Note: Descriptions are shown in the official language in which they were submitted.
CA 02541136 2006-05-12
CONCAVE HELIX IMPELLERS PROPULSION SYSTEM
Technical Field
This proposed invention is intended for, but not limited to, use in the marine
environment.
Background
In previous propeller technology, the blades are attached to a hub at a
predetermined angle
and are often skewed to obtain the overall pitch of the propeller. Blades at
the hub are often
overlapped to reduce the amount of skew required. This is particularly evident
where
additional blades are added to produce higher torque. (The overall area of the
working face
of the blades is reduced and agitation forces are increased.) The overall
working face of the
blades is larger at the hub and decreases towards the blades' tip. Centrifugal
force along the
blade face cause "spillage" at the blade's tip, contributing to cavitation.
The unattached outer
portion of the blades may be rounded or end plates added, to reduce cavitation
and excess
stress. The overall pitch of the blades overcomes the centrifugal forces of
the revolving
blades to produce a forward motion.
Previous concave blade propeller / impeller technology have generally had
their blades
attached to the hub at an angle consistent along the entire blade face. This,
combined with
constant blade width, produce a blade with low tensile strength. At the hub
blades were often
overlapped, due to set rake angles, decreasing usable working face surface and
increasing
agitation.
The impeller and/or propeller blades of the present invention are attached to
a hub at an
angle determined by the mean rake angle to obtain the overall required pitch.
Blades do not
overlap as more blades are added, only the disc area ratio is affected. There
is no "artificial"
skew applied to the blades but rather a "natural" skew is obtained. The
working face of the
blades is larger than any propeller of like disc size, due to the semi-
circular shape and
projected width. The blades are attached to a perimeter cylinder in such a
manner as to
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substantially reduce cavitation and increase overall strength, as the blades
are naturally
skewed and supported at both ends. This support also provides a safety aspect
as there are
no exposed blade tips. The overall pitch of the revolving blades produces a
forward motion.
Accordingly, an important feature of the present invention is to utilize the
previously
underdeveloped, faster moving, outer extremities of a rotating disc. The
forces of cavitation
and agitation are greatly reduced and the overall efficiency and safety
increased.
The concave helix propeller of the present invention is comprised of a
plurality of concave
blades radiating from a hub in a helical fashion and attached to a perimeter
cylinder. The
propeller of the present invention can be driven by any conventional means
such as a centre
shaft or perimeter gearing, chain or belt.
The diameter of the hub is determined by the drive mechanism and the method of
exhaust.
The depth of the hub is consistent with the overall depth of the blades and
perimeter
cylinder. The radial centre of the hub is used to calculate the "arc length
sweep" and thus the
varied pitch of attached blades.
The concave blades are attached to the hub at an angle determined by the depth
of the hub
and the arc length sweep from the radial centre of the hub. The blades radiate
outwardly at
a decreasing rake angle. The width of the blades increase as the rake angle
decreases. The
"mean" rake angle of the blade at the radical centre of the semi-circular
blade determines
the overall blade pitch. (If the desired rake angle at this point is forty-
five degrees, the arc
length sweep would have to equal the propeller's depth.) Where the blades
intersect or blend
into the perimeter cylinder, the rake angle is the smallest, and the blade's
width the largest.
The blades preferably do not overlap at any point but have a natural skew.
The perimeter cylinder is, in essence, an extension of the blades (tying the
blade tips
together into one solid unit). The impeller / propeller is of constant depth
across the hub,
blades and perimeter cylinder. The overall size, therefore, is determined by
available depth
and disc size. The number of blades required depend on the blade's size, it's
disc area ratio
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and designed purpose.
The revolving blades of the propeller / impeller of the present invention move
in a sickle like
manner around the hub, gathering water and pushing it aft. The residual
effects of centrifugal
and centripetal forces are shed along the trailing edge, before the apex of
the blade's curve.
There is no noticeable rotational boundary layer as the blade's junction with
the perimeter slices
the water.
The propeller of the present invention can be mounted on shafts in place of
conventional
propellers or in ducts in places existing impellers. The propeller of the
present invention can be
manufactured in all commonly used methods and a variety of materials,
depending on their
designed purpose. All faces are parallel and require no special consideration
other than beveled
leading edge, feathered trailing edge and such.
The present invention generally provides as follows:
[1] A propeller comprising two or more blades extending radially outwardly
from a hub, each
blade having a continuously concave profile along its axial depth, and
extending helically about
said hub.
