Sikorsky S-72 Sikorsky S-72 The Sikorsky S-72 was an experimental hybrid helicopter/fixed-wing aircraft developed by helicopter manufacturer Sikorsky Aircraft. The Rotor Systems Research Aircraft (RSRA) was developed by Sikorsky for NASA and the Army. The RSRA was developed to allow the inflight measurement of helicopter rotor characteristics. The airframe was developed using an existing Sikorsky S-61 main rotor, an S-61 roller gearbox, and a highly modified Sikorsky S-67 airframe. The RSRA could be fitted with TF34 turbofans and wings to allow compound helicopter configurations to be experimentally investigated at speeds up to . In addition, it could fly as a fixed-wing aircraft
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