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Aviation History
1976
1976 - 0095.PDF
CONCORDE NOW ARRIVING 19 70 tonnes of thrust WHILE THE AERODYNAMICISTS were thrashing out the opti mum shape for Concorde, trying to strike a compromise between theory and practice, so the engine designers were faced with similar compromise decisions. The engine for a supersonic aircraft needs two basic attributes. First it must offer high specific thrust (i.e. engine thrust divided by engine weight) to provide the required thrust for take-off and transonic acceleration. Concorde, which has no wing flaps to aug ment lift, has a high take-off speed and therefore has to accelerate quickly. Secondly, the engine has to have low fuel consumption during the cruise to give optimum range. Three types of engine were avail able : a straight turbojet, a two- spool jet, or a high-bypass-ratio turbofan. The first type of engine would have demanded a turbine temperature too high for con temporary metals technology to produce the thrust needed. A high- bypass turbofan has a very high frontal area, increasing drag un- acceptably. The middle of these three choices was therefore taken, and the result—the Rolls-Royce/ Snecma Olympus 593—is a two- spool powerplant with good charac teristics in both the critical areas. Of the engines available or under development in the early 1960s the Olympus designed for the TSR.2 most nearly fitted the bill. Extensive modifications were necessary before it even met the basic Concorde requirements, and subsequently the engine has been further refined. Bench-testing of the prototype 593D version began in mid-1964, almost five years before the first Concorde flight. A major contribu tion to the success of the pro gramme was made by test flying an Olympus mounted in a repre sentative Concorde nacelle under the fuselage of a Vulcan. This enabled subsonic in-flight prob- Business end of an Olympus pair with stainless-steel honeycomb nozzle lids moving to their full supersonic open ing. For subsonic speeds the ingenious lids reduce nozzle area, and for reverse thrust on landing they shut completely lems to be identified and solved long before Concorde flew, reduc ing the cost of development and increasing the reliability and per formance of the engine eventually installed in the aircraft. Now, more than 11 years after the firs*: bench trial, the Olympus has accumulated nearly 50,000hr of running, both in the test-cell and airborne. It has, with the aid of ground facilities such as the test-cells at the National Gas Tur bine Establishment at Pyestock, been subjected to an environment far more hostile than it will meet in service. A movable ramp inside the top of the intake mouth controls the shock-wave pattern at the front of the intake and the main 20ft dif- fuser section of the intake gas gets the flow down to a speed acceptable to the engine. The com pressor inlet pressure is higher than on subsonic engines, and in let temperature is also higher— 120°C compared with -20°C for most subsonic engines. Other spill valves help to keep the diffuser section of intake, also doubles as '• Li WflWf i L_ _!._ i_- ^1 *WmVL. "AJL!L^JKSilRsKi?3HSl^jail».
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