Originally Posted by fredgrav
pre-pressurization (Packs OFF) is accomplished by using ram air and then keeping RAM air inlet and Outlet flap closed all troughtout the takeoff phase.
No it is not. With packs off there is no pre-pressurisation. The pressurisation system might still enter the pre-pressurisation mode and drive the outflow valve towards closed but there will be no pressurisation. As the aircraft climbs the cabin altitude will then increase at a rate determined by how leaky the particular aircraft is.
Originally Posted by fredgrav
RAM air enters the aircraft before takeoff
No it does not. Unless you have opened the emergency ram air inlet in which case there will be no pressurisation.
Originally Posted by fredgrav
Though the valves (and packs) have remained open while the pre-daperture checks and taxi-out phase, so that a pressure slightly higher than outside has built up inside the cabin: when the valves automatically close for takeoff (TO phase), this slighlty higher pressure remains trapped into the a/c, allowing the so called "cabin pre-pressurization"
There will not be a slightly higher pressure inside the cabin. With packs off the ventilation system will cause it to be slightly lower than ambient.
Originally Posted by fredgrav
Be sure that if I DID NOT know what I'm talking about, I wouldn't have written in this thread
But you did.