Boeing’s 777X analyzed, Part 4

Discussion
777 and A350-1000 compared

When comparing the performance of aircraft it’s useful to look at how they compare physically. It gives a feel for the differences and how these will affect the performance.

We start with the present 777-300ER and compare it to the A350-1000, Figure 2.

Figure 2. The 777-300ER (purple) overlaid with the A350-1000 (yellow). Source: Leeham Co.

We can see the 777-300ER (purple, below) and the A350-1000 (yellow, on top) are almost identical in size. The 777-300ER fuselage is a bit wider at 6.20m compared with 6.02m but their lengths are almost identical.

When operated as nine-abreast economy cabins, the A350 cabin is more efficient as its emergency exit concept only uses four door pairs against five for the -300ER (each door pair needs cross aisle escape routes which block space for seats).

When configured with a 10 abreast economy section, the extra seat in each seat row compensates for the extra emergency exit space and the aircraft have similar seating capacity.

The wings are also similar with the same span and a wing area (both at 64.8m span and 460m2 wing area, measured with the same methods).

The A350-1000 is 15 years younger in its design with CFRP (Carbon Fiber Reinforced Polymer) structure and more efficient engines. This makes it 14 tonnes lighter and its seat mile fuel consumption is 22% lower than the -300ER, measured with identical 369 seat cabins (54 lie flat business seats and 315 economy seats).

777-9 versus A350-1000

The 777-9 is a larger aircraft than the A350-1000, Figure 3. Its fuselage is longer and wider and it has a wider wing and horizontal tail.

Figure 3. The 777-9 (purple) overlaid with the A350-1000 (yellow). Source: Leeham Co.

With fuselage and center wingbox of aluminum, it’s 22 tonnes heavier than the -1000. The heavier aircraft is equipped with a 71.8m span wing, which lowers the drag due to weight (induced drag).

Combined with later designed, more efficient engines it gives the 777-9 a 3% lower eat mile fuel consumption when both aircraft are equipped with our Normalized two-class cabins (60 lie-flat business seats for the 777-9 versus 54 for the A350-1000 combined with 354 economy seats versus 315 seats).

This is valid for long flights. For the typical average sector length for this kind of aircraft, around 3,000nm, the lower weight of the A350-1000 evens this out to 2%.

With the seat mile costs at similar load factors within 3% and the aircraft mile cost of the smaller A350-1000 9.6% better, which one to choose is a question of the capacity needs of the airline on its route structure.

777-8 compared with A350-1000

The passenger capacity of the 777-8 and the A350-1000 is similar at 369 seats for the A350-1000 versus 354 seats for the 777-8. Both then use our Normalized two-class cabin with 54 life flat business seats, with the balance economy seats. But they achieve this in a different way, Figure 4.

Figure 4. The 777-8 (purple) overlaid with the A350-1000 (yellow). Source: Leeham Co.

The 777-8 (purple, below) has a shorter fuselage than the A350-1000 (yellow, on top). Instead, it puts the economy section at 10 abreast instead of nine abreast for the A350-1000.

As before, the 777-8 fuselage and center wingbox are aluminum. Together with a larger wing and empennage (all made from CFRP), the 777-8 is the heavier aircraft by about 15 tonnes.

The large span wing and efficient engines can’t quite compensate. The seat mile fuel consumption of the 777-8 is some 6% higher than for the A350-1000 on the typical 6,000nm long-range routes. On shorter routes like the typical average 3,000nm route, this increases to 7.5%.

The wide wing and efficient engines give the 777-8 Ultra Long Range capabilities. In a typical Ultra Long Range configuration of 74 lie flat Business class seats and 106 premium economy seats the 777-8 can fly for 22 hours, covering a distance of 10,000 nm. It’s large wing, coming from the 777-9, means it has the fuel to fly these long distance, without being fuel limited.

The A350-1000 can also fly such distances but its ultimate range is limited by the fuel quantity. Flying the same distance and configured for the same Ultra Long Range flights, it needs an additional 10,000l fuel in cargo bay tanks.

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