NASA Spinoff

Tail Rotor Airfoils Stabilize Helicopters, Reduce Noise

Given the eye-catching nature of space shuttle launches, deep-space imagery, and Mars exploration, it can be easy to forget NASA’s aeronautics efforts, which have a daily impact on life within the bounds of Earth’s atmosphere. Virtually every flying vehicle in operation today has benefited in some way from NASA advancements, and the helicopter is no exception. In fact, NASA’s involvement in rotorcraft research can be traced back to its predecessor, the National Advisory Committee for Aeronautics (NACA). NACA was founded in 1915, less than a decade after the first successful piloted rotorcraft flight in 1907, and made a number of contributions to rotorcraft development—including a series of airfoils that are still employed in some modern vehicles.

altNASA was formed in 1958, and within a little more than a decade the Agency had begun a collaborative rotorcraft research program with the U.S. Army, establishing laboratories at Ames Research Center, Glenn Research Center (then known as Lewis Research Center), and Langley Research Center. These labs focused on enhancing the performance and safety of helicopters for both military and civilian use. This research improved helicopter airfoil designs, flight control systems, aerodynamics, rotor blade and aircraft body composition, and cockpit configuration.

Partnership

Among the many outcomes of the NASA-Army research partnership are advanced airfoils designed and wind-tunnel tested at Langley. Two of these airfoil designs—the RC(4)-10 and the RC(3)-10—were licensed and commercialized by Carson Helicopters (Spinoff 2007) as a superior replacement main rotor for the Sikorsky S-61 helicopter, allowing the helicopter to fly faster and carry heavier loads while offering a service life twice that of the original rotor.

Carson’s success with its NASA-derived airfoil caught the eye of Dean Rosenlof, general manager and aerospace engineer for Van Horn Aviation LLC (VHA), based in Tempe, Arizona. The company—founded by former Ames engineer Jim Van Horn, who worked on NASA rotorcraft research like the Rotor Systems Research Aircraft in the early 1980s—was looking for airfoil designs to expand its tail rotor blade product offerings, which include an aftermarket carbon composite tail rotor for the UH-1H (“Huey”) military helicopter. Rosenlof brought the Langley RC series of airfoils—the low-speed RC(4)-10 and the high-speed RC(5)-10—to Van Horn’s attention, and they determined these were precisely the designs the company was looking for.

The complex aerodynamics of a helicopter present a challenge to airfoil designers, who must consider a range of aerodynamic forces and how they influence the rotorcraft’s flight capabilities. Among the chief concerns is pitching moment, the twisting force exerted by the airfoil that pushes the noses of the rotor blades up or down. Because this force can interfere with pilot control and rotor blade stability, designers aim to create airfoils with minimal to zero pitching moment.

“The RC airfoils were exactly what we needed,” says Van Horn. “They are very attractive in that they are thin, light, laminar-flow airfoils with essentially zero pitching moment.”