Modal Synthesis of Flexible Mechanisms for Airfoil Shape Control

The use of `compliant' or flexible mechanisms constitutes a very promising option for the successful realization of shape-adaptable airfoil structures. Achieving large deformations by exploiting structural flexibility instead of employing conventional mechanisms with moveable parts offers several advantages: absence of backlash and wear, no need for lubrication, reduced noise, smooth geometry changes, a lighter design, and reduced manufacturing costs. As a counterpart, compliant systems are more complex to analyze and design due to their inherent coupled behavior. Established design procedures, developed in the framework of kinematics design, are of limited use for application to shape-adaptable structures due to differences in requirement priorities. This study presents a novel synthesis procedure for compliant shape-adaptable airfoils. Initially devised for the so-called belt-rib airfoils, the procedure can be extended to the general case of compliant airfoils with an external flexible skin (optionally reinforced by frames) and a system of internal stiffeners. After the description of the core synthesis algorithm, which is based on a modal approach, its integration in a global design procedure is discussed. Application to the case of a belt-rib airfoil is then considered. The compliant structure resulting from the procedure combines the characteristic qualities of a compliant system (smooth deformation pattern, absence of moveable parts, low weight) with the low load-dependence of kinematics which is typical of conventional mechanisms.