An oleo strut is an air–oil hydraulic shock absorber used on the landing gear of most large aircraft and many smaller ones. It cushions the impacts of landing and while taxiing and damps out vertical oscillations.
An oleo strut consists of an inner metal tube or piston, which is attached to the wheel axle, and which moves up and down in an outer (or upper) metal tube, or cylinder, that is attached to the airframe. The cavity within the strut and piston is filled with gas (usually nitrogen, sometimes air – especially on light aircraft) and oil (usually hydraulic fluid), and is divided into two chambers that communicate through a small orifice. When the aircraft is stationary on the ground, its weight is supported by the compressed gas in the cylinder. During landing, or when the aircraft taxis over bumps, the piston slides up and down. It compresses the gas, which acts as a spring, and forces oil through the orifice, which acts as a damper. A tapered rod may be used to change the size of the orifice as the piston moves, and a check valve may be used to uncover additional orifices so that damping during compression is less than during rebound.
Nitrogen is usually used as the gas instead of air, since it is less likely to cause corrosion. The various parts of the strut are sealed with O-rings or similar elastomeric seals, and a scraper ring is used to keep dust and grit adhering to the piston from entering the strut.
- Van Sickle, Neil D., Welch, John F, Bjork, Lewis and Bjork, Linda, "Van Sickle's modern airmanship." Page 125. Retrieved March 12, 2011
- Woodhouse, Mary and Gifford, Scott "How to make your airplane last forever," Tab Books, 1996, Page 75. ISBN 978-0-07-071704-6. Retrieved March 12, 2011