<title>Heavy load vibration isolation system for airborne payloads</title>

Abstract

A high-performance vibration isolation system has been developed to isolate large-sensitive payloads from aircraft disturbances. The isolation system senses and adjusts for low frequency aircraft maneuvers and changes in the aircraft's flight angle of attack. Additionally, the isolation system passively filters higher frequency disturbances from aircraft to payload. Six pneumatic struts configured as a hexapod or Stewart Platform make up the primary portion of the isolation system and accomplish vibration isolation and payload support. Each isolator strut is a unique Patented design that takes advantage of gas (the ultimate smart material), because it has a capacity for large energy storage and it possesses a near linear viscosity over a broad temperature range. Any gas that exhibits a somewhat perfect-gas characteristic can be used inside the strut with similar performance results. For our application, gaseous nitrogen (GN2) was used. The pneumatic strut has shown an ideal isolator roll-off quality that is tunable for a variety of payloads and linear over a large dynamic range. Tunability stems from a dual chamber design that allows air-spring-rate changes while maintaining constant support of the load. The strut performance trait combined with the deterministic nature of the hexapod affords predictability and controllability. The system design enables a soft floating support of large payloads with accurate knowledge of their orientation with respect to the aircraft. Another distinctive feature of the isolation system design is a servo-controlled leveling system that senses a set point from an integrally mounted LVDT and fills or exhausts gas, as necessary, maintaining strut position during the rigors of flight. A combination of Commercial Off The Shelf (COTS) and control cards with custom plumbing provides the leveling function. All tolled, the isolation system has functioned flawlessly in service, and has raised the bar for vibration isolator performance. In this paper the isolation system design will be detailed, and its performance measurements will be presented.