Method of stability computation of the main rotor blades tail section skins subject to wind at a helicopter parking lot

Due to the growing need to operate helicopters in areas with high-intensity winds, existing approaches to the design of main rotor blades (MRB) should be reviewed to ensure that the calculated cases of wind effect are fully taken into account. The helicopter spends the majority of its operational time on the ground, and the blades are exposed to wind load, which can lead to damage impairing their continued serviceability. In particular, types of damage include the formation of skin corrugations and cases of delamination within the composite tail section skin, specifically the separation of the skin from the core filler materials. If the defect dimensions exceed the allowable limits specified in the maintenance documentation, the tail sections are either repaired or replaced at the blade manufacturer’s facility. In this paper, we consider the problem of composite skin stability of the non-rotating MRB tail sections subjected to wind effect. The analytical model of the skin elements corresponds to an orthotropic rectangular plate mounted on an elastic base and loaded along the edge adjoining the blade spar. The stress-strain state (SSS) of the skin is determined by solving planar elasticity boundary value problem, where the applied loads are calculated based on the deformation compatibility condition between the MRB spar and the skin, obtained from the overall wind load analysis of the blade. In this paper, a differential equation of stability of an orthotropic plate on an elastic base is derived, simulating the lining of the tail section of the MRB. An expression for calculating the critical stresses corresponding to the onset of local skin buckling is obtained. Based on the criterion of local skin buckling, the limit wind speed for the MRB of the Mil-38 helicopter type was calculated.

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