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Presented at the American Helicopter Society 67th Annual Forum, Virginia Beach, VA,May 3-5, 2011. Copyright 2011 by the American Helicopter Society International, Inc. All rights reserved.
Testing on the OH58 at NASA
Tests were conducted on the 500HP OH-58 helicopter transmission test stand at NASA GRC. Many researchers have used this test stand to advance the .eld of helicopter HUMS. In 1997, Nachtsheim conducted seeded fault test on the OH-58A transmission on this test stand. (Ref. 19) Seeded damage was introduced using .le marks cut on nine alternating teeth on the 19-tooth input spiral bevel pinion gear. The loading was increased monotonically and the tests were stopped when .ve of the seeded teeth were either fractured or a partially separated. Plots of the data shows increasing spectral activity in the lower frequency range.
Lewicki, et al, conducted accelerated fatigue tests while testing advanced lubricants. (Ref. 5). Tests were conducted on the OH-58A and OH-58C transmissions with the goal of producing planet bearing and sun gear fatigue, mast-shaft ball bearing micropitting, and spiral bevel gear scoring. The test matrix used had different test durations (50-100 hours), input torque (100% to 117%) of design maximum, oil pres-sure (21% to 100%), inlet oil temperature (180o to 275o F), and mast radial loading (0%-100%) of design maximum. The resulting damage components serve as the test compo-nents in this current work.
Jammu, et al, conducted accelerated fatigue tests on the OH-58A generating various component faults. (Ref. 20) The transmission ran from four to eight hours a day, from between nine and .fteen days. The transmission was pe-riodically disassembled and inspected. A condition indi-cator based on the weighted sum of eight mounted ac-celerometers was compared to the same metric determined from a lumped parameter model of identi.ed vibration paths. In addition, these values were used in a fuzzy logic algorithm called Structure Base Connectionist Net-work (SBCN). These test produced three planet bearing pit-ting fatigues, three sun gear pitting fatigue and .ve dam-aged components. Damage due to the sun and the bearing were detected in advanced stages.
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