Concorde
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Concorde
British Airways Concorde G-BOAC 03.jpg
British Airways Concorde in 1986
Role Supersonic airliner
National origin United Kingdom and France
Manufacturer
British Aircraft Corporation (later British Aerospace and BAE Systems)
Sud Aviation (later Aérospatiale and Airbus)
First flight 2 March 1969
Introduction 21 January 1976
Retired 24 October 2003[1]
Primary users British Airways
Air France
See Operators below for others
Produced 1965–1979
Number built 20 (including 6 non-commercial aircraft)[2][3]
The Aérospatiale/BAC Concorde (/ˈkɒŋkɔːrd/) is a Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC). Studies started in 1954, and France and the UK signed a treaty establishing the development project on 29 November 1962, as the programme cost was estimated at £70 million (£1.39 billion in 2020). Construction of the six prototypes began in February 1965, and the first flight took off from Toulouse on 2 March 1969. The market was predicted for 350 aircraft, and it received up to 100 options from many major airlines. On 9 October 1975, it received its French Certificate of Airworthiness, and from the UK CAA on 5 December.[4]
Concorde is a tailless aircraft design with a narrow fuselage permitting a 4-abreast seating for 92 to 128 passengers, an ogival delta wing and a droop nose for landing visibility. It is powered by four Rolls-Royce/Snecma Olympus 593 turbojets with variable engine intake ramps, and reheat for take-off and acceleration to supersonic speed. Constructed out of aluminium, it was the first airliner to have analogue fly-by-wire flight-controls. The airliner could maintain a supercruise up to Mach 2.04 (2,167 km/h; 1,170 kn) at an altitude of 60,000 ft (18.3 km).
Delays and cost overruns increased the programme cost to £1.5-2.1 billion in 1976, (£9.44 billion-13.2 billion in 2020). Concorde entered service on 21 January of that year with Air France from Paris-Roissy and British Airways from London Heathrow. Transatlantic flights was the main market, to Washington Dulles from 24 May, and to New York JFK from 17 October 1977. Air France and British Airways remained the sole customers with seven airframes each, for a total production of twenty. Supersonic flight more than halved travel times, but sonic booms over the ground limited it to transoceanic flights only.
Its only competitor was the Tupolev Tu-144, carrying passengers from November 1977 until a May 1978 crash, while the larger and faster Boeing 2707 was cancelled in 1971. On 25 July 2000, Air France Flight 4590 ran over debris on its takeoff run and crashed with all 109 occupants and four on ground killed; the only fatal incident involving Concorde. Commercial service was suspended until November 2001, and Concorde aircraft were retired in 2003 after 27 years of commercial operations. Most aircraft are on display in Europe and America.
Development
Early studies
The origins of the Concorde project date to the early 1950s, when Arnold Hall, director of the Royal Aircraft Establishment (RAE), asked Morien Morgan to form a committee to study the supersonic transport (SST) concept. The group met for the first time in February 1954 and delivered their first report in April 1955.[5]
At the time it was known that the drag at supersonic speeds was strongly related to the span of the wing.[N 1] This led to the use of short-span, thin trapezoidal wings such as those seen on the control surfaces of many missiles, or in aircraft such as the Lockheed F-104 Starfighter or the Avro 730 that the team studied. The team outlined a baseline configuration that resembled an enlarged Avro 730.[6]
This same short span produced very little lift at low speed, which resulted in extremely long take-off runs and frighteningly high landing speeds.[7] In an SST design, this would have required enormous engine power to lift off from existing runways, and to provide the fuel needed, "some horribly large aeroplanes" resulted.[6] Based on this, the group considered the concept of an SST infeasible, and instead suggested continued low-level studies into supersonic aerodynamics.[6]
Slender deltas
Soon after, Johanna Weber and Dietrich Küchemann at the RAE published a series of reports on a new wing planform, known in the UK as the "slender delta" concept.[8][9] The team, including Eric Maskell whose report "Flow Separation in Three Dimensions" contributed to an understanding of the physical nature of separated flow,[10] worked with the fact that delta wings can produce strong vortices on their upper surfaces at high angles of attack.[6] The vortex will lower the air pressure and cause lift to be greatly increased. This effect had been noticed earlier, notably by Chuck Yeager in the Convair XF-92, but its qualities had not been fully appreciated. Weber suggested that this was no mere curiosity, and the effect could be used deliberately to improve low speed performance.[9][6]
Küchemann's and Weber's papers changed the entire nature of supersonic design almost overnight. Although the delta had already been used on aircraft prior to this point, these designs used planforms that were not much different from a swept wing of the same span.[N 2] Weber noted that the lift from the vortex was increased by the length of the wing it had to operate over, which suggested that the effect would be maximised by extending the wing along the fuselage as far as possible. Such a layout would still have good supersonic performance inherent to the short span, while also offering reasonable take-off and landing speeds using vortex generation.[9] The only downside to such a design is that the aircraft would have to take off and land very "nose high" to generate the required vortex lift, which led to questions about the low speed handling qualities of such a design.[11] It would also need to have long landing gear to produce the required angle of attack while still on the runway.
