Concorde

Concorde
Concorde
RoleSupersonic airliner
ManufacturerBAC (now BAE Systems)
Aérospatiale (now EADS)
First flight2 March 1969
Introduction21 January 1976
Retired26 November 2003
StatusRetired from service
Primary usersBritish Airways
Air France
Braniff International Airways
 
Number built20 (including 6 non-airline aircraft)
Unit cost£23 million in 1977

The Aérospatiale-BAC Concorde aircraft was 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 for 27 years.

Concorde flew regular transatlantic flights from London Heathrow (British Airways) and Paris Charles de Gaulle (Air France) to New York JFK and Washington Dulles, profitably flying these routes at record speeds, in less than half the time of other airliners. Indeed, Concorde held many speed records.

With only 20 aircraft built, the costly development phase represented a substantial economic loss. Additionally, Air France and British Airways were subsidised by their governments to buy the aircraft. As a result of the type's only crash (on 25 July 2000), world economic effects arising from the 9/11 attacks, and other factors, operations ceased on 24 October 2003. The last "retirement" flight occurred on 26 November 2003

Concorde remains an icon of aviation history, and has acquired an unusual nomenclature for an aircraft. In common usage in the United Kingdom, the type is known as "Concorde" rather than "the Concorde" or "a Concorde".

Development

In the late 1950s, the United Kingdom, France, United States and Soviet Union were considering developing supersonic transport. Britain's Bristol Aeroplane Company and France's 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 Britain, 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 Corp. and Aerospatiale.

Concorde's final flight, G-BOAF from Heathrow to Bristol, on 26 November 2003. The extremely high fineness ratio of the fuselage is evident

At first the new consortium intended to produce two versions of the aircraft, one long range and one short range. 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 premier 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 Canada, Braniff, Singapore Airlines, Iran Air, Olympic Airways, Qantas, CAAC, Middle East Airlines and TWA.

The aircraft was initially referred to in Britain as "Concorde," with the French spelling, but was officially changed to "Concord" by Harold Macmillan in response to a perceived slight by Charles de Gaulle. In 1967, at the French roll-out in Toulouse the British Government Minister for Technology, Tony Benn announced that he would change the spelling back to "Concorde." This created a nationalist uproar that died down when Benn stated that the suffixed "e" represented "Excellence, England, Europe and Entente (Cordiale)." In his memoirs, he recounts a tale of a letter from an irate Scotsman claiming: "you talk about 'E' for England, but part of it is made in Scotland." Given Scotland's contribution of providing the nose cone for the aircraft, Benn replied "it was also 'E' for 'Écosse' (the French name for Scotland) — and I might have added 'e' for extravagance and 'e' for escalation as well!"

Pre-production Concorde number 101 on display at the Imperial War Museum Duxford, UK

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 Andre 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. As the flight programme progressed, 001 embarked on a sales and demonstration tour on 4 September 1971. 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 a sudden number of order cancellations: the 1973 oil crisis, acute financial difficulties of many 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. 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.

The United States cancelled its supersonic transport (SST) programme in 1971. Two designs had been submitted; the Lockheed L-2000, looking like a scaled-up Concorde, lost out to the Boeing 2707, which was intended to be faster, to carry 300 passengers and feature a swing-wing design. Other countries, such as India and Malaysia, ruled out Concorde supersonic overflights due to noise concerns.

Concorde G-BOAB in storage at London Heathrow Airport following the end of all Concorde flying. This aircraft flew for 22,296 hours between its first flight in 1976 and its final flight in 2000.

Both European airlines flew demonstration and test flights 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. A total of 2,000 test hours were at supersonic speeds. Unit costs were £23 million (US$46 million) in 1977. Development cost was six times the projected amount.

Design

Concorde was an ogival (also "ogee") delta-winged aircraft with four Olympus engines based on those originally developed for the Avro Vulcan strategic bomber. The engines were jointly built by Rolls-Royce and SNECMA. Concorde was the first civil airliner to have an analogue fly-by-wire flight control system. It also employed a trademark droop snoot lowering nose section for visibility on approach.

The principal designer who worked on the project was Pierre Satre, with Sir Archibald Russell as his deputy.

These and other features permitted Concorde to have an average cruise speed of Mach 2.02 (about 2,140 km/h or 1,330 mph) with a maximum cruise altitude of 18,300 metres (60,000 feet), more than twice the speed of conventional aircraft. The average landing speed was 298 km/h (185 mph, 160 knots).

