Glider angle of attack indicator by SafeFlight

"kirk.stant" wrote in message
...
On Dec 8, 4:29 am, John Galloway wrote:

Having some time in airplanes that used AOA (gauge, lights, and
variable audio cues) in preference to airspeed during low speed flight
(F-4s, in my case) I can vouch that it's a much better way to fly -
especially when the AOA is coupled with an audio signal. But in a
glider, I thing the working AOA range that we are interested in is a
lot smaller than the AOA range that low aspect ratio jets use, so in
practice it may be more difficult to implement.

Actually, I think the opposite is more likely. Gliders operate from near
stall to high speed running. Due to the far lower wing and span loading in
gliders, the minimum AOA may be less than a jet. I'd bet that the AOA range
of a glider is greater.

There are a lot of ways to display AOA data and each pilot may have a
different preference. A vertical column of different colored bright LED's
that could be 'read' (i.e. thermal with the green LED lit.) with peripheral
vision might work.

An old Pratt-Read that I used to fly had two very pleasant windsong tones
that changed pitch right at the best thermalling AOA. Of course, that was
before audio varios. Maybe a better idea is to the replace the vario audio
with bright LED lightbar display and replicate the old PR's windsong for
AOA. The LED part should be easy since most electronic varios have a + or -
5V output for a rear seat repeater.

BTW, 'pitch strings' are sensitive to yaw because they have to be mounted on
the outside of the transparent part of the canopy which puts them way above
the 'beltline' of the fuselage. Mounting them lower and further forward
would make them less sensitive to yaw but of course, you wouldn't be able to
see them.

To find the best place for a AOA vane, you could put a bunch of yarns on the
fuselage side and a video camera on the wing aimed at them. A flight test
at various AOA and yaw angles would show the location least sensitive to
yaw.

Still, I think Wayne is on the right track with pressure ports on the top
and bottom of the nose.

Bill Daniels

On Dec 8, 10:13 am, "Bill Daniels" bildan@comcast-dot-net wrote:
"kirk.stant" wrote in message

...

On Dec 8, 4:29 am, John Galloway wrote:
Having some time in airplanes that used AOA (gauge, lights, and
variable audio cues) in preference to airspeed during low speed flight
(F-4s, in my case) I can vouch that it's a much better way to fly -
especially when the AOA is coupled with an audio signal. But in a
glider, I thing the working AOA range that we are interested in is a
lot smaller than the AOA range that low aspect ratio jets use, so in
practice it may be more difficult to implement.

Actually, I think the opposite is more likely. Gliders operate from near
stall to high speed running. Due to the far lower wing and span loading in
gliders, the minimum AOA may be less than a jet. I'd bet that the AOA range
of a glider is greater.

There are a lot of ways to display AOA data and each pilot may have a
different preference. A vertical column of different colored bright LED's
that could be 'read' (i.e. thermal with the green LED lit.) with peripheral
vision might work.

An old Pratt-Read that I used to fly had two very pleasant windsong tones
that changed pitch right at the best thermalling AOA. Of course, that was
before audio varios. Maybe a better idea is to the replace the vario audio
with bright LED lightbar display and replicate the old PR's windsong for
AOA. The LED part should be easy since most electronic varios have a + or -
5V output for a rear seat repeater.

BTW, 'pitch strings' are sensitive to yaw because they have to be mounted on
the outside of the transparent part of the canopy which puts them way above
the 'beltline' of the fuselage. Mounting them lower and further forward
would make them less sensitive to yaw but of course, you wouldn't be able to
see them.

To find the best place for a AOA vane, you could put a bunch of yarns on the
fuselage side and a video camera on the wing aimed at them. A flight test
at various AOA and yaw angles would show the location least sensitive to
yaw.

Still, I think Wayne is on the right track with pressure ports on the top
and bottom of the nose.

Bill Daniels

Everyone is talking about AoA on the fuselage. This is not the AoA of
the wing. As noted the flap position modifies the reading from the
fueslage. What we need is a AoA that is always reading the stagnation
point on the leading edge of the wing and showing that AoA. Then, I
think, the flap is comprehended in the setup.

This could be done with a set of holes, chord-wise around the LE that
feed independent pressure sensors, integrated by a micro-controller,
then displayed and/or driving an audio signal. Very similar to some
projects I've been working on and easily done with about $400 worth of
parts. Accutate, temperature compensated, pressure sensors are
expensive.

Mike

I would like to place an order if you are game.
Udo

Everyone is talking about AoA on the fuselage. This is not the AoA of
the wing. As noted the flap position modifies the reading from the
fueslage. What we need is a AoA that is always reading the stagnation
point on the leading edge of the wing and showing that AoA. Then, I
think, the flap is comprehended in the setup.

