AIR Glide S

Hi,

I've flown both, CNv XC and Air Glide S (aka Butterfly Vario). In terms of wind indication, Air Glide S has far superior capabilities. I don't know any instrument in gliding that has the same speed and resolution of wind vector and speed.

However, the sensor unit needs to be correctly placed and well compensated. This may require quite some effort, especially in motorgliders with a lot of cables and metal in the fuselage. But probably the same applies to other AHRS units.

Best,
Christoph

torstai 22. lokakuuta 2015 10.31.21 UTC+3 kirjoitti:
How do you know the LX 9000 series with compass doesn't perform as well for winds? The new LX Nav compass module with 3 axis accelerometers and 3 axis magnetometers has only recently become available and I, for one, am waiting to hear how it is performing.

John Galloway

I had the impression that they have been running inertial platform (with wind output) for years as they advertise their variometers have mems gyros and accelerometers already. Compass reading is essential part of inertial platform. For clarification, I have not flown with latest compass module.


torstai 22. lokakuuta 2015 10.51.09 UTC+3 Bruce Hoult kirjoitti:
Instant headwind/tailwind component, yes.

Side gusts are unknown until either the glider equalizes with them, or the pilot uses the rudder to bring the yawstring into the middle (which will change the compass reading and TAS).

Gusts were out of reach for these systems, that's true. But Zander for example shows wind vector as numerical info line. Sure it is harder to interpret when seeing only direction and speed in number rather than animated arrow, but it is "instant wind vector" nontheless.

torstai 22. lokakuuta 2015 10.51.29 UTC+3 Rhubarb kirjoitti:
setup would then be (I guess) something like

AirGlide sensor box IGC - AirGlide S - AIR Glide NMEA Interface Box - GG - XCsoar

You would probably want to keep your Redbox Flarm as AIR Glide doesn't have flarm integrated.


Obviously I am especially interested in the wind info. Is it shown (well) on the AirGlide S or do I need one of the bigger displays to gain full advantage.


The wind arrow is in the middle of the variometer screen, hard to think more prominent way to display it.

Is wind only shown *after* I start circling as mentioned in the linked document which would be a shame

No, wind vector is visible all the time.


Does the AirGlide send out this tasty wind (and inertial) info on the serial cable (at a fast rate) so that XCSoar could displayed it (maybe with some additional programming).

Peter

AIR Glide parses flarm traffic, gps position, altitude and variometer reading together and send them to CU/XCSoar. You can choose the format, AIR Glide can emulate LX or CAI data lines. I use CAI emulation, so my Seeyou Mobile thinks that it is connected to CAI302. AFAIK it does NOT send instant wind data out. For a long final glide I like to use averaged wind from longer time, instant wind gives you a lot of variation to arrival height. When close to airport I tend to follow more AIR Glide final glide calculation. It's nice to have both opinions.

On Thursday, October 22, 2015 at 11:14:37 AM UTC+3, krasw wrote:
I had the impression that they have been running inertial platform (with wind output) for years as they advertise their variometers have mems gyros and accelerometers already. Compass reading is essential part of inertial platform. For clarification, I have not flown with latest compass module.

MEMS devices are cheap and rugged, but they are not necessarily very high precision.

The ones I've played with, in the single digit to very low double digit dollar price range -- which is what you find in smartphones -- are fine for deciding when to switch your screen from portrait to landscape, and can function as an acceptable inertial platform for up to maybe 30 seconds or so.

I've never come across one that could -- purely inertially -- have only 600m position error after half an hour. That implies that the speed is still accurate to better than about 3 knots after that time.

To do that, I think you're going to need at *least* 18 bits of useful precision in each axis. I'd expect that to cost quite a few hundred or even a thousand dollars for the chip alone, unless these things have really come along in the last year or two.

Nice description, thanks!

Most of my experience with shear in New Mexico has involved a long line
of clouds with bases considerably higher on one side of the line. It's
a simple matter to find and use the lift. Next time I get the chance to
fly in shear I'll try to watch the wind indication on my ClearNav
vario. It's pretty quick to update, but I don't think it will be as
useful as you described.

On 10/21/2015 9:09 PM, JS wrote:
Dan et al,
Flying in convergence, the Air-Glide informs you of approaching shear line conditions. The wind changes from a ~10Kt tailwind through 9, 6, 4, 3, to "Still", at which point your vario is going up. If you fly through the shear, there will be a similar indicated headwind.
Running along the shear, if the wind is from your right, move left. If it is from your left, move right. Simple. Accurate. Just as you imagine this shear stuff works.
No other vario I have personally flown with that will do that.
Jim


On Wednesday, October 21, 2015 at 2:33:02 PM UTC-7, Dan Marotta wrote:
That's great for telling me what does, but not how to use it. Are
you saying to always turn downwind in the local micro wind to get to
the center of the thermal?



Maybe my CNvXC vario has this capability, maybe not. I'll have to
do some research on that. In the mean time, I've had good luck with
finding thermals at the upwind edge of cumulus clouds. That's not
always the case but true more often than not.




