AOA indicator poll.

[Luc Job]

Hi!

I have developed last year a solid-state AOA indicator, based on a
differential pressure measurement (total pressure/pressure at angle)

Undoubtedly, this is a primary flight instrument to me:

-It shows where you are aerodynamically speaking, independently of
all the variable parameters: Load, flaps position, airbrakes...etc, and
does not need a calculation or interpretation to check if you are
flying right or not... And if the display is well done you will have a
clear indication of the ongoing tendency towards a safe or dangerous
situation.

-It give me an accurate indication to adapt the flaps position to stay
at the best glide angle through the whole speed range.

-It is a good indication of the optimal attitude during winch launch
and can prevent a high speed stall at high load factor.

Some pictures of my development are available here:
https://bit.ly/aoaindicator
On the video the blinking effect is induced by the camera, the leds
simply fade in or out gradually, only the red one blinks at stall angle
or if the AOA rate of increase will induce a stall within 2 seconds...
you can see that the instrument works as good as its free
alternative...

The present system includes:

-A 5 leds indicator, red-amber-green-white-blue. The corresponding
AOA for each led is programmed in flight with a push-button.

-An audio input and output: Instead of adding a warning while flying
at higher AOA than the maximum Cz (minimum sink rate), the
instrument hashes the audio output of the vario gradually, cutting
the sound at stall. This is an excellent indication that something is
wrong without adding noise... You can continue to watch outside
while climbing at the best speed, and avoid to enter a spin in the
middle of others.

-A serial i/o for software upgrade and continuous transmission of the
data to another instrument.

-An optional light sensor to adapt the luminosity to the ambient light
level... But the indirect illumination and a better reflector (in
development) has proved that it is probably unnecessary.

The only hardware modification is the installation of an angled
pressure port at a suitable place: angle is not critical, but flow must
be as undisturbed as possible. On the DG I've put mine under the
nose, about 170 mm from the tip, where I had access to the outer
hull from the inside. I drilled a 2 mm hole and glued a small
pressure chamber inside to plug a 4 mm hose. That's all.

Power drain is lower than 20 mA @ 12V, less on ground as no led is
switched on... So no switch, but an internal polyfuse to avoid any
dangerous current drain... So it is simply added to the (fused)
instruments circuit.

Now as the system proves to be functional and efficient it's time to
do something with it.

Many options are possible:

1) I can order and sell PCB's only, with a BOM and the software...
This is obviously the cheapest way... But components are mostly
SMD... So you need an oven or a lot of patience and skill... Up to
you to make a box adapted to your needs. Price should be about $10
including shipping.

2) I can sell a complete kit with all the components, PCB, software,
connectors and box... Components are not expensive except the 2
pressure sensors ($35 each)... So I should be able to make this for
about $150...

3) If you prefer a complete instrument, ready to plug-in (except the
pressure port installation) the price should be in the 300-400$
range.

All this depends obviously on quantity... So if I have 1'000 orders it
might be significantly cheaper.

At first I need to know how many people might be interested... And
what is the best option for you.

At least we can fly again in Switzerland and France... So it might
take some time for me to build a website for this product...

Luc JOB
DG-800B

[Jonathan St. Cloud]

On Tuesday, May 19, 2020 at 1:00:05 PM UTC-7, Luc Job wrote:
> Hi!
>
> I have developed last year a solid-state AOA indicator, based on a
> differential pressure measurement (total pressure/pressure at angle)
>
> Undoubtedly, this is a primary flight instrument to me:
>
> -It shows where you are aerodynamically speaking, independently of
> all the variable parameters: Load, flaps position, airbrakes...etc, and
> does not need a calculation or interpretation to check if you are
> flying right or not... And if the display is well done you will have a
> clear indication of the ongoing tendency towards a safe or dangerous
> situation.
>
> -It give me an accurate indication to adapt the flaps position to stay
> at the best glide angle through the whole speed range.
>
> -It is a good indication of the optimal attitude during winch launch
> and can prevent a high speed stall at high load factor.
>
> Some pictures of my development are available here:
> https://bit.ly/aoaindicator
> On the video the blinking effect is induced by the camera, the leds
> simply fade in or out gradually, only the red one blinks at stall angle
> or if the AOA rate of increase will induce a stall within 2 seconds...
> you can see that the instrument works as good as its free
> alternative...
>
> The present system includes:
>
> -A 5 leds indicator, red-amber-green-white-blue. The corresponding
> AOA for each led is programmed in flight with a push-button.
>
> -An audio input and output: Instead of adding a warning while flying
> at higher AOA than the maximum Cz (minimum sink rate), the
> instrument hashes the audio output of the vario gradually, cutting
> the sound at stall. This is an excellent indication that something is
> wrong without adding noise... You can continue to watch outside
> while climbing at the best speed, and avoid to enter a spin in the
> middle of others.
>
> -A serial i/o for software upgrade and continuous transmission of the
> data to another instrument.
>
> -An optional light sensor to adapt the luminosity to the ambient light
> level... But the indirect illumination and a better reflector (in
> development) has proved that it is probably unnecessary.
>
> The only hardware modification is the installation of an angled
> pressure port at a suitable place: angle is not critical, but flow must
> be as undisturbed as possible. On the DG I've put mine under the
> nose, about 170 mm from the tip, where I had access to the outer
> hull from the inside. I drilled a 2 mm hole and glued a small
> pressure chamber inside to plug a 4 mm hose. That's all.
>
> Power drain is lower than 20 mA @ 12V, less on ground as no led is
> switched on... So no switch, but an internal polyfuse to avoid any
> dangerous current drain... So it is simply added to the (fused)
> instruments circuit.
>
> Now as the system proves to be functional and efficient it's time to
> do something with it.
>
> Many options are possible:
>
> 1) I can order and sell PCB's only, with a BOM and the software...
> This is obviously the cheapest way... But components are mostly
> SMD... So you need an oven or a lot of patience and skill... Up to
> you to make a box adapted to your needs. Price should be about $10
> including shipping.
>
> 2) I can sell a complete kit with all the components, PCB, software,
> connectors and box... Components are not expensive except the 2
> pressure sensors ($35 each)... So I should be able to make this for
> about $150...
>
> 3) If you prefer a complete instrument, ready to plug-in (except the
> pressure port installation) the price should be in the 300-400$
> range.
>
> All this depends obviously on quantity... So if I have 1'000 orders it
> might be significantly cheaper.
>
> At first I need to know how many people might be interested... And
> what is the best option for you.
>
> At least we can fly again in Switzerland and France... So it might
> take some time for me to build a website for this product...
>
> Luc JOB
> DG-800B

That is wonderful. An AOA indicator is something that I would purchase for and ASG-29

[[email protected]]

Cool, I did a cal flight in that area this weekend.


Made a new flap setting ring for the ASI. Added an inside piece of tape for the outside pitch string. In flight, added a dot to mark string position for best L/D.

Then checked to see if the center of each flap settings on the ring matched the dot. They did pretty well.

I've been thinking about an electronic AOA for sensing the H&V air direction. I have an Ardinuo and diff transducer rigged to a machined nose piece with a pitot and angled port. It can sense a 1% angle change on the bench with a wind tunnel (some call it a shop vac). But I'm not sure if it would be any better than normal instruments already there.

Your picture shows you also have the pitch string. Have you added the dot and checked to see if the electronics stay's green at different speeds but still on the dot?

[Michael Opitz]

>Many options are possible:
>
>1) I can order and sell PCB's only, with a BOM and the software...
>This is obviously the cheapest way... But components are mostly
>SMD... So you need an oven or a lot of patience and skill... Up to
>you to make a box adapted to your needs. Price should be about
$10
>including shipping.
>
>2) I can sell a complete kit with all the components, PCB, software,
>connectors and box... Components are not expensive except the 2
>pressure sensors ($35 each)... So I should be able to make this for
>about $150...
>
>3) If you prefer a complete instrument, ready to plug-in (except
the
>pressure port installation) the price should be in the 300-400$
>range.
>
>All this depends obviously on quantity... So if I have 1'000 orders it
>might be significantly cheaper.
>
>At first I need to know how many people might be interested...
And
>what is the best option for you.
>
>At least we can fly again in Switzerland and France... So it might
>take some time for me to build a website for this product...
>
>Luc JOB
>DG-800B
>

I'd be interested in #3, the complete instrument, ready to plug in.

