I would imagine that if you have an aircraft with a permanent positive-lift tailplane, the main wheels (assuming a nosewheel configuration, and not a tailwheel aircraft) would be rather further backwards and not roughly below the center of pressure (CEP) of the main wings. After all, a positive-lift tailplane means the CofG is behind the CEP of the main wings, and if you put the main wheels roughly at the CEP of the main wings, the aircraft will fall over backwards.
But I don't think airplanes exist that have their CofG permanently behind the CEP of the main wings. For starters, that would mean they would have an extremely narrow CofG range, so they would not be exactly practical.
To the best of my knowledge, the A380 is loaded on the ground, takes off and performs the initial climb just like any other aircraft, with a tailplane providing negative lift. So the CofG is in front of the CEP of the main wings, and in front of the main wheels. Only once it's in stable cruise, or maybe at the last stages of the cruise climb, is the fuel transferred aft and will the tailplane reach some measure of positive incidence/lift - with the CofG slightly aft of the CEP of the main wings. My gut feeling is actually that the fuel transfer is done until a precise positive incidence of the tailplane is reached. After all, if the positive incidence of the tailplane would exceed a certain value (which is more or less the incidence of the main wings), the inherent dynamic stability would be lost.
Well before landing (I think once the cruise altitude is left), the fuel will be transferred forward until a normal situation, with negative lift of the tailplane, is reached again.
(And if that final fuel transfer fails, or is forgotten, I would imagine the landing and rollout would be rather spectacular - imagine an A380 sitting on its tail...)
Last edited by BackPacker; 7th May 2013 at 10:19.