This could be done with a set of holes, chord-wise around the LE that
feed independent pressure sensors, integrated by a micro-controller,
then displayed and/or driving an audio signal. Very similar to some
projects I've been working on and easily done with about $400 worth of
parts. Accutate, temperature compensated, pressure sensors are
expensive.

Mike- Hide quoted text -

- Show quoted text -

SoaringXCellence wrote:
This could be done with a set of holes, chord-wise around the LE that
feed independent pressure sensors, integrated by a micro-controller,
then displayed and/or driving an audio signal. Very similar to some
projects I've been working on and easily done with about $400 worth of
parts. Accutate, temperature compensated, pressure sensors are
expensive.

Would a series of holes provide any more information than two holes?
What kind of pressure differentials would be involved?

Marc

kirk.stant wrote:

What I would like to see is a simple AOA indicator that would tell me
when I am at the optimum AOA for efficient thermalling.

Does anyone know of documentation that supports the idea showing the
pilot the AOA will actually improve a glider pilot's thermalling? Or
even that the range of AOA needed to be "efficient" is too small for a
pilot to obtain it easily by using airspeed, or by just looking out the
canopy, once he's flown the glider enough to be familiar with it?

For example, I couldn't even find a mention of AOA in "Fundamentals of
Sailplane Design" when discussing thermalling. Circling efficiency is
discussed (page 63-65), but without mention of AOA, which suggests to me
that it's not the important factor. Climb performance, which is what we
really are after, is very dependent on the thermal shape (pages 65-66).
Circling at the best AOA doesn't give you the best rate of climb;
instead, the circling radius is the most important factor.

Look at the "rate of sink versus turn radius" table like the one on page
64 of "Fundamentals...". Does anyone know if the optimum is always at
the same AOA? And if not, what the range of AOA is for the table?

Regardless of the answer is to the question above, what would be useful
would be two additional tables "rate of sink versus turn radius". One
table would use an AOA greater (say, 3 degrees) than optimum; the other
table would use an AOA smaller by the same amount from optimum. This
would give us an idea of how sensitive circling efficiency is to AOA
errors.

If performance is not sensitive to the AOA, there is no need to look for
an indicator of it. A stall warning device would still be useful, but it
doesn't have to be based on AOA: it just needs to tell you when the wing
is getting close to a stall.

--
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

It is true that we get used to the air speed indicator and get a feel
for the glider. But I still would prefer an A of A indicator. Looking
back, when I was testing my glider, I wish I had an A of A indicator.
It would have made the initial tests to find the right flap settings
and corresponding airspeed faster and easier. Pilots generally do not
what to hang around for test, especially when a home built is nibbling
on there tail.
I knew where I needed to be with my flaps and airspeed, based on the
theoretical polars but making adjustment by adding or subtracting a
degree of flap deflection and making speed adjustments at the same
time you either need a good A of A indicator are a very patient pilot
partner. Hence It took many flights nearly 70 to 90 contest hours to
fine tuning the glider (I am not talking about handling the glider)
Once the parameters had been established there was very little need
for an
A of A. Still I would prefer one for changing ballast and when flying
in marginal conditions at a contest to have a glancing look at it the
odd time.

Udo


On Dec 8, 2:49 pm, Eric Greenwell wrote:
kirk.stant wrote:
What I would like to see is a simple AOA indicator that would tell me
when I am at the optimum AOA for efficient thermalling.

Does anyone know of documentation that supports the idea showing the
pilot the AOA will actually improve a glider pilot's thermalling? Or
even that the range of AOA needed to be "efficient" is too small for a
pilot to obtain it easily by using airspeed, or by just looking out the
canopy, once he's flown the glider enough to be familiar with it?

For example, I couldn't even find a mention of AOA in "Fundamentals of
Sailplane Design" when discussing thermalling. Circling efficiency is
discussed (page 63-65), but without mention of AOA, which suggests to me
that it's not the important factor. Climb performance, which is what we
really are after, is very dependent on the thermal shape (pages 65-66).
Circling at the best AOA doesn't give you the best rate of climb;
instead, the circling radius is the most important factor.

Look at the "rate of sink versus turn radius" table like the one on page
64 of "Fundamentals...". Does anyone know if the optimum is always at
the same AOA? And if not, what the range of AOA is for the table?

Regardless of the answer is to the question above, what would be useful
would be two additional tables "rate of sink versus turn radius". One
table would use an AOA greater (say, 3 degrees) than optimum; the other
table would use an AOA smaller by the same amount from optimum. This
would give us an idea of how sensitive circling efficiency is to AOA
errors.

If performance is not sensitive to the AOA, there is no need to look for
an indicator of it. A stall warning device would still be useful, but it
doesn't have to be based on AOA: it just needs to tell you when the wing
is getting close to a stall.

