Is the 777 more fuel effiecent that the 747-400? I've noticed United Airlines has started to assign more and more of there long hauls to the T7 instead of of the 747-400. The LAX-NRT route used to be operated by the 747 now it has since been replaced by the T7. I sure hope this isnt a sign they are preparing to phase out the 747.

Twin-engined aircraft are inherently more fuel efficient than four engined aircraft:

1. Half the engine pylons. so less drag and less weight
2. Less engine nacelle cirumference per square foot of intake surface, so again less drag and less weight per unit of thrust

The ony reasons 3- and 4-engines aircraft were made:

1. Engines were not powerful enough to allow for 2-engine take-off, and
2. Engines were not reliable enough for transoceanic flight.

Finally, the T7's engines are newer and newer engines are always more fuel efficient (otherwise the huge R&D expense to develop them would not be justified.) Cheers, - jahman.

Whilst most of that is true, let's not forget that you do need to make the wings heavier and more robust on an aircraft with only two engines than you do with four, in order to resist the bending forces on the wings when they generate lift, which the weight of the engines counteracts. Thus the reduction in weight from having less engines is not gained for nothing, since the outboard wing spars have to be stronger and the skin panels have to be thicker on a twin-engined jet; all that beefing up of the wing structure takes up more room in the wing's internal spaces, leaving less room available for fuel tankage. Modern composite materials have circumvented that problem to some degree and the reduced amount of plumbing necessary for additional engines offsets things a little too, but it is nevertheless a design consideration which sees it not being as simple a choice as it would appear on the face of things. It was in fact that consideration in the era before composites were a practical choice, and the necessary beefing up of the tail, which saw Boeing decide to drop their planned tri-engined version of the 747 (the 747-3) which would have had two wing-mounted engines and a third engine in the tail in a similar arrangement to the L-1011. Al

it is surprising with these facts that twins are more efficient, yet airbus released the massive A380 and Boeing is now working on extending the 747 project by releasing the 747-8.

it is surprising with these facts that twins are more efficient, yet airbus released the massive A380 and Boeing is now working on extending the 747 project by releasing the 747-8.

No, it's not surprising at all:

1. Airbus estimates the market needs an aircraft significantly larger than the 747, and
2. Today's engines are not powerful enough to make an aircraft the size of the 380 with only 2 engines.
3. The 748 is a low cost stretch to compete with the 380, because
4. Boeing doesn't consider the size of the large-haul, hub-centric shorter routes to justify the investment in a super-jumbo, prefering instead to
5. Design twin engine aircraft to bypass the hub-andspoke system for longer-haul city pair routes instead.

Items 1 and 2 are a repeat of the design decisions of the 747, albeit at a larger scale. Cheers, - jahman.

The efficiency the airlines look at is the cost per seat per mile. 1. If a 777-300ER and a 747-8i both fly the same route with 300 passengers, the 777 will consume less fuel due to less drag. The cost per seat mile will be lower in the 777.2. On the other hand, if the 777 is carrying 365 passengers (full load) and the 747 is carrying 467 (full load) on the same route, The 747 will consume more total fuel, but when divided by the number of passengers, the 747 will have a lower cost per seat mile. In fact, Boeing claims that a fully loaded 747-8i achieves the lowest cost per seat mile of any airliner. The A380 carries more passengers, but because it is a considerable heavier aircraft, it has a higher cost per seat mile. Other factors airlines have to consider besides fuel are maintenance of 2 vs 4 engines, landing fees, landing slots and loads on a certain route.On some routes, ETOPS regulations might cause the 777 to fly a longer distance and consume more fuel. Ben