Forward CG CG at 26%MAC
TOW (kg) 256215.2 257581.3
kgTOW = 1366.1.
.For a given second segment climb gradient, the allowed TOW is increased when the CG is aft.
3.2.4. Basic and alternate CG positions
From the 3 previous paragraphs it can be concluded that :
The best takeoff performances correspond to an aft CG position.
Now, when determining the aircraft takeoff performance (TOW, TOD), the calculation is always performed at the most forward-certified CG position. Therefore, for aircraft having a naturally aft CG position (tail heavy aircraft), everyday operations might be penalized using this very forward value.
The A320 and the A340 usually have a DOW CG of around 30%MAC and their most forward certified CG limit is around 17%MAC. These “tail-heavy” aircraft usually have an aft takeoff CG position. This means that their everyday performance is better than the certified performance for the most forward CG position. So a second CG position forward limit has been certified for these two aircraft.
. at 25%MAC for the A320
. at 26%MAC for the A340. All takeoff performances in the certified Airplane Flight Manual are given for both these CG positions.
However, to take into account the errors in the determination of the CG position, a margin has to
be applied on the calculated takeoff CG.
I.e., for an A320, in order to be able to use the performance calculated for a 25% CG, the
calculated takeoff CG must be of at least 27%.
A. GENERALITIES
Therefore, for the A320, the basic certified CG is the aft CG (25%RC) and the alternate CG is the forward CG.
Takeoff charts and performances published in the FCOM are usually established for the basic CG position (25%)
WEIGHT AND
BALANCE
WEIGHT AND
BALANCE
A. GENERALITIES
b) A340 A340 Basic and Alternate CG
For the A340, the basic CG is the most forward CG and the alternate CG is the aft CG (26%).
Take off charts and performances published in the FCOM are established for the basic CG position.
No corrections are given in the FCOM because the alternate CG performances are better than the basic CG performances. Therefore, an operator that wishes to benefit from the advantages of the alternate CG must establish the appropriate takeoff charts.
Influence on TOW
Note : The following figures come from the PEP for Windows Take Off and Landing application. It takes into account all the limiting factors for take-off (runway length, climb…).
A. GENERALITIES
The following graphs show .TOW (%) as a function of the TORA length. . TOW .TOW .
AlternateCG BasicCG
.TOW(%) = .. ..× represents the difference in term of TOW when
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：Getting to Grips with Aircraft Weight and Balance(40)
