Sikorsky R-4 end of the boom near the tail rotor while others had it positioned at the midpoint of the boom. Additionally, some had short "stub" exhaust pipes from the engine while others had a much longer one which extended vertically and then aft above the main landing gear struts. Sikorsky R-4 The Sikorsky R-4 is a two-seat helicopter designed by Igor Sikorsky with a single, three-bladed main rotor and powered by a radial engine. The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter used by the United States Army Air Forces, the United States Navy, the United
Sikorsky S-6 Sikorsky S-6 The Sikorsky S-6 was a Russian single engine experimental aircraft similar to the S-5, built in 1911 by Igor Sikorsky. Construction of the first S-6 was started in August 1911. The three bay biplane was powered by an Argus 4-cylinder water-cooled engine producing . Initial flight tests in late November were disappointing, revealing a long take-off run and poor climb performance. Sikorsky disassembled the aircraft and took it home where substantial modifications were undertaken, including lengthening the wingspan and reducing aerodynamic drag by enclosing the fuselage with wood veneer. Ailerons on the lower wing were removed and strut