Revelation wrote:Sure, and I'm no expert either, but weight growth is not really linear because to add fuel you need to add strengthening which adds weight, so you need to add more thrust which also adds weight, so you need to add more fuel for the same range, and now we're in a negative feedback loop.
I understand what you mean. By aiming for more range, you need higher MTOW, which means sturdier gear, higher rated engines, fuselage/wing box/wings strengthening, and it all snowballs.
All I'm saying is that most aircraft models in or around this segment has only started selling well when the higher range models became available. That's the case with the A300/A310, the A330, the 757 and especially the 767. They started trimming unnecessary weight, gaining MTOW and thrust. By aiming at a 5500nm range target from the get-go, you do run the chance of designing an overbuilt plane.
What really matters is sales numbers, that Boeing finds a market for the aircraft. And that will be much easier if you offer better range.
I would suggest Boeing build two variants, one shorter 797-8 with 5500nm range, and one larger 797-9 with 4500nm range. A single variant with 4500nm range could fall into the trap where Airbus launches an A322 with stretched fuselage, new wings and a thrust bump, matching the 797 in just about every aspect but fuel burn, while keeping commonality with the garden variety A320-series. I believe Boeing should place the 797 one notch above the Airbus option with regards to range and capacity already at launch. But I'm sure this is something they've been considering.