Helicopters can perform some incredible aerobatic feats, but they're also noisy, shaky, and expensive to run. NASA researchers are developing helicopter blades featuring a shape-shifting smart material that could lead to a smoother, quieter, more fuel-efficient ride.

The blades use piezoelectric actuators--mechanical devices incorporating a material that changes shape when subjected to an electrical field. This shape change deforms the rotor blade as it spins, improving a helicopter's aerodynamic performance.

Last year, NASA, in collaboration with aerospace company Boeing, the Defense Advanced Research Projects Agency (DARPA), and the U.S. Army, tested the first full-scale rotor blade to use the technology in a wind tunnel that simulates flight conditions. The system significantly reduced vibrations, saved energy, and allowed rotor movement to be more precisely controlled. In the future, the system could also reduce noise. It is now ready to be flight-tested, although a date for the first flight has not yet been set.

"Right now, we are trying to understand and appreciate everything that we have accomplished in the full-scale wind tunnel," says William Warmbrodt, the project leader from the Flight Vehicle Research and Technology Division at NASA's Ames Research Center, in California.

As a helicopter blade passes through the air, it leaves behind a wake, and as the blade behind it passes through that wake, it experiences a periodic vibration. "Having blade actuation allows you to put a periodic motion into the blade flaps with the right amplitude, phase, and frequency to cancel out that vibration," says Steven Hall, a professor of aeronautics and astronautics at MIT and a consultant on the NASA project.

"People have been talking about using smart materials in aircraft for a long time, but what [has] really been lacking is the right kind of actuator to make it practical," says Hall. Previous efforts, involving hydraulic actuators, proved too heavy and slow to be practical. "It is hard to do hydraulics in a rotating frame: you need enough force to deflect the flap because the air loads are very high, and you have to do it at the frequency required," Hall says.