MANAGING ANGLE OF ATTACK
Acknowledgements:
AIR FACTS/Richard Collins
Richard offers the following thoughts on the
subject of AoA:
“Managing angle of attack (AOA) is a critical
element in flying safely but it often isn’t emphasized enough in training.
Make no mistake though, it is real and a pilot who understands
only airspeed control is lacking in basic knowledge.
When I was instructing I put a lot of emphasis
on students understanding angle of attack. This was critical in the lower
powered airplanes with not a lot of margin between cruising and stalling
speed.
I told my students that the angle of attack in
level flight was the difference between where the nose is pointed and
where the airplane is going. Power back and slow down and the
nose might be high but the altimeter steady or showing a decline. Push
that difference between where it is pointed and where it is going up to about 18 degrees and the airplane would
stall.
The plot thickens in level turning flight, where
the relative weight increase because of G-loading results in an increase
in angle of attack. Most pilots are aware that stalling
speed increases a bit in a 30-degree bank and a lot when the
bank becomes even steeper as the g-load in a level turn increases, but
I tried to put across that while the stalling speed might vary based
on conditions, the stalling
angle of attack is a constant.
In virtually all low speed loss of control
accidents, the pilot was pulling back on the elevator control when control
was lost. Back stick
increases angle of attack. A pilot should not need instrumentation to
tell him when angle of attack is encroaching on the stalling point, but
maybe the number of this type of accident suggests that pilots do need
help, even though this should be relatively easy for a pilot
to visualize.
I actually had an angle of attack indicator in my
Piper Pacer in the 1950s. It showed angle of attack on an instrument.
It had a tick mark, and when the dial was on that the angle of attack was
presumed right at the value for maximum lift. If the dial was to the right the
angle of attack was less, to the left it was more. Max. performance climbs
and short field approaches were flown with the needle on the
tick mark.
All airplanes do have a form of AOA instrumentation
in the stall warning indicator, which simply tells you that the AOA
is nearing the stalling point. The stall warning is supposed to sound
five knots above the stall, even though the stall warning itself is based
on angle of attack and not airspeed.
So, would angle
of attack instrumentation help to reduce the number of stall/spin
accidents? I don’t
know, but the fact that most of
the airplanes in these accidents have stall warning systems suggests
otherwise. It seems to me to
be more of an area for education.
Also, the criteria for the stall warning to
sound might need to be revised upward and relate to angle of attack
instead of airspeed”.
FLY SAFE!