Sikorsky S-47 XR-4C Hoverfly 41-18874 in Udvar-Hazy Center
C/n 2 marked USAAF 41-18874. Not the first military helicopter, but the first mass-production helicopter and the first successful production rotorcraft of single-rotor configuration. The XR-4 represents the culmination of Igor I. Sikorsky's attempts to create a practical helicopter. His work began in 1909 but did not reach fruition until 30 years later. In Smithsonian Steven F. Udvar-Hazy Center in Chantilly, VA. USA 29. April 2013.