AA Butterfly versus CNv LCD wind calculation

On Sunday, September 18, 2016 at 5:24:31 PM UTC-4, Tango Eight wrote:
On Friday, September 16, 2016 at 4:23:48 PM UTC-4, wrote:

Does the CNv (with latest 3.3.3899 or beta 3.4.4089) calculate wind as quickly as the Butterfly?

No.

T8, what is the wind direction update rate of the CNv?

I don't have a quantitative answer here. Mostly it depends on your flight path. CNv depends on some GPS track variation for vector wind calculation, but it doesn't take a great deal (20 degrees total track seems to do it in most cases). Given sufficient GPS track variation, the fast wind seems to update in just a few seconds ( 10). The auto wind is slower, gives a more stable number. It seems to take a few tens of seconds to update. Either mode is noticeably faster than previous generation flight computers (302, SN-10B). I haven't flown the Butterfly vario. The component head/tail wind is updated very fast (less than a second).

The only difference between "auto" and "fast" winds in CNvXC is the time constant. I see no downside to the fast wind, so I've been lobbying to make this the default. The fast wind is excellent for close in mountain flying.

best,
Evan / T8

Thanks T8.

On Friday, September 16, 2016 at 4:23:48 PM UTC-4, wrote:
If anyone has experience using both varios at the same time, please share your opinions.

When you have 2 or more systems how can you possibly know which wind reading is more accurate?
Without flying in a giant laboratory with controlled winds how do you know what the truth is to compare each system to?
I would imagine each system needs to average the data over some time period, so unless you can set them to be the same how can you tell?
If you make note of the in flight wind indications then reviewed that part of the flight in SeeYou would that be useful?

Chris

Actually in some conditions it is very easy. Stop and circle. I find in mountains and along shear lines that the wind can change 30 to 180 degrees in a very short distance. Many traditional varios and computers will take 10 to 15 minutes to adjust.

On Monday, September 19, 2016 at 2:42:36 AM UTC+2, Sean wrote:
I thought accurate straight line glide computer wind accuracy required a fixed compass (aka LXNAv) for the best not thermaling wind detection sensitivity. My S10 is going to have a compass module shortly. But I really can't imagine a need that that much wind accuracy. The wind where you are now isn't the problem. It's accurate anticipation of what the wind is 1, 5 10 and 20 miles ahead, just like sailing, but much less critical.

Am I right or wrong on the compass module?

I believe the butterfly an fixed compass built in, and this is the reason that it is more energetic on updates? Correct?

There is no need for a compass module with S8x/S10x, the wind calculating system is doing a fine job in straight flight.
I have flown about 150h with the S80 this year, and I’m still surprised every time I take off that the wind calculation is accurate already in the tow. I measure this by comparing the wind vector before and after the first thermal after release and they are more or less the same in most situations.

On Monday, 19 September 2016 03:42:36 UTC+3, Sean wrote:
I thought accurate straight line glide computer wind accuracy required a fixed compass (aka LXNAv) for the best not thermaling wind detection sensitivity. My S10 is going to have a compass module shortly. But I really can't imagine a need that that much wind accuracy. The wind where you are now isn't the problem. It's accurate anticipation of what the wind is 1, 5 10 and 20 miles ahead, just like sailing, but much less critical.

Am I right or wrong on the compass module?

I believe the butterfly an fixed compass built in, and this is the reason that it is more energetic on updates? Correct?

There are ways to calculate wind vector on straight flight without compass module, Oudie claims to do it by comparing track/gs to different straight paths (did not get it to work, though), so it is possible at least theoretically.

But bottom line is: you either have full inertial platform with 3D acceleration, rate gyros and compass data, or you don't. Former gives you instant airmass data in all directions instantly, if implemented correctly. That's big IF.

It is not enough to throw in electric compass if the system is not up to it.. Many variometer systems have compass option that manufacturers do not use for any meaningful data. Representative of one company told me of pilot who was very happy after installing optional compass module. He didn't have the heart to tell pilot that variometer firmware version couldn't use compass data at all. I always take pilot reports with a grain of salt.

And no, we do not *need* anything, you can fly perfectly well with seat-of-pants feeling. It just nice to have all that data.

