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Hello, I would like to perform a modal analysis of a helicopter blade while it is rotating at a constant RPM. I have created two steps in hyper-mesh, first is a linear static with boundary conditions and applied a centrifugal force with the RFORCE card. Second step is a normal modes step with the previous step linked through the STATSUB card and no boundary conditions or forces selected (free-free) modal analysis. Whenever i run this, the first step works, however i get an error: *** ERROR # 15 *** CTETRA element 252760 is distorted (zero or negative Jacobian). I checked my mesh and i have no issues with the Jacobian or mesh at those indicated elements. As a check, i've run both steps separately and both work and give good results. I don't know if this is the right way to perform such an analysis where the blade stiffness is changed by the centrifugal loading due to rotation. Your help is appreciated. Kind Regards, Mohamed FinalModel_01-12-2016_Finalzed_model_Pre_stressed_modal.hm