Take this with a grain of salt since the consequences of being wrong are
huge.

There are a lot of pilots flying out of Boulder, CO who routinely fly above
the freezing level with ballast in the wings and fin tanks. I fly a Duo
Discus with water in the fin tank. I don't know of any problems although
pilots worry about it. Foam core sandwich construction is a pretty good
thermal insulator which probably helps a lot. For sure if the tank is cold
enough long enough it WILL freeze.

I speculate that since the water gets a lot of sloshing from turbulence,
while that doesn't reduce the heat required to freeze, it does keep the
temperature of the whole tank uniform and that helps insure that all the
water will freeze at once or not at all. Sloshing may also add a tiny
amount of heat. Getting the water down to the freezing temperature is one
thing. Removing the heat of crystalization is the other - that takes a
while. Most flights don't stay above the freezing level that long.

One thing I know is that it's important never dump ballast above the
freezing level. That would almost certainly result in a l;arge amount of
ice on the rear fuselage, possibly freezing the rudder.

I'd like to hear of a suitable 'anti-freeze'. That would remove the worry.

Bill Daniels


"Paul Remde" wrote in message
news:LpRog.805639$084.97636@attbi_s22...
Hi,

I am not an expert on high altitude flying as I've done very little of it.
However, I do believe I would take the possibility of water freezing in
the wing and/or tail very seriously if I were flying above 10,000 feet for
more than a few minutes. The reason is that a while back I saw a photo of
a glider with the leading edge of the wing split open due to water
freezing and expanding in the wing. It was a dramatic photo taken in
flight with the leading edge open 4 inches or more over a split that was
perhaps 3 feet long. This is all from memory so I may not be remembering
correctly. It think it was a photo in Soaring magazine.

Good Soaring,

Paul Remde

"Bert Willing" wrote in
message ...
What can happen though is that the small water content in the valve does
freeze, nad then you'll have a bloody leaking valve.

"Marc Ramsey" wrote in message
...
Francisco De Almeida wrote:
The German manufacturers would rather have their customers release the
=
tail ballast at +2=BAC. I suspect solar radiation is the reason why =
people can keep their water at lower air temperatures without =
immediately being awarded a split tailplane.
So if you have both outside temperatures below 2=BAC and no sunlight
... =
beware!

I've been assuming that solar heating is the reason that the tail
ballast doesn't end up freezing during these summer flights. At a few
degrees below 0C in shadow, it should still take something more than an
hour for a few liters of water to freeze to the extent that it would
cause structural damage. Lack of lift and cold toes would cause me to
seek warmer environs long before that point...