Status of application of smart structures technology to rotorcraft systems

This paper reviews the status of smart structures technology development fo r application to rotorcraft systems. Though a large component of research i s focused on the minimization of helicopter vibration, the methodology is e qually applicable to such other problems as aeromechanical stability augmen tation, handling qualities enhancement, stall alleviation, reduction of int erior/exterior acoustic signatures, minimization of blade dynamic stresses and rotor head health monitoring. More than any other system, the structura l, mechanical and aerodynamic complexity and the interdisciplinary nature o f rotorcraft offer many opportunities for the application of smart structur es technologies with the potential for substantial payoffs in system effect iveness. Primarily, two types of smart rotor concepts are under development : trailing-edge flaps actuated with smart actuators, and controllable twist blades with embedded piezoceramic actuators. For flap actuation, actuators range from piezo-bimorphs, piezo/electrostrictive stacks and piezo/magneto strictive-induced composite-coupled actuation. Most smart actuators are mod erate force and extremely small displacement devices and hence some form of mechanical amplification of induced displacement is needed to achieve desi red flap deflections. Because of compactness and weight considerations, the stroke amplification of these devices has been a key barrier for applicati on to rotor blades. Most of the current smart rotor models under developmen t have adopted Froude scaling, but future developments are tending towards Mach-scale and full-scale designs. The state-of-art on modeling of actuator s is improving rapidly. Shape memory alloys (SMA) show potential in providi ng large induced strains (up to 6%), but are limited to low frequency (less than 1 Hz) applications such as tab adjustment for rotor tracking. Also, i t is quite difficult to achieve fine-tune actuation control with SMAs. Data base of smart actuator characteristics under different loads, frequency and temperature are non-existent. For in-flight tracking of rotor SMA-actuated tabs, it is important to incorporate adaptive control strategy and a locki ng mechanism. Comprehensive rotor analyses covering smart materials actuato rs are in development at this time. This paper will identify key barriers f or applications of smart structure technology to rotorcraft systems and poi nt out the need for future research in this area. Research in the applicati on of smart structures technology to rotorcraft systems is in its early pha se, and activities need to be expanded before this promising technology can be exploited in a competitive manner.