Bleed air for start.

[TotalBeginner]

What happens to the bleed air that is used to turn the pneumatic starter on a typical turbofan? Is it returned to the pneumatic manifold, or is it exhausted overboard?

If it's the latter, where is it vented from; The cowling?

[kenparry]

Overboard, within the cowling on the engines I've seen.

[barit1]

The starter derives its energy (to turn the engine) from the pressure drop of pneumatic system air flowing through its rotor. Thus the low-pressure exit air could never find its way back into the higher-pressure pneumatic manifold.

[glum]

http://aeronamic.com/wp-content/uploads/2010/06/ATS2.png

High pressure air enters through the end (covered by a red cap) and spins the turbine inside - imparting its energy. It exits through the grills surrounding the unit at much lower pressure, though this will of course increase as the starter spins faster and all the engine inertia is overcome.

The airflow then finds its way out of the cowling through any holes it can find!

[Natstrackalpha]

Nice.
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