Angle of attack

Originally Posted by hans

Until I read the book 'Ruder and Stick' I thought you can not hear the
AoA. But now I know that I can hear large changes in the AoA. Just turn
down the radio and the variometer and listen to your glider when you are
flying at different AoA at the same speed. You will realize marked
differences in sound of your gilder. Our Duo sounds different at
thermaling AoA and at stall AoA. The sound at stall AoA is much deeper
than at thermaling AoA.

You can feel the distance to the stalling AoA in the elevator. If you
are far away from the stall AoA a small increase in back pressure on the
stick will lead to a much larger change of the attitude than at an AoA
close to stall speed.

This is exactly how I learned to fly hang gliders. I mostly use my ears, but the bar pressure is also important. It also helps to have a helmet with earholes in it - you can sometimes hear which side the thermal is on. An important difference between planes & hang gliders is that the trim is always set at the same speed, so you can tell if you're at min sink or best glide using bar pressure.

Eric Greenwell wrote:


The big problem is AOA is an abstract engineering parameter,
because pilots can't see it, can't hear it, and can't feel it. We can
see attitude and airpeed...

The only airspeed I've ever "seen" in a glider was indicated on the face
of the mechanical ASI--a rather remote approximation--and as a sole
indication of stalling speed can be hugely misleading. AOA, within the
limitations of the instrument and the installation, is never wrong--no
matter the speed, g-loading, or aircraft weight.


...we can hear airspeed and stall rumble, and we
can feel stick position and stick forces, so that is what we use to fly
by. I sure don't think about AOA when I'm flying.

You would if you had an AOA to think about. In its absence you have
learned to substitute those other vague indications, some of which are
present in some situations but not in others, and some of which, though
present, are of little use in any but the narrowest of circumstances.
Don't knock AOA until you've used it.


Until we can hear it, see it, or feel it, we won't be able to use [it].

And until you use it, you won't be able to hear, see, or feel it.

It's basically the difference between a (ASI) love letter and a (AOA)
caress. I know which I prefer, especially when time is of the
essence--which it is anytime an object is in motion.


Jack

toad wrote:


While I agree that understanding of AOA is crucial for a pilot. I
don't think that a AOA indicator would be very useful in gliders


Why would the best reference for the actual performance of the aircraft
be less desirable than an error-prone and very approximate indication
which, like a stopped clock, is exactly right about twice a day?



I think that stall accidents are caused by lack of awareness and lack
of attention. Letting the airspeed "creep away" and incorrectly
responding to the loss of airspeed. Substituting an AOA dial for the
airspeed dial, won't change that.


It is my understanding that one is supposed to be able to fly a glider
safely without reference to the ASI, and I suppose that should also then
apply to AOA as well. Obviously, not everyone can do so. And there are a
few each year that manage to demonstrate the inability to fly safely in
spite of the availability of a working ASI. It is also possible that the
fact that the stall speed of a given sailplane on a given flight could
be +/- 15%, or more, from book speed _in one-g flight_ should be given
more thorough consideration. Do we know then what it might be in a 30-60
degree banked final turn, or in a wind shear condition where the ASI
reads considerably below the book stalling speed? "More" is an answer,
in one case, and "Less" in the other. How much more or less we find by
trial and error, guesswork and luck--or not. An AOA would tell us
instantly and throughout the normal operating range of the glider, and
beyond, just how close to the stall we are operating.



AOA gauges seem best suited for heavy aircraft flown by reference to
instruments. Where you might have to wait a couple of minutes after
setting the AOA and power lever to get the airspeed to respond.
Gliders will change their airspeed much quicker than a 747 or F-14.


I can't use the F-14 or the 747 as a reference, because I have not flown
either. My understanding is that the F-14 can accelerate rather rapidly
and slow down pretty quickly as well. High performance military aircraft
which I have flown certainly exhibited that capability. To say that any
of them, or even a 747, could not accelerate more rapidly than an
unpowered glider in a specified attitude seems an incompletely
considered statement, but perhaps you can provide some evidence to
support your claim.



We also only really fly at 2 or 3 different weights. So we only
really have to remember the best L/D speed for these conditions.

Be my guest--memorize as many speeds as you like. You'll still be
guessing at how close your ASI is to the actual stalling speed at any
particular moment. AOA never lies: any g-load; any altitude; any
attitude; any airspeed.



