"Both the engine (the big one) you want to start and the APU (small guy) have compressors and bleed air. Since the APU is running it has air to spare. As said before it uses this air to spin a much smaller device (the starter) which through gears turns the big engine.
The big engine has no bleed air available during start and no direct connection exist in the air between either the APU (small), plus the starter (tiny) and the big engine.
A neat little schematic might focus your mind on this rather than more words"
Thanks,
But so this is the route of APU BLEED:
APU has it's compressor, combuster. So basically, at the end it will turn a gear which will turn the turbine (so the big fan and the big compressor and the axe, am I right?
"BOAC
You appear to have something of a fixation on putting down posters who are not professional aviators.
Your profile states the following:
Licence Type (eg CPL. Pilots only)
Atpl
Biography
Now retired
Location
UK
Occupation
Sit Vac
If these details are accurate then you are no longer a professional aviator.
You are an EX professional aviator.
As such it might be more appropriate if you were to restrict your posts to those threads that are for EX professional aviators.
As JT has intimated, chasing enthusiastic youngsters (some of whom will become tomorrows professional aviators) into the far corners of pprune, will reduce the chances of them getting the information that they are looking for. In some cases this will drive them away from aviation."
Thanks keith williams, I appreciate, I really didn't want to write that I was a pilot!