AOA; scalar or vector, resolved.

[Neil Gould]

Hi all,

In a tangent many times removed from the original "Who does flight plans?"
thread, I became entangled in an argument about whether "AOA was a scalar
or a vector". Not finding an adequate resource off-line that clearly
resolved the issues involved in assigning either term as a valid math
definition, I went to the alt.math newsgroup and posed what I thought was
the essence of the problem that lead to my confusion. Thanks to the
discussion that followed, I now understand the reason for my confusion
over this matter. Anyone interested in the details can find the discussion
there.

In the end, it was D. Watland's response that provided the clarity that I
needed to put this to rest. In our discussion, we were apparently speaking
in jargon, not math terms. If we had said, "Angle of Attack is a
_variable_ whose value is expressed as a real number...", there would
probably have been no argument.

My apologies to all whom I said were "wrong" about calling AOA a scalar
instead of a vector.

Best regards and blue skies!

Neil

[Gary Drescher]

"Neil Gould" > wrote in message
.. .
> In our discussion, we were apparently speaking
> in jargon, not math terms.

No, we were using math terms (and math terms *are* a jargon, i.e., a
technical terminology). It's true though that your reference to undefined or
null values in the alt.math thread was a mishmash of math jargon and
computer jargon, as Watland pointed out.

> If we had said, "Angle of Attack is a
> _variable_ whose value is expressed as a real number...", there would
> probably have been no argument.

Since you're interested in the terminology, it should be noted that an angle
of attack is *not* a variable, though we can certainly define a variable
whose *value* is an angle of attack, which is a real number. For example, we
can say "Let x equal the angle of attack of this airfoil...".

If an angle of attack were itself a variable, then it would not be correct
to say "the angle of attack is five degrees". Instead, we'd have to say "the
angle of attack has a value of five degrees". In fact, though, that would be
wrong--five degrees *is* the angle of attack. (Similarly, it's correct to
say "my height is 1.7m", not "my height has a value of 1.7m".)

In the case that you were asking about in the alt.math thread (the case
where there is no relative wind), there simply is no angle of attack to be
spoken of. It's analogous to vaporizing you in an atomic explosion and
asking what your height is *then*. It's just undefined. And that doesn't
mean that some "undefined" token is then your height. Rather, it means that
there just isn't any number (or any other object) that is then your height.

But I'm glad we now agree that AOA is a scalar, even if we don't quite agree
on how to reach that conclusion. :)

--Gary