RO

[[email protected]]

Option #3 for me
Will need instruction for installation...
Dan

[GliderCZ]

On Tuesday, May 19, 2020 at 1:00:05 PM UTC-7, Luc Job wrote:
> Hi!
>
> I have developed last year a solid-state AOA indicator, based on a
> differential pressure measurement (total pressure/pressure at angle)
>
> Undoubtedly, this is a primary flight instrument to me:
>
> -It shows where you are aerodynamically speaking, independently of
> all the variable parameters: Load, flaps position, airbrakes...etc, and
> does not need a calculation or interpretation to check if you are
> flying right or not... And if the display is well done you will have a
> clear indication of the ongoing tendency towards a safe or dangerous
> situation.
>
> -It give me an accurate indication to adapt the flaps position to stay
> at the best glide angle through the whole speed range.
>
> -It is a good indication of the optimal attitude during winch launch
> and can prevent a high speed stall at high load factor.
>
> Some pictures of my development are available here:
> https://bit.ly/aoaindicator
> On the video the blinking effect is induced by the camera, the leds
> simply fade in or out gradually, only the red one blinks at stall angle
> or if the AOA rate of increase will induce a stall within 2 seconds...
> you can see that the instrument works as good as its free
> alternative...
>
> The present system includes:
>
> -A 5 leds indicator, red-amber-green-white-blue. The corresponding
> AOA for each led is programmed in flight with a push-button.
>
> -An audio input and output: Instead of adding a warning while flying
> at higher AOA than the maximum Cz (minimum sink rate), the
> instrument hashes the audio output of the vario gradually, cutting
> the sound at stall. This is an excellent indication that something is
> wrong without adding noise... You can continue to watch outside
> while climbing at the best speed, and avoid to enter a spin in the
> middle of others.
>
> -A serial i/o for software upgrade and continuous transmission of the
> data to another instrument.
>
> -An optional light sensor to adapt the luminosity to the ambient light
> level... But the indirect illumination and a better reflector (in
> development) has proved that it is probably unnecessary.
>
> The only hardware modification is the installation of an angled
> pressure port at a suitable place: angle is not critical, but flow must
> be as undisturbed as possible. On the DG I've put mine under the
> nose, about 170 mm from the tip, where I had access to the outer
> hull from the inside. I drilled a 2 mm hole and glued a small
> pressure chamber inside to plug a 4 mm hose. That's all.
>
> Power drain is lower than 20 mA @ 12V, less on ground as no led is
> switched on... So no switch, but an internal polyfuse to avoid any
> dangerous current drain... So it is simply added to the (fused)
> instruments circuit.
>
> Now as the system proves to be functional and efficient it's time to
> do something with it.
>
> Many options are possible:
>
> 1) I can order and sell PCB's only, with a BOM and the software...
> This is obviously the cheapest way... But components are mostly
> SMD... So you need an oven or a lot of patience and skill... Up to
> you to make a box adapted to your needs. Price should be about $10
> including shipping.
>
> 2) I can sell a complete kit with all the components, PCB, software,
> connectors and box... Components are not expensive except the 2
> pressure sensors ($35 each)... So I should be able to make this for
> about $150...
>
> 3) If you prefer a complete instrument, ready to plug-in (except the
> pressure port installation) the price should be in the 300-400$ I

Interested in Option 3.

[SoaringXCellence]

Luc,

Have you looked at the AOA indicators that are currently used in the GA fleet (mostly experimental aircraft)? There is a "standar" (sort of) depiction of the Aoa that you might want to follow.

https://www.aircraftspruce.com/menus/in/angleofattackindicators.html

Most of these use similar patterns to indicate approaching the stall. The center blue dot could be the optimal glide angle for a glider. Many of these systems also have an aural component that aggressively announces "PUSH" if you don't respond to less insistent prompts.

I'm not sure we need multiple ways to demonstrate the same phenomenon.

Mike

[John Foster]

On Tuesday, May 19, 2020 at 9:54:55 PM UTC-6, SoaringXCellence wrote:
> Luc,
>
> Have you looked at the AOA indicators that are currently used in the GA fleet (mostly experimental aircraft)? There is a "standar" (sort of) depiction of the Aoa that you might want to follow.
>
> https://www.aircraftspruce.com/menus/in/angleofattackindicators.html
>
> Most of these use similar patterns to indicate approaching the stall. The center blue dot could be the optimal glide angle for a glider. Many of these systems also have an aural component that aggressively announces "PUSH" if you don't respond to less insistent prompts.
>
> I'm not sure we need multiple ways to demonstrate the same phenomenon.
>
> Mike

I don't mean to be "that guy", but how is this different from a side-mounted yaw string (functionally, that is)? Some pilots mount a yaw string to the side of the canopy which has a vertical excursion, which indicates relative angle of the wind. With a stripe of electrical tape laid out on the inside of the canopy at the angle of stall, this should give you the same information at a much reduced cost, I would think.

[John Foster]

On Tuesday, May 19, 2020 at 11:32:56 PM UTC-6, John Foster wrote:
> On Tuesday, May 19, 2020 at 9:54:55 PM UTC-6, SoaringXCellence wrote:
> > Luc,
> >
> > Have you looked at the AOA indicators that are currently used in the GA fleet (mostly experimental aircraft)? There is a "standar" (sort of) depiction of the Aoa that you might want to follow.
> >
> > https://www.aircraftspruce.com/menus/in/angleofattackindicators.html
> >
> > Most of these use similar patterns to indicate approaching the stall. The center blue dot could be the optimal glide angle for a glider. Many of these systems also have an aural component that aggressively announces "PUSH" if you don't respond to less insistent prompts.
> >
> > I'm not sure we need multiple ways to demonstrate the same phenomenon.
> >
> > Mike
>
> I don't mean to be "that guy", but how is this different from a side-mounted yaw string (functionally, that is)? Some pilots mount a yaw string to the side of the canopy which has a vertical excursion, which indicates relative angle of the wind. With a stripe of electrical tape laid out on the inside of the canopy at the angle of stall, this should give you the same information at a much reduced cost, I would think.

It does seem like a pretty cool idea though, if you want to spend the money for it and not clutter the outside of your canopy with more than one string.

[Luc Job[_2_]]

Hi John...

The side string is perfectly Ok... As long as the middle string is perfectly centered.

Even a slight slip will disturb the side strings too much to have an useable indication. And it is very unlikely that you enter a stall by chance while flying straight with a perfectly centered string.

The electronic instrument seems to be much less sensitive to that: Presently I'm using the pitot + static of the fuselage, plus the centered pressure port under the nose and it is Ok... I should check by using the antenna pressure to confirm...

[Luc Job[_2_]]

Hi!

The basic principle comes from this reference:

http://www.nar-associates.com/technical-flying/angle_of_attack/DFRDAS_AccurateLowCostAoA.pdf

In order to be accurate for any atmospheric pressure (altitude), you can't make a straight differential measurement of your dynamic pressures. You need a reference pressure.

The thing is relatively tricky as you need to calculate a ratio of pressures to get the AOA... And at low speed the dynamic pressure is low... And the difference between the 2 dynamic pressures is equally low. And you must compute an accurate ratio of these 2 low values...

That's why my system uses 2 $35 pressure gauges: They are internally compensated for temperature and other factors, and outputs a 14 bits signal, with a full range corresponding to a 250 km/h dynamic pressure.

That's the price to pay to be below 1% at 70 km/h... And in practice it works...

The pitch string is corresponding to the instrument... But the string is very sensitive to sideslip... Not the instrument... That makes the side string useful only for calibration, when you can concentrate on keeping the middle string absolutely straight...

[Luc Job[_2_]]

Hi!

The basic principle comes from this reference:

http://www.nar-associates.com/technical-flying/angle_of_attack/DFRDAS_AccurateLowCostAoA.pdf

In order to be accurate for any atmospheric pressure (altitude), you can't make a straight differential measurement of your dynamic pressures. You need a reference pressure.

The thing is relatively tricky as you need to calculate a ratio of pressures to get the AOA... And at low speed the dynamic pressure is low... And the difference between the 2 dynamic pressures is equally low. And you must compute an accurate ratio of these 2 low values...

That's why my system uses 2 $35 pressure gauges: They are internally compensated for temperature and other factors, and outputs a 14 bits signal, with a full range corresponding to a 250 km/h dynamic pressure.

That's the price to pay to be below 1% at 70 km/h... And in practice it works...

The pitch string is corresponding to the instrument... But the string is very sensitive to sideslip... Not the instrument... That makes the side string useful only for calibration, when you can concentrate on keeping the middle string absolutely straight...

[Luc Job[_2_]]

Hi Mike!

I fly also with gasoline... And I think that the problem is different.

-GA AOA are relatively big... Gliders panels are small... And I prefer to have as much visibility as possible in the glider, So I won't add something directly in my eyesight, even a HUD... I fly in mountains, so I look at the rocks and other gliders, and it seldom stays straight ahead in front of the nose when it needs attention...

-GA AOA are not progressive, each bar is basically on-off... And it will focus your attention on the instrument each time that one of this bar will change... This is excessively disturbing in my point of view. A progressive change of color and position of the indicator can be caught by the peripheral vision... You can stay focused on what's important without missing the information.

