Glider angle of attack indicator by SafeFlight

As has been pointed out in the past on RAS, pieces
of wool taped to both front/sides of the canopy perform
quite well as angle of attack indications in unflapped
gliders. The angular change between max LD and stall
is surprisingly noticeable. Once 'calibrated' for
the stall position and min sink and best glide positions
they are helpful for optimizing thermalling technique
but don't grab the attention well enough to be a safety
stall warning.

Certainly good value for money.

John Galloway

On Dec 8, 4:29 am, John Galloway wrote:
As has been pointed out in the past on RAS, pieces
of wool taped to both front/sides of the canopy perform
quite well as angle of attack indications in unflapped
gliders. The angular change between max LD and stall
is surprisingly noticeable. Once 'calibrated' for
the stall position and min sink and best glide positions
they are helpful for optimizing thermalling technique
but don't grab the attention well enough to be a safety
stall warning.

Certainly good value for money.

John Galloway

John,

I tried this technique on an LS4. While you could see the difference
in angle of attack quite clearly, there was a huge difference when any
yaw was introduced, with the yarns showing significant differences in
relative airflow on opposite sides of the canopy. In effect, with
this system, you are really showing the instantaneous airflow over the
canopy, and deriving AOA from that indication - which is not much
better than just using airspeed, really, and effectively impossible to
use due to yaw effects and the flapping of the yarn masking the small
AOA changes you are interested in.

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.

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. No fancy
indicator, just a bright LED that would be on steady at thermalling
AOA. Have it start flashing when approaching the desired AOA, and
have a different flash rate when below the desired AOA (which would
also function as a stall warning, since there is really no reason for
ever flying below min sink, especially in the pattern.

To use, pull into the thermal and set your attitude to the approximate
AOA, glance at the LED to adjust to the exact AOA, then fly that,
occasionally crosschecking the light. No figuring for bank angle or
ballast required, the wing takes care of that. Sweet...

AOA is really not that useful in cruise, since we are really more
concerned with the appropriate MC speed, and rarely fly at L/D max.
But again, that would be a single AOA point to measure, and could use
a different color LED.

Obviously, with a flapped ship, flap position would have to be sensed
and compensated for.

Since I'm really only concerned about one angle of attack, a moving
vane should not be necessary - I think it can be done with
differential pressure ports, so no moving parts or drag. Flaps may
complicate things, but even if there has to be a different set of
ports for each thermalling flap position, it may still be easier than
a mechanical AOA vane. Or just pick your favorite flap setting, and
TLAR it from there...

Comments from smarter people out there are welcome!

Kirk
LS6b "66"

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

I agree with your assessment. A simple LED index system of three lights.
One indicating "fast", another "on speed" (Max Cl) and finally one that
flashes when nearing stall. Sound familiar from your F-4 days?

Wayne
Retired A-6 Bombardier.
http://www.soaridaho.com/Schreder

John,

I tried this technique on an LS4. While you could see the difference
in angle of attack quite clearly, there was a huge difference when any
yaw was introduced, with the yarns showing significant differences in
relative airflow on opposite sides of the canopy. In effect, with
this system, you are really showing the instantaneous airflow over the
canopy, and deriving AOA from that indication - which is not much
better than just using airspeed, really, and effectively impossible to
use due to yaw effects and the flapping of the yarn masking the small
AOA changes you are interested in.

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.

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. No fancy
indicator, just a bright LED that would be on steady at thermalling
AOA. Have it start flashing when approaching the desired AOA, and
have a different flash rate when below the desired AOA (which would
also function as a stall warning, since there is really no reason for
ever flying below min sink, especially in the pattern.

To use, pull into the thermal and set your attitude to the approximate
AOA, glance at the LED to adjust to the exact AOA, then fly that,
occasionally crosschecking the light. No figuring for bank angle or
ballast required, the wing takes care of that. Sweet...

AOA is really not that useful in cruise, since we are really more
concerned with the appropriate MC speed, and rarely fly at L/D max.
But again, that would be a single AOA point to measure, and could use
a different color LED.

Obviously, with a flapped ship, flap position would have to be sensed
and compensated for.

Since I'm really only concerned about one angle of attack, a moving
vane should not be necessary - I think it can be done with
differential pressure ports, so no moving parts or drag. Flaps may
complicate things, but even if there has to be a different set of
ports for each thermalling flap position, it may still be easier than
a mechanical AOA vane. Or just pick your favorite flap setting, and
TLAR it from there...

Comments from smarter people out there are welcome!

Kirk
LS6b "66"

Wayne Paul wrote:
I agree with your assessment. A simple LED index system of three lights.
One indicating "fast", another "on speed" (Max Cl) and finally one that
flashes when nearing stall. Sound familiar from your F-4 days?

Using either a vane on a shaft encoder, or differential pressure ports,
the hardware and software are pretty trivial (well under $100US in
parts). The aerodynamics, however, are not. Where does one put the
vane or ports such that one doesn't get large errors due to tiny
variations in yaw?

My DG-600 had an AOA meter (it looked to be a modified electronic
variometer) and two cross connected sets of static ports immediately
above the wing root, one set near the leading edge, and the second set
roughly mid-chord. I never got it to do anything useful.

Marc

"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

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

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

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

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