The MRTT doesn't really gain from MTOW increases beyond ~235t. ( OEW + 110t fuel + some ancillaries. ) apropos: would the 155kl/121t tankage of the A340-200 be available on the A330-200? then that limit would increase to 245t
The A340-213X's extra fuel came from three ACTs in the hold. I am guessing the A330-200 is not plumbed for ACTs and since A330MRTT's start as A330-200s, I would expect they are not plumbed for it, as well.
Unless there is a substantial MTOW increase, the HUGE wingbox tank of the A330-200/300/800/900 cannot be filled. So why are we talking ACTs? (Airbus cargo hold tanks... yea, they have a different name, but that is what they are in normal industry jargon).
But with the A332/A338 based tankers, there is less incentive at the current MTOW to add cargo tanks as the massive wingbox tank in commercial duty can only be half filled. Look at the A332 payload range chart!
For a good A330-200 payload range chart, all I could find what a chart embedded in a Leeham paid article, but google will show the chart. https://www.google.com/imgres?imgurl=ht ... Q..i&w=683
Yes, notice for the MTOW illustrated, the 2nd change in slope of the payload range chart doesn't happen. The slope means that as every 100kg of payload is removed (one passenger and bags), 100kg of fuel is added. If you look at the 757 line on the chart, you will see shortly after a small payload reduction, the slope dives down more. That is because removing payload doesn't allow more fuel as the tanks are full ("Volume limited"). You will never have an A330NEO (800 or 900) in service (pax or freight) that can use even half of the installed wingbox fuel tank.
Without the A340s landing gear/landing gear bay there, the volume available for fuel is HUGE! The simple solution was just line the wingbox with material to contain the fuel for the A332 and that is all airbus did (besides add the plumbing, of course). Even if the A338 gets the full MTOW increase, the wingbox tank will still have volume left to fill. It makes the A330 an ideal and cheap to engineer tanker.
The A339 needs the MTOW increase to install and use that wingbox tank. Even then, we're only talking putting 1/3rd of the volume of the fuel into the tank as passenger & fuselage weight ensure a lot of nitrogen innerting gas gets flown...
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