Analysis and Control of A Magnetorheological Landing Gear System For a Helicopter

This study addresses the design, analysis, and demonstration of an adaptive landing gear system that uses magnetorheological (MR) fluids to provide increased, adaptive impact energy attenuation capability for a lightweight helicopter. A single stage flow-mode type magnetorheological landing gear damper (MRLGD) was designed to achieve a desired stroking load of 4000 lbs over a desired equivalent sink rate range of 6 - 12 ft/s. The MRLGD was designed using an experimentally validated nonlinear analysis that accounts for the Darcy friction factor, as well as for the effects of minor viscous losses that are quadratic functions of velocity. The MRLGDs were designed and fabricated based on these nonlinear flow analyses, as well as magnetic FEM. The stroking load at low sink rates (Vs < 10 ft/s) was experimentally validated using ramp displacement inputs on an MTS machine at low speed. To validate performance at high equivalent sink rates (Vs > 10 ft/s), a drop tests were performed (drop weight was 325 lbs) and the design analysis was validated using this drop test data. The control objective was to maintain the stroking load at 4000 lbs over the desired sink rate range of 6 -12 ft/s. Two force feedback control algorithms were developed to achieve the desired constant stroking load control objective, that is: (1) Bang-bang current control, and (2) Continuous current control. The controlled stroking loads achieved using these two force feedback control algorithms were experimentally evaluated using the damper test setup over the desired sink rate range. To simulate the landing gear system for a lightweight helicopter, an iron-bird drop test setup (total drop weight of 2035 lbs) with four MRLGDs was fabricated and successfully drop tested using these control algorithms.