ADAPTIVELY TUNED VIBRATION ABSORBER FOR REDUCTION OF AIRCRAFT CABIN NOISE

An aircraft engine is attached to the fuselage by a mounting structure that has a vibration absorbing system which includes first and second sensors to produce signals indicating vibration along two orthogonal axes. A third sensor, such as an accelerometer, is coupled to the mounting structure for sensing vibration of the engine. A tachometer circuit, connected to the third sensor, produces first and second speed signals that indicate the speeds of two rotating spools in the engine. Four vibration absorbers are attached to the engine mounting structure and controllers are provided to dynamically tune the resonant frequency of each vibration absorber in response to a unique combination of one of the two vibration signals and one of the two speed signals. Thus the vibration absorbers reduce the engine spool vibrations that are transmitted through the mounting structure along the two orthogonal axes. The resonant frequency of each absorber is altered to track variation of the vibrations due to changes in engine speed.