It is located behind the aerodynamic center (neutral point).
If the CG is located on the maneuver point, the elevator efficiency is infinite.
Experience has shown that for stability reasons the CG must be located ahead of the point and
at a considerable distance.
In order to have an acceptable margin in regards to the maneuver point, a reference point is
established for which the maneuverability of the aircraft is reasonable : Point at 1° per g. This
point is considered as an aft limit.
. Point at 1° per g
Example of a turn.
R = Turn radius
W = Weight = mg
Φ
= Aircraft bank angle
n = Load factor
Apparent Weight
= n.mg
1
cos Φ=The load factor during a turn is:
n
From the previous formula, it appears that the higher the bank angle the higher the load factor. In order to compensate for this higher load factor, the pilot must pull the stick, thus increasing elevator deflection.
WEIGHT AND
BALANCE
WEIGHT AND
BALANCE
A. GENERALITIES
For commercial aircraft the law that gives the elevator deflection (δ) necessary to compensate a given load factor (n) can be represented as follows :
This law depends on the type of maneuver, aircraft speed, weight and CG position. Drawing this graph for fixed conditions except CG position, gives the following:
Elevator deflection (δ
)
Load factor (n)
δ
40%
δ
10%
10% CG
The further forward the CG position, the greater the necessary elevator deflection to compensate on given load factor.
There is a CG position for which 1 degree of elevator deflection compensates a 1 g load factor (for which 1 degree of elevator deflection creates a 1g load factor). This is the 1° per g CG.
The experience has shown that the CG has to be ahead of the 1°/g CG. The position of the 1°/g point depends on the aircraft‘s speed.
1° per g point : AFT limit (all phases)
A. GENERALITIES
d) Maximum elevator deflection and extreme load factor
Civil aircraft are certified according to the JAR/FAR 25 regulations. These regulations require for maximum acceptable load factor with no structural damage of 2.5g.
CG3 : if aircraft CG is located on CG3 load factor 2.5g cannot be reached whatever the elevator
deflection is.
CG1 : if aircraft CG is located on CG1 load factor 2.5g can be reached for an elevator deflection
lower than δmax.
CG2 : if aircraft CG is located on CG2 load factor 2.5g is reached for elevator deflection δmax.
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(46)
