Wake Turbulence

Wind Shadow / Wake Turbulence

Flying sites in Botany Bay can be exciting and rewarding; however, caution must be maintained for the presence of Turbulence.

There are three types of turbulence, all down wind menaces from the source; we are all familiar with wake turbulence from other gliders, particularly when the upwind glider is “chandelling low” across the lip of the hill, landing down wind in this turbulence has to be treated with caution, the further back the better. When “chandelling low, be conscious of others wishing to land.

Another form of turbulence can arise when the wind direction puts Kurnell upwind, in soft wind this can create some interesting phenomena which is “convergence like”, however, as the wind speed increases, so does the chance of been suddenly “dumped”, a rule of thumb for turbulence affected zones is, multiply the upwind objects height x 10 to obtain the effected distance down wind.

Shipping can be another source of turbulence, particularly those large container ships, contrary to belief when a ship is passing by, the wind shadow is not directly upwind but rather somewhat delayed after the ship has passed. This can be evident if the ship has a plume of smoke which obviously shows the “apparent wind” with regard to that ship and therefore gives a visual aid to were the wake turbulence is, however, be wary of wind direction bending as it comes across the bay, we often see “curving” wind lines on the bay. A ship heading East at 10 knots in a South wind of 10 knots will have a wind shadow to the NW of it, conversely, a ship heading West at 10 knots in a South wind of 10 knots will have a wind shadow to the NE of it.

Recently I had the pleasure of flying Portsea in Victoria where there is a famous land mark on the beach called London Bridge. Pics can be viewed on google earth. This rock formation has killed two hang glider pilots in the past due to the wake turbulence. I was surprised at the height of the turbulence when passing it at some 200 ft above the ridge.

Of course, the wind shadow is like a tapered zone 10 x height down wind and immediately behind the object, the turbulence can higher than the object itself

Now given a ridge directly down wind forces that shadow up and over the ridge maintaining its “depth” of effect with some possible compounding, (air being drawn in at the sides immediately behind the object and adding to the shadow)

Fly safe and keep safe.