The Aérospatiale-BAC Concorde is a turbojet -powered supersonic passenger airliner, a supersonic transport (SST). It was a product of an Anglo-French government treaty, combining the manufacturing efforts of Aérospatiale and the British Aircraft Corporation. First flown in 1969, Concorde entered service in 1976 and continued commercial flights for 27 years.

Among other destinations, Concorde flew regular transatlantic flight s from London Heathrow (British Airways) and Paris-Charles de Gaulle Airport (Air France) to New York JFK, profitably flying these routes at record speeds, in less than half the time of other airliners.

With only 20 aircraft built, their development represented a substantial economic loss, in addition to which Air France and British Airways were subsidized by their governments to buy them. As a result of the type’s only crash on 25 July 2000 and other factors, its retirement flight was on 26 November 2003.

Concorde's name reflects the development agreement between the United Kingdom and France. In the UK, any or all of the type—unusual for an aircraft—are known simply as "Concorde". The aircraft is regarded by many as an aviation icon.

Development

Concept

In the late 1950s, the United Kingdom, France, United States, and Soviet Union were considering developing supersonic transport. The British Bristol Aeroplane Company and the French Sud Aviation were both working on designs, called the Type 223 and Super-Caravelle, respectively. Both were largely funded by their respective governments. The British design was for a thin-winged delta shape (which owed much to work by Dietrich Küchemann ) for a transatlantic-ranged aircraft for about 100 people, while the French were intending to build a medium-range aircraft.

The designs were both ready to start prototype construction in the early 1960s, but the cost was so great that the British government made it a requirement that BAC look for international co-operation. Approaches were made to a number of countries, but only France showed real interest. The development project was negotiated as an international treaty between the two countries rather than a commercial agreement between companies and included a clause, originally asked for by the UK, imposing heavy penalties for cancellation. A draft treaty was signed on 28 November 1962. By this time, both companies had been merged into new ones; thus, the Concorde project was between the British Aircraft Corporation and Aérospatiale. At first the new consortium intended to produce one long range and one short range version. However, prospective customers showed no interest in the short-range version and it was dropped. The consortium secured orders (i.e., non-binding options) for over 100 of the long-range version from the major airlines of the day: Pan Am, BOAC and Air France were the launch customers, with six Concordes each. Other airlines in the order book included Panair do Brasil, Continental Airlines, Japan Airlines, Lufthansa, American Airlines, United Airlines, Air India, Air Canada, Braniff, Singapore Airlines, Iran Air, Olympic Airways, Qantas, CAAC, Middle East Airlines and TWA.

Testing

Construction of two prototypes began in February 1965: 001, built by Aerospatiale at Toulouse, and 002, by BAC at Filton, Bristol. Concorde 001 made its first test flight from Toulouse on 2 March 1969, piloted by André Turcat, and first went supersonic on 1 October. The first UK-built Concorde flew from Filton to RAF Fairford on 9 April 1969, piloted by Brian Trubshaw. Both prototypes were presented to the public for the first time on 7–8 June 1969 at the Paris Airshow. As the flight programme progressed, 001 embarked on a sales and demonstration tour on 4 September 1971, which was also the first transatlantic crossing of Concorde. Concorde 002 followed suit on 2 June 1972 with a tour of the Middle and Far East. Concorde 002 made the first visit to the United States in 1973, landing at the new Dallas/Fort Worth Regional Airport to mark that airport’s opening.

These trips led to orders for over 70 aircraft, but a combination of factors led to order cancellations: the 1973 oil crisis, financial difficulties of airlines, a spectacular Paris Le Bourget air show crash of the competing Soviet Tupolev Tu-144, and environmental concerns such as the sonic boom, takeoff-noise and pollution. By 1976 four nations remained as prospective buyers: Britain, France, China, and Iran. In the end only Air France and British Airways (the successor to BOAC) took up their orders, with the two governments taking a cut of any profits made. In the case of BA, 80% of the profit was kept by the government until 1984, while the cost of buying the aircraft was covered by a state loan.

