The fluid in an oleo strut that provides the absorbing effect during landing is what?

• A. Water
• B. Oil
• C. Air
• D. Grease

Answer: (B)

The damping (absorbing) effect in an oleo strut comes from the hydraulic oil inside the strut. As the landing gear compresses, the piston pushes oil through a restricted passage or metering valve. The oil’s viscosity resists that flow, converting the kinetic energy of the impact into heat and providing a controlled, gradual deceleration of the wheel and strut. A compressed gas layer above the oil (often nitrogen) acts primarily as a spring to push the leg back out, but the actual absorption of the landing energy is due to the oil’s viscous flow. Water wouldn’t provide proper damping and can cause freezing and corrosion issues; air offers much less damping unless paired with a hydraulic fluid; grease is too thick to flow and regulate energy transfer. So the absorbing fluid is oil.