Technical Considerations for Managing Aging Rotorcraft

This paper compares the issues of rotorcraft vs. fixed wing aircraft, and discusses several technical considerations confronting the reliable force management of rotorcraft based on damage tolerant and safe life approaches. Completed work is reviewed for a series of tasks required to develop a Structural Integrity Computer Program (SICP) to be used in support of Aircraft Structural Integrity Programs for USAF aging aircraft. A general description of the SICP is provided, followed by a discussion of helicopter fatigue failure modes and results of tasks comparing fracture mechanics techniques for large and small crack growth. The current state of linear elastic technology is reviewed, as well as elastic-plastic approaches, plasticity correction models, and two-parameter crack growth techniques. Finally, recommendations for further technology improvements are given.