Built and tested in February to May 1910, Sikorsky's second helicopter was more sophisticated than the first, with a welded steel-tube airframe and three-blade rotors with metal spars. The emphasis was still entirely on achieving lift, with only collective pitch control of the rotors and no provision for horizontal flight controls. Again the helicopter's weight proved too much for the 25hp Anzani. Sikorsky decided to postpone further rotating-wing research, as his first fixed-wing design, the BIS-1, was ready for testing.
John W.R. Taylor "Images of America - Sikorsky", 1998
The S-2 was a helicopter with two three-bladed counter-rotating propellers. Underpowered aircraft was able to take off... but without a pilot.
Technical data for S-2
Engine: 1 x Anzani rated at 18.4kW, main rotor diameter: 6.55m, take-off weight: 270kg, empty weight: 182kg