On 10/21/2015 8:34 AM, Alex wrote:



Comparing instantaneous wind to average wind will show you any local wind deviations as they occur near thermals. Can't find the thermal under a cloud? Just follow the diverging local wind. Need to find the best line along a cloud street or convergance? Watch the local wind. Feel that blue thermal nearby, but not sure where to turn? The wind will tell you.



Am Mittwoch, 21. Oktober 2015 16:01:38 UTC+2 schrieb Dan Marotta:


Of what use is instantaneous wind? Can you react to it without
flapping control surfaces all over the place? Do you use it for
planning your next turn in a thermal?

Not knocking it, I just don't get it why it would be important.
Please enlighten me.

Dan, 5J

--
Dan, 5J

I have used XCSoar with the Air Avionics ISU. The serial stream mimics either LX or CAI protocol, and either can be used with XCSoar. Wind data is transmitted in both procotols, but in a time filtered form. However XCSoar does not seem to use that data, rather it calculates wind using its own traditional methods.

While others have claimed to have and use inertial sensors going back to the first CAI 302, it appears as though no one except Air is actually using them to a meaningful result even today.

On Friday, 23 October 2015 00:27:41 UTC+3, wrote:

bruce, i think you might be assuming the butterfly is merely doing dead reckoning, but what it's doing is more complex than that. it uses an extended kalman filter (EKF), which is a type of software algorithm that is good for estimating the state of something that cannot be directly measured (the motion of the glider, in this case). the EKF takes various data steams as input: accelerometer, gyroscope, static pressure, pitot pressure, magnetometer (compass), and time. what it outputs is an estimate of the motion of the glider.

now, if the EKF only had acceleration and time as inputs, it would need an extremely accurate accelerometer and clock, as you have surmised. acceleration is relative, so even small errors in acceleration will snowball over time into large errors when doing dead reckoning this way.

fortunately, the EKF has much more data to work with. since it also has access to measurements that are absolute (heading, altitude, airspeed), it can integrate all the data in a way that makes the accelerometer error much less significant. since acceleration is only one piece of the puzzle, it has less influence on the overall motion estimate, and therefore the drift you would expect with dead reckoning is diminished.

thanks to the power of the EKF, an extremely accurate IMU (accelerometer, gyro) is not necessary. i wouldn't be surprised if the butterfly has an IMU of similar quality as that of a smartphone.

Kalman (and EKF) is a process that you run into pretty much everywhere. It's quite elementary way of correct predicted state of something on basis of comparing previous predicted state to current observations. It doesn't do theh inertial navigation itself, it's just way of polishing things numerically. For example, if airspeed measurement is systematically too small, Kalman filter corrects that error (this is maybe too elementary example, reality is more complex for sure). I think important part of achieving this state of inertial navigation (without GPS) is by using measured TAS.

On Friday, October 23, 2015 at 12:57:08 AM UTC-7, krasw wrote:
Kalman (and EKF) is a process that you run into pretty much everywhere. It's quite elementary way of correct predicted state of something on basis of comparing previous predicted state to current observations. It doesn't do theh inertial navigation itself, it's just way of polishing things numerically. For example, if airspeed measurement is systematically too small, Kalman filter corrects that error (this is maybe too elementary example, reality is more complex for sure). I think important part of achieving this state of inertial navigation (without GPS) is by using measured TAS.

TAS (calculated, not measured) is probably the most important input to the algorithm, but navigation without GPS cannot be done without heading information as well. interestingly, accurate heading cannot be computed without at least a rough idea of where you are on the planet due to magnetic declination. so this system would not work as well (in most places) without an initial GPS fix. this purely academic though because any navigation system would be useless without at least knowing the starting point.

also interesting is that having a rough idea of where you are also improves the accuracy of the accelerometer because the force of gravity differs depending on where you are on the planet. remember that at rest, an accelerometer will always show roughly 9.8m/s^2 in the downward direction.

I would assume that the two most common mounting locations of the ISU would be forward of the instrument panel, or behind the pilot's seat. I'm leaning towards installing mine forward of the instrument panel, but the nearby radio concerns me. Behind the pilot's seat would be a less convenient installation, and its proximity to the speaker and the steel spar pin present interference issues as well.

Any installation advice from people with either setup?

Thanks!
Chris Fleming

Mine, in an ASW20, is mounted forward of the instrument panel on the
opposite side from the radio. I've had no interference issues. Love the
instrument.






At 09:01 05 July 2016, Fox Two wrote:
I would assume that the two most common mounting locations of the ISU
would=
be forward of the instrument panel, or behind the pilot's seat. I'm
leanin=
g towards installing mine forward of the instrument panel, but the nearby
r=
adio concerns me. Behind the pilot's seat would be a less convenient
instal=
lation, and its proximity to the speaker and the steel spar pin present
int=
erference issues as well.=20

Any installation advice from people with either setup?

Thanks!
Chris Fleming