A aviation & planes forum. AviationBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AviationBanter forum » rec.aviation newsgroups » Soaring
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Speed of a vario



 
 
Thread Tools Display Modes
  #31  
Old August 12th 20, 04:44 PM posted to rec.aviation.soaring
Tango Eight
external usenet poster
 
Posts: 962
Default Speed of a vario

Fast vario example: https://youtu.be/XAjwVPRTxQE?t=120

CNv set to "0.5s" for both pointer and audio. Panel is badly underexposed, but you can see the orange needle of the old CNv display on left side. I have the vario set to suppress sink tones (I don't need to be scolded when I'm not climbing).

What the TC refers to in this case is the low pass filter on the back end of the data stream. 0.5s effectively turns the low pass "off". There is plenty of digital filtering in front of this, and imo, it works quite well. I think it is about as fast as is useful for sailplanes. There's a reliable, repeatable sequence of boot in the bum followed a couple tenths of a second later by the audio for real thermals. If the boot is missing, that's a gust. It's very easy to train yourself to detect this difference (a good vario helps).

Not yet released CNv color display at upper right (it's quite visible in real life), should be out soon.

OT: At 2:25 you get a nice look at the Appalachian Trail as it ascends Old Speck Mountain just before plunging into Grafton Notch. We fly this route fairly often... but normally a bit higher :-).

T8
  #32  
Old August 12th 20, 05:35 PM posted to rec.aviation.soaring
jfitch
external usenet poster
 
Posts: 1,134
Default Speed of a vario

On Tuesday, August 11, 2020 at 8:54:37 PM UTC-7, Eric Greenwell wrote:
jfitch wrote on 8/11/2020 8:22 AM:
On Tuesday, August 11, 2020 at 6:45:05 AM UTC-7, wrote:
At 11:23 11 August 2020, s6 wrote:
If I remember ok it is the time it takes to reach 80% of the
thermal strength.

Actually (1− 1/e) (approximately 63 percent)
J.

Also, the time constant of the electronics is after mechanical lags, so the delay may be somewhat longer.

And then there is the time constant of the glider, which does not reach a steady
upward speed immediately; ie, the glider is a mechanical filter for lift with, I'm
guessing, a time constant between 1 second (low wing loading with stiff wings) and
3 seconds (high wing loading with bendy wings). Jon may have included the glider
lag in his "mechanical lags".
.
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Yes, the glider is part of the mechanical lags. First a new angle of attack and/or airspeed has to establish over the wing. This itself has a time constant, as velocity gradients are always gradual. Then the wings bend. Then the fuselage begins to move - at that moment an inertial sensor can see it. After some movement the air in the tube from the triple probe begins to move. After some more time the hysteresis in the pressure sensor is overcome and it sends a signal to the electronics. From there the lags are electrical or software.

I'm not convinced that your butt can tell the difference between a horizontal and vertical gust. Take as an example a gust from ahead. This will increase both lift and drag. A sharp edged 10 knot gust will give you approximately 1.36G kick. That is about the same as a 4 knot vertical gust. You may sort out which was which by differentiating airspeed, and I think that is what the Butterfly attempts to do in its inertial system. Your butt has no airspeed sensor.
  #33  
Old August 12th 20, 06:48 PM posted to rec.aviation.soaring
Tango Eight
external usenet poster
 
Posts: 962
Default Speed of a vario

On Wednesday, August 12, 2020 at 12:35:39 PM UTC-4, jfitch wrote:

I'm not convinced that your butt can tell the difference between a horizontal and vertical gust. Take as an example a gust from ahead. This will increase both lift and drag. A sharp edged 10 knot gust will give you approximately 1.36G kick. That is about the same as a 4 knot vertical gust. You may sort out which was which by differentiating airspeed, and I think that is what the Butterfly attempts to do in its inertial system. Your butt has no airspeed sensor.


Gusts, like the wind in general, are 3D. The "useless gusts" we've all encountered might well be horizontal plus vertical downwards.

T8
  #34  
Old August 16th 20, 01:27 AM posted to rec.aviation.soaring
2G
external usenet poster
 
Posts: 1,439
Default Speed of a vario

On Monday, August 10, 2020 at 9:01:37 PM UTC-7, krasw wrote:
There seems to be a misconception about time constant of variometer. Many (all?) think that 2 sec time constant means that it takes 2 seconds after hitting thermal for variometer to show any lift. This is not true. Time constant means that within that time variometer needle reaches 100% of the pressure change signal. That does not mean that variometer needle does not start to show at least something (needle starts to rise) before that 2 secs.


The traditional meaning of "time constant" is exponentially based: after one time constant you reach 63% of its final value, after two time constants this is up to 86%, after three it is 95%. You never reach the final value of 100%.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Best vario for airmass awareness across the speed range Jim Hogue Soaring 50 January 30th 20 01:26 AM
FS: ILEC SB8 Acoustic Vario / Speed Commander Michael Huber Soaring 0 December 17th 07 03:07 PM
Rico Speed to fly+ audio Vario 4 sale Gregg Leslie Soaring 0 October 21st 06 12:39 AM
FS: RICO VACS speed to fly vario computer Victor Bravo Home Built 0 September 7th 05 06:54 AM
FS: RICO VACS speed to fly vario computer Victor Bravo Soaring 0 September 7th 05 06:54 AM


All times are GMT +1. The time now is 05:30 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AviationBanter.
The comments are property of their posters.