De Havilland DH.106 Comet/Hawker Siddeley HS.801 Nimrod..........................................................Specifications
The de Havilland DH.106 Comet was a truely brillant concept, a pioneer far ahead of its time; the prototype Comet 1 flew in 1949, a good five years before the Boeing 707, the closest US rival. Its service debut occurred on the 2 May 1952, with BOAC on a flight from London Heathrow to Johannesburg; the first commercial jet passenger service ever. The engines were installed in the wing roots, feed by inlets at the leading edge, with exhaust nozzles just behind the trailing edge. The design featured high-pressure underwing refuelling, and hydraulically powered flight controls with no manual back-up. The construction introduced Redux metal-to-metal bonding, as oppose to riveting. Because the aircraft was jet propelled, more fuel than comparable piston engined aircraft was needed. A light construction was there fore of the essence. The inner upholstery and the thin metal outer fuselage skin was all that separated passengers from the air outside !! The cabin pressurisation differential was twice that of any previous aircraft, this was because the Comet flew higher and faster than any other airliner up until that time.
Such a pioneering design should have been subjected to far more testing. The Royal Aircraft Establishment at Farnborough warned of findings made, concerning structural fatigue, but the design team of de Havilland wanted to press on without lengthy testing and for that matter so did BOAC, the launch customer. There was after all alot at stake. The British aircraft industry would be in a very strong position indeed, should the gamble pay off. The order books were full! Orders for the proposed Comet 2 from BOAC, Candadian Pacfic, Air France, UAT, Japan Air Lines, LAV venezuela, Panair do Brasil and British Commonwealth Pacific had been made. Even a provisional order for the proposed stretch version, the Comet 3 came in from Pan American and interest for the aircraft had been shown by Air India. Plans were even made for a second production line away from Hatfield at the Shorts plant in Belfast. Nine Comet 1 aircraft had been sold, notably to Air France, Canadian Pacific Airlines and the Canadian Air Force, even before the aircraft had been built. A large chunk of the aircraft market was there for the taking.
Unfortunately the Comet also became a pioneer for all the problems and teathing troubles that such an aircraft must bring with it. Never before had an aircraft flown so high and fast. Sadly however by the time of the introduction of the type into service, the basic airframe had never been through any kind of full scale testing.
A none fatal take off accident at Rome with G-ALYZ, a Comet 1, of BOAC and the fatal crash of CF-CUN of Canadian Pacific, a Comet 1a, at Karachi resulted in the redesigning of the wing to combat poor take off performance and consequent stalling. It was now believed that the major problems in the design, were solved. The problems with the wing had been known all along. But this was just the begining. In its first year of operations the Comet flew 28,000 passengers. All seemed well. Production was switched completely to the mark 1a which had increased fuel capacity and gross weight, but used the same de Havilland Ghost 50 engines with 5,050 lbs of thrust.
How ever on the anniversary of the first flight of the Comet by BOAC, on 02 of May 1953 G-ALYV disintegrated at 9,000ft after having left Calcutta, with the loss of all 42 soles on board. On the 10th of January 1954 G-ALYP of BOAC crashed into the sea off Rome having climbed to 36.000 ft. A third crash on the 8th of April 1954, involving G-ALYY of BOAC/ South African Airlines ended the Comet 1´s career. Evidence drawn from the wreckage of "Yoke Yoke" and the now full scale testing of the Comets fuselage, showed that metal fatigue had downed all three aircraft. The rivets used to hold in the rectangular windows, which had been an after fought as de Havilland could not solve the problem of how to secure the windows, had not helped structurally especially in conection with the flimsy nature of the thin outer skin. Microscopic cracks had occured and the continuous changes in cabin pressure during flying resulted then in catastrophic cabin decompression and the subsiquent implossion of the fuselage.
This series of crashes not only killed a total of 110 passengers and crew but also killed the Comet project stone dead. The aircraft was grounded indeffinately. Orders were cancelled and the American aircraft manufacturers, notibly Boeing were able to catch up the lost ground and benifitted from the experiences de Havilland had now made, especially as all of the findings from the crashes and following tests were made public.
The Comet 1, appart from a few locally rebuilt Canadian Airforce 1a examples, never flew again. The Comet 2 was, as a result of the fiasco, a stillborn. It had a fuselage stretch of 3ft, and incororated the Rolls Royce Avon RA.9 Mk 502 powerplants with 6,500 lbs thrust. The prototype flew on 16 February 1952. After the crashes, production stopped and those few that had been completed were converted, the fuselages reskinned, incorporating amongst other things round cabin windows. These few examples were delivered to the Royal Air Force becoming the T Mk2, later versions were known as the C Mk 2 with strengthened cargo floor forward, and 44 aft facing seats to the rear.
