Adaptive Systems, Rotary Wing Applications

An intelligent or smart structure is generally considered an integrated system of structure, sensors, actuators, and a control module. Currently, there is a great deal of interest in applying smart structure technology to various physical systems. Active vibration, noise, aeroelastic stability, damping, shape control, health monitoring, process monitoring, and damage and delamination detection are a few examples. A significant amount of the early development was devoted to application to space-related systems. Recently, studies have also been conducted to investigate using this concept to improve fixed wing performance. During the last decade, significant research efforts have also been directed toward applying these concepts to rotary wing aircraft which is the topic of this article. The potential for improving performance, handling qualities in stall, and increasing fatigue life is discussed. Actuators that use smart materials require relatively slow-acting shape and shape-distribution changes in this respect. A similar review is made of applications for improving aeroelastic divergence, flutter instabilities, and tail buffeting on fixed-wing aircraft and reducing vibrations, improving external acoustics, and providing flight controls for rotary wing aircraft—all of these require a high-frequency response. Vibration and noise are two long-standing problems that have limited the expansion of military and commercial applications of rotorcraft. Helicopters are particularly susceptible to high vibratory loads compared to fixed wing aircraft due to the high unsteady load and complex aerodynamic environment in which the rotor must operate and the existence of the complex structural, aerodynamic, and dynamic coupling. A major improvement in helicopter performance can be achieved by implementing active rotor control technology. Smart material actuator technology for operation “on the blade” is now becoming available and promises to overcome the size, weight, and complexity of hydraulic and electric on-rotor actuation which should alleviate the problem. Blade actuation by smart materials offers the chance for an electrical system integrated into the blade itself. Unfortunately, the development of high force/high deflection actuators, the most critical issue in all of these applications, has not been addressed adequately and still remains a topic of future research. In all applications involving smart materials, accurate modeling of the material response and the integrated smart structural response is important because control authority can be significantly mispredicted if inaccurate theories are used. In this article, the current state of the art in improving rotor vibratory response and aeromechanical characteristics is reviewed. Advantages and disadvantages of these techniques are discussed. Numerical results from feasibility studies are summarized, and accomplishments already achieved and the goals to be pursued in the near future are discussed. Keywords: Active/passive controls; Damping; Structural response; Trailing edge flaps; Servoflap; Active twist; Health monitoring; Activators; Aerodynamic control