Time-Phased Development Methodology: The Key for Reliable Engines in Future Military Aircraft Weapons Systems

The development of gas turbine engines has been keyed primarily to increases in thrust-to-weight ratio and to greater demands for structural durability. In fewer than 20 years, the thrust-to-weight ratio of turbine engines has doubled, as demonstrated by the F100-PW-100 engine compared to the J75. Also, a new engine life parameter, low cycle fatigue, was recognized. This new parameter results from stress variations in the engine hardware during thrust level excursions and is now included in the latest engine Military Specification (MIL-E-5007D). Since current projections of propulsion systems for the next decade show a continuing trend of increases in thrust-to-weight ratio and required durability, highly sophisticated time-phased structural analysis and verification methodology is being developed [Reference 1] for future engine development programs. This methodology is intended to ensure that the risk of structural distress, which is a primary cause of “high-costs” during system development and after deployment is minimized, and to provide a reliable understanding of the systems structural capability to facilitate expansion of the overall weapons systems to counter new “threats.” The following discussion describes the principal features of the methodology developed.