This paper addresses the development of multiple UAV deployment simulation models so as to include representative aerodynamic cross-coupling effects. Applications may include simulations of autonomous aerial refuelling and various surveillance and search & rescue scenarios. A novel wake vortex model was developed and successfully integrated within a Matlab/Simulink simulation environment. The wake vortex model meets the following requirements: (i) it is sufficiently representative to support studies of aerodynamic interaction between multiple air vehicles; (ii) it is straightforward enough to be used within real time or near real time air-to-air simulations. The emphasis of this paper is put on the integration process, and simulation results of a two vehicles formation flight are presented. The simulation models will be used to support in-depth investigations on the likely impact of dynamic air vehicle interactive coupling on autonomous control requirements for multiple vehicle deployment. The wake vortex model has been integrated within the Cobham Synthetic Environment for air-to-air refuelling studies.
[Show abstract][Hide abstract] ABSTRACT: This paper addresses the unified aeroelastic and flight dynamics characterization of low-speed slender-wing aircraft, including free-wake effects and aerodynamic interference. An analysis framework is presented that targets the prediction of stability and handling qualities of high-altitude long-endurance vehicles, which are prone to experience large wing excursions, leading to an inherently nonlinear and coupled problem between aerodynamics, elasticity and flight dynamics. In this work, the structural dynamics are based on a geometrically-exact composite beam model, discretized using displacement-based finite elements, and cast into an extended flexible-body dynamics model. The aerodynamic model is defined by a general unsteady vortex lattice method. The governing equations of motion of the integrated system are formulated in a tightly-coupled state-space form, which allows for the equations to be solved simultaneously. Verification of the model has been carried out for static and dynamic problems, including both rigid and flexible wings. Numerical studies are presented for the particular case of prescribed rigid-body motions, paying special attention to the likely interference between wake and tail. Results show that the current approach represents a suitable alternative for configuration analysis of flexible atmospheric vehicles, offering a good balance between degree of fidelity and computational cost.
[Show abstract][Hide abstract] ABSTRACT: An evaluation of aerodynamic and structural models is carried out for their application to flight dynamics of low-speed aircraft with very-flexible high-aspect-ratio wings. The structural dynamic approaches include displacement-based, strain-based, and intrinsic (first-order) geometrically-nonlinear composite beam models, while thin-strip and vortex-lattice methods are considered for the unsteady aerodynamics. We first show that all different beam finite-element models (previously derived in the literature from different assumptions) can be consistently obtained from a single set of equations. This approach has been used to expand existing strain-based models to include shear effects. Comparisons are made in terms of numerical efficiency and simplicity of integration in flexible-aircraft flight dynamics studies. On the structural modeling, it was found that intrinsic solutions can be several times faster than conventional ones for aircraft-type geometries. For the aerodynamic modeling, thin-strip models based on indicial airfoil response are found to perform well in situations dominated by small amplitude dynamics around large quasi-static wing deflections, while large-amplitude wing dynamics require 3-D descriptions (e.g., vortex-lattice or similar).
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