-An added aggressive sound is useless in a stress situation... Look at all the planes that made belly landings with the gear warning shouting... A spoken warning is more explicit, but if it is Ok in a GA aircraft and for something that has time to be corrected, it takes too much time on a glider entering stall in a rough thermal... by the time the system says 'Pull' + interpretation of the message by your brain + action on the stick, it's too late...

Altering the normal sound progressively looks more efficient and less disturbing... I had a Zander 940 (It died for 2 years, very good vario), and it did exactly that: distorting the audio when approaching stall... Once you get used to that, your reaction will be instant and automatic. On my system, adding distortion means analog processing of the audio and that's more complex than hashing the signal, and has the same effect... I must tune that but presently the timebase is about 1/10 seconds: If you are at stall AOA, the audio is cut 100%, and if your AOA is half way between Cz max and stall, the signal will be cut 5/100 seconds and audible the remaining 5/100...

And it doesn't take many training hours to push the stick automatically when the sound looks strange... And push it full forward if it becomes dead silent.

[Luc Job[_2_]]

One last point to finalize the design:

4) Would you like a remote display bar that you can glue over your panel, and place the instrument box somewhere else?

The display bar should be about 60x10x4 mm, including the calibration button and light sensor.

The present box is 60x70x15 mm and as you can see on the pictures it fits to the side of a 57 mm instrument, in a 80 mm hole.

I think I will design the new PCB to allow a detachable display bar anyway.

I'm still open to any proposition...

[[email protected]]

> That's why my system uses 2 $35 pressure gauges: They are internally compensated for temperature and other factors, and outputs a 14 bits signal, with a full range corresponding to a 250 km/h dynamic pressure.
>
> That's the price to pay to be below 1% at 70 km/h... And in practice it works...
>
> The pitch string is corresponding to the instrument... But the string is very sensitive to sideslip...

Excellent, looks like a great plan and paper to read.

Are you going to put the design up on github?

Put me down for #2.

[Luc Job[_2_]]

Before I publish it, the code needs some cleaning and complements... I need to test the light sensor functions... It was left aside as it proved to be unnecessary until now.

And now I'm working on the PCB design for the 'production' version.

Basically the idea of the 5 leds is to have an indication for the 5 important AOA's to fly a glider:

1)Blinking red is stall.
2)Red (nonblinking) to amber is below Cz max, or below minimum sink rate if you prefer...So on the bad side of the flight envelope, also indicated by the audio perturbation.
3)amber is Cz max or minimum sink rate.
4)green is approach AOA... Logical color for this part of flight.
5)white is best glide angle AOA
6)blue is lower than best glide angle

With an unflapped glider it is in the right order... With a flapped glider, the approach AOA with the flaps in landing position at the recommended approach speed of 1.3 Vs is lower than the best glide angle... So technically the green led should be between the white and the blue... Assuming that you set the blue at the AOA near the Vne...

But on a flapped glider you can also decide that green is best glide angle and white is approach with landing flaps (white arc on ASI)... That's what I have done on my DG... And on some gliders you have more than 1 landing flaps position... So it's up to you to decide what is the best setting for you and your glider...

On a flapped glider it makes also sense to have the green for the ideal flaps position, increase the flap angle when the color turns towards amber and lower it when it turns white...

[jfitch]

On Wednesday, May 20, 2020 at 6:46:19 AM UTC-7, Luc Job wrote:
> Before I publish it, the code needs some cleaning and complements... I need to test the light sensor functions... It was left aside as it proved to be unnecessary until now.
>
> And now I'm working on the PCB design for the 'production' version.
>
> Basically the idea of the 5 leds is to have an indication for the 5 important AOA's to fly a glider:
>
> 1)Blinking red is stall.
> 2)Red (nonblinking) to amber is below Cz max, or below minimum sink rate if you prefer...So on the bad side of the flight envelope, also indicated by the audio perturbation.
> 3)amber is Cz max or minimum sink rate.
> 4)green is approach AOA... Logical color for this part of flight.
> 5)white is best glide angle AOA
> 6)blue is lower than best glide angle
>
> With an unflapped glider it is in the right order... With a flapped glider, the approach AOA with the flaps in landing position at the recommended approach speed of 1.3 Vs is lower than the best glide angle... So technically the green led should be between the white and the blue... Assuming that you set the blue at the AOA near the Vne...
>
> But on a flapped glider you can also decide that green is best glide angle and white is approach with landing flaps (white arc on ASI)... That's what I have done on my DG... And on some gliders you have more than 1 landing flaps position... So it's up to you to decide what is the best setting for you and your glider...
>
> On a flapped glider it makes also sense to have the green for the ideal flaps position, increase the flap angle when the color turns towards amber and lower it when it turns white...

I am struggling to understand why I would need one, but a couple of technical questions: How well does it work in accelerated flight such as a 50 deg bank? Will you need an adjustment to account for different nose shapes and/or different pressure tube installation locations? What does it indicate in a spin or spin transition to spiral dive?

[Luc Job[_2_]]

You need one precisely to know where your are, aerodynamically speaking, whatever would be the bank angle, load factor, weight (including ballast), flaps position or airbrake extension... On any case it will show the real position of your wing in the surrounding air, and how it changes, and this is the only thing that matters to fly...

Sorry if you learn that speed is life... AOA gives a much more straightforward information of your real safety margin, or 'lift reserve' before you fall from the sky...

And it indicates directly if you fly at the lowest possible rate of descent or at the best glide angle as these angles are purely aerodynamic parameters that does not depend on anything else.

The only thing that will have a slight influence is a modification of the airfoil in front of the separation point, like the extension of a leading edge slat.

Flaps have no influence on stall AOA, as the separation point is before the flap along the airfoil, but as it changes the camber of the airfoil, it changes its maximum lift... reducing the stall speed when positive, and allowing to keep the best angle through an extended speed range when negative... One more reason why speed isn't safety...

Of course, you can compute the stall or best speed form the mass of the glider and actual load factor, flaps position, airbrake position, and compare this computed speed with what your ASI indicates, but presently no instrument does this for you accurately and transparently.

The AOA indicator will be accurate as long as the measured pressures are significant. In a spin, It will indicate that you are above stall... Maybe the exact angle can't be determined as the dynamic pressure is likely to be inaccurate due to the airflow angle Vs the probe, but as soon as you recover the indication will be back instantly...

And this is precisely a situation where it is useful: When you recover from a dive, you will pull at least 2-3 g... You only have your feeling to pull enough to recover and stay below the Vne, but not too much or you risk a high speed stall... With an AOA, you can adjust precisely how much you pull the stick to maintain the indicator in the good range. This will guarantee that you will lose the minimum of altitude to recover from the dive...

The instrument is based on a pressure ratio. It's easy to understand that if the angle difference is low, the pressures will have less difference and the ratio begins to be inaccurate. So the ideal angle is 45°... But this is not common on gliders. AOA probes on fighters have about a 20° angle and they work even in supersonic airflow... So I would say that 20° is a reasonable minimum, and this can be found under the nose of any glider... And this is a place where the flow has no reason to be disturbed or modified within the allowed speed range, whatever will be the camber and shape of the nose.

Then as you calibrate the instrument for the different angles in flight, by pushing a button when you are stabilized at each reference angle, there is no further adjustment needed...

Any other question?

[jfitch]

On Wednesday, May 20, 2020 at 12:50:35 PM UTC-7, Luc Job wrote:
> You need one precisely to know where your are, aerodynamically speaking, whatever would be the bank angle, load factor, weight (including ballast), flaps position or airbrake extension... On any case it will show the real position of your wing in the surrounding air, and how it changes, and this is the only thing that matters to fly...
>
> Sorry if you learn that speed is life... AOA gives a much more straightforward information of your real safety margin, or 'lift reserve' before you fall from the sky...
>
> And it indicates directly if you fly at the lowest possible rate of descent or at the best glide angle as these angles are purely aerodynamic parameters that does not depend on anything else.
>
> The only thing that will have a slight influence is a modification of the airfoil in front of the separation point, like the extension of a leading edge slat.
>
> Flaps have no influence on stall AOA, as the separation point is before the flap along the airfoil, but as it changes the camber of the airfoil, it changes its maximum lift... reducing the stall speed when positive, and allowing to keep the best angle through an extended speed range when negative.... One more reason why speed isn't safety...
>
> Of course, you can compute the stall or best speed form the mass of the glider and actual load factor, flaps position, airbrake position, and compare this computed speed with what your ASI indicates, but presently no instrument does this for you accurately and transparently.
>
> The AOA indicator will be accurate as long as the measured pressures are significant. In a spin, It will indicate that you are above stall... Maybe the exact angle can't be determined as the dynamic pressure is likely to be inaccurate due to the airflow angle Vs the probe, but as soon as you recover the indication will be back instantly...
>
> And this is precisely a situation where it is useful: When you recover from a dive, you will pull at least 2-3 g... You only have your feeling to pull enough to recover and stay below the Vne, but not too much or you risk a high speed stall... With an AOA, you can adjust precisely how much you pull the stick to maintain the indicator in the good range. This will guarantee that you will lose the minimum of altitude to recover from the dive...
>
> The instrument is based on a pressure ratio. It's easy to understand that if the angle difference is low, the pressures will have less difference and the ratio begins to be inaccurate. So the ideal angle is 45°... But this is not common on gliders. AOA probes on fighters have about a 20° angle and they work even in supersonic airflow... So I would say that 20° is a reasonable minimum, and this can be found under the nose of any glider... And this is a place where the flow has no reason to be disturbed or modified within the allowed speed range, whatever will be the camber and shape of the nose.
>
> Then as you calibrate the instrument for the different angles in flight, by pushing a button when you are stabilized at each reference angle, there is no further adjustment needed...
>
> Any other question?

