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Hello all.

This is my first post here and while I have the IXEG 737-300 installed, I am still doing ground school for a few hours, coming from the NG. I am studying in particular the electrical systems and AC and DC BUSSES and I am writing a studying guide.

I have the probems that my data sources for the NG (BRADY, 2014, COJIN, 2015) tell me that :

* in the NG ENG 1&2 START VALVEs are powered from 28V DC - BAT BUS (sect 1&2). - that's OK for engine #2, I tested it in the IXEG model.

* ENGINE 1  & 2 RIGHT IGNITORS are powered from 115V AC STANDBY BUS - that's OK, I tested it in the IXEG model.

 

While 1/ in my 737 NG simulation this assumptions looks correctly simulated and can be verified with experimental procedures (starting both engine only from BAT BUS and AC STANDBY  is possible)

2/ I can in the classic IXEG start the engine #2 from BAT BUS and STANDBY AC BUS (with right igniter selected) and external bleed air source only.

3/ but I can't do the same for the left engine #1 ! BAT BUS and STBY AC BUS as sole AC and DC sources can't start engine #1.

So I started playing with logic with electrical failures, standby power switch and transfer bus switch. I found out that in the IXEG model, while ENG 2 START VALVE is powered as usual from BAT BUS, ENG1 START VALVE would however be powered by AC XFER BUS 1. Because in the IXEG 737 restoring a experimentaly failed XFER BUS 1 with rstarter already in GRD position suddenly awakes the bleed air injection in engine #1. I am very astonished. Is it a bug or a very real difference with the 737 NG ? I was totally unable to find the complete wiring drawing including services for the classic.

Best regards

ELEC737.jpg

REFERENCES

BRADY Chris, The Boeing 737 technical guide version 67. Tech Pilot Services Ltd : Frodsham, 2014

COJIN Ferdi, DE JONG Bert, B737Theory Manual : Boeing 737NG Systems. [En ligne] 2015.

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Hi,

I am glad someone is finally digging a bit deeper into the systems that we spent so much time on!!

You are right, both start valves should be powered by the Battery Bus. However the pneumatic isolation valve is powered by 115VAC XFER bus 1 - and the external air is connected on the right side of it. So what you MAY be seeing is the isolation valve opening with the application of power to it - allowing air to rush across to engine number 1.

Then again, we may have a bug - to test my theory try again with the APU supplying bleed air, it is supplying the left side of the pneumatic system.

Cheers, Jan

 

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Hi, Jan I am glad to have an answer from you. I follow your videos and development of the IXEG simulation from a long period of time. I acquired it very recently to expand my 737 collection and check systems accuracy. Yet I have not flown with it as I am still dealing with ground school.

The explanation of the 115 VAC XFER BUS 1 for the isolation valve is nice catch ! Actually I forgot APU BLEED and Ground PNEU SOURCE are non-equivalent. Because in my NG simulation, engine 1 seems to be starting from external air without problem although I could be incorrect and should cross-check. I have now checked my air diagrams and realised that that Ground Air source is into right side (BRADY, 2015, page 45). Also I am glad the APU BLEED VALVE is on battery bus, therefore I can start from BAT, STANDBY BUS and APU Air.

Below is what a more in depth look gives me (in particular I am paying a more closer look at the orange "start valve open" panel light)

BAT ... ON

SBY POWER ... BAT

EMER EXIT LIGHTS ... ARMED

BLEED AIR ISOLATION VALVE ... OPEN

XFER BUS 1 not powered -> ISOLATION VALVE is closed.

APU ... START
APU BLEED ... ON

ENGINE START 2 ... GRD

(> engine 2 start valve opens but N2 not increasing due to absence of pneumatic air source. Unable to start engine 2 from APU ! ) EXPECTED

ENGINE START 1 ... GRD

(> engine 1 start valve opens, N2 increasing...) EXPECTED

 

Call for GROUND AIR SUPPLY

ENGINE START 2 ... GRD

(> engine 2 start valve opens, N2 increasing...) EXPECTED

APU BLEED ... OFF

(> engine 1  N2 decreasing...) EXPECTED

Conclusion

yes, that is now verified in the IXEG CL :

1/ air sides are isolated when only on DC BAT and AC STANDBY.

2/ both start valves are powered by the Battery Bus.

IGN ... LEFT

ENGINE 2 FUEL ... IDLE from cutoff

(> engine 2 N1 not increasing  Unable to start engine 2 from left ignitor) EXPECTED

IGN ... RIGHT

(> engine 2 starts) EXPECTED

 

IGN ... LEFT

ENGINE START 1 ... GRD

APU BLEED ... ON

ENGINE 1 FUEL ... IDLE from cutoff

(> engine 1 N1 not increasing  Unable to start from left ignitor) EXPECTED

IGN ... RIGHT

(> engine 1 starts) EXPECTED

Conclusion

that was verified in the IXEG CL :

engine 1 right igniter and engine 2 right igniter only are available in this power state (are powered by 115V AC STANDBY BUS).

