Take a short-haul flight anywhere in the world and the chances are you’ll fly on a twin-engined jet made by either Airbus or Boeing. Thousands of Airbus A320-family and Boeing 737 airliners are in service, providing reliable, safe and efficient inter-city travel.
But is the familiar layout – two turbofan engines mounted below the wings – the most efficient design for an airliner? Or is there a better way to build a short-range 100-to-200-seater? Many in the aerospace industry believe there is – and that the future involves not jets but a form of propellers.
We’re not talking about the clanking piston-engined propliners of the past, with evocative names like Lockheed Constellation and Boeing Stratocruiser. And we’re not even talking about modern commuter turboprops such as the Bombardier Q400 or ATR-72. But pressure on airlines to cut operating costs is sparking a revival of interest in a concept that first emerged in the 1980s – the unducted fan (UDF), or “open rotor” engine.
These engines are a close relative of the turbofans used on aircraft such as the A320 – but instead of the fan being shrouded inside the engine casing, it sits outside the main turbine. This allows a larger diameter of fan to be used, increasing the engine’s propulsive efficiency – more fan, less jet.
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