Jack

J a c k wrote:
Eric Greenwell wrote:
The big problem is AOA is an abstract engineering parameter,
because pilots can't see it, can't hear it, and can't feel it. We can
see attitude and airpeed...

The only airspeed I've ever "seen" in a glider was indicated on the face
of the mechanical ASI--a rather remote approximation--

The AIS is close enough, except in a slip, because doesn't have to be
accurate, just consistent. The flight manual values are based on what it
shows, not what the actual airspeed is.

and as a sole
indication of stalling speed can be hugely misleading.

Indeed, and that's why we use other indications in addition.

AOA, within the
limitations of the instrument and the installation, is never wrong--no
matter the speed, g-loading, or aircraft weight.

In fact, the AOA instrument on every glider I've owned (six) was always
"wrong", because none of them had one. I like the idea, but the reality
is I've never had one, so I've never used one. Ditto for most pilots
when flying gliders.


...we can hear airspeed and stall rumble, and we can feel stick
position and stick forces, so that is what we use to fly by. I sure
don't think about AOA when I'm flying.

You would if you had an AOA to think about.

Well, yeah, but I don't.

In its absence you have
learned to substitute those other vague indications

I never had an AOA indicator, so I didn't learn to "substitute" for it,
I learned the vague indications from the very beginning. IF a suitable
AOA indicator became available in my glider, I would probably learn to
substitute it for the vague indications. Or maybe not - I don't know how
much value it would have for my flying until I try it.


, some of which are
present in some situations but not in others, and some of which, though
present, are of little use in any but the narrowest of circumstances.

On the contrary, the "vague indications" have served me well for 5000+
hours of flying cross country!

Don't knock AOA until you've used it.

I have never knocked AOA indicators as a *potentially* useful device. I
like the idea. I am skeptical that teaching pilots about AOA will reduce
accidents, as Bill suggested, UNLESS we have an AOA indicator for them
to look at (or hear/feel). I haven't seen any documentation that AOA
will improve safety or performance significantly, just personal opinions
that it will, so I am skeptical of enthusiastic claims that it will do so.



Until we can hear it, see it, or feel it, we won't be able to use [it].

And until you use it, you won't be able to hear, see, or feel it.

It's basically the difference between a (ASI) love letter and a (AOA)
caress. I know which I prefer, especially when time is of the
essence--which it is anytime an object is in motion.

Which one do you use in your glider, and where can I get one for my glider?

We need to have units in gliders, in use, before we can make any serious
claims about it's effectiveness. It seems like it should help, but so
far, the people that have used them were flying jets. Apparently, it's
essential in then environment, but jets aren't gliders. so we still
don't know.

I hope some pilots will try the Safeflight unit and the DG unit (and
others I'm not aware of), and report their experiences. If the reports
are positive, it might spur further use and lead to improved units, and
the best techniques for using them.

--
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

Be my guest--memorize as many speeds as you like. You'll still be
guessing at how close your ASI is to the actual stalling speed at any
particular moment. AOA never lies: any g-load; any altitude; any
attitude; any airspeed.

While I think an AOA indicator might be useful, isn't this over selling
it's ability? How about with ice, rain, or bugs on the wing - is the
stalling AOA still the same? Does the AOA indicator read correctly in
slip? Does it read the AOA of the inboard tip and the outboard tip in a
turn? What if it freezes, or gets water it?

--
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

Sorry Bob,

I can't agree to that.
In level flight and coordinated turns, the nose attitude as an absolute
reference for the AoA for a given flap setting.
Most stall/spin entries happen exactly in this configuration (at least here
in Europe, maybe in the US you die differently) when people fly at critical
AoA close to the ground and then initiate a turn.
On flapped gliders, this happens with the flaps in thermal position, so who
cares about the AoA for the other flap positions? Haven't heared of any
fatal stall accident where the flaps have been at -10 degree...
If a pilot isn't aware that the nose is too high, why the hell would he care
what an AoA meter tells him?

Bert

"Bob Kuykendall" wrote in message
...
On Dec 13, 2:16 am, "Bert Willing" bw_no_spam_ple...@tango-
whisky.com wrote:

... Nose attitude is the onboard AoA, and it works...

Apologies for the dogpile, but I think that's wrong and wrong. I
believe that thinking like that is exactly what leads to the types of
insidious stall/spin entries that most often become accidents.

That's not to say that nose angle isn't a useful tool. In straight-and-
level flight, and in stable coordinated turns, nose angle and nose
angle rate are key indicators of speed and acceleration.

