The secret to building an efficient jet engine is something called bypass ratio. That massive fan at the front of the jet engine only funnels a small amount of the air it gulps into the turbines, where it mixes with fuel and ignites. The vast majority of the air sucked in by those huge blades bypasses the main engine, goes round the outside and rejoins the heated, compressed and ignited air at the back of the engine. That’s why, if you look at an engine, for a large part, you can see straight through from front to back. This achieves two things. It gives the aircraft more thrust for your money (but only if you are flying below the speed of sound) and it acts as a blanket around the engine to keep the noise down. If you go back in time and look at the airliners of the 1960s and 70s, you’ll see the engines were much narrower. They had very low bypass ratios and as a result, were noisy and thirsty beasts. Over the years the size of those first stage fans has grown – as has the percentage of bypass gas – to the point today where the A350 Trent XWB engine is a true giant, and the bigger the engine, the more efficient and quiet it is.
But that’s not the only incredible stat about this engine. At take-off, each engine sucks up to 1.3 tonnes of air every second, about the equivalent of a squash court full of air. The turbine blades inside the engine rotate at 12,500 rpm, with their tips reaching 1,200mph, with a force equivalent of nine London buses hanging off each blade. Whoosh indeed.