INDUCED BY A PROPELLER WAKE

THE ADVANCED TURBOPROP PROPULSION SYSTEM OFFERS POSSIBILITY OF POVIDING HIGH SUBSONIC FLIGHT SPEEDS WITH FUEL SAVINGS OF15 PERCENT COMPARED WITH TURBOFAN ENGINES. PASSENGER ACCEPTANCE OF THESE TURBOPROPS HOWEVER REQUIRES THAT, INTERIOR NOISE LEVELS BE COMPARABLE WITH CURRENT TURBOFAN POWERED AIRCRAFT. MUCH OF THE ACOUSTIC ENERGY OF PROPELLER DRIVEN AIRCRAFT IS CONCENTRATED IN NARROWBAND TONALS AT AT MULTIPLES OF THE FUNDEMENTALS BLADE PASSING FREQUENCY. THIS ACOUSTIC ENERGY CAN PROPAGATE TO THE INTERIOR VIA BOTH AIRBORNE AND STRUCTURE BORNE PATHS, THE LATTER PATH BEING THE SUBJECT OF THIS STUDY. A PRELIMINARY ESTIMATE INDICATES THAT THE LEVEL OF THE INTERIOR SOUND FIELD RESULTING FROM THE UNSTEADY PROPELLER WAKE ACTING ON THE WING IS LIKELY TO EXCEED THE GOAL FOR INTERIOR NOISE. IN THIS STUDY A NEW ANALYTICAL MODEL INCLUDING THE AERODYNAMIC LOADING ON THE WING, THE WING AND FUSELAGE STRUCTURES, AND THE INTERIOR NOISE FIELD IS DEVELOPED. THIS MODEL IS USED TO OBTAIN ESTIMATES OF THE INTERIOR NOISE FIELD AND TO EXAMINE PARAMETRICALLY MEANS TO REDUCE THE STRUCTURE BORNE CONTRIBUTION TO THE INTERIOR NOISE FIELD.