 

I'd like to check the simulation of the pneumatic isolation valve power source.

We begin by stopping all engines.

Ensure you have GPU bleed air source only (right side)

Then, we must fail transfer bus 1 and then put the isolation valve switch (not the actual valve behind it) to OPEN.

Now, let's start engine #2 and put its drive ON AC BUS.

Check that right ignitors are selected.

 

ENGINE START 1 ... GRD

(> engine 1 start valve opens but N2 NOT increasing because no AIR avail....) EXPECTED

REPAIR Transfer Bus 1

(> N2 increasing...) EXPECTED

Conclusion

that was verified in the IXEG CL :

the pneumatic isolation valve is powered by 115VAC XFER bus 1

Edited by XPJavelin
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I have a further question, in flight with both AC generators connected, I cannot disconnect the battery switch without loosing everything.

The FCOM states :

Battery (BAT) Switch
OFF –> removes power from battery bus and switched hot battery bus when operating with normal power sources available.

I should only loose fonctions from the BATTERY BUS and the SWITCHED BATTERY BUS.

Since I have AC GEN DRIVEs, I should keep CAPT and F/Os displays for instance, and all services from AC busses or DC BUS powered from TRs.

Why not in the IXEG ?

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5 minutes ago, XPJavelin said:

I have a further question, in flight with both AC generators connected, I cannot disconnect the battery switch without loosing everything.

The FCOM states :

Battery (BAT) Switch
OFF –> removes power from battery bus and switched hot battery bus when operating with normal power sources available.

I should only loose fonctions from the BATTERY BUS and the SWITCHED BATTERY BUS.

Since I have AC GEN DRIVEs, I should keep CAPT and F/Os displays for instance, and all services from AC busses or DC BUS powered from TRs.

Why not in the IXEG ?

 

it is my understanding the gen relays are battery feed, loosing the battery will lead to a complete electricity loss as it has happened on real life.

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mmerelles is correct. This may be different on the NG´s (it also is on Airbuses), but when you switch off the battery on the classic, everything goes off (except for the emergency exit lights). It is also impossible to connect the generator breakers or ground power contactor without battery power - if you run down the battery you need to bring over the external DC supply and hook it up.

Cheers, Jan

.

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Thank you very much. Indeed I can find "GENERATOR BUS PWR CONTROL UNIT3 in 28V DC SW HOT BAT BUS.

Thank you for your valuable inputs. I will progress therefore in my understanding of the system. What refrains me is that I am doing the comparison in parrallel with another simulation where things looks a little different (tobe confirmed later) ;-), so I have to separate eventual simulation bias from real architecture, so... ...need to read a lot, test a lot, bark a lot...

 

Edited by XPJavelin
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I am not convincced by the answer " but when you switch off the battery on the classic, everything goes off ".

Let me revise here my previous statement that everyhing goes off, because a more thorough trial tells me that indeed, I keep some systems (STALL WARNING SYSTEM 1 fori nstance, and CAPT displays) even if those systems are clearly different than in my NG simulation.

Then why would the CL FCOM says that DC and AC STANDBY BUS are not deenergised when a normal power source is still available?

BAT SWITCH OFF : removes power from battery bus and switched hot battery bus when operating with normal power source available /  removes power from battery bus, switched hot battery bus, DC STANDBY BUS, static invertor and AC STANDBY BUS when operating with normal power source available /

BAT SWITCH ON : (guarded position) –> provides power to switched hot battery bus –> energizes relays to provide automatic switching of standby electrical system to battery power with loss of normal power [in flight for B737-300]

In the mean time STDBY POWER SWITCH has to be put on BAT (on ground iand n the CL only because relays are not energized to provide automatic switching when BAT SWITCH is OFF).

Also when I restore to ON the battery after having switch to OFF, I have to reconnect the GPU generator in the CL, and not in the NGX.

I can conceptually agree that if the gen relays are battery feed (can't find source), loosing the battery will lead to a complete electricity loss as it has happened on real life [IN FLIGHT]. Because APU dies. But here I am on ground with GPU, so definitively something seems wrong here, in contrast to my other 737 simulation. I should not lost AC connection on ground from GPU in the IXEG simulation without touching the BUS PWR CONTROL UNIT switches. But I do.

I agree and I see that ground power contactor without battery power cannot have effect (verified both in the NG and inthe classic). That does not mean that the GPU connection behind and already established should die. (Which is perfectly modeled in my NG simulaiton).
So after much hours working on it, I am not conviced by how the GPU source and  BUS PWR CONTROL UNIT are modeled in the IXEG or I need more explanations and sources (obviously  would love to have an enginner manual, a pilot operating book seems not enough). Because it is my NG simulation that may be wrong. ;-)

Edited by XPJavelin
Final edit with conclusions
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