Building an electronic Angle of Attack indicator

"Peter Dohm" wrote in message .. .

"bildan" wrote in message
...


The interest for me is a sailplane installation where AOA is a
performance issue in addition to a safety issue.

My glider can be flown at 1000 pounds up to 1433 pounds gross weight
and spends a lot of time in 2G turns thermalling. The AOA for minimum
sink is always the same but the airspeed at which that happens changes
a lot. The same thing with best L/D.

A very 'slippery' glider takes a while for the airspeed to settle down
after a pitch change. Flying to an exact AOA would be easier than
chasing airspeed.

An AOA indicator that shows minimum sink and maximum L/D as well as
stall would be quite useful.



The glider solution could be a simple as the piece of yarn along the side of the canopy...

"Dan D" wrote in message
...


"Peter Dohm" wrote in message
.. .

"bildan" wrote in message
...


The interest for me is a sailplane installation where AOA is a
performance issue in addition to a safety issue.

My glider can be flown at 1000 pounds up to 1433 pounds gross weight
and spends a lot of time in 2G turns thermalling. The AOA for minimum
sink is always the same but the airspeed at which that happens changes
a lot. The same thing with best L/D.

A very 'slippery' glider takes a while for the airspeed to settle down
after a pitch change. Flying to an exact AOA would be easier than
chasing airspeed.

An AOA indicator that shows minimum sink and maximum L/D as well as
stall would be quite useful.



The glider solution could be a simple as the piece of yarn along the side
of the canopy...


Someone's trimming of messages needs work!

My post, immediately above yours, included the following:
"By the way, a pair of "pitch strings" mounted on the lower portion of the
canopy sides would possibly work as well and would be a trivial
installation; but I suspect that they could be difficult and distracting to
read unless they happened to fit well with your use of peripheral vision.
That issue greatly exceeds my "human factors" knowledge."

That seems similar, except that I had suggested a string on each side.

"Peter Dohm" wrote in message .. .
"Dan D" wrote in message
...


"Peter Dohm" wrote in message
.. .

"bildan" wrote in message
...


The interest for me is a sailplane installation where AOA is a
performance issue in addition to a safety issue.

My glider can be flown at 1000 pounds up to 1433 pounds gross weight
and spends a lot of time in 2G turns thermalling. The AOA for minimum
sink is always the same but the airspeed at which that happens changes
a lot. The same thing with best L/D.

A very 'slippery' glider takes a while for the airspeed to settle down
after a pitch change. Flying to an exact AOA would be easier than
chasing airspeed.

An AOA indicator that shows minimum sink and maximum L/D as well as
stall would be quite useful.



The glider solution could be a simple as the piece of yarn along the side
of the canopy...


Someone's trimming of messages needs work!

My post, immediately above yours, included the following:
"By the way, a pair of "pitch strings" mounted on the lower portion of the
canopy sides would possibly work as well and would be a trivial
installation; but I suspect that they could be difficult and distracting to
read unless they happened to fit well with your use of peripheral vision.
That issue greatly exceeds my "human factors" knowledge."

That seems similar, except that I had suggested a string on each side.




Sorry, didn't see it...it does seem great minds think alike!

"Dan D" wrote in message
...


"Peter Dohm" wrote in message
.. .
"Dan D" wrote in message
...


"Peter Dohm" wrote in message
.. .

"bildan" wrote in message
...


The interest for me is a sailplane installation where AOA is a
performance issue in addition to a safety issue.

My glider can be flown at 1000 pounds up to 1433 pounds gross weight
and spends a lot of time in 2G turns thermalling. The AOA for minimum
sink is always the same but the airspeed at which that happens changes
a lot. The same thing with best L/D.

A very 'slippery' glider takes a while for the airspeed to settle down
after a pitch change. Flying to an exact AOA would be easier than
chasing airspeed.

An AOA indicator that shows minimum sink and maximum L/D as well as
stall would be quite useful.



