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National Advisory Committee for Aeronautics, Technical Notes - The Effects of Reynolds Number on the Application of NACA 16 Series Airfoil Characteristics to Propeller Design

An analysis has been made of airfoil data taken on several NACA
l6-series propeller airfoils from tests of 5—inch—chord models in the
Langley 2h—inch high—speed tunnel and lB—inch—chord models in the
Langley 8-foot high-speed tunnel.

This analysis has shown that the combined effects of Reynolds num-
ber changes and variations in airfoil Characteristics resulting.from
differences in models and tunnels are such that, when 5-inch-chord and
lQ-inch-chord data are applied to full-scale propeller design at or near
the design condition, differences of less than 1 percent in efficiency
are involved.

The design of present-day propellers is usually based upon data
obtained under conditions of scale which differ from those of operation.
‘These propellers are made up to a great degree of high-speed airfoil
sections for which data are obtained from tests of models of 2- to
5—inch chord. In addition, most of the tests of model propellers using
NACA l6-series airfoil sections have been conducted on blades of this
same width. The question therefore has arisen as to the validity of
applying these test data directly to larger scale designs.

In order to provide at least a qualitative answer to these questions,
an analysis has been made of some data available_on several NACA l6-series
airfoils of both 5— and 12-inch chord. A comparison of data from 5- and
12-inch-chord airfoils has additional significance because a 12—inch chord
is representative of blade widths commonly used on full-scale propellers.

The tests were made in the Langley 8-foot high-speed tunnel and in
the Langley 2h.1nch high-speed tunnel. At the time of,these tests the
Langley 8—foot high-Speed tunnel was a closed-throat single-return tunnel
and the speed was continuously controllable up to a Mach number of approxi-
mately 0.70. The Langley 2h-inch high—speed tunnel was a nonreturn u
induction type of tunnel with the speed continuously controllable to a
Mach number of approximately 0.80 for'a 5-inch, l5-percent-thick air-
foil. Both tunnels have degrees of turbulencé‘which are small though
slightly higher than that of free air. In both tunnels the models
completely spanned the jet; thus, the results are essentially two—
dimensional.