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I'm having a go at making an angle of attack display using a differential pressure module and an Arduino Uno.
The module senses up to 7Kpa max per port (about 1psi unless I've gone seriously wrong- very possible)
The hardware bit is easy but I'm not yet up to speed on coding for prototyping.
My questions are ; has anyone already written the C++ code for a similar sketch? It's proving to be a steep learning curve and I'm lazily happy to use someone else's work :)
Also has anyone measured/ know what sort of psi a pitot pressure port experiences at about 100 knots?
Supplementary question; is the pressure so found proportional to the cross section area of said port/ tube?
I have a feeIng I read once that pitot tubes can be any size, but that this is often disputed.
If anyone is interested, I found some interesting NASA research on making an Alpha and yaw measuring pitot tube array for their lifting body research program (ages ago now) - no moving parts and very easy to fabricate. Ideal for the microprocessors and modules available now, but undreamed of then.
Fingers crossed :D
I think you need dynamic pressure calc'd as follows,

However, when I've tried calculation, pressure I ended up as 0.18psl for 100mph at sea level, which just doesn't seem much to me.

Does anybody know the input pressure range for an ASI.?
Sooty25 wrote:I think you need dynamic pressure calc'd as follows,

However, when I've tried calculation, pressure I ended up as 0.18psl for 100mph at sea level, which just doesn't seem much to me.

Does anybody know the input pressure range for an ASI.?

0.18psi or 5" water gauge is near correct for 100mph.
Just Google calibrating asi with manometer
Sooty25 liked this
Oooh err, ancient memory cells trying to work. For building /structure design there is a code of practice that shows basic wind speeds around the country, then adding in other factors you come up with the design wind loading for the structure to withstand. Guessing 80mph is a pretty strong wind, I seem to recall that as a rule of thumb 0.25kN/m2 was a good number for first back of a fag packet calculations. An online converter shows this as .036 psi which seems at odds with other posts, so I'd probably ignore this!
All very encouraging.
Carlmeek; thanks, I'll take you up on that.
I have bought a differential pressure module, two ports.
I intend equal pressure on the ports at cruise fading to max available on bottom one and very little on the top one around the stall angle / max alpha.
This will be achieved by two forward facing tubes mounted one above the other with the tips cut back at 45 degrees as per NASA research I saw. They actually did 4 tubes mounted in a cross with the pitot in the middle as they wanted yaw information as well.
The output from the module will then vary from around 2.5v to 5v in a linear-ish way and be fed to the Arduino which outputs to a little 3 colour vertical led stack I got for buttons.
It occurs to me now that attaching the ports to 'static' pitot type ports, one in the top of the wing and one in the bottom is easier, although calibration may be harder.
So the sketch is for getting the Arduino to output the correct led driver voltage to the correct dil pins in proportion to a 2.5v swing from 2.5v to 5v.
Cheers for being interested!
As far as the physical installation is concerned you might benefit from having a look at the Vans Forum. There are many examples of guys mounting a rivet (with a hole through it) or a football inflation valve at 30 degrees to the chord line of the wing and then using that for the AoA pressure measurement and comparing it with normal pitot pressure.

According to Dynon they use a straight line graph between the differential pressure measured at 'high' speed (when you pitch up and down 5 degrees, four times) and the stall (when you stall and press the 'stall' button on the calibration screen).
I am using 2 ports in much the same way as suggested above; although I seem to have re- invented the wheel.
Instead of comparing to existing pitot pressure I think it's easier to have 2 pressures to a separate device as I can avoid mucking about with the aircraft systems and have temporary non- permanently mounted kit to play with.
The reason for the Arduino is that ability to stick on other sensors and potentially process and display other information as well, maybe bluetoothed to an old iphone velcroed to the panel, maybe using one of the little touch screens that are available and cheap online.
Also I have a couple of spare Unos, a massive box of bits, and it's fun to learn new things!
I was unaware until I got into the Arduino stuff that sensors for everything under the sun are available and really cheap, just need to get better/quicker at coding.
And I will remember to look out of the window when and if I ever finish and install anything, :)
Seriously though, I am sure that an angle of attack display would be a very good thing, especially as I fly an aircraft with no flaps or air brakes or stall warning device into a tight strip.
Getting behind the drag curve too far can spoil your day, too much speed and then float off the end would be a mistake as well.
My fellow Jodellers will laugh at me and point out that I've managed perfectly well hundreds of times in all sorts of sporty conditions- and so have they thousands of times, but I reckon if these devices had been around years ago they would have one.
I'd been thinking of a similar project, but not to create a visual indication, but and audible one via the intercom, so eyes can be outside constantly for short field work.

My initial idea was an audible airspeed indicator. Not calling out numbers just a changing pulse rate, similar to the Angle of Attack indicator heard in many of the Trent Palmer Youtube video's.

This thought then moved onto an audible Angle of Attack pulse rate with possibly Air Speed numbers between the pulses using 2 differential pressure sensors. .

for example

Choice of hardware for me being picaxe just because I'm familiar with that and for some reason have never managed to get my head around arduino!
I'm cheating and will be fitting a Dynon pitot/AoA prove to my machine, which then talks to the MGL EFIS. The RV8 I've been testing recently has the same probe connected to the Dynon Skyview. Both give audio as well as visual indications but I tend to use the audio most of the time. AoA is great in a HUD but going heads-down seems to defeat the object a bit.

I linked to the RV Forum mainly because I was really impressed by the ingenuity of some of the ideas the guys had for getting the AoA pressure. There's some clever and imaginative people out there :D
Thanks all for the input, I will definitely look at the RV site as suggested.
The Dynon kit is tempting, but it's really about the challenge of making something and continuing my hobby on non- flying days.
I'm intrigued by the idea of audio, I agree heads- down is counter productive.
A variable tone similar to glider varios use would work well , although I used to find that it was blooming irritating.
For me, it would have to be used on final only.
Hmmm, lots to mull over.
I haven't tried the MGL unit yet but the Dynon Skyview starts to beep at you when the green lines have been gobbled up and the AoA hits the bottom of the inverted yellow triangle. The beeping then gets faster until it hits the red and then remains steady. This works the other way round as well, so you get the tones during take-off that go from steady to beeping. Luckily in an RV this doesn't take very long :D


The only minor snag with a taildragger is the steady tone will very often not be reached when performing a 'wheeler' landing as the angle of attack is still quite low when the aircraft body is level. This is a bit incidental (excuse the pun) as when you NEED to be at the lowest speed (short field, forced landing etc) you're almost certainly going to be 3-pointing it and will get the steady tone.
Flyin'Dutch' liked this