September 3, 2007 6:00 AM PDT
A Sikorsky YR-4B/HNS-1 sits in a wind tunnel as a technician sets up camera equipment to take stop-action photos of the rotors. The R-4 was the first helicopter to be built in any significant number--several hundred were constructed during World War II.
The essence of this design, like that of PV-2 from Piasecki--a large main rotor and a small vertical tail rotor (just one of each)--has been the guiding force for most modern helicopters. Much of the credit for that design, and for turning helicopters into a practical reality, goes to Igor Sikorsky, a Russian immigrant to the U.S.
Photo by Langley Research Center/NASA
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