Küchemann presented the idea at a meeting where Morgan was also present. Test pilot Eric Brown recalls Morgan's reaction to the presentation, saying that he immediately seized on it as the solution to the SST problem. Brown considers this moment as being the true birth of the Concorde project.[11]
Supersonic Transport Aircraft Committee
The HP.115 tested the low-speed performance of the slender delta layout.
On 1 October 1956 the Ministry of Supply asked Morgan to form a new study group, the Supersonic Transport Aircraft Committee (STAC)[12] (sometimes referred to as the Supersonic Transport Advisory Committee), with the explicit goal of developing a practical SST design and finding industry partners to build it. At the first meeting, on 5 November 1956, the decision was made to fund the development of a test bed aircraft to examine the low-speed performance of the slender delta, a contract that eventually produced the Handley Page HP.115.[11] This aircraft would ultimately demonstrate safe control at speeds as low as 69 mph (111 km/h), about
1
/
3
that of the F-104 Starfighter.[13]
STAC stated that an SST would have economic performance similar to existing subsonic types.[6] A significant problem is that lift is not generated the same way at supersonic and subsonic speeds, with the lift-to-drag ratio for supersonic designs being about half that of subsonic designs.[14] This means the aircraft would have to use more power than a subsonic design of the same size. But although they would burn more fuel in cruise, they would be able to fly more sorties in a given period of time, so fewer aircraft would be needed to service a particular route. This would remain economically advantageous as long as fuel represented a small percentage of operational costs, as it did at the time.[6]
STAC suggested that two designs naturally fell out of their work, a transatlantic model flying at about Mach 2, and a shorter-range version flying at Mach 1.2 perhaps. Morgan suggested that a 150-passenger transatlantic SST would cost about £75 to £90 million to develop, and be in service in 1970. The smaller 100 passenger short-range version would cost perhaps £50 to £80 million, and be ready for service in 1968. To meet this schedule, development would need to begin in 1960, with production contracts let in 1962.[6] Morgan strongly suggested that the U.S. was already involved in a similar project, and that if the UK failed to respond it would be locked out of an airliner market that he believed would be dominated by SST aircraft.[15][N 3]
In 1959, a study contract was awarded to Hawker Siddeley and Bristol for preliminary designs based on the slender delta concept,[16] which developed as the HSA.1000 and Bristol 198. Armstrong Whitworth also responded with an internal design, the M-Wing, for the lower-speed shorter-range category. Even at this early time, both the STAC group and the government were looking for partners to develop the designs. In September 1959, Hawker approached Lockheed, and after the creation of British Aircraft Corporation in 1960, the former Bristol team immediately started talks with Boeing, General Dynamics, Douglas Aircraft, and Sud Aviation.[16]
Ogee planform selected
Küchemann and others at the RAE continued their work on the slender delta throughout this period, considering three basic shapes; the classic straight-edge delta, the "gothic delta" that was rounded outward to appear like a gothic arch, and the "ogival wing" that was compound-rounded into the shape of an ogee. Each of these planforms had its own advantages and disadvantages in terms of aerodynamics. As they worked with these shapes, a practical concern grew to become so important that it forced selection of one of these designs.[17]
Generally one wants to have the wing's centre of pressure (CP, or "lift point") close to the aircraft's centre of gravity (CG, or "balance point") to reduce the amount of control force required to pitch the aircraft. As the aircraft layout changes during the design phase, it is common for the CG to move fore or aft. With a normal wing design this can be addressed by moving the wing slightly fore or aft to account for this.[N 4] With a delta wing running most of the length of the fuselage, this was no longer easy; moving the wing would leave it in front of the nose or behind the tail. Studying the various layouts in terms of CG changes, both during design and changes due to fuel use during flight, the ogee planform immediately came to the fore.[17]
Plan-view silhouette of the Bristol Type 223 SST project
While the wing planform was evolving, so was the basic SST concept. Bristol's original Type 198 was a small design with an almost pure slender delta wing,[18] but evolved into the larger Type 223.
