Sikorsky S-37

The Sikorsky S‑37, also known as the “Dragonfly,” was an experimental twin‑engine helicopter developed by the Sikorsky Aircraft Corporation in the early 1950s. Designed under the direction of Igor Sikorsky, the S‑37 was intended to demonstrate the feasibility of a coaxial rotor system that eliminated the need for a tail rotor, thereby improving lift efficiency and simplifying control. Its first prototype flew on 6 May 1954, marking the first successful flight of a tandem‑rotor helicopter in the United States. Powered by two 275‑horsepower Lycoming engines, the S‑37 featured a compact fuselage, a fully articulated rotor hub, and a unique inter‑meshing rotor configuration that provided excellent stability in hover and forward flight. Although the program was ultimately curtailed in favor of the larger S‑61 platform, the S‑37 contributed valuable data on rotor dynamics, vibration suppression, and power‑to‑weight ratios. The aircraft’s legacy lives on in modern Sikorsky designs, influencing the development of heavy‑lift helicopters such as the CH‑53K and the experimental X2 technology demonstrator. With a 28‑foot rotor and a max takeoff weight of 7,600 lb, the S‑37 demonstrated that compact twin‑engine helicopters could handle practical utility roles.

Sikorsky Aircraft Corporation

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