Experimental Aeroelastic Benchmark of a Very Flexible Wing

Abstract

The paper presents the design, analyses, and testing of the Pazy wing, a very flexible wing model that was designed to study aeroelastic phenomena associated with geometrically nonlinear deflections and to provide data for validation of nonlinear aeroelastic simulation models. The Pazy wing is made of a main thin aluminum spar and a Nylon 12 printed ribs chassis providing the NACA0018 aerodynamic airfoil shape. The wing was covered entirely with a polyester film that serves as the skin. Static loading tests were used for model adaptation and to assure that the wing can deform to over 50% of its span without failing. Ground vibration tests were also used for model adaptation. Because there are uncertainties in the characteristics of the polyester skin under loads, both the static and ground vibration tests were used to asses the contribution of the skin to the wing’s stiffness and determine the stiffness bound with and without the skin. Wind-tunnel tests were conducted at conditions that lead to static and unsteady structural responses. The wing deformations were tracked by a motion recovery system, and the strains over the wingspan were recorded with a Bragg-grating fiber-optics system. In the static wind-tunnel tests, the aerodynamic loads were recorded by a force balance. The wind-tunnel tests included angle-of-attack sweeps in constant airspeed and velocity sweeps in fixed angle of attack. The largest wing-tip static deformation recorded in test was of 50% span. In the velocity-sweep tests, the wing showed strong oscillations at a velocity at which the wing-tip deformation was approximately 25% of the span and became stable again at higher speeds. The wing models and test data are publicly available through the 3rd Aeroelastic Prediction Workshop (https://nescacademy.nasa.gov/workshops/AePW3/public).