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Structures and Materials Division Research and Technology Directorate NASA Glenn Research Center

Tribology and mechanical Components Branch
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Aero Drive Systems - Advanced Gear Systems
Research Objectives
Develop technology for advanced gear drive systems for use in rotorcraft and space applications.
Technical Challenges
  • Aircraft, especially military, have historically demanded increased power capacity throughout their lifetime. Future aircraft required increased capacity to perform enhanced missions.
  • There is a continuous goal to reduce aircraft weight and especially drive system weight.
  • Without technology advancements, reduced weight usually leads to reduced life, reduced capacity, and reduced reliability.
Current Research
Face-Gear Surface Durability Investigations: Experimental fatigue tests were performed to determine the surface durability life of a face gear in mesh with a tapered spur involute pinion. Twenty-four sets of gears were tested at three load levels: 7200, 8185, and 9075 lb-in face gear torque, and 2190 to 3280 rpm face gear speed. The gears were carburized and ground, shot-peened and vibro-honed, and made from VIM-VAR Pyrowear 53 steel per AMS 6308. The tests produced 17 gear tooth spalling failures and 7 suspensions. For all the failed sets, spalling occurred on at least one tooth of all the pinions. In some cases, the spalling initiated a crack in the pinion teeth which progressed to tooth fracture. Also, spalling occurred on some face gear teeth. The AGMA endurance allowable stress for a tapered spur involute pinion in mesh with a face gear was determined to be 275 ksi for the material tested. For the application of a tapered spur involute pinion in mesh with a face gear, proper face gear shim controlled the desired gear tooth contact pattern while proper pinion shim was an effective way of adjusting backlash without severely affecting the contact pattern.

Gear tooth under test
Above: Test hardware used to determine pitting fatigue life of face gears.
Measuring gear tooth strains
Above: Results of the face gear pitting fatigue life tests. Tests were performed at three load levels and a total of 24 sets of gears were run.
Turbine Seal Timeline
Method for Fabricating a Split Path Transmission System Providing Equal Torque Splitting Between the Split Load Paths of Each Gear Train Thereof at a Predefined Operating Point
Jules G. Kish, Robert J. Durwin, and Timothy L. Krantz
Patent No. 5,813,292 Link to non-NASA website Issued: September 29, 1998

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Dr. David G. Lewicki
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Last Updated: May 20, 2009