Thanks,
See this photo:
http://upload.wikimedia.org/wikipedi...engine.svg.png
Where is the motor? I didn't really get what you meant by motor...
What is the engine gear box?
EDIT:
http://upload.wikimedia.org/wikipedi...ion-en.svg.png
Do you mean that the apu bleed is normal air which enters in the gearbox, and then goes to compressor and then the combustion chamber to finally turn the turbine, which will turn the prop? But why can't it take air from "outside"?
Thanks to help (very important for me)