Five-Degrees-of-Freedom (5-DOF) characterization of the stability of a gas lubricated conical bearing of the spiral groove design is determined for bearing numbers up to 500. Perturbation analysis is performed separately for axial, cylindrical and conical modes; the results are compiled into frequency-dependent modal impedance data sets that can be graphed as impedance contours to identify critical points in stability analysis. For a symmetrical rigid rotor, the stability-threshold with respect to each mode can be separately determined. For axial and cylindrical modes, the threshold parameter is the rotor mass. For the conical mode, both transverse and polar radii of gyration enter into the picture but the threshold parameter can still be interpreted in terms of rotor mass.

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