Apr 15, 2005, 1:20 PM
Post #1 of 5
Fog layer turbulance?
The other morning i was out with a friend doing a jump off a nice span. There was a fog/cloud layer below opening alt. (not obscuring landing) After opening I was flying a slow approach about 1/2 brakes.When I hit the fog level my canopy slightly stalled and bucked a little. i let up just a little on the brakes and canopy resumed normal flight and i landed fine. Just wondering If anybody else has had this happen to them? Or maybe i stalled the canopy?
Fog usually forms layers where there is a difference in air temperature (which causes the condensation which is the fog). The boundary zone between temperature layers is also a generator of turbulence in many cases.
So, I'd guess you hit a turbulent boundary between air of different temperatures, different humidities, and possible also different flows.
Here's my 2 cents: the density of fog is much less than dry clear air. I imagine you lost a lot of lift, stalled, and then surged. I encounter this where I jump when I jump at night. Everything seems fine until I hit the wet dew region of the last fifty feet, and the canopy speeds up like a rocket.
I've seen this before. When the air is stable it will layer like a cake. Layers don't like to mix, but you will find some shear turbulence between them. As your descending from one layer to the next your canopy could experience turbulence and a loss of airspeed. Say your in one layer with a 10 mph headwind and drop into the next layer with 0 wind ( this is called gradient, which just means change ). Your canopy will drop , due to the loss of airspeed and try to regain it's airspeed. It could stall if your angle of attack is too high (ie. too much brake. Brake travel controls A of A ) which is why it's important to be flying at trim when descending through. The additional speed and brake travel will help with recovery. You'll usually find stable air early morning, depending on the pressure and weather systems. Once the sun heats things up the layers will mix out . Then again in the evening things will cool down and layer .The whole process starts again with the sun.