Boeing to demonstrate piezoelectric cells in active flight control technology


A Boeing team is poised to demonstrate a rotor-based active vibration control system for helicopters, marking a new leap in the emerging field of active flight control technologies.


"There have been a number of model tests and some flight tests of active flight control materials but this is the first one to go into a full-scale flight test," says Friederich Straub, Boeing's principal investigator leading the project.


Flight tests could start in 2005 but the team is waiting to secure funding from an industry or government sponsor.


Boeing's system - called the Smart Material Actuated Rotor Technology (SMART) - aims to reduce helicopter vibration levels by 80% and relies on technology used commercially for several decades in alarm clocks and microwave ovens. Piezoelectric devices are small actuators that change shape when charged by electrical currents. By linking scores of the devices along the trailing-edges of rotor blades, the system can compensate for the disturbed aerodynamic forces over the blade, says Straub.


"The [piezoelectric] actuator will produce a force and stroke output and is coupled with a trailing-edge flap on the rotorblade. The flap moves up and down which modulates the aerodynamic forces and cancels the vibrations," says Straub.


In five years, adds Straub, piezoelectric technology could become a more efficient substitute for the active vibration control systems or networks of mechanical actuators now installed in some helicopter airframes to help counter vibration.


Unlike control systems installed within the airframe, the rotor-based piezoelectric materials are "really controlling the vibratory systems at the source," says Straub.


The system should reduce noise by 10db on take-off and landing - a key improvement for civilian operators, but not enough to reach the US Army's goal of reducing the in-flight acoustic signature of the Boeing AH-64 Apache and CH-47.


So far the Boeing team, which includes academic, military and government personnel, has demonstrated the system only in whirl-tower testing using an MD 900 Explorer's five-bladed rotor. Boeing and the US Defence Advanced Research Projects Agency have funded most of the initial, $10 million effort.



Source: Flight International