The glider solution could be a simple as the piece of yarn along the
side of the canopy...


Someone's trimming of messages needs work!

My post, immediately above yours, included the following:
"By the way, a pair of "pitch strings" mounted on the lower portion of
the
canopy sides would possibly work as well and would be a trivial
installation; but I suspect that they could be difficult and distracting
to
read unless they happened to fit well with your use of peripheral vision.
That issue greatly exceeds my "human factors" knowledge."

That seems similar, except that I had suggested a string on each side.




Sorry, didn't see it...it does seem great minds think alike!


No problem, and I'm glad to have a second on a simple solution.

"Dan D" wrote in message ...

A very 'slippery' glider takes a while for the airspeed to settle down
after a pitch change. Flying to an exact AOA would be easier than
chasing airspeed.

An AOA indicator that shows minimum sink and maximum L/D as well as
stall would be quite useful.


The glider solution could be a simple as the piece of yarn along the side of the canopy...


It isn't that simple. The string will show the angle of flow relative to the fuselage, not the airfoil. The fuselage angle of max L/D and minimum sink change with the flap setting. (Thermal at 15 degrees, cruise between zero and -10 degrees.)

A true AOA would supply a single given Max L/D indication no mater what the flap setting. The software to do this isn't difficult if you know the airflow relative to the fuselage, the angle of incidence of the wing, and the wing's performance curves for various flap setting.

From my perspective a reliable low-drag encoding vane is the tall pole in the tent. The airfoil performance/angle of incidence can be derived from sailplane's handbook. The cockpit indicator can be the designer's/owner's choice.

Wayne
HP-14 N990
Flap range -10 to +90.
http://www.soaridaho.com/Schreder/HP-14/N990/N990.html

"Wayne Paul" wrote in message
m...

"Dan D" wrote in message
...

A very 'slippery' glider takes a while for the airspeed to settle down
after a pitch change. Flying to an exact AOA would be easier than
chasing airspeed.

An AOA indicator that shows minimum sink and maximum L/D as well as
stall would be quite useful.


The glider solution could be a simple as the piece of yarn along the side
of the canopy...


It isn't that simple. The string will show the angle of flow relative to
the fuselage, not the airfoil. The fuselage angle of max L/D and
minimum sink change with the flap setting. (Thermal at 15 degrees, cruise
between zero and -10 degrees.)

A true AOA would supply a single given Max L/D indication no mater what
the flap setting. The software to do this isn't difficult if you know
the airflow relative to the fuselage, the angle of incidence of the wing,
and the wing's performance curves for various flap setting.

From my perspective a reliable low-drag encoding vane is the tall pole in
the tent. The airfoil performance/angle of incidence can be derived
from sailplane's handbook. The cockpit indicator can be the
designer's/owner's choice.

Wayne
HP-14 N990
Flap range -10 to +90.
http://www.soaridaho.com/Schreder/HP-14/N990/N990.html

The idea of the string, or the string on each side, is not that that it is a
true angle; but, if the canopy sides are at a promising height and also an
adiquate distance from the wing, that the positions can be marked as
calibration points for the particular angles of interest--such as best L/D
and minimum sink.

"Peter Dohm" wrote in message .. .
The idea of the string, or the string on each side, is not that that it is a
true angle; but, if the canopy sides are at a promising height and also an
adiquate distance from the wing, that the positions can be marked as
calibration points for the particular angles of interest--such as best L/D
and minimum sink.


I understand the process. I currently have a yaw string on my glider. The other canopy strings might be somewhat effective; however, I'm spoiled. I flew 13 years in the US Navy with "real" AOA systems. I am not looking for a crude substitute. I'm looking for the real thing.

Wayne
http://www.soaridaho.com/

"Wayne Paul" wrote in message
...

