By exploiting the features of the implicit formulation of the elastic blade equations and the quasilinearization solution technique, the sensitivities of the modal, blade and hub inertia loads, and modal structural loads to changes in mass, center of mass offset, and flap bending stiffness can be efficiently determined. Examining the various components of the expression for the sensitivities, obtained through chain rule differentiation, reveals that the terms that are most expensive to obtain are already calculated as part of the basic analysis. Furthermore, it is relatively easy to update or modify the underlying mathematical model of the aicraft, because most of the changes that would then be required in the semianalytical sensitivities are already available once the basic analysis has been updated. The results of this study indicate that: 1) The semianalytical method dramatically reduces the required computational effort while producing results that are in excellent agreement with those generated using finite difference approximations. 2) Changes in mass and chordwise position of the center of mass affect rotor loads both directly, that is, through changes in the distributed forces and moments for mixed steady-state equilibrium position, and indirectly, through changes in the periodic response of the blades and in the trim conditions of the helicopter. Therefore, both types of effects need to be taken into account. This conclusion applies to both blade root loads in the rotating system, and hub loads in the fixed system. Changes in normal modes can be neglected, however, at least for uniform blades.
Efficient sensitivity analysis for rotary-wing aeromechanical problems
Hochauflösende Empfindlichkeitsanalyse für aeromechanische Probleme der Drehflügel
AIAA Journal ; 32 , 12 ; 2337-2344
1994
8 Seiten, 12 Bilder, 13 Quellen
Article (Journal)
English
Efficient Sensitivity Analysis for Rotary-Wing Aeromechanical Problems
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