You flip a switch and the engine roars to life instantly, right? Wrong. Starting a jet engine is one of aviation's cleverest tricks. A jet turbine is basically frozen, heavy, and totally stuck at rest. You cannot just turn a key and spin those massive turbine blades. That is where the APU comes in, a tiny backup engine. The APU starts independently and spins itself up to full speed. Once running, the APU pumps out hot compressed air at high pressure. That pressurized hot air feeds directly into the main engine turbine section. The force of that air blast spins the turbine blades around. As the turbine spins, it sucks in and compresses more air itself. That compressed air gets hot enough to ignite fuel in the combustor. Hot exhaust from combustion drives the turbine even faster, self sustaining now. Once the engine runs itself, the APU air supply slowly cuts off completely. Follow us to unlock more secrets hidden inside the machines we fly.
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