Demonstration and test flights were flown from 1974 onwards. The testing of Concorde set records that have not been surpassed; the prototype, pre-production and first production aircraft undertook 5,335 flight hours; 2,000 test hours were at supersonic speeds. During one such test flight, on 7th of November 1974, 001 performed the fastest civil flight across the North Atlantic, record still valid today. Unit costs were £23 million (US$46 million) in 1977, and development costs were six times the projected amount.

Design

General features

Concorde is an ogival (also "ogee") delta-wing ed aircraft with four Olympus engines based on those originally developed for the Avro Vulcan strategic bomber. Concorde was the first airliner to have an (in this case, analogue) fly-by-wire flight-control system; the avionics of Concorde were unique because it was the first commercial aircraft to employ hybrid circuits. The principal designer for the project was Pierre Satre, with Sir Archibald Russell as his deputy.

Concorde pioneered the following technologies:

For high speed and optimization of flight:

* Double-delta (ogee /ogival) shaped wings

* Variable engine air intake system controlled by digital computers

* Supercruise capability

* Thrust-by-wire engines, predecessor of today’s FADEC -controlled engines

* Droop-nose section for better landing visibility

For weight-saving and enhanced performance:

* Mach 2.04 (~) cruising speed for optimum fuel consumption (supersonic drag minimum although turbojet engines are more efficient at higher speed)

* Mainly aluminum construction for low weight and conventional manufacture (higher speeds would have ruled out aluminum)

* Full-regime autopilot and autothrottle allowing "hands off" control of the aircraft from climbout to landing

* Fully electrically controlled analogue fly-by-wire flight controls systems

* High-pressure hydraulic system of 28 MPa (4,000 lbf/in²) for lighter hydraulic components

* Complex Air Data Computer (ADC) for the automated monitoring and transmission of aerodynamic measurements (total pressure, static pressure, angle of attack, side-slip).

* Fully electrically controlled analogue brake-by-wire system

* Pitch trim by shifting fuel around the fuselage for center-of-gravity control

* Parts made using "sculpture milling" from single alloy billet, reducing the part-number count while saving weight and adding strength

* Lack of an auxiliary power unit, as Concorde would only visit large airports where a ground air start cart would be available.

Movement of center of pressure

When any aircraft passes the critical mach of that particular airframe, the center of pressure shifts rearwards. This causes a pitch down force on the aircraft, as the center of mass remains where it was. The engineers designed the wings in a specific manner to reduce this shift. However, there was still a shift of about 2 meters. This could have been countered by the use of trim controls, but at such high speeds this would have caused a dramatic increase in the drag on the aircraft. Instead, the distribution of fuel along the aircraft was shifted during acceleration and deceleration to move the center of mass, effectively acting as an auxiliary trim control.

Engines

To be economically viable, Concorde needed to be able to fly long distances, and this required high efficiency. For optimum supersonic flight, turbofan engines were considered, but rejected, due to their larger cross-section which would cause excessive drag. Turbojet s were found to be the best choice of engines. The engine developed was the twin spool Rolls-Royce/Snecma Olympus 593, a development of the Bristol engine first used for the Avro Vulcan bomber, and developed into an afterburning supersonic variant for the BAC TSR-2 strike bomber.

The intake design for Concorde’s engines was critical. All conventional jet engines can take in air at only around Mach 0.5; therefore the air has to be slowed from the Mach 2.0 airspeed that enters the engine intake. In particular, Concorde needed to control the shock waves that this reduction in speed generates to avoid damage to the engines. This was done by a pair of intake ramp s and an auxiliary spill door, whose position was moved during flight to slow the air down. The ramps were at the top of the engine compartment and moved down and the auxiliary spill door moved both up and down allowing air to flow in or out. The effectiveness of the intake system is such that, during supersonic flight, 63% of the aircraft's thrust is attributed to the intakes whilst the exhaust nozzles generate 29% and the engines just 8% of the thrust.

