Airfoil Design Off the shelf or made to order?


Deciding what you want from a rotor system is the critical fi rst step in designing main- and tail-rotor blades. Overall performance values for the aircraft fl ow into questions such as, how many blades and how long can or should they be? Even at an early stage of design, many compromises must be accommodated. With those decisions come the next tranche of


questions. How much lift under what conditions? And how can we achieve that?


One possible solution is to select an airfoil design from among


those developed over the history of rotary-wing fl ight, including those from NASA. Incorporating one of these designs requires skill, but because its performance is known, it can be a solid solution. What’s becoming more common is creating custom


airfoils that provide optimal performance for specifi c aircraft. Computer codes exist to facilitate the task, but if designing an airfoil were as simple as pressing a button, everyone would be doing it. That’s where someone such as Dan Somers comes


in. He worked for 15 years at NASA Langley Research Center and in 1980 launched Airfoils, Incorporated, advising aircraft manufacturers and designing airfoils for them. Somers’s enthusiasm for his work was clear as


he told me more (and more!) about how these pre- cisely formed shapes keep hundreds or thousands of pounds airborne. Yet, despite his decades of experience—or because


of it—he says design is part science and part art. The truth comes out only when air fl ows over the wing.


Above: A pressure distribution graph that aligns an airfoil with the measurements obtained in a wind tunnel.


Below: Dan Somers explains elements of airfoil performance and design while seated next to one of his airfoils in the Penn State wind tunnel.


Left: An airfoil test article mounted in the wind tunnel at Penn State University in University Park, Pennsylvania.


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SEPTEMBER 2022 ROTOR 57


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