The Comet 3 also died before it could really get started, so great was the shock in the Aviation world and all orders were cancelled. This aircraft first flew on July 19 1954. This version had an incredible (at that time) fuselage stretch of 18ft 6 in, seating 58-78 passengers. It was powered by Avon RA. 26 engines rated at 9,000 ibs of thrust and It featured pinion tanks on the wings to take on extra fuel. A record breaking flight from Hatfield circling the earth in1955 was hoped to raise interest. The aircraft flew to Australia, New Zealand, Fiji, Hawaii, Vancouver, Montrel and London non-stop. Despite this feat, only a few were later built, being used in full scale fatigue tests, being submerged in giant water tanks. The prototype Comet 3 was used as the prototype for the Comet 4 after being re-engined with Avon RA.29 Mk.524s rated at 10,500 lbs of thrust.
It was with the emergence of the Comet 4, which first flew on 27 April 1958, that confidence in the design was partially restored. The production aircraft could seat 63-81 passengers and had a redesigned fuselage incorporating different alloys. It had reduced fuel consumption, increased tankage and greater fuel reserves, allowing greater range. This version was ordered and flown by BOAC, Aerolineas Argentinas, and East African Airways; altogether 28 were built. It also held the distinction of being the first jet service across the Atlantic from London to New York, stopping at Gander Newfoundland on 4 October 1958 on a BOAC scheduled flight. But this success over shadows the fact that the edge had been lost, it was the Boeing 707 and later the Douglas DC8 which made the running. The Comet 4 was not really designed for north Atlantic service. It was far smaller than its two US "rivals" and also had less range and was slower. The Comet 4, with its high ratio of thrust-to-weight, was really a good medium-haul aircraft, especially suited to routes involving short or hot/high airfields as found in South America.
In 1956, Capitol Airways of the USA ordered a version of the Comet 4, the 4A, which was basically the same airframe as the 4 but with a shortened wing span of 7ft 2in and other structural changes to allow lower cruising altitudes and greater cruising speeds, ideal for domestic flights. How ever Capitol was taken over by United Airlines and the deal never came off !!
British European Airways, who had been against the idea of jet transport and had in 1955 ordered the Vickers Vanguard second generation turbo prop, for short to medium haul flights, suddenly in 1957 made a U turn and ordered 6 Comet 4B aircraft and it was primarily with BEA in mind that this version then emerged. Basically the aircraft shared the same systems as the Comet 4, had fuselage lengthened by 6ft 6in, with the wing span of the Comet 4A. The aircraft, like the 4A, had no extra pinion fuel tanks, and with its shorter range could carry 92 passengers. It also used the Avon RA. 29 engine.This aircraft, again used the Comet 3 as prototype, which was converted to a "3B" and flown in this form on 21 August 1958; the first 4B flew on 27 June 1959. 18 were built, for BEA, and Olympic Airlines.
The final mark of the Comet was the 4C, first flown on the 31 October 1959. This version had the long fuselage of the 4B and the orginal larger wing span with the same powerplant, the Avon RA. 29. This version proved very popular, but still only 28 were built, the last leaving the now Hawker Siddeley production line in1964. Airlines who bought the type include; Mexicana, Misrair (Egyptair), Aerolineas Argentinas, MEA, Sudan Airways and Kuwait Airways. The very final civil flight of any Comet airliner was on the 3 of November 1980 with Dan-Air London. This airline had bought up quite a considerable fleet of used Comet 4 aircraft, 4s, 4Bs and 4Cs after 1966, infact the largest single fleet of Comets ever standing at 47 aircraft.
With the start of the Hawker Siddeley (Later British Aerospace) HS.801 Nimrod project, new life was breathed into the Comet. Various Comet 4 aircraft were purchased by the British MOD, and modifyed to test out future systems for an Electronics/Maritime Patrol aircraft known as the Nimrod, the first of which flew in 1968. These aircraft have formed the back-bone of Britains Electronic /Maritime defences since then. The most ambitious project to come out of the Nimrod development was the proposed AEW.3 (Airborne Early Warning). The first testbed aircraft to fly was an ex BOAC converted Comet 4, G-APDS, which flew in 1977. The first development AEW.3 flew in July 1980, with deliveries of production aircraft scheduled for 1984. Later models were converted from Nimrod MR.1 aircraft which were new production aircraft built between 1969 and 1972. The AEW deadline could not be meet. The development of the GEC Avionics proved to costly and the project was scrapped in 1987 in favour of, ironically enough, the Boeing 707 based E3A AWACS aircraft !!
Development of the Nimrod continued though in its Maritime rôle. Nimrod MR1s were converted to MR2 standard between 1979 and the end of 1985.Today the Nimrod MR2, with modern turbofan power plants, is the RAF`s standard long-range maritime reconnaissance aircraft, capable of upto 12 hours endurance. It is one of the most advanced anti-submarine aircraft in the west, and is armed with bombs, mines, depth charges, stingray torpedoes and sidewinder or Harpoon missiles. The refurbishment of the MR2, to MRA4 standard, which sees the inclusion of new engines, a systems update, airframe refurbishment, a new wing platform and pressure floor, has been given the go ahead and envisages a service entry of 21 aircraft in 2005.
