Building an electronic Angle of Attack indicator

On May 14, 7:30*pm, "Wayne Paul" wrote:
"bildan" wrote in ...

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.

Bill,

I tatally agree! *It would also be nice to have the AOA measure units instead of degrees and be calibrated so to give the same readings for max L/D and Min Sink at all flap settings. *

When I was flying A-6 Intruders 21 units of AOA was the Max Range value (best L/D) at all flap settings. *I don't believe you can develop an effective unit for aircraft with flaps without integrating the flap setting into the system. *This requires knowing the performance curve for each setting in order to calculate a single Max L/D (Max Range) indicator reading and a single Min Sink (Max endurance) indicator reading.

This isn't as simple of a problem as some seem to think it is.

Wayne
HP-14 with flap settings from -5 to +90.http://www.soaridaho.com/Schreder

Yes, there would have to be additional hardware/software to do it with
flaps. But, as long as the AOA system knew what flap setting was
being used, it could still display AOA data for that flap polar. Of
course, a continuously variable system like yours could be
complicated.

To simplify the system, min sink is only of interest at thermalling
flap settings and best L/D only at zero flap. (I'm guessing if you
are in negative flap, you're not interested in flying at best L/D.)

Also, the newer airfoils have made non-flapped gliders just about as
good as flapped ones so the flap issue may be becoming moot anyway.
It could be that a glider without flaps but flown with the precision
possible with an AOA indicator might not be at much of a disadvantage.

"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.

----begin new post--------OE got confused again-----------

Presuming that a moving/rotating vane system would work for you, you might
consider an all mechanical system.

One possibility might involve canibalizing an old VW fuel guage assembly for
some of the parts--the 1965, and possibly the 1964, VW "Beetles" had a
mechanical fuel guage activated through a push/pull cable that was similar
to the throttles on lawnmowers and the hand brakes on bicycles.

Actually, with a little thought and considering that the vane could be
located on the side(s) of the forward cockpit area, it should be possible to
devise a system that would be lighter, simpler, and also having less
friction. You could even make the indicating needle move vertically--which
would seem to me to be more intuitive.

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.

Peter

PS: I was an electronic technician, and occasionally design technician, for
many years and I am confident that I could devise an electronic "lift
reserve" or similar indicator with two or three angles marked for reference;
but I strongly suspect that a simple mechanical system would be simpler and
equally functional on a glider--where there should be no ice and no tractor
propeller.

"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...

Doug Garner! That's his name.
His AOA sensor was the soul of simplicity - and, IIRC, worked very well.
It was a fascinating project.

RST Engineering - JIm wrote:
That was "ElectrRO Fluidic Autopilot and my good friend Doug Garner from
NASA Langley wrote it. I haven't heard from him in some years, but he was
damn near 80 the last time I saw him at Oshkosh 20 years ago.

Jim




"cavelamb" wrote in message
m...
Ed wrote:

Some years back there was a complete discription of a thermistor based
system in Sport Aviation. You might contact the research department or
whatever they call it.
Might refer to "Electo Fluidic Autopilot" article.

wrote:
I learned a great deal from this thread, especially all the references
cited.
Thanks to everyone for contributing.

I think I may build the Jeff Shultz circuit,
with 8 segments if bar LED, plus a red and yellow bar-like LED.

However, I am not quite sure Shulz's logic of the lights is what I
want.

The display logic that makes sense to me is this:
in cruise many green LED are lit (could be 5-8), All greens
at this point, no yellow or red lit. These progressively
go out as the nose is lifted. Then the yellow comes on...with no
greens lit
then the red comes on. I guess the yellow can stay on when the red is
lit.
might want to make the red flash.

a job for a PIC?

-Jeff




You can configure the LM3914 LED driver to light the LEDs as shown in
the article, or one-at-a-time, like climbing a ladder. (Bar or dot mode)

You can also daisy-chain 2 or more drivers if you need finer resolution.

http://www.national.com/mpf/LM/LM3914.html

"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 ...

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

"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.

"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.