"Neil Gould" wrote in message
...
[...] Any discussion about other forms of
flying, whether it be in hovering Harriers or personal batwings are
irrelevant to that context.

Then perhaps you should take that up with the person who brought up such
examples. Todd was not that person. Oh, wait...it was YOU that mentioned
the F-18.

(Minor nitpick: I don't recall for sure whether the F-18 actually has more
thrust than weight; I believe that the F-16 does, and it's the only airplane
I understood to have that characteristic. I will continue saying "F-18" in
this post, with the assumption that you know for a fact it also has more
thrust than weight...perhaps it's just one of the later models, like the
Super Hornet, that does).

I wasn't claiming that it does. It's just that the amount of lift after
stall isn't sufficient to be relevant.

That's a false claim. As the lift drops off in a continuous manner, there
is a region "after stall" where the lift coefficient is just as high as
usable regions "before stall".

You may equivocate on whether a pilot can maintain the airplane at the
angle-of-attack required to obtain that "after stall" coefficient of lift.
But the fact remains that the lift is theoretically obtainable. As long as
you don't want a lift coefficient very close to the maximum lift coefficient
for the wing, it may not even be that hard to obtain the desired
coefficient.

There are, of course, other issues. The graph I'm talking about is
actually the lift coefficient graph; actual lift depends on the lift
coefficient (angle of attack) and airspeed. Drag increases
dramatically at stall, and it would require a lot of extra power to
maintain an airspeed sufficient to produce lift equal to the
airplane's weight, flying just past the stalling angle of attack.
But it certainly is theoretically possibly.

Of course, if you have enough power. That's why my original reply stated,
"Think F-18..."

I fear we're back to square one. The F-18 has more power than is necessary.
You only need enough power to overcome the drag. You don't need enough
power to overcome weight, which is what you seem to be saying.

This theoretical possibility isn't very relevant to the
context of the post to which I originally replied, e.g., "full-stall
greased landings" in a typical SEL.

Sure it is. It discusses the actual aerodynamics, allowing someone to
consider what would be required to make a "full-stall greaser". Physical
characteristics of most airplanes preclude actually stalling the wing when
in a safe landable position (mainly the issue of the tail winding up too low
for a safe landing), but otherwise there's no obvious reason one could not
only make a "full-stall greaser", but could actually *fly* the airplane onto
the runway in the stalled condition.

In fact, if anything (again, ignoring the geometry of the situation) the
landing scenario is the most likely scenario in which a pilot could maintain
the post-stall condition, since ground effect would dramatically reduce
induced drag, induced drag being a primary reason that maintaining the
airplane in a flying condition past the stall is so difficult.

Of course, as Todd correctly pointed out, the physical geometry of most
airplanes preclude stalling the airplane when in a position for a safe
landing (ie just above the runway). But you incorrectly attempt to dispute
that as well.

The AOA is the "angle-of-attack". It's not a vector at all, never
mind the one you describe. It is true that the AOA is relative to
direction of travel through air (ie the "relative wind").

One doesn't have directional motion *without* a vector. ;-)

I never said there were no vectors. I said the angle-of-attack is not a
vector.

"Vector...Etymology: New Latin, from Latin, carrier, from vehere to
carry -- more at WAY
1 a : a quantity that has magnitude and direction and that is commonly
represented by a directed line segment whose length represents the
magnitude and whose orientation in space represents the direction..."

When in doubt, post a definition? Seriously...what purpose was that
supposed to serve?

When one refers to the "angle of attack" (and, yes, I know that "AOA" is
the acronym), one is definitely referring to motion having both direction
and magnitude.

No, they are not. The angle-of-attack is a specific angle, measured between
the wing's chord and the relative wind. In fact, a motionless airplane can
still have an angle-of-attack, just as long as there is some wind.

"Relative wind" is just a non-technical way to state this.

Actually, "relative wind" is a *technical* way to state the apparent wind
relative to the chord of the wing. But angle-of-attack is something else
entirely. Relative wind is indeed a vector. Angle-of-attack is not.

However, it would have been better stated if I had said "... relative
direction of _the wing's_ travel...", even though the typical SEL's wing
pitch isn't drastically different from the rest of the aircraft. ;-)

The angle of incidence (which is what you appear to be talking about
now...that is, the angle between the wing chord and the longitudinal axis of
the airplane) is yet again something else entirely different from
angle-of-attack. The phrase you suggest as a replacement for
angle-of-attack (that is, "relative direction of _the wing's_ travel") would
not be a suitable replacement at all for "angle-of-attack", though it might
serve as an synonymous phrase for "relative wind".

The confusion here is not between the airplane's pitch angle and the wing's
angle-of-attack. It's your insistence on calling the angle-of-attack a
vector, when it's a scalar (and, it appears, your confusion between
"relative wind" and "angle-of-attack").

My reply specifically separates the AOA from any ground reference.

Actually, your reply implies that Todd doesn't understand that the
angle-of-attack isn't measure relative to the ground. He does understand
that, but the fact that angle-of-attack isn't measured relative to the
ground doesn't change the fact that you can't stall most planes while in a
position for a safe landing.

And it is true that with most airplanes, the
stalling angle-of-attack produces a pitch angle so nose-high that the
tail will hit the ground before the main gear does.

I responded to that. In the context of landing, if one flies slowly enough
to stall, one can stall "flat" relative to the ground because the decrease
in forward "relative wind" increases the AOA. That is what my remark
addresses.

Your claim is incorrect. As long as the airplane is flying just above the
ground, the relative wind is parallel to the ground. No change in the
angle-of-attack will occur from any decrease in speed, not directly.

It is simply impossible to do what you suggest one might do. If one "flies
slowly enough to stall", the angle-of-attack is at the stalling
angle-of-attack, period. Furthermore, if one flies at a constant altitude
(as one must do when landing an airplane, once over the runway), the
relative wind is parallel to the ground, and thus the airplane's pitch angle
is the same as the wing's angle-of-attack (ignoring the angle of incidence,
of course).

What WILL happen is that as the aircraft slows, the pitch angle of the
aircraft will need to be increased, so as to continually increase the
angle-of-attack of the wing. The increase in AOA increases the lift
coefficient, compensating for the reduction in airspeed to maintain a lift
force equal to the airplane's weight. If you do not increase the pitch
angle, the airplane will simply descend onto the runway.

You will not stall "flat" relative to the ground. Only one of two things
can happen in the scenario you describe. You will either prevent the
airplane from touching the runway by continually increase the
angle-of-attack (which means no stall "flat" relative to the ground) , or
the airplane will descend and touch the runway (again, no stall "flat"
relative to the ground). In *either* case, the airplane will touch the
runway before the wing stalls, assuming a safe landing.

You are certainly correct that an airplane can be stalled in any
attitude. But that in no way provides a basis for disagreement with
Todd's statements.

I think it does with regard to necessarily hitting the tail before
stalling.

You think wrong.

Pete