Aircraft Transmission Systems: Maintenance and Components

Aircraft Transmissions

A transmission is a mechanism used to transfer power. It operates through various components such as gears, lash and pattern, belts and pulleys, chains and sprockets, jack screws, and push-pull rods. Proper functioning of these systems is critical, and it is essential to ensure regular lubrication and preventive maintenance to avoid wear and ensure long-term reliability.

Gears

The primary purpose of a gear is to transmit power through motion. It is important to visually inspect all gears for cracked or chipped teeth, as well as for the presence of pitting or excessive wear. Deep pitting marks or excessive wear on gear teeth are reasons for rejecting and replacing a gear.

Lash and Pattern

The lash and pattern of gears are essential for proper functioning. The lash must be appropriate to allow effective lubrication between the teeth, while the pattern ensures even load distribution. An incorrect pattern or improper lash can cause wear or breakage of the gear teeth. Adjusting these parameters is done using shims and is crucial for maintaining the efficiency and durability of the gears. If they cannot be properly adjusted, gear replacement should be considered.

Belt Systems

Belt systems are uncommon in modern aircraft due to the risk of slippage, especially when the belt stretches. Toothed belts are used to reduce slippage. Maintenance of these belts involves:

• Checking their tension
• Inspecting for signs of wear
• Adjusting the pulleys if necessary

Belts have a limited lifespan and require regular monitoring.

Chains and Sprockets

The main issues with this type of transmission are cleanliness and lubrication for proper operation, as well as excessive wear due to elongation of the chains. Regular inspection and lubrication are essential to ensure these components function correctly and efficiently.

Jack Screws

Jack screws are commonly used as the drive mechanism for lowering and raising flaps and other flight controls. Ensuring the correct lubrication and cleaning process helps prevent wear and maintains the performance of the jack screws.

Push-Pull Rods

Push-pull rods eliminate the issue of varying tension and allow the transfer of either compression or tension stress through a single tube. A push-pull tube assembly consists of a hollow aluminium alloy, with an adjustable end fitting and a check nut at each end.