Vario flask insulation

"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

"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

"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

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
|
|

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
|
|

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.

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.

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