Engine failure causes problems on conventional subsonic aircraft; not only does the aircraft lose thrust on that side but the engine creates drag, causing the aircraft to yaw and bank in the direction of the failed engine. If this had happened to Concorde at supersonic speeds, it could theoretically cause a catastrophic failure of the airframe. However, during an engine failure, air intake needs are virtually zero, so in Concorde, the immediate effects of the engine failure were countered by the opening of the auxiliary spill door and the full extension of the ramps, which deflected the air downwards past the engine, gaining lift and streamlining the engine, minimizing the drag effects of the failed engine. Although computer simulations predicted considerable difficulties, in practice Concorde was able to shut down both engines on the same side of the aircraft at Mach 2 without any of the predicted control problems. Concorde pilots were routinely trained in simulators to deal with a double engine failure.

The aircraft used reheat (afterburners) at takeoff and to pass through the transonic regime (i.e., "go supersonic") between Mach 0.95 and Mach 1.7, and were switched off at all other times. Due to jet engines being highly inefficient at low speeds, Concorde burned two tonnes of fuel (almost 2% of the maximum fuel load) taxiing to the runway. To conserve fuel only the two outer engines were run after landing. The thrust from two engines was sufficient for taxiing to the ramp due to low aircraft weight upon landing at its destination.

Heating issues

Beside engines, the hottest part of the structure of any supersonic aircraft is the nose. The engineers wanted to use duralumin, an aluminum alloy, throughout the aircraft due to its familiarity, cost and ease of construction. The highest temperature that aluminum could sustain over the life of the aircraft was 127 °C, which limited the top speed to Mach 2.02.

Concorde went through two cycles of heating and cooling during a flight, first cooling down as it gained altitude, then heating up after going supersonic. The reverse happened when descending and slowing down. This had to be factored into the metallurgical modeling. A test rig was built that repeatedly heated up a full-size section of the wing, and then cooled it, and periodically samples of metal were taken for testing.

Owing to the heat generated by compression of air as Concorde traveled supersonically, the fuselage would extend by as much as 300 mm (almost 1 ft), the most obvious manifestation of this being a gap that opened up on the flight deck between the flight engineer ’s console and the bulkhead. On all Concordes that had a supersonic retirement flight, the flight engineers placed their hats in this gap before it cooled, where the hats remain to this day.

To keep the cabin cool, Concorde used the fuel as a heat sink for the heat from the air conditioning, the same method also cooled the hydraulics. During supersonic flight the surfaces forward from the cockpit became heated, a visor was used to deflect much of this heat from directly reaching the cockpit.

Structural issues

Due to the high speeds at which Concorde traveled, large forces were applied to the aircraft's structure during banks and turns. This caused twisting and the distortion of the aircraft’s structure. In addition there were concerns over maintaining precise control at supersonic speeds; both of these issues were resolved by active ratio changes between the inboard and outboard elevons, varying at differing speeds including supersonic. Only the innermost elevons, which are attached to the stiffest area of the wings, are active at high speed.

Additionally, the narrow fuselage meant that the aircraft flexed. This was visible from the rear passengers’ viewpoints.

Brakes and undercarriage

Due to a high average takeoff speed of 250 mph, Concorde needed upgraded brakes. Like most airliners, Concorde has anti-skid braking – a system which prevents the tres from losing traction when the brakes are applied for greater control during roll-out. The brakes, developed by Dunlop, were the first carbon-based brakes used on an airliner. They could bring Concorde to a stop from an aborted takeoff within one mile (1600 m) when weighing up to 185 tons (188 tonnes ) and traveling at 190 mph. This braking maneuver brought the brakes to temperatures of 300–500 °C, requiring several hours for cooling.

Another issue uncovered during development was the undercarriage. Because of the way Concorde's delta-wing generated lift, the undercarriage had to be unusually strong. At rotation, Concorde would rise to a high angle of attack, about 18 degrees. Prior to rotation the wing generated almost no lift, unlike typical aircraft wings. Combined with the high airspeed at rotation (199 KIAS), this unexpectedly increased the stresses on the rear undercarriage and during the development required a major redesign. Due to the high alpha needed at rotation, a small set of wheels were added aft to prevent tailstrikes. The rear main undercarriage units swing towards each other to be stowed but due to their great height also need to retract telescopically before swinging in order to clear each other when stowed.

