Structural Analysis and Testing of an Ultralight Unmanned-Aerial-Vehicle Carbon-Composite Wing

This paper presents the results of an investigation examining the strength and stiffness characteristics of a carbon composite wing of an ultralight unmanned aerial vehicle. The wing consists of foam-core sandwich skins and multiple spars with varying laminate ply patterns and wall thickness dimensions. A three-tier whiffletree system is designed and used to load the wing in a manner consistent with a pull-up-maneuver condition. Multiple strain and deflection gauges are used to measure the static response of the wing at several spanwise and chordwise locations, and the wing is loaded incrementally beyond the limit and design ultimate loads to the point of structural failure. A geometric nonlinear finite element model is developed that accounts for the variations in laminate geometry of each component as well as the properties of the adhesively bonded joints in the wing assembly. By carefully matching the boundary conditions with those of the experimental setup, the static response of the wing under a simulated whiffletree loading condition is obtained. The strain and deflection predictions from the finite element simulations are found to be in good agreement with the experimental observations. Despite its light weight, the wing is found to be very strong, with a strength-to-weight ratio of more than 40 at failure.