I should have phrased that differently, I'm pretty familiar with AOA and what it does. To me it is generally communicated by numerous other cues but that may be from a lifetime of hang gliding, sailing, soaring, etc. A high speed stall it is harder to feel from these things, but a high speed stall isn't a normal occurrence in a sailplane.

I'd think that flap setting would definitely affect it, as you are really measuring the AOA of the fuselage and inferring AOA of the wing assuming fixed angle of incidence? Increasing flap changes the angle of incidence, increasing the AOA of the wing compared to the fuselage?

Anyway, it sounds like you have the calibration tools to adapt to installation differences. One suggestion I have is to make the display as narrow as possible, panel space is very tight with today's gliders. You might even consider an option to mount discrete panel mount LEDs as these could be fit in-between instruments or at the edge of a panel in many situations where your current display could not.

[Luc Job[_2_]]

When I say that flaps have non influence on stall AOA, I shoud have said 'simple flaps'... For the same reasons as leading edge slats, slotted flaps are another story... But the only glider I'm aware of with slotted flaps was the Breguet 904... That's history but I will never regret the day I had one at disposal...

Basically it is a question of definition:

If you consider that the AOA is the angle between the tip of the leading edge and the trailing edge, then the critical AOA will decrease with flaps down... But that's not what we measure... We measure the angle of the fixed part of the wing and unless you have a variable incidence this angle is the same on the fuselage or on the wing.

When I say that flaps position has no influence on the best glide angle or maximum lift angle, it assumes also that I consider low flaps deflection, say +- 15°... This might not be true for 45° flap deflection or more as this will modify the airflow regime considerably, create a lot of turbulence on top and new stagnation points under the profile... Indeed it will lower the critical AOA (as measured).

Same for critical stall angle... Stick a sidestring on a flapped glider and check for any flaps position, and stick some colored tape at stall angle! Wind tunnel experiments or calculation shows that we are within 1-2°.... Over a 25° range. This is sufficient to say that it will make no difference in flight...compared for example to stall speed in various configurations. And if we suppose that the pilot is sufficiently skilled to keep the right flaps settings it makes no sense anyway... And the AOA indicator is a precious instrument to set the flaps at the right position anytime.

As I said on a previous mail, I'm designing a detachable indicator... Dimension will be about 10x50x8 mm with a back connector and it might be integrated in the panel or simply stuck over the surface... I think to integrate it into a 80 mm ASI... I have a spare... And don't forget that the data will be available in any suitable format for your calculator to have something displayed there... Next step is to integrate this into XcSoar... Next winter?

And to anticipate the next remark: My system is not designed to work in inverted flight... But it is possible to setup a second one with a top pressure port for this purpose.

[Luc Job[_2_]]

I have uploaded a new video on https://bit.ly/aoaindicator.

It shows the display nearly without camera flickering... Video was taken in full light but I had to darken the exposure to avoid (mostly) a blueish effect due to saturation of the sensor with the green led.

This is nearer to the production version.

For me it is essential to have a relatively large color spot to notice it with the peripheral vision. That's why I will use leds with a wide beam, illuminating a reflector.

I've used a special plexiglas that catches the light internally, spreading it even more... But you still notice the up-down motion effect of the light.

It is possible with this material to build a kind of HUD, with the leds facing up through a prismatic plexiglas part.

New PCB almost designed...

[Matt Herron Jr.]

On Tuesday, May 19, 2020 at 1:00:05 PM UTC-7, Luc Job wrote:
> Hi!
>
> I have developed last year a solid-state AOA indicator, based on a
> differential pressure measurement (total pressure/pressure at angle)
>
> Undoubtedly, this is a primary flight instrument to me:
>
> -It shows where you are aerodynamically speaking, independently of
> all the variable parameters: Load, flaps position, airbrakes...etc, and
> does not need a calculation or interpretation to check if you are
> flying right or not... And if the display is well done you will have a
> clear indication of the ongoing tendency towards a safe or dangerous
> situation.
>
> -It give me an accurate indication to adapt the flaps position to stay
> at the best glide angle through the whole speed range.
>
> -It is a good indication of the optimal attitude during winch launch
> and can prevent a high speed stall at high load factor.
>
> Some pictures of my development are available here:
> https://bit.ly/aoaindicator
> On the video the blinking effect is induced by the camera, the leds
> simply fade in or out gradually, only the red one blinks at stall angle
> or if the AOA rate of increase will induce a stall within 2 seconds...
> you can see that the instrument works as good as its free
> alternative...
>
> The present system includes:
>
> -A 5 leds indicator, red-amber-green-white-blue. The corresponding
> AOA for each led is programmed in flight with a push-button.
>
> -An audio input and output: Instead of adding a warning while flying
> at higher AOA than the maximum Cz (minimum sink rate), the
> instrument hashes the audio output of the vario gradually, cutting
> the sound at stall. This is an excellent indication that something is
> wrong without adding noise... You can continue to watch outside
> while climbing at the best speed, and avoid to enter a spin in the
> middle of others.
>
> -A serial i/o for software upgrade and continuous transmission of the
> data to another instrument.
>
> -An optional light sensor to adapt the luminosity to the ambient light
> level... But the indirect illumination and a better reflector (in
> development) has proved that it is probably unnecessary.
>
> The only hardware modification is the installation of an angled
> pressure port at a suitable place: angle is not critical, but flow must
> be as undisturbed as possible. On the DG I've put mine under the
> nose, about 170 mm from the tip, where I had access to the outer
> hull from the inside. I drilled a 2 mm hole and glued a small
> pressure chamber inside to plug a 4 mm hose. That's all.
>
> Power drain is lower than 20 mA @ 12V, less on ground as no led is
> switched on... So no switch, but an internal polyfuse to avoid any
> dangerous current drain... So it is simply added to the (fused)
> instruments circuit.
>
> Now as the system proves to be functional and efficient it's time to
> do something with it.
>
> Many options are possible:
>
> 1) I can order and sell PCB's only, with a BOM and the software...
> This is obviously the cheapest way... But components are mostly
> SMD... So you need an oven or a lot of patience and skill... Up to
> you to make a box adapted to your needs. Price should be about $10
> including shipping.
>
> 2) I can sell a complete kit with all the components, PCB, software,
> connectors and box... Components are not expensive except the 2
> pressure sensors ($35 each)... So I should be able to make this for
> about $150...
>
> 3) If you prefer a complete instrument, ready to plug-in (except the
> pressure port installation) the price should be in the 300-400$
> range.
>
> All this depends obviously on quantity... So if I have 1'000 orders it
> might be significantly cheaper.
>
> At first I need to know how many people might be interested... And
> what is the best option for you.
>
> At least we can fly again in Switzerland and France... So it might
> take some time for me to build a website for this product...
>
> Luc JOB
> DG-800B

I am interested, but I would like to make the following design suggestions;

1) Make the LEDs remote from the PCB. Panel space is at a premium, in front and behind. I have a much better chance of retrofitting this in my panel if I can just drill a small hole in the panel and double stick the LED strip some place, while the "Box" with the PCB can get stashed behind the panel with some mounting tabs. Make sure the connector is small enough to go through a 1/4 hole that the LED strip then covers. This approach leaves you room for different display ideas in the future.

2) make the LED strip smaller. With the color scheme you have, the size seems too large, and makes install more challenging.

3) make the external ports easy to install, and modular. Perhaps there is a version that can be installed in the nose with the Pitot tube and the thermistor, and one for the belly as you have done. How small can the hoses be that go through the hull? would it work to mount on the side of the cockpit rather than underneath?

Sign me up for option #3 if you can incorporate the above changes.

