Airline preflight adjustment of CG for least fuel burn?
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Airline preflight adjustment of CG for least fuel burn?
Does anyone know if airlines adjust the CG when allocating seats and storing
baggage to minimise fuel burn? Since the tailplane has to provide a downward
force to balance the CG/CoP coupe, which to the wing is exactly the same as
carrying that amount of additional weight, by moving the CG forward could
save fuel.
To give an example consider two identical airliners A and B, with the same
number of pax (say 90% of capacity which would be a fairly common
utilisation rate today) and their luggage ie both have the same payload
weight. A allocates pax seats randomly while B sits them up front first so
that all empty seats are at the rear and so its CG is forward of A's. If
sitting everyone up front isn't enough to move the CG to its most forward
allowable limit then also placing the heaviest pallets and/or bags up front
could
also be done (they weight them anyhow so this information is already known)
to further move it forward to this limit (taking into account any zero fuel
weight CG limitations too of course). Then over the same travel distance
surely B would have a slightly lower total fuel burn since its tailplane
needs a smaller downforce (for the same payload weight) and hence produces
less drag.
Even if this were only done for cattle ah economy class it would surely
still have a noticeable effect but having flown a lot over the years on
various airlines I've never seen this done, why not??
baggage to minimise fuel burn? Since the tailplane has to provide a downward
force to balance the CG/CoP coupe, which to the wing is exactly the same as
carrying that amount of additional weight, by moving the CG forward could
save fuel.
To give an example consider two identical airliners A and B, with the same
number of pax (say 90% of capacity which would be a fairly common
utilisation rate today) and their luggage ie both have the same payload
weight. A allocates pax seats randomly while B sits them up front first so
that all empty seats are at the rear and so its CG is forward of A's. If
sitting everyone up front isn't enough to move the CG to its most forward
allowable limit then also placing the heaviest pallets and/or bags up front
could
also be done (they weight them anyhow so this information is already known)
to further move it forward to this limit (taking into account any zero fuel
weight CG limitations too of course). Then over the same travel distance
surely B would have a slightly lower total fuel burn since its tailplane
needs a smaller downforce (for the same payload weight) and hence produces
less drag.
Even if this were only done for cattle ah economy class it would surely
still have a noticeable effect but having flown a lot over the years on
various airlines I've never seen this done, why not??
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Not common at all in the industry. The company I work for has been doing it for many years.
One thing to bear in mind is that many large long-haul aircraft have airborne CG management using fuel transfer to/from a tail tank. This works well until the fuel quantity reduces to the point where this tank starts to empty. Then the original planned CG will affect the fuel burn.
It can save milllions.
One thing to bear in mind is that many large long-haul aircraft have airborne CG management using fuel transfer to/from a tail tank. This works well until the fuel quantity reduces to the point where this tank starts to empty. Then the original planned CG will affect the fuel burn.
It can save milllions.
Last edited by Canuckbirdstrike; 17th Dec 2007 at 11:29. Reason: spelling
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Re:
An aft CoG will reduce the downforce required by tailplane therefore reducing drag - not the other way round.
OK then just reverse what I said, fill the rear seats first, everything else is true otherwise.
OK then just reverse what I said, fill the rear seats first, everything else is true otherwise.
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Aft CG
In Argentina, (747-200) we load baggage containers for best "AFT" CG...
Load Control people have guidelines for proper loading to that effect.
Passenger loading is rather approximate, and has little effect... Worse, they like to move.
For Y pax, we only recommend "zone" (cabin) loading... Put them in Cabin E, then D...
The fuel-burn tank sequence is also based on most favorable "AFT" CG in cruise. To give you an idea (10 tanks) ...
xxx
- Main tanks to engines for takeoff/intial climb (Boeing SOP), then...
- Reserve tanks nš 2 and nš 3 to empty ASAP in climb (reduced Vmo reason - Boeing SOP), then...
- CTR Wing tank to be emptied ASAP (get nose light, tail heavy), then...
- AUX tank (forward of CTR Wing tank) next to be emptied into CTR Wing tank, then...
- Main tanks to engine... (end of cruise)...
- Empty Reserve tanks nš 1 and nš 4 during descent...
xxx
This fuel burn sequence is designed to keep a CG close to the AFT CG limit...
All manufacturer's SOPs are designed that way.
Most important - The big/fat F/As stations are L-5 and R-5. Skinny ones at L-1 and R-1...
N.B. Captain's preference. Besides that, I weigh only 59 Kg...
I assume the cabin staff will poison my coffee on next flight.
xxx
Happy contrails
Load Control people have guidelines for proper loading to that effect.
Passenger loading is rather approximate, and has little effect... Worse, they like to move.
For Y pax, we only recommend "zone" (cabin) loading... Put them in Cabin E, then D...
The fuel-burn tank sequence is also based on most favorable "AFT" CG in cruise. To give you an idea (10 tanks) ...
xxx
- Main tanks to engines for takeoff/intial climb (Boeing SOP), then...
- Reserve tanks nš 2 and nš 3 to empty ASAP in climb (reduced Vmo reason - Boeing SOP), then...
- CTR Wing tank to be emptied ASAP (get nose light, tail heavy), then...
- AUX tank (forward of CTR Wing tank) next to be emptied into CTR Wing tank, then...
- Main tanks to engine... (end of cruise)...
- Empty Reserve tanks nš 1 and nš 4 during descent...
xxx
This fuel burn sequence is designed to keep a CG close to the AFT CG limit...
All manufacturer's SOPs are designed that way.
Most important - The big/fat F/As stations are L-5 and R-5. Skinny ones at L-1 and R-1...
N.B. Captain's preference. Besides that, I weigh only 59 Kg...
I assume the cabin staff will poison my coffee on next flight.
xxx
Happy contrails
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I knew of a F/E on UAL DC-6's who earned a nice bonus 45 years ago for implementing a neat procedure for doing exactly that.
(Yes, an aft CG - within AFM limits - is lowest drag, so long as you don't create a taildragger during loading/unloading)
BelArgUSA: ROFL!
(Yes, an aft CG - within AFM limits - is lowest drag, so long as you don't create a taildragger during loading/unloading)
BelArgUSA: ROFL!
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Did a sight seeing trip to Antarctica with QF on a 744 and not an empty seat in the house. I assume they had full fuel and of course no baggage. Seem to recall they mentioned carrying three tons of ballast. Would that have been likely to get the CG in the right place? Absolutely great trip by the way, and free access to the flight deck for anyone who cared (before the current security fiasco).
