The effects of hub drag, solidity, dual rotation, and number of blades upon the efficiency of high-pitch propellers Page: 4 of 52
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3
All of the models were 36 inches in diameter. Attention is
called to the muniformity of size because previously tested six-blade
models have been 37 inches in diameter; this irregularity was
eliminated by reconstruction of the six-way hub, In all but two
special models (used to investigate the effect of number of blades
with fixed solidity) the blade width was that defined by the b/D
curve designated E in figure 6; at corresponding radii the chords
of the wider blades, E and E" were, respectively, 4/3 and 3/2
those of the E blades. All blade-angle values refer to the sec-
tion at 0.75R.
Spinners. - Spinners of two sizes were tested; their forms are
illustrated by figures 1 to 5. The forward sections were halves of
ellipsoids of revolution and the rear sections were circular cylinders.
The half-ellipsoids had axial lengths equal to their maximum diameters
which were 4.25 inches (0.118D) and 10.00 inches (0.278D). The planes
of rotation of single propellrsa and those of the forward members of
tandem combinations were located 3.625 inches (0,101D) aft of the
bases of the ellipsoidal noses. The concentric dynamomotr shrouds
slightly overlapped the spinners, cleared them radially by 0.05 inch
and terminated 2.2 inches aft of the plane of rotation of the single
propellers and 1.4 inches aft of the plane of the roar propeller when
two were mounted in tandem.
The small spinners had the minimum diameter which would permit
enclosure of the hubs; they wore pierced with holes just large enough
to admit the circular blade shanks and the butts of the blades
touched the spinners when set at largo angles. (See fig. 4.) The
large spinners enclosed considerable portions of the blades and the
diameter of the circular apertures was therefore slightly greater than
the blade chord. All of the spiimers had internal diaphragms which
prevented centri-'ugal pumping action, that is, drawing air from the
base of the spinner and discharging it through the blade apertures.
To provide strictly comparable blade-root conditions, the apertures
in the large spinners wore closed with cellophane tape and when small
spinners were used the irregularities at the roots of the blades were
"illed with plasticine, The torms "plain" and fillede" blade roots
are used to distinguish the conditions illustrated by figures 4 and
5, respectively.
Tests. - To determine the effects of spinner diameter, pre-
liminary tests were made with six-blade model propellers which were
fitted successively with the large and small spinners. In the case
of the small one, tests were made at blade angles of 350, 450, 55o0,
and 650 with plain blade roots and at 450 and 850 with filleted roots.
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Reid, Elliott G. The effects of hub drag, solidity, dual rotation, and number of blades upon the efficiency of high-pitch propellers, report, October 1941; (https://digital.library.unt.edu/ark:/67531/metadc62144/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.