On Nov 23, 10:20*pm, Scott Alexander
wrote:
Anyone have any bright ideas on how to keep the water from freezing?

Salt?
Antifreeze?
Anything?

The two best solutions are Methanol and Propylene glycol. Salt
absolutely not! Cost wise it will depend on how much of a freezing
point depression you need.

Freezing Point
Propylene Glycol Solution
(% by mass) F

0 32
10 26
20 18
30 7


Methanol Concentration
(% by mass) F
0 32
10 20
20 0
30 -15

Methanol will cost about $3 to $4 per gallon, Propylene Glycol can be
purchased as RV antifreeze in either -50 or -100 solutions. These are
25% and 50% solutions so you will need to to dilute accordingly.
Price for the -50 runs about $4 a gallon.

Lets do a back of the envelope calculation of what you need for a day
where you want to protect down to about 15 F.

Propylene Glycol you will need a 22% solution by mass or about 27% by
volume so you for a 40 gallon total load in your glider you will need
about 35 gallons of off the self -50 antifreeze. Cost of about $140
per flight.

Methanol you will need about 13% by mass or 16.5% by volume. So you
will need about 6.6 gallons of menthanol at a cost of about $25 USD
per flight.