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Silica Gel and the resulting drop in relative humidity inside the aircraft

Just wondering how many people use Silica gel over the winter?

I have a few bags on the yoke each side and resting on the throttle quadrant. I find it stops the engine gauges getting condensation during temp changes.

How do you dry out he bags? I have heard of some people lightly heating them in the oven!

Alex
Shoreham (EGKA) White Waltham (EGLM), United Kingdom

I am using such bags: Pingi.
And put it in the microwave for 6 minutes when it turns pink (after about 2-3 weeks). Condensation on the instruments disappeared after I started to put one inside the cockpit. Worth the 100 grams of extra load!

Belgium

i keep one of these (or similar) in the plane

and replace them when used

fly2000

I keep a 0.5kg bag, sometimes two, in the plane the whole time.

Measurements show that the RH is reduced by roughly 10 percentage points, which reduces condensation massively.

One cannot get much better with an unpressurised hull which has loads of holes in it.

It doesn’t matter much where in the cockpit the bag is left. Mine are normally left in the boot.

Weighing the bags before/after shows that each one absorbs about 30g (30cc) of water. That’s a LOT of water. It also showed that after a week or so they aren’t much good.

I bake the bags after 1 week, +120C for 48hrs, to recycle them, in an oven at work which is otherwise used for baking chips before they are reflow soldered.

I get my bags from here Stitched cloth, not paper, because the paper ones cannot be baked.

Administrator
Shoreham EGKA, United Kingdom

Ive used this not just for the plane. Put it on the radiator and by next morning its dry (recharged).

Thomar 604100 AirDry Auto-Entfeuchter im

KHTO, LHTL

Peter_Paul wrote:

i keep one of these (or similar) in the plane

and replace them when used

I as well use this, all year long.
Some call them dehumidifiers some call then moisture absorbers.

http://www.uhu-profishop.com/adhesives/moisture-absorbers.html

The advise from friends is “don’t come in contact with the gelly type of liquid at the bottom, just dump it in the toilet and through away the little bag in trash”
I wipe the box clean and then insert new bag. That takes place every ~2 months.

I don’t fly with the box on board because I hate the idea of the liquid spilling in the aircraft !

Last Edited by petakas at 04 Sep 06:08
LGMG Megara, Greece

I am not sure it will work for 2 months.

The tests I did showed a 500g pack increasing by about 30g in 1 week in the aircraft. A week later it would go up another 10g only. So the stuff seems to saturate at around 10% of its own weight.

Maybe there is data out there on maximum absorption of silica gel because babies’ nappies use the stuff. OTOH when a baby has a pee you are getting liquid which goes straight into the stuff, whereas in the aircraft you are absorbing water vapour from the air, only.

So I change the bags whenever I fly which is usually once a week.

Administrator
Shoreham EGKA, United Kingdom

Peter
The dehumidifiers PeterPaul and Petakas are talking about are different. I used those in my vacation home when left inhabitated for a few months. The salt or whatever it is will disappear almost entirely and the w water will be in liquid form in the box. I can assure you that it was quite more than just 30gr. of water. These packs cannot be reused.

LSZH

The UHU absorbers are CaCl2, which is highly hygroscopic as it releases quite a bit of energy when it dissolves in water. It drips off a hydrate of CaCl2, which is a bit corrosive, and this is the gelly stuff that collects in a container.

A kg of CaCl2 absorbs around 2kg of water, while a kg of Silica Gel absorbs around 300g, so by weight it is 6x as effective; by volume even more so as CaCl2 has a higher density.

But: it only works once and needs a container to collect the brine, so you need some flat area to put the container, while Silica Gel can be regenerated and put pretty much anywhere.

Last Edited by Cobalt at 04 Sep 07:54
Biggin Hill

We have a Thermo-Electric Dehumidifier that just fits through the door in the bagage compartment.
We have a timer and a thermostat connected so it will run for an hour a day and only when the temperature is positive.
When going to the plane in the winter we empty the water container.
For short flights where the weight or space is no problem i will just leave it in the back.

pmh
ekbr ekbi, Denmark
36 Posts
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