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United States Patent (19) 11 Patent Number: 4,836,469 Wagenfeld 45 Date of Patent: Jun

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United States Patent (19) 11 Patent Number: 4,836,469 Wagenfeld 45 Date of Patent: Jun United States Patent (19) 11 Patent Number: 4,836,469 Wagenfeld 45 Date of Patent: Jun. 6, 1989 (54) SYSTEM FOR REDUCING AIRCRAFT NOISE 4,723,626 2/1988 Carr et al. ........................... 181/213 AND HUSHKT OTHER PUBLICATIONS (75 Inventor: Robert E. Wagenfeld, New York, "Silencing an Executive Jet Aircraft', Noise Control N.Y. Engineering, vol. 5, No. 2, Sep.-Oct. 1975, J. R. Brooks, 73) Assignee: Walsan Partners Limited Partnership, et al. New York, N.Y. "Quieting the JT3D Powered 707", Sound and Vibra (21) Appl. No.: 55,635 tion, vol. 8, No. 2, Feb. 1974, J. Woodall. Primary Examiner-Galen Barefoot (22 Filed: May 29, 1987 Assistant Examiner-Rodney Corl 51) Int. Cl........................ B64D 29/00; B64D 33/04 Attorney, Agent, or Firm-Cooper & Dunham 52) U.S. Cl. ................................... 244/1 N; 181/213; [57] ABSTRACT 181/220; 181/222; 181/296 58) Field of Search ................. 244/1 N, 55; 181/213, A system is provided for existing three-engine jet air 181/220, 222, 296 craft to reduce the noise levels at take-off and landing in order to meet governmental noise regulations. The (56) References Cited system is particularly suitable for 727-200 aircraft hav U.S. PATENT DOCUMENTS ing three JT8D engines. A hush kit is formed of the 3,002,341 10/1961 Muzzy et al. ....................... 181/220 modified components for installation in existing air 3,237,891 3/1966 Wotton ................................. 244/55 planes. 4,379,191 4/1983 Beggs et al. .......................... 52/806 4,456,204 6/1984 Hapke ................................... 244/55 4 Claims, 4 Drawing Sheets U.S. Patent Jun. 6, 1989 Sheet 1 of 4 4,836,469 U.S. Patent Jun. 6, 1989 Sheet 2 of 4 4,836,469 U.S. Patent Jun. 6, 1989 Sheet 3 of 4 4,836,469 U.S. Patent Jun. 6, 1989 Sheet 4 of 4 4,836,469 4,836,469 1. 2 ments. Those regulations affect the usefulness and value SYSTEM FOR REDUCING AIRCRAFT NOISE AND of a much greater number of aircraft, including particu HUSH KIT larly Boeing 727-200 aircraft having Pratt & Whitney JT8D engines. About 1,700 of those airplanes currently BACKGROUND OF THE INVENTION are in operation. Heretofore, no one has successfully Prior to 1969, the aircraft industry paid little concern developed a system and hush kit to extend the useful life to commercial jet aircraft engine noise. In Dec. 1969, of those airplanes. the U.S. Federal Aviation Administration (“FAA') It is a difficult task to make those existing airplanes promulgated specific noise level regulations for aircraft meet the stage 3 noise level requirements. Studies which under authority of public Law 90-411. Existing air 10 have been conducted show that noise radiates from a planes were required to be certificated for compliance low bypass, fan jet engine in several directions. High with Federal Air Regulation No. 36 (“FAR 36'). Simi frequency fan noise radiates both forward though the lar noise standards were prescribed by international air inlet cowl and afterward through the exhaust ducts. civil aviation organizations (for example, "ICAO Low-frequency jet noise generally radiates rearwardly. Annex 16”). Several states and municipalities also estab 15 At low engine thrust, the high-pitch whine of the fan is lished maximum airport noise levels. Thus, it became more pronounced. At high engine thrust, the low-pitch imperative for airframe and engine manufactures and jet rumble is more noticeable. Each of those noise com owners to take noise considerations into account in ponents must be dealt with separately, as well as in designing, building and using jet aircraft. combination. But, making a modification to suppress In the 1970's, The Boeing Co. conducted research to noise may also severely degrade airplane performance, determine how noise levels could be reduced upon the substantially increase final consumption, require longer take-off and landing of its various models of commercial runways for take-offs or landings, mandate lesser pay airplanes. Boeing, of course, was concerned with design loads or otherwise greatly increase costs or require of future airplanes to meet more stringent noise stan operational limitations. dards, although it was also interested in modifications to 25 currently operated aircraft to meet current noise stan SUMMARY OF THE INVENTION dards. With respect to its Model 727 aircraft with pratt & One object of the present invention is to provide a Whitney JT8D engines, Boeing proposed to treat the system which will permit three-engine jet aircraft to nacelles for the jet engines with sound-attenuating ma 30 take-off and land at noise levels which meet FAR 36, terial. Boeing suggested adding the material to the inlet Stage 3, and ICAO Annex 16, Chapter 3, requirements. cowl, on some of the engine