An Investigation of Hydrofoils in the NACA Tank 1: Effect of Dihedral and Depth of Submersion Page: 3 of 36

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
ADVANCE CONFIDENTIAL REPORT
AN: VES.TIQATION . HYDRQI7O0ILS. N .-T-Z NOA. .TASNK
.. : ... .I:- ,E.lC.T OF DIHEDRAL AND DBP.T.0. .SUBMESI ION
"B....y.. .. .- B ames N. .Benson and Norman:S'. Lr d : ':
.. . ., ... .
SUMMARY
Efforts to employ hydrofoilB:..on seaplanes and surface
boas - have frequently been .hndicapped by the lack of in-
; .forrma.tion on the characteristics of the hyd:ro"foils' when
nea. the surface ,of the water or when breaking the surface.
I. :athe .present teste:a series .bf hydrofoils,- eah supported
by two struts, was towed at various depths ranging from
partial submersions to a depth of.5 chord lengths. results
are presented showing tbheo:sift azdd drag of bydrofoils hav-
ing a chord. of 5 inches a scan: of .30 inches, adri for
'. angles o.f dihdral at Q. :10 20 , and 30 . The tests
S included. speeds up to 95 feet "p-er second and lift forces
up to about 250OQ.pounds.. . The hydzofoils tested :icluded
: : two secti ons, t.he NAQ1'.6 -1 ..fair.foil., sect ion and a section
derived from the 1 509rOby. b&harpening.the leading edge.
.At depths greater than 4 ox 5 chords the pre-sence of
the free water surface appeared not to affect the lift and
drag. As the hydrofoil approached the surface, the lift
and drag decreased and the speed at which cavitation first
appeared on the :hydrofoi1'was increasedd. In the range of
very shallow immersions (less than, say, 1/2 chord) abrupt
changes in lift and drag occurred 'when the flow of water
.over. the upper surface separated from the hydrofoil. For
applications .requiring that the hydrofoil emerge from the
water, the larger angles of dihedral .(20 and 300) appeared
desirable because they produced less abrupt changes in
1 if t and. drag.
Two major effects of seed were noted; ffirsta lim-
itation. of the total hydrofo,il4. loading p.ossible (about 2200
lb/sq. tt for the depths tested) under conditions of com-
plete upper-.urface .cavitation; and second, aloss of lift
at high speeds and low angles of attack, probably due to
l rr cecavitation.f

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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/m1/3/ocr/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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