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-11 Sikorsky S-11 The Sikorsky S-11 " Polukroogly " (Half Round) was a Russian single engine prototype reconnaissance aircraft completed in July 1913 by the Russian Baltic Railroad Car Works while Igor Sikorsky was the chief engineer of the aircraft manufacturing division. The S-11 was a two seat mid-wing monoplane with wire-braced wings powered by a Gnome Monosoupape air-cooled rotary engine rated at . It was smaller and lighter than the S-7 on which it was based, and had a conventional wooden fuselage. The cockpit featured side-by-side seating with controls for the pilot only on the left. Originally built with ailerons