Originally Posted by
BEagle
Well, the A310MRTT could have had 5 x ACT, but when the numbers were crunched it was realised that an increase in allowable MTOW would have been needed if max fuel was carried - and the Net Flight Path limits at the tanker's MOB were significant even though the RW length was not. So 4 x ACT was the final choice. In the case of the A330 though, it already had a 111 tonne max fuel capability, so it was retained for the MRTT, although with the added structural mass it is rare that 111 tonne can actually be carried, I gather it's normally around 109.
According to wiki, OEW of A330-200 is 265,900lb. 256,900 + 244,200 (111 tonne) = 501,100lb. MTOGW is listed as 533,519. That leaves 12,419 lb for payload/cargo with fuel fuel. OK, the A330MRTT OEW is higher because besides the full passenger suite, it's carrying the tanker stuff. But nearly 6 tons for the tanker stuff? And Voyager doesn't have a boom and boom camera system. So what got added to Voyager to bring its OEW up nearly 6 tonnes, or got changed that brought its MTOGW down nearly 6 tonnes? Or is this a runway limitation? Is the runway so short that it needs to be below MTOGW to meet critical field length requirements?