Building an electronic Angle of Attack indicator

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.

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.

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.



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

Those might get me airspeed but I'm not at all sure how you would get theta
from any one of these schemes.

Jim


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

"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

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!

Okay, found some, like this one:
http://commons.wikimedia.org/wiki/Fi...ndicator_1.jpg

And a simple mechanical kit (looks like no longer available):
http://www.aircraftspruce.com/catalo...baconsaver.php

My suspicion is that designers get fancy and use things like two non-
parallel pitots and use some mechanism to compute the AoA from their
differential pressures, which is then presented in some fancy digital
display. The irony is that AoA is easy to show, and if one is flying a
glider or pusher, a simple mechanical device could probably be mounted so
it is visible out front (i.e. "heads up") so that one can see the AoA at
the same time one is controlling their approach. But I suppose it'd be too
distracting during crusing flight and mess up the "look" of the airplane.


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

And after all is said and done, we remind ourselves that we are supposed to
be building inexpensive airplanes that look good and fly well.

So a vane on a synchro? Sure, we had those on the Boeing 3-holer (7-deuce)
at a cost of slightly less than $10k a copy in 1965 dollars. Surplus
synchros? Sure, now you are doing a one-off and how to tell another builder
how to use another brand of surplus synchro isn't feasible...not to mention
the fact that most synchros are set up to use the 115v 3phase power that the
Air Force/Boeing is so pleased with.

Or a gas tank sender with a big flap on it? Well, that looks like hell,
doesn't it? Besides that wirewound pot on the gas gauge needs some REAL
FORCE to push it around and consumes a fair amount of current in the
process.

Or some thermistors inside the pitot? WIthout a little more description you
can't tell exactly what the scheme of that is. One thermistor on the inside
top of the pitot and one on the inside bottom, each thermistor heated
equally (difficult task) and then you hope that the incoming air is laminar
and not swirling around? This might be feasible with a little more
explanation.

Differential pressure sensors? Haven't done the research lately, but the
last time I looked Motorola had stopped making the inexpensive variety and I
don't know if anybody else picked up that ball.

So, let's take it from scratch and think about what the optimum solution for
cost, looks, and reliability might be ... and the rotated yaw string is a
good idea except for the fact that 95% of the homebuilts are tractors and
the prop blast will decalibrate anything we might come up with...

Jim

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.

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.

Jim


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



The vane types are self explanatory.

http://www.aircraftmech.com/pics/aoa.jpg

http://spaceagecontrol.com/4239-01image.jpg

The cone type is a bit more complicated. Picture a hollow stainless
cone with two sets of slots running between base and apex. The slots
face towards the front of the airplane. Each set opens to its own
chamber in the cone. The pressure in each chamber is measured and the
cone is rotated until the pressures are equal. The position is then
transmitted to an indicator.

http://www.avionics-specialties.com/...thumb_stat.jpg

The cone types are usually heated to prevent icing.

If I were to build one for small aircraft I'd go with a vane and
resistance strip. In that case a standard d'arsonval meter or column of
LEDs could be used to indicate AOL.

Pressure differential systems have the disadvantages of icing or dirt
contamination.

Dan, U.S. Air Force, retired

Didja ever look at the nose of the x-15? The "ball" was a bit of magic!




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

Jim


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