The S-52 (aka HO5S-1) helicopter was a utility helicopter developed by Sikorsky Aircraft in the late 1940s.
The design process for the S-52 began near the end of 1945. The first prototype flew a mere two years later in 1947. The S-52 was created because of a need for a utility helicopter in the Navy, Marines and Coast Guard. All three of whom adopted this model into their respective fleets.
The S-52 is remarkable for being the very first US helicopter with all-metal rotor blades. These gave it significant performance advantages at the time. The S-52 set numerous speed and aerobatic records. It is widely believed that this is the first ever helicopter to be successfully looped.
The S-52 used a downward-sloping (or “anhedral”) v-tail stabilizer. It had sliding doors on both sides. One fore on the starboard side and one aft on the port side. It also had a novel vertically split front bubble that allowed the port half to swing open.
The prototype was a two-seater, but later production models had three or four seats.
The engine was situated aft and canted forward by 30 degrees in order to mate it with the drivetrain. In the two-seater prototype the engine was an air-cooled Franklin flat-six that put out a scant 178 horsepower. Later version would stick to a Franklin engine, but up the power to 245 horsepower.
The S-52 would later serve as a basis for the S-59 turbine powered helicopter.
The helicopter was operated by the US Navy as a utility craft and by the Marine Corps for observation missions in Korea. The US Army evaluated four units, but never ordered them in quantity.