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-3 Sikorsky S-3 The Sikorsky S-3 was an early Russian single seat biplane design by Igor Sikorsky. Work on the machine started in July 1910 and was completed in late November. The S-3 was a larger improved version of the S-2 with a more powerful Anzani three-cylinder engine. The main wings were manufactured in a more uniform manner with the ribs held to a closer tolerance and the fabric covering was of better quality. Other refinements included larger ailerons and faster responding flight control surfaces. The S-3 exhibited performance superior to the S-2 and Sikorsky made a dozen successful flights starting