At 07:42 13 October 2007, wrote:
For flights limited to a single day and the ballast
added the day of
flight, I do not believe antifreeze is necessary.
Given the very high
heat capacity of water, the large volume, and the agitation
that
occurs during flight, it would not freeze. Dumping
partial loads
might be a problem in that the valves may ice up, preventing
further
dumping.

Environmentally, ethanol would be the safest. Propylene
glycol iand
isopropyl alcohol are very toxic and very attractive
to mammals.

It is good to see glider pilots considering environmental
concerns, so I will add this. Isopropanol is mildly
toxic yes, but evaporates molecularly free (this is
why surgeons used it to clean instruments before autoclaves),
at pretty low temps and would very likely evap before
hitting the ground with the rest of the water it was
entrained in. Also it is not at all attractive to animals,
as in liquid form it is fumy, bitter, and really smells
bad (offer your dog some on a rag, you'll see).
Propylene glycol is what is used in eco-friendly antifreeze,
as opposed to the highly toxic ethylene glycol which
as already pointed out, is what is in regular antifreeze
(and tastes good to cats/dogs).
To wrap it up, ethenol, although not toxic in and of
itself, is not available without spending a great deal
of money/gallon, or being denatured--made toxic. This
keeps the bartender in business, and makes the otherwise
drinkable effluent rather poisonous (more so than isoproanol)
to man or beast, rendering it a poor choice for eco
friendly ballast tank antifreeze.
The non-toxic propylene glycol based antifreeze (commonly
called RV Antifreeze), at around $5-$7 a gallon would
probably be the best, cheapest 'responsible' choice.
If you are right about the valves being the weak link
in the freezing chain, it surprises me that none of
the manufacturers offer heated dump valves. (after-market
retrofit maybe?) Winter temps at altitude can be...well
a little balmy. I wonder, what kind of studies have
already been done on this?

Paul Hanson