Range

Concorde needed to travel between London and New York, or Washington, non-stop, and to achieve this the designers gave Concorde the greatest supersonic range of any aircraft. This was achieved by a combination of careful development of the engines to make them highly efficient at supersonic speeds (actually the world's most energy-efficient jet engine), by using a slender fuselage, and very careful design of the wing shape to give a good lift to drag ratio, by having a modest payload and high fuel capacity, and by moving the fuel to trim the aircraft without introducing any additional drag.

Nevertheless, soon after Concorde began flying, a Concorde "B" model was designed with slightly larger fuel capacity and slightly larger wings with leading edge slats to improve aerodynamic performance at all speeds. It featured more powerful engines with sound deadening and without the fuel-hungry and noisy reheat. It was speculated that it was reasonably possible to create an engine with up to 25% gain in efficiency over the Rolls-Royce/Snecma Olympus 593. This would have given additional range even with greater payload, and would have made new commercial routes possible. This was cancelled due in part to poor sales of Concorde, but also to the rising cost of aviation fuel in the 1970s.

Cabin pressurisation

Airliner cabins were usually maintained at a pressure equivalent to 6,000–8,000 feet (1,800–2,400 m) elevation. Concorde’s pressurization was set to an altitude at the lower end of this range, 6,000 ft. Concorde’s maximum cruising altitude was 60,000 ft. Above 50,000 ft, the lack of air pressure would give a "time of useful consciousness " in even a conditioned athlete of no more than 10–15 seconds. A sudden reduction in cabin pressure is hazardous to all passengers and crew. At Concorde’s altitude, the air density is very low; a breach of cabin integrity would result in a loss of pressure severe enough so that the plastic emergency oxygen masks installed on other passenger jets would not be effective, and passengers would quickly suffer from hypoxia despite quickly donning them. Concorde, therefore, was equipped with smaller windows to reduce the rate of loss in the event of a breach, a reserve air supply system to augment cabin air pressure, and a rapid descent procedure to bring the aircraft to a safe altitude. The FAA enforces minimum emergency descent rates for aircraft and made note of Concorde’s higher operating altitude, concluding that the best response to a loss of pressure would be a rapid descent. Pilots had access to Continuous Positive Airway Pressure (CPAP) which used masks that forced oxygen at higher pressure into the crew’s lungs.

Droop nose

Concorde’s drooping nose was a compromise between the need for a streamlined design to reduce drag and increase aerodynamic efficiency in flight and the need for the pilot to see properly during taxi, takeoff, and landing operations. A delta-wing aircraft takes off and lands with a high angle of attack (a high nose angle) compared to other wing planforms, due to the way the delta wing generates lift. The pointed nose would obstruct the pilots’ view of taxiways and runways, so Concorde’s nose was designed to allow for different positioning for different operations. The droop nose was accompanied by a moving visor that was retracted into the nose prior to the nose being lowered. When the nose was raised back to horizontal, the visor was raised ahead of the front cockpit windscreen for aerodynamic streamlining in flight.

A controller in the cockpit allowed the visor to be retracted and the nose to be lowered to 5° below the standard horizontal position for taxiing and takeoff. Following takeoff and after clearing the airport, the nose and visor were raised. Shortly before landing, the visor was again retracted and the nose lowered to 12.5° below horizontal for maximum visibility. Upon landing, the nose was raised to the five-degree position to avoid the possibility of damage. On rare occasions, the aircraft could take off with the nose fully down.

A final position had the visor retracted into the nose but the nose in the standard horizontal position. This setup was used for cleaning the windscreen and for short subsonic flights. The two prototype Concordes had two fixed "glass holes" on their retractable visors. The US Federal Aviation Administration objected to that restrictive visibility and demanded a different design before it would permit Concorde to serve US airports, which led to the redesigned visor used on the production aircraft and the four "pre-production" aircraft (101, 102, 201, and 202).

Flight characteristics

While commercial jets take eight hours to fly from New York to Paris, the average supersonic flight time on the transatlantic routes was just under 3.5 hours. Concorde had a maximum cruise altitude of and an average cruise speed of Mach 2.02, about 1155 knots (2140 km/h or 1334 mph), more than twice the speed of conventional aircraft.