ducts and to the tailpipe. It Another object of the invention is to provide a system was suggested that the treatment would reduce high for three-engine jet aircraft which permits operation at frequency fan noise, but would have virtually no effect a quiet level conforming with more stringent govern on low-frequency jet rumble during take-off. Other 35 mental airplane noise regulations, while maintaining modifications attempted by Boeing were reported to cost-effective performance and providing at least no severely degrade airplane performance. greater fuel consumption. With respect to its Model 737 aircraft with Pratt & Still another object of the invention is to provide a Whitney JT8D engines, Boeing proposed similar sound retrofit or hush kit for existing three-engine jet aircraft attenuating treatment. Boeing further suggested using a which will permit continued operation of airplanes mixer device to mix the air flow from the fan with the which otherwise would not comply with governmental air flow through the engine to reduce the peakjet ve noise regulations and thus could not be flown, at least locity and thus the jet noise from the engine. Boeing on a cost-effective basis. reported its test results in its "Summary In accordance with the system of the present inven 707-727-737-747 Noise and Emission Reduction Activi 45 tion, an airplane is modified so as to comply with FAR ties', April 1980, Document D6-40613-K. 36, Stage 3, and ICAO Annex 16, Chapter 3, noise Thereafter, the major airplane manufacturers and regulations. The system comprises replacement of the others continued substantial research effort toward two existing outboard jet engines with new engines, developing retrofit kits for existing airplanes to attempt including the associated nacelles, thrust reversers, struts p meet FAR 36 noise level requirements. However, it 50 and other structural support. The existing center engine was difficult to develop a kit which would meet FAR is retained, but is fitted with an internal forced air mixer 36, Stage 2, requirements without, at the same time, and acoustically treated nozzle, in lieu of a center en degrading aircraft performance, increasing fuel con gine cascade thrust reverser, which is removed. sumption and unreasonably increasing costs. Although The system is particularly useful in the modification the effective date of the FAR 36 noise requirement was 55 of existing Boeing Model 727-200 aircraft having Pratt extended on several occasions, and the requirement was & Whitney JT8D-7/9/15/17 engines. However, the modified, FAR 36, Stage 2, went into effect on JUN. 1 system also may have applicability to other aircraft and , 1985. Implementation of that regulation affected the other jet engines. The components of the system may be usefulness and value of many existing aircraft, including combined in a hush kit for retrofitting existing airplanes. particularly Douglas DC-8 airplanes with Pratt & Whit ney JT3D engines. Aeronautic Development Corp. DESCRIPTION OF THE DRAWINGS Ltd. was successful in devising a quiet nacelle system FIG. 1 is a perspective view of a Boeing 727-200 and hush kit to make those airplanes economically via aircraft as modified in accordance with the system of ble. That system and hush kit is shown in allowed appli the present invention. cation Ser. No. 06/769,141, now U.S. Pat. No. 65 FIG. 2 is a graphic depiction of the reduced noise 4,723,626. level contour achieved by the present invention, as Many municipalities and airports have now adopted compared to the noise level contour of an unmodified the more stringent FAR 36, Stage 3, noise level require aircraft. 4,836,469 3 4. FIG. 3 is a side elevational view of a nacelle for one mesh 46 covers the perforated sheet 44 and forms a outboard engine of the modified aircraft, as compared smooth surface for laminar airflow. The honeycomb to a nacelle of an unmodified aircraft. core cells 40 communicate with the atmosphere FIG. 4 is a cross-sectional elevational view of a modi through the perforated sheet 44 and the woven wire fied outboard nacelle containing a JT8D-217C/219 jet 5 mesh 46. As is known to those skilled in the art, material engine. of this type may be tuned to particular noise frequencies FIG. 5 is a perspective view, partially cut-away of to provide effective acoustic performance. The particu the sound-attenuating material used in the nacelle. lar preferred material also provides aerodynamic FIG. 6 is a perspective view, partially cut-away, of smoothness and structural integrity. The smooth sur the nose dome within the nacelle. 10 face avoids drag, which impedes performance and in FIG. 7 is a cross-sectional elevational view of the creases fuel consumption. The acoustic material gives inlet cowl of the nacelle. linear performance and is a broadband noise absorber. FIG. 8 is an exploded, perspective view of a modified The material is sometimes referred to as a "liner', but in outboard nacelle showing the engine.
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