The F-22 AMAD Gear Drive Optimization of Resonance Characteristics by Detuning, Coulomb Damping & Damped Force Response Analyses


Finite element analyses were performed during design and development of the F22 AMAD gearbox to ensure a design free of damaging resonant responses within its operating speed range. Ideally, design with respect to resonance characteristics would have no natural frequencies within the operating speed range. However, the wide speed range (from 1445 to 17 931 rpm) combined with the weight and geometric constraints imposed by the application (the F-22 is an advanced technology, next generation, fighter aircraft) made it impossible to attain this goal directly in the F-22 AMAD design. The analysis and evaluation therefore involved several interrelated iterative steps which included detuning by geometric modification, evaluation of gear to forced vibration, and damping treatment to develop an optimum, lightweight design free of damaging resonant responses within 15% of the operating speed range. This paper discusses the overall analytical approach, analytical methods and evaluation of gear response to achieve acceptable accessory gear designs. Design modifications, including developments in the modeling techniques required to accommodate the unique characteristics of these relatively small (compared to the usual helicopter main power gear) gears are also discussed. Test and analytical results are also presented and compared.
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