Jesus bolt is a colloqialism which refers to the nut and bolt used to hold the main rotor to the main drive gear in an R/C helicopter.
The term, originally coined as Jesus pin or Jesus nut was used to refer to the same bolt in the full-scale Bell UH-1 Iroquois helicopter used extensively by American forces in the Vietnam War.
Though the origin of the term is uncertain, it has come to refer to any single component which, if it were to fail, would cause catastrophic failure of a larger assembly. One theory regarding the term's origin is that failure of the bolt in flight would cause the main rotor to separate from the rest of the helicopter; the only thing left for the crew to do would be to pray to Jesus for deliverance from the inevitable crash. Another theory attributes the term to helicopter builder and engineer Igor Sikorsky. That theory stems from the fact that Sikorsky was a deeply religious man.
As it applies to model helicopters, the term may come from the fact that the pressed-fit pin or bolt used to secure the main rotor is made of low-tensile steel designed to deform or shear in the event of a crash, sacrificing itself to help save other main rotor components.
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