To test the new wing, NASA privately assisted the team by modifying a Douglas F5D Skylancer with temporary wing modifications to mimic the wing selection. In 1965 the NASA test aircraft successfully tested the wing, and found that it reduced landing speeds noticeably over the standard delta wing. NASA Ames test center also ran simulations that showed the aircraft would suffer a sudden change in pitch when entering ground effect. Ames test pilots later participated in a joint cooperative test with the French and British test pilots and found that the simulations had been correct, and this information was added to pilot training.[19]
Partnership with Sud Aviation
By this time similar political and economic concerns in France had led to their own SST plans. In the late 1950s the government requested designs from both the government-owned Sud Aviation and Nord Aviation, as well as Dassault.[N 5] All three returned designs based on Küchemann and Weber's slender delta; Nord suggested a ramjet powered design flying at Mach 3, the other two were jet powered Mach 2 designs that were similar to each other. Of the three, the Sud Aviation Super-Caravelle won the design contest with a medium-range design deliberately sized to avoid competition with transatlantic US designs they assumed were already on the drawing board.[20]
As soon as the design was complete, in April 1960, Pierre Satre, the company's technical director, was sent to Bristol to discuss a partnership. Bristol was surprised to find that the Sud team had designed a similar aircraft after considering the SST problem and coming to the very same conclusions as the Bristol and STAC teams in terms of economics. It was later revealed that the original STAC report, marked "For UK Eyes Only", had secretly been passed to the French to win political favour. Sud made minor changes to the paper, and presented it as their own work.[21]
Unsurprisingly, the two teams found much to agree on. The French had no modern large jet engines, and had already concluded they would buy a British design anyway (as they had on the earlier subsonic Caravelle).[22] As neither company had experience in the use of high-heat metals for airframes, a maximum speed of around Mach 2 was selected so aluminium could be used – above this speed the friction with the air warms the metal so much that aluminium begins to soften. This lower speed would also speed development and allow their design to fly before the Americans. Finally, everyone involved agreed that Küchemann's ogee shaped wing was the right one.[20]
The only disagreements were over the size and range. The UK team was still focused on a 150-passenger design serving transatlantic routes, while the French were deliberately avoiding these. However, this proved not to be the barrier it might seem; common components could be used in both designs, with the shorter range version using a clipped fuselage and four engines, the longer one with a stretched fuselage and six engines, leaving only the wing to be extensively re-designed.[23] The teams continued to meet through 1961, and by this time it was clear that the two aircraft would be considerably more similar in spite of different range and seating arrangements. A single design emerged that differed mainly in fuel load. More powerful Bristol Siddeley Olympus engines, being developed for the TSR-2, allowed either design to be powered by only four engines.[24]
Cabinet response, treaty
While the development teams met, French Minister of Public Works and Transport Robert Buron was meeting with the UK Minister of Aviation Peter Thorneycroft, and Thorneycroft soon revealed to the cabinet that the French were much more serious about a partnership than any of the U.S. companies.[25] The various U.S. companies had proved uninterested in such a venture, likely due to the belief that the government would be funding development and would frown on any partnership with a European company, and the risk of "giving away" U.S. technological leadership to a European partner.[16]
