Aircraft weight and payload question

[Ray Proudfoot]

I'm hoping that someone can clear up my confusion over aircraft weights in the aircraft.cfg and those in an aircraft text file held in the Types subfolder under CDU.

Let's take the Project Opensky 747-400 as an example. The empty weight for this aircraft as shown in the aircraft.cfg is 299,000lbs. If I then add the payload of 98,000lbs it results in a ZFW value of 397,000lbs.

Now if I look at a 747.txt file in the Types subfolder the following entries are present...

NetWeight=440000
Payload=35000

Why is there such a large difference between the weights held in the aircraft.cfg file and those in the 747.txt file? Are these just arbitary values that are replaced when the user enters the actual ZFW? Or are all those calculations further down in the 747.txt based on the payload values above?

Is NetWeight the weight without adding payload? If I press the ZFW button on the CDU it presents a value of 440 suggesting it does not include payload. It should, shouldn't it?

I would like both sets of data to match but I'm reluctant to change either as they may impact adversely on performance and calculations.

I understand that ZFW is the sum of empty weight + payload but before fuel is loaded.

I'm sure when I enter a ZFW of 397.0 the correct CDU calculations will be made but I'd feel happier if someone could confirm this.

Any help would be appreciated.

[michelmvd]

Hi Ray,

First at all ZFW is indeed the basic operational weight (weight of the aircraft plus some standard liquids (hydrolic oil etc) + your payload.

The BOW can change from aircraft to aircraft, basicly due to company configuration ( first class / business / sleeping seats etc etc)

I'm not sure these figures in aircraft.txt are relevant when you are using a CDU, but maybe Jonathan can confirm here.

B. RGds
Michel

[Ray Proudfoot]

Thanks for your reply Michael. Hopefully Jonathan will spot this and give me the answer.

[JonathanRichardson]

Hi Ray

>NetWeight=440000
Payload=35000

>Why is there such a large difference between the weights held in the aircraft.cfg file and those in the 747.txt file?

I think I added a section in the manual about this. These values are just samples, every flight model will have a different netweight and payload. So, you need to update these re your flight model. Or at least know the figures yourself for your given flight.

>I understand that ZFW is the sum of empty weight + payload but before fuel is loaded.

Correct. Make sure not to get confused between KG / LBS with all this - that is the most common mistake.

If you enter your ZFW in the LSK of the CDU, the CDU will then compute the GW based on the sensed fuel. So, 200ZFW +50F, should = 250. Next to it (if you have not disabled it) will be the bracketed (XXX) actual read weight from the airfile. These two should match. If they are way out, then you have a problem somewhere. This is why we have the facility there to check this re the bracketed value. You can of course disable it because it is not in the real CDU.

>I'm sure when I enter a ZFW of 397.0 the correct CDU calculations will be made but I'd feel happier if someone could confirm this.

Might want to check docs, I',m sure I added a fuller section on weight and balance but it was sometime ago. You are right to be concerned about it, this is really important.

Regards
Jonathan Richardson
Project Magenta

[Jackpilot]

Jonathan, while you are at it, how can we find the right figure to input for the Center of Gravity.
I know how to on a real airplane but we do not have the data avail in the simulated airc rafts, unless i miss something.
Jack

[JonathanRichardson]

Hi

The CofG is indicated in the CDU along with the Trim, unless you use a third party program for this. See attached.

Regards
Jonathan Richardson
Project Magenta

[fweinrebe]

... how can we find the right figure to input for the Center of Gravity.
I know how to on a real airplane but we do not have the data avail in the simulated airc rafts, unless i miss something....

Jack,

for the PSS B777LRF there is a formulae in the weight and balance Excel spreadsheet that relates to this formulae:

Mac% = (5.4 - (Aircraft Total Moment/ Aircraft Gross Weight )) / 21.65

Not sure where the 5.4 and 21.65 comes from. That is probably the moments of the Forward and Aft limits. Each aircraft will have a different values.

[sas550]

Hi

The CofG is indicated in the CDU along with the Trim, unless you use a third party program for this. See attached.

Regards
Jonathan Richardson
Project Magenta

Problem is that it's empty, just the squares.

B737-800 Steve Reyling is used.

[Ray Proudfoot]

Hi Jonathan,

Thanks for your reply. I'd forgotten about the documentation. :oops:

I'll have a read through it and hopefully it will give me all the answers. I always stay in Lbs and the weights in the Posky aircraft are also in Lbs so hopefully there will be no confusion.