Matt

[John Foster]

On Friday, May 22, 2020 at 8:04:18 AM UTC-6, Luc Job wrote:
> I have uploaded a new video on https://bit.ly/aoaindicator.
>
> It shows the display nearly without camera flickering... Video was taken in full light but I had to darken the exposure to avoid (mostly) a blueish effect due to saturation of the sensor with the green led.
>
> This is nearer to the production version.
>
> For me it is essential to have a relatively large color spot to notice it with the peripheral vision. That's why I will use leds with a wide beam, illuminating a reflector.
>
> I've used a special plexiglas that catches the light internally, spreading it even more... But you still notice the up-down motion effect of the light.
>
> It is possible with this material to build a kind of HUD, with the leds facing up through a prismatic plexiglas part.
>
> New PCB almost designed...

Nice.

[Shaun Wheeler]

On Tuesday, May 19, 2020 at 3:00:05 PM UTC-5, Luc Job wrote:
> Hi!
>
> I have developed last year a solid-state AOA indicator, based on a
> differential pressure measurement (total pressure/pressure at angle)
>
> Undoubtedly, this is a primary flight instrument to me:
>
> -It shows where you are aerodynamically speaking, independently of
> all the variable parameters: Load, flaps position, airbrakes...etc, and
> does not need a calculation or interpretation to check if you are
> flying right or not... And if the display is well done you will have a
> clear indication of the ongoing tendency towards a safe or dangerous
> situation.
>
> -It give me an accurate indication to adapt the flaps position to stay
> at the best glide angle through the whole speed range.
>
> -It is a good indication of the optimal attitude during winch launch
> and can prevent a high speed stall at high load factor.
>
> Some pictures of my development are available here:
> https://bit.ly/aoaindicator
> On the video the blinking effect is induced by the camera, the leds
> simply fade in or out gradually, only the red one blinks at stall angle
> or if the AOA rate of increase will induce a stall within 2 seconds...
> you can see that the instrument works as good as its free
> alternative...
>
> The present system includes:
>
> -A 5 leds indicator, red-amber-green-white-blue. The corresponding
> AOA for each led is programmed in flight with a push-button.
>
> -An audio input and output: Instead of adding a warning while flying
> at higher AOA than the maximum Cz (minimum sink rate), the
> instrument hashes the audio output of the vario gradually, cutting
> the sound at stall. This is an excellent indication that something is
> wrong without adding noise... You can continue to watch outside
> while climbing at the best speed, and avoid to enter a spin in the
> middle of others.
>
> -A serial i/o for software upgrade and continuous transmission of the
> data to another instrument.
>
> -An optional light sensor to adapt the luminosity to the ambient light
> level... But the indirect illumination and a better reflector (in
> development) has proved that it is probably unnecessary.
>
> The only hardware modification is the installation of an angled
> pressure port at a suitable place: angle is not critical, but flow must
> be as undisturbed as possible. On the DG I've put mine under the
> nose, about 170 mm from the tip, where I had access to the outer
> hull from the inside. I drilled a 2 mm hole and glued a small
> pressure chamber inside to plug a 4 mm hose. That's all.
>
> Power drain is lower than 20 mA @ 12V, less on ground as no led is
> switched on... So no switch, but an internal polyfuse to avoid any
> dangerous current drain... So it is simply added to the (fused)
> instruments circuit.
>
> Now as the system proves to be functional and efficient it's time to
> do something with it.
>
> Many options are possible:
>
> 1) I can order and sell PCB's only, with a BOM and the software...
> This is obviously the cheapest way... But components are mostly
> SMD... So you need an oven or a lot of patience and skill... Up to
> you to make a box adapted to your needs. Price should be about $10
> including shipping.
>
> 2) I can sell a complete kit with all the components, PCB, software,
> connectors and box... Components are not expensive except the 2
> pressure sensors ($35 each)... So I should be able to make this for
> about $150...
>
> 3) If you prefer a complete instrument, ready to plug-in (except the
> pressure port installation) the price should be in the 300-400$
> range.
>
> All this depends obviously on quantity... So if I have 1'000 orders it
> might be significantly cheaper.
>
> At first I need to know how many people might be interested... And
> what is the best option for you.
>
> At least we can fly again in Switzerland and France... So it might
> take some time for me to build a website for this product...
>
> Luc JOB
> DG-800B



I'm kinda sorta interested. If the BOM can be sourced in the US....I'm even more interested. I'd like to play with one either way just to see what I can do with it.

[Luc Job[_2_]]

Hi Matt!

> 2) make the LED strip smaller. With the color scheme you have, the size seems too large, and makes install more challenging.
>

Latest desing of the remote led strip is a bar of 47 mm height and 10.2 mm width, 8.2 mm thick, plus a 10x3 mm protrusion in the middle for the connector... I will setup the website with a download section so that you can download a drawing soon. The smallest useable connector I have found has a 8x3 mm section (or 10x3), so you should drill 3 holes of 3.5 mm next to the other and finish with a small file... Or if you have room to put it behind the panel, the slit for the display should be 47x7 mm.


> 3) make the external ports easy to install, and modular. Perhaps there is a version that can be installed in the nose with the Pitot tube and the thermistor, and one for the belly as you have done. How small can the hoses be that go through the hull? would it work to mount on the side of the cockpit rather than underneath?
>

There is presently no protrusion or pass-through tubes in the installation.

The system uses the pitot + static ports already installed on any glider, plus this famous angled pressure port.

It's only a drilled hole similar to the static ports.

It has to be under the nose where the angle is sufficient and in front of any perturbation (for example if the front tow hook is under the nose). Then you have to glue a small cap inside the hull (like for the statics, I think), with the tube connected to it parallel to the hull. Total thickness inside can be as low as 5 mm if you use a 4 mm PU tube. On the DG, most of the outer hull isn't easily reachable from inside except where the canopy hinge fits when closed... I had more than enough clearance to put my port there and this is precisely where the hull angle is acceptable. I will make pictures of my setup and post on the website. (glideraoa.com)

This is the simplest and most reliable setup, but if it is really impossible to have the pressure port under the nose tip for some reason, then it is possible to design a customized profiled protrusion with a 45° flat area and the port hole on it... And place it somewhere else but where the flow is undisturbed and far enough from the hull and without possible interaction with the tow/winch rope... Best place could be under a wing, if you have access... But I'm afraid that the customized antenna will be more expensive than the instrument.

Let me know first on which glider it is impossible to set it up under the nose... The Stemme, maybe... If I have a demand, I will study a suitable antenna for it... No tow rope problem.

Putting the pressure port 'antenna' on the side of the fuselage will make it sensitive to sideslip and this has to be avoided.

[Luc Job[_2_]]

Last update before I order the new PCB's:

1) Having tested last season without it and without problems I will drop completely the light sensor... I see no situation where it is really useful with the present display... The colors can be seen in any situation except maybe with the direct sunlight over the display, that means very low sun from behind and In this case it will be hard to beat the sun anyway.

In the opposite situation, with the sun facing you, a light sensor on the panel will be in the shade and reduce the led's intensity instead of increasing it to allow you to see the panel despite the facing sun... Bad...

For these reasons I will replace the light sensor with a rotary encoder so that you can adjust the light yourself if needed. And the push function of the encoder will be for calibration (it needs a quite long push to trigger the calibration routine).

What do you think?

[Matt Herron Jr.]

On Saturday, May 23, 2020 at 3:52:21 AM UTC-7, Luc Job wrote:
> Last update before I order the new PCB's:
>
> 1) Having tested last season without it and without problems I will drop completely the light sensor... I see no situation where it is really useful with the present display... The colors can be seen in any situation except maybe with the direct sunlight over the display, that means very low sun from behind and In this case it will be hard to beat the sun anyway.
>
> In the opposite situation, with the sun facing you, a light sensor on the panel will be in the shade and reduce the led's intensity instead of increasing it to allow you to see the panel despite the facing sun... Bad...
>
> For these reasons I will replace the light sensor with a rotary encoder so that you can adjust the light yourself if needed. And the push function of the encoder will be for calibration (it needs a quite long push to trigger the calibration routine).
>
> What do you think?

Since you only have to calibrate once, please make the calibration button on a cable you can hold in your hand while you fly for that one flight. then it can be unplugged and never seen again.

47 x 10mm sounds reasonable for the display. Thanks

For the connector, you should only need 6 pins, yes? Why not hard wire a 6 conductor phone cable out the back of the display, with an RJ-11 phone connector on the end. Then if I want to make a small hole, I can cut the connector, feed the cable through, and crimp on another RJ-11 once through the panel.

I understand about the port mounting now, thanks. One further question; is the sensor at the port, or do you need to run tubing back to the PCB? Much easier to run a wire to the PCB than a tube...

Matt

[Luc Job[_2_]]

>
> For the connector, you should only need 6 pins, yes? Why not hard wire a 6 conductor phone cable out the back of the display, with an RJ-11 phone connector on the end. Then if I want to make a small hole, I can cut the connector, feed the cable through, and crimp on another RJ-11 once through the panel.
>
Now that I have canceled the light sensor option I have gained some room for a RJ-25 plug on the PCB... I planned to use this kind of cable anyway... But it is 2.5x7 mm, so the hole through the panel will be only marginally smaller...

