Vario flask insulation

[Bill Daniels]

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

[Chris Nicholas]

All the installations I have seen use a standard vacuum flask with no
additional insulation, but they were all buried either beneath/behind
the instrument panel, or inside the fuselage - anyway in shadow.

A key element I have read about, and all mine have been fitted with, is
copper pan scourers loosely filling the interior of the flask, so that
temperature variation within the capacity is elinimated.

However, I am no expert, and I look forward to some who are telling how
it really should be done.

Chris N.

[Pete Russell]

If you have a true vacuum bottle as a flask you should not need more
insulation but if you are using a winter capacity you can use anything to
put airspace between the vario and the glare shield the white beaded foam is
probably best but a pain and messy to work with there are some flexible foam
rubbers you could use. There are other reasons to insulate your capacity and
use the copper wool inside, maybe we can hear from Mike Borgelt he can
describe the reasons more better er er than I.

Pete




"Chris Nicholas" > wrote in message
...
> All the installations I have seen use a standard vacuum flask with no
> additional insulation, but they were all buried either beneath/behind
> the instrument panel, or inside the fuselage - anyway in shadow.
>
> A key element I have read about, and all mine have been fitted with, is
> copper pan scourers loosely filling the interior of the flask, so that
> temperature variation within the capacity is elinimated.
>
> However, I am no expert, and I look forward to some who are telling how
> it really should be done.
>
> Chris N.
>
>
>
>
>

[Tim Ward]

"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

Well, vacuum, of course.
Now that the smartass answer is out of the way, the local hardware store
sells some insulation that might be of interest:
It looks and feels like aluminized bubble wrap. There's a demo made of the
stuff that's just a cylinder about six inches in diameter with one open
end. You put your hand inside and you _immediately_ feel the temperature
rise.
It comes in rolls. I think it's a couple of bucks a foot for the two foot
width. I wish I could remember a brand name, but I can't.
Scissors and packing tape should be all you'd need to apply it, though
contact cement would probably work, too.

Out of curiosity, what happens when you leave the instrument in the sun and
the flask in the shade, and then alternately shade and unshade the
instrument? This seems like it would be more like what would actually
happen in the glider.

Tim Ward

[clay thomas]

"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

You might try the urathane foam that comes in a can or blue dow foam
you could hollow out so that you would have no seams.

[Bill Daniels]

"Tim Ward" > wrote in message
...

> Out of curiosity, what happens when you leave the instrument in the sun
and
> the flask in the shade, and then alternately shade and unshade the
> instrument? This seems like it would be more like what would actually
> happen in the glider.
>
> Tim Ward
>
I tried exactly this and saw no thermal response from the instrument at all.
The case appears to be made of a thick engineering plastic like Delrin. A
taut-band vario should be sensitive to changes in length caused by thermal
expansion but I didn't see any effect. The bellows and band are supported
on a brass frame inside the instrument that is carefully shaded from the
sun. I had been critical of the white face since it reflects on the inside
of the canopy but maybe I was hasty there. The white face may be useful in
controlling solar heating of the instrument.

Bill Daniels

[VentusDriver]

Bill,

Use a vacuum flask and put 2 or 3 copper pot scrubbers (chore girl
brand works OK) in the bottle, then cap the bottle and make sure you
test for leaks. Leaks on the bottle side of a vario make for huge
errors.

Jim

[Bill Daniels]

"clay thomas" > wrote in message

>
> You might try the urathane foam that comes in a can or blue dow foam
> you could hollow out so that you would have no seams.

You know, I had thought of that urethane foam in an aerosol can. Maybe I
could suspend the flask in a tube made of polyethylene sheet and fill the
annulus with foam. After the stuff hardens I could trim off the excess.
Could be messy though.

I'm wondering if I should try to find a pint size glass thermos bottle and a
one hole stopper. That way I could stuff in some of that copper wool
everyone likes. All I can remember are 1 quart size though.

Bill Daniels

[Michael McNulty]

Bill Daniels wrote:
<snip>
> 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

A vacuum

[Andy Durbin]

Chris Nicholas > wrote in message >...
> All the installations I have seen use a standard vacuum flask with no
> additional insulation, but they were all buried either beneath/behind
> the instrument panel, or inside the fuselage - anyway in shadow.
>
> A key element I have read about, and all mine have been fitted with, is
> copper pan scourers loosely filling the interior of the flask, so that
> temperature variation within the capacity is elinimated.
>
> However, I am no expert, and I look forward to some who are telling how
> it really should be done.
>
> Chris N.


