Doman LZ-1, Sikorsky R-6 Doman Conversion, Sikorsky S-51 (H-5A)
New England Air Museum, Windsor Locks, Connecticut.
The museum is close to the home of the Sikorsky company, so they have a lot of helicopters.
Igor Sikorsky started out building airplanes for the Russian Air Force, under the Tsar. He moved to the US and started building amphibious landers, because there were not enough airports in the world, but there were always rivers and streams. Finally, he pioneered helicopter design, for which he is best known. There is a picture at the museum of him with 3 of the Apollo astronauts who paid him a visit because they wanted to meet the legend.