> I understand about the port mounting now, thanks. One further question; is the sensor at the port, or do you need to run tubing back to the PCB? Much easier to run a wire to the PCB than a tube...
>
The sensor I2C data isn't supposed to travel more than inches away... And it is a differential gauge... So you should run a static tube to the sensor+ wiring to the panel... More complex than pulling another tube along the existing pitot and/or static... And the panel is probably less than 3-4 feets away... I'm using relatively flexible PU tubing for pneumatic applications.... It's stiff enough to be pushed everywhere, will not be pinched by chance, will not wear out and can still be bent much easier than nylon... This will be a part of the kit, I think.

And having about the same volume of air between the 2 ports and the sensors might induce a comparable damping of both sensors... I don't know if it has a real influence, but it can't hurt... Electronic damping has been introduced in the software as I manage to get the AOA data about 600 times/second.... A 1/10 second average value looks still instant and filters most of the unsignificant turbulence...

By monitoring the rate of change of this dampened value, I can predict if a stall is likely to be reached within 2 seconds... And display the corresponding warning before the critical AoA is reached, giving you some time to react before loosing control...

[[email protected]]

This is an intriguing idea. I've been interested in AOA since my university days in the 1970s. I flew my LS-3 for over a decade using a small bubble level to set the continuous flap setting of that glider (not perfect but not bad). And I had the side strings on my ASW 24 canopy for about the same amount of time (helpful at times but susceptible to gusts and slight slips/skids, as you said).

I'd be more interested in the kit than the finished instrument.

One concern: any port on the underside of the fuselage is subject to clogging when landing in dirt fields. It's not likely given the angles that you're talking about but I'd have to add one more item to my pre-flight checklist. Oh, well.

How robust are the pressure sensors? I assume if the electronics are not switched on that there is no danger of damaging them even if some idiot blows into a probe or port.

Chip Bearden
JB

[Luc Job[_2_]]

>
> How robust are the pressure sensors? I assume if the electronics are not switched on that there is no danger of damaging them even if some idiot blows into a probe or port.
>

The datasheet say that the proof pressure is 35psi.. about 2.3 bar... So not foolproof, but I bet that neither the mechanical ASI, nor the electronic calculator will do better...

The port is just under the nose... If you land into a swamp or a very soft field other parts of the plane will be clogged and need cleaning... It's not impossible that a bug crashes precisely there... But we have no MCAS to worry about if the AoA fails.

[Tim from Pure Glide]

Very awesome! I'd really like one that's displayed like this...
http://www.youtube.com/watch?v=2wlvpJLcf-A

[[email protected]]

On Sunday, May 24, 2020 at 5:34:54 AM UTC-5, Tim from Pure Glide wrote:
> Very awesome! I'd really like one that's displayed like this...
> http://www.youtube.com/watch?v=2wlvpJLcf-A

Neat, I'm thinking tweak the S/W for some NeoPixels just under the glareshield.
https://www.adafruit.com/category/168


I wonder what the gadget shows if you are holding constant attitude and fly trough a thermal?

[Luc Job[_2_]]

On Sunday, 24 May 2020 14:48:05 UTC+2, wrote:
> On Sunday, May 24, 2020 at 5:34:54 AM UTC-5, Tim from Pure Glide wrote:
> > Very awesome! I'd really like one that's displayed like this...
> > http://www.youtube.com/watch?v=2wlvpJLcf-A
>
> Neat, I'm thinking tweak the S/W for some NeoPixels just under the glareshield.
> https://www.adafruit.com/category/168
>
>
> I wonder what the gadget shows if you are holding constant attitude and fly trough a thermal?

I have some NeoPixels in the drawer... But for this project it looks not significant to me: I always want the same color at the same position...

The Icon AoA is nice on any airplane with room on the panel. I don't have to say more... This can be displayed on the glass side of our cockpits... It's just a question of software when the serial data stream is available... But the fact is that when the AoA information is the most relevant for safety, I have no time to look for it or find the right page/option of the calculator. The led bar, at a fixed place near the ASI, which is a complementary information and a kind of cross-check indication, is all I need to keep on flying and stay concentrated on the outside.

I choose a 5 leds display AoA with 5 different colors for several reasons:

- Visually, the color gives me an instant indication and doesn't need a lot of training or attention to be interpreted: Green is Ok, Amber means high AoA and high lift, Red = warning, blinking Red = danger. On the other side blue is too low, I should push the flaps forward... white is landing configuration (for a flapped glider) All these color are progressively changing so that the in-between information is there. Ok, it's slightly different for a glider without flaps but it follows the same logic: Green becomes approach AoA and white will be best glide... And this has the same logical aerodynamic meaning in both cases and values are relatively near to each other.

[Jonathan St. Cloud]

On Tuesday, May 19, 2020 at 1:00:05 PM UTC-7, Luc Job wrote:
> Hi!
>
> I have developed last year a solid-state AOA indicator, based on a
> differential pressure measurement (total pressure/pressure at angle)
>
> Undoubtedly, this is a primary flight instrument to me:
>
> -It shows where you are aerodynamically speaking, independently of
> all the variable parameters: Load, flaps position, airbrakes...etc, and
> does not need a calculation or interpretation to check if you are
> flying right or not... And if the display is well done you will have a
> clear indication of the ongoing tendency towards a safe or dangerous
> situation.
>
> -It give me an accurate indication to adapt the flaps position to stay
> at the best glide angle through the whole speed range.
>
> -It is a good indication of the optimal attitude during winch launch
> and can prevent a high speed stall at high load factor.
>
> Some pictures of my development are available here:
> https://bit.ly/aoaindicator
> On the video the blinking effect is induced by the camera, the leds
> simply fade in or out gradually, only the red one blinks at stall angle
> or if the AOA rate of increase will induce a stall within 2 seconds...
> you can see that the instrument works as good as its free
> alternative...
>
> The present system includes:
>
> -A 5 leds indicator, red-amber-green-white-blue. The corresponding
> AOA for each led is programmed in flight with a push-button.
>
> -An audio input and output: Instead of adding a warning while flying
> at higher AOA than the maximum Cz (minimum sink rate), the
> instrument hashes the audio output of the vario gradually, cutting
> the sound at stall. This is an excellent indication that something is
> wrong without adding noise... You can continue to watch outside
> while climbing at the best speed, and avoid to enter a spin in the
> middle of others.
>
> -A serial i/o for software upgrade and continuous transmission of the
> data to another instrument.
>
> -An optional light sensor to adapt the luminosity to the ambient light
> level... But the indirect illumination and a better reflector (in
> development) has proved that it is probably unnecessary.
>
> The only hardware modification is the installation of an angled
> pressure port at a suitable place: angle is not critical, but flow must
> be as undisturbed as possible. On the DG I've put mine under the
> nose, about 170 mm from the tip, where I had access to the outer
> hull from the inside. I drilled a 2 mm hole and glued a small
> pressure chamber inside to plug a 4 mm hose. That's all.
>
> Power drain is lower than 20 mA @ 12V, less on ground as no led is
> switched on... So no switch, but an internal polyfuse to avoid any
> dangerous current drain... So it is simply added to the (fused)
> instruments circuit.
>
> Now as the system proves to be functional and efficient it's time to
> do something with it.
>
> Many options are possible:
>
> 1) I can order and sell PCB's only, with a BOM and the software...
> This is obviously the cheapest way... But components are mostly
> SMD... So you need an oven or a lot of patience and skill... Up to
> you to make a box adapted to your needs. Price should be about $10
> including shipping.
>
> 2) I can sell a complete kit with all the components, PCB, software,
> connectors and box... Components are not expensive except the 2
> pressure sensors ($35 each)... So I should be able to make this for
> about $150...
>
> 3) If you prefer a complete instrument, ready to plug-in (except the
> pressure port installation) the price should be in the 300-400$
> range.
>
> All this depends obviously on quantity... So if I have 1'000 orders it
> might be significantly cheaper.
>
> At first I need to know how many people might be interested... And
> what is the best option for you.
>
> At least we can fly again in Switzerland and France... So it might
> take some time for me to build a website for this product...
>
> Luc JOB
> DG-800B

I think this is awesome. Gliders have needed this, in fact I think years the SSA even had a contest to develop to an AOA. Once a unit (any style working unit) goes into production, more innovation will follow. Just make sure instead of demands for differing styles, you pony up the $ to purchase when it hits the market.

[[email protected]]

The 5 led moving + color sounds well thought out. That would certainly be the first thing I'd do with the NeoPixels.

