de Havilland Comet

https://en.wikipedia.org/wiki/De_Havilland_Comet

The de Havilland DH 106 Comet was the world's first commercial jetliner.
Developed and manufactured by de Havilland at its Hatfield Aerodrome,
Hertfordshire, United Kingdom headquarters, the Comet 1 prototype first flew on
27 July 1949. It featured an aerodynamically clean design with four de Havilland
Ghost turbojet engines buried in the wings, a pressurised fuselage, and large
square windows. For the era, it offered a relatively quiet, comfortable
passenger cabin and showed signs of being a commercial success at its 1952
debut.

A year after entering commercial service, the Comets began suffering problems,
with three of them breaking up during mid-flight in well-publicised accidents.
Two of these were found to be caused by catastrophic failure resulting from
metal fatigue in the airframes, not well understood at the time. The other one
was due to overstressing of the airframe during flight through severe weather.
The Comet was withdrawn from service and extensively tested to discover the
causes of the fatigue failures. Design flaws, including dangerous stresses at
the corners of the square windows and installation methods, were ultimately
identified. As a result, the Comet was extensively redesigned with oval windows,
structural reinforcement, and other changes. Rival manufacturers meanwhile
heeded the lessons learned from the Comet while developing their own aircraft.

Although sales never fully recovered, the improved Comet 2 and the prototype
Comet 3 culminated in the redesigned Comet 4 series which debuted in 1958 and
had a productive career of over 30 years. The Comet was adapted for a variety of
military roles such as VIP, medical and passenger transport, as well as
surveillance. The most extensive modification resulted in a specialised maritime
patrol aircraft variant, the Hawker Siddeley Nimrod. Nimrod remained in service
with the Royal Air Force (RAF) until June 2011, over 60 years after the Comet's
first flight.

The Comet was an all-metal low-wing cantilever monoplane powered by four jet
engines; it had a four-place cockpit occupied by two pilots, a flight engineer,
and a navigator. The clean, low-drag design of the aircraft featured many design
elements that were fairly uncommon at the time, including a swept-wing leading
edge, integral wing fuel tanks, and four-wheel bogie main undercarriage units
designed by de Havilland. Two pairs of turbojet engines (on the Comet 1s,
Halford H.2 Ghosts, subsequently known as de Havilland Ghost 50 Mk1s) were
buried into the wings.

The original Comet was approximately the length of the later Boeing 737-100, but
carried fewer people in a significantly more spacious environment. BOAC
installed 36 reclining "slumberseats" with 45-inch (1,100 mm) centres on its
first Comets, allowing for greater leg room in front and behind; Air France had
11 rows of seats with four seats to a row installed on its Comets. Large picture
window views and table seating accommodations for a row of passengers afforded a
"feel of comfort and luxury" atypical of transportation of the period. Amenities
included a galley that could serve hot and cold food and drinks, a bar, and
separate men's and women's toilets. Provisions for emergency situations included
several life rafts stored in the wings near the engines, and individual life
vests were stowed under each seat.

One of the most striking aspects of Comet travel was the quiet, "vibration-free
flying" as touted by BOAC. For passengers used to propeller-driven airliners,
smooth and quiet jet flight was a novel experience.


Role
Narrow-body jet airliner

Manufacturer
de Havilland

First flight
27 July 1949

Introduction
2 May 1952 with BOAC

Retired
14 March 1997 (Comet 4C XS235)

Status
Retired

Primary users
BOAC
British European Airways
Dan-Air
Royal Air Force

Number built
114 (including prototypes)

Unit cost

Comet 1: £275,000 (1952)

Developed into
Hawker Siddeley Nimrod

The Comet was a hit with passengers including Queen Elizabeth, the Queen Mother
and Princess Margaret, who were guests on a special flight on 30 June 1953
hosted by Sir Geoffrey and Lady de Havilland, and thus became the first members
of the British Royal Family to fly by jet. Flights on the Comet were about 50
percent faster than on advanced piston-engined aircraft such as the Douglas DC-6
(490 mph for the Comet compared to the DC-6's 315 mph), and a faster rate of
climb further cut flight times. In August 1953 BOAC scheduled nine-stop London
to Tokyo flights by Comet for 36 hours, compared to 86 hours and 35 minutes on
their Argonaut piston airliner. (Pan Am's DC-6B was scheduled for 46 hours 45
minutes.) The five-stop flight from London to Johannesburg was scheduled for 21
hr 20 min.

In their first year Comets carried 30,000 passengers. As the aircraft could be
profitable with a load factor as low as 43 percent, commercial success was
expected. The Ghost engines allowed the Comet to fly above weather which
competitors had to fly through. They ran smoothly and were less noisy than
piston engines, had low maintenance costs, and were fuel-efficient above 30,000
ft (9,100 m). In summer 1953 eight BOAC Comets left London each week: three to
Johannesburg, two to Tokyo, two to Singapore and one to Colombo.

In 1953 the Comet appeared to have achieved success for de Havilland. In
addition to the sales to BOAC, two French airlines, Union Aéromaritime de
Transport and Air France, each acquired three Comet 1As, an upgraded variant
with greater fuel capacity, for flights to West Africa and the Middle East. A
slightly longer version of the Comet 1 with more powerful engines, the Comet 2,
was being developed, and orders were placed by Air India, British Commonwealth
Pacific Airlines, Japan Air Lines, Linea Aeropostal Venezolana, and Panair do
Brasil. American carriers Capital Airlines, National Airlines, and Pan Am placed
orders for the planned Comet 3, an even larger, longer-range version for
transatlantic operations. Qantas was interested in the Comet 1 but concluded
that a version with more range and better takeoff performance was needed for the
London to Canberra route.

With the discovery of the structural problems of the early series, all remaining
Comets were withdrawn 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. 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 thickness was increased slightly. Remaining
Comet 1s and 1As were either scrapped or modified with oval windows and rip-stop
doublers.

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 programme to
produce a Comet 2 with more powerful Avons was delayed. The prototype Comet 3
first flew in July 1954, and was tested in a non-pressurised state pending
completion of the Cohen inquiry. Comet commercial flights would not resume until
1958.

Development flying and route proving with the Comet 3 allowed accelerated
certification of what was destined to be the most successful variant of the
type, the Comet 4. All airline customers for the Comet 3 subsequently cancelled
their orders and switched to the Comet 4, which was based on the Comet 3 but
with improved fuel capacity. BOAC ordered 19 Comet 4s in March 1955, while
American operator Capital Airlines ordered 14 Comets in July 1956. Capital's
order included 10 Comet 4As, a variant modified for short-range operations with
a stretched fuselage and short wings, lacking the pinion (outboard wing) fuel
tanks of the Comet 4. However, because of financial problems and a subsequent
takeover by United Airlines, Capital would never operate the Comet.

Specifications Comet 4

Cockpit crew: 4 (2 pilots, flight engineer and radio operator/navigator)
Length: 111 ft 6 in (33.99 m)
Passengers: 56–81
Wingspan: 115 ft (35 m)
Tail height: 29 ft 6 in (8.99 m)
Wing area: 2,015 sq ft (187.2 m2)
Maximum takeoff weight: 156,000 lb (71,000 kg)
Operating range: 3,225 mi (2,802 nmi; 5,190 km)
Cruising speed: 840 km/h (450 kn; 520 mph)
Cruise altitude: 42,000 ft (13,000 m)
Powerplants (x 4): Rolls-Royce Avon Mk 524 turbojets: 10,500 lbf





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