However, straight-and-level flight and stable coordinated turns
constitute a very small subset of the available flight regimes, and
are among those least likely to offer unanticipated stall spin
entries.

Also, in flapped ships, and especially in glidepath-flapped ships,
nose angle is virtually useless as a speed reference independent of
flap deflection. In a good old HP glider, you can have your toes on
the horizon and be tearing along at a stable 80 kts. Or you can be
going almost straight down at a stable 80 kts and viewing the horizon
through the crown of the canopy.

So far as soaring and sailplanes go, I'm basically an anti-
gadgetarian. For years, the most complicated device in my ship was the
digital clock. However, I think that a simple, effective AOA indicator
with an intuitive display would be a real asset. And, it would be
useful not only for stall/spin protection but also for cruise and
thermal optimization.

Thanks, Bob K.

Eric Greenwell wrote:

Be my guest--memorize as many speeds as you like. You'll still be
guessing at how close your ASI is to the actual stalling speed at any
particular moment. AOA never lies: any g-load; any altitude; any
attitude; any airspeed.

While I think an AOA indicator might be useful, isn't this over selling
it's ability? How about with ice, rain, or bugs on the wing - is the
stalling AOA still the same? Does the AOA indicator read correctly in
slip? Does it read the AOA of the inboard tip and the outboard tip in a
turn? What if it freezes, or gets water it?


See both Daniels' and Pfeiffer's recent comments in the nearby "AoA Keep
it Going" thread.


Jack

On Dec 16, 8:06 pm, J a c k wrote:
toad wrote:
While I agree that understanding of AOA is crucial for a pilot. I
don't think that a AOA indicator would be very useful in gliders

Why would the best reference for the actual performance of the aircraft
be less desirable than an error-prone and very approximate indication
which, like a stopped clock, is exactly right about twice a day?

I think that stall accidents are caused by lack of awareness and lack
of attention. Letting the airspeed "creep away" and incorrectly
responding to the loss of airspeed. Substituting an AOA dial for the
airspeed dial, won't change that.

It is my understanding that one is supposed to be able to fly a glider
safely without reference to the ASI, and I suppose that should also then
apply to AOA as well. Obviously, not everyone can do so. And there are a
few each year that manage to demonstrate the inability to fly safely in
spite of the availability of a working ASI. It is also possible that the
fact that the stall speed of a given sailplane on a given flight could
be +/- 15%, or more, from book speed _in one-g flight_ should be given
more thorough consideration. Do we know then what it might be in a 30-60
degree banked final turn, or in a wind shear condition where the ASI
reads considerably below the book stalling speed? "More" is an answer,
in one case, and "Less" in the other. How much more or less we find by
trial and error, guesswork and luck--or not. An AOA would tell us
instantly and throughout the normal operating range of the glider, and
beyond, just how close to the stall we are operating.

AOA gauges seem best suited for heavy aircraft flown by reference to
instruments. Where you might have to wait a couple of minutes after
setting the AOA and power lever to get the airspeed to respond.
Gliders will change their airspeed much quicker than a 747 or F-14.

I can't use the F-14 or the 747 as a reference, because I have not flown
either. My understanding is that the F-14 can accelerate rather rapidly
and slow down pretty quickly as well. High performance military aircraft
which I have flown certainly exhibited that capability. To say that any
of them, or even a 747, could not accelerate more rapidly than an
unpowered glider in a specified attitude seems an incompletely
considered statement, but perhaps you can provide some evidence to
support your claim.

We also only really fly at 2 or 3 different weights. So we only
really have to remember the best L/D speed for these conditions.

Be my guest--memorize as many speeds as you like. You'll still be
guessing at how close your ASI is to the actual stalling speed at any
particular moment. AOA never lies: any g-load; any altitude; any
attitude; any airspeed.

Jack

AOA is my favorite subject to teach. It is not easy but is a life
saver. Most pilots really don't understand relative wind. Ask them to
explain it. What happens when a gust is encountered + or -? Near a
stall the asi pitot tube is at an angle to the wind and is less
accurate. I use a pieceof yarn taped to the side od the canopy with a
"normal" air flow line marked. A the moment of the stall, the string
rises as you approach the stall. It is only a cheap teaching aid. I
probe my students understanding of why and where does the AOA COME
FROM AND WHY. Lift depends on speed of the air and angle of
attack...and it varies in many ways. At altitude, my students get a
lot of slow flight experience. They know! Fred