"Jim Macklin" wrote:
I don't care what you believe. Maybe I just wanted a heated
discussion to start

This is called being a troll, and is generally not something which most
people appreciate.

aircraft is slowed to near stalling speed by the application
of back pressure on the elevator which increases the down
force on the aircraft tail cone which levers the nose upward
by dynamically shifting the CG to a point behind the CP
which is the moment arm of the tail times the force produced
by the tail in an algebraic balance with the arm of the CG
and CP.

This is gibberish. The CG doesn't shift unless stuff moves around in the
airplane. A study of shifting loads (such as fuel sloshing around in
half-full tanks) would be a fascinating but very complicated endeavor, and
not particularly germane to this discussion.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude?

OK, I explained this once, but I'll do it again, slowly, and more carefully.

Let's invent a hypothetical airplane where the main wing stalls at an alpha
(angle of attack, AOA) of 18 degrees, which happens to be a fairly typical
number for the kinds of wings most of us fly. Let's also imagine that it's
got a symmetric one-piece stabilator (such as found on an Archer), which
also stalls at 18 degrees (positive or negative). Vso for this plane is 60
kts (that's a pretty high value, but it makes the math easier

Now, let's put the plane at the edge of stall in a typical power-off stall
demonstration. The main wing AOA is 17.9 degrees. The yoke is almost all
the way back, and the stabilator is set at an AOA of -15 degrees. Power is
at idle, true airspeed is 50 kts, and you're maintaining altitude.

Now, pull back on the yoke just a bit more. The AOA increases to 18.1
degrees, and the main wing is now stalled. The wing is now producing less
lift than the airplane weighs, so it starts to accelerate downward. After
a short time, it's in a 100 fpm descent, but we're still holding the same
pitch attitude.

If you work the math, 60 KTAS and 100 fpm down works out to a glide slope
of just about -1 degree, which means the relative wind is now coming from 1
degree below the horizontal. Since the pitch angle hasn't changed, the AOA
of both the main wing and the tail will change by this same 1 degree. For
the main wing, that means the AOA has been driven from 18.1 degrees to 19.1
degrees; further into stall, and further reducing the amount of lift being
generated (increasing drag too, but that's a secondary issue).

Now, here's the interesting part. The tail has gone from -15 to -14. It's
moved further away from stall. But, it too, is producing less (downward)
lift because the AOA is reduced. Less downforce from the tail means the
nose will start to drop. No tail stall, just reduced downwards lift from
the tail due to decreased tail AOA caused by the downward motion of the
aircraft.

That's it, I'm done. If you really want to be a troll, enjoy yourself.





If
the wing is stalled does the lift not decrease and thus the
CP force decrease? Would that not reduce the moment needed
to rotate the nose downward to regain flying speed reduce
the angle of attack)?

FAR 23 has design limits for control degradation, the rudder
must be able to yaw the aircraft at a speed less than
lift-off speed, the elevator must be able to apply forces
and even the ailerons have limits. But when the aircraft is
stalled, out of ground effect, what force or forces change
that cause the nose to pitch downward? The wing is
producing less lift which means that the moment produced by
wing lift also decreases, reducing the nose down force. The
tail was supplying the force needed to establish the
attitude and what would cause THAT forced to be reduced if
it is not at least a stall (partial or complete) of the
elevator?

If the aircraft is held in a stalled condition, with the
elevator full back and the aircraft has a stall break, the
nose drops and then the nose pitches back up and the stall
break happens again and again in a cycle, the pilot keeping
the elevator full back and the wings level with rudder and
some aileron if the ailerons still function, what change in
forces on the aircraft is causing the cycle? Did the wing
regain lift or did the tail regain down-force?