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#31
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"Bill Daniels" wrote in message ... "Mike Borgelt" wrote in message Vacuum. Use a glass wall vacuum flask. Fill with copper pot scourers. See Reichmann for a complete explanation of why this is a good idea. Mike Borgelt I agree, but I can't find a source of half liter glass vacuum flasks. The consumer variety are stainless steel these days. Bill Daniels I just fat fingered the delete of a post from Tim Ward (I think) with some links to 1 Pt. glass vacuum bottles. Anyway thanks for the links. As for the stainless steel vacuum, bottles, I had tested them way back on another project involving liquid nitrogen and they were far inferior to the glass bottles. The LN2 would evaporate from the stainless ones three times faster than from the glass dewars. On the other hand, they were a lot more rugged. Bill Daniels |
#32
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"Bill Daniels" wrote in message ... "Bill Daniels" wrote in message ... "Mike Borgelt" wrote in message Vacuum. Use a glass wall vacuum flask. Fill with copper pot scourers. See Reichmann for a complete explanation of why this is a good idea. Mike Borgelt I agree, but I can't find a source of half liter glass vacuum flasks. The consumer variety are stainless steel these days. Bill Daniels I just fat fingered the delete of a post from Tim Ward (I think) with some links to 1 Pt. glass vacuum bottles. Anyway thanks for the links. As for the stainless steel vacuum, bottles, I had tested them way back on another project involving liquid nitrogen and they were far inferior to the glass bottles. The LN2 would evaporate from the stainless ones three times faster than from the glass dewars. On the other hand, they were a lot more rugged. Bill Daniels Yep, it was me. I just Googled for "vacuum bottle" glass pint A factor of 3 does seem significantly faster. On a slightly different subject, I keep seing references to "Chore Girl" copper scrubbers, and yet all I can find to buy is "Chore Boy" copper scrubbers. It's not that I think the name will make a difference, but it makes me wonder when the name changed and why. Tim Ward |
#33
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"Tim Ward" wrote in message ... "Bill Daniels" wrote in message ... "Bill Daniels" wrote in message ... "Mike Borgelt" wrote in message Vacuum. Use a glass wall vacuum flask. Fill with copper pot scourers. See Reichmann for a complete explanation of why this is a good idea. Mike Borgelt I agree, but I can't find a source of half liter glass vacuum flasks. The consumer variety are stainless steel these days. Bill Daniels I just fat fingered the delete of a post from Tim Ward (I think) with some links to 1 Pt. glass vacuum bottles. Anyway thanks for the links. As for the stainless steel vacuum, bottles, I had tested them way back on another project involving liquid nitrogen and they were far inferior to the glass bottles. The LN2 would evaporate from the stainless ones three times faster than from the glass dewars. On the other hand, they were a lot more rugged. Bill Daniels Yep, it was me. I just Googled for "vacuum bottle" glass pint A factor of 3 does seem significantly faster. On a slightly different subject, I keep seing references to "Chore Girl" copper scrubbers, and yet all I can find to buy is "Chore Boy" copper scrubbers. It's not that I think the name will make a difference, but it makes me wonder when the name changed and why. Tim Ward Thanks Tim. I did the same thing with Google and never came up with your sites. I'm starting to wonder about Google. I now have a glass 0.45 liter vacuum bottle with two copper scrub pads in it. I repeated the solar heating test with the glass bottle and there was no detectable change in the vario reading after one hour in the sun. I also bought a pint stainless steel flask and it failed the test almost as badly as the plastic one I tested yesterday. A glass vacuum flask is the way to go. "Chore Boy vs. "Chore Girl" it's probably just more annoying "Political Correctness". I think copper wool is pretty much the same no matter what the name. A lot of the same stuff is sold as a rust proof pest barrier in hardware stores. All you are asking it to do is add some heat sink without contaminating the vario system. Now for the next test. I want to determine the vario system time constant. (The vario experts on this forum are welcome to jump in here.) The experiment I have in mind is to inject a calibrated amount of air into the capacity side of the vario with a tiny medical syringe such that it produces a half scale up reading on the vario. Then I will record the time it takes for the vario reading to decay to half that value. (Is there a standard for measuring vario lag?) I guess I could also suck out the same amount of air and make the experiment symmetrical. The reason for my curiosity is a flight in December at Warner Springs, CA. There was some ridge lift mixed with weak thermals. Because the inversion layer was just about at the level of the mountain peaks, I spent most of the flight working lift very near the slopes. When encountering a thermal, I could feel the glider surge and see myself climbing relative to the nearby slopes. Neither vario showed any indication for about three seconds after encountering the lift. That seems way too slow to me. It would be nice to get the response down to one second. Bill Daniels |
#34
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Another aspect to be aware of is the need to keep the flasks in a T.E.
