Airbus A340 – Why Not?

This may have been asked before, but I might as well ask and see what kind of discussion I can drum up…

I got to wondering why the A340 has never been considered for the tanker mission while the A330 has seemingly been Airbus’ choice airframe-wise for the tanker mission from the beginning.

I just looked at some basic numbers comparing the A330-200/300 to their respective A340 equivalents the A340-200/300….this discussion doesn’t relate to the larger A340-500/600 models.

On paper at least, the A340 models seem to be of the same size, similar weights, and overall similar performance with one exception…….range. The A340 has a much greater range than any A330 model……which to me translates to endurance, both of which are great assets in a tanker.

Field performance (i.e. take-off distance) slightly favors the A330, but that was the only area which I could really see the A330 being a better aircraft in terms of what the tanker mission might require. The fuselages are identical so cargo capacity is the same. Fuel capacity is larger (based on the sources I saw) on the A340, which means more gas for receiver airplanes.

I figure some will say that four engines is a lot more expensive than two, but when the airplane in question can fly much greater distances and seemingly orbit for longer periods, is the cost difference even noticeable if there is one? I mean the A340-200/300 series use the largest members of the CFM56 family….a family of engines well-known to provide superb fuel efficiency.

So what gives? The KC-135 & VC-10 (both four-engined airplanes) have both provided sterling service as tankers with four engines, and indeed there is a large fleet around the world of converted 707 tankers (707’s & 747’s in Iran’s case)…all of which have four engines.

Perhaps I’m missing something here? What’s wrong with the A340 as a tanker as opposed to the A330?