AA Butterfly versus CNv LCD wind calculation

tiistai 27. syyskuuta 2016 22.23.28 UTC+3 kirjoitti:
Den tirsdag den 27. september 2016 kl. 15.19.03 UTC+2 skrev krasw:
On Tuesday, 27 September 2016 11:15:02 UTC+3, Tango Whisky wrote:
Why would a mechanical vario give you more information on airmass?

That is interesting question. If it would give identical information, the varios should read exactly the same. They obviously are not, so they are either measuring TE pressure differently, or one of them is measuring same thing but poorly (which I don't agree with, in some gusting thermals my Bohli reacts more realistically than electric vario). I feel getting two "opinions" from same thing is advantage (three actually if you count inertial variometer). Heck, I would gladly install fourth variometer if that tells me something new, instead of duplicating something I already have.

I think the mechanical vario and the electrical transducer based vario should have different responses simply due to physics.

Consider a sudden small pressure drop in the TE line (like hitting very sudden lift). The mechanical vario measures the flow rate from the flask to the TE line. This flow is proportional to the pressure difference between the flask and the TE pressure. The pressure difference, and hence the vario reading, is largest right after the pressure drop and then decays exponentially back to zero. That explanation is consistent with a simple experiment done a few years ago with a 57 mm Winter vario, a syringe and a video camera. The vario reading peaked after just 0.3 s. The subsequent decay fitted perfectly with an exponential decay with a time constant of 3 s.

The electrical vario indicates the time derivative of the measured TE pressure after some low pass filtering. The response depends on the actual filtering, but the response to a sudden small pressure drop will peak after some time given by the filter type and time constant. The lab experiment with a syringe and a video camera showed that a late generation LX5000 on minimum time constant (0.5 s) would peak after 2.5 s. On the other hand, the following decay to zero was much faster than for the Winter vario.

The tests were repeated with both the Winter and the LX5000 on the same TE line in order to evaluate the influence of the mechanical vario and flask on the LX5000 response. Surprisingly, the LX5000 response to a sudden small pressure drop was essentially unchanged, and if anything it measured a bit faster.

Another test with an LX7007 showed similar results, except now the Winter on the same TE line did seem to slow the LX7007 a bit when operated on the shortest possible time constant of 0.2 s (peak after 2.0 s without Winther, peak after 2.5 s with Winther on TE line).

I prefer the electrical vario, but I know one regular WGC pilot who keeps a mechanical vario claiming that it has a faster response to sudden changes in the air mass. He doesn’t know why – and I don’t know if the considerations above are relevant at all in the real world…

-J

That is very interesting, thanks. I think many pilots recognize good mechanical variometers fast peaking / slow decay behaviour vs. electricals somewhat opposite response. I've often considered would it be possible to build a vario that has adjustable, separate time constants/filters for peak and decay. Cannot think any reason why not.

Sorry, but comparing the two varios mentioned in the original post:

When flying through turbulence that nets neither up nor down and not worth circling in, ever wonder what it is? A mechanical or old school vario won't soon display anything useful about the change in airmass horizontal vector..
Correction, a mechanical vario will never tell you about it.

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim

On Thursday, September 29, 2016 at 9:29:18 PM UTC-4, JS wrote:
Sorry, but comparing the two varios mentioned in the original post:

When flying through turbulence that nets neither up nor down and not worth circling in, ever wonder what it is? A mechanical or old school vario won't soon display anything useful about the change in airmass horizontal vector.
Correction, a mechanical vario will never tell you about it.

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim

JS...do you use electronic compensation on both varios?

On Thursday, September 29, 2016 at 7:35:50 PM UTC-7, wrote:
On Thursday, September 29, 2016 at 9:29:18 PM UTC-4, JS wrote:
Sorry, but comparing the two varios mentioned in the original post:

When flying through turbulence that nets neither up nor down and not worth circling in, ever wonder what it is? A mechanical or old school vario won't soon display anything useful about the change in airmass horizontal vector.
Correction, a mechanical vario will never tell you about it.

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim

JS...do you use electronic compensation on both varios?

Using electronic on the CNv, a (50/50?) mix in the Air-Glide.
Jim

On 9/29/2016 7:29 PM, JS wrote:
snip

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim
How much head down time did that take? Were there other aircraft nearby?
--
Dan, 5J

On Friday, September 30, 2016 at 8:37:21 AM UTC-7, Dan Marotta wrote:
On 9/29/2016 7:29 PM, JS wrote:
snip

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim
How much head down time did that take? Were there other aircraft nearby?
--
Dan, 5J

Well mum, there was no more heads down than checking airspeed, etc. The Air is next to the ASI in the top row of the panel.
Some of that wind direction crap was remembered from post-flight analysis.
As for the train spotting bit:
Saw Cezzna, MD80, 727, bizjet, condor, hawk, raven, vulture, various F-things.
Didn't steal any thermals from any of the inorganic ones.
Jim

Cool. Thanks for the reply! That's a lot of aircraft.

My wife and I flew 2.2 hours yesterday and, during that time I saw one
airliner up in the 30s and got one PCAS alert at 5 miles. Never saw
him. I love flying in the desert! Oh, yeah... We were the only glider up.

Dan

On 9/30/2016 12:18 PM, JS wrote:
On Friday, September 30, 2016 at 8:37:21 AM UTC-7, Dan Marotta wrote:
On 9/29/2016 7:29 PM, JS wrote:
snip

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim
How much head down time did that take? Were there other aircraft nearby?
--
Dan, 5J
Well mum, there was no more heads down than checking airspeed, etc. The Air is next to the ASI in the top row of the panel.
Some of that wind direction crap was remembered from post-flight analysis.
As for the train spotting bit:
Saw Cezzna, MD80, 727, bizjet, condor, hawk, raven, vulture, various F-things.
Didn't steal any thermals from any of the inorganic ones.
Jim

--
Dan, 5J

Will slipping or skidding influence the instantanei0us wind reading ? The compass shows your heading which changes when slipping/skidding.
Dan
On Saturday, October 1, 2016 at 10:04:48 AM UTC-4, Dan Marotta wrote:
Cool. Thanks for the reply! That's a lot of aircraft.

My wife and I flew 2.2 hours yesterday and, during that time I saw one
airliner up in the 30s and got one PCAS alert at 5 miles. Never saw
him. I love flying in the desert! Oh, yeah... We were the only glider up.

Dan

On 9/30/2016 12:18 PM, JS wrote:
On Friday, September 30, 2016 at 8:37:21 AM UTC-7, Dan Marotta wrote:
On 9/29/2016 7:29 PM, JS wrote:
snip

Today's flight was in wind from SE then NW then SW then SE then NW then SW then S then SW then SE then SW then NW. When approaching convergence lines the wind change was indicated on the Air-Glide S before the airmasses converged, by showing velocity reduction then change of direction then - on both mentioned varios - up indication.
Jim
How much head down time did that take? Were there other aircraft nearby?
--
Dan, 5J
Well mum, there was no more heads down than checking airspeed, etc. The Air is next to the ASI in the top row of the panel.
Some of that wind direction crap was remembered from post-flight analysis.
As for the train spotting bit:
Saw Cezzna, MD80, 727, bizjet, condor, hawk, raven, vulture, various F-things.
Didn't steal any thermals from any of the inorganic ones.
Jim

--
Dan, 5J