driven vario system with a number of varios each with its own flask - such as is often found with two-seater gliders - identical physically and thermodynamically. You can demonstrate the issue in the following way provided you operate with care. Set up a pneumatic line to a Tee junction with branches to two identical model mechanical varios (say Winter and perferrably new or near new) and have each vario plumbed to a flask with a different construction, or same construction but with one with heat sink material inside and the other without heatsink. Introduce a small signal to the pneumatic line simulating a signal from the TE head (care required - you don't want to drive the varios off scale and have to have them repaired!!) A needle valve will enable control of flow rate so one can record the two vario readings at different flow rates. The varios will read different, one against the other, and the appearance is that the varios have different calibrations perhaps leading one to question the quality of the varios. Run the experiment a second time with the flasks swapped over, and you will find that the recorded calibration swaps between the varios!! You don't have a problem with the quality of the varios, you have the inlfuence of cross flow between the varios due to the different mechanical/thermodynamic characteristics of the flasks. Use identical flasks in a multi vario system with flask type varios. Roger Druce "Mike Borgelt" wrote in message ... | On Mon, 12 Jan 2004 16:40:45 -0700, "Bill Daniels" | wrote: | | I'm fiddling with a Bohli Variometer that originally had a TE compensation | diaphragm that connected to the pitot. (A Bohli uses the same taut band | technology as the Sage except it's shorter and the needle is at the face of | the instrument.) | | I have removed the compensating diaphragm and its housing and installed a | tubing nipple in its place. (The diaphragm compensator utilized several | "O"-rings that had dried out and were leaking.) My intention is to convert | the instrument to use a tail mounted TE probe and a capacity flask. | | With the instrument modifications complete, I decided to test the | temperature sensitivity of the instrument with a 0.45L (1 pint) capacity | flask I had handy. I first placed the instrument in direct sunlight coming | through my office window and the flask in shadow. After 10 minutes, the | Bohli still had a stable zero reading - no heating effect at all. | | Then, I placed the flask in the sunlight and the instrument in shadow. | Within 60 seconds, the vario read 1.5 meters/second (3 Kts.)up. This reading | slowly dropped back to 0.5 MPS (1 Kt) after 10 minutes. Moving the | instrument back to my desk in shadow, the reading dropped to 0.5 MPS down, | then slowly crept back toward zero over about 10 minutes. | | Clearly, as every instrumentation book says, the flask has to be insulated. | The purpose of the above narrative is leading up to the question about the | best material to insulate the flask. I want to mount the flask behind the | instrument panel to keep the tubing runs as short as possible. | | What's the best insulation material? | | Bill Daniels | | Vacuum. | | Use a glass wall vacuum flask. Fill with copper pot scourers. | See Reichmann for a complete explanation of why this is a good idea. | | Mike Borgelt | | |
#35
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Another possible way with two identical flow type varios, is
to use a single capacity flask and put the two varios in series. i.e. TE probe to "static" on Vario #1, "capacity" of #1 vario to "static" on #2 vario, "capacity" on #2 vario to flask. This won't work if one of the varios is a different type, requiring either no capacity or a different capacity. Cheers, John G. "Roger Druce" wrote in message u... Another aspect to be aware of is the need to keep the flasks in a T.E. driven vario system with a number of varios each with its own flask - such as is often found with two-seater gliders - identical physically and thermodynamically. You can demonstrate the issue in the following way provided you operate with care. Set up a pneumatic line to a Tee junction with branches to two identical model mechanical varios (say Winter and perferrably new or near new) and have each vario plumbed to a flask with a different construction, or same construction but with one with heat sink material inside and the other without heatsink. Introduce a small signal to the pneumatic line simulating a signal from the TE head (care required - you don't want to drive the varios off scale and have to have them repaired!!) A needle valve will enable control of flow rate so one can record the two vario readings at different flow rates. The varios will read different, one against the other, and the appearance is that the varios have different calibrations perhaps leading one to question the quality of the varios. Run the experiment a second time with the flasks swapped over, and