CG value in yellow on the Payload screen

[WebMaximus 372]

What exactly does it mean when the CG value on the Payload screen in the FMC turns yellow, an indication your weight balance is off...?

 

Right now I'm planning a flight from ESSA-ENZV. The ETE is 0130 and to land with approx 1 hour fuel left where the B738 I'm flying burns approx 2400 kg/h I decided to take 6000 kg fuel with me.

 

I then used the 'SET RANDOM' feature in the FMC for the payload which resulted in 61 out of 174 PAX. SAS (which is the airline I mimic in FSX) calculates 13 kg/PAX for flights within EU. For this flight that gives me 61x13=793 kg which I then divide between FWD CARGO and AFT CARGO as seen in the screenshot below.

 

 

This however also makes the CG value turn yellow so apparently these calculations is somehow off according to the NGX FMC and I would like to understand what the problem is?

 

If I don't change the FWD and AFT CARGO values myself they are always much higher when calculated by the NGX FMC but using those values on the other hand always results in V-speed and VREF values much higher compared to what I've seen IRL for the very same aircraft. For instance the VREF in the NGX could be let's say 148 where IRL the VREF is let's say 133.

 

So...how can I type in realistic figures on the payload screen (for the airline I mimic) but at the same time making sure not to upset the FMC in the NGX?

[Fabo 213]

PMDG defaults to much higher values for random cargo. This can either be because they have higher value per pax, or that include actual revenue cargo.

 

As for distribution, usually more goes to the back. But you would need to see company manuals to know more precisely. 28 might or might not be a problem, depending on your load.

[777cap 12]

What exactly does it mean when the CG value on the Payload screen in the FMC turns yellow, an indication your weight balance is off...?

 

Right now I'm planning a flight from ESSA-ENZV. The ETE is 0130 and to land with approx 1 hour fuel left where the B738 I'm flying burns approx 2400 kg/h I decided to take 6000 kg fuel with me.

 

I then used the 'SET RANDOM' feature in the FMC for the payload which resulted in 61 out of 174 PAX. SAS (which is the airline I mimic in FSX) calculates 13 kg/PAX for flights within EU. For this flight that gives me 61x13=793 kg which I then divide between FWD CARGO and AFT CARGO as seen in the screenshot below.

 

 

This however also makes the CG value turn yellow so apparently these calculations is somehow off according to the NGX FMC and I would like to understand what the problem is?

 

If I don't change the FWD and AFT CARGO values myself they are always much higher when calculated by the NGX FMC but using those values on the other hand always results in V-speed and VREF values much higher compared to what I've seen IRL for the very same aircraft. For instance the VREF in the NGX could be let's say 148 where IRL the VREF is let's say 133.

 

So...how can I type in realistic figures on the payload screen (for the airline I mimic) but at the same time making sure not to upset the FMC in the NGX?

Hi Richard,

the C.G depends value are different for some airlines,if you have chosen a particular livery and it has the same equip.and settings as the real airline,you are trying to mimic,some have it fixed at 15 some at 28 etc.

also are you sure it is 13kg per PAX,seems a little stretched.

also for such low cargo weights,you might want to redistribute it,preferably more towards the back(as stated above),that of course will be compensated for by your trim settings,also help in lift.the values calculated by the default FMC,are reliable,also are you getting any warnings about your c.g values.

regards,

H.Mahesh 

[WebMaximus 372]

Ok, maybe I'll try distributing the cargo 60-40 or even more like 70-30 next time to see if that will make the NGX happy.

 

Already did one flight with a yellow CG value with no problems but does feel a bit so-so flying with yellow values in the FMC indicating something isn't perfectly in order.

 

Regarding 13 kg/PAX I got that number from someone working for SAS at ESSA so I would like to think it's a correct value.

 

Again this was for flights within EU. Outside EU I was told the same value is 15 kg/PAX.

[777cap 12]

Ok, maybe I'll try distributing the cargo 60-40 or even more like 70-30 next time to see if that will make the NGX happy.

 

Already did one flight with a yellow CG value with no problems but does feel a bit so-so flying with yellow values in the FMC indicating something isn't perfectly in order.

 

Regarding 13 kg/PAX I got that number from someone working for SAS at ESSA so I would like to think it's a correct value.

 

Again this was for flights within EU. Outside EU I was told the same value is 15 kg/PAX.

Alright!these calculations in reality would have been done for the pilot,I should think..yes it doesnt feel nice when you have something wrong during flight...even if it is in the SIM!.

Okay..i wasn't very sure about the 13kg/pax,will check it out.

warm regards

[WebMaximus 372]

Now I'm even more confused...check this out after playing around with the values some more...

