LR/ULR Twins or Quads?
In my simplistic world view I always considered a 4 engine aircraft to be the optimal for long /extreme range ie. 5000-8000nm legs. This was due to my understanding of the twin having to be so overpowered at T/O to get the weight off the runway in the event of an engine failure ,that it was overpowered for those 10/12/14 hour legs up at altitude.A quad would jump off the ground in a less sprightly manner but could sit up there more happily with its engines less throttled and therefore more efficient.
However with the latest 777ER/LRs beating the socks off the A345/6s it seems I may be missing something .
Anyone care to explain? Is it advances in engine technology or something else?
Also how much do structural considerations affect this debate? Surely 2 engines require bigger fin/rudder assemblies for the assymetric case thereby increasing weight and what about the wing bending relief of 4 vs. 2 engines affecting the weight of the wing structure?