US NAVY PHOTO
Pencils to PCs, Spruce to Carbon Fiber Long before you start hammering together a rotor blade, much design work is required across manifold disciplines. At the dawn of rotary-wing fl ight, it made sense that existing fi xed-wing airfoils,
developed with pencils and slide rules, guided the design of helicopter rotor blades. Likewise, wood-and-fabric construction was the logical choice. Those airfoil designs and construction techniques were found wanting, however.
For instance, air pressure changes in hollow, fabric-covered trailing edges would change performance during fl ight, and moisture from rain, or even just humidity, could alter the weight of blades disproportionately on a single helicopter. Moreover, the inherent diffi culty of making every blade for a specifi c aircraft model the same size, shape, and weight was so severe that blades had to be installed and, when needed, replaced in complete sets. Soon, legacy designs yielded to the results of intensive (and ongoing) research
into not just the shape of airfoils—the 2D cross section—but also a full 3D opti- mization of the blade from root to tip, calculated with computers and verifi ed in wind tunnels. Construction materials and manufacturing processes progressed similarly. (See sidebar, p. 57, for more on airfoils.)
Above: What is possibly the only extant set of Sikorsky S-51 main-rotor blades not mounted on a helicopter currently rests on a hangar wall at Vertical Aviation Technologies in Sanford, Florida. The blades were manufactured in 1952.
Right: A Sikorsky HO3S-1, the US Navy designation for the Sikorsky S-51, hovers above the battleship USS New Jersey while off the coast of Korea in 1953.
Previous spread: Van Horn Aviation design engineer Chris Gatley brought with him 13 years of experience when he joined the company in 2019, including work on main-rotor blades for the AH-64D/E Apache, foreground.
SEPTEMBER 2022 ROTOR 49
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