During normal operation, the ends of helicopter rescue hoist ropes, to which a hook is attached, can be subject to bending stress caused by vibrations. This happens in the event of partial or total recovery of the hook into its lodging without a spring-loaded blocking system. The swinging of the rope end consequently causes bending of the rope near the terminal, with resultant fatigue stress that can lead quickly to breakage or damage of the rope. A series of alternating bending fatigue tests using a constant load, similar to those known as BoS (bending over sheave) tests, were carried out. These simulate the effective working conditions of a rescue hoist. This paper describes modifications to test machinery, the test method and the data obtained; statistical analysis of this data enabled us to make a rope life prediction which was then experimentally confirmed by run-outs on test ropes.
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