An Investigation of Hydrofoils in the NACA Tank 1: Effect of Dihedral and Depth of Submersion Page: 5 of 36
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cause a large increase in drag. Consequently it seemed
desirable to employ this section in the "p'resen t 'tests of
hydrofoils with dihedral. Three hydrofoils of this sec-
tion having dihedral angles of 100, 20, :and 830o.were
constructed. In addition, three hydrofoils with the same
.dihedral angles' but with the section modified to give .a
.'.sbarp 'leading..edage were const.ruQted. Sections of these
..hydrofol..s,: normal .to .the chord plane, are -shown in fig-
ure .., :,The NACA-16-509 section hydrofoil with sero di-
he4dral:... .which was used in the previous tosts," was retested
to form .a check, between the two programss, 'All thes6: by-
:. drofoil.had the same projected 'area, that is ,- 30-inch
S an and 5r.-inch chord. They were rectangular. 'in' plan 'torm
,rith -quar.: tips .and were machined' from hard brass' and'
highly polished. . ... .
Each hydrofoil' was supported by twb truta' ~ Each
strut was spaced 8 inches from the center .section of the
hydrofoil. The struts are biconvex in section, approxi-
mately 28 inches long, a nd..t:ape:red toward the hydrofoil.
At the point of attachment to the upper surface of the hy-
drofoil, the struts have a chord of 2.9 inches.and a thick-
ness of 3/8 inch; at the top., the, chord of the strut is 4
-inches. and the. thicknes. is.. 3/4: inch., The'center -lne 'of
th.e strut intersects .the..upper. surface at the half-chord
point... i.th' the. struts. ver.tical,'the angle .of attack of
..the-hydrofoil is 69. .This arrangement (hydrofoil supportedd'
from. its.upper surface....by rather.large struts) is not' ideal
from considerations .of po-ssibl'e interfer~eco eff6c'ts.- This
arrangement, howeverr, &ppears to be. necessary-in appliea4
. tione employing.hydrofoil s to ..lift.- a surface boat 'or a
... . . : TOWING : APPARATUS . . '
.+ A..description of the-NACA tank, towing .carriage, :'nd
the.nethod of measuring carriage speed, is giveii in refer-
pnce,2.. . ' . . y . .
The special dynamometer used in measuring the lift
and drag forces .isashown- diagramrmtically in"figure 2.
It. isX.of-.massive, construction, because-of the' rge forces
.to be. measured, .andis supported by 'the .main'-struet1al
members of'the.ncarriage '-This dtiyambmeter se't-up is "-in
general, the same as that used.fort!heearlier teste'de-
scribed, in reference 1..' Changes were ma-de, however, that
improved the accuracy. of setting :the depth and 'angle of
. . , . ,
o, _ .
. . . , ... , . . . .
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Benson, James M. & Land, Norman S. An Investigation of Hydrofoils in the NACA Tank 1: Effect of Dihedral and Depth of Submersion, report, September 1942; (https://digital.library.unt.edu/ark:/67531/metadc61720/m1/5/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.