Carl J. Wenzinger, Oscar Loeser
naca-tn-326
Oct 1929
This report deals with pressure distribution tests on an airfoil with a conventional trailing edge flap. These tests were conducted in the Atmospheric Wind Tunnel of the National Advisory Committee for Aeronautics. Maximum chord loadings were obtained with the flap displaced downward and with the airfoil at large angles of attack. Greater changes were produced in the normal force and in the center of pressure travel by up-flap than by an equal down-flap displacement.
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http://naca.central.cranfield.ac.uk/reports/1929/naca-tn-326.pdf