Sikorsky downsized the basic S-38 design to create the S-39. The original prototype, powered by two tractor mounted Cirrus Hermes engines, was test flown in mid-1929 but crashed later that year after an engine failure. Sikorsky followed with the S-39-A, flown in early 1930, with a single R-985 Wasp Junior engine mounted directly to the wing. The S-39-A was the first US aircraft to be certified with the R-985.
Twelve S-39-As, marketed at an average price of US$17,500, were sold to civil owners by the end of 1930.
The S-39-B, introduced in 1931 with a larger fin and rudder, sold six examples to private owners, plus one to the US Army Air Corps as the YIC-28.
Two S-39-B, refitted with 400 hp R-1340 Wasp engines, were recertified as S-39-C.
The final example, an S-39-CS Special named “Spirit of Africa”, was built in 1932 to an order from explorers and photographers Martin and Osa Johnson. In a giraffe paint scheme, the Spirit of Africa covered more than 60,000 miles across Africa and East Indies.
Several civilian S-39s were operated by the Civil Air Patrol during World War II on search and rescue missions.
A total of 21 were built.
Engine: Pratt & Whitney R-985 Wasp Junior, 300 hp