Prior to receiving airworthiness certification, extensive testing is required during the development of rotary wing aircraft drive systems. Many of these tests are conducted to demonstrate the drive system’s ability to operate at extreme conditions, i.e. — beyond that called for in the normal to maximum power operating range.

The effect of the lubrication regime on gear performance has been recognized, qualitatively, for decades. Often the lubrication regime is characterized by the specific film thickness defined as the ratio of lubricant film thickness to the composite surface roughness. It can be difficult to combine results of studies to create a cohesive and comprehensive data set. In this work gear surface fatigue lives for a wide range of specific film values were studied using tests done with common rigs, speeds, lubricant temperatures, and test procedures.

I must confess I sometimes find myself a bit dazed when discussing lubrication issues with either staff or vendors. The terminology seems to be all over the lot, with some terms having double meanings. Can you help cut through the confusion?

A reader asks: While I have read a reasonable amount of the literature on the pros and cons of anti-wear and anti-scuff additives, I find that the more I read, the more confused I become. I could use some clarity in my life.

Historically, wind turbine gearbox failures have plagued the industry. Yet an effective oil analysis program will increase the reliability and availability of your machinery, while minimizing maintenance costs associated with oil change-outs, labor, repairs and downtime. Practical action steps are presented here to improve reliability.

When it comes to purchasing gear lubricants, many people on both the sales and purchasing side decide to play the numbers game. The person with the most numbers, or the biggest numbers, or the lowest numbers, must have the best product - right? Wrong; gear oil selection is not a game, and numbers alone cannot determine the right product for an application.

A reader asks about how to specify a method of lubrication for a speed reducer with a three-stage helical gear with a low peripheral speed.

This work establishes a baseline for aerospace spur gear behavior under oil-off conditions. The collected test results document a different oil-off time, dictated by material used.

A sampling of newsletter articles and videos related to gear manufacturing from March/April 2013.

Understanding the morphology of micropitting is critical in determining the root cause of failure. Examples of micropitting in gears and rolling-element bearings are presented to illustrate morphological variations that can occur in practice.