Concorde pioneered a number of technologies:

For high speed and optimisation of flight:

The flight deck
  • Double-delta (ogee/ogival) shaped wings
  • Variable inlet ramps controlled by digital computers
  • Supercruise capability
  • Thrust-by-wire engines, predecessor of today's FADEC-controlled engines
  • Droop-nose section for improved visibility in landing

For weight-saving and enhanced performance:

  • Mach 2.04 (~2,200 kilometres per hour (1,400 mph) cruising speed for optimum fuel consumption (supersonic drag minimum, although turbojet engines are more efficient at high speed)
  • Mainly aluminium construction for low weight and relatively conventional manufacture (higher speeds would have ruled out aluminium)
  • 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
  • Multifunction flight control surfaces
  • High-pressure hydraulic system of 28 MPa (4,000 lbf/in²) for lighter hydraulic systems components
  • Fully electrically controlled analogue brake-by-wire system
  • Pitch trim by shifting fuel around the fuselage for centre-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 Auxiliary power unit (Relying on the fact that Concorde will be used for premium services to big airports, where a ground air start cart would be readily available)
  • Flush fitting lights

The Concorde programme's primary legacy is in the experience gained in design and manufacture which later became the basis of the Airbus consortium. Snecma Moteurs' involvement with the Concorde programme prepared the company's entrance into civil engine design and manufacturing, opening the way for Snecma to establish CFM International with General Electric and produce the successful CFM International CFM56 series engines.

Although Concorde was a technological marvel when introduced into service in the 1970s, 30 years later its cockpit, cluttered with analogue dials and switches, looked dated. With no competition, there was no commercial pressure to upgrade Concorde with enhanced avionics or passenger comfort, as occurred in other airliners of the same vintage, for example the Boeing 747.

The key partners, BAC (later to become BAE Systems) and Aerospatiale (which was later merged into EADS), were the joint owners of Concorde's type certificate. Responsibility for the Type Certificate transferred to Airbus with formation of Airbus SAS.

Movement of centre of pressure

When any aircraft passes the critical mach of that particular airframe, the centre of pressure shifts rearwards. This causes a pitch down force on the aircraft, as the centre 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 metres. 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 centre of mass, effectively acting as an auxiliary trim control.

Heating issues

Beside engines, the hottest part of the structure of any supersonic aircraft is the nose. The engineers wanted to use (duralumin) aluminium throughout the aircraft, due to its familiarity, cost and ease of construction. The highest temperature that aluminium 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 modelling. An expensive 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. This cost millions of pounds per year to run.

In fact, owing to the heat generated by compression of the air as Concorde travelled 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. In the Seattle Museum of Flight's Concorde a protruding cap was cut off by a thief in an apparent attempt to steal it, leaving a part behind. An amnesty led to the severed cap being returned.

In order to keep the cabin cool, Concorde used the fuel as a heatsink for the heat from the air conditioning. The same method also cooled the hydraulics. During supersonic flight the windows in the cockpit became too hot to touch.

Concorde also had restrictions on livery; the majority of the surface had to be painted with a special highly reflecting white paint to avoid overheating the aluminium structure due to the supersonic heating effects of Mach 2. In 1996, however, Air France briefly painted F-BTSD in a predominantly-blue livery (with the exception of the wings) as part of a promotional deal with Pepsi Cola. In this paint scheme, Air France were advised to remain at Mach 2 for no more than 20 minutes at a time, but there was no restriction at speeds under Mach 1.7. F-BTSD was chosen for the promotion because the aircraft was not then scheduled to operate any long flights that required extended Mach 2 operations.

Structural issues

Due to the high speeds at which Concorde travelled, large forces were applied to the aircraft structure during banks and turns. This caused twisting and the distortion of the aircraft's structure. This was resolved by the neutralisation of the outboard elevons at high speeds. Only the innermost elevons, which are attached to the strongest area of the wings, are active at high speed.

Additionally, the narrow fuselage meant that the aircraft flexed more, particularly during takeoff. Pilots were able to look back down the cabin and see this occurring, but it was less visible from most of the passengers' viewpoints. The cabins of both Air France and British Airways featured lavatories and bulkheads midway down the cabin to reduce the appearance of the "long tube effect" to passengers in the aft of the aircraft.

Concorde tyres and brakes

Brakes and undercarriage

Due to a high average takeoff speed of 250 miles per hour (400 km/h), Concorde needed upgraded brakes. Like most airliners, Concorde used an anti-skid braking system which prevents the tyres from sliding 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, weighing up to 185 tons (188 tonnes) and traveling at 190 miles per hour (310 km/h), to a stop from an aborted takeoff within one mile (1600 m). This braking manoeuvre brought the brakes to temperatures of 300 °C to 500 °C, requiring several hours for cooling.

Another issue during the research for Concorde was the undercarriage. It turned out that the undercarriage had to be unusually strong. This was due to the unusual loadings due to the high angle of attack that Concorde needed during take-off, due to its delta-wing. This increased the weight and required a major redesign.

One interesting note about the main undercarriage is that if both were to just swing up to be stowed away they would hit each other and jam. The combined length of both undercarriages is greater than the distance between both undercarriage roots. This problem required that the undercarriage be first retracted vertically and then swung inwards to be tucked in the wing and fuselage belly.

Range

Concorde needed to travel between London and New York or Washington nonstop, 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, by 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 and featuring more powerful engines with sound deadening and without the fuel-hungry and noisy reheat. This would have given 500 km greater range even with greater payload, and would have opened up new commercial routes. This was cancelled due to poor sales of Concorde.