[2] A propeller as in [1], including a plurality of said blades regularly
spaced around a said hub.
[3] A propeller as in [2], wherein each said helix extends around sad hub by
360
( x )o, where x is
the number of blades plus disc ratio spacing intervals in a said propeller.
[4] A propeller as in [3], wherein the concave profile of a said blade defines
an
arc that is 180 or less.
[5] A propeller as in [4], wherein the apex of both the leading and trailing
edges are further from
the hug than the radius centre of said edges.
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[6] A propeller as in any one of [1] to [5], wherein said propeller is
provided with a cylindrical
perimeter shroud integrally connected to the outer edges of the blades.
Description of the Drawings
Figure 1 is a schematic diagram of double helix in side view.
Figure 2 is a schematic diagram of a double helix in a top view.
Figure 3 is a schematic diagram of a triple helix in top view.
Figure 4 is a top view of a propeller according to the present invention.
Figure 5 is a top view of a top view of a blade of concave helix impeller
according to the present
invention.
Figure 6 is an angle diagram of a straight helix blade.
Figure 7 is an angle diagram of a concave helix blade of the present
invention.
Figure 8 is a schematic of water flow across a concave helix blade according
to the
present invention.
Figure 1 is a schematic of a double helix in side view. Cords of equal length
spiraled around an
imaginary centre.
Figure 2 is a schematic of a double helix in top view. Cords of equal length
stacked upon each
other and spiraled around an imaginary centre.
Figure 3 is a schematic of a triple helix in top view. As in Figures 1 and 2,
arms of the helix are
of equal length and are evenly spaced along their arcs. They are also spiraled
around an
imaginary centre.
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Figure 4 is a progressive sectional view of a single blade of a concave helix
propeller according
to the present invention with x1 indicating its leading edge. The trailing
edge is represented by
x4 whereas x2 and x3 are intermediary stations.
Figure 5 is a top view of a single blade of a concave helix with a large hub.
The hub's centre is
used to draw three arcs within a common sector. The perimeter arc "x" is the
outer perimeter,
which is in essence the perimeter cylinder. The arc "y" represents the radius
centre of the semi
circles used to plot the concave lines of the impeller. The smaller arc "z"
represents the hub end
of the blade. The depth of the impeller, being constant from hub to perimeter
and the varying
lengths of the arcs, indicate the varying rake angles obtained from this
configuration. This is
further described in Figure 6.
Figure 6 is an angular view of a straight helix blade. The hub section of the
drawing has the
points CT and CB indicated on it. These points represent centre top "CT" and
centre bottom
"CB" of the imaginary centre of the hub. The straight line drawn from CT
though points A to C
represents the leading edge of the blade. The straight line drawn from CB
through points B to D
represents the trailing edge of the blade. The connection of points A-B-D-C-A
indicate the
perimeter of a single helix blade. The angles represented x, y and z degrees
are angles of right
triangles formed by the imaginary perpendicular lines of the blades depth and
arcs described in
Figure 5.
Figure 7 is an angular view of a concave helix blade. This view is similar to
Figure 6 but the
angle "y" is projected to accommodate the concave form. The base of the right
triangle at "y"
degrees follows the middle arc "y" described in Figure 5 (the radius centre of
the semi-circles
forming the leading and trailing edges of the blade). The semi-circles A-C and
B-D are joined by
lines A-B and C-D to produces an outline of a concave helix blade of the
present invention.
Figure 8 is a schematic of water flow across the concave helix blade of the
present invention.
This drawing is a rendition of the blade of Figure 7 with the hub end of the
blade at A & B and
perimeter end at C & D. The smaller darkened arrows at the hub represent
centrifugal forces. At
the perimeter end the darkened arrows represent centripetal forces. The arrows
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with darkened tips only, represent the overall water flow unidirectional. The
broken line Y-Y1
represents the apex centre of the semi-circular concave blade. The broken line
X-X1
represents the actual centre of the concave blade radiant from the hub centre.
Figure 9 is a top view of a six blade concave helix impeller, drawn to
emphasize the before
mentioned conceptual differences between the blade's centres. The outer broken
circle is
along the apex of the semi-circular blade plotted along points x, A & z with
"A" indicating the
apex of the blades trailing edge. The inner broken circle is along the blades
diameter centre
indicated by the point "y". It is between these two lines where residual
centrifugal and
centripetal forces converge. This drawing indicates a disc area ratio of fifty
percent.
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