The jet engine

A jet engine is a gas turbine turned into a thrust machine. Air is pulled in at the front and squeezed by a compressor; in the combustion chamber fuel sprays into that compressed air and burns continuously; the hot, expanding gas rushes rearward through a turbine — a bladed wheel it spins on its way out — and that turbine drives the compressor at the front, so the engine feeds itself. Whatever energy is left after the turbine has taken its share leaves through a narrowing nozzle at very high speed, and by Newton's third law the reaction to that backward jet pushes the engine, and the aircraft, forward. Unlike a piston engine's four separate strokes, everything happens at once, in different places along one flow of gas.

The propeller driven by a piston engine hits a wall. As an aircraft nears about 400 to 500 miles an hour the propeller tips approach the speed of sound and lose their grip on the air, and the piston engine needed to push through that grows impossibly heavy for the power it must make at altitude. The jet has no propeller to run out of air and gives enormous thrust from a light engine, and it works *better* the faster and higher it flies. It lifted the ceiling that had held aviation to a few hundred miles an hour and opened sustained high-subsonic and, later, supersonic flight.

Within twenty years the jet remade travel. The jet airliner — the de Havilland Comet of 1952, then the Boeing 707 — cut intercontinental journeys from days to hours and made crossing an ocean an ordinary act. The same core, in its variant forms, drives nearly everything that flies fast today: the turbofan under an airliner's wing, the turboprop and the turboshaft that spins a helicopter's rotor. And run to make shaft power on the ground rather than thrust, the gas turbine now generates a large and growing share of the world's electricity, alongside the steam turbine it descends from.