U.S. patent application number 14/419120 was filed with the patent office on 2015-08-06 for propeller including a blade back flow guide.
The applicant listed for this patent is Russel Ian Hawkins. Invention is credited to Russel Ian Hawkins.
Application Number | 20150217846 14/419120 |
Document ID | / |
Family ID | 49354719 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150217846 |
Kind Code |
A1 |
Hawkins; Russel Ian |
August 6, 2015 |
Propeller Including a Blade Back Flow Guide
Abstract
THIS invention relates to a propeller and more particularly but
not exclusively, to a propeller for use with inboard and outboard
boat engines. The propeller includes a hub, and a plurality of
blades, each blade having a blade face, a blade back and a blade
peripheral zone comprising a leading edge, a trialing edge and a
blade tip zone extending between the leading edge and the trialing
edge. The propeller is characterized in that a flow guide is
provided on the blade back of each blade.
Inventors: |
Hawkins; Russel Ian;
(Johannesburg, ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hawkins; Russel Ian |
Johannesburg |
|
ZA |
|
|
Family ID: |
49354719 |
Appl. No.: |
14/419120 |
Filed: |
July 31, 2013 |
PCT Filed: |
July 31, 2013 |
PCT NO: |
PCT/IB2013/056280 |
371 Date: |
February 2, 2015 |
Current U.S.
Class: |
416/223B |
Current CPC
Class: |
B63H 1/26 20130101; B63H
1/28 20130101 |
International
Class: |
B63H 1/26 20060101
B63H001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2012 |
ZA |
2012/05758 |
Claims
1-11. (canceled)
1-12. (canceled)
13. A propeller including: a hub; and a plurality of blades, each
blade having a blade face, a blade back and a blade peripheral zone
comprising a leading edge, a trialing edge and a blade tip zone
extending between the leading edge and the trialing edge; wherein
the blade face is substantially smooth, and a flow guide is
provided on the blade back of each blade in order for incoming
water to flow across a part of the blade back before it is
redirected towards a blade face of an oncoming blade.
14. The propeller of claim 13, wherein the flow guide is in the
form of a single elongate ridge protruding from a surface of the
blade back.
15. The propeller of claim 14, wherein the flow guide is spaced
apart from the leading edge of the blade at a distance of between
40% and 60% of the width of the blade, with the blade back surface
between the flow guide and the leading edge being substantially
smooth.
16. The propeller of claim 13, wherein the flow guide is
linear.
17. The propeller of claim 16, wherein the flow guide is angularly
offset relative to a radially outwardly direction of the propeller
blade.
18. The propeller of claim 17, wherein the flow guide is at least
partially parallel to a trailing edge of the blade.
19. The propeller of claim 13, wherein the flow guide is located
closer to the trialing edge of the blade than the leading edge of
the blade.
20. The propeller of claim 13, wherein the flow guide is of a
tapering profile when viewed in cross-section.
21. The propeller of claim 20, wherein a side of the flow guide
disposed towards the trialing edge of the blade is higher than a
side disposed towards a leading edge of the blade.
22. The propeller of claim 21, wherein an upper surface of the flow
guide is disposed at an angle of between 10 and 40 degrees relative
to the surface of the blade back.
23. The propeller of claim 22, wherein an upper surface of the flow
guide is disposed at an angle of between 25 and 35 degrees relative
to the surface of the blade back.
24. The propeller of claim 13, wherein the flow guide extends from
the blade root towards at least half the distance to the periphery
of the blade.
Description
BACKGROUND TO THE INVENTION
[0001] THIS invention relates to a propeller and more particularly
but not exclusively, to a propeller for use with inboard and
outboard boat engines.
[0002] A propeller is a device that transmits power by converting
rotational motion into thrust. A pressure differential is produced
between forward and rear surfaces of the airfoil-shaped blade, and
a fluid (such as air or water) is accelerated behind the blade,
thus resulting in thrust required to drive a means of transport to
which the propeller is attached. One specific type of propeller is
a propeller for use as means of propulsion in boat engines, whether
outboard or inboard.
[0003] Many different propeller designs are known in the trade, and
they all share some of the same design characteristics. A propeller
comprises a plurality of blades extending radially outwardly from a
central rotating hub. Each blade is in the form of an airfoil
having two opposite surfaces, being a blade face (which is the
pressure side of the blade facing the stern), and the blade back
(which is the suction side of the blade facing the bow). Each blade
furthermore has a leading edge, which is the edge of the propeller
adjacent the forward end of the hub. The leading edge leads the
blade into the flow when the propeller is providing forward thrust.
