Window Fog

[jau]

Hiya,
Seeking clarification on this.

Was driving the other day and it was quite cold outside, the windows started to fog and so I put the window blower on with hot air. Immediately the windows fogged up completely. The aircraft I fly has a defogger and I started to think hat I didn't want the same thing happening up there!!!

So, what causes windows to fog and how do you clear them?

I thought that is due to differences in OAT and cabin temp, so if it occurs then try to equalize the temps, (i.e. cold air on the window if OAT is colder, and hot air on the window on a hot and/or humid day). Is this right?

Also I'm guessing wet clothes in a warm cabin (due to evaporation) is a big no?

Thanks for your help.

jau

[DHthe2nd]

Condensation forms on the dust/dirt particles so if you thoroughly clean the inside of the screen then no/less condensation will form.

[AerBabe]

If you smear a thin layer of washing up liquid on the inside of windows, it prevents condensation.

[AerBabe]

Better still, fly something with no windows.

[Ultralights]

if you have air conditioning in your car, use that to defog the windows, it will work immediatly.

as for fogging when the heater is on, its the same as breathing onto cold glass, the air inside is already humid, and condensation is forming when the air contacts the glass, as the air isnt moving, condensation isnt that much, then you blow warm humid air onto it, it will fog up completely until the warm air heats the glass and surrounding air to a temperature where the water content in the air is absorbed.

Using the air conditioning de-humidifies the air, so its blowing colder DRY air onto the glass, the dry air absorbes water, which it draws off the glass its blown over..

use the heat on full hot and air conditioning at the same time if possible. no more fog.

[nobby]

Do not use air recirculate in the conditons you describe if windows fog up open windows, air temp to cold, fan mid, recirculate to outside, aircon on.

Cars with air con are more prone to fogging they may have pollens filters fitted and have slightly restricted air flow. use recirculate for rapid warm and then switch to outside. make sure the air outside matches air inside. no damp clothing etc. I fly with a good chamois leather clean and graese free.

[GOLF_BRAVO_ZULU]

Ultralight sums this up quite well. Until the glass warms up, warm moist air will dump water on cold glass.