The Bell Helicopter Model 429 commercial helicopter was recently certified with flaw-tolerant composite main rotor blades. The substantiation criteria and qualification process for these blades were developed in accordance with FAR 27.571 and MG8 (Substantiation of Composite Rotorcraft Structure). The flaw-tolerant methodology defined the testing required to substantiate a safe inspection interval to ensure continued airworthiness and safe operation. The testing incorporated facets of a building block approach to qualification, including coupon, element, and full-scale specimens. Specific processes were used to develop the rationale for the determination of the sizes and locations of embedded flaws, locations and energy levels of impact damage, test loads, test monitoring requirements, and methodology for nondestructive inspections during testing. The flaw-tolerance test specimens included embedded flaws to simulate manufacturing defects, detectable impact damage, and environmental effects. Additionally, the test specimens were subjected to a conservative spectrum of flight representative loads, including high-cycle and Ground-Air-Ground cycle loads, to simulate loading during normal flight operations. The periodic application of a static residual strength load during the test was required to establish the inspection interval.
展开▼