The opposing edge is referred to as the trailing edge, and the
radially outer zone extending between the leading edge and the
trailing edge is referred to as the blade tip. The root of the
blade is the fillet area in the region of transition between the
blade surface to the hub periphery.
[0004] A few other terms that are commonly used in in propeller
nomenclature include:
[0005] Diameter: Two times the distance from the center of the hub
to the tip of the blade, i.e. equal to the diameter of a circle
that the tip of the propeller would make when rotating.
[0006] Pitch: Pitch is defined at the theoretical forward movement
of a propeller during one revolution, assuming that there is no
`slippage` between the propeller blade and the water. In practice
some slippage does occur, and the design pitch is therefore more
than the actual pitch.
[0007] Cupping: Many existing propellers incorporate a cup
formation at the trailing edge of the propeller blade. Propeller
cup is the deformation of a propeller's trailing edge toward the
pressure face. Cupping provides a measure of camber to the blade,
and therefore changes the pressure distribution along the blade's
chord length, adding lift toward the trailing edge.
[0008] Cavitation: Cavitation, (which is often confused with
ventilation), is a phenomena of water vaporizing or "boiling" due
to the extreme reduction of pressure on the back of the propeller
blade. Many propellers partially cavitate during normal operation,
but excessive cavitation can result in physical damage to the
propeller's blade surface due to the collapse of microscopic
bubbles on the blade. There may be numerous causes of cavitation
such as incorrect matching of propeller style to application,
incorrect pitch, and physical damage to the blade edges.
[0009] Ventilation: Ventilation is a situation where surface air or
exhaust gasses are drawn into the propeller blades. When this
situation occurs, boat speed is lost and engine RPM climbs rapidly.
This can result from excessively tight cornering, a motor that is
mounted very high on the transom, or by over-trimming the
engine.
[0010] Hole Shot: Hole shot refers to rapid acceleration of a boat,
i.e. from a standing rest or very slow speed until the boat is
"on-plane" and riding on top of the water. During this acceleration
phase the engine works particularly hard, and it is therefore
important to have the best possible propeller for the particular
application. A propeller that offers excessive hole shot (i.e. too
much acceleration) will typically yield low tops speeds and may
cause the engine to operate above its designed RPM. On the other
hand, a propeller that offers too little hole shot typically result
in poor acceleration performance, and may not bring the engine up
to its designed RPM range. Either of these scenarios cause undue
strain on the engine and reduces its overall performance and fuel
efficiency.
[0011] Blade surface area refers to the total surface area of the
propeller blade. When a propeller rotates on a fixed axis for any
period of time a centrifugal force creating a negative pressure on
the blade back of each rotating blade draw water inwards, and when
the oncoming blade face comes into contact with the inward flow of
water the water is compressed. A positive pressure is therefore
induced, and the water in this positive pressure zone then exerts a
force against the adjacent body of water, resulting in thrust.
Standard blade designs allow the inward flow of water to flow over
the entire curvature of the blade back. This is believed to result
in about 40% of the energy being wasted because on average only 60%
of the negative pressure water mass is compressed by the blade face
of an oncoming blade. Further energy is lost between the blade
roots of each blade back, which fragments the flow of water when
the positive pressure water mass collides with the negative
pressure water mass. This disturbance affects the volume of water
mass that gets displaced.
[0012] It will be appreciated that blade surface area plays an
important part in propeller performance. This is important because
the more blade surface area a prop has the more water it displaces.
However, this can also result in more drag on the blade and thus
the engine, due to the effects described hereinbefore. Increased
blade area can result in better hole shot, and will allow a boat to
remain on plane at lower engine speeds. However, too much blade
area can result in excessive drag, and can therefore restrict the
RPM that that the engine can develop, and can in addition also
result in boat handling issues. The operation of the engine outside
its recommended specification results in the engine having to work
harder or faster than it is designed to do. This will result in
reduced efficiency, fuel economy and possibly also damage to the
engine.
[0013] It would therefore be beneficial if a propeller can de
designed that has a reduced effective blade back area, without
reducing the effective area of the blade face.
[0014] It is accordingly an object of the invention to provide a
propeller that will at least partially alleviate the above
disadvantage.
[0015] It is also an object of the invention to provide a propeller
having reduced drag characteristics without impacting on the
surface area of the blade face.