Panel space in my glider is a bit like Survivor. An addition usually means something has to go. The theory on a Neopixel array just under the glareshield is that is will work for this AOA display, but also remain useful if/when it morphs into something else.

Having a functional AOA may change my mind, but I'm hoping it may turn out to be more useful for sensing airmass in addition to impending stall.

On another issue, when you drilled the sensing hole, did you go through a layer of foam? On some gliders, I'm wondering if the hole should be epoxy lined to prevent water intrusion into a inner foam layer.


Looking forward to having one.

[Luc Job[_2_]]

> On another issue, when you drilled the sensing hole, did you go through a layer of foam? On some gliders, I'm wondering if the hole should be epoxy lined to prevent water intrusion into a inner foam layer.
>
On most gliders I know, the nose cone isn't made of sandwich... At least on the symmetry plane where you have to drill, as it is the joint of the 2 1/2 parts of the fuselage.
>
> Looking forward to having one.

PCB modified to include an optional 4 wire led control...

[[email protected]]

Sounds great, thanks

[[email protected]]

On Tuesday, May 19, 2020 at 3:00:05 PM UTC-5, Luc Job wrote:
> Hi!
>
> I have developed last year a solid-state AOA indicator, based on a
> differential pressure measurement (total pressure/pressure at angle)
>
> Undoubtedly, this is a primary flight instrument to me:
>
> -It shows where you are aerodynamically speaking, independently of
> all the variable parameters: Load, flaps position, airbrakes...etc, and
> does not need a calculation or interpretation to check if you are
> flying right or not... And if the display is well done you will have a
> clear indication of the ongoing tendency towards a safe or dangerous
> situation.
>
> -It give me an accurate indication to adapt the flaps position to stay
> at the best glide angle through the whole speed range.
>
> -It is a good indication of the optimal attitude during winch launch
> and can prevent a high speed stall at high load factor.
>
> Some pictures of my development are available here:
> https://bit.ly/aoaindicator
> On the video the blinking effect is induced by the camera, the leds
> simply fade in or out gradually, only the red one blinks at stall angle
> or if the AOA rate of increase will induce a stall within 2 seconds...
> you can see that the instrument works as good as its free
> alternative...
>
> The present system includes:
>
> -A 5 leds indicator, red-amber-green-white-blue. The corresponding
> AOA for each led is programmed in flight with a push-button.
>
> -An audio input and output: Instead of adding a warning while flying
> at higher AOA than the maximum Cz (minimum sink rate), the
> instrument hashes the audio output of the vario gradually, cutting
> the sound at stall. This is an excellent indication that something is
> wrong without adding noise... You can continue to watch outside
> while climbing at the best speed, and avoid to enter a spin in the
> middle of others.
>
> -A serial i/o for software upgrade and continuous transmission of the
> data to another instrument.
>
> -An optional light sensor to adapt the luminosity to the ambient light
> level... But the indirect illumination and a better reflector (in
> development) has proved that it is probably unnecessary.
>
> The only hardware modification is the installation of an angled
> pressure port at a suitable place: angle is not critical, but flow must
> be as undisturbed as possible. On the DG I've put mine under the
> nose, about 170 mm from the tip, where I had access to the outer
> hull from the inside. I drilled a 2 mm hole and glued a small
> pressure chamber inside to plug a 4 mm hose. That's all.
>
> Power drain is lower than 20 mA @ 12V, less on ground as no led is
> switched on... So no switch, but an internal polyfuse to avoid any
> dangerous current drain... So it is simply added to the (fused)
> instruments circuit.
>
> Now as the system proves to be functional and efficient it's time to
> do something with it.
>
> Many options are possible:
>
> 1) I can order and sell PCB's only, with a BOM and the software...
> This is obviously the cheapest way... But components are mostly
> SMD... So you need an oven or a lot of patience and skill... Up to
> you to make a box adapted to your needs. Price should be about $10
> including shipping.
>
> 2) I can sell a complete kit with all the components, PCB, software,
> connectors and box... Components are not expensive except the 2
> pressure sensors ($35 each)... So I should be able to make this for
> about $150...
>
> 3) If you prefer a complete instrument, ready to plug-in (except the
> pressure port installation) the price should be in the 300-400$
> range.
>
> All this depends obviously on quantity... So if I have 1'000 orders it
> might be significantly cheaper.
>
> At first I need to know how many people might be interested... And
> what is the best option for you.
>
> At least we can fly again in Switzerland and France... So it might
> take some time for me to build a website for this product...
>
> Luc JOB
> DG-800B

Luc I'm confused by some of your statements.

I am a professional, semi-retired, applied aerodynamicist who had done design and performance analysis work for most of the US General Aviation companies.
Aircraft angle of attack (AoA) is defined using a reference line fixed to the fuselage. For a zero-flap configuration, there will be s specific AoA at stall. For a landing-flap deflection, the the maximum lift coefficient will be higher, however, it will occur at an AoA that is several degrees lower. All lift curves for aircraft design at factories worldwide use this convention.

I also have extensive experience with using 5-hole probes in the wind tunnel and in flight (even a rakes of 21 probes behind several locations on the Beech Starship). These are excellent for providing AoA, angle of sideslip (or yaw), and can be calibrated to provide a good measurement of static pressure and total pressure. I have calibrated probes myself in a wind tunnel with calibration curves out well beyond stall angles.

I have seen simple probes systems proposed and developed Garmin and others, however, these do not fully generate a true AoA. I would be interested in seeing how your single probe can generate a true AoA, and particularly for multiple flap angles. I'm skeptical at this point. I look forward to seeing more information.

...... Neal
Wichita, KS
Consulting Engineer

[Luc Job[_2_]]

Hi Neal

Your statements are not in contradiciton with mine... And I already mentionned the limits of this sooner in the thread:

The key factors to assume that flaps have little influence on stall AoA of the aircraft are:

1)simple airtight whole span flaps, I could add small chord ratio, the kind of flaps we only have on gliders, in summary...

2)low deflection angle, say lower than +-10 degrees to give indicative numbers

3)experimemtal data with a side string: I haven't noticed a significant difference of the side string angle when buffeting and loss of control starts through the whole flaps position range.

There is relatively few publications regarding the above conditions... Please let me know if you find some.

The idea behind the AoA indicator is to help setting the flaps in the right position during normal transition flight, so the first expected pilot's reaction is to adapt the flaps to stay at the right angle whatever could be the wing loading and other factors.

Another useful AoA value corresponds to the lowest sink rate, as you can see on speed polars the lowest sink speed range in relatively narrow and there is about a 10km/h margin between the lowest sink and the complete stall, where the sink rate increase abruptly... If you want to climb, you must avoid this range... And the only instrument that can give you an idea when you are thermalling with a continously changing speed and load factor is the AoA... And this is also in this configuration that safety comes into play.

In the case my sidestring had shown a different critical angle for different flaps position, I would have set the stall point with the maximum positive position before landing postions. So I have a right idea of my margin when thermalling. For any lower flaps position, the stall AoA could only be a few degrees higher... So I'm on the safe side through the whole flight envelope, except maybe with flaps in landing position...

At the recommended approach speed, the AoA with landing flaps is very low, giving a huge margin to reach stall, and in this configuration the goal isn't to be near stall angle, it's to stay at or above approach AoA. And on most if not all gliders the recommended flaps position in gusty contitions is not landing, ist last positive to keep more ailerons control... And this is where the AoA should have been tuned for stall...

And finally, for most of the gliders, you have no flaps to worry about... And the AoA remains a precious helper, specially at low speed when thermalling.

In practice, I think that this simple and cheap AoA indicator is much more than an additional gadget, it gives more significant information than the ASI through the whole flight envelope and an accurate stall warning.

So I don't know if I measure the true AoA... Maybe by chance the instrument gives the same indication as the sidestring only because it sustains the same perturbation and that by chance this perturbation compensate exactely the difference of critical AoA with the flaps for my DG-800B glider only.

But I'm confident that it should work on any glider. I will check this soon on my club's ASK21 and a Ventus 2cxa...

[[email protected]]

I think I will just keep my side strings. Relatively accurate for my purposes (mainly only thermalling). And I can’t beat the price or simplicity.
Dan

[Sci Fi]

If you had two of these, one on each wing-tip, you would also be able to
see on which side the thermal was..

[Luc Job[_2_]]

Well, it's probably true... But only for the kind of thermal able to lift your wing, which is a very good indication of where you should turn...

The anatomy of thermals is something strange and complex with many variations... No technical device is giving a right effective solution for the right first turn... But any gadget that others don't have will be very effective in competition even if it doesn't make you fly better...

[kirk.stant]

Luc,

I'm a big fan of using AOA (ever since my days long ago in F-4s, that relied heavily on AOA!) and would be interested in your instrument. My problem is I fly an LS6 with a small panel and there is absolutely no place to mount such a display. In the past I have tried yaw stings on the sides of the canopy and as you say, they work but are extremely sensitive to yaw (and not in your field of view when thermalling, anyway).

