Vibration Isolation Systems for Advancing Blade Concept Rotorcraft

Abstract

A vibration isolation system for an advancing blade concept rotorcraft having a pylon assembly and an airframe. The vibration isolation system includes one or more pylon links each having first and second ends with the first end coupled to the pylon assembly and the second end coupled to the airframe. Each pylon link includes a vibration isolator, such as a Liquid Inertia Vibration Eliminator unit, that is interposed between the pylon assembly and the airframe. The vibration isolator system is operable to reduce or eliminate transmission of the pylon assembly vibration to the airframe.

What is claimed is: 
     
         1 . A vibration isolation system for an advancing blade concept rotorcraft having a pylon assembly and an airframe, the pylon assembly subject to vibration, the vibration isolation system comprising:
 at least one pylon link having first and second ends, the first end coupled to the pylon assembly and the second end coupled to the airframe;   wherein the at least one pylon link each further comprises a vibration isolator such that the vibration isolator is interposed between the pylon assembly and the airframe, the vibration isolator operable to reduce transmission of the pylon assembly vibration to the airframe.   
     
     
         2 . The vibration isolation system as recited in  claim 1  wherein the pylon assembly further comprises a transmission, the first end of the at least one pylon link coupled to the transmission. 
     
     
         3 . The vibration isolation system as recited in  claim 1  wherein the vibration isolator further comprises a passive vibration isolator. 
     
     
         4 . The vibration isolation system as recited in  claim 1  wherein the vibration isolator further comprises a Liquid Inertia Vibration Eliminator unit. 
     
     
         5 . The vibration isolation system as recited in  claim 4  wherein the Liquid Inertia Vibration Eliminator unit further comprises:
 first and second fluid chambers; 
 a tuning passage providing fluid communication between the first and second fluid chambers; and 
 a tuning fluid moveable between the first and second fluid chambers via the tuning passage to isolate the vibration of the pylon assembly. 
 
     
     
         6 . The vibration isolation system as recited in  claim 5  wherein the Liquid Inertia Vibration Eliminator unit further comprises a housing and a piston disposed within the housing, the piston forming the tuning passage. 
     
     
         7 . The vibration isolation system as recited in  claim 6  wherein the piston is operable to move within the housing such that the tuning fluid moves between the first and second fluid chambers via the tuning passage in response to the vibration of the pylon assembly at one or more frequencies. 
     
     
         8 . The vibration isolation system as recited in  claim 6  wherein the at least one pylon link further comprises a first portion including the first end and a second portion including the second end; and
 wherein the first portion of the at least one pylon link is coupled to one of the housing or the piston and the second portion of the at least one pylon link is coupled to the other of the housing or the piston. 
 
     
     
         9 . The vibration isolation system as recited in  claim 1  wherein the at least one pylon link further comprises a plurality of pylon links each further comprising a respective vibration isolator. 
     
     
         10 . The vibration isolation system as recited in  claim 9  wherein the pylon assembly is subject to vibration in a plurality of degrees of freedom including first and second degrees of freedom; and
 wherein the plurality of pylon links further comprise first and second pylon links, the first pylon link oriented to isolate vibration of the pylon assembly in the first degree of freedom, the second pylon link oriented to isolate vibration of the pylon assembly in the second degree of freedom. 
 
     
     
         11 . The vibration isolation system as recited in  claim 9  wherein the plurality of pylon links further comprise at least one substantially horizontal pylon link and at least one substantially vertical pylon link. 
     
     
         12 . The vibration isolation system as recited in  claim 11  wherein the at least one substantially horizontal pylon link further comprises a plurality of substantially horizontal pylon links circumferentially disposed around the pylon assembly; and
 wherein the at least one substantially vertical pylon link further comprises a plurality of substantially vertical pylon links circumferentially disposed around the pylon assembly. 
 
     
     
         13 . The vibration isolation system as recited in  claim 9  wherein the plurality of pylon links further comprise first and second pylon links each oriented along a first axis and a second axis, respectively; and
 wherein the first and second axes are non-parallel and converge at a focal point. 
 
     
     
         14 . The vibration isolation system as recited in  claim 13  wherein the first and second pylon links form a converging pair of pylon links; and
 wherein the plurality of pylon links further comprise a plurality of converging pairs of pylon links circumferentially disposed around the pylon assembly. 
 
     
     
         15 . The vibration isolation system as recited in  claim 9  wherein the plurality of pylon links further comprise at least one angled pylon link. 
     
     
         16 . The vibration isolation system as recited in  claim 1  wherein the at least one pylon link further comprises a torque restraint and fore/aft vibration isolation subsystem. 
     
     
         17 . The vibration isolation system as recited in  claim 1  further comprising:
 one or more active force generators adjacent to the pylon assembly, the one or more active force generators operable to produce a force to counteract the vibration of the pylon assembly, thereby reducing vibration of the advancing blade concept rotorcraft. 
 
     
     
         18 . An advancing blade concept rotorcraft comprising:
 an airframe;   a pylon assembly subject to vibration; and   at least one pylon link having first and second ends, the first end coupled to the pylon assembly and the second end coupled to the airframe;   wherein the at least one pylon link further comprises a vibration isolator such that the vibration isolator is interposed between the pylon assembly and the airframe, the vibration isolator operable to reduce transmission of the pylon assembly vibration to the airframe.   
     
     
         19 . The advancing blade concept rotorcraft as recited in  claim 18  wherein the pylon assembly further comprises a dual rotor system having coaxially disposed top and bottom rotor assemblies that counter rotate relative to one another. 
     
     
         20 . The advancing blade concept rotorcraft as recited in  claim 18  wherein the advancing blade concept rotorcraft further comprises a compound helicopter including a pusher propeller operable to propel the compound helicopter in a forward direction.