A light weight fan with a novel tip damper, designed and rig tested in the sixties, sustained a cataclysmic vibratory failure during a test with consistently smooth running and an explanatory dynamic mechanism was not found. It is now shown that instability potentially could have been induced in a synchronous backward wave by phase shift due to difference between kinetic and static friction in the damper. Moreover, the same mechanism could have augmented the steady forward harmonic wave recorded by Campbell in the twenties.

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