Nose gear shimmy damping

Lord Corp. has adapted surface-effect technologies to the development of nonhydraulic nose gear shimmy dampers.

The need for frequent maintenance has been an ongoing problem with current hydraulic nose landing gear shimmy dampers. High temperatures can cause the hydraulic fluid to expand and leak past the seals, thereby reducing the damping efficiency of the device. This typically occurs after only 100 hours of operation. Maintenance costs associated with this can reach unacceptable levels, and replacement costs can mount. For these reasons, engineers at Lord Corp. began developing a more robust, less expensive shimmy damper. Development of the damper began in August 1998, resulting in a surface effect damping concept that could be used for a more reliable design.

Nose wheel shimmy is an oscillatory motion that is brought on by runway surface irregularities and nonuniformity of the tire (Figure 1). It is further exaggerated by worn landing gear components that allow significant play in the linkages. When the steering axis is rotated, a force is generated that tends to push the wheel back into alignment. Under some conditions the restoring force causes the wheel to overshoot the aligned position. If the oscillation grows, the system becomes unstable.