Collection of zero-lift drag data on bodies of revolution from free-flight investigations Page: 10 of 374
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NACA TN 4201
a very large percentage of the total drag for boattailed bodies. Some
published wind-tunnel data on the base drag of conical afterbodies sug-
gest the empirical expression
CD,base = CD,cylinder base rb se
Care must be taken in applying this equation at subsonic Mach numbers
since it does not account for the possibility of negative base drags
which can exist (ref. 24).
Two-dimensional base pressures.- Figure 3 also presents base-
pressure coefficients for a two-dimensional base from references 21 and
25. The data represent the base pressures behind slab wings. They are
presented herein as an estimate of the pressures behind a rearward
facing step on a body of revolution.
Pressures on a Forward Facing Step
Figure 23 presents the pressure coefficients required to separate
the turbulent boundary layer in front of a step of several times the
boundary-layer thickness. (See ref. 26.) It appears from page 52 of
reference 18 that a pressure coefficient of Cp = 0.41 is valid at sub-
sonic speeds as well as Mach 1. Again these essentially two-dimensional
values are presented as estimates for the pressures ahead of forward
facing steps on bodies of revolution.
Fin Pressure Drag
Figure 5 presents the pressure-drag coefficients based on the
exposed plan-form area of the fin (note this is one-half the value of
Sf/A given on model sheets) for most of the fins used in this report.
Extreme accuracy has not been striven for or obtained, since in most
cases the fin pressure drag is such a small part of the total drag that
a 50-percent error in fin drag is of the order of the test accuracy.
The pressure drag of fin type A , which is used by the
majority of the models, was measured by means of special helium-gun
models. The drag of fin type B d was measured by special rocket
models, the data for which are presented in reference 27. The super-
sonic pressure drag thus obtained is so similar to that measured on10
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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/m1/10/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.