Index calculation.

[lbh]

Hey

Does anybody know how to calculate W/B index, from BA(in) and empty mass for CL and NG?
If so how does the formula go?

Best regards

Lasse

[sjap]

Hello Lasse,

It's all in the weight and balance manual. It must be available in your company. I checked myboeingfleet but didn't find it yet.
Best regards
sjap

[Marc]

Hello Lasse,

Below is maybe what your looking for.
Its from the "Loading Schedules", part of the weight and balance manual(737-400). e.g. how to make a load sheet.
This part is full of tabels and figuers.

Best regards
Marc




The general form of the equation used to develop this loading schedule is shown in Equation 2-2.


Index = Weight x (B.A. – Index Datum B.A.) / C + K (2-2)


Where, for the development of this loading schedule:

Weight = Weight of the item under consideration in Pounds (LB).
B.A. = Balance arm of the item under consideration in Inches (IN.).
Index Datum B.A. = 648.5 IN., Index Datum selected near the midpoint of the C.G. limits (17% MAC).
C =65000 LB-IN., Moment Constant selected to normalize moments to more manageable numbers.
K = 40.0, Index Datum Constant selected to prevent the occurrence of negative index values.

Therefore, the index equation used in this document is

Index = Weight x (B.A. – 648.5) / 65000 + (40)


Equation 2-3 is used only to calculate absolute index values. The Dry Operating Index (DOI) of the airplane and the center of gravity limit inflection points are generally the only index values that must be determined using this form of the equation. When calculating the balance effect due to items loaded on the airplane (i.e. delta index values), the Index Datum Constant (K) is omitted from Equation 2-3.

[lbh]

Hi Sjap and Marc

Thank you very much for the replies! I looked in the W/B manual, but I couldn't find the index formula. Other fomulas are mentioned, but not for index. Ill might have a look again... But I guess thats where this forum is very handy!

Thanks again

Lasse

[sjap]

The only thing i can help you with now is zero fuel weight numbers of:
-300 32500 KG
-400 34500 KG
-800 40800 KG
-900 42000 KG
These are approx basic numbers we use, but are adjusted after the a/c is weighted from time to time.
Best regards
sjap

[lbh]

hi Sjap

Thanks for the approx ZFW, but dont you meen DOW? Anyway its always nice to get some tips and thumb rules from the mechanics point of view. And I must say -the numbers are scaringly close to ours DOW.

Does any of you know if the constant of "40" see Marc's reply is changeing throughout the series to compensate for inserted sections between series?

The reason why Im asking is that im programming a electroninc loadsheed for my calculater. I know that I kan just use the already calculated DOI and DOW so Its only for my own iterest of how these numbers come up. Reason to make it easier/faster for me as FO to calculate approx how much load to put in C1-C4, since Im also flying to countries where groundhandlings precalculation is limited before I do the manual loadsheet...

Furthermore I would like to see how optimum we could have loaded the A/C seen from a C/G point of view, concerning all flights.

So next question. Does anybody have any data concerning fuel flow vs C/G on CRZ?

Have a nice weeking

Lasse