The struts present on small aircrafts like Cessnas provide much-needed shock absorption functionality to prevent the airframe mechanism from undergoing too much stress as a result of impact loads incurred on landings. These essential components absorb massive loads and avoid them from being transferred to the airframe.
There are different types of struts used for shock absorption in aircrafts. In the past, airplane manufacturers have been utilizing various materials in order to limit the amount of stress from the impact of landing, including spring steel, bungee cords, and rubber biscuits. However, the most common type present on most planes is the hydraulic oil/air cylinder, also known as oleo struts.
The oleo strut is an increasingly reliable aircraft component used on the aircraft landing gear that can withstand tremendous loads and has a relatively more straightforward design. It utilizes hydraulic fluid and air pressure to create a spring effect. All struts contain compressed air (or nitrogen) in the upper section and hydraulic fluid in the lower part.
Upon landing, the piston drives into the cylinder, the fluid forces through an opening, orifice, which slows down the flow rate. The oleo strut design's primary function helps in cushioning the impacts of landing and dampening out vertical oscillations.
Essential equipment required for servicing a strut includes at least three feet long clear, flexible tubing with ¼ inch inside diameter to fit over the Schrader valve, a valve stem instrument, and an empty container to receive the old fluid. The aircraft needs to be jacked, or at least its nose should be raised if only the nose requires servicing.
When the airplane gets jacked, it's time to gradually remove the valve stem from the strut's filler valve. After removing the valve stem, press the tubing over the open Schrader valve and attach the other end into the empty container. Now, push the strut up toward its entirely collapsed position to flush out the old fluid.
Remove the container containing the old fluid and attach the hose into a can with about half a gallon of fresh hydraulic fluid. Then, pull the strut down to its fully extended position. This will result in enhanced suction in the fluid, which will siphon for a few seconds after the strut gets fully extended. Now, push the strut up gradually to its wholly collapsed position. After some of the fluid is pushed back out, this will lead to coming out of the air bubbles.
Then, enlarge the strut again; repeat the procedure until all fluid comes out in the form of a solid stream on the compression stroke. After removing all the air bubbles, it will be considerably even challenging to push the strut up to its collapsed state. After collapsing the strut completely, remove the hose from the valve and reinstall the valve core.
Adequately serviced struts usually have a certain amount of buoyancy in them. Struts that are low on hydraulic fluid and filled with air pressure tend to stick in place. Struts that stay extended for some time after a plane's landing and then collapse suddenly are also generally low on fluid. Correctly serviced struts help in softening landings and avoiding airframe damage, thus, increasing flight safety.