Home made AOA

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bullojm1
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Home made AOA

Postby bullojm1 » Thu Apr 23, 2015 6:03 pm

One thing I have wanted for my airplane for some time is an Angle of Attack (AOA) indicator. However, none of the ones out there fit my needs.

1) GRT - Grand Rapids has a sensor-less AOA which figured out the AOA of the wing based on its AHRS and other inputs (They call it dervived AOA). It's OK, but the display can't be put on the dashboard where it would be valuable. Also, there is no connectivity of sound for warning.

2) Advanced Flight System - AFS has a nice AOA system, and it is complete, but it is expensive.

So I decided to see what it would take to roll my own. I built a box which will take three pressure inputs - Pitot, Static and the AOA port on the pitot tube. Using these three pressures, I will output the Airspeed, AOA and altitude. The whole thing is powered by an Arduino Micro microcontroller.
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Getting it all plumbed up took some time to make it all fit into my prototype box.
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The wiring was very straight forward. Each sensor needed 5V and Ground, and then a return with the analog signal back to the Arduino. I'm pretty impressed with the Arduino - it has a lot of bang for the buck.
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The back panel - I am using push connectors.
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All assembled and ready to install! I think I have about $100 total into this project so far.
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I wrote a simple program that outputs the data of the sensors to a serial port (The Arduino's USB port looks like a serial port to a PC). For testing, I will output the data to a laptop in a delimited format of raw data. The data I am outputting is as follows:

[Milliseconds since Start],[Altitude Sensor],[Airspeed Sensor],[AOA Sensor]

The sensor data is all raw - 1023 is the max value it could be, and that indicated 5V. 0 means 0V. So it's pretty simple math to figure out what voltage I am looking at. Once I have data collected, I can analyze it in excel and plot things out.
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Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!

tmbg
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Postby tmbg » Mon Apr 27, 2015 9:36 am

this is something I had planned to do; let me know if I can help :)

btw, GRT has true AOA now, but I would have to send them my ahrs and have it upgraded to a three port, and I think it's going to be too expensive.
Ian
RV-7 SB, chugging toward final assembly
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bullojm1
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Postby bullojm1 » Mon Apr 27, 2015 10:58 am

tmbg wrote:btw, GRT has true AOA now, but I would have to send them my ahrs and have it upgraded to a three port, and I think it's going to be too expensive.


Hi Ian,

I just noticed this last week. However, my Sport system doesn't appear on the upgrade list, and they also don't have an indication for the dashboard.

Angle-of-Attack (AOA) Sensing/Stall Warning -- $249


Angle-of-attack sensing is now available for all current models of the GRT EFIS and as an upgrade to all versions of the Mini-EFIS, SX200A EFIS (identifiable by their digital magnetometer), and Adaptive AHRS. Sensing is via a two-port 45 degree pitot tube, such as those commonly available from a variety of manufacturers, or using a probe fashioned by the builder. This method has no moving parts, and allows the use of heated pitot tubes that preserve the stall warning function even in the presence of icing.


The GRT Avionics AOA function drives on-screen AOA symbology that shows too fast/too slow/optimal approach speeds, as well as stall warning. In addition, an audio output is provided on the SX200A, HX, and HXr display units. This audio provides an approaching stall warning annunciation (a pulsating tone that varies with proximity to the stall warning angle) and a solid tone indicating stall is imminent.
Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!

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Brantel
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Postby Brantel » Mon Apr 27, 2015 2:29 pm

Mike,

I did much of the same a while back. Mine never made it into a nice box like that.

What differential sensors did you use?

I had done a bunch of work around the code to make it work but I did not document it very well and since Garmin came out with AOA built in, I had no reason to finish it.

Keep us informed...

Brian C.

Image

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http://youtu.be/jK5h2KlsCT8

More stuff in the tread over on the other site.
Brantel (Brian Chesteen), RV-7/TU, #72823, N159SB
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bullojm1
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Postby bullojm1 » Mon Apr 27, 2015 4:51 pm

Brantel wrote:What differential sensors did you use?


Brian,

I used the Freescale MPX5010DP Differential Temperature Compensated sensors. They are good from 0-10kPA, which gives me up to about a ~245 kts max speed it will detect.

I haven't gotten around to analyzing any data to a real AOA angle. I do have an 8-segment RGB LED array picked out for the display. Adafruit makes a nice product which is addressable using 3 wires.

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http://www.adafruit.com/products/1426

Not bad for $5.95!
Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!

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Brantel
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Postby Brantel » Mon Apr 27, 2015 6:56 pm

Mike,

I bought a bunch of those addressable LED strips from them and they are awesome.

I made a Star for my Christmas tree out of them. I had fun playing with all the combinations of lights/colors/patterns etc I could get out of them. They can go from very dim to very bright and basically all colors of the rainbow. I used the Arduino to run em.

