tailieunhanh - Thiết kế kỹ thuật máy bay chiến đấu Episode 2 Part 5

Tham khảo tài liệu 'thiết kế kỹ thuật máy bay chiến đấu episode 2 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 320 THE DESIGN OF THE AEROPLANE two light aeroplane projects from a French source ref. which were designed for quietness - one uses the rear fuselage and tail surfaces the other a ducted fan. Fig. shows some propeller developments. In spite of claims for the quietness of ducted fans there is some evidence that a free propeller fitted to a full-scale model in a wind-tunnel may be quieter than a shrouded propeller under certain circumstances ref. . Results showed the propeller to generate 97 dB A as against 102 dB A from the shrouded unit for the same thrust. One should beware of results and claims of this kind regardless of which unit is being supported by them. Comparability depends upon design features and the stations around the aircraft at which measurements are made. It may be that shrouded propellers and ducted fans emit narrow lobes of intense noise in certain directions the duct acting rather like a megaphone or loud-hailer so that the noise energy is directed. Certainly the noise pattern of a shrouded or ducted unit is very different from that of a free propeller. British and American noise requirements are to be found in refs. and . References Pratt Whitney Aircraft May 1976 The Aircraft Engine and its Operation. United Aircraft Corporation East Hartford Conn. Jan. 1949 Aircraft Powerplant Handbook. CAA Technical Manual No 107 Experimental Aircraft Association EAA Hales Corners Wisconsin. Nelson J. L. 1974 Modern Lightplane Engines. Modern Aircraft Series Sports Car Press New York. Federal Aviation Administration Nov. 1970 Wet Air . Aviation News. Lycoming Avco Corporation Aug. 1960 Report no. 2268 1 Horsepower Correction Factors and Operating Techniques for Engine Development and Calibration. Experimental Aircraft Association Oct. 1979 A Year of Energy and Ultralights . Sport Aviation. Irving F. G. and Morgan D. 1974 The Feasibility of an Aircraft Propelled by Solar Engergy Al A A Paper no. 74-1042. .

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