AoA keep it going!

On 16 Dec, 15:22, "Bill Daniels" bildan@comcast-dot-net wrote:

The thing was a little messy. To see the smoke streamers clearly you needed
to be in a dimly lit room which quickly filled with kerosene smoke. That's
probably why it isn't used much anymore. Still, I'd love to have one.
Maybe a computer program could be just as good.

Everyone should -in my opinion - fly a tufted glider while training.

Ian

"Ian" wrote in message
...
On 16 Dec, 15:22, "Bill Daniels" bildan@comcast-dot-net wrote:

The thing was a little messy. To see the smoke streamers clearly you
needed
to be in a dimly lit room which quickly filled with kerosene smoke.
That's
probably why it isn't used much anymore. Still, I'd love to have one.
Maybe a computer program could be just as good.

Everyone should -in my opinion - fly a tufted glider while training.

Ian

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

On 16 Dec, 23:19, "Bill Daniels" bildan@comcast-dot-net wrote:

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.

Every gliding club should have a copy of "An Album of Fluid Motion" by
Milton Van Dyke!

Ian

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

This discussion needs to be divided into two subjects, stall warners and AOA
indicators. They are really two very different devices.

A stall warning device tells you that you've made a mistake. An AOA
indicator can tell you that you are about to make a mistake. A stall warner
is just a on-off binary device. An AOA indicator provides a continuum of
information across the whole speed range.

AOA tells you about safety margins and the rate of change of that margin. A
stall warning device doesn't - unless it's set at a large margin over stall
in which case it will be constantly triggered by turbulence and pilots will
turn it off. A Cessna-style stall warning would drive a pilot nuts if
installed in a glider.

The point that AOA varies across the span when thermalling is a good one.
Any device mounted on the fuselage won't provide data on the flow at the
wing tips. But, modern gliders have wings designed to prevent tip stall so
fuselage mounted AOA sensors are still useful. Damning AOA indicators
because they aren't perfect is a straw man argument. We have no perfect
instruments but they are still useful.

AOA indicators are better than ASI's at low speed where there are large
errors in airspeed indications but ASI are better at high speed for things
like Va and Vne. AOA indicators are faster responding and easier to
interpret. i.e. if the needle is in the yellow, push until it isn't. The
airspeed will take care of itself.

Maneuvering for landing in gusty wind shear is exactly where I'd want an
AOA. It will show the maximum gust induced AOA so the airspeed can be
increased just enough that no gust stalls the glider but not so much that
you'll need to dump a lot of energy in ground effect.


Bill Daniels




"Neal Pfeiffer" wrote in message
et...
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

Bill Daniels wrote:

Maneuvering for landing in gusty wind shear is exactly where I'd want an
AOA. It will show the maximum gust induced AOA so the airspeed can be
increased just enough that no gust stalls the glider but not so much that
you'll need to dump a lot of energy in ground effect.

Bill, have you used an AOA indicator in the conditions you describe?
What one was it? And how did you know the "maximum gust induced" AOA it
showed you was the maximum you were going to encounter before landing?

My experience with selecting the proper airspeed in gusty wind shear
conditions is it's better done with a rule of thumb, like "add one-half
the wind speed to the approach speed", or from experience, than a
measurement made (like controllability) when I am high enough not to be
in danger.

My other observation is it's not stalling that's the problem in those
conditions, but controllability: I'm usually well above stalling speed,
but fighting to keep the attitude correct, and especially the altitude
during the flare. I hate it when I'm slammed into the ground, so I
usually touch down well over stall speed.

I suggest 5 to 10 proponents of AOA meters, and other interested pilots,
buy some AOA meters (like from Safeflight, DG , Aircraft Spruce) as a
group. This will reduce the cost for each pilot to try several AOA
meters. Have each member of the group try each of the meter(s) for
while, then report their experiences.

Without experience with meters in cockpits in actual flying conditions,
we're just guessing about how useful they are.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

"Eric Greenwell" wrote in message
news:UCz9j.4239$Xh1.3090@trndny03...
Bill Daniels wrote:

Maneuvering for landing in gusty wind shear is exactly where I'd want an
AOA. It will show the maximum gust induced AOA so the airspeed can be
increased just enough that no gust stalls the glider but not so much that
you'll need to dump a lot of energy in ground effect.

Bill, have you used an AOA indicator in the conditions you describe? What
one was it? And how did you know the "maximum gust induced" AOA it showed
you was the maximum you were going to encounter before landing?

Yes, Eric. I've flown with very high quality instruments in airplanes and
jury-rigged "pitch strings" in gliders. The pitch strings don't work as
well as the expensive units but, aside from the hassle, they are nonetheless
very useful.

There's no big mystry about AOA indicators, they go back to the very
beginnings of aviation. They aren't common because of cost and difficulty
implementing them on small airplanes. Until now, nobody gave much thought
to gliders.

