AoA keep it going!

In my early hours of being instructed, not one went by without stall
and spin practice. They also taught me to look out of the window.
Maybe I've done a thousand or more turns before I found myself in a
spin that I did not intend to happen. I was in an HP11, over a ridge,
with a 1-26 out climbing me. "He can't do that!" With over 60 degrees
bank, I just tightened my turn by pulling back on the stick. I
increased my AoA without concern. Snap!
The ridge was spinning below my nose and getting larger very fast. My
old instincts kicked in. I was looking at the grass when I recovered.

Now, AoA is my favorite subject to teach. My God! The ignorance is
rampant. A tow pilot applied for a job. I asked him what the
approximate angle of attack was for the Super Cub wing when it
stalled. A commercial pilot raised his arm and pointed up about 40
degrees above the horizon. He went home. I was stunned.

A favorite question I use for instruction... Which wing in a turn has
the greatest angle of attack? The pilot has a 50-50 chance at the
correct guess. No matter what his answer, I ask why? I get no answer.

A problem I find is a lack of understanding of "relative wind" Is
there no hope?

I have witnessed a low altitude spin to impact. It was not nice.

Another spin to impact gave me the opportunity to ask the pilot the
question..."What makes the glider turn?
His answer:"The rudder" He was a military acadamy pilot.

We absolutly must teach and demonstrate more angle of attack
recognition and recovery. It doesant take long before you hear or
read about a stall spin fatality, Don't let your stundent go out into
the wold without being trained in ALL aspects of AoA and stall spin
recovery.Maybe the instructor should learn first.
God bless good instructors,Fearless Fred

On 16 Dec, 07:14, fred wrote:

Another spin to impact gave me the opportunity to ask the pilot the
question..."What makes the glider turn?
His answer:"The rudder" He was a military acadamy pilot.

I myself am amazed at how many pilots think the ailerons make the
glider turn.

Ian

I recall a teaching aid used to train WWII pilots. It was a simple table
top wind tunnel made of plexiglass with a "test section" about an inch wide
and 6" high. It came with various aerodynamic shaped bits of plastic that
could be used to visualize flow. There was a small exhaust fan to pull air
through the tunnel and a clever "smoke rake" made with a small electrically
heated pot and a rake made of small diameter brass tubes soldered together.
It was a simple two dimensional wind tunnel.

You put an ounce or so of kerosene in the pot and turned on the heat. After
a bit, smoke started coming out of the dozen or so rake tubes. You then
turned on the fan and neat parallel streams of smoke flowed around the shape
in the test section.

The reynolds number was all wrong but the visualization of air flow was way
more than good enough to get the idea of angle of attack across. The
airfoil shaped test bit was nearly perfect. At about 16 degrees of AOA, the
smoke streams would burble and separate from the upper surface. No one left
the demonstration unconvinced.

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.

The thought occurs to me that those WWII flight schools went to a lot of
trouble to teach AOA and the graduates were among the best pilots ever
trained. Maybe we should take a look at that they did to train them.

Bill Daniels


"fred" wrote in message
...
In my early hours of being instructed, not one went by without stall
and spin practice. They also taught me to look out of the window.
Maybe I've done a thousand or more turns before I found myself in a
spin that I did not intend to happen. I was in an HP11, over a ridge,
with a 1-26 out climbing me. "He can't do that!" With over 60 degrees
bank, I just tightened my turn by pulling back on the stick. I
increased my AoA without concern. Snap!
The ridge was spinning below my nose and getting larger very fast. My
old instincts kicked in. I was looking at the grass when I recovered.

Now, AoA is my favorite subject to teach. My God! The ignorance is
rampant. A tow pilot applied for a job. I asked him what the
approximate angle of attack was for the Super Cub wing when it
stalled. A commercial pilot raised his arm and pointed up about 40
degrees above the horizon. He went home. I was stunned.

A favorite question I use for instruction... Which wing in a turn has
the greatest angle of attack? The pilot has a 50-50 chance at the
correct guess. No matter what his answer, I ask why? I get no answer.

A problem I find is a lack of understanding of "relative wind" Is
there no hope?

I have witnessed a low altitude spin to impact. It was not nice.

Another spin to impact gave me the opportunity to ask the pilot the
question..."What makes the glider turn?
His answer:"The rudder" He was a military acadamy pilot.

We absolutly must teach and demonstrate more angle of attack
recognition and recovery. It doesant take long before you hear or
read about a stall spin fatality, Don't let your stundent go out into
the wold without being trained in ALL aspects of AoA and stall spin
recovery.Maybe the instructor should learn first.
God bless good instructors,Fearless Fred

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