Sikorsky Seal Leakage Criteria and Prevention Methods

Helicopter gearbox seals typically exhibit a zero-leakage condition, especially on new helicopters. Improved lip seal materials and molding techniques, special attention to grinding seal liners, application of break-in grease, and smooth lead-in chamfers to prevent assembly damage have all contributed to excellent seal performance. Operational leakage criteria, especially for military aircraft is established for completion of missions and exceeds what is expected by operators of new helicopters or by crew chiefs and pilots who are accustomed to zero leakage or minor seal wetness. There are, on occasion, conditions where wetness or drips occur that are questioned by operators because a norm has been established. There are also occurrences where miniscule scratches in seal liners barely visible by the naked eye or microscopic nicks in seal rubber can allow minor seepage. Seal replacement can result in removal of rotors or shafting, requiring reservicing with all new lubricants and serviceability inspections, which can cause mission or delivery delays and put an extra burden on maintenance crews. This paper describes methods to eliminate leakage and provides recommended leakage criteria for safe and reliable operation.