History and Challenges for Structural Health Monitoring (SHM) for Fixed Wing Military Aircraft

The concept of using permanently attached sensors to detect damage in fixed wing aircraft structure has been explored since the late 1970s. The types of sensing that has been explored include various acoustic, eddy current, mechanical, and strain-based sensing systems. However, to date none of these systems have been installed on Department of the Air Force (DAF) fixed wing aircraft except for experimental applications. This paper reviews past efforts within the DAF to investigate using integrated sensors to replace current nondestructive inspection (NDI) processes. The discussion of past projects cannot be comprehensive due to the large volume of literature in this field, but will cover each primary sensing modality, typical sensor types, and signal processing approaches. In addition, how the sensing techniques integrate with the DAF Aircraft and Structural Integrity (ASIP) Military Standards, such as MIL STD 1530D, is a critical attribute for sensing systems to become direct replacements for current NDI processes. The needs of fixed wing aircraft are compared to the successful implementation of sensors on helicopters to detect evolving change in rotating drivetrains.