SUPPLEMENTARY INFORMATION
CENTRE OF GRAVITY
 
The CG envelope must also allow passengers to move in the cabin. Therefore, when the takeoff CG and landing CG envelope have been determined, the in flight envelope is deducted from takeoff/landing CG envelope by adding a 2 % margin, provided that all the criteria for the handling characteristics are met.
Note: In approach with flaps extended, there is a nose down moment. This is counteracted by THS nose up setting. The further forward the CG is, the more the THS nose up setting is required. This can result in a THS stall, particularly in cases of push over when the pilot pushes hard on the sidestick, in reaction to a significant speed decrease. This limits the forward CG during approach.
IN FLIGHT
On a fly-by-wire aircraft, in direct law, the handling characteristics are affected by the location of the CG, in the same way as in a mechanically controlled aircraft.
STABILITY ISSUE – THE AERODYNAMIC CENTER OR NEUTRAL POINT
In case of a perturbation or a gust, the aircraft is considered as stable, if it tends to revert toward its previous status. The aerodynamic center or neutral point is the point where there is an increase (or decrease) of lift, when the aircraft angle-of-attack changes.
Aircraft longitudinal stability
 
The gust illustrated here causes an increase in the angle-of-attack, therefore an additional lift. The nose down moment, due to the lift increase, causes a decrease in the angle-of-attack. The aircraft is stable.
If the CG is behind the aerodynamic center, the increase in lift creates a nose up moment, that adds to the initial nose up moment caused by the gust. The aircraft is unstable.
The CG must be forward of the aerodynamic center for stability.
MANEUVERING CRITERIA – MANEUVER POINT
Depending on where the CG is, a deflection of the elevator causes a sharper, or less aircraft maneuver. In other words, the CG has a direct influence on the maneuverability of the aircraft.
 
SUPPLEMENTARY INFORMATION
CENTRE OF GRAVITY
 
If a very small deflection of the elevator causes "a lot of g", the efficiency of the elevator is very high. The aircraft is considered to be very sensitive to maneuver. The maneuver point is the CG, for which the elevator is infinitely effective. The CG must obviously be as far forward
from the maneuver point as possible. This distance is defined by a maneuverability criteria, that determines that "at least 1 ° of elevator deflection is required to pull 1 g load factor". This condition defines the aft CG limit in terms of maneuverability.
But the CG must not be too far forward. The maximum elevator deflection must enable at least the maximum acceptable load factor (e.g. 2.5 g) to be pulled. This condition defines the forward CG limit in terms of maneuverability.
　
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本文鏈接地址：A330/A340 機(jī)組訓(xùn)練手冊(cè) FCTM Flight Crew Training Manual 2(72)