Voyager does not have any additional fuel tanks; unlike the KC-46A it doesn't need any.
Voyager's under floor cargo area isn't compromised by additional centre tank 'plugs', whereas KC-46A's is. Hence it needs an upper deck cargo door whereas Voyager does not.
From what has been posted, typical ZFW for Voyager means that it's about 2.1T short of being able to operate with full fuel. But it can still take about 98% of max fuel. Why is it heavier than an A330-200? Consider the weight of AAR pods, FRU, camera equipment, additional avionics and DASS, the MSO's equipment etc. and there you have the answer.
I doubt whether the KC-45A would have been able to operate with 111T of fuel at start either - particularly given the weight of the ARBS.
Incidentally, the A330 centre tank is indeed considered to be a 'centre wing' tank rather than a 'fuselage' tank.
D-IFF_ident makes a good point regarding fuel volume. Airliner brochures tend to use low SG values in order to delude customers into thinking that a higher payload will be available than will actually turn out to be the case in service. Whereas a tanker manufacturer is more interested in ensuring that a high fuel mass, rather than volume, is available - so will quote a higher SG value. The A330MRTT brochure uses a realistic SG value of 0.799, whereas if the value of 0.785 as used in other brochures was quoted, 139000 litre would have a mass of 109T....and MTOW with max fuel (apart from that used during taxying) would be possible.
Last edited by BEagle; 7th Nov 2014 at 16:13.