AA Butterfly versus CNv LCD wind calculation

TAS and GPS are sufficient to determine
headwind / tailwind component flying in a
straight line.

To get crosswind component, you need a
compass to supply heading, then apply
that to the GPS track.

On Monday, September 19, 2016 at 12:45:13 PM UTC-4, George Haeh wrote:
To get crosswind component, you need a
compass to supply heading, then apply
that to the GPS track.

That is incorrect.
Multiple observations on different headings allow wind calculation.

On Monday, September 19, 2016 at 10:15:18 AM UTC-7, Dave Nadler wrote:
On Monday, September 19, 2016 at 12:45:13 PM UTC-4, George Haeh wrote:
To get crosswind component, you need a
compass to supply heading, then apply
that to the GPS track.

That is incorrect.
Multiple observations on different headings allow wind calculation.

George, not sure how up you are on Dave Nadler's background. He developed the software for the SN-10 which for many years was the gold standard for providing in-flight wind values. I was thrilled & impressed when I heard him describe his very elegant solution for computing winds with a limited information set.

Cheers,
Craig

Reminds me of my Father, 'it isn't what it is, it is what I call it, that matters". Found out this meant a pipe can be a hammer

So the "best Vario" is the one you think is the best.


On Monday, September 19, 2016 at 7:50:48 AM UTC-7, Dan Marotta wrote:
Whichever one you like better "must" be the most accurate.

Dave Nadler is quite correct in his
assertion that "Multiple observations on
different headings allow wind calculation",
but that methodology necessarily requires
more time than AA's wind updates at 20
Hz, for which you need a heading source
when flying a straight line.

At 17:34 19 September 2016, Craig
Funston wrote:
On Monday, September 19, 2016 at
10:15:18 AM UTC-7, Dave Nadler wrote:
On Monday, September 19, 2016 at
12:45:13 PM UTC-4, George Haeh wrote:
To get crosswind component, you
need a=20
compass to supply heading, then
apply=20.
that to the GPS track.
=20
That is incorrect.
Multiple observations on different
headings allow wind calculation.

George, not sure how up you are on Dave
Nadler's background. He developed
t=
he software for the SN-10 which for
many years was the gold standard for
pr=
oviding in-flight wind values. I was
thrilled & impressed when I heard
him=
describe his very elegant solution for
computing winds with a limited
info=
rmation set.

Cheers,
Craig

On Monday, September 19, 2016 at 4:30:20 PM UTC-4, George Haeh wrote:
Dave Nadler is quite correct in his
assertion that "Multiple observations on
different headings allow wind calculation",
but that methodology necessarily requires
more time than AA's wind updates at 20
Hz, for which you need a heading source
when flying a straight line.

Of course. But Evan has said get wind the CNv requires
flying on different headings and takes some time,
which means it is not incorporating a heading source.

Without a doubt, the SN10 when introduced was the best at wind. Believe Dave would like to produce something more modern, but Ilec is no longer interested in building varios.

Probably paid too much attention to the panel today, watching winds.
After a change in wind eventually the two varios agree, but the change is displayed immediately on the Air-Glide. Sometimes it was several minutes before the CN caught up.

I have installed and configured but no flight time with the LX90x0/V8 system a few in this thread have asked about.

Looking at flight logs in SeeYou PC isn't the determining factor of which wind is accurate. When SeeYou PC shows 7Kts and a thermal's 360 degree turns don't overlap at all, it's time to say "********". At that point Air indicated 23Kts, way more believable.
Jim

Memory is cheap, advanced instruments that generate IGC files should log all air data for later analysis. Then programs such as SeeYou could use this to not only preset flight traces but a picture of the airmass the glider(s) flew through.

We often experience some phenomena that these logs might help explain.

On Monday, September 19, 2016 at 6:57:20 PM UTC-7, JS wrote:
Looking at flight logs in SeeYou PC isn't the determining factor of which wind is accurate. When
SeeYou PC shows 7Kts and a thermal's 360 degree turns don't overlap at all, it's time to say
"********". At that point Air indicated 23Kts, way more believable.

If I have understood the workings of AA Vario correctly, the wind is simply the difference between the GPS observations (fixed axis system compared to earth) and the inertial axis system (drifts with the wind).

A thought regarding usage of IAS, TAS and GS for wind calculations: I have been a long term abuser of this, when flying with the Zander GP940 who only calculate the wind during circling. The wind component calculation is of great information on final glide to detect any changes of wind when getting closer to the ground. But I just got a second thought about this.

When reading this tread and putting 1+1 together do I realize that using the difference between TAS and GS is not an useful approach to calculate the wind. Read any of the Johnsson reports and figure out why he is so keen on calibrating the IAS readings!
It is not uncommon that the IAS differs from TAS(at ground level) with more than 5%, it is individual both between types of gliders and most likely also within gliders of the same type depending on which static probe you are using.
This error in reading the IAS in the glide computer is not calibrated, therefore can it not use the difference TAS / GS to calculate the wind. The error would be of dignity 5-15 km/h.