According to the Museum’s website (which also provides technical specifications):

The R-4 was the world’s first production helicopter and is the offspring of Igor Sikorsky’s famed VS-300 which flew in 1940. After an initial prototype was built and flown in January, 1942, 30 were built for test use by the U.S. Army Air Force, Navy, Coast Guard and the British Royal Navy. One went to Burma for hot weather operations and another to Alaska for cold weather trials. Results were highly successful and the USAAF ordered another 100. The first to enter combat served with Philip Cochran’s 1st Air Commando Group.

The Hoverfly was built at the Sikorsky factory in Bridgeport, CT and this R-4 served as a test aircraft at Sikorsky.

Taken with a Sony RX-100 M3.