Edit: forgot DOW. I would have used OWE (operators empty weight) in the past but after looking at discussions here I have realised that DOW (direct operating weight) is more suitable. DOW is the weight without fuel or payload so includes food, cutlery, water, toilet paper, 3 extra bottles of fizz if my employer lets me go n the pointy end. That sort of thing. From Zekes posts I take that to be ~5t for a long/ultralong flight.
OEW - Operating Empty Weight, not used by airlines, we use Basic Weight which includes:
• aircraft structure.
• unremovable equipment.
• unusable liquids (fuel, oil and others).
• standard loose equipment.
DOW = Dry Operating Weight. Basic weight plus operational items such as crew and pantry (equipment, food, beverages).
I would have assumed that the maximum volume of 124t (artificially limited) would be the volume to cover the 8400nm spec range flight with 360pax. This would arguably be around 3.5hrs longer than that flight and at 6t/hr would give another 18t+.
There is a fundamental problem somewhere with your model somewhere, the fuel burn on the A350 is too high. The nominal payload/range for both the A350-1000 and 777-8 are MTOW limited, not fuel volume. Your assumption that 8400 is fuel volume limited is incorrect.
That is the benefit of the GE9X. If it meets its promises, the main one of which is 5% better than XWB at EIS (not to make this an A vs B contest, but pointing out why Boeing and GE might accept an engine which is 3000 lb heavier than an already heavy GE90-115 rather than PIPing the GE90-115 one more time), then the heavier plane is more efficient. Otherwise, why bother with the GE9X?
Have a look at what GE has said about the GE9x, it is aimed
to be 10% better than GE90. It has taken GE 15-20 years to aim for that efficiency, the GE9x will not reach that 10% at EIS. There is only 2 years development between the Trent XWX-97 and the GE9x (first run 2014 vs 2016), rule of thumb for engine efficiency technology improvement is circa 0.5% reduction in TSFC per year.
In reality I would expect the difference in TSFC between the GE9X at EIS and Trent XWB-97 to be in the order of 0.005 lb/lbf/h (the ICAO emissions database has no difference between the engines). I would only expect a total improvement in the order of 0.05 lb/lbf/h between the GE90 and GE9X.
I'm firmly of the opinion that whatever is chosen, the largest variant will also be used to replace the 380 in the future. If QF chose the 350-1000 then they will have two seating configurations, a premium heavy for the Sunrise flights and a denser configuration for the remainder. If QF chose the 777, then they will get 8's for the Sunrise and 9's for the 380 replacement.
The QF 380's start to get cabin refurbishment later this year, this is being done by Airbus and is said to be where the cancelled 380 deposits are going.
Any order will see the Sunrise aircraft delivered first and once completed, then the heavier aircraft will come in and start to replace the 380's, but that wouldn't be till 2025 at least and going through till the end of the 2029-2030. That still gives 10 years of 380 ops at QF.
I agree the A380 will be for sometime, but I dont agree the Sunrise aircraft will dictate what they purchase in a decade. They will reassess the situation when it is time to make the order.
broadly speaking (I’ll explain below the a350 will cruise at M0.85 and the 778x at M0.84 and with this difference over 21hrs one would expect about 15mins difference.
That just will not be the case, difference today on 15 hr sectors between the A350 and 77W is already 20+ minutes.
The model climbs to the max attainable altitude based on meeting a number of functions.
1. The aircraft must be able to climb at least 600ft/minute at max continuous thrust ( there is a function to broadly determine thrust lapse based on velocity and local air density).
2. It must be within the aircrafts max allowable altitude.
3. It must allow the aircraft to have suitable buffet margin. I have a function involving Mcrit, lift coefficient, wing sweep, wing thickness and assumes a level of ‘peakiness’ from a modern supercritical aero foil.
I don’t think this is working over this scenario. The aircraft should be stepping throughout the flight, at each step the L/D and TSFC will change. As fuel is burnt off L/D will also change. The 787/A350 also have variable camber wings which enables near optimum L/D to be maintained by moving the CP as weight is reduced (reduces drag from horizontal stabilizer).
Could I suggest EDSU 73019 and “Aircraft conceptual design synthesis” by Denis Howe are useful references. The book by Howe has spreadsheet methods for range analysis included.
One of the reasons that the 777 seems often to go fast in my models is that (particularly for the 77W) when it has to be low at the start of cruise and the aircraft hasn’t yet reached the tropopause it cruises at a constant Mach which is higher in the hotter air (standard atmosphere model is used).
Which in reality probably is not accurate, more likely to see a constant TAS of around 485 KTAS on the 77W below transition to Mach 0.84 which is LRC (FL300 M0.81, FL320, M0.82, FL340 M0.83 FL360 M0.84), in airline operation the aircraft would fly between Mrc and Lrc at ECON speed. The A350 would be ballpark 5 kts faster, initial climb after takeoff to FL340 and maintaining 0.84 (490 KTAS).
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