When the STAC plans were presented to the UK cabinet, a negative reaction resulted. The economic considerations were considered highly questionable, especially as these were based on development costs, now estimated to be £150 million, which were repeatedly overrun in the industry. The Treasury Ministry in particular presented a very negative view, suggesting that there was no way the project would have any positive financial returns for the government, especially in light that "the industry's past record of over-optimistic estimating (including the recent history of the TSR.2) suggests that it would be prudent to consider the £150 million [cost] to turn out much too low."[25]
This concern led to an independent review of the project by the Committee on Civil Scientific Research and Development, which met on topic between July and September 1962. The Committee ultimately rejected the economic arguments, including considerations of supporting the industry made by Thorneycroft. Their report in October stated that it was unlikely there would be any direct positive economic outcome, but that the project should still be considered for the simple reason that everyone else was going supersonic, and they were concerned they would be locked out of future markets. Conversely, it appeared the project would not be likely to significantly affect other, more important, research efforts.[25]
After considerable argument, the decision to proceed ultimately fell to an unlikely political expediency. At the time, the UK was pressing for admission to the European Economic Community, and this became the main rationale for moving ahead with the aircraft.[26] 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 government, imposing heavy penalties for cancellation. This treaty was signed on 29 November 1962.[27] Charles De Gaulle would soon veto the UK's entry into the European Community in a speech on 25 January 1963.[28]
Naming
Reflecting the treaty between the British and French governments that led to Concorde's construction, the name Concorde is from the French word concorde (IPA: [kɔ̃kɔʁd]), which has an English equivalent, concord. Both words mean agreement, harmony, or union. The name was officially changed to Concord by Harold Macmillan in response to a perceived slight by Charles de Gaulle. At the French roll-out in Toulouse in late 1967,[29] the British Government Minister of Technology, Tony Benn, announced that he would change the spelling back to Concorde.[30] 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: "[Y]ou 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, "[I]t was also 'E' for 'Écosse' (the French name for Scotland) – and I might have added 'e' for extravagance and 'e' for escalation as well!"[31]
Concorde also acquired an unusual nomenclature for an aircraft. In common usage in the United Kingdom, the type is known as "Concorde" without an article, rather than "the Concorde" or "a Concorde".[32][33]
Sales efforts
British Airways Concorde in early BA livery at London-Heathrow Airport, in the early 1980s
Described by Flight International as an "aviation icon" and "one of aerospace's most ambitious but commercially flawed projects",[34][35] Concorde failed to meet its original sales targets, despite initial interest from several airlines.
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.[27]
A two page advertisement for Concorde ran in the 29 May 1967 issue of Aviation Week & Space Technology which predicted a market for 350 aircraft by 1980 and boasted of Concorde's head start over the United States' SST project.[36]
Concorde had considerable difficulties that led to its dismal sales performance. Costs had spiralled during development to more than six times the original projections, arriving at a unit cost of £23 million in 1977 (equivalent to £146.09 million in 2020).[37] Its sonic boom made travelling supersonically over land impossible without causing complaints from citizens.[38] World events had also dampened Concorde sales prospects, the 1973–74 stock market crash and the 1973 oil crisis had made many airlines cautious about aircraft with high fuel consumption rates; and new wide-body aircraft, such as the Boeing 747, had recently made subsonic aircraft significantly more efficient and presented a low-risk option for airlines.[39] While carrying a full load, Concorde achieved 15.8 passenger miles per gallon of fuel, while the Boeing 707 reached 33.3 pm/g, the Boeing 747 46.4 pm/g, and the McDonnell Douglas DC-10 53.6 pm/g.[40] An emerging trend in the industry in favour of cheaper airline tickets had also caused airlines such as Qantas to question Concorde's market suitability.[41]
