I have seen gliders with frozen tail tanks.

I always used to use plain old automotive anti-freeze in the tail tank
as it wont attack GRP or rubber and 1-2 gallons at 10-20% mix released
as an aerosol at 10,000ft is not going to harm anything!!

Also be aware that the wings with their foam cores are like thermos
flasks, just be sure to not have any dripping valves or dump water
above the freezing layer.
Tail tanks however are usually single skinned and can be frozen
relatively easily.

Regards

Al


wrote:
I've read the past posts on using ~20% methanol to prevent tail ballast
from freezing. I have these questions three:

1) Is methanol in any way corrosive to rubber parts/seals?

2) Is there a reason not to use ethanol if methanol can't be found?

3) Does a glider flying in the Great Basin area in July, between 15k
and 18k for 7+ hours, really need tail ballast anti-freeze?

~ted/2NO