On Sunday, September 18, 2016 at 5:24:31 PM UTC-4, Tango Eight wrote:
...CNv depends on some GPS track variation for vector wind calculation

You're saying that, unlike for example Butterfly, CNv does not use compass?
And therefore cannot do instantaneous winds?

Sounds like the same algorithm SN10 introduced two decades ago (GPS track and airspeed)?

Whichever one you like better "must" be the most accurate.

On 9/18/2016 9:39 PM, wrote:
On Friday, September 16, 2016 at 4:23:48 PM UTC-4, wrote:
If anyone has experience using both varios at the same time, please share your opinions.
When you have 2 or more systems how can you possibly know which wind reading is more accurate?
Without flying in a giant laboratory with controlled winds how do you know what the truth is to compare each system to?
I would imagine each system needs to average the data over some time period, so unless you can set them to be the same how can you tell?
If you make note of the in flight wind indications then reviewed that part of the flight in SeeYou would that be useful?

Chris

--
Dan, 5J

Do you really fly a perfect circle of constant radius? I certainly
don't. I think without that, the wind calculation is really a best
guess based on the assumption that you're flying a circle. One could
argue that an accurate wind calculation is necessary to fly the correct
drift angle to your target, but this is soaring. Who flies in a
straight line?

On 9/18/2016 10:05 PM, Tim Taylor wrote:
Actually in some conditions it is very easy. Stop and circle. I find in mountains and along shear lines that the wind can change 30 to 180 degrees in a very short distance. Many traditional varios and computers will take 10 to 15 minutes to adjust.

--
Dan, 5J

On Sunday, September 18, 2016 at 5:42:36 PM UTC-7, Sean wrote:
I thought accurate straight line glide computer wind accuracy required a fixed compass (aka LXNAv) for the best not thermaling wind detection sensitivity. My S10 is going to have a compass module shortly. But I really can't imagine a need that that much wind accuracy. The wind where you are now isn't the problem. It's accurate anticipation of what the wind is 1, 5 10 and 20 miles ahead, just like sailing, but much less critical.

Am I right or wrong on the compass module?

I believe the butterfly an fixed compass built in, and this is the reason that it is more energetic on updates? Correct?

The Butterfly (Air) vario wind is inertially derived and calculated many times a second. As far as I know they are the only ones really doing this. I'm pretty sure they use air speed, GPS speed, etc for long term calibration, but the instantaneous wind is derived from the MEMS sensors. For example I will get an accurate instantaneous wind in my motorglider with the engine running. The tail pitot is in the prop wash and indicates about 45 knots over the actual speed. The Oudie or XCSoar will say I have a 45 knot headwind whenever it is running. The Air vario gives accurate wind, even with it running.

It is pretty difficult to get an independent verification of the wind vector. Headwind and tailwind component not that hard in stable conditions. Circling, unless very close to the ground, will only give you a vague notion. In the western mountains at least, the wind is quite dynamic in and around thermals, a fact that iGlide uses as a thermal centering device.

The instantaneous wind IS of immediate interest at least some times. I have found many days (in western mountains again) when there is a rather abrupt shear at say 14,500 ft. The cloud bases are 15,500. But you are heading upwind. When you hit the shear you leave the thermal. Going downwind, obviously carry it right to the cloud. This information is verifiable by checking TAS agains GPS speed. But most soaring instruments determine this too late to be of much use. There are other times when wave was dipping into the boundary layer again producing a sudden change of instantaneous wind. When I saw this I knew to look around for wave. I have discovered there is often a strong south wind blowing up the Minden valley late in the afternoon above about 12,000 ft. Never saw that before on other instruments, I'm not in it long enough for their filters to figure it out. Yet it can be exploited by flying down the middle of the valley rather than cutting straight across which seems otherwise more logical. Again these readings can be verified by observing TAS and GPS speeds.

On Monday, September 19, 2016 at 10:57:42 AM UTC-4, Dan Marotta wrote:
I think without that, the wind calculation is really a best
guess based on the assumption that you're flying a circle.

That is incorrect for any decent wind calculation algorithm;
certainly precise circles are not required. With SN10 you will
often have estimated wind before you are off of tow...