PS. I've installed the latest builds but haven't had a chance to input a plan to the Canary Islands which was causing that error with earlier builds. I'm hopeful it has been resolved. :)

[JonathanRichardson]

>PS. I've installed the latest builds but haven't had a chance to input a plan to the Canary Islands which was causing that error with earlier builds. I'm hopeful it has been resolved. :)[/QUOTE]

We could not re-create that one, but there were a lot of changes, perhaps it has sorted itself out. I think it was possibly a very specific navdata / interpretation error (no idea where the fault was/is), if it remains, I'd suggest to drop us a line at support.

Regards
Jonathan Richardson
Project Magenta

[Jackpilot]

Problem is that it's empty, just the squares.

B737-800 Steve Reyling is used.


Same for me, I double checked and the CG entry is empty, using 737-700 Opensky and S.Reyling 700.
It is an important data and no pertinent data to figure it.
FS9 fuel and payload window shows where the CG is on a rough little scale.
How to interpret it in % is a mystery to me.

[fweinrebe]

FS9 fuel and payload window shows where the CG is on a rough little scale.
How to interpret it in % is a mystery to me.

That little scale shows you your MAC% although it doesn't say what it is. The more back it is the greater the Mac%. Because it is expressed as a percentage relative to the forward MAC limit. See the glossary item MAC (http://www.mycockpit.org/forums/vbglossar.php?do=showentry&id=38).

And oops :oops: the formulae below was mixed up, but I corrected it.

[Jackpilot]

Well, I can follow that...BUT where can I get those numbers (except the gross weight)
for the simulated airplane.
JP

[fweinrebe]

I made a little example, hope it is clear. I can't still figure out where the AFT MAC setting comes from.

From aircraft.cfg:


[WEIGHT_AND_BALANCE]
station_load.0 = "170.0, 80.0, -2.0, 0.0, Pilot" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.1 = "170.0, 80.0, 2.0, 0.0, Co-Pilot" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.2 = "1250.0, 60.0, 0.0, 0.0, Crew" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.3 = "5200.0 , 22.0, 0.0, 0.0, First Class" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.4 = "11549.0 , 11.0, 0.0, 0.0, Business Class" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.5 = "15305.0 , -22.0, 0.0, 0.0, Coach 1-16" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.6 = "15305.0 , -38.5, 0.0, 0.0, Coach 16-29" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.7 = "6000.0 , 47.0, 0.0, 0.0, Forward Cargo" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.8 = "45000.0 , -67.0, 0.0, 0.0, Aft Cargo" //Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
max_gross_weight = 656000 // (pounds)
empty_weight = 314000 // (pounds)

[airplane_geometry]
wing_root_chord = 42.0 //Feet
wing_pos_apex_lon = 15.0 //Feet, longitudinal distance from reference point, negative going aft

Now an example using the above weights and arms:

Moment = Weight x Arm



Weight (lbs) Arm (ft) Moment (Lb*Ft)
Pilot 170 80 13600
Co-Pilot 170 80 13600
Crew 1250 60 75000
First Class 5200 22 114400
Business Class 11549 11 127039
Coach 1-16 15305 -22 -336710
Coach 16-29 15305 -38.5 -589242.5
Forward Cargo 6000 47 282000
Aft Cargo 45000 -67 -3015000

TOTAL: 99949 -3315313.5

PAYLOAD 99949 (PILOTS, CREW, PAX and FREIGHT)
EMPTY WEIGHT 314000 (empty_weight in [WEIGHT_AND_BALANCE])
ZERO FUEL WEIGHT 413949 (PAYLOAD + ZERO FUEL WEIGHT)
FUEL WEIGHT 250000 (WEIGHT OF THE FUEL)

Here are the data needed to calculate the MAC%:

GROSS WEIGHT 663949 (WEIGHT OF AIRCRAFT BEFORE TAXIING)
TOTAL MOMENT -3315313.5 (MOMEMENT)
AFT MAC LIMIT 42.0 (wing_root_chord in [airplane_geometry])
FWD MAC LIMIT ??.?? (DO NOT KNOW WHERE THIS IS YET ???)

During a search I discovered this Take-Off & Landing Performance Calculation Tool: TopCat. TOPCAT Home page (http://www.topcatsim.com/?page=main). It calculates the MAC% for you.

[Michael Carter]

That's why they pay dispatchers to do this stuff! :D

All you need to know is the %MAC from the dispatcher and look up the TO trim setting.

[AchillesP]

Hi to all,

I can tell you how I procced with this problem.

1.) I start at parking position, with changing the payload and the fuel load depending the flight I want.

2.) I configure the flight route to FMC.

3.) At init ref page I inform the weights.

4.) The CG% is always 22 at me. I press the LSK to be reseted and I have only the squares.

5.) I open pmcheckfile and I type the offset 2EF8 8 getting the CG%.

6.) I enter the valve to pm cg% and I get the trim which I configure to aircraft.

