Wind blown: Full-scale helicopter blades fitted with the actuators were tested in the world’s largest wind tunnel, located at NASA’s Ames Research Center, in California. The wind tunnel simulates flight conditions equivalent to traveling at 155 knots.
The new actuator sits inside the steel frame of a rotor blade near both the tip of the blade, where aerodynamic forces are greatest, and a flap on the rear portion that moves up and down as it turns. Power amplifiers transmit an electric field to the piezoelectric material inside the actuators, and that material responds by changing length, expanding a very small amount (roughly 10 to 20 thousandths of an inch). This moves a rod perpendicular to the blade flap, which pushes the flap. “You are taking a small motion, amplifying it enough to move the flap a few degrees,” says Hall.
But movement of the flap creates a dramatic aerodynamic change to the blade. The flap can help generate lift or air speed, and, whereas an airplane can only use flaps for takeoff and landing, such flaps can be used anytime during a helicopter flight.
What is really important is that the piezoelectric materials are stiff and can change shape rapidly. “That is what makes it an acceptable actuator,” says Hall. The smart materials also make the actuator system lightweight and compact. Furthermore, the NASA researchers have designed the actuator system to fit into the blade structure of existing helicopters without significantly modifying the rotor blades’ design.
“Smart materials hold a tremendous promise for revolutionizing how we design, build, and operate our helicopter aircraft,” says Warmbrodt.
The project could have several spin-offs: the U.S. Army is developing a second rotor using electric motors, and DARPA just announced a Mission Adaptive Rotor (MAR) program, which is going to look at a number of technologies, including smart materials, to improve the rotor blades used in military helicopters.
Warmbrodt adds, “The DARPA MAR program is the next step in looking at how we are going to radically change the design of helicopter blades to achieve a new level of performance.”