Just look at the jitter or swing in the needle/string. The max swing in the
positive direction is the max gust induced AOA. By the time you have flown
the pattern and are on short final, you should have a pretty good idea about
the level of turbulence you are dealing with and have selected a minimum
safe margin for the "over the fence" airspeed.

I've seen pilots who have no real knowledge of just what their gust-stall
margin is so they keep adding airspeed until it's a problem for them on roll
out. It does no good to have a wide margin over stall in the air only to
hit a fence on rollout. Just standing on the ground watching glider
landings shows a wide range of techniques. Some patterns look like a ground
attack fighter rolling in on a target. Others float around the pattern tail
low. I have to believe if they had an AOA indicator, they be more
consistent - or at least, have rational excuses.

In off field landings especially, it's a balance between stall margin in
the air and rollout distance on the ground. I practice a short landing on
every flight - partly to be ready for a possible off field landing and
partly because my trailer is near the approach end and I hate pushing back.
I'd love to have a quality AOA indicator to make those landings easier and
safer.

Bill Daniels

On Dec 17, 12:37 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
"Eric Greenwell" wrote in message

news:UCz9j.4239$Xh1.3090@trndny03...

Bill Daniels wrote:

Maneuvering for landing in gusty wind shear is exactly where I'd want an
AOA. It will show the maximum gust induced AOA so the airspeed can be
increased just enough that no gust stalls the glider but not so much that
you'll need to dump a lot of energy in ground effect.

Bill, have you used an AOA indicator in the conditions you describe? What
one was it? And how did you know the "maximum gust induced" AOA it showed
you was the maximum you were going to encounter before landing?

Yes, Eric. I've flown with very high quality instruments in airplanes and
jury-rigged "pitch strings" in gliders. The pitch strings don't work as
well as the expensive units but, aside from the hassle, they are nonetheless
very useful.

There's no big mystry about AOA indicators, they go back to the very
beginnings of aviation. They aren't common because of cost and difficulty
implementing them on small airplanes. Until now, nobody gave much thought
to gliders.

Just look at the jitter or swing in the needle/string. The max swing in the
positive direction is the max gust induced AOA. By the time you have flown
the pattern and are on short final, you should have a pretty good idea about
the level of turbulence you are dealing with and have selected a minimum
safe margin for the "over the fence" airspeed.

I've seen pilots who have no real knowledge of just what their gust-stall
margin is so they keep adding airspeed until it's a problem for them on roll
out. It does no good to have a wide margin over stall in the air only to
hit a fence on rollout. Just standing on the ground watching glider
landings shows a wide range of techniques. Some patterns look like a ground
attack fighter rolling in on a target. Others float around the pattern tail
low. I have to believe if they had an AOA indicator, they be more
consistent - or at least, have rational excuses.

In off field landings especially, it's a balance between stall margin in
the air and rollout distance on the ground. I practice a short landing on
every flight - partly to be ready for a possible off field landing and
partly because my trailer is near the approach end and I hate pushing back.
I'd love to have a quality AOA indicator to make those landings easier and
safer.

Bill Daniels

This is a life saving discussion and the best I've heard or read.
Most, or too many instructors do not know how to teach the subject.
Most cannot tell you why "relative wind" exists,. much less how to
anticipate the maximum aoa. Airfoils are much more forgiving now, but
there is a video of a DG spinning in on final. It's late now and I
don't have the link. The ship that spun in on my field in 68, ended
with bones sticking out and no bleeding. Some of the pieces are still
there to remind skepticks. Bless all of you that care .Fred

Bill Daniels wrote:
I'd love to have a quality AOA indicator to make those landings
easier and safer.

What did you think of this idea from my post:

I suggest 5 to 10 proponents of AOA meters, and other interested
pilots, buy some AOA meters (like from Safeflight, DG , Aircraft
Spruce) as a group. This will reduce the cost for each pilot to try
several AOA meters. Have each member of the group try each of the
meter(s) for while, then report their experiences.

Someone has to try some these devices in gliders, so we have some data
that applies to our sport. As the primary promoter of the value of an
AOA gauge, you seem to be the obvious choice to lead an effort that
proves the value. At that point, a few of the clever people in the sport
will likely develop units more suited to gliders, and maybe bring the
cost down.

There are units available, but I don't see anyone buying and using them.
That suggests to me that, while we all agree it's probably a good idea,
we don't think it's good enough to spend the $500-$2000 to actually buy
and install one. So, someone has to just do it and show the results to us.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On 17 Dec, 20:37, "Bill Daniels" bildan@comcast-dot-net wrote:

I'd love to have a quality AOA indicator to make those landings easier and
safer.

I generally find that my attention is fully occupied while landing. If
I had an AoA indicator, I would have to take attention away from
something else to look at it (I always have the audio vario and radio
off for the final approach). Would an AoA also indicator free up some
of my attention, and if so, from what?

Ian