views with a table seating accommodation for each row of passengers. In as much as BOAC had the desire to have the airliner fly, there was the need to use materials that would withstand stress and tension forces (Davies & Birtles 1999, 22). The engineers acknowledged the fact that although the plane needed a small weight to compensate for the large weight of passengers and luggage that the liner would ferry, there was the need to have firm architecture that would not place the lives of those on board at risk. Additionally, engineers had to ensure that the airliner would allow for simplicity of training and fleet conversation. For this reason, the engineers designed a cockpit that included complete twin controls for the first officer and the captain. The flight engineer controlled most other systems in the liner including air conditioning, fuel and electrical systems. Engineering design of the flight also demanded that a space for navigator be provided, and this was a station with a table from the flight engineer. Engineering Material Requirements Material requirement for the airliner were based on the basic principle requirements for flight. There was the need to have materials that were light enough to allow the airliner float on air. At the same time, BOAC had to ensure that the light materials were strong enough to sustain the weight of the passengers and luggage the airliner would carry. Given the diverse cabin pressure and destinations of the airliner, there was the need to use a high proportion of plastics, alloys and other materials that were novel to the civil aviation of the time (Jones 2001, 54). Atomic Structures Atomic structures of the alloys used were not to blame for the crash of the aircraft. The alloys improved the reliability of the materials that made the flight light and firm enough to fly. Selection of Materials De Havilland Comet’s elevated cabin pressure and unusually fast operating speed were at that time unprecedented in the aviation field. These factors influenced the selection of materials that were used in the edifice of the airline. De Havilland Comet’s thin metal covering was made of advanced new alloys. BOAC decided that the materials would be riveted and chemically bonded. This saved the weight of the craft as well as lessened the possibilities of fatigue cracks that would broaden from the rivets. The process of chemical bonding for the materials used was completed with the use of by then a new adhesive; Redux (Davies & Birtles 1999, 26). The adhesive was preferred as it was already used in the building of wings and had admirable reputation. This had the benefit of making simple the manufacturing process. Fatigue The use of metal and chemical bonding rather than the traditional riveting contributed vastly to metal fatigue of the aircraft. This would later cause break-up of the De Havilland Comet. There are allegations that the design of De Havilland Comet had been rushed through the testing process and chances of fatigue were not anticipated. Yields Within the first year of operation of De Havilland Comet, three crashes were recorded. The yield was below par, as BOAC had anticipated no errors in their design. Two of the crashes were blamed upon pilot faults. Designers blamed over rotation on takeoff. A public enquiry into the origin of the crash revealed that metal fatigue was the cause of the crashes. Investigator’s report showed that a crack had developed due to metal fatigue next to the radio direction finding aerial view. A small weakness as the one discovered would rapidly deteriorate and quickly lead to sudden break-up of fuselage under high pressure. Modulus Incorporation of geogrids in De Havilland Comet had significant impacts on the resilient modulus as well as the permanent deformation of the alloys and metals used on the body of the aircraft. Linear Elasticity The effect of plasticity on the path of high stress concentration was a potential candidate for the crash of the airplanes. The materials used in the alloys and thin metal sheets had aspects of linear elasticity. In this case, the stress concentrations on the fatigue points lead to peak stress. Beyond this point, the airplanes broke up and led to the fatal crashes. Failure Mode and Effect Analysis Testing the probability of failure of the aircraft was hasty. This was evident in the inquiry that was made on the design of the craft after the crashes. Water torture test found out that stress around the window areas of the craft were abnormally high. This had the effect of causing fatigue that led to the crashes. Environment and Intended Conditions of Use The environmental friendliness of the craft was not in doubt. Other than using materials that were recyclable, the aircraft provided a comfortable environment for revelers. It afforded a feel of luxury and comfort. It had a gallery that could serve cold and hot drinks and food, a separate woman and men’s toilets and a bar. Given the time in history of designing De Havilland Comet, there would be no better alternatives for building the aircraft. Creep and Oxidation The four engine chambers of De Havilland Comet operated at high temperatures. Materials around the chambers were subject to creep, erosion, hot corrosion and phase change. Additionally, there was possibility of oxidation of the materials at high temperatures. This greatly affects the load bearing and heat-withstanding capability of the materials in contact with the engine chambers. Heat Stress Given the hot corrosion, phase change, erosion and creep, materials around the heat chambers of the De Havilland Comet could not stand heat stress. This was one of the probable reasons for the crash. Thermodynamics Changes in temperature and pressure affected the alloy compositions that were used in the De Havilland Comet. It caused changes in thermodynamic equilibrium. The imbalance worsened and cracks in the fatigued portions of the craft body widened, leading to the ultimate break-up and crash of the aircraft. Pollution As stated before, De Havilland Comet used some of the most environmentally friendly materials. There was little pollution of the atmosphere despite the relatively remote quality of the engines. Globalization De Havilland Comet was the first machine that made the efforts of globalizing the world at a fast speed and on large scale. As it was the first passenger jet, De Havilland Comet moved more people from one part of the world to another at speed twice the usual aircraft speeds. It connected England to Africa, America and Asia. London to Tokyo took 36 hours up from over 72 hours. London to Johannesburg took 21 hours and 20 minutes, contrary to over 48 hours before (Davies & Birtles 1999, 26). Reference List JONES, D. R. H. (2001). Failure analysis case studies. Amsterdam, Elsevier. DAVIES, R. E. G., & BIRTLES, P. (1999). Comet: the world's first jet airliner. McLean, Va, Paladwr. Read More