Low-speed tests of a model simulating the phenomenon of control-surface buzz Page: 2 of 18
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3 1176 01327 9444
NACA RM LSOF1, UNCLASSIFIE
NATIONAL ADVISORY CO MITTEE FOR AERONAUTICS
LOW-SPEED. TESTS OF A MODEL SIMULATING THE PHENOMENON
OF CONTROL-SURFACE BUZZ
By William H. Phillips and James J. Adams
Low-speed tests have been made of an airfoil model with a freely
hinged flap attached to spoilers which passed through slots in the air-
foil ahead of the hinge line. The spoilers were intended to simulate
the action of shock waves in producing flow separation. When the model
was fitted with spoilers which had an initial projection of 1.7 percent
chord at zero flap deflection, a continuous oscillation of the flap of
about 14 amplitude occurred under certain conditions. This oscillation
was similar in nature to control-surface buzz. Results of tests with
other spoiler arrangements are also presented.
The tests indicate that buzz is not caused simply by buffeting of a
flap by separated flow. Instead, it is an oscillation involving
coupling between the flap motion and the shock-wave-separation pattern.
The occurrence of an oscillation similar to buzz with no associated com-
pressibility effects indicates that flow separation may be an important
factor in the conditions which produce control-surface buzz at transonic
Previous experimental studies of control-surface buzz at transonic
speeds have shown that these oscillations may occur when only one degree
of freedom, that of control-surface rotation about the hinge line, is
involved. The tendency for an oscillation to cccur may be attributed to
lag in the development of hinge moments when the control surface is
oscillating. (See reference i.) This lag has been ascribed, by previous
investigators, to the effects of flow separation caused by shock waves
at transonic speeds and to the time required fcr pressure impulses to be
transmitted upstream from the flap against the air stream moving at
near-sonic velocity. The time required for the transmission of these
UNCLAS :; cr
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Phillips, William H. & Adams, James J. Low-speed tests of a model simulating the phenomenon of control-surface buzz, report, August 16, 1950; (digital.library.unt.edu/ark:/67531/metadc59818/m1/2/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.