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The de Havilland Comet


The de Havilland Comet, the world's first ever commercial jet airliner to reach production. Developed and manufactured by de Havilland, the Comet was considered a landmark British aeronautical design. It not only revolutionised air travel but also brought the world closer together with its high speed, compared to older turbo prop planes.

Although not used in the commercial world, the Comet's military derivative, Hawker Siddeley Nimrod, is still in service and is expected to serve the Royal Air Force until the 2020s, almsot 70 years after its first flight.

Design and Development...

The Comet was designed to fulfill the need for a transatlantic airliner and Sir Geoffrey de Havilland, head of the de Havilland company, used his power and influence, plus his company's expertise with jets, to persuade the Brabazon Commitee that a transatlantic jet mailplane is needed after the war. Subsequently, the Commitee accepted de Havilland's proposal, calling it the Type IV (of five designs), and awarded the production contract to de Havilland's DH.106. The British Overseas Airways Corporation (BOAC) found the Type IV rather attractive and in the last month of 1945, agreed to buy ten aircraft.

The Type IV was officially christened Comet in December 1947. First deliveries were expected five years later. The first flight of the Comet was held on July 27th, 1949, and lasted for 31 minutes, by de Havilland Chief Test Pilot John Cunningham, a famous wartime night-fighter pilot. It was then publicly displayed at the 1949 Farnborough Airshow before beginning flight trials. A second prototype made its maiden flight a year later.

The Comet has an all-metal low-wing cantilever monoplane, and was powered by four jet engines. About the size of a Boeing 737, the Comet was quite luxurious for the first jet airliner. There was lots of room, with 36 seats to each aircraft, and each had its own ashtray. The galley served hot and cold food and drinks, and there was even a bar. Men's and Women's washrooms were seperate, which is something you don't see on modern airliners, and the passenger cabin was much quieter compared to its propeller-driven airliners counter-parts. The Comet's four-man cockpit held two pilots, a navigator and flight engineer. The Comet was also the first pressurised jet-propelled commercial aircraft.

de Havilland's clean, low-drag design featured many unique or innovative design elements, including a swept leading edge, integral wing fuel tanks and four wheel bogie main undercarriage units. Emergencies were countered with lift rafts, which were storeed in the wings near the engines and every seat had a life vest stowed under each seat bottom.

The Comet was powered by two de Havilland Ghost 50 Mk1 turbojet engines buried in the wings close to the fuselage. British engineers chose this configuration as it avoided the drag created by podded engines and allowed fin and rudder, since the hazards of asymmetric, or non-balanced thrust, were reduced. The engines' higher mounting on the wings also lessened the risk of ingestion damage, which is a major problem for turbine engines. However, this design does have its setbacks, such as increased structural weight and complexity of the air frame, as well as a higher chance for wing failure when an engine is on fire, which was cited as the main reason Boeing Aircraft Company chose podded engines over engines buried in the wings.

The Comet's skin is a composition of new and advanced alloys, chemically bonded together with Redux, which is a type of epoxy adhesive, and riveted. It saved weight and reduced the risk of fatigue cracks spreading from the rivets.

Testing...

When the Comet went into service on May 2nd, 1952, it was the most exhaustively tested airliner in history. Water tanks were used to test airframe for metal fatigue by repeatedly pressuring and depressuring the airframe through more than 16 000 cycles, which is equivalent to about 40 000 hours of airline service. The windows were also tested to their max capabilities, and one window frame survived a massive 100 psi, which about 1 250% over the maximum pressure it would encounter in service.

Early Comet disasters...

Early versions of the Comet suffered from catastrophic metal fatigue, which was the root cause of a string of well-publicised accidents. The first of these occured on January 10th, 1954 when Comet G-ALYP ("Yoke Peter"), BOAC Flight 781, broke up in flight mysteriously and crashed into the Mediterranean off the coast of the Italian island Elba. There were no survivors. The entirely Comet fleet was subsequently grounded while the Abell Commitee met to determine the cause of the crash. The conclusion was fire, and modifications were made to the aircraft to protect the engines and wings from damage which might start another fire. However, three months later, another crash of the sort occured in the waters near Naples. Investigators were extremely puzzled and a large investigation board was formed under the direction of the Royal Aircraft Establishment (RAE). They subjected Comet airframes to pressurisation cycles and found the cause of the crashes was metal fatigue. The Comets were redesigned and most served with the military, until 1958 when it resumed commercial service, by which time the much-improved Comet 4 was introduced, and became the first jet airliner to enter transatlantic service. However, by then, United States aircraft manufacturers caught up with Boeing's 707 jetliner and Douglas' DC-8, which were both faster and cost effective, rendering the Comet less profitable. De Havilland later went on to long-range missiles, and in 1962 went back to the airline world with the three-engine jetliner, Trident, but was beat again by Boeing with its 727, also a tri-jet.

De Havilland's hard-learned lessons benefited aircraft manufacturers all over the world, and according to John Cunningham, representatives from Boeing and Douglas "admitted that if it had not been for our problems, it would have happened to them." [Faith 1996, pp. 158-165]

Specifications... (Comet 4)

General characteristics

Crew: 4
Capacity: 56-109 passengers
Length: 34 m (112 ft)
Wingspan: 35 m (115 ft)
Height: 9 m (30 ft)
Wing area: 2,120 ft² (197 m²)
Airfoil: NACA 63A116 mod root, NACA 63A112 mod tip
Empty weight: 75,400 lb (34,200 kg)
Loaded weight: 162,000 lb (73,470 kg)
Powerplant: 4× Rolls-Royce Avon Mk 524 turbojets, 10,500 lbf (46.8 kN) each

Performance

Maximum speed: 500 mph (430 kn, 810 km/h)
Range: 2,800 nmi (3,225 mi, 5,190 km)
Service ceiling: 40,000 ft (12,000 m)

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