Propeller

The propeller includes a central hub with a plurality of blades extending radially from equal circumferentially spaced points on the periphery of the hub. The width of each blade at its root is equal to the spacing between adjacent blades and the width of each blade at its tip is equal to one half the width of its root. The leading edge of each blade is normal to a line tangential to the point of connection of the blade to the hub periphery while the trailing edge slants from the tip to the broader root. The length of each blade is one half the diameter of the hub and each blade has an angle of attack of about 17.degree.. This structural dimensioning results in a propeller providing a substantially constant air discharge from the roots to the tips of the blades with a substantial elimination of radial air flow, all to the end that a greater static thrust can be realized for a given horsepower input.

This invention relates to propellers or fans of the axial flow type 
particularly useful for propelling aircraft, boats and the like. 
BACKGROUND OF THE INVENTION 
The design of propellers for powering aircraft and boats and the like and 
for use as axial flow propeller fans has become quite sophisticated with 
complex aerodynamic shapes being devised for the blades used on such 
propellers. Theory and practical aspects of such designs may be found, for 
example, in Marks' Mechanical Engineers Handbook, by McGraw-Hill Book Co., 
Inc. 6th Edition, at pp. 11-105 to 11-115 and pp. 14-66 to 14-76. 
As set forth in the foregoing handbook at p. 11-109, static thrust produced 
by the usual propeller, per horsepower input to the propeller, is usually 
in the range of 3 to 4 pounds and is seldom if ever over about 5 pounds. 
It is apparent, accordingly, that a propeller which could produce a 
substantially greater static thrust per horsepower input would allow 
propulsion of aircraft and boats to be attained with substantial savings 
in energy as compared to that required at present. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
With the foregoing in mind, the present invention contemplates an improved 
propeller structure so dimensioned as to provide a greater static thrust 
for a given input horsepower than is realizable with known propellers. 
More particularly, the dimensioning and geometrical design of the 
propeller of this invention is such that a substantially constant air 
discharge is realizable from the roots to the tips of the propeller blades 
together with a substantial elimination of radial air flow. These 
desirable results provide for the greater static thrust since energy is 
not wasted in radial flow. Moreover, the flow pattern lies in a relatively 
narrow path so that the use of shrouds or ducts as might be required in 
certain applications is not necessary. 
Briefly, the propeller of this invention includes a central imperforate hub 
and a plurality of blades greater than two having roots and tips connected 
by straight line leading and trailing edges. The roots are secured to 
equal circumferentially spaced points on the periphery of the hub, each 
blade extending radially from its root connection on the hub to its tip a 
distance equal to one half the diameter of the hub. 
Each of the blades is identically dimensioned. Thus, the width of each 
blade at its root is equal to the spacing measured circumferentially along 
the periphery of the hub between adjacent blades, the straight leading 
edge of each blade being normal to a line tangential to the periphery of 
the hub passing through the point of securement of the root of the blade, 
the width of the tip of each blade being one-half the width of the root 
such that the straight trailing edge of each blade defines a tapered blade 
decreasing uniformly in width from its root to its tip. 
The major portion of the cross section of each blade taken along its width 
dimension has a camber defined by an upper curved line convex when viewed 
from the top of a first given radius of a curvature and a lower curved 
line concave when viewed from the bottom of a second given radius of 
curvature greater than the first given radius of curvature. The angle of 
attack of the cord of each blade is from 10.degree. to 17.degree..

