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WebMaximus

CG value in yellow on the Payload screen

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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.

 

CG%20yellow%20on%20the%20NGX%20Payload%2

 

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?

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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.

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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.

 

CG%20yellow%20on%20the%20NGX%20Payload%2

 

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 

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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.

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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

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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

 

CG%20OK%20on%20the%20NGX%20Payload%20scr

 

 

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 % !?

 

CG%20value%20with%202%20kg%20less%20payl

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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

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

 

Right, but even if you think the staff might see it, you should also think collectively.  Sure, you might want to resolve your own issue, but think about other people's issues out there, too.  Additionally, you have to remember that the staff member will have to remember to keep checking back on this thread, whereas the support portal is all automated so they don't have to keep checking the forums (or set a reminder).

 

Submitting a ticket allows them to track the issue in their support system.  This allows them to recognize similar issues and help other people with similar issues.  Say you provide information that helps them solve an issue.  Since it's in the system, any other similar issues might be able to be closed using that same method/fix/workaround.

 

I'm not saying don't post issues here, because sometimes users can simply address each other's issues (or point out that it's not an issue at all), but if it's a legitimate issue, it helps everyone if it's appropriately reported, tracked, and logged.

 

Legitimate issues (bugs you're sure of, license issues, etc): Portal

Potential issues to be validated: Here (and then Potal, without question, if suggested)

General help (technique, clarification on procedures): Here

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Right, but even if you think the staff might see it, you should also think collectively.  Sure, you might want to resolve your own issue, but think about other people's issues out there, too.  Additionally, you have to remember that the staff member will have to remember to keep checking back on this thread, whereas the support portal is all automated so they don't have to keep checking the forums (or set a reminder).

 

Submitting a ticket allows them to track the issue in their support system.  This allows them to recognize similar issues and help other people with similar issues.  Say you provide information that helps them solve an issue.  Since it's in the system, any other similar issues might be able to be closed using that same method/fix/workaround.

 

I'm not saying don't post issues here, because sometimes users can simply address each other's issues (or point out that it's not an issue at all), but if it's a legitimate issue, it helps everyone if it's appropriately reported, tracked, and logged.

 

Legitimate issues (bugs you're sure of, license issues, etc): Portal

Potential issues to be validated: Here (and then Potal, without question, if suggested)

General help (technique, clarification on procedures): Here

 

Wow Kyle, what is your problem? You really must have quite some spare time to kill making this kind of hen out of a feather simply because I asked in here about a strange thing I noticed today.

 

And I'm not even sure what you're implying writing I should be thinking not only about my own problems but think of other's problems as well?! I suggest you do some Google searching for my nickname (WebMaximus) and check out the posts and various contributions I made within the FS community the last +10 years or so.

 

The ticket was submitted even before you wrote this reply I'm quoting here so you can sit back and relax now and enjoy the ride and I'll report back in here any answer I get from PMDG for everyone to see sharing anything I think can be of interest to others as well just like I always do and always did...

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.

 

Yep, the ticket has been submitted and I'll let you know what PMDG says.

 

Thanks for confirming 13 kg/PAX sounds like a realistic figure to you.

 

I've now asked about this elsewhere as well in a forum that is frequently visited by real world SAS pilots just to double-check this figure. Speaking about the estimated PAX weight I got from the same source 87 kg/PAX which includes any carry-on luggage.

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Wow Kyle, what is your problem? You really must have quite some spare time to kill making this kind of hen out of a feather simply because I asked in here about a strange thing I noticed today.

 

And I'm not even sure what you're implying writing I should be thinking not only about my own problems but think of other's problems as well?! I suggest you do some Google searching for my nickname (WebMaximus) and check out the posts and various contributions I made within the FS community the last +10 years or so.

 

The ticket was submitted even before you wrote this reply I'm quoting here so you can sit back and relax now and enjoy the ride and I'll report back in here any answer I get from PMDG for everyone to see sharing anything I think can be of interest to others as well just like I always do and always did...

 

Forgive me for a moment, but I'm feeling a little blindsided here...

 

You posted your issue.

  • I, along with a few others, noted that it's definitely something that needs to be looked into, and referred you to the official support portal.
  • You (very clearly, and in multiple posts) made it seem that the request was somewhat questionable, given the PMDG staff occasionally answer questions here in the forum.
  • I provided reasons as to why it's smart, and in the best interest of everyone, to submit tickets, instead of relying on the forum.

Honestly, your response could have been as simple as saying "cool - went ahead and submitted a ticket - will report back."  Instead, you seemed (this may not have been your intention, but re-read your posts and you'll see that it could have been interpreted) to argue that submitting a was somehow unnecessary/redundant.  That is the only thing I was addressing.  Not you.  Not your character.  Not your contributions.  I addressed the idea that submitting tickets was redundant because PMDG staff occasionally views the forum.  End.

