Doublet Lattice Modeling and Analysis of Unsteady Aerodynamic Effects for a Flexible Unmanned Aircraft during Maneuvers and Gust Encounters

This paper presents the modeling and analysis of unsteady aerodynamics for a slightly flexible 25 kg unmanned aircraft during maneuvers and gust encounters. The unsteady model is based on a doublet lattice method (DLM) implemented in MATLAB. It is combined with an existing high-fidelity quasi-steady aerodynamics model derived from system identification using flight test data. Utilizing the physical rational function approximation, it is possible to differentiate between the steady and unsteady components of the DLM. Consequently, the steady component of the DLM can be replaced by the high-fidelity model such that quasisteady and unsteady DLM forces and moments are superimposed. The combined unsteady aerodynamics are integrated with linear structural dynamics identified from ground vibration tests and nonlinear equations of motion based on the practical mean-axes formulation. Simulation studies are conducted to analyze the impact of unsteady aerodynamic effects on the flexible aircraft. The results indicate that unsteady effects, while noticeable during rapid maneuvers in the aeroelastic frequency range, are especially significant when considering high-frequency control surface deflections and encounters with short gusts. The proposed modeling approach successfully combines high-fidelity quasi-steady aerodynamics with unsteady DLM aerodynamics,demonstrating validity across a wide range of reduced frequencies.

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Doublet Lattice Modeling and Analysis of Unsteady Aerodynamic Effects for a Flexible Unmanned Aircraft during Maneuvers and Gust Encounters