"Peter Dohm" wrote in message
.. .
The idea of the string, or the string on each side, is not that that it is
a
true angle; but, if the canopy sides are at a promising height and also an
adiquate distance from the wing, that the positions can be marked as
calibration points for the particular angles of interest--such as best L/D
and minimum sink.


I understand the process. I currently have a yaw string on my glider. The
other canopy strings might be somewhat effective; however, I'm spoiled. I
flew 13 years in the US Navy with "real" AOA systems. I am not looking for
a crude substitute. I'm looking for the real thing.

Wayne
http://www.soaridaho.com/

I can certainly understand that, and there is no question about which is
"better".

Also, the issue of whether the string(s) can be easily, accurately and
safely read in flight is open to question--and certainly must be resolved
under conditions other than ridge lift. IIRC, you were amoung the
participants, a number of months ago, in a human factors discussion
regarding the effects of head movement while circling and the relationship
of that to an otherwise unexplained glider crash into a mountain side. The
issue is not one that I would take lightly, and anything that requires a
head movement up or down while also turning the head to either side should
probably be avoided; but a cheap and dirty solution could conceivably work
if peripheral vision, or an eyes only glance, is truly sufficient.

OTOH, a true AOA system that can be calibrated over the full reasonable
range of angles is far from trivial--and probably well beyond my design
capabilities.

Peter

"Peter Dohm" wrote in message news

Also, the issue of whether the string(s) can be easily, accurately and
safely read in flight is open to question--and certainly must be resolved
under conditions other than ridge lift. IIRC, you were amoung the
participants, a number of months ago, in a human factors discussion
regarding the effects of head movement while circling and the relationship
of that to an otherwise unexplained glider crash into a mountain side. The
issue is not one that I would take lightly, and anything that requires a
head movement up or down while also turning the head to either side should
probably be avoided; but a cheap and dirty solution could conceivably work
if peripheral vision, or an eyes only glance, is truly sufficient.

OTOH, a true AOA system that can be calibrated over the full reasonable
range of angles is far from trivial--and probably well beyond my design
capabilities.

Peter


The old A-3D and A-6A AOA required a lot of maintenance in order to keep them calibrated.

Speaking of ridge soaring, there is a current video on YouTube that may be enlightening to those who have not explored soaring flight.

Most of my soaring is thermal flight; however, once a year a group of us head to Logan, UT to fly the ridge up into Southern Idaho. The YouTube video is from near the Idaho border heading south toward Logan. Here is the link.
(http://www.youtube.com/watch?v=2Xo6N6_9rNQ)

Wayne
http://www.soaridaho.com/

"Wayne Paul" wrote in message
m...
"Peter Dohm" wrote in message
news

Also, the issue of whether the string(s) can be easily, accurately and
safely read in flight is open to question--and certainly must be resolved
under conditions other than ridge lift. IIRC, you were amoung the
participants, a number of months ago, in a human factors discussion
regarding the effects of head movement while circling and the
relationship
of that to an otherwise unexplained glider crash into a mountain side.
The
issue is not one that I would take lightly, and anything that requires a
head movement up or down while also turning the head to either side
should
probably be avoided; but a cheap and dirty solution could conceivably
work
if peripheral vision, or an eyes only glance, is truly sufficient.

OTOH, a true AOA system that can be calibrated over the full reasonable
range of angles is far from trivial--and probably well beyond my design
capabilities.

Peter


The old A-3D and A-6A AOA required a lot of maintenance in order to keep
them calibrated.

Speaking of ridge soaring, there is a current video on YouTube that may be
enlightening to those who have not explored soaring flight.

Most of my soaring is thermal flight; however, once a year a group of us
head to Logan, UT to fly the ridge up into Southern Idaho. The YouTube
video is from near the Idaho border heading south toward Logan. Here is
the link.
(http://www.youtube.com/watch?v=2Xo6N6_9rNQ)

Wayne
http://www.soaridaho.com/

Very cool indeed!

Perhaps, someday, I'll get to try my hand at that.

Peter