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  1. #1
    300+ Forum Addict Ray Proudfoot's Avatar
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    Aircraft weight and payload question

    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.
    Ray
    3 miles east of EGCC - home to British Airways Concorde 'Alpha Charlie'

  2. #2
    150+ Forum Groupie michelmvd's Avatar
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    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
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    website B744 : users.telenet.be/michel.vandaele/sim1.htm
    general website : users.telenet.be/michel.vandaele
    my spaces: http://michelmvd.spaces.live.com/
    email : michelmvd@hotmail.com

  3. #3
    300+ Forum Addict Ray Proudfoot's Avatar
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    Thanks for your reply Michael. Hopefully Jonathan will spot this and give me the answer.
    Ray
    3 miles east of EGCC - home to British Airways Concorde 'Alpha Charlie'

  4. #4
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    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
    Jonathan Richardson

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  6. #5
    1000+ Poster - Fantastic Contributor Jackpilot's Avatar
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    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
    Jackpilot
    B737-700 Posky
    FS9/P.Magenta
    without PMSystem

  7. #6
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    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
    Attached Images Attached Images
    Jonathan Richardson

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  9. #7
    Heli Builder fweinrebe's Avatar
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    Quote Originally Posted by Jackpilot View Post
    ... 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.
    Last edited by fweinrebe; 03-05-2009 at 03:56 PM. Reason: spelling & formulae
    Fritz -> Helicopter Cockpit Builder
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  10. #8
    150+ Forum Groupie sas550's Avatar
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    Quote Originally Posted by JonathanRichardson View Post
    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.
    Regards Anders Eriksson


    www.simcockpit.se

    FS9

  11. #9
    300+ Forum Addict Ray Proudfoot's Avatar
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    Hi Jonathan,

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

    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.
    Ray
    3 miles east of EGCC - home to British Airways Concorde 'Alpha Charlie'

  12. #10
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    >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
    Jonathan Richardson

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