Sikorsky R-4 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 States Coast Guard and the United Kingdom's Royal Air Force and Royal Navy. In U.S. Navy and U.S. Coast Guard service, the helicopter was known as the Sikorsky HNS-1. In British service, it was known as the Hoverfly. The VS-316 was developed from the famous experimental VS-300 helicopter,
Sikorsky S-20 Sikorsky S-20 The Sikorsky S-20 (named after its designer) or RBVZ S-XX (named after its manufacturer) was a Russian single-bay unequal span two-seat biplane designed by Igor Sikorsky in 1916. Displaying some Nieuport influence, it saw very little service during World War I. Five S-XX aircraft were built in September 1916, with the first two powered by the 100 hp Gnome rotary engine which had powered its predecessor, the RBVZ S-XVI. However, the other three were powered with the 120 hp Le Rhone engine, with which they were allegedly faster than the French Nieuport 17. The S-XX saw little service