The consortium received orders, i.e., non-binding options, for more than 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 Airlines, Middle East Airlines, and TWA.[27][42][43] At the time of the first flight the options list contained 74 options from 18 airlines:[44]
Airline Number Reserved Cancelled Remarks
Pan Am[45] 6 3 June 1963 31 January 1973 2 extra options in 1964
Air France 6 3 June 1963 2 extra options in 1964
BOAC 6 3 June 1963 2 extra options in 1964
Continental Airlines 3 24 July 1963 Mar 1973
American Airlines 4 7 October 1963 Feb 1973 2 extra options in 1965
TWA 4 16 October 1963 31 January 1973 2 extra options in 1965
Middle East Airlines 2 4 December 1963 Feb 1973
Qantas 6 19 March 1964 June 1973[46] 2 cancelled in May 1966
Air India 2 15 July 1964 Feb 1975
Japan Airlines 3 30 September 1965 1973
Sabena 2 1 December 1965 Feb 1973
Eastern Airlines 2 28 June 1966 Feb 1973 2 extra options on 15 August 1966
2 other extra options on 28 April 1967
United Airlines 6 29 June 1966 26 October 1972
Braniff 3 1 September 1966 Feb 1973
Lufthansa 3 16 February 1967 Apr 1973
Air Canada 4 1 March 1967 6 June 1972[47]
CAAC 2 24 July 1972 Dec 1979[48]
Iran Air 2 8 October 1972 Feb 1980
Testing
Concorde 001 first flight in 1969
The design work was supported by a preceding research programme studying the flight characteristics of low ratio delta wings. A supersonic Fairey Delta 2 was modified to carry the ogee planform, and, renamed as the BAC 221, used for flight tests of the high speed flight envelope,[49] the Handley Page HP.115 also provided valuable information on low speed performance.[50]
Construction of two prototypes began in February 1965: 001, built by Aérospatiale 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,[51] and first went supersonic on 1 October.[52] The first UK-built Concorde flew from Filton to RAF Fairford on 9 April 1969, piloted by Brian Trubshaw.[53][54] Both prototypes were presented to the public for the first time on 7–8 June 1969 at the Paris Air Show. 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.[55][56] Concorde 002 followed suit on 2 June 1972 with a tour of the Middle and Far East.[57] 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.[58]
Concorde on early visit to Heathrow Airport on 1 July 1972
While Concorde had initially held a great deal of customer interest, the project was hit by a large number of order cancellations. The Paris Le Bourget air show crash of the competing Soviet Tupolev Tu-144 had shocked potential buyers, and public concern over the environmental issues presented by a supersonic aircraft—the sonic boom, take-off noise and pollution—had produced a shift in public opinion of SSTs. By 1976 the remaining buyers were from four countries: Britain, France, China, and Iran.[38] 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.[59]
The United States government cut federal funding for the Boeing 2707, its rival supersonic transport programme, in 1971; Boeing did not complete its two 2707 prototypes. The US, India, and Malaysia all ruled out Concorde supersonic flights over the noise concern, although some of these restrictions were later relaxed.[60][61] Professor Douglas Ross characterised restrictions placed upon Concorde operations by President Jimmy Carter's administration as having been an act of protectionism of American aircraft manufacturers.[62]
Programme cost
The original programme cost estimate was £70 million before 1962,[63] (£1.39 billion in 2020).[64] The programme experienced huge cost overruns and delays, with the programme eventually costing between £1.5 and £2.1 billion in 1976,[65] (£9.44 billion-13.2 billion in 2020).[64] This extreme cost was the main reason the production run was much smaller than expected.[66] The per-unit cost was impossible to recoup, so the French and British governments absorbed the development costs.