With no other civil traffic operating at its cruising altitude of about, dedicated oceanic airways or "tracks" were used by Concorde to cross the Atlantic. Due to the nature of high altitude winds, these SST tracks were fixed in terms of their co-ordinates, unlike the North Atlantic Tracks at lower altitudes whose co-ordinates alter daily according to forecast weather patterns. Concorde would also be cleared in a block, allowing for a slow climb from 45,000 to during the oceanic crossing as the fuel load gradually decreased. In regular service, Concorde employed an efficient ''cruise-climb'' flight profile following take-off.

During a landing approach Concorde was on the "back side" of the drag force curve, where raising the nose would increase the sink rate. The delta-shaped wings allowed Concorde to attain a higher angle of attack than conventional aircraft, as it allowed the formation of large low pressure vortices over the entire upper wing surface, maintaining lift. The normal landing speed was 170 mph.

BA flights flown by Concorde added "''Concorde''" in addition to the standard "''Speedbird ''" callsign to notify air traffic control of the aircraft’s unique abilities and restrictions.

Operational history

Scheduled flights

Scheduled flights began on 21 January 1976 on the London–Bahrain and Paris–Rio (via Dakar ) routes. The Paris-Caracas route (via Azores ) began on 10 April of the same year. The US Congress had just banned Concorde landings in the US, mainly due to citizen protest over sonic booms, preventing launch on the coveted transatlantic routes. However, the US Secretary of Transportation, William Coleman, gave permission for Concorde service to Washington Dulles International Airport, and Air France and British Airways simultaneously began service to Dulles on 24 May 1976.

BA buys its Concordes outright

By around 1981 in the UK, the future for Concorde looked bleak. The British government had lost money operating Concorde every year, and moves were afoot to cancel the service entirely. A cost projection came back with greatly reduced metallurgical testing costs because the test rig for the wings had built up enough data to last for 30 years and could be shut down. Despite this, the government was not keen to continue. In late 1983, the managing director of BA, Sir John King, convinced the government to sell the aircraft outright to (the then state owned, later privatised) BA for £16.5 million plus the first year’s profits.

Sir John King realized that he had a premier product that was under priced, and after carrying out a market survey, British Airways discovered that their target customers thought that Concorde was more expensive than it actually was. They progressively raised prices and service quality to match these perceptions. It is reported that British Airways then ran Concorde at a profit, unlike their French counterpart. British Airways's profits have been reported to be up to £50 million in the most profitable years, with a total revenue of £1.75 billion, before costs of £1 billion.

Between 1984 and 1991, British Airways flew a thrice-weekly Concorde service between London and Miami, stopping at Washington’s Dulles International Airport. Until 2003, Air France and British Airways continued to operate the New York services daily. Concorde also visited Barbados’s Grantley Adams International Airport during the winter holiday season. Until the Air France Paris crash ended virtually all charter services by both AF and BA, several UK and French tour operators operated charter flights to European destinations on a regular basis; the charter business was viewed as lucrative by British Airways and Air France.

Concorde Flight 4590 crash

On 25 July 2000, Air France Flight 4590, registration F-BTSC, crashed in Gonesse, France, killing all 100 passengers and nine crew members on board the flight, and four people on the ground. It was the only fatal incident involving Concorde.

According to the official investigation conducted by the French accident investigation bureau (BEA), the crash was caused by a titanium strip that fell from a Continental Airlines DC-10 that had taken off minutes earlier. This metal fragment punctured a tyre on the Concorde's left main wheel bogie during takeoff. The tyre exploded, a piece of rubber hit the fuel tank, and while the fuel tank was not punctured, the impact caused a shock-wave which caused one of the fuel valves in the wing to burst open. This caused a major fuel leak from the tank, which then ignited due to sparking electrical landing gear wiring severed by another piece of the same tyre. The crew shut down engine number 2 in response to a fire warning, and with engine number 1 surging and producing little power, the aircraft was unable to gain height or speed. The aircraft entered a rapid pitch-up then a violent descent, rolling left and crashing tail-low into the Hotelissimo Hotel in Gonesse. On 6 December 2010, Continental Airlines and John Taylor, one of their mechanics, were found guilty of involuntary manslaughter.

