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Optimum CG positionWhat is the best CG position for an aircraft ?
Catherine BONNETFlight Operations,
Weight and Balance Engineer
Presented by:
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Introduction
The influence of some parameters on
fuel consumption
By Monique Fueri and Yves LemelleSlide 10
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Impact of Centre of Gravity
Centre of gravityCentre of gravity
Optimize CG:For best takeoff performance
Usually aft CG minimizes fuel consumption
To be able to reach optimum CG in flight (aircraftwith trim tank)
COCKPIT
PREPARATION
TAXI IN
DISPATCH
TRANSIT
DEPARTURE
TAXI OUT
TAKEOFF
CLIMB
CRUISE
APPROACH
LANDING
HOLDING
DESCENT
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Introduction
AFT
as AFT as
possible
AFT of what ?
What is the best CG position
for an aircraft ?
25%MAC so
that the aircraftis balanced
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Introduction What is the best CG positionfor an aircraft ?
Well, any CG inside the limits isOK.
But there is a range of
recommended CG positions andthis range differs from one
aircraft to the other."
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum CG position ?
What is the best Center of Gravity position for an
aircraft?
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum CG position ?
What is the best Center of Gravity position for an
aircraft?
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VCC
C C
How to place aircraft CG at the optimum ?
Aircraft Basic configuration
Low flexibility
Operators items and DOW
Low flexibility
Fuel
NO flexibility
VCC
C C
VCC
C C
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How to place aircraft CG at the optimum ?
Passengers
VCC
C C NO flexibilityPartial flexibility
High flexibility
Cargo
Several constraints:
Priority
Temperature and ventilation Incompatibilities
Pyramidal loading
Aircraft stability on ground
.
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How to place aircraft CG at the optimum ?
Conclusion:Main actor is the Load Planner
He can control ZFCG and TOCG positions
He has many constraints to consider
It is not so easy to place the CG at the optimum
Any CG inside the operational limits
is OK
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How to place aircraft CG at the optimum ?
Conclusion:
Give Load Planners an
Optimum ZFCG range or an
Optimum TOCG range
instead of an optimum CG position
Load and trim Sheet
ZFCG
TOCG
What is the best CGposit ion for an aircraft ?
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum CG position ?
What is the best Center of Gravity position for an
aircraft?
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How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum
What is the best Center of Gravity position for an
aircraft?
Content
range of CG positions ?
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum range of CG positions ?
To reduce my fuel consumption
To benefit from better Takeoff and Landing performance
What is the best Center of Gravity position for an
aircraft?
To reduce my fuel consumption
To benefit from better Takeoff and Landing performance
Wh ld I l t ti f CG
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Why would I select an optimum range of CGpositions ?
To reduce my fuel consumption
Lift
Natural pitchdown effect
AircraftStabilisation
Tail downforce
To maintain the aircraft stable, tail down force is mandatory.
Weight
Wh ld I l t ti f CG
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Tail downforce
Why would I select an optimum range of CGpositions ?
To reduce my fuel consumption
Lift
Natural pitchdown effect
AircraftStabilisation
Tail downforce
The more forward the CG, the higher the tail down force.
The higher the tail down force,
the higher the lift necessary to maintain the flight
the higher the dragthe higher the fuel consumption.
Weight
Natural pitchdown effect
AircraftStabilisation
Lift
To maintain the aircraft stable, tail down force is mandatory.
Wh ld I l t ti f CG
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Difference in fuel consumption between two CGpositions inside the CG limits is low
Optimum CG position highly depends on aircraftFlight Level (FL)
Optimum CG is not the most aft but somewhereinside the CG limits
Complex aerodynamic interaction Wing-Tail
The more forward the CG, the higher the fuel consumption, IN GENERAL, IN GENERAL
But for Single Aisle aircraft
Why would I select an optimum range of CGpositions ?
To reduce my fuel consumption
The more forward the CG, the higher the fuel consumption, IN GENERAL
For Single Aisle aircraft, NO effect of CG position on fuel consumption.
FL1
FL2
FL3
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum range of CG
positions ?
To reduce my fuel consumption
To benefit from better Takeoff and Landing
performance
What is the best Center of Gravity position for anaircraft?
Wh ld I l t ti f CG
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Why would I select an optimum range of CGpositions ?
To benefit from better Takeoff and Landing performance
Lift
Weight
Natural pitchdown effect
AircraftStabilisation
Tail downforce
The higher the tail down force,
the higher the lift necessary to maintain the flight
the higher the minimum speed (Vs1g) necessary to maintain the flight.
To fly the aircraft, Lift must be higher than (Weight + Tail down force).
The more forward the CG, the higher the tail down force.
Tail downforce
Lift
Wh ld I l t ti f CG
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Why would I select an optimum range of CGpositions ?
The more forward the CG,
the higher the minimum speed (Vs1g) necessary to maintain the flight.
V2
1.13 VS1g
To benefit from better Takeoff and Landing performance
35 ftV1 VR
V2
VLOF
Take-off performance
VS1g
V2
TOD
TOW
The more forward the CG, the lower the takeoffand landing performance.performance.
Why would I select an optimum range of CG
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Why would I select an optimum range of CGpositions ?
The more forward the CG,
the higher the minimum speed (Vs1g) necessary to maintain the flight.
Vapp
1.23 VS1g
To benefit from better Takeoff and Landing performance
VS1g
Vapp
LD
LW
Landing performance
Vapp
The more forward the CG, the lower the takeoff and landing performance.
Why would I select an optimum range of CG
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Why would I select an optimum range of CGpositions ?
To benefit from better Takeoff and Landing performanceThe more forward the CG, the lower the takeoff and landing performance.
Maximum Allowed Takeoff and Landing Weight
Takeoff and Landing performance is computed not knowing what is the real aircraft CGposition.
