What is Controllable slope soaring?

Controllable-slope soaring is a type of slope soaring where a slope is made to follow a walkalong glider , both sustaining and controlling the glider's trajectory by modifying the wind in the vicinity of the airplane.

A controllable slope is any object which can be used to affect the air under the airplane: a piece of cardboard, the pilot's hands or even head. The controllable slope is usually manipulated by a person following the glider in flight.

Controllable-slope soaring allows a glider to achieve sustained flight without the need for an onboard aircraft engine or onboard flight control system.