WEIGHT AND
BALANCE
WEIGHT AND
BALANCE
A. GENERALITIES
3.5. Summary
. H.arm . H.arm .
CG Leading Edge of MAC
%MAC = .. ..×100
Length of MAC
..
Length of MAC × %MACH.arm = H.arm +
CG Leading Edge of MAC
100
Stall speed
The further aft the CG, the smaller the stall speed (Vs) value.
Take off
The further aft the CG, the smaller the TOD (the greater the TOW). the better the take off roll performance. the better the take off climb performance.
3.6. Conclusion
The best take-off performances will correspond to an aft CG position.
In-Flight
The further aft the CG, the lower the fuel consumption.
Landing
The further aft the CG, the smaller the LD (the greater the LW).
The further aft the CG, the better the aircraft performance.
A. GENERALITIES
4. CERTIFIED LIMITS DESIGN PROCESS
The previous chapter has dealt with the influence of the position of the aircraft center of gravity on performance. The conclusion was that in general the further aft the CG, the better the aircraft performances. However, the CG has to stay within certain certified limits. These limits are defined in the Limitations volume of the Flight Manual (Chapter 2.02.00) and are also in the Weight and Balance Manual (Chapter 1.10, Limitations)
. Example : A320-212
The purpose of this chapter is to explain briefly how these limits are defined and why these limits vary according to the flight phase (take off, landing or in-flight)
These limits are mainly due to:
. structural limitations
. handling qualities
. a compromise between performances and aircraft loading
WEIGHT AND
BALANCE
WEIGHT AND
BALANCE
A. GENERALITIES
4.1. Certification requirements
Certain rules have to be respected when designing a CG envelope. The following is an extract from the JAR 25.
. J.A.R 25.27: Center of gravity limits
The extreme forward and the extreme aft center of gravity limitations must be established
for each practicably separable operating condition.
No such limits may lie beyond:
(a)
The extremes selected by the applicant;
(b)
The extremes within which the structure is proven; or
(c)
The extremes within which compliance with each applicable flight requirement is shown.
. J.A.R 25.143 : General
(a)
The airplane must be safely controllable and maneuverable during
(1)
Take-off;
(2)
Climb;
(3)
Level flight;
(4)
Descent;
(5)
Landing.
(b)
It must be possible to make a smooth transition from one flight condition to any other flight conditions without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane limit-load factor under any probable operating conditions including:
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