Sooner or later we all encounter the wake from other aircraft. Usually this comes in the form of a 'bump', but has been known to cause deflations and 'dumpings' resulting in injury. The curious thing about wake turbulence is that it doesn't always seem to be a problem, and unfortunately we only know find out about it when it hits us ourselves. Our small, light, aircraft can produce a remarkably large and long lived disturbance in the atmosphere.

A vortex of rotating air is shed from each wing tip of an aircraft as it flies. These vortices represent the energy lost as induced drag which is a necessary by-product of lift. In the case of hang-gliders and paragliders the vortices seem to persist for up to about fifteen seconds after the aircraft has passed and are blown in the direction that the air is moving; i.e. towards and up the slope in ridge lift, and upwards in a thermal.

On our sometimes crowded sites it is impossible to avoid wake turbulence altogether. What we have to do is to ensure that we don't encounter it or cause others to encounter ours in situations that make it dangerous; i.e. near the ground.

Obviously a pilot who is scratching close and can feel turbulence must move away from the hill. More importantly, a pilot seeing someone scratching close to the hill must find the courtesy to leave an adequate amount of room as they pass. It's surprising how a pilot's idea of 'adequate' clearance multiplies after being 'dumped' by wake turbulence!