Durability modeling and design of a helicopter rotor Tie Bar
Sauter, Gregory P.
Wu, Edward M.
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The CH.46 Tie Bar is a multiple leaf, stainless steel system that attaches the rotor blade to the rotating hub and carries rotor blade centrifugal force. The Tie Bar twists as the rotor blade feathers and bends slightly as the Pitch Housing bends. Originally designed to last 3,000 hours without any component breakages, the Tie Bar has experienced field failures that have necessitated inspections every 10 flight hours. Traditional fatigue qualification and life methodology have not reconciled the unusually large number of CH-46 Tie Bar component failures. One CH-46 experienced 15, 10, and 6 component failures on the three aft rotor head Tie Bars after only 93 flight hours. One complete Tie Bar (140 components) failed and caused an aircraft crash. This research developed a probability modeling predictive method that can aid the design of a Tie Bar that will meet desired life and reliability levels. Laboratory coupon tests were interpreted to provide material properties for several manufacturing processes. Finite element analysis of the current Tie Bar design as well as two modified designs was used to determine the Tie Bar stress state for many component failure combinations. The reduced constraint design produced a dramatic stress concentration reduction and may provide large gains in life over the current and elliptical slot designs.
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