Study of effects of sweep on the flutter of cantilever wings Page: 12 of 25
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REPORT 1014-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
varying the center of gravity is shown in figure 2 (g). In
order to obtain data at zero sweep angle it was necessary,
because of the proximity of flutter speed to wing-divergence
speed, to use three different wings. These zero-sweep-angle
wings, of 8-inch chord and 48-inch length, had an internal
The models were mounted from the top of the tunnel as
cantilever beams with rigid bases (fig. 3). Near the root of
each model two sets of strain gages were fastened, one set for
recording principally bending deformations and the other
set for recording principally torsional deflections.
Determination of model parameters.-Pertinent geometric
and structural properties of the model are given in tables I
to VII. Some parameters of interest are discussed in the
As an indication of the nearness to sonic-flow conditions,
the critical Afach number is listed. This Mach number is
determined by the KArm n-Tsien method for a wing section
normal to the leading edge at zero lift.
The geometric aspect ratio of a wing is here defined as
Semispan2 (1 cos A)'2 A
A-= = - cOS' A-
Plan-form area le c 2
The geometric aspect ratio A, is used in place of the con-
ventional aspect ratio A because the models were only
semispan wings. For sheared swept wings, obtained from a
given unswept wing, the geometric aspect ratio is constant,
whereas for the wings of constant length-chord ratio the
geometric aspect ratio decreases with cos'A as the angle of
sweep is increased.
The weight, center-of-gravity position, and polar moment
of inertia of the models were determined by usual means.
The models were statically loaded at the tip to obtain the
rigidities in torsion and bending GJ and EI.
A parameter occurring in the methods of analysis of this
report is the position of the elastic axis. A "section" elastic
axis located at x., was obtained for wings from each series
of models as follows: The wings were clamped at the root
normal to the leading edge and at a chosen spanwise station
Model 75 74 73 . 72
24ST aluminum alloy slotted /;"
from traih edge of /" spo cing
engfhwise bolso lomintions ,' 94
(e) Swept models having a length-chord ratio of 6.5. Series V.
(f) Models used to investigate the effect of tip shape on the flutter velocity. Series VI
41/6 leod fostened with
Scotch celdose tcoe
91-1, 92-2, - 15
93-, 93-2, .-3......... 30
94-1,94- 2.94-3- - ----- 4. 5
* Chord-8", lead inside balsa.
(g) Models used to determine the effect of center-of-gravity shift on
the flutter velocity of swept wings. Series VII.
Fiounv 3.-Model 12 in the tunnel test section.
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Barmby, J. G.; Cunningham, H. J. & Garrick, I. E. Study of effects of sweep on the flutter of cantilever wings, report, September 9, 1948; (digital.library.unt.edu/ark:/67531/metadc60354/m1/12/: accessed July 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.