CG line changes to boxes

[Will]

I am using the NG FMC, and have dual wight and balance system installed. I noted during preflight that the calculated CG (on TAKEOFF REF, line 3L) was displayed in small font, something like 18.4. This was expected.

Then I did some things (I can't remember what) and when I came back to TAKEOFF REF, the CG was showing boxes. Of course, I could manually enter "18.4" but I got confused...

(1) What action would convert a small font CG to boxes? And (2) if the dual W&B system is installed, what can you do to change the boxes back to the small font, so you can just accept the computed CG without having to enter it manually?

Thanks...

[Hardy Heinlin]

Was it a freighter?

Maybe your ground service bus was off and your cargo handling bus was powered, that is, the cargo handling bus was powering your W&B system. The cargo handling bus also powers the nose cargo door. Do you remember the special requirements with the cargo handling bus to get the nose cargo door to move? It needs EXT GEN 2 or APU GEN 2 in AVAIL status, not in ON status. If it's ON, the cargo handling bus is off. Maybe you were playing with the EXT or APU switches?

[Jeroen Hoppenbrouwers]

It needs EXT GEN 2 or APU GEN 2 in AVAIL status, not in ON status. If it's ON, the cargo handling bus is off.

What again was the technical reason for this?

/-/

[Will]

Okay, I think I know what may have happened.

Load Basic 001 - On ground and IRS aligned.situ
On the CDU, select the TAKEOFF page. On 4R, you'll see 20%> in small font.

Now go to the Instructor Pages and select the NG FMC. (Or select a different model, perhaps a non-freighter, that has the NG FMC installed.)

The CG is now on 3L, but it shows boxes instead of 20%.

To get the small number back, you have to go to Instructor > Model > Airframe and cycle the Weight & Balance system from Dual to one of the other choices and then back to Dual. Now 3L shows <18.5 in small font.

(Note also that the "%" sign is absent on the NG when the CG is in small font. Is this intentional?)

Another way to see this is:

Select Basic 001
Change the model to a non-freighter
Connect APU GEN 2
Select TAKEOFF Page (CG is 20% in small font)
Change the FMC to the NG (CG is now boxes)
Cycle Weight & Balance on the Instructor Page from Dual, to Single, to Dual
Now CG is 18.5 in small font

[Hardy Heinlin]

Well, that's just a little CDU screen refresh problem because that old "Basic 001" situ file doesn't contain NG FMC data (which provides a higher resolution on the CG display). It needs a CG change event to generate the NG data. You can also refresh it by moving the Instructor's CG slider a bit. That old "Basic 001" situ also contains a different rounding for the legacy FMC's CG display. It's actually rounded to 19 rather than 20 (it shows 19 after a refresh). And the NG resolves that 19 to 18.5.


Cheers,

|-|ardy

[John H Watson]

It needs EXT GEN 2 or APU GEN 2 in AVAIL status, not in ON status. If it's ON, the cargo handling bus is off.

What again was the technical reason for this?

/-/

I'd say that the cargo drive (loading) system is fairly energy hungry and is used in bursts which may upset the power going to more critical airplane systems.

[Will]

Thanks, Hardy. Understood.

[Jeroen Hoppenbrouwers]

Just for reference: cargo loading on a (KLM) 744.

https://www.youtube.com/watch?v=HfOWKzaEdJM

And a more technical video. I suppose all these loading systems are roughly the same but their operation is different?

https://www.youtube.com/watch?v=OM4eld9hCAI
https://www.youtube.com/watch?v=Sij5q_O4MV8

etc. (lots of it)

[John H Watson]

I suppose all these loading systems are roughly the same but their operation is different?

In what way different?

I couldn't find an examples of nose door loading of long, wide and heavy items. The drive wheels have optic sensors so that only the motors required are activated (for energy saving), but long/wide/heavy loads such as military vehicles probably test these systems to the maximum. Also, you can have loading at both ends simultaneously. I don't have any specs on the rubber wheeled drive motors other than they are 3 phase 200vac with 1100Nm of "tractive force"

[Jeroen Hoppenbrouwers]

I may be biased by my environment which is mostly STC-based... I'll ask it differently: is there just one cargo loading system available on the B744 that therefore is as much the same as the general flight deck is the same, or can customers choose a cargo loading system at manufacturing time for the dedicated freighters? And if it is an ex-pax plane that got converted, does Boeing usually do this conversion ($$$) or are there several competing companies that each have their own STC and likely install a different loading system?

3-phase 200V AC?  So the aircraft itself cannot deliver it at all?  Which external systems pump out 200V?

Hoppie

[John H Watson]

I rechecked and the actual wording is "115/200-volt", whatever that means. There are no internal or external transformers shown in the wiring schematics. I thought it might be an "RMS" value, but that is only 162 volts for 3 phase 115vac power.

There are also drive wheel lift actuators which are "220-volt". No idea what's going on here.

[Avi]

And if it is an ex-pax plane that got converted, does Boeing usually do this conversion ($$$) or are there several competing companies that each have their own STC and likely install a different loading system?

Well, the IAI does conversions. I don't know which loading system they use.

Cheers,

[Hardy Heinlin]

The CG refresh problem is now solved in PSX 10.150: https://aerowinx.com/board/index.php?topic=4191.0


|-|ardy

[Will]

Hardy, what is the "B" on the TAKEOFF REF page?

PSX Version 10.150
Load Basic 001
Look at TAKEOFF REF 1/2
Change to NG FMC

Line 3L reads: <18.5%   B

I can't recall seeing the "B" before.

[Hardy Heinlin]

Oh, I forgot to turn it off. Please redownload PSX 10.150.