Very fun project to work on! I may finish mine just for fun!
Brantel (Brian Chesteen), RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Mag/P-Mag
Dual Garmin G3X Touch
Track N159SB (KK4LIF) http://aprs.fi/?call=N159SB&mt=m&z=10&timerange=3600

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bullojm1
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Postby bullojm1 » Wed May 06, 2015 10:50 am

Off with 1/2 of the wing root fairing.
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I cut the Static tubing and inserted a "Tee" fitting.
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I am using 3/16" tubing for the AOA lines - and yes, I know, my tubing should be properly color coded to be white.
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Thank god for my conduit runs! They made life easy to get the Static pressure up front.
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This is where the static line ended up at.
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Next up was tapping the AOA port. Same deal as the static port - 1/4" to 3/16" union.
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Instead of routing this line through the grommets on the forward side of the wing ribs, I though it would be easiest to just add it in the conduit.
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Ah, all three tubes in one location!
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Next up was putting some nutplates on the AOA box. Yes, I am well aware my edge distances are terrible.
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And AOA box is mounted under the pilots seat!
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Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!

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bullojm1
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Postby bullojm1 » Wed May 06, 2015 10:50 am

The location is perfect. I am thrilled so far.
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All plumbed up. I know from the way the photo looks, the green pitot tube looks kinked. I made sure to heat up the tubing and bend it into this orientation -- it's not kinked.
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And then I went flying and collected over 10,000 data points recorded at 100 ms intervals (10 samples a second). Good news is my airspeed looked great! Climbout at 100 kts, a stall, then back home.
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More good news - altitude seemed to work well. It's a little on the low side, but that is because it is calibrated for 29.92....and the barometric pressure today was 30.20.
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OK, here is the not-so-good. I used a differential pressure sensor between my AOA sensor port and the static port. I assumed the AOA port would receive positive pressure the entire flight. However, this is not true. Right after takeoff, the AOA port was in a vacuum compared to the static port. You can see for most of the flight, the data was flatlined at the bottom, because the sensor is not able to read vacuums properly. I am going to have to do more research into exactly how the pressure port for the AOA works. This is definitely a perplexing outcome I was not expecting.
Image
Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!

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bullojm1
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Postby bullojm1 » Wed May 06, 2015 10:51 am

I was obsessing with the issue I had with my AOA yesterday all day. I needed to head back to the hangar tonight to fix my AOA detection box to work with the new data I found from yesterdays run.
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I was quickly able to re-plumb the AOA sensor box. The biggest change is what the AOA differential pressure sensor was using. Before, I was comparing the pressure between the AOA port on the pitot tube to the static pressure. This didn't work out so well, because the AOA port would sometimes be less than the static port. I replumbed the AOA pressure sensor to detect the difference between the AOA port and the pitot port.
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The details of my change. The AOA pressure is on the low pressure side of the sensor, and the Pitot Pressure is on the high pressure side of the sensor.
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Another look at the Pitot Tube. I still am baffled as to why the AOA sensing port pulls a vacuum compared to the static pressure during some phases of flight. The only thing I can think of is a Venturi effect happens as high airspeed passes over the AOA sensing port.
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It was a great night to be at the airport. A few scattered thunderstorms in the distance. I was lucky and I was able to get my AOA sensor fixed and reinstalled with plenty of daylight left in the day.
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I went on a quick ~20 minute flight to get more data. Here is the airspeed plot of my flight.
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The pressure Altitude for the flight.
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The raw AOA data - it tracks pretty close to airspeed.
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Now here's the data I've been looking for - when you divide the AOA pressure (Differential Pressure) by the Pitot pressure (Dynamic or Impact Pressure)- you get the AOA! The two extremes of the AOA are indicated in this chart. The two zero-G maneuvers give me data where there wing is producing no lift. The other end of the spectrum is when the wing is at a high angle of attack during a stall. Notice that the AOA for a no-flap stall is lower than the AOA for a full-flap stall - as to be expected. Flaps add lift to the wing, causing it to be able to survive a higher AOA before stalling.
Image
Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!

JefferyWer
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Re: Home made AOA

Postby JefferyWer » Wed Aug 09, 2017 1:36 am

Any updates on the AOA bullo?

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bullojm1
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Re: Home made AOA

Postby bullojm1 » Sat Aug 12, 2017 6:22 pm

JefferyWer wrote:Any updates on the AOA bullo?


Hi Jeffery,

Unfortunately not. The breadboard is still on my work desk, so it will eventually make it back to the top of the list.
Mike Bullock
http://www.rvplane.com
RV-7 | Superior IO-360 | Whirlwind 200RV
Garmin GTN650 | GRT Dual Sport SX EFIS
Status: FLYING!


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