morrisond wrote:FluidFlow wrote:B777LRF wrote:
Let’s get som facts straight. A freighter first and foremost needs high MZFW and high MLW. MTOW is “nice to have”, but only really governs range - not payload.
Let’s have a look at what limits these weights, in a very simplified manner
MTOW: Limited by engine power. Fit larger engines, and up goes to MTOW
MZFW: Limited by wing bending. Strengthen the wing/wingbox interface, reduce the amount of fuel carried in centre tanks, reduce maximum number of airframe cycles to increase
MLW: Limited by landing gear. Fit a stronger gear or reduce maximum number of airframe cycles to increase
What Boeing (and Airbus) needed first and foremost was a MZFW and MLW to carry the required payload. Seems like both had to raise MTOW to reach an acceptable range, and I suspect both will have to employ a small thrust bump to meet the target. Thrust bumps comes at an increased maintenance cost.
While you are of course right with MZFW and MLW, the 77XF (and the A350F for that matter) are catering to high payload high range market. Therefore a high MTOW is needed to bring all the payload as far as possible. So for the case of the 77XF Boeing also needs as much MTOW as possible if they want to sell it as a true 77F/747F replacement. The market for high MLW/short range freighters is relatively limited.
But you raise an interesting concern, if Boeing will increase MTOW above the 351t, will they have to boost thrust? If so, that puts more work on GE to get more out of their engine even though they did not make any money yet with the current 77X engine.
EDIT: Especially with QRs hot climate, the engine has to be durable in dusty conditions and bring a lot of thrust to get all that weight of the ground. I added a gc map with 4000nm, 4500nm and 5000nm out of DOH.
As we can see the US is out of reach and East Asia is also at the limit, depending on the final specs of the XF as well as weather and airspace related constrains.
The good thing is, China, South East Asia and Africa are well within reach at maximum payload.
They already have gone to 110,000 lbs of takeoff thrust on the Ge9X and given that it reached 134,300 lbs in ground testing vs the 127,900 of the Ge90-115, getting more thrust out of it would seem to be relatively easy and an adjustment they maybe could do in software, granted at the cost of higher maintenance.
See this https://en.wikipedia.org/wiki/General_Electric_GE9X
You know its QR, so of course it is possible but if durability decreases, Boeing will soon be were Airbus is right now. So if they just up the thrust without improving durability in hot/dusty conditions it will be a problem.
Good thing is the 77X was tailored to the ME but up to 6% more MTOW will put a toll on the engine if it needs to use full thrust at least once daily in DOH in summer.