de Havilland Comet

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

also see https://simpleflying.com/de-havilland-comet-first-jet/

The de Havilland DH 106 Comet was the world's first commercial jet airliner.
Developed and manufactured by de Havilland at its Hatfield Aerodrome in
Hertfordshire, United Kingdom, the Comet 1 prototype first flew in 1949. It
featured an aerodynamically clean design with four de Havilland Ghost turbojet
engines buried in the wing roots, a pressurised cabin, and large square windows.
For the era, it offered a relatively quiet, comfortable passenger cabin and was
commercially promising at its debut in 1952.

However, within a year of entering airline service, problems started to emerge,
with three Comets lost within twelve months in highly publicised accidents,
after suffering catastrophic in-flight break-ups. Two of these were found to be
caused by structural failure resulting from metal fatigue in the airframe, a
phenomenon not fully 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was withdrawn from service and extensively tested. Design and construction
flaws, including improper riveting and dangerous concentrations of stress around
some of the square windows, were ultimately identified. As a result, the Comet
was extensively redesigned, with oval windows, structural reinforcements 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
remained in commercial service until 1981. The Comet was also adapted for a
variety of military roles such as VIP, medical and passenger transport, as well
as surveillance, with the last Comet 4, used as a research platform making its
final flight in 1997. The most extensive modification resulted in a specialised
maritime patrol derivative, the Hawker Siddeley Nimrod, which remained in
service with the Royal Air Force until 2011, over 60 years after the Comet's
first flight.

Overview

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 the approximate length of but not as wide as the later
Boeing 737-100, and 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 feeling of comfort and luxury unusual for 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.

Diverse geographic destinations and cabin pressurisation alike on the Comet
demanded the use of a high proportion of alloys, plastics, and other materials
new to civil aviation across the aircraft in order to meet certification
requirements. The Comet's high cabin pressure and fast operating speeds were
unprecedented in commercial aviation, making its fuselage design an experimental
process. At its introduction, Comet airframes would be subjected to an intense,
high-speed operating schedule which included simultaneous extreme heat from
desert airfields and frosty cold from the kerosene-filled fuel tanks, still cold
from cruising at high altitude.

The Comet was powered by two pairs of turbojet engines buried in the wings close
to the fuselage. Chief designer Bishop chose the Comet's embedded-engine
configuration because it avoided the drag of podded engines and allowed for a
smaller fin and rudder, since the hazards of asymmetric thrust were reduced. The
engines were outfitted with baffles to reduce noise emissions, and extensive
soundproofing was also implemented to improve passenger conditions.

Placing the engines within the wings had the advantage of a reduction in the
risk of foreign object damage, which could seriously damage jet engines. The
low-mounted engines and good placement of service panels also made aircraft
maintenance easier to perform. However, the Comet's buried engine configuration
increased its structural weight and complexity. Armour had to be placed around
the engine cells to contain debris from any serious engine failures; also,
placing the engines inside the wing required a more complicated wing structure.


Role
Narrow-body jet airliner

National origin
United Kingdom

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


Produced
1949–1964

Number built
114 (including prototypes)

Unit cost

Comet 1: £275,000 (1952)


Developed into
Hawker Siddeley Nimrod

The earliest production aircraft, registered G-ALYP ("Yoke Peter"), first flew
on 9 January 1951 and was subsequently lent to BOAC for development flying by
its Comet Unit. On 22 January 1952, the fifth production aircraft, registered
G-ALYS, received the first Certificate of Airworthiness awarded to a Comet, six
months ahead of schedule. On 2 May 1952, as part of BOAC's route-proving trials,
G-ALYP took off on the world's first jetliner flight with fare-paying passengers
and inaugurated scheduled service from London to Johannesburg. The final Comet
from BOAC's initial order, registered G-ALYZ, began flying in September 1952 and
carried cargo along South American routes while simulating passenger schedules.

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. Popular
Mechanics wrote that Britain had a lead of three to five years on the rest of
the world in jetliners. 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 an unpressurised 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 takeover by
United Airlines, Capital would never operate the Comet.

Legacy

The Comet is widely regarded both as an adventurous step forward and a supreme
tragedy; nevertheless, the aircraft's legacy does include numerous advances in
aircraft design and in accident investigations. The inquiries into the accidents
that plagued the Comet 1 were perhaps some of the most extensive and
revolutionary that have ever taken place, establishing precedents in accident
investigation; many of the deep-sea salvage and aircraft reconstruction
techniques employed have remained in use within the aviation industry. In spite
of the Comet being subjected to what was then the most rigorous testing of any
contemporary airliner, pressurisation and the dynamic stresses involved were not
thoroughly understood at the time of the aircraft's development, nor was the
concept of metal fatigue. While these lessons could be implemented on the
drawing board for future aircraft, corrections could only be retroactively
applied to the Comet.

According to de Havilland's chief test pilot John Cunningham, who had flown the
prototype's first flight, representatives from American manufacturers such as
Boeing and Douglas privately disclosed that if de Havilland had not experienced
the Comet's pressurisation problems first, it would have happened to them.
Cunningham likened the Comet to the later Concorde, and added that he had
assumed that the aircraft would change aviation, which it subsequently did.
Aviation author Bill Withuhn concluded that the Comet had pushed "'the
state-of-the-art' beyond its limits.

Aeronautical engineering firms were quick to respond to the Comet's commercial
advantages and technical flaws alike; other aircraft manufacturers learned from,
and profited by, the hard-earned lessons embodied by de Havilland's Comet. While
the Comet's buried engines were used on some other early jet airliners, such as
the Tupolev Tu-104, later aircraft, such as the Boeing 707 and Douglas DC-8,
would differ by employing podded engines held on pylons beneath the wings.
Boeing stated that podded engines were selected for their passenger airliners
because buried engines carried a higher risk of catastrophic wing failure in the
event of engine fire. In response to the Comet tragedies, manufacturers also
developed various means of pressurisation testing, often going so far as to
explore rapid depressurisation; subsequent fuselage skins were of a greater
thickness than the skin of the Comet.

Comet 1A Aircraft Specifications:

Power Unit: Four 5,000 lb.s.t. de Havilland Ghost 50 Mk.2 turbojets

Wing Span: 115 ft (35 m)

All-up Weight (A.U.W): 115,000 lb (52,164 kg)

Cruise Speed: 475 mph (764 kph)

Cruise Altitude: 40,000 ft (12,192 m)

Range: 1750 miles (2,816 km)

Passengers: 36 to 44

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Comet 4 Aircraft specifications:

Power Unit: Four 10,500 lbst Rolls Royce Avon 524 turbojets

Wing Span: 114 ft 10 inches (35 m)

All-Up Weight (A.U.W): 160,000 lb (72,575 kg)

Cruise speed: 503 mph (809 kph)

Cruise Altitude: 42,000 ft (12,802 m)

Range: 3,225 miles (5,190 km



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