Installing 2 Varios / TE question

[roger.l...@gmail.com]

I'm in the process of getting an AC4 Russia back in the air after it has not flown in 9 years. During this project, I am having to update the panel and replace some instruments.

The end game is to have both the original Winter mechanical vario and a new LXNav S-80 in the panel. I know that I could leave the TE probe and the flask on the mechanical and plumb the S80 just to static and use electronic compensation on the S80 without the TE probe. I'm curious if this is the best way to go or is it possible (and better or worse) to use the TE on both instruments?

I understand the theoretical issue of using a single TE line on a pressure type and flow type vario...but....what about in practice?

I can't split the TE line anywhere other than behind the panel. What if I just installed 6 feet or so of tubing between the instruments and wrapped and secured it? In reading I found the following from Borgelt:

"Unless all the varios connected to the TE line are of the pressure transducer type, split the line as close to the TE probe as possible. This minimises interaction between the instruments caused by flow in the line from variometers which use capacity flasks and also prevents the pressure transducer vario response from being slowed by the presence of the flask causing a pneumatic low pass filter to be formed. In practice, placing the T piece under the seat near the rear of the seat area is good enough."

So, since I have to split under the panel, would my idea of using a bunch of extra tubing have the same effect? Is it worth the effort or should I just use electronic compensation on the S80? I guess I could also use the TE on the S80 and plumb the mechanical to static and the flask and use it with zero compensation as well.

Thoughts are appreciated.

Roger

[Dan Daly]

I used a long coil (15') of tubing after a TE tee to isolate a winter from both a Borgelt B-500 which suffered from cross-talk and after its replacement, to an LX-7007. It cured the cross-talk problem. That said, electronic compensation works as well on a wide range of modern varios, eliminates losing performance on both varios if you develop a leak, and gives you independent TE on the varios. It also reduces behind-panel clutter. I'd go electronic TE on the S80, pure TE to the mechanical.

I eventually replaced my Winter with a V3 (now S3), and the 7007 with a Clearnav vario, so no capacity in the system. I use electronic compensation with CNv and it works very well (as does pure TE in the S3).

Dan
2D

[Dave Walsh]

Well the standard system in the Lange Antares 20E is: Flask -
Winter vario - Zander vario (pressure transducer type) - TE
tube. The flask is close to the panel, the tube runs are as short
as you'd expect. So far as I can see there are no restrictors in
the system.
It seems to work well.
It's simple to plumb so why not try it? If it's rubbish you can
always try another approach.
>

[Dan Marotta]

I use electronic compensation on my ClearNav vario and TE on my winter.
Works just fine and their speed to fly indications match almost exactly.

--
Dan, 5J

[Per Carlin]

I run a S80 and a Sage variometer on the TE, splitting is just behind the panel. It could be that there is a overflow problem, but i'm 100%.
Using electrical sompensation is ony usefull if you have a multi-probe back in the fin. The standad fuselage static holes a not good enouge for electrical compensation. i once tried electrical compensation but it was totally useless as the static holes is nonlinear and it was impossible to get the compensation correct for more than one speed.

[Justin Couch]

On Sunday, 11 June 2017 21:48:25 UTC+10, roger.l...@gmail.com wrote:

> I understand the theoretical issue of using a single TE line on a pressure type and flow type vario...but....what about in practice?
>
> I can't split the TE line anywhere other than behind the panel. What if I just installed 6 feet or so of tubing between the instruments and wrapped and secured it? In reading I found the following from Borgelt:

Mike's words are very relevant. I've fixed at least 4 gliders with cross talk between the two varios just by moving the T to back behind the pilot's seat. If you can't do that, then two big loops behind the instrument panel would be acceptable. The T needs to be a long way back from both varios, so don't put a T in, run a short section to one vario and a long piece to the other.