I thought the pot scrubbers were used to reduce the flask capacity to
compensate for the capacity added by a long tubing run.


Andy

[W.J. \(Bill\) Dean \(U.K.\).]

No. The copper (they should be copper not some other metal) pot scourers
are there as a heat sink, nothing to do with volume.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Andy Durbin" > wrote in message
> om...
>
> >
> > Chris Nicholas > wrote in message
> > >...
> >
> > All the installations I have seen use a standard vacuum flask with no
> > additional insulation, but they were all buried either beneath/behind
> > the instrument panel, or inside the fuselage - anyway in shadow.
> >
> > A key element I have read about, and all mine have been fitted with, is
> > copper pan scourers loosely filling the interior of the flask, so that
> > temperature variation within the capacity is eliminated.
> >
> > However, I am no expert, and I look forward to some who are telling how
> > it really should be done.
> >
> > Chris N.
> >
>
> I thought the pot scrubbers were used to reduce the flask capacity to
> compensate for the capacity added by a long tubing run.
>
> Andy.
>

[Ian Johnston]

Chris Nicholas > wrote in message >...
> All the installations I have seen use a standard vacuum flask with no
> additional insulation, but they were all buried either beneath/behind
> the instrument panel, or inside the fuselage - anyway in shadow.
>
> A key element I have read about, and all mine have been fitted with, is
> copper pan scourers loosely filling the interior of the flask, so that
> temperature variation within the capacity is elinimated.

It's interesting to note that these two measures have very different
effects. The insulation ensures adiabatic expansion, which means that
the temperature of the air drops as the pressure falls. The copper is
there to make sure that the temperature stays the same.

Isn't thermodynamics fun?

Ian

[John Galloway]

At 14:00 13 January 2004, Andy Durbin wrote:

>I thought the pot scrubbers were used to reduce the
>flask capacity to
>compensate for the capacity added by a long tubing
>run.
>
>Andy

Andy,

You can fill a pint beer glass with water to the brim
and then slowly introduce a fine pot scrubber wihout
spilling a drop if you are careful. I can't remember
where I first heard that but I didn't believe it until
I tried it.

John Galloway

[Bob Lepp]

Michael McNulty > wrote in message news:<DCLMb.408$
> A vacuum

Awwww. you cheated, that's not a 'material'....isn't a vacuum a lack
of material?? ;-)

[Cliff Hilty]

At 14:36 13 January 2004, Bob Lepp wrote:
>Michael McNulty wrote in message news: A vacuum
>
>Awwww. you cheated, that's not a 'material'....isn't
>a vacuum a lack
>of material?? ;-)
>

That what makes it so good! No material to conduct
heat!')

Cliff

[Bill Daniels]

"Todd Pattist" > wrote in message . They'll
corrode and put junk into the Bohli.
>
Snip-----

> 2) I had to disconnect the Bohli from the TE probe as it
> interfered with my older Ilec system which uses a small
> internal capacity. It wasn't the Bohli's fault, but the
> large capacity on the mechanical and the small capacity on
> the electric produced capacity to capacity crossflow that
> interfered with the Ilec.
> Todd Pattist - "WH" Ventus C

Yeah, I've been thinking of this possibility if I ever want to add something
like the Ilec. I plan to recondition the Bohli compensation diaphragm with
new o-rings and store it carefully so that it can be converted back to
pitot/static connections if the need arises.

Bill Daniels

[Charles Yeates]

Everyone is talking about copper insulation inside the vario capacity
bottle but two years ago a German made bottle installed in my PW6 had
steel material -- the compass went nuts. The bottle had to be sent back
for demagnetizing !!

