Dive inside the propulsion system that gets low-speed aircraft off the ground.
Anormal jet engine (often called a turbojet) uses fan blades in order to compress air pulled in at the front, and then adds fuel and ignites it. Some of the exhaust energy is used to keep the compressor fan turning, but most of it is expelled at the rear to produce thrust.
A turboprop engine turns this on its head; almost all of the energy is harnessed to turn the propeller shaft at the front, and only about ten per cent of the thrust comes from the exhaust gas. The propellers are much larger than the diameter of the jet engine, so most of the air they push flows past, rather than through it.
This is more efficient at lower speeds, because the engine only adds fuel to the small proportion of the airflow that generates thrust.
Turboprops are slower than jet engines but cheaper to run. They are mostly used in short-hop commuter planes. A helicopter engine is also a kind of turboprop (called a turboshaft) where the rotor blades are driven through a more complicated transmission system.
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