Landing Gear Struts: How They Work


Landing gear is an integral part of any aircraft, and perhaps the most important part of landing gear is the struts. The struts are the piece of equipment that bears the brunt of the force an aircraft experiences when it touches back down on ground after flight. Struts ensure that even a rough landing doesn’t cause serious damage to your entire plane.

Types of landing gear struts :-

  1. Rigid Struts
  2. Springs Steel Struts
  3. Bungee Cord Struts
  4. Shock or Oleo Struts

Rigid Strut :-

The first type of landing gear struts, rigid struts, was the original landing gear. The idea and technology were both simple - the wheels were welded to the airframe. The main problem encountered by this configuration was its unforgiving nature during imperfect landings. If a touchdown was harsh, the strong force of shock was transferred directly to the airframe component, making it a bumpy and uncomfortable experience for pilots and passengers alike. To help soften the blow, aircraft engineers began developing inflatable tires and implementing them on aircraft. Rigid struts are far less common today, although they are still used in some cases. They are found on almost all helicopters, in the form of metal skids attached to the frame.

Spring Steel Strut :-

The second type of landing strut, spring steel struts, are the most common landing strut system on general aviation aircraft. This type of landing strut is found on all Cessna aircraft. They use strong but flexible materials such as steel, aluminum, or composites to withstand the impact of landing. When the plane touches down, the springs flex upward, distributing and sharing the load to the airframe at a safe rate that will not bend the plane. This configuration is so popular because of its mechanical simplicity, lightweight nature, and the fact that it generally requires little or no maintenance.

Bungee Cord Strut :-

The third type of landing gear struts might surprise you. This type, the bungee cord configuration, is typically found on tailwheel and backcountry aircraft such as the Piper Cub, a light aircraft from the 1940s built by Piper Aircraft. This landing gear consists of a series of elastic cords wrapped between the airframe and the flexible gear system, allowing the gear to transfer the load of the impact at a rate the airframe can handle. While a select few aircraft use a donut-type rubber cushion, mazny of them use a collection of elastic strands combined to diminish the shock of touchdown.

Shock or Oleo Strut :-

The final type of strut, and the only type that is a true shock absorber, is the shock strut. These are also called oleo or air/oil struts, and use a combination of nitrogen or compressed air and hydraulic fluids to bear and spread the shock loads encountered during landing. These can be found on small aircraft, but are more commonly found on large aircraft like business jets and commercial airliners. Shock struts employ two telescoping cylinders, both of which are sealed at their external ends. The top cylinder is affixed to the aircraft, while the bottom cylinder is attached to the landing gear. The bottom cylinder slides freely in and out of the upper cylinder like a piston. In most cases, the bottom cylinder is filled with hydraulic fluid, while the upper cylinder contains nitrogen. Between the two cylinders is a hole called an orifice that connects the two components.

Read More :-  The Functionality Of Shock Struts

Working of Landing Gear Strut :-

Upon landing, pressure from the wheels hitting the ground pushes the hydraulic fluid up through the orifice into the upper chamber of the top cylinder. The action of the fluid rapidly moving through the orifice creates heat, essentially transferring the kinetic energy of the rapidly-moving hydraulic fluid into thermal energy, thereby absorbing the shock of landing. Efficient performance of the shock struts requires proper fluid and air pressure levels to be maintained. If there is insufficient air or fluid in the strut, the compression will not be properly controlled, resulting in detrimental issues. The cylinders could bottom out, resulting in the force of impact being directly transferred to the airframe. 

While the cylinders and orifice are the main parts of the strut, the piece also consists of parts such as the servicing valve, metering pin, torque arms, wheel axle, and towing eye. Each part has a critical role within the operation of the landing gear strut. As shock struts are a more advanced type of landing gear strut, their maintenance is more complicated. The first step in maintenance is to remove the servicing valve and check the swivel nut’s tightness. Loosen the swivel nut, allowing all air to leave the cylinders. After this, remove the servicing valve altogether. Then, fill the cylinder with hydraulic fluids to the specified level and with the appropriate fluid. 

Once this is complete, reassembly can begin. Install the servicing valve with a new O-ring fitting with and a torque in accordance with the manufacturer specification. Next, inflate the strut, controlling the flow of air via the servicing valve. The correct amount of air pressure will vary from strut to strut, but will be specified in the instruction manual as an amount in psi. Shock struts must always be inflated slowly, avoiding excess heat and over-inflation. Once the strut is properly inflated, tighten the swivel nut to a specified torque. Finally, remove the hose fitting and tighten the valve cap using your finger.

While all pilots strive for perfect landings at the end of each flight, the landing gear struts are always there to assist in carrying out a smooth touchdown. At ASAP Buying, owned and operated by ASAP Semiconductor, we can help you find all types of landing gear struts for the aerospace, civil aviation, and defense industries. In addition to this, ASAP Buying is the premier supplier of aviation, NSN, and electronic parts. We’re always available and ready to help you find all the parts and equipment you need 24/7-365. For a quick and competitive quote, email us at sales@asapbuying.com or call us at 1-509-449-7700. Our team of dedicated account managers is standing by and will respond to you in 15 minutes or less.


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