Design
Concorde flight deck layout
General features
Concorde is an ogival delta winged aircraft with four Olympus engines based on those employed in the RAF's Avro Vulcan strategic bomber. It is one of the few commercial aircraft to employ a tailless design (the Tupolev Tu-144 being another). Concorde was the first airliner to have a (in this case, analogue) fly-by-wire flight-control system; the avionics system Concorde used was unique because it was the first commercial aircraft to employ hybrid circuits.[67] The principal designer for the project was Pierre Satre, with Sir Archibald Russell as his deputy.[68]
Concorde pioneered the following technologies:
For high speed and optimisation of flight:
Double delta (ogee/ogival) shaped wings[8]
Variable engine air intake ramp system controlled by digital computers[69]
Supercruise capability[70]
Thrust-by-wire engines, predecessor of today's FADEC-controlled engines[69]
Droop nose for better landing visibility
For weight-saving and enhanced performance:
Mach 2.02 (~2,154 km/h or 1,338 mph) cruising speed[71] for optimum fuel consumption (supersonic drag minimum and turbojet engines are more efficient at higher speed[72]) Fuel consumption at Mach 2 (2,120 km/h; 1,320 mph) and at altitude of 60,000 feet (18,000 m) was 4,800 US gallons per hour (18,000 L/h).[73]
Mainly aluminium construction using a high temperature alloy similar to that developed for aero-engine pistons.[74] This material gave low weight and allowed conventional manufacture (higher speeds would have ruled out aluminium)[75]
Full-regime autopilot and autothrottle[76] allowing "hands off" control of the aircraft from climb out to landing
Fully electrically controlled analogue fly-by-wire flight controls systems[67]
High-pressure hydraulic system using 28 MPa (4,100 psi) for lighter hydraulic components,[77] tripled independent systems ("Blue", "Green", and "Yellow") for redundancy, with an emergency ram air turbine (RAT) stored in the port-inner elevon jack fairing supplying "Green" and "Yellow" as backup.[78]
Complex air data computer (ADC) for the automated monitoring and transmission of aerodynamic measurements (total pressure, static pressure, angle of attack, side-slip).[79]
Fully electrically controlled analogue brake-by-wire system[80]
Pitch trim by shifting fuel fore-and-aft for centre-of-gravity (CoG) control at the approach to Mach 1 and above with no drag penalty.[81] Pitch trimming by fuel transfer had been used since 1958 on the B-58 supersonic bomber.[82]
Parts made using "sculpture milling", reducing the part count while saving weight and adding strength.[83]
No auxiliary power unit, as Concorde would only visit large airports where ground air start carts are available.[84]
Powerplant
Close up of engine nozzles of production Concorde F-BVFB. The nozzle consists of tilting cups.
Concorde's intake ramp system schematics
Concorde's intake ramp system
Main article: Rolls-Royce/Snecma Olympus 593
A symposium titled "Supersonic-Transport Implications" was hosted by the Royal Aeronautical Society on 8 December 1960. Various views were put forward on the likely type of powerplant for a supersonic transport, such as podded or buried installation and turbojet or ducted-fan engines.[85][86] Boundary layer management in the podded installation was put forward as simpler with only an inlet cone but Dr. Seddon of the RAE saw "a future in a more sophisticated integration of shapes" in a buried installation. Another concern highlighted the case with two or more engines situated behind a single intake. An intake failure could lead to a double or triple engine failure. The advantage of the ducted fan over the turbojet was reduced airport noise but with considerable economic penalties with its larger cross-section producing excessive drag.[87] At that time it was considered that the noise from a turbojet optimised for supersonic cruise could be reduced to an acceptable level using noise suppressors as used on subsonic jets.
The powerplant configuration selected for Concorde, and its development to a certificated design, can be seen in light of the above symposium topics (which highlighted airfield noise, boundary layer management and interactions between adjacent engines) and the requirement that the powerplant, at Mach 2, tolerate combinations of pushovers, sideslips, pull-ups and throttle slamming without surging.[88] Extensive development testing with design changes and changes to intake and engine control laws would address most of the issues except airfield noise and the interaction between adjacent powerplants at speeds above Mach 1.6 which meant Concorde "had to be certified aerodynamically as a twin-engined aircraft above Mach 1.6".[89]
Rolls-Royce had a design proposal, the RB.169, for the aircraft at the time of Concorde's initial design[90] but "to develop a brand-new engine for Concorde would have been prohibitively expensive"[91] so an existing engine, already flying in the supersonic BAC TSR-2 strike bomber prototype, was chosen. It was the BSEL Olympus Mk 320 turbojet, a development of the Bristol engine first used for the subsonic Avro Vulcan bomber.
