We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not a subscriber? Subscribe now for unlimited access to online articles.

Intelligent Machines

Energy-Saving Helicopter Blades

NASA researchers are using smart materials to improve helicopter performance.

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.

Smart blades: NASA tested its new actuators in a wind tunnel at Ames Research Center using full-scale helicopter blades (top). The actuator (bottom) contains piezoelectric materials, which change shape when subjected to an electrical field. The wires in the upper right of the image are piezoelectric stacks. When voltage is applied, they extend a small amount, creating a mechanical motion that moves a flap up and down. (The flap is the long, thin, yellow portion of the blade in the top image.)

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.

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.”

Keep up with the latest in intelligent machines at EmTech Digital.

The Countdown has begun.
March 25-26, 2019
San Francisco, CA

Register now
More from Intelligent Machines

Artificial intelligence and robots are transforming how we work and live.

Want more award-winning journalism? Subscribe to Print + All Access Digital.
  • Print + All Access Digital {! insider.prices.print_digital !}*

    {! insider.display.menuOptionsLabel !}

    The best of MIT Technology Review in print and online, plus unlimited access to our online archive, an ad-free web experience, discounts to MIT Technology Review events, and The Download delivered to your email in-box each weekday.

    See details+

    12-month subscription

    Unlimited access to all our daily online news and feature stories

    6 bi-monthly issues of print + digital magazine

    10% discount to MIT Technology Review events

    Access to entire PDF magazine archive dating back to 1899

    Ad-free website experience

    The Download: newsletter delivery each weekday to your inbox

    The MIT Technology Review App

You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.