What is carryover lift?

[EZY_FR]

I have been doing some research on futuristic aircraft designs and came across the D8 "Double-Bubble" aircraft. One of the main benefits that this aircraft has over conventional airliners is the increase in fuselage carryover lift, which results in a reduction in the spanwise length of the wing.
http://web.mit.edu/drela/Public/N+3/tasaa.pdf

In addition to this, the nose design is interesting but confusing at best. Apparently the nose produces nose lift and a nose up pitching moment, thus a smaller horizontal tail can be designed. Can anyone clarify why this is the case, as I am very confused by it all.

[TURIN]

I'm guessing it's just the lift created by the fuselage on its own.
Interesting engine config. I wonder what the deep stall characteristics are? Not to mention engine changes.


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[Genghis the Engineer]

The tail classically generates a downforce, and thus a nose-up pitching moment.

So an upforce at the nose will have the same effect.


These "oddball" configurations are a mainstay of future projects work, and entirely conventional in that regard. They invariably however manage to miss a few big issues such a handling qualities (TURIN's deep stall), evacuation criteria, or simply the ability to park at a normal airport. Which doesn't mean there isn't value in looking at these things - just you need to be very careful to spot what's missing in any given feasibility study.

G

[EZY_FR]

I am still finding it difficult to understand how the fuselage nose has the ability to generate lift, when the velocity over the top surface has to be greater than the lower surface. When looking at it, it seems counter-intuitive, since the velocity would be much greater on the lower surface of the fuselage nose than the upper. Am I looking into this too much guys? http://2012.oversetgridsymposium.org/assets/pdf/presentations/1_4/D8_reducedSize.pdf (page 24).

[Genghis the Engineer]

No, too little.

You are applying the very simplistic PPL explanation of lift to a situation that doesn't allow for such gross simplification.

Slide 28 of that presentation shows the result, which seems intuitively correct to me - but is based upon a far more complex explanation of lift than anything seen on any pilots licence syllabus, or the first couple of years of most undergraduate degree courses.

G