The artificial horizon (AH) will only tell you if you are climbing or
descending. It works on the direction you are travelling in.
Most larger aircraft will have an angle of attack device, either a
vane or probe, mounted on either side of the nose. This can be used in
a stall warning system.
Stall angle is not as simple on high speed / high altitude aircraft
as it is to low speed / low altitude aircraft like gliders. Unlike
gliders where the stall angle is a constant, an airliner cruising at
~Mach 0.8 (give or take a bit) stall angle is a complex variable. At
those mach numbers it doesn't take too much accelleration of the air
flow over (and under) the wing to exceed Mach 1. The presence of
strong shock waves on the surface of the wing can greatly alter the
lift. The typical affect is that the stall angle is greatly reduced.
(Note that the lift that the wing produces per degree of angle of
attack increases with Mach number up to a certain point which can
compensate a bit.) Note also that when the airliner is low and slow,
the stall angle returns to a relative constant as per what we are used
to as glider pilots.
Stall angle gets really complicated and modern airliners will have a
computer to work it all out and provide warning to the crew. Most of
the time this takes the form of a 'stick shaker' - a system which
mechanically shakes the control column to alert the crew.
it is not the first time that this has happened in recent history. I
read in an Air Safety magazine relatively recently that an airliner
pilot on approach into Alice Springs encountered stall warning twice.
The first time he tried to power out of it as allegded with the Air
France crew. the second time he remembered to lower the nose as well.
On Mon 30/05/11 12:26 PM , DMcD slutsw...@gmail.com sent:
I know nothing about nothing which is probably apparent from my
postings, but can someone tell me, do instruments like an artificial
horizon give these pilots any indication of nose angle or angle of
incidence?
I was attempting to explain a stall like this to #2 wife and had
difficulty understanding why they did not put the nose down or look
at
an instrument to tell them their AOA since they would have had some
minutes to think about this during what appears to have been a tail
down plunge.
At least if the SOPs have changed, I can persuade her to get on
another plane.
D
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