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AIRCRAFT GAS-TURBINE ENGINES There are THREE types of aircraft engine:
GAS-TURBINE TURBO-FAN ENGINES (Used by most modern aircraft)
The fan rotates & sucks in air. About 80% of the air passes through the by-pass duct, cools the engine, & makes most of the thrust. The other 20% of the air is compressed, mixed with fuel, & ignited. The explosion passes through the turbine, making the turbine rotate. A shaft connects the turbine to the fans & compressors, so when the turbine rotates, the fans & compressors also rotate. The gases then pass through smaller & smaller areas, increasing the pressure. Finally, the gases pass out of the exhaust nozzle at very high speed, giving the engine thrust - Newton III (Action/Reaction)
(Old Technology - Concord) Gas-turbine turbo-jet engines are similar to gas-turbine turbo-fan engines, but they have no fans and no by-pass duct. The advantages are: 1. The engine is good at high speed (more air goes directly into the compressors).
1. The engine is hot and very loud (no by-pass duct). 2. The engine's fuel consumption is very high. With turbo-fan engines, more than 80% of the thrust comes from the fans. 3. The engine is not so good at low speed (less air goes directly into the compressors).
(Newer Technology - ATR 72) Gas-turbine turbo-prop engines are similar to gas-turbine turbo-fan engines, but they have no by-pass duct. The shaft from the turbine is connected to the compressors and directly to a propeller, using a series of gears. The advantages are: 1. Thrust is generated by the propeller and by the exhaust nozzle, so the engine's fuel consumption is lower than turbo-jet engines. As a result, gas-turbine turbo-prop engines have a better range than even gas-turbine turbo-fan engines. 1. The engine is quite hot and very loud (no by-pass duct). 2. Thrust from the exhaust nozzle is limited to only 10%. Too much thrust will break the propeller blades. This makes gas-turbine turbo-prop engines quite slow compared to gas-turbine turbo-fan and turbo-jet engines. However, there is an advantage. The 90% of thrust that is lost at the exhaust nozzle is forced downwards and out. This helps to increase lift. As a result, aircraft need less runway distance to take off. |
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