QUEST FOR QUIETNESS

This article describes a development aimed at reducing the noise produced by propellers used in "general aviation" light aircraft, which, although considerably less noisy than large civil transports, are much more numerous and operate from airfields closer to centers of population, thus affecting more people, and are being subject to noise-abatement regulations. After considering the shortcomings of small-diameter fast-turning propellers and large-diameter slow-turning propellers, both of which could reduce noise, the design described here (the Dowty Rotol) is a low-pressure-ratio ducted fan called a Ducted Propulsor. Basically this consists of a small diameter multiblade rotor and a set of stator blades surrounded by a duct. The principle of operation is similar to that of the big high by-pass ratio turbofans where the angular momentum or swirl imparted to the air by the rotor blades is converted into useful thrust by means of a row of flow-straighteners or stators. In this way the losses associated with a small propeller are avoided, and furthermore a larger static thrust is obtained than that generated by a comparable propeller, owing to a substantinal portion of the thrust being carried on the duct inlet lip. Compared with a conventional propeller (87 dBA flyover noise), the Ducted Propulsor produces 65 dBA flyover noise. Used with the usual horizontally opposed piston engine, the cooling air enters the engine nacelle at a pressure above ambient. After being heated by the engine it still has sufficient residual pressure to be efficiently discharged through a nozzle at the rear of the nacelle and produce a small but useful thrust.

  • Corporate Authors:

    Shell Oil Company

    1 Shell Plaza, P.O. Box 2463
    Houston, TX  United States  77001
  • Authors:
    • Kemp, J D
  • Publication Date: 1978

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00195054
  • Record Type: Publication
  • Source Agency: Engineering Index
  • Files: TRIS
  • Created Date: Jul 31 1979 12:00AM