spirit pilot

Ok guys, here's one from the Say What? file.
I would be rejecting this one outright, if it were'nt for the source of the information. This was told to me by a friend name of Jim Porter of Iowa. Jim is a man of few words, and not known to bull ****. He is a veteran of the hobby having started many years ago. That being said, this sounds a little too strange to be true, coming even from Jim.
The story goes that lift can be found over a frozen lake. as the entire lake is not frozen to the bottom. The liquid water under the ice is warmer than 32 degrees, so warm air is coming up from under the ice, and producing lift.
Again, this is more than a little out there.
Has anyone else heard, or better yet seen this? I still betting this is a line of bull...

perttime

Whatever the situation with lift, frozen lakes can be great places for flying. I've watched a small glider contest on ice. Flights weren't particularly long from high-start launches - but they did find a winner.

Depending on your lake, you might find a sort of slope lift if the terrain rises sharply at the shore, or if you have dense trees there.

jetmaven

If Jim says so , then it likely is.
He has probably forgotten more than most of us know . ( but I doubt he has forgotten a whole lot )

aeajr

My Feedback: (2)

Lift can originate from any uneven heating. Shoreline, trees, whatever. That lift can drift over the lake.

I have hit strong lift over a 40 acre snow covered field. Could not tell you exactly what was generating it, only that I could have stayed up all day.

SBS_Pilot

From what I've heard (but haven't tried myself yet) there can be quite good lift on snow-covered lakes if the snow isn't covering all the lake. The snow reflects about 90% of the sunrays, whereas bare ice acts like a black body and absorbes most of the heat from the sun. The difference in temperature can generate good lift.

Jennifer Curtis

Snow is a good insulator. Ice not so good.
Soil is also a better insulator than water.

If it is cold and the ground is covered with
snow, the warmth of the subsoil will not
reach the air as much as the warmth of
the water under the ice.

If the surrounding air is 20 degrees below
freezing, the air over the lake may be 7
degrees below freezing and thus 13
degrees warmer, causing thermal lift
to occur.

Jenny

SBS_Pilot

+1 on that!

I was out at the club field yesterday. Temperature just below freezing. Two decimeters (8 inch) of snow. Wind from 0 - 2m/s, but mostly close to zero. Despite the forecasts the sky was completely overcast. But then, as I set up my plane, there was a tiny, tiny, gap in the cloud and a small spot, I would guess about the size of a hockey rink, of the farmers field was sunlit. I launched and headed over there and the variometer began beeping happily. It wasn't strong, and it wasn't large, but I managed to keep between 54 and 67 meters for approx five minutes.

BMatthews

All it takes for a warm ground convection current to form is that the surface of the lake ice has to be warmer than the snow bound land around it. If the conditions were seriously below freezing for some time so there was a good layer of deeply frozen frost in the ground or snow pack on the ground and the lake is warmer then it could happen.

I suspect it would manifest itself similarly to the "pillow of lift" or ground lift that I've seen occur over farm fields where I was able to soar up to a set height and no farther. And flying out towards the limits of the field made me sink until I would return to the middle area of the field. On a couple of occasions I've had 20'ish minute flights where I was stuck at 80 to 100 feet in such conditions. Typically I've seen this during still conditions of early morning.

I've also caught thermals on dull grey days with light rain falling. Thermals that lifted my model up just fine.

The Sun's warmth certainly makes lift more common but again all it takes is a bit of a difference for some reason or other in temperature from one area to another to set a convection current flow going. It doesn't really matter that "warmer" area is still well below freezing.

longsoar

Winter lift is among the strongest I've seen in RC and full scale. Although conditions must be right. Thermals are on temp difference and clouds work great too. On cold day if you have huge snow filed next to the pine woods - there could be great temp difference and with lift.
I did not fly triangles on a full scale in a WInter, but stayed up for hours.
As for the lakes - I'd imagine if snow got blown by the wind and cleaned-up some ice surface while leaving snow covered portions of the lake - it could produce some temp difference. Although I have never seen thermals over the lakes myself, just great sinks in a Summer time.