|Quoting Baroque (Reply 28):|
The question I did ask was does the later information that (T)SFC was unchanged from the smaller engine make any difference to your calculations? Previously it had been assumed the larger version would be a bit more thirsty. Now it seems this may not be the case
Sorry Baroque, I made a fault with the reference, of course it was my part of the post I referenced, not yours. To your questions:
My calculations are not affected by any changes in the engine., they calculate the factual fuel used for the spec mission, i.e. it is based on the OEMs own calculations for spec range with the actual engines including any changes. The only source of any fault there (once you know their assumed OEW) is how they calculate the reserves. Now there is a well established standard there so that should be OK
Re the TXWB, the original 93k version was identical to the 84k version except for a tweaking of the fan blade aero and small but important changes to the high pressure turbine. The idea was that these improvements could be waterfalled down to the 84k version as time passed. Important log lead-time items like castings etc were kept.
The 97k version increases the size of the fan by making the inner hub diameter smaller = longer blades, keeping the outer diameter and it introduces more thorough changes to the core for more mass flow. If they touch the core parts they might just as well re-optimise the core blades/vanes for the higher RPM, that was my point.
Also please note what RR
said, the "SFC" is unchanged, i.e. the fuel used per pound of thrust is the same. This is clever of them as the unassuming audience equates that to no higher fuel consumption for the frame, but this is not what they said! The heavier 35JN uses more pounds of thrust to keep M0,85 at cruise as it has a higher drag due lift (it is heavier), i.e. it burns more trip fuel. It does this even with the same payload as it is 2,4t heavier in the MEW then the original version.
[Edited 2011-11-13 00:32:56]