An Investigation of Hydrofoils in the NACA Tank 1: Effect of Dihedral and Depth of Submersion Page: 6 of 36
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attack, eliminating any:change .in depth as..the angle of
attack was shifted; Improved spring and. da.ehpot units
.were constructed also.. . .
. ..The appembly .of hy.drofoil. and... supporting strutss is
" bolted to ai rigi.d floating. frame in. wbich. th.rec. i.s provi-
sion for, co.nt.tnuously varying the angle of. a.tta.ckand the
depth-of.., the..hydrofoil .within a wide range... This-;" f.loating
frame isn suspended .by..linkages from two'hbeavy cantilever
springs, the deflections. of which. are.mea-su.red, .by.dial
7 gag.es, ...Drag force-s are balanced.by a combination of dead
weightp and. spring restraint, the- spring boeing- that of the
regular .towing dynamometer..as describ:ed:.in reference 2.
.Gouaterbalancesa ar.e provided to minimise the effect of ver-
tical and horizontal accelerations. .Guide rollers restrain
the floating frame against side motion.
Thea.force. measurements were made at: constant speed,
angle of attack, and.depth.of.Submer.sion. .The range of
speeds in most ca:se.s extended well beyond the speed at
which cavitation started.. At. low angles.of attack, :the
range of spe.eds..extended to the:maximum oih'sidered. practi-
cable with -the apparatus s .. The depth: ranged. from 5 chords
' below the surface .(mea.suared.from the. qua:rt.er- chord point
of the center. sec,tbn) to..partial- submer.s:ib.ns with half or
..more of th.e hydrofoil .area out of-.the-water.,.. As the angle
of attack: was: changed, the. depthof the. quarter.-,chb.rd point
at the center section was held constant. There: is.,.then a
slight error in referring to the depths of tips as constant.
This error is les....thsn the.: systematic errors involved in
measuring the depth. The angle of. attack was varied from
-40 to 120 for most of the tests but was varied over a
..smaller .range. for i.test...at partial. submers.io.ns The .speed
Sat.. which cavitatio.n first-.:appear-ed on the nppe.r surface at
each angle of attack was noted.
The.-snpporting .t.rut.s wre towee.d al.one at: different
dep.ths. and the .resulting -teasurement; of-.drag: were.. sub
t:r.acted from the., measurements. of drag obtained with- com-
.: .pl-ete - assemblies of struts and-. hyd.r.ofpils-.. The. lift
:tares-: of the strut.a:alonek measured in .the'.. same. manner,
proved to.be negli'gible..for all conditions included in
Sthe text. The drag .t-ares:of the struts (f.ig.. 3) were
dd-ducted to. facil:tate.. use, of the dat:a indes igning.
.. .. . . . .., . , . ., ..,.,& . . . , .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/m1/6/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.