W dodatku do FS9, 747-4000 zrobionym przez PMDG zauważyłem ciekawą rzecz: APU włączone, APU bleed tak samo;
3 packi włączone: duct pressure wynosi 28 PSI
2 packi włączone: 27 PSI
1 pack włączony: 19 PSI
wszystkie packi wyłączone: 22 PSI
Po uruchomieniu silników, włączanie packów powoduje spadek ciśnienia, co wydaje mi się normalne. Dziwią mnie natomiast zmiany ciśnienia przed włączeniem silników, zdawało mi się, że zawsze więcej działających packów=mniejsze ciśnienie w instalacji. Czy ktoś mnie może oświecić, czy tak jest w prawdziwym 744?Dane z prawdziwego 744 napisał/a:

Healthy, new aircraft... CF6-powered
TAT 23degC

0 packs = 21-22 psi
1 pack = 19 psi
2 packs = 26/27 psi
3 packs = 28 psi

Wniosek - PMDG symuluje to poprawnie. Dlaczego jednak tak jest? Jedyny opis, jaki wyszukałem, brzmi tak:
The APU is designed to output more air as the load (demand) increases, but the system doesn't always operate as designed (in real life).

Main engine start signals the APU to put out maximum bleed pressure.
But, if the APU is getting a bit old or the outside air temperature is hot, you may not get the pressure you expect.

If the aircraft is new and everything is running perfectly, you would expect the pressure to rise in steps as each pack is turned on, but even on new aircraft, I've seen it step down(at some point). However, I can't recall at what point this happens.

When you start an engine, the system logic looks at Start Switch position, Autostart switch position.... and the fuel cutoff lever (if the autostart switch is ON). If the Autostart Switch is on and you pull the Start Switch, nothing should happen to the bleed system (I've confirmed this this in real life)

27psi is low-ish pressure, but you shouldn't have too much trouble starting an engine with this pressure. Just make sure the engine continues to accelerate.

Running all packs and starting 1 or 2 engines at the same time will put a huge demand on the APU and it may not be able to handle it. Rapid increases in pressure can also be a problem. If you go from no packs mode to main engine start mode, you can get a huge change in pressure. Sometimes it's best to run a single pack whilst starting and engine. It all depends on what modifications have been carried out on the aircraft.