With this way, I always can rotare the plane at VRotate speed and not before or after.

* I will build a small program today or later tommorow to read the aircraft weights, the CG% and the trim value. It will be for free. So it will really easy to run this proggram and get the values you want.:wink:

[fweinrebe]

Achilles,

thks for that one. That is a great solution. :)

At least I had lots of fun learning about the MAC% calculations. At least now I can calculate the missing FWD MAC LIMIT if the AFT MAC LIMIT is indeed the same as the wing_root_chord in [airplane_geometry].

Maybe TasKing or you can write a Gauge to show the CG%? That will be really cheating. No dispatchers needed thank you. ;)

[AchillesP]

Ok,

I uploaded a program I made. It is calling payload manager.

Works via fsuipc and wideclient. Reads the data from Fs and also the CG%.

http://www.mycockpit.org/forums/downloads.php?do=file&id=310

Options
Aircraft type
Flight number
Tail number
Airline name
Max Gross weight
Basic operating weight
Payload
Zero fuel load
Fuel weight
Total weight
CG%
CG% Fwd
CG$ Aft
Trim indicator as value.
Overload Warning.

If someone have any new ideas to add to this program just post it.

[carlos hermida]

Thanks, any chance to use it with KG ?

[Jackpilot]

Kg.....? what's that...(lol)

[paulj]

To convert lbs to kg just divide the lbs by 2.20462 this will give you a pretty accurate conversion

cheers

Paul

[Ray Proudfoot]

>PS. I've installed the latest builds but haven't had a chance to input a plan to the Canary Islands which was causing that error with earlier builds. I'm hopeful it has been resolved. :)

We could not re-create that one, but there were a lot of changes, perhaps it has sorted itself out. I think it was possibly a very specific navdata / interpretation error (no idea where the fault was/is), if it remains, I'd suggest to drop us a line at support.

Regards
Jonathan Richardson
Project Magenta[/quote]

Hi Jonathan,

I've just entered this route from LEMG to GCLP.

PIMOS UN869 RBT RUSIK and after entering UN869.RBT I received Run-time error '9' - Subscript out of range.

Oh well, there are plenty of alternatives. This was with version 1.1.0.401 dated 27 Feb.

[AchillesP]

Thanks, any chance to use it with KG ?

noted for the next update

[Ray Proudfoot]

file:///C:/DOCUME%7E1/Ray/LOCALS%7E1/Temp/moz-screenshot.jpgCould some kind soul please explain these readings on the Payload Manager kindly provided by Achilles.



The Basic Operating Weight is shown as over 2 million pounds.
The Payload weight is minus 1.75 million pounds.
The CoG is only 0.03% which doesn't seem right.


These values are taken from the Project Opensky 777-200.

Thanks to Achilles for providing this utility but its purpose is a mystery to me.

[carlos hermida]

noted for the next update

Thanks AchillesP !

[AchillesP]

Hi Ray,

It seems that you have a problem with your aircraft.cfg file. The only think I do is to read the FSUIPC offsets from FS. I do not do any calculations.



file:///C:/DOCUME%7E1/Ray/LOCALS%7E1/Temp/moz-screenshot.jpgCould some kind soul please explain these readings on the Payload Manager kindly provided by Achilles.



The Basic Operating Weight is shown as over 2 million pounds.
The Payload weight is minus 1.75 million pounds.
The CoG is only 0.03% which doesn't seem right.

These values are taken from the Project Opensky 777-200.

Thanks to Achilles for providing this utility but its purpose is a mystery to me.

[AchillesP]

file:///C:/DOCUME%7E1/Ray/LOCALS%7E1/Temp/moz-screenshot.jpgCould some kind soul please explain these readings on the Payload Manager kindly provided by Achilles.



The Basic Operating Weight is shown as over 2 million pounds.
The Payload weight is minus 1.75 million pounds.
The CoG is only 0.03% which doesn't seem right.

These values are taken from the Project Opensky 777-200.

Thanks to Achilles for providing this utility but its purpose is a mystery to me.

http://www.mycockpit.org/photopost/data/564/medium/payload.JPG

[Matt Olieman]

Achilles, Thank You, Thank You, Thank You :) :) :)

Matt Olieman

[Ray Proudfoot]

Hi Achilles,

Thanks for posting your screenshot. I have switched to several different aircraft and I'm now using the PMDG737-900 without their panel of course. But these strange values persist.

The BOW is 2149936lbs
Payload is -2035356lbs
ZFW is 114580lbs
Fuel Weight is 1.0lbs

CG Fwd and Aft are both 0% and the red value is 0.26%

The Trim Indicator Value changes in flight but I don't see a Trim Value Box.

Just to confirm I'm running FS9.1 with FSUIPC 3.85.

