The development of the Ultra High Bypass (UHB) engine for transport aircraft introduces sonic fatigue as a major structural design challenge. UHB engines generate high intensity acoustic tones associated with the harmonics of the propeller blades. Current analysis methods and structural design approaches to prevent sonic fatigue cracks are based on techniques developed in the 1960s for broadband random jet-noise excitation.

The high intensity noise testing and analysis completed to develop a sonic fatigue treatment design for the UHB Demonstrator aircraft are discussed. The evaluation included progressive wave tube (PWT) and shaker table testing conducted on representative aircraft components in the laboratory.

Also discussed are the sonic fatigue treatment designs developed and flight tested on the UHB Demonstrator aircraft by Douglas Aircraft Company. The tests proved that lightweight and inexpensive treatments can be developed that will provide protection against sonic fatigue.

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