Vibration Investigation of Helicopter Engine Cooling Fan.

摘要

An investigation into the cause of the unacceptably high incidence of fatigue failure of blades in the engine cooling fan fitted to Sioux helicopters led to a search for resonant frequencies of the fan blades. Tests on a stationary fan and in a rotating rig showed resonant vibration at various fan speeds; in particular, high stresses were generated by a second shaft order resonance close to the normal operating speed. A modification to overcome the problem was proposed, consisting of a stainless steel shroud fitted over the blade tips. Tests showed that this modification reduced stresses to a negligible level, and the mechanical soundness of the scheme was confirmed by an endurance run followed by an overspeed test. The modified fan was fitted to a helicopter and measurements comparing its cooling performance with a standard fan showed only small differences. (Author)