Tufts are probably the best way to visualize the unsteady flow near
stall (as long as the tufts are not so large that they affect the flow.)
The tufts show when, where, and how the wing actually stalls. The
flight can be straight ahead, in a turn, with an accelerated entry, ...

The real question is, when does the wing stall and how can information
be passed to the pilot to avoid the stall?

Tufts are not a very practical method in normal operation, but they are
great during the development of a aircraft.

Airspeed has been used widely as the indirect means to avoid stall.
Airspeed is readily available on any glider and by using a relatively
simple weight and bank angle correction, one can determine a safe airspeed.

AOA vanes on the fuselage are often used on a range of powered aircraft.
On commercial ones, these are often linked electronically to a stick
pusher in the cockpit to inhibit stall.

Some small airplanes use leading-edge vanes on the inboard wing and I've
even seen a small vane on the upper aft portion of the wing on a 1947
Bonanza.

If you are concerned about circling flight, a long-span glider flying in
a moderately-tight circle, a fuselage-mounted AOA or one on the inboard
wing would be somewhat useless, since the inboard wing would stall well
before reaching the critical AOA at the fuselage. So now we need
multiple sensors, one at each wing tip and possibly one or two at the
fuselage with a complex set of electronics and software to sort all the
data out and decide the proper answer to give the pilot.

Then there are the atmospheric effects. Say you're flying along on
final into a strong headwind (common here in Kansas) and you encounter a
significant wind shear. This could be caused by a frontal passage or
gust from a nearby storm that you are trying to avoid, but more likely a
simple wind shadow from a hill, a row of tall trees, a hangar, ... You
go from 15 or 20 knots above stall speed to 5 knots below in a matter of
a couple of seconds. What sensor would alert you quickly, reliably, and
give you extra time to react and avoid the stall?

Most of the fatal and serious injury accidents occur while setting up
the landing pattern when the glider is allowed to slow too much and go
to too large an AOA. If I were want to equip my glider with a warning
system, and a purely uncertified one at that since I do know first hand
about certification in my day job, I would use a simple differential
pressure sensor to measure the airspeed from the delta between total and
static pressure and use electronics to trigger an audable warning
whenever the airspeed was less than say 12 knots over 1-g stall (not too
loud though, maybe my wife's voice saying 'Speed Up'). I would only
turn this system on when I enter downwind and am preparing to land.
Extra info when most needed.

Just my 2 cents worth,

...... Neal

Bill Daniels wrote:

Tufts are good and yes, students should see them.

However, tufts show boundary layer behavior not angle of attack and
streamlines. Start with the little smoke tunnel in the classroom and then
show them the tufts in flight.

Bill Daniels