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.  Inaccuracy on the item weight
Each item weight is known with a certain inaccuracy (.WItem ) so for each item :
Witem real = Witem assumed ±.WItem
The inaccuracy on the item weight generates an inaccuracy on the final aircraft weight and CG position that can be determined in term of moment (Eitem weight). The inaccuracy value depends on the relation between the position of the .WItem and the assumed position of the aircraft final CG
.  If the .WItem is forward of the assumed aircraft final CG then a positive weight inaccuracy +.WItem will move the CG forward, a negative weight inaccuracy -.WItem will move the CG aft

C. BALANCE CHART DESIGN

.  If the .WItem is aft of the assumed aircraft final CG then a positive weight inaccuracy +.WItem will move the CG aft, a negative weight inaccuracy -.WItem will move the CG forward

Note : the item position is considered to be accurately known.
The .WItem impact is critical when the aircraft assumed CG is close to the limits, because the weight inaccuracy may lead to a real CG out of the limits.
. Eg : impact of .
WItem if .
WItem is located in front of CGassumed. Positive weight inaccuracy : +.WItem
a/c FWD CG limit  a/c CGassumed a/c Wassumed a/c CGW+.
WItem a/c W+.
WItem .
WItem located in front of a/c CGassumed  a/c AFT CG limit  a/c CGW+.
WItem a/c W+.
WItem a/c FWD CG limit  a/c CGassumed a/c Wassumed .
WItem located in front of a/c CGassumed  a/c AFT CG limit 

non critical situation  critical situation
Negative weight inaccuracy : -.WItem
a/c FWD  

a/c AFT
a/c FWD  
a/c AFT
CG limit  CG limit
CG limit  CG limit
a/c CGassumeda/c CGassumed a/c Wassumeda/c Wassumed

a/c CGW-.
WItem a/c W-.
WItem
a/c CGW-.
WItem
a/c W-.
WItem
located in frontlocated in front
.
WItem.
WItem
of a/c CGassumedof a/c CGassumed
non critical situation  critical situation
WEIGHT AND
BALANCE
WEIGHT AND
BALANCE
C. BALANCE CHART DESIGN

The impact in term of moment (Eitem weight) of this inaccuracy is determined by the difference between the aircraft real moment at aircraft weight : Witem assumed ±.WItem and the aircraft moment if the aircraft CG remains in the limit at aircraft weight : Witem assumed ±.WItem.
a/c CGlimit
a/c W+.
WItema/c CGW+.
WItem a/c W+.
WItem
a/c CGassumed a/c Wassumed
Eitem weight
Eitem weight is maximum when a/c CGassumed is on the aircraft CG limit.
a/c CGlimit a/c W+.
WItema/c CGW+.
WItem a/c W+.
WItem
a/c CGassumed a/c Wassumed
Eitem weight

So Eitem weight is determined by the difference between the moment of the aircraft ±.WItem on board and the moment of the aircraft at (Waircraft assumed ±.WItem) in case ±.WItem has no impact on the aircraft CG, in other words in the case when with the inaccuracy in weight the aircraft CG remains at the same position, on the limit.
　
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本文鏈接地址：Getting to Grips with Aircraft Weight and Balance(64)