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In recent years, Unmanned Air Vehicle (UAV) has been widely used in military, civil and scientific fields, and plays an increasingly important role. It can be used for reconnaissance, target acquisition, electronic warfare, guided firepower, the battle assessment and target simulation in military; It can be used for geodetic, meteorological observations, urban environmental monitoring, Earth resource exploration and forest fire prevention in civil fields; It can be used for atmospheric research, meteorological observation, pilot new technologies and equipment validation in scientific fields. Nowadays, a lot of countries and regions have paid close attention to UAV and do a lot of important technical research.This paper studies UAV, analyses the aerodynamic characteristics of ducted propeller and load-bearing structure of UAV, then discusses the structural problems of UAV, at last optimizes the structure.This paper adopts the way of computational Fluid Dynamics, establishes the model of numerical calculation of ducted propeller. Then the paper establishes the Multiple Reference Frame model of the dynamic spin using Fluent, analyses the aerodynamic characteristics of ducted propeller, and determine the aerodynamic loads.The paper analyzes the force of disc UAV, calculates the various load coefficient of UAV under different flight attitude,and does the force calculation of support arm, which is the principle force bearing component. Also the paper does on the modal analysis on UAV’s support arm. The finite element strength analysis and the problems of its structure in the intensity of the structure of support arm is analyzed. Analyzing the modal of support arm of UAV, prepares for the dynamic performance analysis and optimization of the structure.According to the structure requirements of UAV, the paper takes structural density of support arm structure as design parameters, selects structural strength and the natural frequency of the structure as constraints, selects minimum volume as the objective function, optimizes the topology of the support arm, gets the support arm structure which can avoid the resonance excitation frequency and has good carrying capacity. On this basis, selecting structural dimensions and structure of the cross-section dimensions as the design parameters, selecting the stress conditions as constraints, selecting minimum volume as the objective function, finally got the design optimized parameters of the support arm.Based on the optimization results and the actual assembly state of support arm, the paper designs a new support arm structure of UAV,which has a rational and high efficient layout. The weight and the finite element analysis comparison results in Comparison between new structure and original structure of UAV proved that the design result meets the requirements of the structural weight lightening, vibration reduction and increase carrying capacity of the structure..
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