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 the propeller includes a central imperforate hub 10 
having a given hub diameter D. A plurality of propeller blades greater 
than two are shown, by way of example, at 11, 12 and 13. Preferably, there 
are provided a total of nine such blades having roots and tips connected 
by straight line leading and trailing edges, the roots being secured to 
equal circumferentially spaced points on the periphery of the hub such as 
14, 15 and 16. Each blade extends radially from its root connection on the 
hub to its tip a distance equal to one half the given diameter D, this 
distance being depicted in FIG. 1 as D/2. As a result, the circular locus 
swept out by the tips of the various blades indicated in phantom lines at 
17 has a diameter equal to 2D. 
Referring to FIG. 2, further details of the blade structures will be 
evident. Thus, there is depicted for the blade 11 the root portion at 18 
and its tip portion at 19. The straight leading edge of the blade 11 is 
indicated at 20 and the straight trailing edge at 21. The securement of 
the root 18 to the hub 10 at the point 14 is accomplished by a shank 
portion 22 shown in phantom lines secured as by a fastening nut 23 within 
an appropriate cavity as indicated by the phantom lines so that the root 
18 of the blade smoothly blends in with the periphery of the hub 10. 
It will be noted with reference to the blades 11 and 12 shown in FIG. 2 
that the width of each blade at its root designated W for the blade 12 is 
equal to the spacing circumferentially along the periphery of the hub 
between the adjacent blades such as the blades 12 and 11. This spacing 
width is also indicated by the letter W in FIG. 2. 
It will also be clear that the straight leading edge such as 20 for the 
blade 11 of each blade is normal to a line tangential to the periphery of 
the hub passing through the point of securement of the root of the blade. 
This tangential line is indicated at 24 for the blade 11 wherein it is 
tangent to the periphery of the hub 10 at the securement point 14. The 
90.degree. relationship of the leading edge 20 is also indicated in FIG. 2 
so that in essence the leading edge 20 is parallel to a radial line 
passing through the securement point 14 from the center of the hub. 
Necessarily, this radial line forms an angle of 90.degree. with the 
tangent line 24. 
Referring to the tip portion 19 of the blade 11, the width at the tip is 
one-half the width of the root, this tip dimension being indicated by W/2. 
By this dimensioning the straight trailing edge of each blade such as 
indicated at 21 for the blade 11 defines a tapered blade decreasing 
uniformly in width from its root to its tip. 
The significance of the foregoing can now be appreciated. With reference 
still to FIG. 2, because the length of the blade from the root to the tip 
designated D/2 is one half the diameter D of the hub 10, the tangential 
speed of the root portion 18 of the blade 11 when the same is rotating in 
a counterclockwise direction as depicted in FIGS. 1 and 2 will be one-half 
the tangential speed of the tip 19 of the blade. In other words, for each 
complete revolution of the blade, the root portion 18 will travel a 
distance defined by the circumference of the hub 10 while the tip portion 
19 of the blade will travel a distance twice as great defined by the 
circumference or locus line 17. However, the width at the tip 19 is 
one-half the width at the root 18. Because of the straight line tapered 
configuration, it will be evident that the tangential speed of each cross 
sectional portion of the blade from its root to its tip increases from the 
root to the tip while the width of the blade decreases from root to tip. 
The relationship is such that a constant air discharge is provided from 
the roots to the tips of the blades. 
Stated still somewhat differently, the amount of air being moved by the 
root portion of the blade will be the same as the amount of air being 
moved by the tip portion of the blade this result being a consequence of 
the wider width of the blade at the root portion compensating for the 
slower tangential speed of the root portion and the narrower width of the 
blade at the tip compensating for the higher tangential speed of the tip. 
A further consequence of this design is the substantial elimination of any 
radial air flow thereby avoiding wasted energy which occurs when blades 
are twisted or so dimensioned as to give rise to radial components of air 
flow. 
Referring now to FIG. 3, there is illustrated a cross section of the blade 
11 at an intermediate point between its root and tip such as provided by 
viewing the blade 11 in the direction of the arrows 3--3 of FIG. 2. The 
major portion of this cross section for each blade taken along its width 
dimension has a camber defined by an upper curved line 25 convex when 
viewed from the top of a first given radius of curvature R1. The circular 
arc defining this upper curved line 25 is indicated at 26. The lower 
portion of the cross section in turn is defined by a lower curved line 27 
concave when viewed from the bottom having a second given radius of 
curvature R2 greater than the first given radius of curvature. This lower 
curved line 27 constitutes part of the arc of a circle extending in 
phantom lines shown at 28. 
The area enclosed within the circular arcs 26 and 28 between their 
intersection points defines the cross section of the blade except for a 
rounding off of the leading edge 20 as shown. This slight rounding of the 
leading edge avoids a whistle as the blade cuts through the air and also 
minimizes erosion. The trailing edge 21, in turn, terminates in a sharp 
edge defined by the intersection point of the arcs. 
The blade is oriented such that its cord forms an angle of attack A which 
may vary from 10.degree. to 17.degree. but in the preferred embodiment is 
preferably 17.degree.. The angle of attack at the leading edge 20 of the 
cross section of FIG. 3 is about 6.degree. while the angle of attack of 
the trailing edge 21 is about 30.degree.. The cord angle of attack remains 
constant throughout the length of the blade from the root to the tip. In 
other words, there is no twist to any of the blades. In the preferred 
embodiment, the ratio of the first radius of curvature R1 of the camber of 
FIG. 3 to the second radius of curvature is substantially 5 to 9. 
In an actual embodiment of the invention, the hub diameter might be about 
30 cm. with the length of each of the blades 15 cm. In the preferred 
embodiment of nine blades the circumferential spacing W between the blades 
which spacing also defines the width of the root would be about 20.degree. 
of arc or about 5.2 cm. The tip width would be one-half this value, or 
about 2.6 cm. With respect to the radii of curvature of the arc portions 
of the circles defining the chamber of the cross section, and which 
reference to FIG. 3, R1 would be about 12.7 cm and R2 about 22.8 cm. 
From numerous experiments, it has been found that the thrust per input 
horsepower is markedly increased with the propeller designed in accord 
with the foregoing, all to the end that a greatly improved propeller 
structure has been provided by the present invention wherein substantially 
constant air discharge obtains from the roots to the tips of the blades 
together with a substantial elimination of radial air flow. This latter 
feature avoids the necessity of shrouds and cowling and the like in 
certain applications.