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-28 was approved. The French ordered five examples and preparations were made to start construction, but the order was cancelled when World War I ended and no S-28s were completed. Sikorsky S-28 The Sikorsky S-28 was a proposed four engine biplane bomber aircraft designed by Igor Sikorsky to be built in France during World War I. Sikorsky moved to France in March 1918 and soon met with officers of the "Armée de l'Air" who asked him to design an aircraft capable of carrying a new 1,000 kg (2,200 lb) bomb. Although the aircraft was initially designed to be powered by two