Originally Posted by
M2dude
...on this APU issue...we are talking here about a duct with sufficient size that can provide enough mass flow to turn over an Olympus engine to at least between 10 and 20% N2. You are looking at an least 10" diameter duct
Not really..
We are looking at two 4 inch diameter ducts, the same that are still used to this day on aircraft such as the B777.
One for the air start turbine, which was driven at about 45 psi nominal by the same kind of ASUs (Air Start Units) as are still in use today.
The other for the aircon... not to be confused with the huge near-ambient pressure hoses that were connected directly to the cabin, rather than to the aircon packs.