Remember your high school chemistry (or was it physics?).Â* Water gives
up 1 calorie per gram per degree C while cooling.Â* To transition from
water at zero deg C to ice at zero deg C requires the loss of 80
calories per gram per degree C.Â* That's a lot of heat to be lost!Â* Sure,
you have a large surface area, but you have a very large volume as
well.Â* It would take quite some time to freeze a ballast tank.

Bottom line is I never worried about icing the ballast tanks (when I had
them) at sub-freezing temperatures.Â* Now freezing the dump valves is a
different issue, but not really if you fly your glider all the way to a
stop.Â* I once landed my LAK-17a with nearly 50 gallons on board and
didn't notice until after getting out of the glider.Â* Another time, one
dump valve stuck closed and, again, I landed with 25 gallons in one wing
and empty in the other.Â* I didn't notice until coming to a stop and the
full wing dropped heavily.

On 8/18/2020 8:06 PM, Eric Greenwell wrote:
wrote on 8/18/2020 3:54 PM:
On Tuesday, August 18, 2020 at 10:39:00 AM UTC-7, Eric Greenwell wrote:
jld wrote on 8/18/2020 9:57 AM:
Â*Â* "Glider pilots on the Allegheny Ridges (ridge soaring), in
Western US high deserts (thermal soaring), and in the Sierra wave
sometimes use higher wing loading"

Then the GP15 might be able to satisfy these US pilots as long as
they use antifreeze in the ballast :-).
Also you might not be able to get all the benefits of high WL if
you are limited by Vne due to high altitude.

I have been lucky to fly in Minden before.
Unless you compete in the WGC or are trying to beat a world record,
60 kg/m2 would already be A lot.

Bottom line, lets look for news from GP or the dealers to get
confirmation of configuration and delivery dates...

No antifreeze needed in the summer, as the temperatures at 18,000'
are not cold
enough to freeze the water in the wings. Winter wave flying is much
colder, of
course, and wave runners that get permission to fly above 18,000'
have to consider
the temperature at any time of the year.

According to the recent provisional manual, the GP15 VNE is 162 kts
IAS up to 3000
meters; 143 kts IAS at 6000 meters. That's about 195 kts TAS from
3000 meter on
up, so a pretty high limit, especially compared to my ASH26E, with
it's 143 kt
VNE. I don't know what modern gliders have for VNE, or wing loading,
for that matter.



Eric, what air temp do you regard as cold enough to freeze water in
the wings?

The situation I mentioned - summer in high desert areas - means ground
elevations of 5000' or more, and with ground temperatures of 90+, it
will be 25 deg F at 18,000. With the ups and downs of thermal flying,
the average temperature will be around freezing, so the water ballast
won't be cold enough long enough to freeze.

For other situations, I really don't know. In thermal conditions, I
wouldn't worry unless the minimum temperature went below 20 deg F.
Perhaps a temperature meter with a remote probe in the wing tank is
the safest thing. The glider handbook may have guidance, too. A
wireless sensor might be easiest to use for the wing



--
Dan, 5J