SAE AS4052C – Gland Design: Scraper Landing Gear Installation

This SAE Aerospace Standard (AS) covers an alternate gland design for the installation of scraper/ wiper rings in the lower end of landing gear shock struts for the purpose of contaminant exclusion.

The defined scraper gland covered by this document as shown in Table 1 is a variant of AS4716 the accepted gland standard for AS568 O-ring packing seals. Piston rod diameters gland internal diameters groove sidewall angles and the surface finish are all defined by AS4716 but the gland outer retaining wall diameter is changed. The traditional scraper design installed into the glands detailed in Table 1 typically utilize components made from PTFE urethane or nitrile materials. These scraper designs while still acceptable must be reviewed in consideration to deicing cleaners and disinfectant fluids applied to or in contact with the landing gear as the materials of construction for the installed scrapers may not be compatible to these fluids. Exposure of the scraper to incompatible fluids is likely to reduce the performance of the scraper.

In addition an alternative scraper gland is also covered by this document and shown in Table 2. It is also a variant of AS4716; however this gland has a reduced atmospheric gland lip and profiled lead in geometry to allow for a PTFE jacket metal spring energized scraper to be installed. The advantages of the PTFE jacket metal spring energized scraper design are that the materials of construction are chemically inert greatly reducing the possibility of negative performance due to incompatibility with deicers cleaners and disinfectant fluids.

AS4088 is similar to the hardware design in Tables 1A and 1B of this document which was developed by SAE A-6 for flight control and general-purpose cylinders. It differs from this document primarily by the clearance between the rod (piston) and outer gland wall.