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National Advisory Committee for Aeronautics, Technical Notes - Resistance of Streamline Wires

This note contains the resfilts of tests to determine the
resistance of four sizes of streamline wire. The investigation
was conducted in the six—inch wind tunnel of the National Advisory
Committee for Aeronautics. 'The tests were made at various veloc—
ities and it was found that the resistance of streamline wires
was considerably less than that of round Wires of equivalent
strength. Scale effect was also found since, with an increase of
Reynolds Number, a decrease in the resistance coefficient was ob—
tained.

The tests were conducted in the six—inch Open—throat wind
tunnel o? the National Advisory-Committee for Aeronautics at
Langley field, Virginia, to determine the resistance of a series
of streamline wires. Very little information was available from
previous tests on this type of wire. The results of these tests
are compared with those of a streamline wire in the variable
density wind tunnel, and with the curves given by Prandtl and
Bairstow for the resistance of round wires. The sizes of wire
tested were as follows:

d (thickness) 1 (length of cross section)
0.025 in. 0.092 in. (Special size wire)
0.098 0.362
0.138 0.544

0.181 0.754

The last named three sizes correspond to streamline wires in
general use.

The wires were fastened in a square wooden frame which was
attached to the wire balance in the wind tunnel. The number of
wires used depended on the size, since it was necessary to have
a total length of wire which would cause a large enough resist—
ance to move the wire balance. The wires in each frame were
spaced at intervals of five times the thickness of the wire used,
which was considered sufficient to eliminate interference be—
tween them. The wires extended through the air stream in the
horizontal direction, and were spaced in the vertical direction
to use the central four inches of the sixsinch air stream.