W. H. Abbott, Battelle, Columbus, OH

Summary:

Studies have been in progress for several years to examine the feasibility for the use of sensors to monitor environmental severity as it relates to corrosion on operational aircraft. This work is in support of the Air Vehicle Health Monitoring Program.

The sensor being used is a small, credit card size, passive device developed at Battelle. Corrosion is directly measured as a cumulative response in which the information of interest is permanently retained on the sensor. This is important, since in the current operating environments it is impractical to expect that data can be obtained on any fixed or ideal schedule. At present, measurements are being made in a manual mode requiring visits to the aircraft. Cumulative corrosion is measured as an electrical signal obtained by powering the device on-site.

This study was initiated as part of a learning process. This simply means to determine whether and under what conditions sensors of this type could be deployed in large numbers on operational aircraft, whether data could be obtained in a timely manner, and what limitations may be imposed on such work. The acquisition of corrosion related data was viewed as a secondary objective.

This work has actually proceeded very smoothly with both objectives being achieved. To date more than 300 sensors have been installed on Air Force aircraft flying worldwide. These include KC135, C141, C130, F16, and F15s. Typically 12-20 sensors have been installed per aircraft with a target objective of installations at critical structural locations but not directly in the airstream. More than 200,000 sensor-flight hours have been logged with no safety of flight issues and no problems reported from any of the participating bases.

Early data are showing a sufficient sensitivity to detect changes in critical areas within months, to demonstrate large differences within areas of the aircraft structure of >10:1 while obtaining a sensor life likely to be in excess of one depot cycle (>5 years), and to demonstrate a large attenuation factor between the external and internal environments in the range of 4-5:1. These results are confirming that many areas within typical aircraft are likely to exhibit very low severity to an extent that corrosion is not likely to be a factor in structural integrity. At the same time, the data present an optimistic appraisal that areas of high severity can be quickly detected.

This work is in its early stages and no attempt has yet been made to relate sensor data to reported structural corrosion. At the same time, these results may be providing a basis for corrosion management by tail number in the future.