Hand Solo:
Does wheeltugs designer have any figures for the fuel penalty involved in lugging around all that extra weight for the many hours the aircraft is in the air as opposed to the time it spends taxying?
Who says it's a penalty? If you've got to load fuel for the engines to do the same job, it's quite possible that the efficiency of the wheeltug is such that it's still more economical to lug it around than it is to have to burn fuel in the engines to move the aircraft on the ground. However, it would be interesting to see figures for a full flight profile gate to gate with typical taxi delays.