--
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" atwww.motorglider.org

On Dec 8, 12:49 pm, Eric Greenwell wrote:

Does anyone know of documentation that supports the idea showing the
pilot the AOA will actually improve a glider pilot's thermalling? Or
even that the range of AOA needed to be "efficient" is too small for a
pilot to obtain it easily by using airspeed, or by just looking out the
canopy, once he's flown the glider enough to be familiar with it?

Eric, when we fly airspeed while thermalling we are actually trying to
fly AOA. We start with the minimum sink speed (specifically, the
point on the polar we want to thermal at), add speed for ballast, then
add speed for bank angle, then come up with an adjusted airspeed that
approximates our ideal AOA for the selected gross weight and bank
angle.

Using AOA directly (once one has chosen where on the polar one wants
to thermal at) eliminates the need to make all those guesses. The
wing does it all, automatically.

Guess what - when you fly attitude - "what feels right" - in a
thermal, glancing at the airspeed to see what it is - you are flying
AOA!

For example, I couldn't even find a mention of AOA in "Fundamentals of
Sailplane Design" when discussing thermalling. Circling efficiency is
discussed (page 63-65), but without mention of AOA, which suggests to me
that it's not the important factor. Climb performance, which is what we
really are after, is very dependent on the thermal shape (pages 65-66).
Circling at the best AOA doesn't give you the best rate of climb;
instead, the circling radius is the most important factor.

I disagree. Thermalling at the most efficient bank angle/AOA for the
size of the thermal is the most important factor. Waddling around a
knot above the stall with landing flaps down will give me the smallest
circling radius, but a horrible climb rate.

Look at the "rate of sink versus turn radius" table like the one on page
64 of "Fundamentals...". Does anyone know if the optimum is always at
the same AOA? And if not, what the range of AOA is for the table?

My guess it that the optimum AOA may vary based on turbulence, but
only a very small about - probably less than can be accurately flown
by the average pilot in a typical thermal. And this would only be for
airfoils that are susceptible to turbulent flows. In most cases, the
AOA range for effective Cl max (which I assume is close to the optimum
for min sink and thermalling) is probably big enough to be measured
and flown accurately.

Regardless of the answer is to the question above, what would be useful
would be two additional tables "rate of sink versus turn radius". One
table would use an AOA greater (say, 3 degrees) than optimum; the other
table would use an AOA smaller by the same amount from optimum. This
would give us an idea of how sensitive circling efficiency is to AOA
errors.

If performance is not sensitive to the AOA, there is no need to look for
an indicator of it. A stall warning device would still be useful, but it
doesn't have to be based on AOA: it just needs to tell you when the wing
is getting close to a stall.

If performance is not sensitive to the AOA, we wouldn't need an
airspeed indicator! At low speeds, that old ASI is at best a poor
compromise - the only good thing about it is that is doesn't fail
often (although, the only instrument I've ever had fail in a glider
was the airspeed indicator). And how can anything tell you the wing
is getting close to the stall without measuring AOA? Excessive AOA is
what defines a stall. Airspeed is just an approximation - and can
easily trick you. Try landing back after a low altitude rope break
full of ballast, if you haven't flown wet in a while. Slow to the
airspeed you are used to using to turn back and you will get a big
surprise! In the same situation, slow to the same AOA, and you have
the same margin over the stall you had dry. This isn't opinion, it's
basic aerodynamics.

I think the lack of references to angle of attack in gliding
publications is largely due to the fact that AOA is still mainly
limited to military jets and expensive airliners/biz jets. Most
general aviation pilots never have a chance to be exposed to the joys
of knowing exactly what their wing is doing. Or not doing, as the
case may be! Funny thing is, the common Cezzna uses a crude AOA
sensor for it's stall warning (the little paddle on the leading edge).

Kinda like audio varios - once you try it, you'll never want to go
back to airspeed as a low speed control instrument.

Any real aero majors lurking out there, please join in!

Cheers,

Kirk

"kirk.stant" wrote in message
...
On Dec 8, 12:49 pm, Eric Greenwell wrote:

Does anyone know of documentation that supports the idea showing the
pilot the AOA will actually improve a glider pilot's thermalling? Or
even that the range of AOA needed to be "efficient" is too small for a
pilot to obtain it easily by using airspeed, or by just looking out the
canopy, once he's flown the glider enough to be familiar with it?

Eric, when we fly airspeed while thermalling we are actually trying to
fly AOA. We start with the minimum sink speed (specifically, the
point on the polar we want to thermal at), add speed for ballast, then
add speed for bank angle, then come up with an adjusted airspeed that
approximates our ideal AOA for the selected gross weight and bank
angle.