The method applied must be conservative -> computation at the most forward allowed
CG position.
For aircraft that are naturally aft loaded ->
the aircraft could takeoff or land higher weight than the dispatch ones.
so there are two certified forward CG limits
CG in the forward part of CG range -> conservative performance
CG in the aft part of CG range -> better performance
Why would I select an optimum range of CG
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Why would I select an optimum range of CGpositions ?
To benefit from better Takeoff and Landing performance
F
orwardCG
ForwardCG
2
5%MAC
25%
MA
C
Why would I select an optimum range of CG
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Why would I select an optimum range of CGpositions ?
To benefit from better Takeoff and Landing performanceTAKEOFF LANDING
A318
Forward CG
22%MAC
A319Forward CG
25%MAC
A320Forward CG
25%MAC
Forward CG
25%MAC
A340-200/300Forward CG
26%MAC
Forward CG
26%MAC
A340-500Forward CG
28%MAC
Forward CG
28%MAC
A340-600
Forward CG
23%MAC
Forward CG
23%MAC
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum range of CG
positions ?
What is the best Center of Gravity position for anaircraft?
To reduce my fuel consumption
To benefit from better Takeoff and Landing
performance
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What is the best CG position for an aircraft ?
Best CG is
.
Optimum
ZFCG range is
.
Optimum
TOCG range is
.
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What is the optimum CG range for an aircraft ?
To reduce my fuel consumption
Single Aisle Family:
The optimum
CG is
Wide Body, Long
Range Famil ies:
The optimumCG is
Large Aircraft Family:
The optimum
CG is
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What is the optimum CG range for an aircraft ?
To reduce my fuel consumptionWide Body, Long Range
Families:
The optimum
CG is
These aircraft are equipped with a Trim tank and with in-flightCG target system.
The system optimises the aircraft CG in-flight by tranferingfuel from the wing area to the trim tank.
ZFCG aft enough to reach AFTCG Target during the flight
ZFCG too forward to reach AFTCG Target during the flight
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What is the optimum CG range for an aircraft ?
To reduce my fuel consumption
Wide Body, Long Range
Families:
The optimum
ZFCG is
aft enough to enable reaching
AFT CG target during flight
3 ZFCG zones can be defined:
1.CG range with AFT CG target notreachable
2.CG range with AFT CG targetreachable after transfer to the trimtank
3.CG range with AFT CG targetreachable after transfer to the trimtank and fuel burn
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What is the optimum CG range for an aircraft ?
To reduce my fuel consumption
Large Aircraft Family:
The optimum
ZFCG or TOCG range is
any CG inside
the operational CG limits
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What is the optimum CG range for an aircraft ?
To reduce my fuel consumption
Single Aisle Family:
The optimum
ZFCG or TOCG range is
any CG inside
the operational CG limits
The more forward the CG, the higher the fuel consumption, IN GENERAL
For Single Aisle aircraft, NO effect of CG position on fuel consumption.
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Content
How to place aircraft CG position at the optimum ?
Is it a flexible process ?
Why would I select an optimum range of CG
positions ?
What is the best Center of Gravity position for anaircraft?
To reduce my fuel consumption
To benefit from better Takeoff and Landing
performance
Why would I select an optimum range of CG
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Why would I select an optimum range of CGpositions ?
To benefit from better Takeoff performance
F
orwardCG
2
5%MAC
Operational margin
Wh t i th ti CG f i ft ?
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What is the optimum CG range for an aircraft ?
To benefit from better Takeoff performance
Any aircraft concerned:
The optimum
TOCG range is
any CG aft of the most aftcertified takeofflimit
taking into account
operational CG margin
Wh t i th ti CG f i ft ?
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What is the optimum CG range for an aircraft ?
To benefit from better Takeoff performance
TAKEOFF
A320 Aft of (25+2)%MAC
A340-200/300 Aft of (26+2)%MAC
A340-500 Aft of (28+2)%MAC
A340-600 Aft of (23+2)%MAC
2% is an average operational CG margin
Wh t i th ti CG f i ft ?
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What is the optimum CG range for an aircraft ?
To benefit from better Landing performance
Any aircraft concerned:
The optimum
LDCG range is
any CG aft of the most aftcertified landing limit
taking into account
operational CG margin
Load and trim Sheet
ZFCG
TOCG
Wh t i th ti CG f i ft ?
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What is the optimum CG range for an aircraft ?
To benefit from better Landing performance
Wh t i th ti CG f i ft ?
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Any aircraft concerned:
The optimum
LDCG range is
any CG aft of the most aftcertified landing limit
taking into account
operational CG margin
What is the optimum CG range for an aircraft ?
To benefit from better Landing performance
Any aircraft concerned:
The optimum
LDCG range is
any CG aft of the most aftcertified landing limit
taking into account
operational CG margin
The optimum
ZFCG range is
any CG in the aft ZFCG limit
C l i Wh t i th b t CG iti
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Conclusion
Any CG inside the operational limits
is OK
Load and trim Sheet
ZFCG
TOCG
What is the best CG position
for an aircraft ?
C l i Wh t i th b t CG iti
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Conclusion What is the best CG positionfor an aircraft ?
Optimum ZFCG range or Optimum TOCG range
is better than Optimum CG position
Landing performance
Single Aisle and Large
Aircraft:
NO OPTIMUM
Wide Body, Long
Range Aircraft:
ZFCG aft enough to
reach AFT CG target
Fuel Consumption
A320, A340:
TOCG aft of most aft
certif ied Takeoff CG
limit + operational
margin
Takeoff performance
A318, A319, A320, A340:
ZFCG in the aft ZFCG
limit (Landing CG is
aft of most aft
certif ied Landing CG)
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