Butterfly vario side-by-side with ClearNav vario

krasw wrote, On 5/17/2013 10:33 AM:
(and as a side produt most accurate speed-to-fly commands I've seen).
In this respect Butterfly Variometer is not comparable with other
current systems. I think this fundamental difference is not
completely understood here.

I really curious about what an "accurate" speed-to-fly command is. What
is the command based on that makes it more accurate than the usual
variometer, like a 302?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

In theory, both the butterfly and the CN have enough innards to really advance variometry, because they have the potential to measure the vertical speed of air around the glider.

If you fly in to a thermal, the g meter increases. If you pull back on the stick the g meter increases. But the gyros can tell that the glider nosed up in the latter case. So, the vario can measure "netto g" if you will, the acceleration of the glider caused by changes in the surrounding air.

This is much faster than a vario. For a vario to work, you have to fly into the rising air, g increases, F = MA does its work, the glider starts rising vertically, then the vario can start to measure it. The system based on g and heading does it instantly, at least giving a second or two earlier lift detection.

Looking at sideways g, correcting for yaw, also can tell the vario if there is a sideways gust. Looking at fore and aft g can tell the vario if the glider has entered a wind shear on the nose rather than vertical thermal.

Eventually, by comparing the GPS track through space with the relative wind, these various could also measure outside air motion directly.

I don't know how much of this is currently programmed in to either one, but the potential seems intriguing.

John Cochrane

On Friday, May 17, 2013 6:20:24 PM UTC-7, wrote:
If you fly in to a thermal, the g meter increases. If you pull back on the stick the g meter increases. But the gyros can tell that the glider nosed up in the latter case. So, the vario can measure "netto g" if you will, the acceleration of the glider caused by changes in the surrounding air.


What happens when the flaps go positive?

Marc

On Saturday, 18 May 2013 02:33:22 UTC+3, Eric Greenwell wrote:
krasw wrote, On 5/17/2013 10:33 AM:

(and as a side produt most accurate speed-to-fly commands I've seen).

In this respect Butterfly Variometer is not comparable with other

current systems. I think this fundamental difference is not

completely understood here.



I really curious about what an "accurate" speed-to-fly command is. What

is the command based on that makes it more accurate than the usual

variometer, like a 302?



--

Eric Greenwell - Washington State, USA (change ".netto" to ".us" to

email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm

http://tinyurl.com/yb3xywl

Speed-to-fly is essentially function of vertical airmass movement. When you get inertial-based netto, which is very fast and accurate, your speed-of-command accuracy goes up order of magnitude. With normal TE-based speed-to-fly you normally try to filter out gusts with longer time constant. With inertial netto this gust-induced noise transforms into data that you can use for calculating optimum STF.

With Butterfly I have actually started experimenting with extremely short time constant for inertial netto. It can be set so short that netto becames essentially a quantitative indicator of your seat-of-the-pants feeling. There seems to be no reason to filter or average this data so heavily.

krasw

Watching the Butterfly vario video, it sure looks nice and smooth, with lots of information - then it occurred to me that this is a potential downside that the pilot will have to guard against - "clock watching" while thermalling, trying to make sense of all the changing data, and perhaps relying on Flarm to stay safe!

It's bad enough with all the data available on our glide computers and PNA displays, but that data is usually checked during cruise, and is more static in nature; while thermalling we try to rely on the audio vario and occasionally check inside for the average. Will conventional audio be sufficient to convey the data that the Butterfly (and by extension, CNv and other future varios) will be generating?

Perhaps more synthetic voice data to give trend info would allow the pilot to keep his eyes out of the cockpit and still make use of all the new data. "Gust", "Roll out - Turn in" (for thermal centering), "two six, two six" for the average, etc.

Or a head mounted display - JHMCS anyone? That would need a big battery!

It would be a shame to equip the fleet with Flarm just so we can thermal on instruments!

Kirk

On Saturday, May 18, 2013 5:14:58 AM UTC-4, kirk.stant wrote:

Perhaps more synthetic voice data to give trend info would allow the pilot to keep his eyes out of the cockpit and still make use of all the new data. "Gust", "Roll out - Turn in" (for thermal centering), "two six, two six" for the average, etc.

Maybe Themi got it right, ten years ago. Two LEDs in peripheral vision.

What happens when the flaps go positive?

Marc

You get a single transient, which you know about because you just moved the flap handle

krasw wrote, On 5/17/2013 11:30 PM:
On Saturday, 18 May 2013 02:33:22 UTC+3, Eric Greenwell wrote:
krasw wrote, On 5/17/2013 10:33 AM:


I really curious about what an "accurate" speed-to-fly command is.
What

is the command based on that makes it more accurate than the usual

variometer, like a 302?


Speed-to-fly is essentially function of vertical airmass movement.
When you get inertial-based netto, which is very fast and accurate,
your speed-of-command accuracy goes up order of magnitude. With
normal TE-based speed-to-fly you normally try to filter out gusts
with longer time constant. With inertial netto this gust-induced
noise transforms into data that you can use for calculating optimum
STF.

With Butterfly I have actually started experimenting with extremely
short time constant for inertial netto. It can be set so short that
netto becames essentially a quantitative indicator of your
seat-of-the-pants feeling. There seems to be no reason to filter or
average this data so heavily.

Does it give the correct STF for 1 second from now? I can't possibly
change the speed of the glider that fast.

Or does it give me the STF for 10 seconds from now, which I might be
able to achieve with abrupt control movements?

And then, 10 seconds later, when I'm going the speed I was given, but
now I'm in air going down faster/slower, does it give me another STF
that will be wrong by the time I achieve that speed?

I'm trying get an idea of what you mean by "accurate" STF commands. The
top contest pilots I've followed seem to fly pretty steadily - will it
give me the STF that a top contest pilot will cruise at? That's what I
would call "accurate"!


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

Maybe there's a good use for Google Glass here. Much easier than a HUD.

Chris

I'm trying get an idea of what you mean by "accurate" STF commands. The

top contest pilots I've followed seem to fly pretty steadily - will it

give me the STF that a top contest pilot will cruise at? That's what I

would call "accurate"!





--

Eric Greenwell - Washington State, USA (change ".netto" to ".us" to

email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm

http://tinyurl.com/yb3xywl

I tried to tell that without accurate info on vertical airmass movement you can't have working STF command. This is where inertial system seems to be very good at. Sorry if I was unclear about this. Without good STF you would probably fly with predetermined still-air mc-speeds. Sure it works also, but it is not optimal. Plus if you know the airmass movement you have a better idea where to fly during glide.

krasw