studiously avoiding a contretemps with J-T...in lay terms:. .an aft CG (never mind the datum,we are talking 'relative' here)makes the tail want to lift up - to keep the thing balanced. tails do not provide positive lift (except in eurofighter) but they can be encouraged to donate less down-lift. aft cg will do this.. .a fwd cg will require the tail to provide 'down-lift'. this increases the Apparent All Up Weight. the wings have no idea what is going on, they just provide the rqd lift, and so the total drag increases. hence more fuel rqd. to hand fly an aicraft with fwd cg is very pleasurable as it is more stable (think of throwing a dart - big weight at the front=good:big weight at the back=bad).my 330 shoves fuel backwards and forwards as it sees fit to maintain the cg in fuel-economy-trip-mode.no idea how it works though....... .QED <img src="tongue.gif" border="0">