Pneumatic starter motor??
 

I'm hoping that someone might be able to answer a couple of questions?

1) Where is the hot bleed air that is used to drive the pneumatic starter on a turbofan engine expelled?

2) How is the starter connected to the N2 shaft so that it doesn't block the passage of the bypass air from the N1 fan? (considering that the starter is housed on the outside of the engine?

1) Usually through a port on the side of the nacelle.

2) Through a high speed gearbox, and in the case of a large Roller, N3 shaft is thus turned by the starter.

This is from a CF6-50 engine. Other engines have different location of the accessory gearbox.

http://i20.photobucket.com/albums/b2...ce_Oveur/1.jpg

In the picture above you can see the location of the starter in relation to the fan.

http://i20.photobucket.com/albums/b2...ce_Oveur/3.jpg

Above is a picture of the starter. Bleed air enters at the front and is expelled out through the mesh into the nacelle. It is eventually discharged overboard through vents in the cowling.

http://i20.photobucket.com/albums/b2...ur/gearbox.jpg

Above is a picture of how the starter is connected to the HP spool via the accessory gearbox, transfer gearbox and tower-shaft.

Thanks very much, that's very helpful!

I'm assuming that in the last diagram, the radial drive shaft would be housed inside a fairing of some sort?

It does indeed... via the lower aerodynamic support strut (one of several).