Loss of lubrication in helicopter gears

Loss of lubrication has been investigated since 70s from the battlefield experiences especially in helicopter transmission technologies of that time. Many aviation safety regulations were developed over years in order to ensure the helicopter gearbox components maintenance as well as oil condition monitoring. In 2009, a fatal accident took place before Newfoundland causing loss of 17 human lives where the critical components in the transmission failed due to loss of lubrication in the main gearbox lead to a complete failure of the tail rotor drive. Helicopter gearbox is a complex tribo-system with many high performance requirements. Though the transmission components are made to the higher standards its behavior is unpredictable under maximum thermal loading conditions as the lubrication in the system or gearbox is no longer available. In that case, it is required to have a continued safe flight for at least 30 minutes after the flight crew recognizes the loss of lubricant failure.

Absence of lubrication under heavy loading contacts generates heat due to friction thus degrading the surface hardness, roughness. The damaged surfaces produce more heat causing unstable thermal effects until the elements are failed to carry the intended loads. Several projects around the globe were trying to improve the loss of lubrication performance by superfinishing of gears, improved lubricants, ceramic bearings etc. The aim of this study is to understand the loss of lubrication behavior tribologically and to create a loss of lubrication prediction tool at the early design phase. This involves to a certain extent the transmission design, materials, lubricants, simulation, testing of the machine elements (gears, bearing, ecetera) and certification requirements.

Helicopter gearbox cut open

© Forschungsbereich Tribologie