Summary of Airfoil Data Page: 76 of 724
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NACA ACR No. L5C05
Although some of these conclusions may be modified when
more systematic data are available, they are believed to
be essentially correct:
1. Airfoil sections permitting extensive laminar
flow, such as the NACA 6- and 7-series sections, result
in substantial reductions in drag at high-speed and
cruising lift coefficients as compared with other
sections if, and only if, the wing surfaces are fair
and smooth.
2. Experience with full-size wings has shown that
extensive laminar flows are obtainable if the surface
finish is as smooth as that provided by sanding in the
chordwise direction with No. 320 carborundum paper and
if the surface is free from small scattered defects and
specks. Satisfactory results are usually obtained if
tbe surface is sufficiently fair to permit a straight-
edge to be rocked smoothly in the chordwise direction
without jarring or clicking.
3. For wings of moderate thickn-ess ratios with
surface conditions corresponding to those obtained with
current construction methods, minimum drag coefficients
of the order of 0.0000 may be expected. The values of
the minimum drag coefficient for such wings depend
primarily on the surface condition rather than on the
airfoil section,
4. Substantial reductions in drag coefficient at
high Reynolds numbers may be obtained by smoothing the
wing surfaces, even if extensive laminar flow is not
obtained.
5. The maximum lift coefficients for moderately
cambered smooth NACA 6-series airfoils with the uniform-
load type of mean line are as high as those for NACA 24-
and 44-series airfoils. The NACA 250-series airfoils
have somewhat higher maximum lift coefficients for thickness
ratios less than 0.20.
6. The maximum lift coefficients of airfoils with
flaps are about the same for moderately thick NACA
6-series sections as for the NACA 23012 section but appear
to be considerably lower for thinner NACA 6-series
sections.CONFIDENTIAL
70
CONFIDE NTIAL
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Stivers, Louis S.; Abbott, Ira H. & von Doenhoff, Albert E. Summary of Airfoil Data, report, March 1945; (https://digital.library.unt.edu/ark:/67531/metadc61319/m1/76/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.