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DeHavilland DH 106 Comet

In 1942 the Brabazon Committee met and came up with a postwar plan for the industry. Through misassignment, prevarication, lack of responsibility, and cold-shouldering of genius, among other causes, not all of the committee's proposed types were successfully developed. The Comet well illustrates the longevity of some technological developments, for it was conceived in 1943 and modifications were being built decades later.

The age of jet transportation began on May 5, 1952, with the inauguration of scheduled service from London to Johannesburg, South Africa. Later in the year, service was established from London to Ceylon and from London to Singapore. Then, in April 1953, scheduled flights were begun from London to Tokyo, a distance of 10 200 miles. The flying time was 36 hours, as compared with 85 hours for the propeller-driven aircraft then in use on the route. The pioneering jet transport that began commercial operations in 1952 was the DeHavilland Comet 1.

The design of the Comet airliner had its origins in the waning days of World War II, and the layout of the aircraft was completed in 1947. The first flight of the prototype took place on July 27, 1949, with John Cunningham as pilot. The configuration, of the Comet was not significantly different from that of contemporary long-range propeller-driven aircraft. A comparison of the characteristics of the Comet with those of the Lockheed Constellation indicates that the Comet was a somewhat lighter aircraft, had a lower wing loading and a wing of lower aspect ratio but had a cruising speed of 490 miles per hour at 35 000 feet as compared with 331 miles per hour at 23 000 feet for the Constellation. The range with maximum payload of 44 passengers was 1750 miles. At a much reduced payload, a range of slightly over 4000 miles was possible. By present-day standards, the Comet 1A was a small, relatively low performance aircraft. By comparison with other aircraft of the early 1950's, however, it was extremely fast.

The Comet 1A was powered with four DeHavilland Ghost turbojet engines of 5000 pounds thrust each. The takeoff thrust-to-weight ratio was a very low 0.17. As a consequence of this low thrust-to-weight ratio, very precise control over the aircraft attitude was required during the takeoff roll to prevent overrotation and subsequent high drag and loss of acceleration. At least one aircraft was lost as a result of overrotation during takeoff. The four engines were mounted in the wing roots, two on each side of the fuselage. This engine arrangement has the advantages of placing the engines near the longitudinal center-of-gravity position and of minimizing the asymmetrical yawing moment that accompanies loss of an engine during takeoff; at the time, it was also thought to be a low-drag arrangement. The proximity of the engines to each other and to the passenger cabin, however, posed a possibly hazardous situation in the event one of the engines disintegrated. Engine disintegration was a very real concern in 1950. Engine maintenance was also complicated by the wing-root mounting arrangement.

The aerodynamic design of the wing was conventional except for the use of 20 of sweepback. The aspect ratio of 6.6 was low, as compared with contemporary long-range propeller-driven aircraft. The high-lift system consisted in a combination of simple plain and split trailing-edge flaps. Some aircraft employed fences on the wings. The aerodynamic controls were hydraulically boosted. The passenger cabin was pressurized to maintain a cabin altitude of 8000 feet at an aircraft altitude of 40,000 feet.

When this airliner entered commercial service it created an immediate sensation - and considerable alarm on the other side of the Atlantic. It was simply years ahead of its time. The Comet I was sold to British, French, and Canadian airlines, and it appeared that Great Britain had produced a truly outstanding new aircraft that would be sold in large numbers throughout the world.

Unfortunately a poor accident record marred the aircrafts introduction. There were two early take-off accidents. No one was injured in the first, at Rome in October 1952. It was put down to pilot error and, as a result, higher air speeds were prescribed for take-off. The second accident resulted in the loss of all 11 people on board. It took place on a delivery flight from Karachi in March 1953 and was similarly attributed to an error of judgement on the part of the pilot. The solution this time was to modify the wing leading edge to increase lift at low speed and avoid the possibility of stalling on take-off.

Then a third tragedy occurred, in January 1954, when the aircraft entered a violent thunderstorm just after take-off from Calcutta. It simply disintegrated in mid-air. At the time it was regarded as no more than a freak accident, on the grounds that turbulence within a severe thunderstorm could literally tear an aircraft apart. The Comet was nevertheless grounded for nearly two months while 50 modifications were carried out despite the fact that the precise cause of this terrible accident remained unknown. It was not until a fourth accident, April 1954, when an aircraft departing from Rome again broke up in mid-air, resulting in the loss of all 43 people on board, that long, detailed and methodical investigations into the precise circumstances began.

All Comet 1 aircraft, over 20 in number, were withdrawn from service in 1954. Extensive laboratory studies were undertaken in an effort to diagnose the problem. Fatigue failure and subsequent rupture of the pressurized fuselage as a result of pressure recycling was finally identified as the cause of the accidents.

The Comet was completely reengineered and emerged as a much changed and improved aircraft in 1958. This version, identified as the Comet 4, was not really competitive with the new generation of jet transports coming into use at that time, and only 74 were built.

The commercial success of the Comet was limited, but it was the first jet transport and represented a large step forward in our concepts of air transportation and its utility. It is unfortunate that the pioneering work of the designers and builders of the Comet was not rewarded with greater success. The Comet, in highly modified form, survives today as a marine reconnaissance aircraft known as the Nimrod.







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