Flight Measurements of the Vibratory Bending and Torsion Stress of a Supersonic-Type Propeller for Flight Mach Numbers Up to 0.95 Page: 4 of 23
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NACA RM L56D20a
EQUIPMENT
The propeller was a three-blade configuration of 7.2-foot diameter,
designed for a forward Mach number of 0.95, advance ratio 2.2, and power
coefficient of 0.26. The blades are made of solid steel (SAE 4340)
having an ultimate tensile strength of 180,000 pounds per square inch.
The blade is composed of NACA 16-series symmetrical airfoil sections,
and the plan form is tapered from an 11.1-inch chord at the spinner
surface to an 8.4-inch chord at the tip, while thickness varies from
4 percent to 2 percent of the chord. The blade-form curves are shown in
figure 1.
The propeller was tested in conjunction with a "spherical" spinner.
(See fig. 2.) The spinner contour is a 17.5-inch radius sphere fairing
into a 600 included-angle conical nose section. This type of spinner,
in which the contour of the blade-spinner juncture is spherical, is used
to obtain a mechanically simple blade-spinner seal and to maintain a
constant juncture geometry under all conditions of operation.
The propeller flight test vehicle is the McDonnel XF-88B airplane
which was modified by the addition of a turboprop engine in the nose.
General specifications of the airplane can be found in reference 4.
The turboprop drives the propeller at 3,500 rpm.
INSTRUMENTATION
Determination of Stress
One of the propeller blades was instrumented with two strain-gage
bridges (fig. 3) for measuring vibratory bending strain and one bridge
for vibratory torsion strain. The gages were located on the blade
center line; bending gages at 37.0 and 39.4 percent radius and the
torsion gage at 78.7 percent radius as noted in table I. The gages
were located so as to bracket the positions of maximum vibratory stress
calculated in reference 5.
Each strain-measurement location consisted of a four-component
strain-gage bridge. Four gages were used to increase sensitivity,
cancel centrifugal strains, and cancel temperature effects. The out-
put of the strain-gage bridges was recorded on a Consolidated oscillo-
graph. The galvanometers used to record bending strain had a natural
frequency of 150 cps; the natural frequency for the torsion gage was
200 cps.3
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O'Bryan, Thomas C. Flight Measurements of the Vibratory Bending and Torsion Stress of a Supersonic-Type Propeller for Flight Mach Numbers Up to 0.95, report, July 11, 1956; (https://digital.library.unt.edu/ark:/67531/metadc62513/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.