Variable Camber Compliant Wing - Wind Tunnel Testing

Abstract

This paper describes initial wind tunnel testing of a Variable Camber Compliant Wing developed by the U.S. Air Force Research Laboratory. The current version of the Variable Camber Compliant wing has a two foot chord length and was designed to demonstrate the ability to actively change wing section camber at low flight speed. The intent of the design was to adjust the wing camber by six percent chord while holding maximum camber location, and maximum thickness constant (emulating a change from a NACA 2410 to NACA 8410 profile) using a single continuous outer skin. The design is unique; the entire skin is seamless, continuous, and made of a single piece of non-stretchable composite skin. Smooth elastic deformation of the wing is attained by the underlying compliant mechanism. 2D camber change is achieved by a single actuation direction to control both leading and trailing edge deflection. 3D shape change is also capable through variation of camber along the span wise direction using a distributed actuation system along the span. Relatively low speed design and testing conditions were chosen to support air vehicle noise modeling efforts, for which low speed flight results in lower noise. Wing shape change without aerodynamic load was measured using an optical measurement system, indicating nearly six percent camber change measured at the middle rib. The wing was tested in the U.S. Air Force Vertical Wind Tunnel Facility in order to demonstrate operation of the wing under aerodynamic load. Increasing the profile camber resulted in an increase in section lift coefficient and vice versa. The variable camber wing is an inherently flexible structure that deforms under aerodynamic load. Digital image correlation of the model with wind off and wind on was used to understand the flexibility of the structure and its effect on aerodynamic forces. Aerodynamic modeling of the wings actual windoff shape and wind on shape are used to provide insight into the wind tunnel results and discuss the complexity of aerodynamic measurements on a flexible structure.