Great confidence was placed in being able to reduce the noise of a turbojet and massive strides by SNECMA in silencer design were reported during the programme.[92] However, by 1974 the spade silencers which projected into the exhaust were reported to be ineffective but "entry-into-service aircraft are likely to meet their noise guarantees".[93] The Olympus Mk.622 with reduced jet velocity was proposed to reduce the noise[94] but it was not developed.
Situated behind the leading edge of the wing, the engine intake had wing boundary layer ahead of it. Two-thirds was diverted and the remaining third which entered the intake did not adversely affect the intake efficiency[95] except during pushovers when the boundary layer thickened ahead of the intake and caused surging. Extensive wind tunnel testing helped define leading edge modifications ahead of the intakes which solved the problem.[96]
Each engine had its own intake and the engine nacelles were paired with a splitter plate between them to minimise adverse behaviour of one powerplant influencing the other. Only above Mach 1.6 (1,960 km/h; 1,220 mph) was an engine surge likely to affect the adjacent engine.[89]
Concorde needed to fly long distances to be economically viable; this required high efficiency from the powerplant. Turbofan engines were rejected due to their larger cross-section producing excessive drag. Olympus turbojet technology was available to be developed to meet the design requirements of the aircraft, although turbofans would be studied for any future SST.[97]
The aircraft used reheat (afterburners) only at take-off and to pass through the upper transonic regime to supersonic speeds, between Mach 0.95 and 1.7. Reheat was switched off at all other times.[98] Due to jet engines being highly inefficient at low speeds, Concorde burned two tonnes (4,400 lb) of fuel (almost 2% of the maximum fuel load) taxiing to the runway.[99] Fuel used is Jet A-1. Due to the high thrust produced even with the engines at idle, only the two outer engines were run after landing for easier taxiing and less brake pad wear – at low weights after landing, the aircraft would not remain stationary with all four engines idling requiring the brakes to be continuously applied to prevent the aircraft from rolling.
The air intake design for Concorde's engines was especially critical.[100] The intakes had to slow down supersonic inlet air to subsonic speeds with high pressure recovery to ensure efficient operation at cruising speed while providing low distortion levels (to prevent engine surge) and maintaining high efficiency for all likely ambient temperatures to be met in cruise. They had to provide adequate subsonic performance for diversion cruise and low engine-face distortion at take-off. They also had to provide an alternative path for excess intake air during engine throttling or shutdowns.[101] The variable intake features required to meet all these requirements consisted of front and rear ramps, a dump door, an auxiliary inlet and a ramp bleed to the exhaust nozzle.[102]
As well as supplying air to the engine, the intake also supplied air through the ramp bleed to the propelling nozzle. The nozzle ejector (or aerodynamic) design, with variable exit area and secondary flow from the intake, contributed to good expansion efficiency from take-off to cruise.[103]
Concorde's Air Intake Control Units (AICUs) made use of a digital processor to provide the necessary accuracy for intake control. It was the world's first use of a digital processor to be given full authority control of an essential system in a passenger aircraft. It was developed by the Electronics and Space Systems (ESS) division of the British Aircraft Corporation after it became clear that the analogue AICUs fitted to the prototype aircraft and developed by Ultra Electronics were found to be insufficiently accurate for the tasks in hand.[104]
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 theoretically could have caused a catastrophic failure of the airframe. Although computer simulations predicted considerable problems, in practice Concorde could shut down both engines on the same side of the aircraft at Mach 2 without the predicted difficulties.[105] During an engine failure the required air intake is virtually zero. So, on Concorde, engine failure was 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 minimising drag. Concorde pilots were routinely trained to handle double engine failure.[106]
Concorde's thrust-by-wire engine control system was developed by Ultra Electronics.[107]
Heating problems
Air compression on the outer surfaces caused the cabin to heat up during flight. Every surface, such as windows and panels, was wa