Airspeed Indication and Relative Wind

"Dan Thomas" wrote in message
m...
"Casey Wilson" wrote in message
.. .
"Scott Lowrey" wrote in message
news:35Cmc.33788$TD4.5609844@attbi_s01...
If I'm descending slowly with a relatively nose-high attitude - say,
in
preparation for a short field landing - does the high angle of the
pitot
tube have any effect on indicated airspeed? (I suppose all designs
are
different - say this is a 172.)

The effective area of the pitot orfice is reduced by the cosine of
the
angle of the pressure wave impinging on it. Presuming an angle of twelve
degrees or less [the stall AOA of most wings] the effective orfice area
is
reduced to 97.81% of the normal area. Short of a digital ASI, you
couldn't
tell the difference from the parallax error in reading the instrument in
the
first place.
In any case, the error is on your side, since the result is a lower
than normal[real] reading.

I think there's more than the cosine at work here. That
theory would say that at 90 degrees the pitot would generate no
dynamic pressure, but at (or even before) 90 degrees an open tube will
generate suction. I have flown airplanes at high AOAs, lots of power
on, and seen zero indication on the ASI; I don't think static error is
responsible for all of it.

Put the cigar back in the box, you don't earn it with your response. In
the conditions set by the original post [see top paragraph above] the cosine
function will be predominate. Extreme alpha is not relevant.