I have thought about how I would like AOA displayed and concluded that what I want is an indication that I am at the optimum thermalling AOA (for the flap setting) and that I am at the correct approach AOA.

When thermalling, once the proper AOA is determined, it is pretty easy to maintain that by reference of the nose position on the horizon, so an occasional check of the AOA indicator would be sufficient. For that I think just 3 lights would be sufficient - Red for too fast, Green for on-speed, and Yellow for too slow (with transitions lighting the adjacent light, while extremes would flash the appropriate light). This could be 3 bright LEDs on top of the panel, or on each side - taking up no panel space. To use, just roll into the turn, slow to the approximate speed you want, check the lights, adjust your AOA until the Green light is on, then stay at that pitch angle/airspeed.

For landing, I would want an aural cue so that I could fly the whole pattern concentrating outside the cockpit. Based on how AOA tones were used in the F-4, as you approached "on-speed" (say 1.3 Vstall) you would get a slow interrupted tone, increasing to a steady medium frequency tone when on-speed.. Too slow and a rapid higher frequency interrupted tone would blend in, transitioning to a steady high frequency tone at the stall. This could be setup to only come on when the landing gear (or air brakes) was extended, cutting out any vario tones to avoid confusion.

Once used to an audio AOA system, it becomes extremely easy to fly a pattern without ever looking at the airspeed, adjusting nose position as needed to maintain the desired AOA by how the tones change.

Anyway, put me down as seriously interested in your AOA system, probably as a full device (option 3, I believe).

Cheers,

Kirk
66

[Luc Job[_2_]]

Hi Kirk!

I will within days put the website online... You will have the opportunity to upload a picture of your panel... Maybe it's not hopeless...

I really don't like to have a led directly in front of my eye... that's why I designed an indirect display with a reflector and 5 leds, but this is easy to adapt to any other led display: there is 2 options: you can control up to 5 discrete leds, or any 3-wire or 4-wire led strip with any number of RGB or RGBW leds... Only the software needs to be adapted.

I'm relatively more skeptical about the audio AoA in approach for a simple reason: Gliders have low wing loading (compared to jet fighters, not to paragliders...) and this makes these beasts quite more sensitive to gusts and turbulence... And this will make your AoA much less stable in these conditions... Maybe I'm biased by the fact that I fly mostly in mountains where conditions are generally windy and gusty, at least when it's interesting to fly... So you won't be really able to get a constant tone... The goal looks more like dynamically counteracting the AoA variation due to the turbulence and for this the up-down movement on the indicator is a faster signal than the changing tone... But it doesn't look very complex to add an audio amp in a next version of the system to be able to generate sound instead of cutting the audio... And this can easily be coupled with the landing gear extension to switch from one mode to the other...

Cheers

[kirk.stant]

On Tuesday, May 26, 2020 at 6:29:06 PM UTC-5, Luc Job wrote:
> Hi Kirk!
>
> I will within days put the website online... You will have the opportunity to upload a picture of your panel... Maybe it's not hopeless...
>
> I really don't like to have a led directly in front of my eye... that's why I designed an indirect display with a reflector and 5 leds, but this is easy to adapt to any other led display: there is 2 options: you can control up to 5 discrete leds, or any 3-wire or 4-wire led strip with any number of RGB or RGBW leds... Only the software needs to be adapted.
>
> I'm relatively more skeptical about the audio AoA in approach for a simple reason: Gliders have low wing loading (compared to jet fighters, not to paragliders...) and this makes these beasts quite more sensitive to gusts and turbulence... And this will make your AoA much less stable in these conditions... Maybe I'm biased by the fact that I fly mostly in mountains where conditions are generally windy and gusty, at least when it's interesting to fly... So you won't be really able to get a constant tone... The goal looks more like dynamically counteracting the AoA variation due to the turbulence and for this the up-down movement on the indicator is a faster signal than the changing tone... But it doesn't look very complex to add an audio amp in a next version of the system to be able to generate sound instead of cutting the audio... And this can easily be coupled with the landing gear extension to switch from one mode to the other...
>
> Cheers

Hi Luc,

You have a good point about the difference between low wingloading/high aspect ratio and high wingloading/low aspect ratio wings and AOA. So I will have to see how your approach works! Looking forward to your instrument; looking at my panel I may be able to squeeze it in between my varios.

Cheers,

Kirk
66

[Luc Job[_2_]]

One last thing I will probably integrate is a tunable damping factor for the indicator.

The system produce about 600 values/second... I'm computing a first order estimate of the present AoA value based on the x preceding values, this is scientifically more accurate than a simple average and doesn't overload the cpu... Presently my setup is based on 10 values which makes the indicator quite reactive, but it is quite easy to program the software to have this adjustable.

3 positions should be sufficient, but we have 5 leds... So I plan to make tests and see what could be the suitable range. One short pulse on the button will let you choose the damping factor with the rotary knob...

Maybe one reason to keep it on the panel... Or not. It is plugged with a miniature connector on the PCB, so you can also simply use it for calibration, light intensity and damping factor tuning, and unplug it once you're happy... It will ship with a long cable.

PCB & hardware ordered...

[[email protected]]

>> I'm computing a first order estimate of the present AoA value based on the x preceding values, this is scientifically more accurate than a simple average and doesn't overload the cpu... Presently my setup is based on 10 values which makes the indicator quite reactive, but it is quite easy to program the software to have this adjustable.

Sounds great, not sure if it would work better to filter the raw sensor values or the computed AOA.

Also maybe could get by with an IIR running in Int32's.

Xavg += (Newsamp - Xavg) >> k; // maybe k=3 for short up to k=8 for long

Looking forward to having h/w. Starting to think about how to add the new ports with the nose release.

[[email protected]]

Or keep the measurement lsb's?

Xavg += Newsamp - (Xavg >> k); // maybe k=3 for short up to k=8 for long
Dispval = Xavg >>k;

[Luc Job[_2_]]

I got the PCB's yesterday...

And I've put some pictures of the probe hole setup on my DG on the Google album: https://bit.ly/aoaindicator

Too bad that the stencil is still missing... It comes in a separate parcel which takes a different way than the other one...

Next step will be to solder 1-2 circuits and test on other gliders.

I'm exploring different ways to display the most likely present value of the AOA, based on the 'past' values and filtered for turbulence... This is more for scientific reason than necessity... The 0.1 second average I've used last year is not a bad estimate and has proved to be very useable.

I'm setting up a logger to record individual values in order to have a better idea on what it looks like...

But no flyable conditions forecasted in the next days...

Cheers,

Luc

[Matt Herron Jr.]

On Tuesday, June 9, 2020 at 2:38:43 AM UTC-7, Luc Job wrote:
> I got the PCB's yesterday...
>
> And I've put some pictures of the probe hole setup on my DG on the Google album: https://bit.ly/aoaindicator
>
> Too bad that the stencil is still missing... It comes in a separate parcel which takes a different way than the other one...
>
> Next step will be to solder 1-2 circuits and test on other gliders.
>
> I'm exploring different ways to display the most likely present value of the AOA, based on the 'past' values and filtered for turbulence... This is more for scientific reason than necessity... The 0.1 second average I've used last year is not a bad estimate and has proved to be very useable.
>
> I'm setting up a logger to record individual values in order to have a better idea on what it looks like...
>
> But no flyable conditions forecasted in the next days...
>
> Cheers,
>
> Luc

Eror 500 on your posted link, Lic.

[Luc Job[_2_]]

> Eror 500 on your posted link, Lic.

Strange... Anybody else? Long link is:

https://photos.google.com/share/AF1QipNKV7fgYepjUs6MOq4KeYFttBsvU03pEX7RCchbaoFPqe f05Iw9hWmEAdib5A1Izg?key=b2oxU2Y0YjlDanRqX3BDWlNUc mRmalA0dlZ2bl9R

It works for me from any computer/account I could try... Maybe your firewall banned bit.ly?

[Dan Marotta]

Works for me.

On 6/10/2020 12:16 PM, Luc Job wrote:
>> Eror 500 on your posted link, Lic.
> Strange... Anybody else? Long link is:
>
> https://photos.google.com/share/AF1QipNKV7fgYepjUs6MOq4KeYFttBsvU03pEX7RCchbaoFPqe f05Iw9hWmEAdib5A1Izg?key=b2oxU2Y0YjlDanRqX3BDWlNUc mRmalA0dlZ2bl9R
>
> It works for me from any computer/account I could try... Maybe your firewall banned bit.ly?

--
Dan, 5J

[Charlie M. (UH & 002 owner/pilot)]

Eastern US @5:21pm......iPad, current Safari.....link works from home.....shrug....interesting gadgit none the less...