The aircraft ZFW, TOW and CG position computation is based on initial aircraft configuration corresponding to DOW and DOCG. Due to some item movements during the flight the aircraft configuration may change, this CG movement needs to be taken into account in the operational limits determination. Operational margins are the sum of the total possible inaccuracy and the possible aircraft CG movements due to :
. landing gear movements
. flaps/slats movements
. water movements
. movements in the cabin.
Operational Limits
80000
75000
Operational Margin
Aircraft Weight (kg)
70000 65000 60000 55000 50000 45000 40000
Operational envelope Certified envelope
35000
20 70
INDEX
The following paragraphs detail each error and CG movement evaluation.
The method is to determine the influence that each lack of precision or each CG movement will have on the aircraft final CG position. This influence can be quantified as the difference between the trimming document final index and the index that would result of a calculation with no accuracy. Instead of using the index value the following method uses the moment and evaluate difference between the aircraft moment determined using the trimming document (assumed) and the real one.
Operational margins = (Real Aircraft Moment) . (Assumed Aircraft Moment)
Note : inaccuracies and movements can shift the aircraft CG forward or aft. If the CG shifts forward the CG H-arm decreases and so the resulting moment also decreases. The inaccuracy shifting the CG forward reduces the aircraft total moment so this inaccuracy or movement results in a negative moment.
C. BALANCE CHART DESIGN
3.2.2. Resulting moments determination
After evaluating the individual moments corresponding to each lack of precision and/or to each
movement it is necessary to determine their total effect in term of moment.
This total effect definition depends on the type of situation.
Lets consider the total effect (E) is made of several individual effects E1, E2...En.
e.g. The resulting cargo loading effect is the made of the effects due to the different cargo compartments.
When the individual effects are SYSTEMATIC (if they occur surely at each flight) then they will
CUMULATE and the total effect is,
E = E1+E2+...+En
it is also said they are NON RANDOM or DEPENDENT,
When the individual effects are NON SYSTEMATIC (if they may occur or not at each flight) then they can COMPENSATE and the total effect is,
22 2
E =
E1+E 2+...+E n
it is also said they are RANDOM or INDEPENDENT,
When effects are non-systematic, they can compensate each other and the resulting error is always less important with independent effects than with systematic effects.
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本文链接地址：Getting to Grips with Aircraft Weight and Balance(61)
