john_tullamarine
A bit off-thread, but as an aside, consider the following, although I accept it is not typical, and I have simplified for the sake of brevity.
On my aircraft type, on every take-off, we actually do target the Aft Limit of the CoG.
We avoid much of the chaos that would arise on other aircraft types during loading because we are able, within limits, to move the CoG into the correct position - after pushback from the ramp and before take-off - by using the VAPOUR system (Voice Activated Pilots Onboard Universal Resource), or Flight Engineer as he is otherwise known, to move fuel around the aircraft.
At heavy weights we are glad of the RTOW improvement that this brings, but we have to be careful at lighter weights, particularly with lower fuel loads, for the following reason. Once the desired take-off CoG has been achieved, the question then is "Will it stay there during take-off?"
Well the crew and passengers are strapped in, hopefully so is all the freight, so what else is left that can move about during the take-off roll? The answer, of course, is the fuel in those tanks which are not completely full.
The relatively rapid acceleration encountered during take-off will tend to make this fuel surge rearwards in the tanks, and the high pitch attitudes encountered after take-off will tend to keep it there.
Both these effects would combine to move the CoG a bit further rearward than we could accept, given that we were planned at the Aft Limit to start with, and so, on those lighter weight take-offs, where fuel tanks are not full and this surge effect may be encountered, the AFM imposes reduced (further forward) Aft CoG Limits as the aircraft weight decreases.
On very short sectors, or with low fuel loads, we can end up with an RTOW decrement, because of the reduced Aft CoG Limit.
The aircraft Zero Fuel Weight CoG position is also very important to us, and leads to an interesting little dilemma.
A Forward ZFWCG position means we can load more fuel (high fuel loads move the aircraft CoG rearwards) and still stay within take-off CoG limits, but it will also require a greater amount of fuel to be transferred aft, as ballast, during SuperCruise at M2.0, to move the CoG to the optimum cruise position.
This ballast fuel is unusable whilst at M2.0, and the more that is required at the rear of the aircraft, obviously the less there is available in the wings to feed the engines. A point will arrive when this ballast fuel is required back in the wing tanks, to feed the engines, and this will force the aircraft to decelerate to subsonic flight, as if we can't keep the CoG aft, then we must make the CoP move forward.
With a Forward ZFWCG position, this point can be reached before the ideal TOD point, which can prove a trifle awkward, given that the subsonic range is considerably less than the supersonic range!
Sometimes asking for the aircraft to be loaded to a slightly more rearward ZFWCG, reducing the maximum fuel load somewhat, but allowing a longer SuperCruise, may actually be an improvement on a long sector!
Anyway, I've just noticed it's the 25 December where you are, so enough of this, and a very Happy Christmas to all "Down Under".
Seasons Greetings
Bellerophon