Most airlines don't opt for the aux fuel tanks because there are very few routes in the world that actually need them, and they add to aircraft weight and take up rear cargo compartment space when not in use. The economic reality is that any ULH route that would necessitate use of those tanks is probably a non-starter to begin with as they're incredibly difficult to generate a profit on, regardless of the capabilities of the aircraft involved.

 

-jp

Queensland

And

Northern

Territory

Aerial

Services

 

which gives QANTAS (minus the U)... B)

 

....Oh if I had a dollar for everytime someone spelt it wrong. :Money Eyes: :Money Eyes:

KWUONTISS

http://www.lockheedmartin.com/content/dam/lockheed/data/aero/documents/global-sustainment/product-support/2012HOC-Presentations/Tuesday/Tues%201400%20Marshall%20Aerospace.pdf

 

The 2nd generation tanks (for 744ER) are explicitly "dual-wall honeycomb" construction. The 3rd generation (77L) looks to be constructed with the same materials. It's likely a kevlar/aramid composite of some sort. Honeycomb structure is renowned for being resistive to out-of-plane shear and compressive forces for its weight and is a good choice for a fuel tank design.

Thanks for that, interesting read. Honeycombs could be fully metal (see also e.g., F28, Breguet Atlantic), but it does look like they were using composite here. I was kind of surprised, because usually fuel and resins don't play very nicely together. I guess they must solve that problem with a liner.