Replies

Definitely looks different from the wings on the 744.

In addition, how difficult would it be for the engineers at Boeing to extend that upper deck all the way back to the tail, if they really needed to?? I am guessing that it would not be all that difficult. If Boeing truly needed to have an aircraft to compete with the A380, I am guessing it would be fairly simple for them to transform the 747, and avoid having to design a completely new aircraft from scratch.

In addition, how difficult would it be for the engineers at Boeing to extend that upper deck all the way back to the tail, if they really needed to??

I'm not an aerospace engineer, but from what I've read, the hump is optimally placed in front of the wings. If it were moved back farther, it would increase drag. Boeing has some artists renderings of using the existing space behind the hump for crew rests, passenger bunk suites, conference centers and food cart storage areas.

Several years ago, Boeing actually had plans for a stretch version of the 747 that would have seated well over 500 passengers and competed with the Airbus A380. Airlines did not show any interest, so the project was dropped. The plan was to add plugs to the main fuselage that would have extended the length by around 35 feet, IIRC. The "hump" on top was to remain about the same length.

Back in the 1980s, McDonnell-Douglas had plans for a double decker (the "MD-12") that would have seated around 600 passengers. Again, there was not much interest in the plane. Based on the drawings, it was a far better looking aircraft than Airbus's whale jet.

The verdict is still out whether the A380 will even break even (especially considering the huge discounts reportedly given to the early customers).

In addition, how difficult would it be for the engineers at Boeing to extend that upper deck all the way back to the tail ...

... from what I've read, the hump is optimally placed in front of the wings. If it were moved back farther, it would increase drag.

This is correct. In the early 1980s Boeing looked into a full-length upper deck, but the drag was too high.

The reason for this is something called "The Area Rule". It regards something called "form" or "bluff" drag. Think of slicing the airplane into sectional views. If you can keep these sections at a constant area (which means a skinnier fuselage where the wings attach), the drag is reduced. This is why some 1960s era fighter jets had a "wasp waist". This is a factor for high subsonic speeds. On most airliners, which have a constant fuselage cross-section, this is hard to do. You see it more on large military cargo aircraft like the C-5, C-17, and the big Russian planes.

As for the "guppy-ized" 747, in the case of oversized cargo, you just have to throw the rulebook out.

BTW, I am not an aerospace engineer, but I do have an aerospace engineering degree.