DESTRUCTIVE-INTERFERENCE MUFFLERS FOR UAW ENGINE NOISE SUPPRESSION

STATE-OF-THE-ART UAVS HAVE REDUCED COVERT CAPABILITY AND SURVIVABILITY DUE THEIR HIGH ENGINE NOISE SIGNATURES. IN ORDER TO IMPROVE THEIR EFFECTIVENESS IN COVERT OPERATIONS IT IS ESSENTIAL THAT THEIR NOISESIGNATURE BE REDUCED TO BELOW 60 DB AT 1000 FEET FOR THE ENTIRE RANGE OF THEIR ENGINE OPERATION WHILE SIMULTANEOUSLY MAINTAINING THE POWER LOSS OF THE ENGINE TO LESS THAN 2 PERCENT. CONVENTIONAL MUFFLERS CANNOT ACHIEVE THESE REQUIREMENTS. A NEW CONCEPT BASED ON DESTRUCTIVE INTERFERENCE IS PROPOSED TO MEET THESE OBJECTIVES. IN THIS METHOD,NOISE REDUCTION IS ACHIEVED BY FIRST PROVIDING THE SOUND FROM THE NOISY SOURCE INTO TWO PARTS AND THEN LATER RECOMBINING THE PARTS WITHTHE APPROPRIATE PHASE RELATIONSHIP. THE ENGINE NOISE IS FIRST REDUCED BY A CONVENTIONAL MUFFLER TO A MODERATE LEVEL. FURTHER REDUCTIONIS THEN ACHIEVED BY COMBINING DISTRUCTIVELY THE RESIDUAL NOISE (AFTER THE CONVENTIONAL MUFFLER) WITH A PORTION OF THE PRIMARY NOISE SOURCE USING A PHASE-SHIFTOR. THE PHASE I EFFORT IS AIMED AT DEVELOPING THE THEORETICAL BASIS OF THIS NEW CONCEPT. THE THEORETICAL MODELS DEVELOPED WILL THEN BE USED TO DESIGN MUFFLERS CAPABLE OF MEETING THE REQUIREMENTS.