Good idea, there are sensors available that can measure the weight of lorries as they are moving (sensors in the macadam). We use them to catch overweight lorries. Shouldn't be too challenging to do someting simaltar for a plane (ie measure the load on each of the undercarriage legs) and that can give a fairly good CoG. Only issue will be the stiffiness of avaition authorities.
Biting the hand that feeds IT
