Building an electronic Angle of Attack indicator

Jim Logajan wrote:
Jim Logajan wrote:
I'd post a link to a picture of what it would look like
(pretty simple concept) but can't see to find one!

My favorite one has no moving parts.

Just two thermosistors in the pitot tube...
and an opamp circuit to read differential cooling.

I would start with two small ports in the leading edge of the wing,
with capillary tubes running to a MEMS differential pressure sensor.

Since the purpose of the device is to tell the pilot how
close the AOA is to the stall value these ports should be
placed straddling the stall stagnation point. (maybe plus-minus 1/2
inch?) Then
the pressure difference is zero at stall, at any airspeed.

The differential pressure IC can feed an LED bar graph.
This should give very good stall prediction accuracy.

Isn't there a voltage-to-LED-bar-graph IC? I seem to
remember such a thing. That would make the circuit simple.

When approaching
an accelerated stall (at higher airspeed than while landing)
the unit would tend to overestimate angle. Actually, it measures
something more like "lift reserve" than angle of attack. But isn't
that
the better quantity to report to the pilot?

Anyway. the feel of the controls is very different in these two
cases,
so I think most pilots would learn to adjust their interpretation
of the reading, as long as the yellow light comes on, then red, then
the
plane stalls.

-Jeff

Hmmmm...for something you could sink your teeth in, Jim, how about a
chip that could be hard mounted inside - with no access to the airflow,
that would keep indicating AoA even with a 1/2 inch of ice over the
entire airframe? $20 gets you a 3-axis accelerometer, which uses
about a couple milliwatts from a 3 volt supply, and provides 300 mV per
g. [ADXL330)
I have it in mind that the arctan [g(vertical) / g(longitudinal)] gives
a useful proxy for AofA, if you process through an op amp ($3), an a/d
on a microcontroller ($25). That way, you could have it play Dixie at
the appropriate angle if you wanted? :-)
That's if a mouth organ reed in a tube from a wing LE aperture is too
low tech?
Brian W

RST Engineering - JIm wrote:
If somebody can tell me how to convert angle of attack to an electrical
signal, the rest is rather trivial.

Jim


"Mike" wrote in message
...
Has anyone built an electronic angle of attack meter kit. It seems to
be something that would be easy to design but beyond my feeble
electronics background.

I have seen the products that are out there and they are simple
differential pressure gauges and are expensive. I don't like the
round differential pressure gauges that many of the companies offer
for this kind of system. I was wondering if there would be a way to
put something together that would light up different color LED's for
the different levels of lift that we could build at home without
having to pay out hundreds of dollars for a prebuilt one.

On May 9, 8:35*pm, wrote:
I would start with two small ports in the leading edge of the wing,
with capillary tubes running to a MEMS differential pressure sensor.

Since the purpose of the device is to tell the pilot how
close the AOA is to the stall value these ports should be
placed straddling the stall stagnation point. (maybe plus-minus 1/2
inch?) Then
the pressure difference is zero at stall, at any airspeed.

The differential pressure IC can feed an LED bar graph.
This should give very good stall prediction accuracy.

Isn't there a voltage-to-LED-bar-graph IC? *I seem to
remember such a thing. *That would make the circuit simple.

When approaching
an accelerated stall (at higher airspeed than while landing)
the unit would tend to overestimate angle. *Actually, it measures
something more like "lift reserve" than angle of attack. But isn't
that
the better quantity to report to the pilot?

Anyway. the feel of the controls is very different in these two
cases,
so I think most pilots would learn to adjust their interpretation
of the reading, as long as the yellow light comes on, then red, then
the
plane stalls.

-Jeff

The LED bar graph chip used to be call LM3916, now replaced by
NTE1549

Mike wrote:
Has anyone built an electronic angle of attack meter kit. It seems to
be something that would be easy to design but beyond my feeble
electronics background.

I have seen the products that are out there and they are simple
differential pressure gauges and are expensive. I don't like the
round differential pressure gauges that many of the companies offer
for this kind of system. I was wondering if there would be a way to
put something together that would light up different color LED's for
the different levels of lift that we could build at home without
having to pay out hundreds of dollars for a prebuilt one.

Something like
http://www.barkeraircraft.com/AOA_kit.html

EAA web site says June 07 Sport Aviation Magazine, but I thought it was
more recent than that.

Charlie

Charlie wrote:
Mike wrote:
Has anyone built an electronic angle of attack meter kit. It seems to
be something that would be easy to design but beyond my feeble
electronics background.

I have seen the products that are out there and they are simple
differential pressure gauges and are expensive. I don't like the
round differential pressure gauges that many of the companies offer
for this kind of system. I was wondering if there would be a way to
put something together that would light up different color LED's for
the different levels of lift that we could build at home without
having to pay out hundreds of dollars for a prebuilt one.

Something like
http://www.barkeraircraft.com/AOA_kit.html

EAA web site says June 07 Sport Aviation Magazine, but I thought it was
more recent than that.

Charlie

That's a nice set up. It shouldn't be too hard to add an audio alarm
or shaker. I just hope the pitot tube isn't heated.

