Case Studies

Nonlinear Modeling Improves Rotorcraft Safety
By Frank A. Smith Jr. Lead Stress Engineer, Boeing Rotorcraft
Paul M. Hopkins, Stress Analyst, Boeing Rotorcraft

As part of the mission of the Structural Technology and Prototyping group, Boeing Rotorcraft engineers are pursuing greater uniform margins of safety for aircraft load capacity. They set an important benchmark in 2003 when they simulated fatigue-causing loads on a CH-46E helicopter and defined an improved, efficient methodology for nonlinear finite-element analysis (FEA).

Boeing created the CH-46E in the 1980s, upgrading the CH-46 to include a larger stub- wing that accommodates a bigger fuel tank. The stub-wing also houses the landing gear and other equipment. Over time, some of the upgraded helicopters developed fatigue cracking at the attachment locations for the stub-wings, both in the wing fittings and on the airframe nearby. To determine the cause of the cracking, the Navy asked Boeing to analyze the CH-46E, focusing on the stub-wing and the area of fuselage around it.

In 2001, stress analysts at Boeing had made a business case for purchasing new computing resources that could perform exactly this sort of analysis. With advanced hardware that could run the latest generation of nonlinear stress analyses, the engineers could perform a post-buckled simulation of a known condition that occurred in the CH46E at field-determined load levels.

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