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Vario Comparison



 
 
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  #61  
Old September 15th 18, 02:37 AM posted to rec.aviation.soaring
Charlie Quebec
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Default Vario Comparison

The difference is the slow response of the mechanical ASI damps the transients, whereas an electronic device can respond fast enough to track them.
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  #62  
Old September 15th 18, 02:43 PM posted to rec.aviation.soaring
[email protected]
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Default Vario Comparison

On Friday, 14 September 2018 21:37:03 UTC-4, Charlie Quebec wrote:
The difference is the slow response of the mechanical ASI damps the transients, whereas an electronic device can respond fast enough to track them.


OK, understood, thank you. This generates a new question from me (sorry if this is turning out to be a lesson in instrumentation design...):

Can you slow down the response of your electronic system so that it behaves similarly to your mechanical ASI, or does this bring on poorer performance elsewhere?
  #63  
Old September 15th 18, 04:54 PM posted to rec.aviation.soaring
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Default Vario Comparison

On Saturday, 15 September 2018 09:43:19 UTC-4, wrote:
On Friday, 14 September 2018 21:37:03 UTC-4, Charlie Quebec wrote:
The difference is the slow response of the mechanical ASI damps the transients, whereas an electronic device can respond fast enough to track them.


OK, understood, thank you. This generates a new question from me (sorry if this is turning out to be a lesson in instrumentation design...):

Can you slow down the response of your electronic system so that it behaves similarly to your mechanical ASI, or does this bring on poorer performance elsewhere?




Please disregard my previous comments and questions. I just read Mike Borgelt's 'Horizontal Gusts' article and this article gives answers to my questions.

  #64  
Old September 20th 18, 04:13 AM posted to rec.aviation.soaring
2G
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Default Vario Comparison

On Wednesday, September 12, 2018 at 8:47:09 PM UTC-7, Mike Borgelt wrote:
On Tuesday, 11 September 2018 07:30:43 UTC+10, wrote:
Hi all,

I've been looking for a good electrical vario for many years. Having good knowledge in both digital signal processing and gliding I know what to look for. First, a lot of pilots can't even recognise if the vario is compensated or not, let alone if it's fast/slow or even accurate. I've conducted test like these to get the real respons from varios: https://www.youtube.com/edit?o=U&video_id=UfeGWYwVdas

I've owned the airglide and used it for about 200h. Airglide is not a good variometer, very unstable, the filtering is not done correctly. The LXnav /LXnavigation stuff I've flown with have also been quite bad. Old Zander ZS1/940 has a much better variometer. The modern stuff just haven't got the filtering or sensor precision correct. The only modern vario i've tested that was good is the westerboer vw1020: https://www.youtube.com/edit?o=U&video_id=UfeGWYwVdas

More info at my homepage: http://niklaslofgren.net/gliding/var...ariometer.html

/Niklas


Yup, I had a club who got a new DG505. Complained the B500 and B400 varios worked OK when settled in thermal but not otherwise especially in cruise. After about 9 months they got around to doing a leak check and the TE system would not hold pressure. They did not know they had a triple probe fitting in the fin and only a TE probe plugged in. The other two lines we open in the cockpit, hence no TE. Nobody managed to figure out this was the problem. This was the same outfit that years before had a problem in their Twin Astir with a B50 installation. A voltage check at the instrument revealed 8 volts or so which wasn't enough. They rewired the glider and 3 weeks later called to say all was OK and even the radio now worked properly which it hadn't for about 18 months since the electrical fire in the back of the glider! No names to protect the guilty.

I looked at your videos. A better test of the vario response is the time taken to return to 63% of the zero from the peak. This is the time constant.. When connected as a TE vario this will optimally be around 2 to 3 seconds.. Any faster the vario will move around a lot and you will spend time averaging by eye or ear which is workload intensive and effectively slower. Alternatively the 10% to 90% response time is another better measure.
Other comments:
1. The advantage of electronic varios isn't just the various kinds of averagers (running, total) but audio and all the other (netto, relative,speed command) signal processing.
2. I disagree about electrical pitot static compensation. The low drag argument goes away if you have a TE probe anyway for the mechanical or other TE probe compensated vario. The effect of sideslip on a static port on the nose of a glider is usually greater than on a good design TE probe. Then we have the problem of getting two large signals to arrive at the vario at the same time. We subtract these from each other to get the TE vario and any phase errors can cause large spurious transient response on that. Been there, done that, don't need the support calls. Then there is the problem when the static ports do not have constant percentage errors over the speed range. If you use the Prandtl pitot static on the fin you may as well use the TE probe there. There are errors due to changing G loads and rotation of the glider
3. Time constants in the plumbing. I measured these. Without any vario capacities but including the probe, its holes and the mount in the fin the TE line has a time constant of around 90 to 100 milliseconds. I put an inflated balloon around the probe, hooked the pressure transducer connected in the cockpit to a DSO and popped the balloon. If a typical mechanical vario 450 ml flask is in the cockpit but no vario it went to about 270 to 300 milliseconds.
The time constant of the glider at thermal speeds is about 0.5 seconds on entering lift, as mentioned in an earlier post. If you have a vario connected to static that further slows the vario. If connected to TE that time constant disappears. George Moffat mentioned that a vario is "livelier" when connected to TE in the early 1970s but not the reason why.
Just yesterday Carol and I flew in to South East Queensland gliding club in our BD-4 and ran into a guy from Czech Republic. When he found out who we were, we had a nice discussion on variometers. I was pleased that he had flown extensively with Borgelt varios and he found that they confirmed what his other senses were telling him which he said was unlike most of the others, which confirms your observations about some modern varios.
I've also heard from a German customer that his club bought one of the LCD display devices and he considered it more of a "glider entertainment system" than a vario.

Mike


I am interested in your Dynamis system, but am being frustrated by your website. I keep getting nagged about a java update (most websites have dropped java), and the one time I was able to install it, there was nothing of substance on this vario. Certainly not even pricing or availability. Yet it says it is in production. Can you elaborate?

Tom
  #65  
Old September 20th 18, 05:06 AM posted to rec.aviation.soaring
Charlie Quebec
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Default Vario Comparison

As far as I know, the dynamis is an add on to the B800 etc, an external sensor box.
Not yet released for sale, undergoing testing.
 




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