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 because it was viewed as inferior to newer enemy aircraft, and no series production was undertaken. As such, only five aircraft were ever produced.