Low-speed tests of a model simulating the phenomenon of control-surface buzz Page: 4 of 18
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NACA RM L50F19
APPARATUS AND TESTS
A drawing of the model used is given in figure 1, and a photograph
of the model is given as figure 2. The model, which was constructed of
mahogany, had an NACA 65-009 airfoil section, a span of 9 inches, and a
chord of 6 inches. This airfoil was mounted as a semispan model simu-
lating a wing of aspect ratio 3. The full-span radius-nose flap was .
hinged at the 75-percent-chord line. Arms attached to the flap carried
the spoilers which moved into the air stream when the flap was deflected;
these arms also carried lead weights which were used for mass balancing
the flap. The moment of inertia of the flap, spoilers, and lead weights
was approximately 6.0 x 10-6 slug-feet squared. The spoilers were
located at 66 percent chord and were made as thin as practicable with
sharpened edges in order to reduce to a minimum hinge moments on the
spoilers themselves. The spoilers passed through slots in the airfoil
with small clearance and were rigidly attached to the flap. The stops
on the spoilers limited the flap deflections to 14. The hinges con-
sisted of thin strips of spring steel which crossed at the hinge line;
this type of hinge held the flap rigid in translation while the flexi-
bility of the springs allowed rotation with a negligible amount of
The restoring and friction forces provided by the flap hinges are
illustrated in figure 3 by a record taken of the motion of the flap at
zero airspeed. The restoring force provided by the flap hinges, which
was measured to be 0.01.5 foot-pound per radian, was small in comparison
with the aerodynamic hinge moments acting in flight as can be seen by
comparing the period of the oscillation of figure 3 with those from the
flight records. The friction was very small as shown by the small
damping of the oscillations.
Three different combinations of spoilers and model were used. The
first tests were run with 0.4-inch-wide spoilers which were flush with
the surface of the airfoil when in the neutral position. For the
second tests, the spoilers were enlarged to 0.6-inch width so that they
extended into the air stream 1.7 percent chord when in the neutral
position. A plot of spoiler projection against flap deflection for
these two configurations is given in figure 4. The final test was made
with these large spoilers removed from the flap arms and fixed to the
airfoil so that they would not oscillate with the flap, but would remain
in the neutral position. Whenever the spoilers were changed, weights
were added or subtracted as necessary to maintain mass balance.
The model was mounted on a wing-flow panel of an F-51D airplane.
This panel is ordinarily used for testing in the transonic speed range,
but in this case it was used only to obtain a turbulence-free air stream
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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/m1/4/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.