Todd Pattist wrote:
> "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've got a Bohli - it's a nice vario. You've got lots of
> answers to your insulation question, so I'll just add this -
>
> 1) When you add the copper scrubbers to your capacity (good
> idea), first pull off any metal buttons on the top of the
> scrubbers. They'll corrode and put junk into the Bohli.
>
> 2) I had to disconnect the Bohli from the TE probe as it
> interfered with my older Ilec system which uses a small
> internal capacity. It wasn't the Bohli's fault, but the
> large capacity on the mechanical and the small capacity on
> the electric produced capacity to capacity crossflow that
> interfered with the Ilec.
> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)

[Keith W]

>
> You can fill a pint beer glass with water to the brim
> and then slowly introduce a fine pot scrubber wihout
> spilling a drop if you are careful. I can't remember
> where I first heard that but I didn't believe it until
> I tried it.
>
> John Galloway
>
What a waste of beer! Hopefully the scrubber didn't have any soap or
detergent? 8-)

Keith

[Andy Durbin]

John Galloway > wrote in message >...
> At 14:00 13 January 2004, Andy Durbin wrote:
>
> >I thought the pot scrubbers were used to reduce the
> >flask capacity to
> >compensate for the capacity added by a long tubing
> >run.
> >
> >Andy
>
> Andy,
>
> You can fill a pint beer glass with water to the brim
> and then slowly introduce a fine pot scrubber wihout
> spilling a drop if you are careful. I can't remember
> where I first heard that but I didn't believe it until
> I tried it.
>
> John Galloway

That seems to say that the volume of copper is *very* small so its
mass would be too. Is there any useful heat exchange between a
negligible mass of copper and .45 litres of air?

I'll add the knowledge to my useful pub tricks list though.

Andy

[John Galloway]

At 15:54 13 January 2004, Keith W wrote:
>
>> You can fill a pint beer glass with water to the brim
>> and then slowly introduce a fine pot scrubber wihout
>> spilling a drop if you are careful. I can't remember
>> where I first heard that but I didn't believe it until
>> I tried it.
>>
>> John Galloway
>>
>What a waste of beer! Hopefully the scrubber didn't
>have any soap or
>detergent? 8-)
>
>Keith
>
Keith,

I may be daft but not that daft as another read will
confirm:-)

John

[John Galloway]

At 21:00 13 January 2004, Andy Durbin wrote:
>John Galloway wrote in message news:...
>> At 14:00 13 January 2004, Andy Durbin wrote:
>>
>> >I thought the pot scrubbers were used to reduce the
>> >flask capacity to
>> >compensate for the capacity added by a long tubing
>> >run.
>> >
>> >Andy
>>
>> Andy,
>>
>> You can fill a pint beer glass with water to the brim
>> and then slowly introduce a fine pot scrubber wihout
>> spilling a drop if you are careful. I can't remember
>> where I first heard that but I didn't believe it until
>> I tried it.
>>
>> John Galloway
>
>That seems to say that the volume of copper is *very*
>small so its
>mass would be too. Is there any useful heat exchange
>between a
>negligible mass of copper and .45 litres of air?
>
>I'll add the knowledge to my useful pub tricks list
>though.
>
>Andy

Andy,

The mass may be small but, more importantly, the surface
area to volume ratio of the scrubber is huge, thus
allowing for rapid heat transfer between the copper
and the air. I can't quote you figures for the heat
capacity of the copper but 'New Soaring Pilot' says:

'Although its volume may be small, its relative heat
capacity will be large and the air temperature stays
almost constant with pressure changes.' They go on
to say that this reduces the time constant to about
one fifth of its initial value BC [Before Copper]

The vario capacity is a system with rapid but small
positive and negative pressure changes and commensurately
rapid but small positive and negative temperature changes
so you need rapid heat exchange much more than large
heat capacity in the heat sink.

(I can't be bothered with mechanical varios and flasks
any more and just use the excellent B40 for back up
- in fact often as the primary thermalling vario too
- not that there's much in the way of thermals around
here at present)

John Galloway

[Ian Johnston]

On Tue, 13 Jan 2004 20:47:07 UTC, (Andy Durbin)
wrote:

: That seems to say that the volume of copper is *very* small so its
: mass would be too. Is there any useful heat exchange between a
: negligible mass of copper and .45 litres of air?

I bet the trick wouldn't work if the glass was really, really full.
You can pile a lot of water up in a meniscus.