Increased radiation exposure

The high altitude at which Concorde cruised meant passengers received almost twice the flux of extraterrestrial ionising radiation as those travelling on a conventional long-haul flight. Due to the proportionally reduced flight time, however, the overall equivalent dose was less than a conventional flight over the same distance. Unusual solar activity led to an increase in incident radiation, so the flight deck had a radiometer and an instrument to measure the rate of decrease of radiation. If the level was too high, Concorde descended to below 47,000 feet (14,000 m). The rate of decrease indicator indicated whether the aircraft needed to descend further, decreasing the amount of time the aircraft was at an unsafe altitude.

Concorde fuselage

Cabin pressurisation

Airliner cabins are usually pressurised to 6-8,000 ft (1,800-2,400 m) elevation while the aircraft flies much higher. Concorde's pressurisation was set to an altitude at the lower end of this range, 6,000 feet (1,800 m). Some passengers can have difficulty even with that pressurisation. A sudden reduction in cabin pressure is hazardous to all passengers and crew. Concorde's maximum cruising altitude was 60,000 feet (18,000 m) (though the typical altitude reached between London and New York was about 56,000 feet (17,000 m)); subsonic airliners typically cruise below 40,000 feet (12,000 m). Above 50,000 feet (15,000 m), the lack of air pressure would give a 'time of useful consciousness' in even a conditioned athlete to no more than 10–15 seconds. A cabin breach could even reduce air pressure to below the ambient pressure outside the aircraft due to the Venturi effect, as the air is sucked out through an opening. 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 CPAP (Continuous Positive Airway Pressure) which used masks that forced oxygen at higher pressure into the crew's lungs.

Droop nose

Concorde's famous 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 quickly 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 possible 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.

Concorde's cockpit layout

The two prototype Concordes had two fixed "glass holes" on their retractable visors. The USA 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).

Avionics

The avionics of Concorde were unique as it was the first commercial aircraft to employ hybrid microcircuits, these were a combination of discrete electronic components and laser-etched silicon microcircuits. These were produced at the Sperry manufacturing plant in Bracknell, Berkshire (this later became BAe dynamics group which remained in Bracknell until the plant closed in 1989).

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. In transatlantic flight, Concorde travelled more than twice as fast as other aircraft — other aircraft frequently appeared to be flying backwards.

British Airways Concorde interior before 2000

In regular service, Concorde employed an efficient cruise-climb flight profile. As aircraft lose weight from consuming fuel, they can fly at progressively higher altitudes. This is (generally) more efficient, so conventional airliners employ a stepped climb profile, where air traffic control will approve a change to a higher flight level as the flight progresses.

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. This low pressure caused Concorde to disappear into a self-induced bank of fog on humid days. These vortices formed only at low air speeds, meaning that during the initial climb and throughout the approach Concorde experienced light turbulence and buffeting. Interestingly, the vortex lift created by Concorde's wing just prior to touchdown supplied its own mild turbulence.

With no other civil traffic operating at its cruising altitude of about 56,000 ft (17,000 m), dedicated oceanic airways or "tracks" were used by Concorde to cross the Atlantic. These SST, ("Super-Sonic Transport"), tracks were designated:

  • Sierra Mike (SM); A uni-directional track used by westbound flights of both Air France and British Airways.
  • Track Sierra November (SN); A uni-directional track used by eastbound flights of both Air France and British Airways.
  • Track Sierra Oscar (SO); A bi-directional track used by westbound Air France flights which might conflict with westbound British Airways flights routing simultaneously on Track SM, and by eastbound Air France flights which might conflict with eastbound British Airways flights routing simultaneously on Track SN.
  • Track Sierra Papa (SP); A uni-directional seasonal track used by westbound British Airways flights routing from London Heathrow to Barbados.
Concorde toilet facilities

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 15,000-foot (4,600 m) block, allowing for a slow climb from 45,000 to 60,000 ft (18,000 m) during the oceanic crossing as the fuel load gradually decreased.

Concorde actually flew fast enough that the weight of everyone onboard was temporarily reduced by about 1% when flying east. This was due to centrifugal effects since the airspeed added to the rotation speed of the Earth. Flying west, the weight increased by about 0.3%, because it cancelled out the normal rotation and, with it, the normal centrifugal force and replaced it with a smaller rotation in the opposite direction. Concorde flew high enough that the weight of everyone onboard was reduced by an additional 0.6% due to the increased distance from the centre of the Earth.

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. The flight numbers of BA's Concorde flights to/from the USA were 001–004; these BA Concordes therefore used callsigns "Speedbird Concorde 1" through to "Speedbird Concorde 4". The service to/from Barbados, special charter flights and test flights prior to a return to service following maintenance used the prefix "Speedbird Concorde" followed by the relevant four digit flight number. With the retirement of Concorde, the BA flight numbers 001 - 004 are now unused. Air France Concordes used the standard "Airfrans" callsign.