 

Regardless, thank you for submitting a ticket.

 

Still, I'm really not sure why I got the response I got...

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Although not using the exact same wording I thought I pretty much said just the same thing in post #10 and #15 that I will submit a ticket after having it confirmed this seems to be a real bug. How you interpreted what I said in those posts as I was "arguing" I really have no idea.

 

If you're not sure why you got the response you got I suggest you read the first couple of lines in your own post #16 telling me how I should "think collectively" and "think about other people's issues out there, too" and not only my own problems.

 

I thought that was exactly what I did when I posted about my issue in here rather than sending a support ticket privately to PMDG and without anyone else knowing about the issue I discovered. Fact is since buying the NGX when it was first released I have only submitted one ticket before the one I just sent regarding this issue. In every other situation and with every other problem I've been able to find the answer in this forum with help from fellow NGX drivers.

 

This will conclude this highly unnecessary discussion on my part and instead I'll spend my time on the actual issue and again of course I will share anything of interest in this thread both for you and everyone else to read.

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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.

 

I did my research,yes it is the correct figure,as for outside europe it is usually at 15kgs.

 

 

As for the bug you are having there...I tried to replicate your figures,I did of course get a difference because I do not have the SAS livery installed,but the C.G value does seem to jump around.

What i did was set the payload to empty,fuel to empty.then do my calculations for the flight =(fuel needed etc),and then put the those figures in the FMC,and it seemed to like what i did,as i got no yellow colour,just a solid steel grey.

So I hope this works out for you as well,

Do tell us how it goes

warm regards

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Whenever you enter a value via the payload manager it seems that the NGX will redistribute the weight of the PAX. The aircraft in it self weighs around 36-50 tonnes empty. So moving 800 KG between compartments close to the dry and empty CoG won't do much. But changing distribution of 100 passengers will. They are 10 times as heavy and can be seatet further from the MAC (longer arm means more influence on the CoG).

 

28% might not be a problem at takeoff. But if you burn fuel it can change to a bigger value during flight.

 

I would recommend to everyone to downliad the B737NG performance sheet from AVSIM file library. It is a performance and fuel calculator in one excel sheet. Its relatively easy to use and you can also use it for precise CoG calculations. Search the library. I uploaded the latest version quite a while ago. 4.95 i believe.

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Thanks for all input guys!

 

A good friend of mine discovered an interesting thing in the NGX Tutorial 1 where it on page 15 says

 

"Change the rear compartment first in a case like this where you’re reducing the load to avoid an out of balance situation."
 
Haven't had time testing this myself yet but maybe the simple solution to this issue is simply to make sure you always start by modifying the AFT CARGO weight before you enter type anything into the FWD CARGO.
 
Again, thanks for confirming the values I've been using are correct and realistic ones.
 
Edited to add that I also found some information about the Payload screen on page 99 in the NGX Introduction manual but there it didn't say anything about the importance of the load order between AFT and FWD CARGO.

 

 


I would recommend to everyone to downliad the B737NG performance sheet from AVSIM file library. It is a performance and fuel calculator in one excel sheet. Its relatively easy to use and you can also use it for precise CoG calculations. Search the library. I uploaded the latest version quite a while ago. 4.95 i believe.

 

This is a great tip, thanks for sharing!


Just did some very quick testing and when entering the CARGO weights in the correct order, first AFT and then FWD I was not able to produce a yellow CG value so I guess that is good news.

 

However I also noticed how the CG value still will be different from time to time although using the exact same values which seems a bit odd.

 

I wonder if the changing CG value also will affect the handling of the aircraft in a noticeable way...?

Edited by WebMaximus

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I would submit a ticket.

 

As a guideline, when I loadplan 737-800's (in the real world) The cargo is split 50/50. Ryanair put more in H2 (a lot of the time, exclusively).

 

Now, most aircraft benefit from a more AFT Mac because it is more fuel efficient. #TL;DR More aft = more fuel economic 

 

However, the -800 is notorious for being a little unstable at this AFT CG's so that's why we aim for a pretty central CG. 

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As a guideline, when I loadplan 737-800's (in the real world) The cargo is split 50/50. Ryanair put more in H2 (a lot of the time, exclusively).

 

Thats weird because i thought cargo is almost never distributed evenly on small aircrafts,or that must be when there aren't to many passengers.

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Thats weird because i thought cargo is almost never distributed evenly on small aircrafts,or that must be when there aren't to many passengers.

 

Depends on the plane, the operator and their SOP.

 

Working with UAX carriers, I'm pretty sure each one of them had a different way to load each aircraft.  As far as the 170s, it was always "bulk out the front - spill over to rear (if necessary, and it usually wasn't)."

 

...but that was just RPA's way of running their op.  FDX, on the other hand, gets that down to a science.

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