Landing gear assemblies consist of more than wheels and struts; many of them feature shimmy dampers as well. They are typically found on airplanes with tricycle-style landing gear where they prevent wheel oscillation. Here’s everything you need to know about shimmy dampers and how they work.
What Are Shimmy Dampers?
Shimmy dampers are devices that prevent landing gear wheels from oscillating or “shimmying.” Landing gear wheels should remain straight upon touching down on the runway. If they oscillate from side to side, pilots may struggle to control the airplane during landings. Shimmy dampers reduce the risk of accidents by stabilizing the wheels so that oscillation doesn’t occur.
If left unchecked, wheel oscillation can lead to a wide range of problems, including the following:
- Increased stress on the airplane’s frame
- Damage to the tires
- Loose fasteners
- Increased risk of accidents when landing
The Science Behind Shimmy Dampers
Shimmy dampers are designed to prevent wheel oscillation by leveraging a pressurized cylinder. The cylinder is filled with a hydraulic fluid. When the wheel begins to wobble or oscillate, a piston will push the fluid through a series of small passages. This mechanism restricts the flow of the fluid, which in turn creates resistance.
Most shimmy dampers feature a cylinder with hydraulic fluid. Some, however, use an elastomeric material, instead. They work via compression. The elastomeric material, such as a specialized rubber, compresses to create resistance.
What Causes Wheels to Oscillate?
Landing gear wheels can oscillate for many reasons. If the wheels aren’t properly balanced — meaning one or more wheels is higher than the others — they may oscillate. Uneven tread wear can also cause oscillation. Like with automotive tires, landing gear tires should experience even tread wear.
Runway conditions can cause landing gear wheels to oscillate as well. Holes, cracks or other imperfections in the runway may result in oscillation when the airplane touches down.
Do All Airplanes Have Shimmy Dampers?
While most airplanes have landing gear, they don’t all have shimmy dampers. Rather, shimmy dampers are typically used exclusively on airplanes with tricycle-style landing gear.
Also known as nosewheel-style landing gear, tricycle-style landing gear is characterized by one nosewheel and two rear wheels, the latter of which are located behind the airplane’s center of gravity. This design improves visibility for pilots but increases the risk of wheel oscillation. Shimmy dampers, though, act as shock absorbers to resist unwanted movement so that the wheels remain straight and stable.