Using AOA directly (once one has chosen where on the polar one wants
to thermal at) eliminates the need to make all those guesses. The
wing does it all, automatically.

Guess what - when you fly attitude - "what feels right" - in a
thermal, glancing at the airspeed to see what it is - you are flying
AOA!

For example, I couldn't even find a mention of AOA in "Fundamentals of
Sailplane Design" when discussing thermalling. Circling efficiency is
discussed (page 63-65), but without mention of AOA, which suggests to me
that it's not the important factor. Climb performance, which is what we
really are after, is very dependent on the thermal shape (pages 65-66).
Circling at the best AOA doesn't give you the best rate of climb;
instead, the circling radius is the most important factor.

I disagree. Thermalling at the most efficient bank angle/AOA for the
size of the thermal is the most important factor. Waddling around a
knot above the stall with landing flaps down will give me the smallest
circling radius, but a horrible climb rate.

Look at the "rate of sink versus turn radius" table like the one on page
64 of "Fundamentals...". Does anyone know if the optimum is always at
the same AOA? And if not, what the range of AOA is for the table?

My guess it that the optimum AOA may vary based on turbulence, but
only a very small about - probably less than can be accurately flown
by the average pilot in a typical thermal. And this would only be for
airfoils that are susceptible to turbulent flows. In most cases, the
AOA range for effective Cl max (which I assume is close to the optimum
for min sink and thermalling) is probably big enough to be measured
and flown accurately.

Regardless of the answer is to the question above, what would be useful
would be two additional tables "rate of sink versus turn radius". One
table would use an AOA greater (say, 3 degrees) than optimum; the other
table would use an AOA smaller by the same amount from optimum. This
would give us an idea of how sensitive circling efficiency is to AOA
errors.

If performance is not sensitive to the AOA, there is no need to look for
an indicator of it. A stall warning device would still be useful, but it
doesn't have to be based on AOA: it just needs to tell you when the wing
is getting close to a stall.

If performance is not sensitive to the AOA, we wouldn't need an
airspeed indicator! At low speeds, that old ASI is at best a poor
compromise - the only good thing about it is that is doesn't fail
often (although, the only instrument I've ever had fail in a glider
was the airspeed indicator). And how can anything tell you the wing
is getting close to the stall without measuring AOA? Excessive AOA is
what defines a stall. Airspeed is just an approximation - and can
easily trick you. Try landing back after a low altitude rope break
full of ballast, if you haven't flown wet in a while. Slow to the
airspeed you are used to using to turn back and you will get a big
surprise! In the same situation, slow to the same AOA, and you have
the same margin over the stall you had dry. This isn't opinion, it's
basic aerodynamics.

I think the lack of references to angle of attack in gliding
publications is largely due to the fact that AOA is still mainly
limited to military jets and expensive airliners/biz jets. Most
general aviation pilots never have a chance to be exposed to the joys
of knowing exactly what their wing is doing. Or not doing, as the
case may be! Funny thing is, the common Cezzna uses a crude AOA
sensor for it's stall warning (the little paddle on the leading edge).

Kinda like audio varios - once you try it, you'll never want to go
back to airspeed as a low speed control instrument.

Any real aero majors lurking out there, please join in!

Cheers,

Kirk

No need. That was a damn good explanation.

Bill Daniels

Ever since I got a copy of the book Ruder and Stick by Wolfgang L. I
think about ways to implement an effective AoA indicator for my flapped
glider.

I have the AoA string on the right side of my canopy, but it is not very
helpful, as it has to be calibrated for every flap setting.

On Dec 8, 5:21 pm, "kirk.stant" wrote:

We start with the minimum sink speed (specifically, the
point on the polar we want to thermal at), add speed for ballast, then
add speed for bank angle, then come up with an adjusted airspeed that
approximates our ideal AOA for the selected gross weight and bank
angle.

Using AOA directly (once one has chosen where on the polar one wants
to thermal at) eliminates the need to make all those guesses. The
wing does it all, automatically.

I realized a bit late that what I really meant to say is that when
using airspeed, we find the performance point on the polar we want (L/
D max, min sink, stall, whatever), then move the polar for ballast and
bank angle, and use the resulting adjusted airspeed. This is made
necessary when using the common sink rate vs airspeed polars for all
the desired conditions of ballast and bank angle. Using AOA directly
(which would require the polar in sink rate vs AOA and L/D vs AOA)
eliminates the need to move the polar (and refigure the resulting
airspeed), as the AOA for a specific flight condition is not affected
by ballast or bank angle.

Has anyone seen glider polars with sinkrate plotted against angle of
attack? That would be interesting. I've seen plots for aircraft of
Cl vs AOA, and L/D vs AOA, neither of which is very useful in this
discussion.

I should have listened up more in aero classes, long time ago...

Kirk