Tests of Airfoils Designed to Delay the Compressibility Burble

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Development of airfoil sections suitable for high-speed applications has generally been difficult because little was known of the flow phenomenon that occurs at high speeds. A definite critical speed has been found at which serious detrimental flow changes occur that lead to serious losses in lift and large increases in drag. This flow phenomenon, called the compressibility burble, was originally a propeller problem, but with the development of higher speed aircraft serious consideration must be given to other parts of the airplane. Fundamental investigations of high-speed airflow phenomenon have provided new information. An important conclusion of this work has been ... continued below

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Stack, John June 1, 1939.

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  • Main Title: Tests of Airfoils Designed to Delay the Compressibility Burble
  • Series Title: NACA Special Reports

Description

Development of airfoil sections suitable for high-speed applications has generally been difficult because little was known of the flow phenomenon that occurs at high speeds. A definite critical speed has been found at which serious detrimental flow changes occur that lead to serious losses in lift and large increases in drag. This flow phenomenon, called the compressibility burble, was originally a propeller problem, but with the development of higher speed aircraft serious consideration must be given to other parts of the airplane. Fundamental investigations of high-speed airflow phenomenon have provided new information. An important conclusion of this work has been the determination of the critical speed, that is, the speed at which the compressibility burble occurs. The critical speed was shown to be the translational velocity at which the sum of the translational velocity and the maximum local induced velocity at the surface of the airfoil or other body equals the local speed of sound. Obviously then higher critical speeds can be attained through the development of airfoils that have minimum induced velocity for any given value of the lift coefficient. Presumably, the highest critical speed will be attained by an airfoil that has uniform chordwise distribution of induced velocity or, in other words, a flat pressure distribution curve. The ideal airfoil for any given high-speed application is, then, that form which at its operating lift coefficient has uniform chordwise distribution of induced velocity. Accordingly, an analytical search for such airfoil forms has been conducted and these forms are now being investigated experimentally in the 23-inch high-speed wind tunnel. The first airfoils investigated showed marked improvement over those forms already available, not only as to critical speed buy also the drag at low speeds is decreased considerably. Because of the immediate marked improvement, it was considered desirable to extend the thickness and lift coefficient ranges for which the original forms had been designed before further extending the investigation.

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  • URL: http://hdl.handle.net/2060/20090015112 External Link
  • Report No.: NACA-SR-118
  • Center for AeroSpace Information Number: 20090015112
  • Archival Resource Key: ark:/67531/metadc65121

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National Advisory Committee for Aeronautics Collection

The National Advisory Committee for Aeronautics (NACA) was a U.S. federal agency founded on March 3, 1915 to undertake, promote, and institutionalize aeronautical research. On October 1, 1958 the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and Space Administration (NASA).

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This selection of materials from the Technical Report Archive and Image Library (TRAIL) includes hard-to-find reports published by various government agencies. The technical publications contain reports, images, and technical descriptions of research performed for U.S. government agencies. Topics range from mining, desalination, and radiation to broader physics, biology, and chemistry studies. Some reports include maps, foldouts, blueprints, and other oversize materials.

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Creation Date

  • June 1, 1939

Added to The UNT Digital Library

  • Nov. 17, 2011, 5:13 p.m.

Description Last Updated

  • Nov. 30, 2016, 12:48 p.m.

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Stack, John. Tests of Airfoils Designed to Delay the Compressibility Burble, report, June 1, 1939; (digital.library.unt.edu/ark:/67531/metadc65121/: accessed September 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.