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British Industrial History

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Concorde

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Concorde 002. Exhibit at the Fleet Air Arm Museum.
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In the late 1950s, the UK, France, US and the Soviet Union were considering developing supersonic transport. Britain's Bristol Aeroplane Co and France's Sud Aviation were both working on designs, called the Type 233 and Super-Caravelle, respectively.

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.

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 Aerospatiale.

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 and first went supersonic on 1 October. As the flight programme progressed, it 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.

Concorde was an ogival delta-winged ("OG delta wing") aircraft with four powerful 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.

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 a relatively high 298 km/h (185 mph, 160 knots).

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 gravity 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 gravity, effectively acting as an auxiliary trim control.

To be economically viable, Concorde needed to be able to fly reasonably long distances, and this required high efficiency. For optimum supersonic flight, the engines needed to have a small frontal cross-sectional area to minimise drag and a low bypass ratio to give a high, supersonic exhaust speed. Turbojets were thus the best choice of engines. The more efficient and quieter high bypass turbofan engines such as used on Boeing 747s could not be used. The engine chosen was the twin spool Rolls-Royce/Snecma Olympus 593, a version of the Olympus originally developed for the Vulcan bomber, developed into an after-burning supersonic engine for the BAC TSR-2 strike bomber and then adapted for Concorde.

The inlet design for Concorde's engines was critical. All conventional jet engines can intake air at only around Mach 0.5; therefore the air needs to be slowed from the Mach 2.0 airspeed that enters the engine inlet. 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 ramps and an auxiliary flap, 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 flap moved both up and down allowing air to flow in or out. During takeoff, when the engine's air demand was high, the ramps were flat at the top and the auxiliary flap was in, allowing more air to enter the engine. As the aircraft approached Mach 0.7, the flap closed; at Mach 1.3, the ramps came into effect, removing air from the engines which was then used in the pressurisation of the cabin. At Mach 2.0, the ramps had covered half their total possible distance. They also helped reduce the work done by the compressors as they not only compressed the air but also increased the air temperature.

Engine failure causes large problems on conventional subsonic aircraft; not only does the aircraft lose thrust on that side but the engine is a large source of 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 have caused 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 flap and the full extension of the ramps, which deflected the air downwards past the engine, gaining lift and streamlining the engine, minimising the drag effects of the failed engine. In tests, Concorde was able to shut down both engines on the same side of the aircraft at Mach 2 without any control problems.

The aircraft used reheat (afterburners) at take-off and to pass through the transonic regime between Mach 0.95 and Mach 1.7, and were switched-off at all other times. The engines were just capable of reaching Mach 2 without reheat, but it was discovered operationally that it burnt more fuel that way, since the aircraft spent much longer flying in the high-drag transonic regime even though reheat is relatively inefficient.

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. 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'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 heat-sink 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 white 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.

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 relatively narrow height of the fuselage meant that the aircraft flexed more, particularly during takeoff, and pilots were able to look back down the cabin and see this occurring, but it was less visible from most of the passengers' viewpoints.

Due to a relatively high average takeoff speed of 250 mph (400 km/h), Concorde needed good brakes. Concorde's brakes were one of the first major users of anti-lock braking systems, which stop the wheels from locking when fully applied, allowing greater deceleration and control during braking, particularly in wet conditions.

The brakes were carbon-based and could bring Concorde, weighing up to 185 tons (188 tonnes) and travelling at 190 mph (305 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.

Concorde needed to travel between London and New York or Washington nonstop, and to achieve this the designers gave Concorde the greatest range of any supersonic aircraft at the time (since beaten by the Tu-160). 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 relatively modest payload, a 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, featuring more powerful engines without the fuel-hungry and noisy reheat, slightly larger fuel capacity and slightly larger wings with leading-edge slats to improve aerodynamic performance at all speeds. This would have given 500 km greater range even with greater payload. This was cancelled due to poor sales of Concorde.

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. Because of 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 ft (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.

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 a lower altitude than most other commercial jets. Concorde's maximum cruising altitude was 60,000 ft (18,000 m) (though the typical altitude reached between London and New York was about 56,000 ft (17,000 m)); subsonic airliners typically cruise below 40,000 ft (12,000 m). Above 50,000 ft (15,000 m), the lack of oxygen would limit 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.[citation needed] Pilots had access to CPAP (Continuous Positive Airway Pressure) which used masks that forced oxygen at higher pressure into the crew's lungs.

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 subsonic aircraft, 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.

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 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.

In total, 20 Concordes were built, six for development and 14 for commercial service.

These were:

  • Two prototypes
  • Two pre-production aircraft
  • 16 production aircraft

The first two of these did not enter commercial service. Of the 14 that flew commercially, 12 were still in service in April 2003. All but two of these aircraft, a remarkably high percentage for any commercial fleet, are preserved; the two that are not preserved are F-BVFD (cn 211), parked as a spare-parts source in 1982 and scrapped in 1994, and F-BTSC (cn 203), which crashed in Paris on 25 July 2000.

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