Flying’s new gear A quieter, more economical jet engine (geared turbofan) is about to arrive

http://www.economist.com/news/science-and-technology/21684775-quieter-more-economical-jet-engine-fitted-gearbox-about?fsrc=scn/tw/te/pe/ed/flyingsnewgear

Geared turbofans, as their name suggests, include a gearbox as part of the mechanism. Those on the A320neo are the brainchildren of engineers at Pratt & Whitney, a division of United Technologies, an American conglomerate. Designing and building geared turbofans, which Pratt & Whitney brands “PurePower”, is a gamble. The firm has spent two decades and more than $10 billion developing them. Connecting an engine’s inlet fan to the compressor and turbine in its core through a gearbox should give better fuel economy and make the thing quieter—both desirable outcomes. But the bigger the engine the bigger the forces on the gearbox and the more likely it is that something will go wrong. So, though gearboxes are found in turboprops (jet engines that turn a propeller) and in a few executive jets, no one had until now managed to scale one up to cope with the 30,000 horsepower delivered by the core of an airliner’s engine.