Electrical System - A few observations
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Hi everyone,
first of all: I’m really enjoying this aircraft and have spent a lot of time in the cockpit over the past few days. The 146 is just a special airplane and it’s a real pleasure to fly. Big kudos to the developers for the work that went into this!I’ve been taking a closer look at the electrical system and doing some testing on the ground. I came across a few things I’d like to share, hopefully it’s useful for further refinement.
- BATT OFF LINE Annunciator on Manual Deselection
When the batteries are manually switched OFF during normal operation (EXT AC on the busbars, TRs running), no BATT 1/2 OFF LINE annunciator appears. According to the manual, these should illuminate since the battery contactors are open and the batteries are no longer connected to EMERG DC. The warning lights busbar is powered via DC BUS 2 and EMERG DC, so the annunciators should have power.
- AC Priority: APU GEN vs. EXT AC
I know the normal procedure calls for starting the APU and selecting APU GEN on before using EXT AC, and that the manual says to select APU GEN OFF/RESET if starting using EXT AC. So in normal operations you’d typically use one or the other. Still, I was curious and tested what happens when both are available at the same time.
With EXT AC already on the busbars, I switched the APU GEN on. The APU GEN immediately took over and displaced EXT AC. To my understanding of the 146 Operations Manual, it should be the other way around: EXT AC has priority over APU GEN. The manual also states that the APU GEN OFF LINE annunciator illuminates when „EXT AC power has taken precedence in supporting the AC busbars,” which seems to confirm that EXT AC should take priority.
I believe the priority order for Channel 1 should be:
1. GEN 1
2. EXT AC
3. APU GEN
4. GEN 4 (with bus-tie AUTO)
On top of that, when the APU GEN is then switched to OFF/RESET with the GPU still connected and available (EXT AC PWR AVAILABLE green), the system does not fall back to EXT AC. Instead, all AC and DC busbars are lost and EXT AC has to be manually reselected.
Either the priority logic differs from what the 146 Operations Manual describes, or there may be an issue with the bus-tie and transfer implementation. Happy to be corrected if I’m reading the manual wrong!Things that are correctly simulated and work as expected:
∙ ESS DC supply via START MASTER (ESS/EMERG ACO forced closed – ESS DC OFF extinguishes)
∙ TR charging logic (batteries correctly charged via EMERG DC, positive charge current shown on battery ammeter)
∙ DC voltmeter and meter selectors work correctly
∙ Basic busbar supply and AC instruments (115V, 400 Hz)
∙ STBY GEN starts automatically on loss of both AC busbars (ARM position)Once again: great work overall! This is not meant as criticism of the package as a whole. Looking forward to future updates.
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After some more testing I realised I can't really make a definitive statement about the AC priority between APU GEN and EXT AC, as there is no dedicated EXT AC ammeter on the panel to directly compare.
However, what I did notice is that the APU GEN ammeter continues to show load even after switching EXT AC on. I would have expected the APU GEN ammeter to drop to zero once EXT AC takes over the busbars, as the APU GEN contactor should open and the generator should no longer be supplying current to the busbar network.
I tested this by switching back and forth, and the APU GEN ammeter consistently shows load regardless of whether EXT AC is on or off. To my understanding, if EXT AC has priority over APU GEN (as I believe the manual suggests), the load should transfer and the APU GEN ammeter should read zero.Could you perhaps clarify how the AC priority between APU GEN and EXT AC is intended to work in the sim? I might well be wrong on this one, so happy to learn!
One more thing I noticed: the APU GEN OFF LINE annunciator only seems to illuminate when the APU is running at governed speed (APU PWR AVAILABLE lit) but the APU GEN switch is at OFF LINE or OFF/RESET.
However, it does not illuminate when:The APU GEN switch is at ON but the APU is not running.
The APU is not running at all and only battery power or EXT AC is available.By comparison, GEN 1 and GEN 4 OFF LINE illuminate correctly whenever their switches are at ON but the associated engines are not running.
To my understanding, the logic should be the same for all three generators: if the switch is commanded ON but the generator is not delivering power, the OFF LINE annunciator should illuminate. Is this intentional or am I misunderstanding something? -
One other observation:
If the STBY INV logic works the same way on the 146 as described in the Avro FCOM (which I would assume it does, given the shared electrical architecture), then the STBY INV switch should control a relay that switches the EMERG AC busbars between ESS AC and the STBY INV output.
With the switch at OFF, the STBY INV should not be powered, but the EMERG AC busbars should be disconnected from ESS AC and connected to the (unpowered) inverter outputs instead. This should result in EMERG AC being unpowered, and the EMERG AC OFF annunciator should illuminate.
In the sim, switching STBY INV to OFF does not produce an EMERG AC OFF annunciator. It appears that EMERG AC continues to be fed directly from ESS AC regardless of the STBY INV switch position. The inverter itself seems to work correctly (selecting STBY INV on the AC meter shows voltage at O/RIDE and no voltage at OFF), but the changeover relay that should switch EMERG AC between ESS AC and the inverter output does not seem to be implemented.
This would also explain why selecting O/RIDE with ESS AC powered does not cause the heading bug on the left HSI to wander, as described in the manual. I imagine that particular effect would be quite complex to implement in a sim anyway, so that is entirely understandable.
Related to this: when the STBY GEN is running (O/RIDE with engine 3 providing green hydraulic pressure), the batteries are correctly disconnected from EMERG DC and BATT 1/2 OFF LINE illuminate, which is great. However, according to the Avro FCOM, selecting STBY INV to O/RIDE while the STBY GEN is delivering power should reconnect the batteries to EMERG DC and open the ESS/EMERG ACO. In the sim, the batteries remain disconnected. This is likely related to the missing STBY INV relay implementation.
Of course, if the 146 differs from the Avro in this regard, please disregard!