Air Force C-130 Rainbow Fitting Diagnostic Technology Development

Abstract

The C-130 Hercules has been a workhorse for the U.S. Air Force for decades and is projected to continue to accrue flight hours for years to come as a highly capable platform utilized for numerous mission profiles. In the past few years, many C-130 aircraft have developed fatigue cracks in the center wing box rainbow fittings. These cracks can be a significant flight safety risk, when the damage is extensive. In order to detect the existence of cracks in the rainbow fittings so that they can be repaired, implementation of labor intensive eddy current nondestructive inspection technology has been used to assess the condition of each aircraft on a scheduled basis. The Air Force is interested in the development and application of alternative fault detection techniques that are less time demanding to implement by the maintainers, while providing a high damage detection probability. Additionally, the future capability to embed effective rainbow fitting fault detection capability into the aircraft as an integrated systems health management (ISHM) solution is also desired.ARL Penn State has evaluated acoustic emission (AE) technology for detection, fault localization and fault severity indication of cracks in the rainbow fittings of C-130 aircraft. The AE technology involves monitoring for the emission of high frequency vibration (> 100,000 Hz) as an existing structural defect (crack) is stressed from the static loading of the wing. Testing has been conducted on undamaged rainbow fittings at the component level in the laboratory and on a damaged rainbow fitting at the platform level on aircraft. The preliminary analysis results indicate that this technology could provide an effective indication for crack detection, and localization, that is less time and labor intensive to implement than other conventional technologies. The purpose of this paper is to provide the project background information, describe the capability of the Eddy Current and AE technologies and show the analysis results from AE testing. The presentation will also discuss how the technology could be implemented as an onboard ISHM solution for aging C-130 aircraft.

Analyzing the defects of C-130 aircraft through maintenance history

“…Expert systems technology may be used to provide the aircraft mechanic the knowledge and experience to repair aircraft and its systems. The U.S. Air Force as well as many others have used C-130 aircraft as a workhorse for decades and still consider it as a highly capable platform for numerous mission profiles for years to come [2]. Like any other aircraft C-130 has also been undergoing a number of modifications in its various systems including airframe, engine, electrics and instruments.…”

The design and testing of subscale smart aircraft wing bolts

“…Various SHM technologies have previously been applied or proposed for C-130 and similar aircraft structures. These include strain gauges, embedded fiber optic sensors, ultrasonic transducers, natural frequency assessment and acoustic emission [1]. While such damage monitoring systems may add to the safety and longevity of the infrastructure and reduce maintenance expenses, they are likely to add significantly to its complexity and capital expense.…”