The pilot stated he was returning to his private heliport after refueling at a local airport. As he approached the heliport, he flew over a local lake to determine the wind direction. He stated he made a normal approach. According to the pilot, as the helicopter approached the ground, a 'right quartering tailwind' was encountered. The helicopter began to 'sink rapidly,' tail rotor authority was lost, and the pilot lost directional control of the helicopter. In order to prevent a spin, the pilot turned off the ignition and allowed the helicopter to drop to the ground.