×
(10.44 .
18.51) =.
1258kg.m
cabinOA weight
Cabin OB :
EcabinOB weight = ±.Wpassengers in cabin OB x (H-armcabin OB - H-armlimit) HOB=16.39 m is forward for the limit so a positive .Wpassengers in cabin OB may cause the CG move out of the limit. The more conservative EcabinOB weight is obtained for H-armlimit = 18.51 m
E=
3 ×
15
66 ×
(16.39 .
18.51) =.
755kg.m
cabinOC weight
Cabin OC :
EcabinOC weight = ±.Wpassengers in cabin OC x (H-armcabin OC - H-armlimit) HOC=25.53 m is aft for the limit so a negative .Wpassengers in cabin OC may cause the CG move out of the limit. The more conservative EcabinOC weight is obtained for H-armlimit = 18.43 m
E=
-3 ×
15
72 ×
(25.53 .
18.43) =.
2711kg.m
cabinOA weight
Total inaccuracy for all the cabins
E=.
1258× +
755× +
2711× =.
3082kg.m
passenge weight fwd
C. BALANCE CHART DESIGN
3.4.3. Inaccuracy on fuel loading on board the aircraft
a) Inaccuracy on the fuel location
On the balance chart the fuel influence is taken into account as a delta index per total fuel quantity, this delta index is based on a fuel H-arm for the corresponding fuel weight. Now the fuel H-arm depends on the fuel volume contained in each tank and this volume is linked to the fuel weight through the fuel density. So an inaccuracy on fuel density will generate an inaccuracy on the fuel H-arm and consequently on the aircraft CG determination.
In addition the Zero Fuel limit design is based on the theoretical fuel vector at a chosen density (usually 0.785 kg/l). This Zero Fuel limit is used to ensure that flight CG all along the flight and landing CG before landing are within their own operational limits. As a standard density value is used for the Zero Fuel limit determination it is necessary to take into account the possible differences on actual aircraft CG due to density impact.
This inaccuracy is named fuel density inaccuracy.
Note : Fuel density is also called fuel specific gravity, in this document the word density will be used.
. Fuel density inaccuracy
1. Inaccuracy on the fuel .index determination. Fuel index table can be available for one single fuel density (usually for single aisle aircraft) or for a discrete range of fuel densities (for aircraft equipped with a trim tank).
On single aisle aircraft (A318/A319/A320/A321, A319 corporate jet excluded), total fuel quantity is around 20 tons, consequently the fuel density variation does not lead to huge fuel quantity variation, furthermore the fuel tanks position is close to the Reference Chord. That is why fuel index table is established at a single reference density (usually 0.785 kg/l). As the fuel density can be assumed to vary between 0.76 kg/l and 0.83 kg/l, the maximum forward and aft .index between the reference fuel index table and the fuel index values determined at extreme fuel densities must be included into the fuel allowance.
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