DeHavilland DH 106 Comet - History
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.
With a great degree of foresight, in 11 March 1943, the British Government formed the BrabazonCommittee to determine Britain's airliner needs after the Second World War. In this same year, deHavilland had flown their first jet aircraft, the Vampire. This twin-boom fighter was powered by a deHavilland Goblin turbojet. One of the Brabazon Committee’s recommendations was for a high-speed,pressurized, transatlantic mail-plane that could carry six passengers and a half-ton of mail at a cruising speed of 640 km/h (400 mph). Challenging the widely held skepticism of the early jet engines were too fuel-hungry and unreliable, committee member Sir Geoffrey de Havilland, the head of the de Havilland company, used his personal influence to have the committee further specify a turbojet-powered design. The committee accepted the proposal, calling it the "Type IV" (of five designs) with the other designs being turbo-prop or piston-powered aircraft.
In February 1945, de Havilland was awarded a productioncontract to bring a Type IV specification aircraft into service under the designation “Type 106”. Thedevelopment of the DH.106 consequently focused on short / intermediate range mail-plane designs with asmall passenger compartment and as few as six seats, before evolving into a longer range airliner with acapacity of 24 seats. Out of all the Brabazon designs, the DH.106 was seen as the riskiest both in terms of introducing untried design elements and for the financial commitment involved. Nevertheless, theBritish Overseas Airways Corporation (BOAC) found the Type IV's specifications attractive, and initially proposed a purchase of 25 aircraft but, in December 1945, when a firm contract was laid out, the ordertotal was reduced to just 10 aircraft.
As the Type IV was intended as the premiere project for the United Kingdom, the Ministry of Supply decided that further research was required to better evaluate some the design ideas being put forward. A number of unorthodox configurations were considered, ranging from canard to tailless designs. The Ministry of Supply was, however, interested in the most radical of the proposed designs and ordered two (later three) experimental tailless DH.108 Swallows to serve as proof of concept aircraft for testing swept-wing configurations in both low-speed and high-speed flight. The DH.108 Swallow was based on the Vampire jet fighter, using that aircraft’s fuselage design. During subsequent flight tests, the DH.108 gained a reputation for being both accident-prone and unstable, leading de Havilland and BOAC reconsider more conventional configurations for the DH.106 with less technical risk.
In September 1946, prior to the completion of the DH.108s, BOAC had also requested a redesign of theDH.106 from its previous 24-seat configuration to a larger 36-seat version. The redesigned aircraft was named the DH.106 Comet in December 1947. Revised first orders for the type from BOAC and British SouthAmerican Airways totaled 14 aircraft with deliveries projected for 1952. 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. Many companies were competing for the title of first passenger jet, including the Avro Jetliner which flew its first test flight just two weeks after the Comet's first test flight in 1949. The Jetliner never reached production; however, the name has become the colloquial term for any jet airliner.
The first prototype (G-5-1 / G-ALVG) flew at Hatfield for the first time on 27th July 1949 and it was immediately apparent that the type would set new standards for both flight performance and passenger comfort. The flight also took place on Sir Geoffrey de Havilland's 67th birthday, an occasion he shared with Chief Test Pilot John Cunningham who was just 33 years old on the same day. The second prototype (G-5-2 / G-ALZK) flew a year later carrying out over 500 hours of flight test and route proving trials with technical observers on board from interested International Airlines such as Qantas.
The first production aircraft (G-ALYP) flew on 9th January 1951 and recorded the types first ‘fare-paying’ flight to Johannesburg with BOAC in May of the same year. The aircraft was an instant hit with the passengers including Queen Elizabeth, the Queen Mother and Princess Margaret who were VIP’s on a special flight in June 1953. 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.
Around 50% faster than equivalent piston engine aircraft, scheduled flights from London to Tokyo on Comet took just 36 hours compared to the 86½ hours recorded by aircraft such as the BOAC Argonauts who had previously dominated the route. In its first year, Comets carried over 30,000 passengers and at least 8 Comet flights departed London each week, destined for Johannesburg, Tokyo, Singapore and Columbo.
Unfortunately a poor accident record marred the aircraft’s 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.
However, just when it seemed the Comet had sewn up the commercial-transport market, tragedy struck. Two deadly crashes within 16 weeks of each other revealed a design flaw that would eventually ground the original Comets for good.
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.
With the discovery of the structural problems of the early series, all remaining Comets, over 20 in number, were with drawn from service, while de Havilland launched a major effort to build a new version that would be both larger and stronger. All outstanding orders for the Comet 2 were cancelled by airline customers.
Extensive laboratory studies were undertaken in an effort to diagnose the problem. Following the recovery of the wreckage extensive investigation carried out at the Royal Aircraft Establishment (RAE) Farnborough by the Air Accident Investigation Board (AAIB) and it reported to the National Board of Enquiry that the primary cause was a catastrophic failure of the pressure cabin due to metal fatigue. It identified that despite extensive testing in the design stage, the cyclical pressurisation and de-pressurisation of the fuselage had accelerated the stress levels around the corners of the ADF and some the main passenger windows, causing disastrous fractures in the structure and almost instant failure of the airframe. 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 square windows of the Comet 1 were replaced by the oval versions used on the Comet 2, which first flew in 1953, and the skin sheeting was thickened slightly. The remaining Comet 1s and 1As were either scrapped or modified with oval window rip-stop doublers (a thick, structurally strong ring of material that prevented a crack from spreading further). All production Comet 2s were also modified to alleviate the fatigue problems (most of these served with the RAF as the Comet C2), while a program to produce a Comet 2 with more powerful Avon jet engines was delayed.
|
NEWSLETTER
|
| Join the GlobalSecurity.org mailing list |
|
|
|