Dan, U.S. Air Force, retired

Dan wrote:
Charlie wrote:
Mike wrote:
Has anyone built an electronic angle of attack meter kit. It seems to
be something that would be easy to design but beyond my feeble
electronics background.

I have seen the products that are out there and they are simple
differential pressure gauges and are expensive. I don't like the
round differential pressure gauges that many of the companies offer
for this kind of system. I was wondering if there would be a way to
put something together that would light up different color LED's for
the different levels of lift that we could build at home without
having to pay out hundreds of dollars for a prebuilt one.

Something like
http://www.barkeraircraft.com/AOA_kit.html

EAA web site says June 07 Sport Aviation Magazine, but I thought it
was more recent than that.

Charlie

That's a nice set up. It shouldn't be too hard to add an audio alarm
or shaker. I just hope the pitot tube isn't heated.

Dan, U.S. Air Force, retired


Speaking of which, I have a heated pitot tube head
If anyone is in need of one, drop me a note.

I've worked this problem for a number of years. Let me offer a few
simple points.

Any system of measuring AOA will need to be calibrated. It doesn't
really need to be linear since the major interest is in the region
near stall and Cl max. It just needs to give a variable output that
is related to AOA - and be very repeatable.

If the cockpit is in clean free air flow as with a pusher or
sailplane, an effective AOA indicator can be made with a simple string
taped to the side of the canopy. On sailplanes, these 'pitch strings'
tends to 'over-indicate' by about 2:1 which is fine as it increases
the resolution of the indicator. Stall, Cl max and L/D max can be
marked on the inside of the canopy with grease pencil. It helps to
put one on each side of the canopy as they tend to validate each
other.

If you like the pressure differential AOA probes, this is a good one.
http://www.cgmasi.com/aviation/index.html

If you want NASA quality data, the gold standard is the pitch vane
mounted on an air-data nose boom. There are a number of vendors who
sell these for UAV's which are about the right size for homebuilt
airplanes.
Here's an example: http://www.spaceagecontrol.com/Adpmain

Bill D


On May 9, 6:30*am, Mike wrote:
Has anyone built an electronic angle of attack meter kit. *It seems to
be something that would be easy to design but beyond my feeble
electronics background.

I have seen the products that are out there and they are simple
differential pressure gauges and are expensive. *I don't like the
round differential pressure gauges that many of the companies offer
for this kind of system. *I was wondering if there would be a way to
put something together that would light up different color LED's for
the different levels of lift that we could build at home without
having to pay out hundreds of dollars for a prebuilt one.

In addition to Bill's comments the calibrations process must consider the position of the flaps. Remember you are measuring the AOA of the airfoil, not just the airflow relative to the fuselage.

Wayne
http://www.soaridaho.com/Schreder
..
"bildan" wrote in message ...
I've worked this problem for a number of years. Let me offer a few
simple points.

Any system of measuring AOA will need to be calibrated. It doesn't
really need to be linear since the major interest is in the region
near stall and Cl max. It just needs to give a variable output that
is related to AOA - and be very repeatable.

If the cockpit is in clean free air flow as with a pusher or
sailplane, an effective AOA indicator can be made with a simple string
taped to the side of the canopy. On sailplanes, these 'pitch strings'
tends to 'over-indicate' by about 2:1 which is fine as it increases
the resolution of the indicator. Stall, Cl max and L/D max can be
marked on the inside of the canopy with grease pencil. It helps to
put one on each side of the canopy as they tend to validate each
other.

If you like the pressure differential AOA probes, this is a good one.
http://www.cgmasi.com/aviation/index.html

If you want NASA quality data, the gold standard is the pitch vane
mounted on an air-data nose boom. There are a number of vendors who
sell these for UAV's which are about the right size for homebuilt
airplanes.
Here's an example: http://www.spaceagecontrol.com/Adpmain

Bill D

bildan wrote:
I've worked this problem for a number of years. Let me offer a few
simple points.

Any system of measuring AOA will need to be calibrated. It doesn't
really need to be linear since the major interest is in the region
near stall and Cl max. It just needs to give a variable output that
is related to AOA - and be very repeatable.

If the cockpit is in clean free air flow as with a pusher or
sailplane, an effective AOA indicator can be made with a simple string
taped to the side of the canopy. On sailplanes, these 'pitch strings'
tends to 'over-indicate' by about 2:1 which is fine as it increases
the resolution of the indicator. Stall, Cl max and L/D max can be
marked on the inside of the canopy with grease pencil. It helps to
put one on each side of the canopy as they tend to validate each
other.

If you like the pressure differential AOA probes, this is a good one.
http://www.cgmasi.com/aviation/index.html

It occurs to me that a differential system should be fairly simple to
build. Solid state pressure sensors have been around a long time. Since
AOA would be the ratio between the two sensors it should be simple to
make a comparator to voltage converter since actual pressures are
irrelevant as long as they are sufficient to be read. Airspeed would
also not be a factor. I suppose a purely mechanical system could also be
built by a mechanically inclined type. Pressure from each port would be
sent to opposing bellows in an indicator which would position a needle.

Dan, U.S. Air Force, retired