you will find that the recorded calibration swaps between the varios!! You don't have a problem with the quality of the varios, you have the inlfuence of cross flow between the varios due to the different mechanical/thermodynamic characteristics of the flasks. Use identical flasks in a multi vario system with flask type varios. Roger Druce "Mike Borgelt" wrote in message ... | On Mon, 12 Jan 2004 16:40:45 -0700, "Bill Daniels" | wrote: | | I'm fiddling with a Bohli Variometer that originally had a TE compensation | diaphragm that connected to the pitot. (A Bohli uses the same taut band | technology as the Sage except it's shorter and the needle is at the face of | the instrument.) | | I have removed the compensating diaphragm and its housing and installed a | tubing nipple in its place. (The diaphragm compensator utilized several | "O"-rings that had dried out and were leaking.) My intention is to convert | the instrument to use a tail mounted TE probe and a capacity flask. | | With the instrument modifications complete, I decided to test the | temperature sensitivity of the instrument with a 0.45L (1 pint) capacity | flask I had handy. I first placed the instrument in direct sunlight coming | through my office window and the flask in shadow. After 10 minutes, the | Bohli still had a stable zero reading - no heating effect at all. | | Then, I placed the flask in the sunlight and the instrument in shadow. | Within 60 seconds, the vario read 1.5 meters/second (3 Kts.)up. This reading | slowly dropped back to 0.5 MPS (1 Kt) after 10 minutes. Moving the | instrument back to my desk in shadow, the reading dropped to 0.5 MPS down, | then slowly crept back toward zero over about 10 minutes. | | Clearly, as every instrumentation book says, the flask has to be insulated. | The purpose of the above narrative is leading up to the question about the | best material to insulate the flask. I want to mount the flask behind the | instrument panel to keep the tubing runs as short as possible. | | What's the best insulation material? | | Bill Daniels | | Vacuum. | | Use a glass wall vacuum flask. Fill with copper pot scourers. | See Reichmann for a complete explanation of why this is a good idea. | | Mike Borgelt | | |
#36
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Earlier, John Giddy wrote:
Another possible way with two identical flow type varios, is to use a single capacity flask and put the two varios in series.... That also works well with blind audio units. I did that with a PZL mechanical and a Piep audio in my HP-11, and it worked fine for many years. Bob K. |
#37
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Yes,
Will work with any flow type varios which use the same capacity size. Cheers, John G. "Bob Kuykendall" wrote in message ... Earlier, John Giddy wrote: Another possible way with two identical flow type varios, is to use a single capacity flask and put the two varios in series.... That also works well with blind audio units. I did that with a PZL mechanical and a Piep audio in my HP-11, and it worked fine for many years. Bob K. |
#38
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Why wreck up a great instrument? Contact Bohli directly and order a set of
new O-rings: http://www.bohli-magnete.ch/English/...e/instr_e.html Simon "Bill Daniels" wrote in message ... I'm fiddling with a Bohli Variometer that originally had a TE compensation diaphragm that connected to the pitot. (A Bohli uses the same taut band technology as the Sage except it's shorter and the needle is at the face of the instrument.) I have removed the compensating diaphragm and its housing and installed a tubing nipple in its place. (The diaphragm compensator utilized several "O"-rings that had dried out and were leaking.) My intention is to convert the instrument to use a tail mounted TE probe and a capacity flask. With the instrument modifications complete, I decided to test the temperature sensitivity of the instrument with a 0.45L (1 pint) capacity flask I had handy. I first placed the instrument in direct sunlight coming through my office window and the flask in shadow. After 10 minutes, the Bohli still had a stable zero reading - no heating effect at all. Then, I placed the flask in the sunlight and the instrument in shadow. Within 60 seconds, the vario read 1.5 meters/second (3 Kts.)up. This reading slowly dropped back to 0.5 MPS (1 Kt) after 10 minutes. Moving the instrument back to my desk in shadow, the reading dropped to 0.5 MPS down, then slowly crept back toward zero over about 10 minutes. Clearly, as every instrumentation book says, the flask has to be insulated. The purpose of the above narrative is leading up to the question about the best material to insulate the flask. I want to mount the flask behind the instrument panel to keep the tubing runs as short as possible. What's the best insulation material? Bill Daniels |
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