On Friday, October 11, 2019 at 11:32:14 AM UTC-4, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
On Friday, October 11, 2019 at 10:06:16 AM UTC-5, Dave Nadler wrote:
On Friday, October 11, 2019 at 11:01:09 AM UTC-4, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Ever seen one of these? Pictures at; http://derosaweb.net/aviation/cambridge/filter. It seems to have a large ID at one end and a much small ID at the other end.

- What is its function?
- What airline does it go with?
- Which direction should it point?

Back Story: A friend (IA/A&P) was working on the airlines of a glider..
From what I gather there is a Cambridge CVS-50 installed. There is also a
Winter vario installed. He removed all the airlines from instruments
before noticing this hard plastic component until it was too late.
Now he is lost as to what to do with it.

Thanks, John OHM Ω

Oh dear.
Always take pictures prior to removing/disassembling stuff.
I still have a polaroid box camera I used to use for this!
But in these modern times a phone camera is excellent.
Though useless unless one takes the photos, and puts prints
in the box with the parts...
End of sermon, you can genuflect now.

Anyway, you're looking at a calibrated leak for a netto system.
Works in either direction.
But, such things only work correctly at a single weight and
a particular density altitude.
And thus are rarely seen anymore...

See ya, Dave

Pictures?? *I* have sworn on a stack of FAR/AIMs to take a boat load of pictures, only removing one tube at a time and carefully labeling where it went to/from. See my genuflection in http://aviation.derosaweb.net/presentations/#airlines. It is another poor soul I am trying to save from oblivion!

So assuming (!) that this will be the same instruments/glider/pilot would there be any value in replacing the netto "calibrated leak"? If so how would it be plumbed?

PS - I got a response from Gary Kammerer who said it was a "restrictor" and pointed me to a 2012 article from Dave Ellis "Variometer pneumatics – probes, tubing, restrictors, etc." that seems to point to the restrictor not being needed.

Thanks, John

I don't think it's a netto leak. I've made a few of those. IIRC the tube ended up about 3.5 - 4" long, 0.012" ID. I used on an original Schuemann Compensator (remember those?) when I found one that was still serviceable, about ten years ago, but you should be able to adapt to any capacity style vario. IIRC (and without thinking hard about it) if using a TE probe, you would connect the leak between static port and the flask, vario goes between flask and TE probe.

Side note: modern pressure transducer based electronic varios like to be on pneumatic circuits without leaks, without large capacities and without any flows to speak of. Sharing a TE probe with one (and only one) mechanical vario may be done with reduced performance of the electronic vario. Sharing static with any mechanical instrument generally goes bad, don't do it. Sharing the pitot with one ASI can be done in a pinch, it is the least critical of the three.

best,
Evan Ludeman