SUMMARY OF THE INVENTION
[0016] According to the invention there is provided a propeller
including: [0017] a hub; [0018] a plurality of blades, each blade
having a blade face, a blade back and a blade peripheral zone
comprising a leading edge, a trialing edge and a blade tip zone
extending between the leading edge and the trialing edge; [0019]
characterized in that a flow guide is provided on the blade back of
each blade.
[0020] There is provided for the flow guide to be in the form of an
elongate ridge extending from a surface of the blade back.
[0021] The flow guide may be linear, and may be angularly offset
relative to a radially outwardly direction of the propeller.
[0022] Preferably the flow guide is at least partially parallel to
a trailing edge of the blade.
[0023] Preferably the flow guide is located closer to the trialing
edge of the blade than to the leading edge of the blade.
[0024] There is provided for the flow guide to be of a tapering
profile when viewed in cross-section.
[0025] Preferably a side of the flow guide disposed towards the
trialing edge of the blade is higher than a side disposed towards a
leading edge of the blade.
[0026] An upper surface of the flow guide may be disposed at an
angle of between 10 and 40 degrees relative to the surface if the
blade back. Preferably, the angle is between 25 and 35 degrees.
[0027] There is provided for the flow guide to extend from the
blade root towards at least halve the distance to the periphery of
the blade.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] A preferred embodiment of the invention is described by way
of a non-limiting example, and with reference to the accompanying
drawings in which:
[0029] FIG. 1 is a front perspective view of the propeller
including flow guides in accordance with one embodiment of the
invention;
[0030] FIG. 2 is a side view of the propeller of FIG. 2;
[0031] FIG. 3 is top plan view of the propeller of FIG. 1.
DETAILED DESCRIPTION OF INVENTION
[0032] Referring to the drawings, in which like numerals indicate
like features, a non-limiting example of a propeller in accordance
with the invention is generally indicated by reference numeral
10.
[0033] The propeller 10 comprises a hub 20, which may be of many
different configurations. In one embodiment the hub 20 incorporates
a secondary propulsion system as described in the applicant's
co-pending application ZA2012/05757 entitled "Propeller
incorporating a secondary propulsion system", the contents of which
is incorporated herein by reference. In one embodiment the
propeller also includes the provision of edge members on the blades
of the propeller as described in the applicant's co-pending
application ZA2012/05753 entitled "Propeller including a discrete
edge member", the content of which is also incorporated herein by
reference.
[0034] A plurality of blades 30 extend radially outwardly from the
hub 20, with each blade being in the form of an airfoil extending
from the hub 20 at a root 23 section thereof, and terminating in a
peripheral tip zone 34. The blade 30 includes a blade face 31 and a
blade back 32. The periphery of the blade 30 comprises a leading
edge 35, a trailing edge 36, and an outer tip zone 34 extending
between the leading edge 35 and the trailing edge 36.
[0035] Flow guides 50 in the form of elongate ridges are provided
on the surface of the blade backs 32. Each flow guide 50 is in the
form of a linear ridge that is somewhat angularly offset relative
to a radially outwardly direction of the propeller. More
particularly, each flow guide is at least partially aligned and
parallel relative to a trialing edge of the blade 30. The flow
guide 50 is disposed towards a proximal zone of the blade surface
32, with a first end 50.1 of the flow guide being located adjacent
the hub 20 of the propeller 10, and with a second end 50.2
extending towards the periphery of the blade.
[0036] In cross-section, the flow guide 50 is of a tapered
configuration, with a first side 50.3, which is the side facing the
leading edge of the blade, being flush with the surface of the
blade back 32, but with an opposite side 50.4, which is the side
facing the trialing edge of the blade, being raised relative to the
surface of the blade back. The gradient between the first side 50.3
and the second side 50.4, and hence the upper surface of the flow
guide, is linear in this particular embodiment, and more
particularly forms an angle of about 30 degrees relative to the
blade back 32. The gradient and hence upper surface may however
vary in terms of profile and magnitude, and may for example also be
arcuate, and in particular somewhat convex.
[0037] The flow guide has the effect of directing incoming water
away from the blade back and towards the oncoming blade face. The
incoming water therefore only flow across between 40% and 60% of
the back blade before it is redirected towards the oncoming blade.
This results in an increase efficiency accompanied by a reduction
in drag, as is discussed in detail in the background to this
invention.
[0038] The propeller 10 body is made from magnesium or a magnesium
alloy, which is made in a moulding process known in the art. The
flow guides 50 are integrally formed with the propeller blades and
body.
[0039] It will be appreciated that the above is only one embodiment
of the invention and that there may be many variations without
departing from the spirit and/or the scope of the invention.
* * * * *