On Mon, 27 Jan 2020 18:43:59 -0800, AS wrote:

On Monday, January 27, 2020 at 9:20:56 PM UTC-5,
wrote:
We’ve had a particularly wet winter in the Pacific Northwest this year,
and I got a chance to fly my motorglider today for the first time in
over a month. Just prior to takeoff I noticed that my LXNAV S7 Vario
had a small spot of visible condensation on the interior of the glass.
I’ve noticed this one or two times before, and it has usually been on
days when you might expect condensation to form, normally disappearing
within a few minutes.

Today, however, in addition to the condensation I noticed a progressive
failure of the vario screen image which gradually deteriorated into
diagonal lines. With the engine warmed up enough I was able to add some
heat to the cabin, and over the next half hour repeated restarts of the
vario allowed it to last a little bit longer each time before the
screen deterioration occurred once again. After about an hour of
flying I returned the motorglider to the hanger, and one last check of
the vario showed it to be working properly for at least the 10 minutes
I ran the final test.

I’ll have to follow this over time to see if there are any obvious
patterns of malfunction, but it occurs to me that condensation within
the instrument may have resulted in reversible problems with the
electronics. Over the years I’ve been watching for potential corrosion
issues with the airframe, but this is the first time I realized that
the avionics might be affected as well.

Has anybody seen anything like this and have any advice? I can probably
deal with this by placing a small heat source in the cabin since the
aircraft is hangared. I’ve also had variable success with dehumidifying
granules in the past.

I fly in SC and our climate is humid, too with temperatures falling
below the dew point. To prevent condensation from accumulating in the
cockpit, I place two tubs of Damp-Rid into the cockpit and additional
ones in the trailer. It has helped tremendously with the musky odor and
I am always baffled by how much water is collecting in them over the
course of just a few days.
Many years ago, a fellow in our club in the NE built a clever
heater/blower from a 100W incandescent light bulb and a computer fan in
series inside a PVC pipe. The fan would blow air through the pipe and
the light bulb would act as the heat source. When the bulb failed, the
fan would stop as well. Suspended in the trailer, this contraption did
help control condensation.

Incandescent bulbs make excellent heaters but terrible light sources: as
a light source they're only about 5% efficient, so used as a heater, 95%
of the energy they use goes into heating the fluid they're immersed in.

Back when I was an undergraduate, we used 100 watt lightbulbs to heat
constant temperature water baths. A vertical tube containing mercury and
contacts switched a relay that controlled the lightbulb. This setup could
easily keep a stirred 10-20 litre waterbath within 0.1C of the required
temperature.

Since then I've built a fairly decent oven for curing glass/carbon epoxy
mouldings up to 1.5m long. Its an insulated ply box, heated by a 30w
lightbulb in front of a PC cooling fan in a duct along one side of the
box. This makes sure that air circulates throughout the whole volume
inside the box. Switching is controlled by a thermistor in the duct
upstream of the fan, connected to an off-the shelf electronic module that
drives the switching relay to maintain a preset temperature.


--
Martin | martin at
Gregorie | gregorie dot org