Yes. So? Not relevant to the statement you quoted (which was about
thrust).

The issue under discussion was how much less lift was needed when
thrust supported some of the weight of the aircraft. The reduction in
necessary lift could accommodate a lower airspeed at the same AOA, or
a lower AOA at the same airspeed. But, as you said, the reduction in
lift is not a whole lot.

It would have been nice of you to provide the name of one popular
(i.e. easy to find) one, so that I can read up on it.

It's not always easy to find a reference to something I've read; I
often lose hours doing so. Anyway, here's one: "Introduction to
Flight", by John D. Anderson. p. 290. Quote:

"As seen in this example, for steady climbing flight, L (hence Cl) is
smaller, and thus induced drag is smaller. Consequently, total drag
for climbing flight is smaller than for level flight at the same
velocity."

Still, there's not much "unused AOA" in the regime of flight we're
talking about, nor did David suggest that might be required (his
implication, to my reading, was that his suggestion applied ??

True

But the reason I don't want to believe is that the proposal bears no
resemblance to the behavior of any airplane I've flown, not while I've
been flying it anyway.

If the effect exists, I agree that it would probably be small and
might well be lost in the wash.

I'd be more than happy to see someone step in with some real math
that shows the answer one way or the other.

Anderson shows some numbers. I hate trying to depict the math in this
forum, because it looks so ugly.

I don't happen to be patient enough with the math. There's a reason
that, when I was working on my math degree,

I only delve into math when the concepts are not clear. Putting some
numbers to the theory makes things real sometimes.

That is, he's proposing that at the same speed, there are multiple
steady states that produce different amounts of drag.

There are precedents. A banked aircraft at a given airspeed will have
a larger AOA than a non-banked one, and thus incur larger amounts of
induced drag.

I envision that a climbing airplane is essentially a lighter one,
since thrust will support a small amount of weight.

Still, I'm boggled by the lack of induced drag in a wind tunnel. If
the wing's not creating lift (0 AOA), I can see how there wouldn't be
induced drag. But this would happen in the real world too. If the
wing is creating lift, shouldn't there be a measurable force parallel
to the relative wind? Even in a wind tunnel?

I should qualify that. The great body of wing sections that NACA
tested in the early part of the last century were placed flush against
the walls; no wingtips. It is the wingtip vortices which cause the
local relative wind to be different from the "real" relative wind.
Absent that, the total aerodynamic force is perpendicular to the
incoming freestream.

They did this intentially, since the actual induced drag on a real
wing will depend on its aspect ratio. Better to make their data
"pure" and allow builders to adjust it to fit their specific
planforms. There is still drag, of course, but just not induced drag.