I can talk about commercial jets, from the Boeing 707 through all other Airbus and Boeing models till the Boeing 787.
Until the Boeing 787, all commercial jet engines had pneumatic (air driven) starters, also known as air starters. Hot air from an outside source or from the pneumatic system on board the aircraft would be directed into each pneumatic starter, which was mounted on the engine gearbox, and coupled to the engine N2 rotor. Inside was a turbine, which would start spinning at high speed upon receipt of the hot air input. This speed would be reduced by a set of gears and finally the output shaft would turn the engine rotor through the gearbox. After the engine had “started” and become self-sustaining, the starter clutch would be disengaged from the gearbox and its pneumatic supply cut off.
Shown: a jet engine air starter. The blue arrows are the path of the hot air fed into the starter during engine start.
- How do aircraft generate thrust?
- Is there any man-made spacecraft/debris at the Earth-Moon or Earth-Sun lagrange points?
- Are commercial passenger aircraft required to fly with call sign, source, and destination data in their transponder, as visible in various websites? Can a 100 passenger aircraft fly without transponder data? Can it be turned off during takeoff?
- Can I fly to the US with my aircraft without a visa?
- Theoretically, what would be the best aircraft?
On the GenX engine on the Boeing 787, each engine is started by a electric motor coupled to the engine gearbox. This motor also serves as a generator after the engine has started, thus serving a dual purpose.