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 (crater) named after Igor Sikorsky, a Russian-American aviation pioneer. By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Sikorsky. Sikorsky (crater) Sikorsky is a crater on the far side of the Moon. It is situated behind the southeastern limb of the Moon, just out of sight from the Earth. It lies to the northwest of the huge walled plain Schrödinger. To the northwest is the smaller crater Moulton. In 1967 the Lunar Orbiter 4 photographed this region in high resolution, discovering a 310-km-long gouge cutting through