Collection of zero-lift drag data on bodies of revolution from free-flight investigations Page: 4 of 374
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NACA TN 4201
tracked by an NACA modified SCR-584 position radar tracking unit, the
data of which were used to obtain the space-position time records used
in the data reduction. In general, the rocket models were of a fair
size: 5 to 8 inches in diameter and up to 12 feet in length. The data
were obtained with the models at all altitudes up to over 50,000 feet and
Mach numbers over 4. A few carried telemetering equipment and from these
the total drag was also obtained from decelerometers and the base drag
from pressure cells.
The second technique, the helium-gun test, was the launching of
small models (roughly 2 inches in diameter and 12 inches long) from a
helium gun. The helium gun used to launch these models was a 24-foot
smooth-bore barrel 6 inches in diameter attached by valves to a
100-cubic-foot tank of helium under a pressure of 200 pounds per square
inch absolute. The models were ejected at Mach numbers up to 1.4. The
space time histories of these models were calculated from the velocity-
time data, and the data were reduced as before. A satisfactory check
of the flight-path calculation method was made by tracking several models
with the SCR-584 unit. The models were fired at an angle of 200 to the
horizontal and never rose over an altitude of 2,000 feet.
Inasmuch as the tests have been made over a period of several years
with continually varying techniques, it is difficult to assign a general
figure for their accuracy. The velocimeter record is accurate to within
0.2 percent, and the derived accelerations, although the result of a
short-time averaging process, are accurate to within 1 percent except in
the region of the drag rise where it is possible for abrupt changes to
be somewhat softened by the averaging process.
One approach to a value of accuracy is the comparison of the drag
of identical models, since all the variable factors, inaccuracies in body
ordinates, velocity measurement, atmospheric conditions, wind velocity,
and data reduction are included.
From the variations shown by the models of configurations 8, 22, 27
to 30, 75 to 77, 106 to 109, 128, 139, and 151 reasonable limits of error
for CD and Mach number appear to be
ACD = +0.01
AM = 0.01
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Stoney, William E., Jr. Collection of zero-lift drag data on bodies of revolution from free-flight investigations, report, September 3, 1957; (https://digital.library.unt.edu/ark:/67531/metadc56974/m1/4/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.