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APU and AC Packs on the ground


Garyo

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I think the logic of the APU on the ground is to power the AC packs regardless of engine operation.  The CRJ Sim shows the respective engine powering is AC pack after start.  According to Mesa Airlines Training, the APU has priority until WOW, flaps out of 20° and climb power set.  Is this correct?

 

GaryO

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You are correct APU will supply bleed air on the ground with the engines running in auto mode unless the cowls and or wing anti ice is turned on, then the apu lcv and isol close and the eng bleeds open.  Once the apu is shut down on the ground it will transfer to the engines, if you keep the Apu on for takeoff it will transfer in auto mode to the engines when the takeoff bit is set as you described below.  Not sure if aerosoft intends to simulate this though but you are correct

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I have some difficulties here. Can you give me an "how it currently is vs. how it should be"? That would be helpful. Unless it means a total rewrite of the whole aircraft code, it's likely that I'll fix it.

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How it is now

1. When you start an engine that engine bleed valve opens and supplies the bleed air manifold with pressure at the same time the APU is supplying bleed air. The real system has an interlock protection logic which will never allow the engines and the apu to supply the manifold at the same time

 

what should happen (auto mode)

1. after an engine start the engine bleed valves should remain closed when the aircraft is at weight on wheels (wow) and the apu supplies the manifold with bleed air. Once the APU is shut down the APU LCV closes the isol valve closes then both engine bleed valves open. If the APU is kept on for take off then once the aircraft is weight off wheels, thrust out of toga and flaps 20 or less then the APU lcv closes isol closes and eng bleed valves open. 

 

2. On the ground if APU is on and wing and or cowl anti ice is turned on then the APU lcv closes isol closes and eng bleed valves open

 

3 in the air if the APU is turned on in flight the eng bleeds close and the APU lcv and isol open when the approach bit is set (when the gear is down and or flaps greater then 20. )

 

4 once on the ground and you start the APU on the ground the eng bleeds close and the APU lcv and isol valve open

 

This is all in auto mode. To summerize

the APU and the engines can never supply the manifold withbleed air at the same time nor can the APU supply bleed air for anti ice.  This is called interlock protection. On the ground APU always has priority until it is shut down. In the air the function as per described above

 

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If you taxi single engine and you shut the APU down then the running engine bleed valve does open along with the isol valve to supply the manifold with bleed air.  Also the 700/900 regulates bleed air to 45psi and the crj200 is to 30psi. Currently the sim is at 30psi

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