 

I started by instead of having 397-397 changed to 200-600 and that still resulted in a yellow CG value. Then I tried 100-700 and still same thing. Then I went back to 400-400 and by adding these extra 6 kg (3 kg to the aft cargo and 3 kg to the forward cargo) all of a sudden the CG value was happy and the yellow color turned into the normal grey color. I was really puzzled how only adding another 6 kg could make such a difference so I decided to try 397/397 again just like in the original screenshot above and what do you know...now all of a sudden the NGX FMC is happy with those exact same values but without making the CG value turn into yellow.

 

Here is how it looks and as you can see the values are the very same in both screenshots but still the CG value is different and marked in yellow in the first screenshot but not in the second one

 

 

 

Then to further add to the confusion check what happens to the CG value when decreasing the payload with as little as 2 kg...all of a sudden the CG value has dropped from 25.2 % down to 17.2 % !?

 

[777cap 12]

Richard,

One thing you need to be careful about,while planning payloads,fuel etc.is precision.

You have taken your cargo as 397-397,which gives a combined weight of..794kg.

I think what you have done is round it off to 800kg,which the FMC seems to enjoy,maybe if you had tried rounding it of to 395-395,you would have got good results,it seems the fmc like even numbers ^_^ ,which is weird.

Try using TOPCAT(if you have it) to plan your weights,it should give you an idea of how the payload distribution works,sadly there isnt much matter to study off the internet.(My grandfather worked on the 737-200's,but there is an ocean of difference between the two,so i couldnt ask him),also i would suggest asking PMDG,they have after all coded the information,they might give you a good answer.

It is weird that the C.G should fall so low on changing the value,I shall try replicating your payloads once i get the time.

Tell us about your findings.

warm regards

[kevinh 409]

Second time around the calculated CG is different. With such small cargo loads a small change can have a big difference on the CG of the cargo. However the CG of the whole plane shouldn't be that much affected. You may have uncovered an error in PMDG's mass properties calculation. Might be worth a support request.

 

As for cargo, airlines don't just carry bags. There may be other items not related to passengers. 13 kg per passenger seems very low. Some people carry that much in hand luggage, let alone checked baggage. Are you sure that's not what the SAS figure represents? An average unchecked baggage weight per passenger? After all they have the exact figure for hold baggage from checkin.

 

I never use random load as it can be unrealistic. On all my recent travels the cabin has been full or nearly full. On the plus side flying a nearly empty airliner can be more challenging.

[scandinavian13 5,192]

 

 

Here is how it looks and as you can see the values are the very same in both screenshots but still the CG value is different and marked in yellow in the first screenshot but not in the second one

 

That looks weird.  I'm with Kevin.  Submit a ticket - perhaps that's something that could be looked into / evaluated for SP2.

[WebMaximus 372]

I was thinking maybe someone from PMDG would jump into the discussion but sure, I'll submit a support ticket.

 

I will also double-check the 13 kg/PAX value and will report back in this thread.

[dave_paige 11]

I'm just curious, was the amount of fuel loaded the same in both pics? Disregard, it looks like the GW is the same in both so probably so.

 

Dave

[WebMaximus 372]

I'm just curious, was the amount of fuel loaded the same in both pics? Disregard, it looks like the GW is the same in both so probably so.

 

Dave

 

Affirm, the only value changed was the cargo weight.

[scandinavian13 5,192]

 

 

I was thinking maybe someone from PMDG would jump into the discussion but sure, I'll submit a support ticket.

 

Never assume.

 

Remember that this is the community support forum.  While the team members are in here, one should never assume that they'll see an issue, or will happen by a thread.  Actual issues, or those people assume are actual issues should go to the portal.  Always.

[Fabo 213]

OK, that jump was a definite bug. Submit a ticket, best if it is reproducible.

 

 

As for 13kg - that is a very realistic figure for intra-european flight on a carrier such as SAS.

 

I am not sure what experience H.Mahesh has, but it does probably not enter European air market.

 

 

Air carrier such as SAS carries a lot of business travellers. Most of these will only have a light baggage piece, or none at all. Some will have a heavy one. 13kg per pax in average is a good conservative estimate, erring on the side of caution (e.g. heaviness). Carryon luggage is included in normal pax weights.

As for having exact weights - sometimes they do have, sometimes they don't. Mostly when pilots make the loadsheet, there is no exact weight, sometimes not even number of bags.

[WebMaximus 372]

Haven't been a very frequent visitor here lately but I remember in the past PMDG staff were very active in here answering and commenting on lots of questions but no problem, I submitted a ticket now.