Question about Duct pressure and PACKS

[Guest Bill Kingsford]

Gentleman,With SU1 when I started up the packs with APU running and ducts pressurized with APU bleed air, the duct pressure would surge down under the increased pnuematic load as you'd expect. With SU2 there doesn't seem to be any pnuematic load with pack operation. No big deal, just wondering about it. Thanks.-Bill Kingsford"The Kingsford Edge"

[Guest tcable]

Don't qote me on this, but the NG's APU is an on demand system as opposed to an always on system. The APU throttles up to maintain the duct pressure when a load is placed against it. (ie packs or start) Whether or not the APU can maintian the duct pressure when starting I do not know, but I suspect that this behavior is correct, and the old system was not.Tim

[Guest Bill Kingsford]

See, I learn something new every day. What do you know about that, interesting, thank you.

[Guest tmetzinger]

>Don't qote me on this, but the NG's APU is an on demand>system as opposed to an always on system. The APU throttles up>to maintain the duct pressure when a load is placed against>it. (ie packs or start) Whether or not the APU can maintian>the duct pressure when starting I do not know, but I suspect>that this behavior is correct, and the old system was not.>>TimBased on my studies so far, you are correct. Unless you have a significant electrical load on the APU, it should be able to provide normal duct pressure during a start.