Keywords: static loads, model, aeroelastic correction, modal approach, aerodynamic influence coefficients, residual vectors.

The estimation of the flexible aerodynamic loads for the elaboration of loads models is nowadays performed at the EADS-CASA Airbus Military Static Loads Dept. using the so-called aerodynamic influence coefficients (AIC), relating aerodynamic pressure increases with the orientation variations of the normal vectors of the panels contained in the aerodynamic model. These coefficients, organized in matrix form, are usually determined via a potential aerodynamics approach. As soon as a more refined representation of the aircraft surface is needed, thus increasing the number of panels of the aerodynamic model, an alternative way to define the mentioned coefficients is deemed necessary, for the actual procedure may lead to unduly oversized matrices.

The aim of this study is to evaluate a new approach to the calculation of static aeroelastic loading effects, by defining a modal basis of static deformations that allows capturing the deformations of the aircraft with sufficient accuracy and, simultaneously simplifies the determination of the AIC.

The present paper gives a short introduction to the basic aeroelastic problems, concentrating on aeroelastic divergence, which is explained using a simple two-dimensional airfoil model. Then a description of the standard procedure employed nowadays at Airbus Military Static Loads Dept. to calculate the flexible aerodynamic loads is presented, including a brief description of the reduction methods applied to both the structural finite element model and the aerodynamic panel model.

Finally a new methodology to perform the calculation of the flexible aerodynamic loads is proposed, based on a combination of standard modal analysis techniques with more sophisticated residual vector methodologies. The final goal is to achieve a modal basis that describes with sufficient accuracy the aircraft´s deformation, reducing thus the order of the problem significantly. Once the modal base has been defined, the overall aeroelastic problem is translated to and solved in it.

Currently the Airbus Military Loads Department is working on the assessment of this methodology. If it proves successful in defining an adequate modal base, the possibility of using high fidelity representations of the aircraft surface, like those used for refined computational fluid dynamics computations, may become real, and the replacement of pure potential methods using linear representations based upon more sophisticated techniques would then be feasible in static aeroelasticity for loading applications at an industrial level.

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