Normal commercial operations resumed on 7 November 2001 by BA and AF (aircraft G-BOAE and F-BTSD), with service to New York JFK, where passengers were welcomed by the mayor Rudy Giuliani.

Retirement

On 10 April 2003, Air France and British Airways simultaneously announced that they would retire Concorde later that year. They cited low passenger numbers following 25 July 2000 crash, economic effects and the slump in air travel following 11 September 2001, and rising maintenance costs. Although Concorde was a technological marvel when introduced into service in the 1970s, 30 years later its cockpit, cluttered with analogue controls and dials, looked dated, as there had been little commercial pressure or reason to upgrade Concorde due to a lack of competing aircraft, unlike other airliners of the same vintage, for example the Boeing 747. By its retirement, it was the last aircraft in British Airways' fleet that still had a flight engineer; other aircraft, such as the modernised 747-400, had eliminated that role.

Records

The fastest transatlantic airliner flight was from London Heathrow to New York JFK on 7 February 1996 by British Airways' G-BOAD in 2 hours, 52 minutes, 59 seconds from takeoff to touchdown. Concorde also set other records, including the official FAI "Westbound Around the World" and "Eastbound Around the World" world air speed records. On 12–13 October 1992, in commemoration of the 500th anniversary of Columbus’ first New World landing, Concorde Spirit Tours (USA) chartered Air France Concorde F-BTSD and circumnavigated the world in 32 hours 49 minutes and 3 seconds, from Lisbon, Portugal, including six refuelling stops at Santo Domingo, Acapulco, Honolulu, Guam, Bangkok, and Bahrain.

The eastbound record was set by the same Air France Concorde (F-BTSD) under charter to Concorde Spirit Tours in the USA on 15–16 August 1995. This promotional flight circumnavigated the world from New York/JFK International Airport in 31 hours 27 minutes 49 seconds, including six refuelling stops at Toulouse, Dubai, Bangkok, Andersen AFB in Guam, Honolulu, and Acapulco. By its 30th flight anniversary on 2 March 1999 Concorde had clocked up 920,000 flight hours, with more than 600,000 supersonic, much more than all of the other supersonic aircraft in the Western world combined.

Comparison with other supersonic aircraft

The only other supersonic airliner in direct competition with Concorde was the Soviet Tupolev Tu-144, which was nicknamed "Concordski" by Western Europeans for its outward similarity to Concorde. Soviet espionage efforts had resulted in the theft of Concorde blueprints, ostensibly to assist in the design of the Tu-144. As a result of a rushed development program, the first prototype of the Tu-144 was substantially different from the preproduction machines, but both were cruder and less refined than Concorde. The Tu-144''S'' had a significantly shorter range than Concorde, due to its low-bypass turbofan engines. The vehicle had poor control at low speeds because of a simpler supersonic wing design; in addition the Tu-144 required parachutes to land while Concorde had sophisticated anti-lock brakes. The Tu-144 had two crashes, one at the 1973 Paris Air Show, and another during a pre-delivery test flight in the summer of 1978. Later production versions had retractable canards for better low-speed control, and a 126-seat research version used turbojet engines that gave them nearly the fuel efficiency and similar range to Concorde. With a top speed of Mach 2.35 it was potentially a more competitive aircraft – but was quickly taken out of service due to severe safety defects.

The American designs, the Boeing 2707 and the Lockheed L-2000 were to have been larger, with seating for up to 300 people. Running a few years behind Concorde, the winning Boeing 2707 was redesigned to a cropped delta layout; the extra cost of these changes helped to kill the project. The operation of US military aircraft such as the XB-70 Valkyrie and B-58 Hustler had shown that sonic booms were quite capable of reaching the ground, and the experience from the Oklahoma City sonic boom tests led to the same environmental concerns that hindered the commercial success of Concorde. The American government cancelled the project in 1971, after having spent more than $1 billion.

The only other large supersonic aircraft comparable to Concorde are strategic bombers, principally the Russian Tupolev Tu-22 /Tu-22M and Tu-160 and the American B-1B Lancer.

The original source for this article was the Wikipedia Concorde article.