Building an electronic Angle of Attack indicator

On Sat, 9 May 2009 09:50:56 -0700, "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.


Generally "lift reserve" is more accurate than angle of attack as a
description.

On Sat, 09 May 2009 12:35:38 -0500, Jim Logajan
wrote:

"RST Engineering - JIm" wrote:
Those might get me airspeed but I'm not at all sure how you would get
theta from any one of these schemes.

I believe he means the vane is lightweight and freely pivots up or down so
that it is always pointing into the relative wind. The angle the vane makes
with some reference line on the wing or fuselage is thus the AoA. I'd post
a link to a picture of what it would look like (pretty simple concept) but
can't see to find one!

Just think of the yaw string on gliders (e.g. the red string in this
pictu http://www.highonadventure.com/Hoa08...eYawString.jpg)
but used to show vertical component of the relative wind, not horizontal.

Use variable capacitance, variable reluctance, resistor strip or
synchro connected to a vane. For a real giggle do as some Air Force
systems and employ a slotted, rotating cone for a probe. It involves
a feedback loop.

Dan, U.S. Air Force, retired




See
http://www.pegazair.on-the-net.ca/Cl...rframe/lri.htm
and use electronic differential pressure in place of the DWYER
MINIHELIC II.
The diagram of the probe dissapeared, sorry.

On Sat, 09 May 2009 19:58:21 -0500, Brian Whatcott
wrote:

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.




Won't indicate RELATIVE AIR FLOW, only absolute attitude - useless as
AOA or lift reserve (iminent stall) indicator.

On Sun, 10 May 2009 21:43:15 -0500, Dan wrote:




I forget who makes it, but there's a commercially available system
that uses ports in the leading edge of a wing. My primary concern would
be how one protects from fouling while parked. I like your probe idea
since one could easily make a protective sleeve with a "remove before
flight" streamer attached.

Dan, U.S. Air Force, retired


Any reason not to incorporate the LR sensor ports in a custom main
pitot pylon?

wrote:
On Sat, 09 May 2009 19:58:21 -0500, Brian Whatcott
wrote:

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.



Won't indicate RELATIVE AIR FLOW, only absolute attitude - useless as
AOA or lift reserve (iminent stall) indicator.


In case there are folks who can't see it: it is possible to stall out
'flat' - in fact a few WW1 era pilots did it and walked away. The air
flow is 50+ degrees to the long axis - from underneath.

Brian W

Well of course, the best is to use an AOA vane, like the jets use. The
biggest problem is where the jets conveniently mount it on the side of
the fuselage, on most singles, that's right in the prop blast,
rendering it useless. If you could find someplace to mount it outside
of the prop blast, then it would work great. But finding that
place......

On Sat, 9 May 2009 05:30:37 -0700 (PDT), 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.

rich wrote:
Well of course, the best is to use an AOA vane, like the jets use. The
biggest problem is where the jets conveniently mount it on the side of
the fuselage, on most singles, that's right in the prop blast,
rendering it useless. If you could find someplace to mount it outside
of the prop blast, then it would work great. But finding that
place......


Kitplanes once did an article on a boom mounted vane called "bacon
saver." No reason a similar set up couldn't be used.

Dan, U.S. Air Force, retired

Dan wrote:
Rip wrote:
RST Engineering - JIm wrote:
The electronics are trivial. The sensors are everything. Please
post detailed information.

Jim



"Rip" wrote in message
...


My pleasure. This topic is timely, since I recently built myself a
"Lift Reserve Indicator" based on the LM3914 and a Honeywell sensor.
Now I'm doing a "true" angle of attack indicator based on the Maxim
4210 multiplier (and an op amp) to correct for airspeed ram pressure.

A terrific treatise on the subject (with one inconsequential math
error) can be found he
http://users.cablemo.net/~jjshultz/sonex/aoa.html

Rip


I used a Honeywell ASDXL05D44D on my initial "lift reserve indicator",
mainly be cause I had a spare kicking around.

The true angle of attack design uses 2 Freescale MPXV7002 sensors.

The sensors really aren't that critical.You're after a repeatable
differential pressure signal, rather than absolute accuracy.


I forget who makes it, but there's a commercially available system
that uses ports in the leading edge of a wing. My primary concern would
be how one protects from fouling while parked. I like your probe idea
since one could easily make a protective sleeve with a "remove before
flight" streamer attached.

Dan, U.S. Air Force, retired

Thanks Dan, but credit where it's due. The page I linked to is by Jeff
Shultz, who went through the same exercise I went through, and was kind
enough to make a web-page out of his research.

In article , rich wrote:
Well of course, the best is to use an AOA vane, like the jets use. The
biggest problem is where the jets conveniently mount it on the side of
the fuselage, on most singles, that's right in the prop blast,
rendering it useless. If you could find someplace to mount it outside
of the prop blast, then it would work great. But finding that
place......


I would like to see a vain mounted on each wingtip with two indicators on the
glareshield.

I'd like to see how much difference there is in AA from one side to the other
during steep turns, slow turns, and less than perfect rudder work.

who cares? schreef:
I would like to see a vain mounted on each wingtip

Great idea, yes. Any preference of vains in the glossy magazines?
For myself I'd much like Madonna and Prince - if they are more or less
balanced.



(or could it be you meant a couple of vanes? That's a whole another
story...)