A standard radius for S-turns cannot be specified, since the radius depends on the airspeed of the helicopter, the velocity of the wind, and the initial bank chosen for entry. 
 

TURNS AROUND A POINT
This training maneuver requires you to fly constant radius turns around a preselected point on the ground using a bank of approximately 30°, while maintaining a constant altitude. [Figure 9-17] Your objective, as in other ground reference maneuvers, is to develop the ability to subconsciously control the helicopter while dividing attention between the flight path and ground references, while still watching for other air traffic in the vicinity.
 

The factors and principles of drift correction that are involved in S-turns are also applicable in this maneuver. As in other ground track maneuvers, a constant radius around a point will, if any wind exists, require a constantly changing angle of bank and angles of wind correction. The closer the helicopter is to a direct downwind heading where the groundspeed is greatest, the steeper the bank, and the faster the rate of turn required to establish the proper wind correction angle. The more nearly it is to a direct upwind heading where the groundspeed is least, the shallower the bank, and the slower the rate of turn required to establish the proper wind correction angle. It follows, then, that throughout the maneuver, the bank and rate of turn must be gradually varied in proportion to the groundspeed.