Reduction of wave drag of wing-body combinations at supersonic speeds through body distortions Page: 4 of 10
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NACA RM A56B10
This difference between theory and experiment is due to the fact that
linear theory predicts too large a value for the wave drag of a wing
with sonic leading edge. This means that the body shapes obtained are
not the best possible for reducing the drag. If a better wing-alone
theory were available for wings with sonic leading edge, a body shape
that would give greater experimental drag reduction could be obtained.
In the upper right of figure 4, theory predicts a large drag reduction
for the nonaxisymmetric distortion of B3. Actually the drag is increased.
Liquid-film pictures showed that this increase is not due to flow separa-
tion. Instead it is a result of the large indentation in body B3 which
violates the quasi-cylindrical restriction of the theory. If this body
is made more quasi-cylindrical by arbitrarily reducing the nonaxisymmetric
distortion by one-half to obtain B4, drag reduction in addition to that
due to the axisymmetric distortion is obtained - as shown in the lower
left part of the figure. The last part of figure 4 shows that the total
effect of both types of distortion (B4 - Bl) is to provide about 35 counts
of drag reduction for all aspect ratios.
Figure 5 shows the effect of Mach number on drag reduction. As in
figure 4, the quantity ANCD is compared for each of the distortions.
The upper left part of the figure shows the effect of the axisymmetric
distortion of B2. The upper right part is for the nonaxisymmetric dis-
tortion of B4. The lower part is for the combined effect of these two
distortions. This figure supports the statement made for figure 4 that
the difference between theory and experiment is due to the sonic leading
edge of the wing. As the Mach number is increased from the value at which
the leading edge is sonic (M = ), theory and experiment come into good
agreement. Figure 5 also shows that the nonaxisymmetric distortion is
the most effective for maintaining drag reduction at other than the design
Mach number. The axisymmetric distortion slightly increases the drag at
M = 1.75. At.this same Mach number the nonaxisymmetric distortion still
provides about 10 counts of drag reduction. The loss of drag reduction
as the Mach number is changed from its design value is primarily due to
.the movement of the Mach wave across the wing surface. The importance of
this effect increases as the aspect ratio increases. This means that the
Mach number range over which drag reduction is maintained will increase
as the aspect ratio is decreased. For example, theory shows that the
wing with aspect ratio of 1.33 maintains a drag reduction up to M = 1.95,
compared with M = 1.8 for the wing with aspect ratio of 2.66.
The question arises as to how the supersonic area rule compares with
these linear theories when applied to nonslender configurations. In order
to compare the body shapes, the area rule and the quasi-cylindrical theory
were applied to a wing with sonic leading edge and an aspect ratio of 1.33.
The results are shown in figure 6. As might be expected, the body shapes
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Pitts, William C. Reduction of wave drag of wing-body combinations at supersonic speeds through body distortions, report, April 13, 1956; (digital.library.unt.edu/ark:/67531/metadc62821/m1/4/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.