That said, the specific heat capacities for copper and air are 380 and
1004 J/kgK, but since the densities are 896 and 1.225 kg/m^3, the
volumetric heat capacities are 340 and 1.23 kJ/Km^3, a ratio of 276:1.
In other words, filling 1% of the capacity with copper will nearly
treble the heat capacity of the, um, capacity.

Ian
--

[Bill Daniels]

"Ian Johnston" > wrote in message
news:cCUlhtvFIYkV-pn2-slrYLOWSYEIp@localhost...
> On Tue, 13 Jan 2004 20:47:07 UTC, (Andy Durbin)
> wrote:
>
> : That seems to say that the volume of copper is *very* small so its
> : mass would be too. Is there any useful heat exchange between a
> : negligible mass of copper and .45 litres of air?
>
> I bet the trick wouldn't work if the glass was really, really full.
> You can pile a lot of water up in a meniscus.
>
> That said, the specific heat capacities for copper and air are 380 and
> 1004 J/kgK, but since the densities are 896 and 1.225 kg/m^3, the
> volumetric heat capacities are 340 and 1.23 kJ/Km^3, a ratio of 276:1.
> In other words, filling 1% of the capacity with copper will nearly
> treble the heat capacity of the, um, capacity.
>
> Ian
> --

I've been doing some searching for a 0.45L vacuum flask - no luck. All
consumer thermos bottles these days are heavy, bulky, not very insulating
stainless steel. Laboratory glassware suppliers do sell 500ml glass dewars.
The ones that I could find however, are short, wide mouth containers which,
with the large rubber stopper required, wouldn't be very good either.

Anybody got a lead on a narrow-mouth, half liter glass dewar?

The other approach is to use the tan plastic 0.45 liter capacity flask that
comes with varios these days like the one that failed the test for thermal
effects. Insulating one of these might be acceptable but there is no way to
insert a copper scrub pad.

Bill Daniels

[Bob Kuykendall]

Earlier, "Ian Johnston" > wrote:

> ...You can pile a lot of water up in a meniscus.

I think you just named Pez's next sailplane!

[Tim Ward]

"Andy Durbin" > wrote in message
om...
<snip>
> That seems to say that the volume of copper is *very* small so its
> mass would be too. Is there any useful heat exchange between a
> negligible mass of copper and .45 litres of air?
>
> I'll add the knowledge to my useful pub tricks list though.
>
> Andy

Rather than squeeze this out a piece at a time, take a look at:
http://www.betsybyars.com/guy/soaring_symposia/69-vario.html

and get a perhaps-useful overview.

Tim Ward

[Mike Borgelt]

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
>

[Bill Daniels]

"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

[Tim Ward]

"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

What's wrong with this one?
http://www.polsteins.com/pinglasvacbo.html

or this one:
http://housewares.aubuchonhardware.com/kitchen_dishes_and_pans/thermos_bottl
es/glass_vacuum_bottle-624462.asp

or this one:
http://shop.store.yahoo.com/appliancesourcecom/ther155ozvac.html

or this one:
http://hectorshardware.com/therstanun.html
(look for 624462)


But as far as that goes, the whole point of a dewar is that you lose heat by
conduction only across the very small area at the neck. (And through the
stopper, of course) If the stainless is as shiny as the aluminum on the
glass, you shouldn't lose any more by radiation than a glass flask.
Do you have some indication that the stainless dewars are significantly
worse than glass? i.e. claims that they keep a liquid hot or cold for
longer.
Demonstrably, your foam capacity wasn't good enough, but how different is
the stainless model?

Tim Ward

[Pete Russell]

PZL makes a good vacuum bottle made for glider use I last got one from Wings
And Wheels.

Pete

[Bill Daniels]

"Pete Russell" > wrote in message
...
> PZL makes a good vacuum bottle made for glider use I last got one from
Wings
> And Wheels.
>
> Pete
>
The ones pictured at W&W are the same as the one I tested.

Bill Daniels

[Bill Daniels]

"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

[Tim Ward]

"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

[Bill Daniels]

"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

[Roger Druce]

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
| >
|

[John Giddy]

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
> | >
> |
>
>

[Bob Kuykendall]

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.

[John Giddy]

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.
>
>
>
>

[Simon Waddell]

Why wreck up a great instrument? Contact Bohli directly and order a set of
new O-rings:
http://www.bohli-magnete.ch/English/Products/instr_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
>
>