All You Should Know About Struts and Their Servicing
A strut is a common structural component that can be found in a number of industries and applications for adding resistance for assemblies against longitudinal compression. When used for aircraft construction in particular, struts are a bracing element that was originally used to add strength and rigidity to the main functional aircraft frame. Since then, struts have changed in their applications and now serve new uses for aircraft assemblies with their provided capabilities. In this blog, we will discuss the aircraft strut and its servicing, allowing you to best care for your aircraft and its components.
For small aircraft such as Cessna models, struts serve to mitigate the impact loads and forces that are induced on the airframe during landing procedures. With shock absorption capabilities, struts can prevent the massive loads of landing from being transferred to the airframe so that it avoids damage. In the past, many solutions were proposed for landing shock absorption such as bungee cords, spring steel, and rubber biscuits. While these have all proved useful for protecting the airframe to some degree, the most common solution comes in the form of oleo struts which are hydraulic oil/air cylinders.
As bracing struts began to drop in their appeal due to the rise of low-drag cantilever construction, engineers started using struts for other means such as mitigating tension loads. Additionally, struts also proved very useful for landing gear to mitigate their loads, such as with oleo struts. With their design, oleo struts are implemented on aircraft landing gear to cushion their impact on the ground and to dampen out vertical oscillations. This is extremely important as oleo struts reduce the tendency for the aircraft to bounce when it is landing. As bouncing of the aircraft landing gear can lead to a loss of control, the oleo strut will absorb impact energy released by the spring steel coil.
For oleo struts to benefit landing gear in the way that they do, they contain compressed air within the upper section of their body and have hydraulic fluids below. As the aircraft lands on the runway, the strut’s piston will launch into the cylinder, causing hydraulic fluid to be pushed through a small orifice that controls the rate of flow. As fluids are extremely incompressible, this method of operations ensures that a heavy amount of impact forces are not being transferred to the aircraft frame all at once.
Due to the role that struts play for modern aircraft, it is important that they are well maintained and serviced to keep them operational as long as possible. When beginning service for struts, one should always have flexible tubing that can snugly fit over the Schrader valve. Additionally, one also requires a valve stem instrument and something to capture and remove old fluids. To ensure safety during such operations, the aircraft should always be jacked or have its nose raised.
Once the aircraft is secured, the valve stem instrument can be used to connect the Schrader valve and fluid container. By pushing the strut upwards, the older fluids can be removed from the system and replaced with fresh hydraulic fluid with a hose. When replacing fluids, it is important to always remove all air bubbles before finishing the replacement process. Once bubbles have been removed, the strut can be returned to its collapsed state and the valve core is reattached.
When one is finished servicing a strut, components should be checked for their buoyancy. Generally, struts that have trouble moving will often have an insufficient amount of hydraulic fluids, causing air pressure within the component to increase. A low amount of hydraulic fluid can also lead to the collapsing of struts after a period of time following a landing. By providing struts with the correct amount of fluids and efficient servicing, airframes can be better protected throughout flight procedures and landings.
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