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
|
|
|