On Sep 7, 1:46*am, Darryl Ramm wrote:
On 9/1/11 2:44 PM, Bill D wrote:
[snip]

This is yet another case where an angle of attack indicator with stall
warning stick vibrator would have saved a life. *Tiny cellphone/pager
vibrator motors embedded in the stick grip would be an excellent stall
warning.

I have no idea how you know enough about what was going on with the
aircraft and its pilot (especially inside his head/his perception of the
aircraft situation and flight performance) to know he would have
responded to a stall warning device appropriately and in time to
prevented the crash.

I would like to think maybe there is a stall warning device that might
be developed but I am pessimistic about the effectiveness of these
devices and false alarms while thermalling. And I am a bit bemused by
the mention a *small cellphone like shaker device to vibrate the control
stick. Many of our gliders give us some pretty good signals about an
impending stall. And in situations like where people are being killed in
pull-up/turn or flat over-rudder turns to base etc. I expect these
accident pilots are so far behind their aircraft that a subtle warnings
(e.g. vibrating the stick with a small shaker) would not be noticed. A
loud alarm or voice alert might at least have a chance of registering at
all with the pilot but whether the warning can be issued to allow them
enough time to react and whether the pilot will react correctly who
knows... (e.g. in a heading towards the dirt "ground rush" situations
the pilot has to sort out an audible stall alert vs. a pretty strong
visual cue that causes them to likely want to pull back and its not
clear what they will do).

I suspect something that is going to help the pilot who is well behind
their glider will require fairly loud/very obvious warning with a decent
pre-stall margin and that risks being annoying when thermalling slow.
e.g. its unclear if a system would be airspeed or AoA based, but
spoilers open often increase stall speeds *by a few knots so does the
stall warning need to know the spoiler position and factor this or do
you just pad the stall warning by a few more knots and further increase
false alarms/disturbances when thermalling? Flap position needs to be
factored as well on flapped gliders. If somebody is far enough behind
the glider and doing something that is about to bite them then how much
warning margin before the stall is actually needed to give the pilot a
good chance of avoiding or recovering faster/more effectively from the
stall/spin? Will those warning margins added together cause lots of
false alerts when thermalling say 10 knots above the stall in a gusty
thermal? And although I want something really obvious like a loud beep
or similar for a stall warning I also don't want noises that might be
confused with a FLARM/PowerFLARM alert while in a thermal.

There are glider stall warning systems available today, so the the
question may really be how do these systems work in practice and why are
there not more of them in use. DG built a visual and audible stall
warning system in the DG-600 and they have a stall warning in the DEI-NT
(and DEI??).

Safe Flight have their vane driven AoA meter which has an audible alarm
but besides seeing one installed in a glider at the SSA show in
Albuquerque a few years ago I have never hear of one of these installed
in the wild, or of a glider manufacturer offering these as options.
Anybody know any different? Or know what these cost? I believe the
fairly large vane is removable but how easy is it to damage e.g. on
ground handling?

The Cambridge 302 *has a stall warning based on pitot airspeed, wing
loading (it knows the % ballast) and G-meter (but it does not take into
effect flap or spoiler position). I used a C302 in my DG-303 and ASH-26E
and in both cases turned down the warning airspeed because it produced
too many false alarms while thermalling, based on my own use I don't
think its a useful tool for real stall/spin avoidance. Other pilot's
have experiences/opinions with the C302 stall warning?

So who has actually flies with any of these or other stall warning
indicators today and how useful have they found them? And do you think
they will be useful for preventing some of the
behind-the-aircraft/confused pilot stall/spin accidents we've seen?

I know there are these videos on YouTube athttp://www.youtube.com/user/DT38000?blend=23&ob=5, I assume showing the
DG DEI system alerting but without more information like the airspeeds
and seeing the glider thermalling I can't really draw any conclusion at
all from the videos.

In the meantime, looks like instructors doing BFRs and spring checkouts
next year have lots and lots of stuff to go through that may save
lives... from tow-signals to stall/spin aerodynamics, recognition and
recovery.

Darryl

How do I know it works? Because it works and is therefore considered
essential in hundreds of thousands of airplanes.

So, what solution do you propose?

I'm trying to think of ways to save lives. What is your objective?

The "lets train them better" idea has been around 100 years with
generally dismal results. The stall warning device idea has been
around probably 50 years and works well enough it has been widely
adopted throughout the aviation world. Only the gliding world has
successfully resisted stall warning devices and we pay for it in our
accident record.

Stall sensors could be either airspeed or AoA based. A simple and
rugged sensor is a pair of pressure ports on the top and bottom of the
nose cone. The differential pressure between these ports is
proportional to AoA.

Would there be false warnings? Of course there would. It happens on
light airplanes but there's no confusion since a intermittent warning
in rough air has an obvious and benign cause. A steady warning at low
airspeed signals an impending stall. If an AoA display is part of the
system, a glance at it would show the cause of a warning.

It's also possible to set sensitivity depending on the phase of
flight. If the gear is down signaling an impending landing, the
warning could be more sensitive sounding at a lower AoA/higher
airspeed. Our computers detect thermalling and set themselves to that
mode automatically - they could also set the stall warning to be less
sensitive when thermalling.

If a stick vibrator isn't sufficient, adding a bright light to the
glare shield or audible warning would be easy. It could even be set
so the vibration starts early to be followed by a loud warning if the
dangerously high AoA condition persists. This could avoid annoying an
attentive pilot while providing an unmistakeable warning to the
distracted pilot.

It is so easy for people to set back and think of reasons why
something might not work while never putting forward one which would
work. They never have to prove an idea won't work, they just raise
doubts by suggesting it might not work perfectly every time. They're
called "Negative Experts".

A stall warning device doesn't have to work every time. If it saves a
life 10% of the time it would be worthwhile. Good research says it
will work far more often than that.