Are you using FSX perhaps?

[AchillesP]

Sorry forgot to mention that I tested with FSX. :roll:

I will prepare a new version for fs9 also.


Hi Achilles,

Thanks for posting your screenshot. I have switched to several different aircraft and I'm now using the PMDG737-900 without their panel of course. But these strange values persist.

The BOW is 2149936lbs
Payload is -2035356lbs
ZFW is 114580lbs
Fuel Weight is 1.0lbs

CG Fwd and Aft are both 0% and the red value is 0.26%

The Trim Indicator Value changes in flight but I don't see a Trim Value Box.

Just to confirm I'm running FS9.1 with FSUIPC 3.85.

Are you using FSX perhaps?

[fweinrebe]

[IMG]
Thanks to Achilles for providing this utility but its purpose is a mystery to me.

The purpose of the program is to read some values from FS like the MAC%. Entering the MAC% on the FCU / FMS then gives a trim value. Setting this trim value results in a better rotation on take-off. Setting the trim too far forward will result in a heavy to lift nose, while too aft will result in an aircraft that just wants to get airborne by itself.


The Trim Indicator Value changes in flight but I don't see a Trim Value Box.


In flight the autopilot uses the trim to set the correct pitch for climb, cruise etc. On a B737 for example one can actually see the trim wheels move. And hear them cluck cluck cluck if it is bigger movements.

[Ray Proudfoot]

Sorry forgot to mention that I tested with FSX. :roll:

I will prepare a new version for fs9 also.

Ah, thanks. I thought there must be something strange happening. ;)

I think you'll find many people here are still using FS9 so that version will be appreciated.

[Ray Proudfoot]

The purpose of the program is to read some values from FS like the MAC%. Entering the MAC% on the FCU / FMS then gives a trim value. Setting this trim value results in a better rotation on take-off. Setting the trim too far forward will result in a heavy to lift nose, while too aft will result in an aircraft that just wants to get airborne by itself.



In flight the autopilot uses the trim to set the correct pitch for climb, cruise etc. On a B737 for example one can actually see the trim wheels move. And hear them cluck cluck cluck if it is bigger movements.

Thanks for the explanation Fritz. It was because I was seeing such crazy figures it made it difficult to appreciate its use. I usually set my trim to the same value irrespective of weight so it will be useful to be able to set it accurately.

And now that I know the original version only works correctly with FSX it explains everything.

[fweinrebe]

In flight the autopilot uses the trim to set the correct pitch for climb, cruise etc. On a B737 for example one can actually see the trim wheels move. And hear them cluck cluck cluck if it is bigger movements.

Sorry I have to correct myself. The autopilot does not use the Trim to change pitch. It uses the actuators to do that. And then does it trim to reduce the loads on the controls. Same as a human would have done.

As an observer on the flight deck, one will think the autopilot uses the trim only because that is the most obvious movement you see.

[JonathanRichardson]

Hi

Great program, nice tool to have handy when you need it for sure. We actually have place holders for this in the Instructor Station under the fuel / load page, but due to other things it dropped off the development radar a bit. We will try and get that done shortly. I also noticed that during our update process in the past couple of weeks we seem to have broken the facility in the CDU for the trim, we will get that fixed as well - sorry about that.

Regards
Jonathan Richardson
Project Magenta

[Ray Proudfoot]

Sorry forgot to mention that I tested with FSX. :roll:

I will prepare a new version for fs9 also.

Hi Achilles,

I was wondering if you had started on the FS9 version of this program. It looks very useful and many of us still fly with FS9.

Thanks.

[AchillesP]

Hi Achilles,

I was wondering if you had started on the FS9 version of this program. It looks very useful and many of us still fly with FS9.

Thanks.

Hi Ray,

I am working about 1 hour max per day. Hope to finish the fsx version this weekend and start immediattely with fs9 version. Take a look what other options the program will include

http://www.mycockpit.org/forums/showthread.php?t=15435

[Jackpilot]

Fantastic help. Well appreciated. Patiently waiting.
Cheers
jack

[Ray Proudfoot]

Hi Ray,

I am working about 1 hour max per day. Hope to finish the fsx version this weekend and start immediattely with fs9 version. Take a look what other options the program will include

http://www.mycockpit.org/forums/showthread.php?t=15435

Hi Achilles,

That's an impressive list. But you've missed one thing out. I don't see a button to press that will make me a cup of tea!:D

Seriously, I appreciate your efforts and thank you for providing this to our community.

[jonnydaz53]

Ray are you father ted !:D

[Ray Proudfoot]

Ray are you father ted !:D

:lol: You're not the first person to ask that. Sorry to disappoint but no, I'm not. ;)