Date of Award


Document Type

Open Access Thesis


Mechanical Engineering

First Advisor

Abdel Bayoumi


The intermediate gearbox (IGB) on the AH-64D was chosen as the subject for this study based on the persistent grease leaks that require grounding aircraft. The aircraft is not currently equipped with a method of detecting grease loss during flight, so techniques for analyzing the usefulness of old metrics and possible new techniques can be tested. The main objective of this study is to use the aircraft’s on-board sensors to develop a method of determining the lubrication level of the IGB. Currently, the most reliable method for detecting a fault on the aircraft is through the use of vibration-based condition indicators (CIs). The results of this research show a negative correlation between vibration and grease service levels when analyzing specific CIs for the IGB on the AH-64, which can be basis for automated leak detection.

Another objective of this study is to quantify the standard operational grease level for IGBs in the AH-64 fleet. This standard would be created by measuring the amount of grease left in each gearbox after burping. This grease level would then be used to insure that if lubricant was leaking out of the component, it is due to a fault instead of an overfilled article. If the level is the same for each gearbox then a new standard can be implemented to prevent burping. By being able to use an installed on-board sensor to indicate the level of grease in the gearbox this would relieve the burden of the maintainer from having to check the level every 25 flight hours. The soldier would then be able to spend his time in another area that is more critical than a routine maintenance item.

For this analysis three gearboxes of similar condition were used. Each one was run for two hours at five different grease service levels of 0%, 25%, 50%, 75%, and 100%, based on the Army Depot standard amount of 964 grams. These gearboxes were tested on the USC tail rotor drivetrain (TRDT) test stand according to a test plan defining operational conditions. The test plan specifies torque and speed values that are similar to those experienced by the component during flight. The existing on-board modernized signal processing unit (MSPU) CIs, the raw time-domain data, and temperature data were collected and analyzed to try and identify a CI to indicate grease level.

By using statistical analysis tools and some know fault cases. CIs can give the user a different view into the operation of the gearbox as opposed to standard vibration analysis. This happens to hold true for this experiment, in which investigation of the two CIs, output bearing energy and input bearing energy, revealed an inverse correlation between grease level and vibration magnitude. Out of the two algorithms mentioned, the input bearing energy had the strongest correlation, making it the best candidate for monitoring grease level through vibration in the field. The raw vibration data collected, unlike the conditioned MSPU, data was too noisy and did not yield any valuable results. It was also noted that gearbox temperature increased as the grease service level increased; this was unexpected because it was believed that the greater the service level of the component, the lower the operating temperature would be. This trend was more stable and consistent from gearbox to gearbox than the one seen using the vibration data. These results prove that it is possible to monitor the quantity of grease in the gearbox through on-board sensors, and also serve as a testament to the usefulness of putting condition-based maintenance techniques into practice in the field.