Answer
External spiral retaining rings are limited by centrifugal forces that causes the ring to expand and lose contact with the groove. The maximum rotational speed $V$ (in RPM) is calculated using $V = \sqrt{\frac{4.8 \cdot E \cdot H^2 \cdot I}{D^3 \cdot \gamma \cdot (1-\mu^2)}}$, where $E$ is the Modulus of Elasticity, $H$ is the radial wall, $I$ is the moment of inertia, $D$ is the free diameter, $\gamma$ is the material density, and $\mu$ is Poisson's ratio. For high-speed aerospace applications, self-locking features (tabs and slots) are integrated to mechanically prevent the ring from expanding. If the calculated limit is exceeded, the ring will lift off the groove bottom at a critical velocity $V_{crit}$, resulting in loss of axial retention and potential catastrophic system failure.
