Airspeed Indication and Relative Wind

At high angles of attack the air flow pattern around the pitot tube is
modified by the wing and the fuselage. This is the biggest source of
error. Of course, the horizontal component of the free flowing air also
gets smaller (cosine of the AOA), but this is a minor effect as you just
demonstrated.


"Rod Madsen" wrote in
:

A normal glide slope is about 3 degrees. If you were doing a real
steep decent you might have a glide path of 6 degrees. Then, let's
say your nose is 4 degrees above the horizon giving us an angle of
attack for the pitot tube of 10 degrees. The cosine of 10 degrees is
about .985 meaning your airspeed indication might be 1.5% low. At 65
knots you ain't gonna notice a half knot.

Rod
"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.)

If the descent was steep, the relative wind would be coming from
below and forward with respect to the wing, right? Add the pitch
angle, and it seems like the pitot tube would be at a fairly angle
with respect to the direction of air flow. I suppose this is a
simple angle of attack question....

Seems like the air would be passing slightly "over" the pitot tube
opening rather than "into" it, thus reducing the measure air
pressure. Is this correct? Is indicated airspeed affected by high
AOA?

-Scott