My LS-6a, winner of the 85 Worlds, had one.Â* That with the Scheumann
(Sage) variometer worked really well!

On 3/6/2020 12:19 PM, wrote:
The diaphragm-type TE compensator was tee'd into the line going from the flask to the vario. The other side of the diaphragm was connected to pitot pressure. From my layman's perspective, when a glider zoomed up, normally air would flow out of the flask and through the vario to indicate lift. But as the speed dropped, the diaphragm that had been pushed out by higher pitot pressure (from higher airspeed) would return to its normal position, precisely matching the amount of air exiting the flask. So instead of the vario needle jumping wildly up in the "stick" thermal, it would move smoothly to the sink rate at the slower speed. That's what was supposed to happen if everything were adjusted properly, which involved adjusting the volume of the flask+tubing plus the diaphragm range.

The original [Wil] Schuemann box was a self-contained flask and bellows (instead of the rubber diaphragm of the ubiquitous PZL compensators) and included a small capillary that bled pitot pressure into the line between the flask and vario to exactly offset the air entering the flask through vario as the glider descended. So when everything worked, the vario read zero all the time except when in lift or sink. Magic!

The original Schuemann box had to be adjusted for one altitude range. The later model included a second bellows that adjusted the system for different altitudes.

IIRC, Wil Schuemann also included insulation on the outside of the flask and metal mesh inside to mitigate the effects of temperature changes plus gust filters that helped remove the effects of gusts without appreciably slowing the response times of the varios in use then.

I loved my Schuemann box, which worked very well. I flew mostly Eastern contests at the time so I seldom needed the altitude compensation once I got the box adjusted. It was a little bulky, had some steel in it (read: don't mount it directly below the compass), required some setup/config time, and once in a great while needed service from the maestro himself (apparently the big "can" was soldered shut). In the LS-3, I had to mount it behind the spars, which required very small diameter tubing runs forward to the vario to keep the total volume of the flask+tubing within limits. In addition to Wil's instructions for setting them up, there are tips and tricks for adjusting the netto for different gliders as well as when the plastic connectors break away from the brass pneumatic fittings.

But is anyone still using these?

Chip Bearden
JB

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Dan, 5J