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Concorde Design

The aircraft that evolved from discussions between the British and French designers was essentially an all-aluminum design with a thin ogee-delta wing. It was to be powered by four Bristol/Siddeley (BS-593) Olympus engines in the 35,000-pound thrust category. These straight turbojets were equipped with afterburners for use in takeoff and acceleration to cruise flight conditions. This was a "civilianized" version of the Olympus 22R - a then 10-year-old military engine that had been developed by Bristol-Siddeley for the TSR-2 multimission combat plane (which was canceled in 1965 after $532 million had been spent). Originally, the aircraft was to carry 112 to 128 pasengers a distance of 4000 statute miles at a cruise speed of 1450 mph (Mach 2.2). During the course of development, however, the cruise speed was reduced to 1350 mph (Mach 2.05), and the passenger load was reduced to the order of 90 to 100 on transatlantic missions.

The speed of the Concorde was limited to Mach 2.2 because of a decision to employ aluminum instead of titanium, which was more difficult and risky to use but would have allowed speeds up to Mach 3. The flight requirements for a Mach 3 airliner similar to the XB-70 were far more complicated than those for a Mach 2 aircraft, such as the Anglo-French Concorde SST. A Mach 3 airliner's structure required more exotic alloys, such as titanium, because the conventional aluminum airframe of a plane like the Concorde could not survive the aerodynamic heating at greater speeds. Although Mach 2 military aircraft were commonplace in the late 1960s, no type had previously been required to last for 50,000 service hours of which at least 20,000 will be spent at the maximum cruising speed. This requirement was of prime importance in the choice of materials, the development of manufacturing processes, and the design of the structure itself.

The first structural decision was to choose the appropriate aluminum alloy to meet the new environmental conditions. The most important of these is the effect of kinetic heating from the high-speed boundary layer. The surface temperature depends on the balance of the heat transfer to the skin from the boundary layer, the heat picked up by solar radiation, the heat radiated back from the surface itself to the atmosphere, and the heat transferred from the surface to the internal structure. The most significant new design considerations are creep and thermal fatigue. Creep affects the choice of basic material, the design of joints, and the design of structures through its interaction with fatigue life. Thermal stresses, arising from differential expansions within the structure, have a more important effect on fatigue design than on static strength.

Some advantage is obtained by painting the external surface white. A white surface can be made almost as good as a black surface at radiating heat whereas it is much better than a black surface in reflecting solar radiation. Use of such a white surface will result in a cooling of about 8C at around Mach 2. This cooling is well worth having from the structural and from the air-conditioning point of view.

The main structural components of modern aircraft are the fuselage; wings; empennage, or tail surfaces; power plant; and landing gear, or undercarriage. The fuselage is the main body structure to which the wings, tail, landing gear, and power plants are attached. It contains the cockpit or flight deck, passenger compartment, cargo compartment, and-especially in the case of fighter aircraft--the engines and fuel tanks.

The Concorde fuselage diameter of 113 inches is very small because of the strong impact of fuselage diameter on wave drag. It is known that in supersonic flight, a wing and fuselage can have a significant influence on each other, including the possibility of a reduction in total volume wave drag compared to the sum of the drag of each separately. One well-known example is the so-called area rule, where the fuselage is indented in such a way as to partially offset the volume drag of the wing. Methods for designing the indentation are generally known. The large Boeing 2707 design had a fuselage whose diameter varied over the cabin section. This "wasp waist / coke bottle" are rule configuration was adopted by Boeing to reduce the interference wave drag between wing and fuselage. This was not done on the Concorde as it was felt that the increase in production costs would be too high. Indeed the variable cross-section introduces many difficulties and affects the seating arrangement.

Supersonic transports like the Anglo-French Concorde droop the front of the jet (the nose) downward to allow the pilots to see forward during takeoffs and landings. Under constrains of minimizing weight and preserving stream lines, providing a pilot with "out-the-window" vision has become a major design criterion for modern supersonic aircraft. The Concorde supersonic transport provides such visibility to its crew through a "droop-nose" arrangement whereby the nose section, forward of the cockpit and flight crew, is hinged downward during its low speed takeoff and landing operations. If the nose were not lowered, the airplane's long nose in front of the pilot and the fact that the airplane is at a high angle of attack during landing, would prevent the pilots from looking over the nose and seeing the runway. The nose is drooped hydraulically to improve forward view during take-off, initial climb, approach and landing. The retractable visor is raised hydraulically to fair in windscreen in cruising flight.

The Concorde aircraft rudders and elevons are similar in construction although the former were and remain the design responsibility of BAE Systems (was BAe) while the latter are the responsibility of EADS (was Aerospatiale), France. In order to maintain the stiffness required of a slender crosssection with the minimum weight, the surfaces are of metal honeycomb construction faced with aluminium alloy skins, chemically milled locally to achieve the optimum skin thickness. The skins are bonded to the honeycomb core using an autoclave-cured film adhesive, this process being carried-out under pressure conditions to ensure positive contact of the skin to the core.

The Concorde has a nose gear, an auxiliary gear situated at the rear of the fuselage and two main landing gears, each with a bogie with four wheels. The bogies are equipped with a system which detects under-inflation of a tyre and transmits a visual signal to the cockpit. When all of the landing gear is locked in the "up" position, the gear doors close. During retraction of the main gear, the shock struts are retracted into the gear leg to allow them to fit in the gear well. The wheels are automatically braked when the gear selector is in the "up" position. The deflectors are made of composite materials and fibreglass (to make them frangible) except for the bogie fasteners. Each deflector weighs around 4 kg and is located at the front of each main landing gear. Their function is to deflect water and spray to ensure it does not enter the engine air intakes. The wheels were manufactured by Dunlop, and the tires used by Air France were manufactured by Goodyear in the United States. No retread tires had been used since 1997.

The operation of airplanes at altitudes above 40,000 feet usually involves a number of novel or unusual design features that are not addressed by the airworthiness requirements in the current regulations. The greatly increased operational altitudes envisioned for supersonic transport (SST) airplane designs prompted extensive investigation, beginning in the early 1960s, of the additional standards that would be necessary to allow safe operation at even higher altitudes. Although development of the U.S. SST was discontinued, the Anglo-French Concorde SST was eventually certificated for operation to a maximum altitude of 60,000 feet.



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