Note: Descriptions are shown in the official language in which they were submitted.
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COMBINED CEILING FAN AND FIGHT FITTING
TECHNICAL FIELD
The invention described.herein relates to a combined light fitting and
ceiling fan having blades that are compactly folded when the fan is not in use
and that move outwardly when the fan is started. More particularly the
invention relates to improved fan blades for such an appliance.
BACKGROUND ART
Ceiling fans have long been recognized and used as an inexpensive
way to provide movement of air within rooms of buildings. They can be simple
to use and install, safe, and inexpensive to buy and run when compared to
such alternatives as for example refrigerated and evaporative air conditioning
units. They can often provide a surprisingly effective alternative to air
conditioning as the air movement they generate can evaporate skin
perspiration with a resulting cooling effect.
It is known to combine ceiling fans with lighting means, as firstly it is a
common requirement to provide ceiling mounted light sources, and secondly it
is' -convenient to provide a single power supply to operate a combined fan and
light fitting.
Less commonly, it has also been known to provide a combined light
fitting and ceiling fan with some form of folding or retracting blade
arrangement. Le Velle has described three versions. US Patent 1445402
discloses a light fitting and ceiling fan in which blades move outwards under
centrifugal force when the fan is switched on, and are retracted by springs
when the fan is switched off. US Patents 1458348 and 2079942 disclose
improved versions, in which (unlike the early version of Patent 1445402) the
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inward and outward movements of the blades are synchronized.
Synchronizing blade movement is important for preserving satisfactory
balance of the rotating parts of the fan. More recently, a combined light
fitting
and ceiling fan has been disclosed by Villella (see international patent
publication WO 2007/006096) with a concealed and simple blade movement
synchronizing arrangement that lends itself to modern design.
A problem in the design of a combined light fitting and ceiling fan is to
provide blades that when in use can provide useful air moving performance
without requiring' excessive power and that when'not in use can fold into a
reasonably compact overall form. The present invention addresses this
problem.
References above and elsewhere in this specification to certain patents
are not intended as or to be taken as admitting that anything therein forms a
part of the common general knowledge in the art in any place.
--SUMMARY OF THE INVENTION
A combined ceiling fan and light fitting will in this specification be
referred to as a fan/light for convenience and brevity.
The invention relates to fanilights having a plurality of fan blades that
move outwardly to operating positions during fan operation and inwardly to
stowed positions when fan operation ceases. Movement of the fan blades
outwardly may be by action of centrifugal force when the blades are rotated
about a fan axis by a motor. Retraction of the fan blades to their stowed
positions may be by action of resilient means, for example one or more
springs.
The blades are adapted and arranged when.in their operating positions
to move air downward as they rotate, and when in their stowed positions to lie
within a defined radius from the fan axis, such as the radius of a translucent
enclosure of circular form (when seen in plan view) for light emitting devices
such as incandescent lamps. Each blade when stowed may overlap at least
one other blade.
Preferred forms and relative positionings.of.blades are disclosed that
are believed to provide a useful balance between the requirements of
reasonable air movement and compact stowage of the blades when not in
use. These forms are particularly characterized by certain distributions of
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incidence, blade chord (distance measured from leading edge to trailing edge)
and dihedral. They are preferably of aerofoil cross section with such camber
that lower blade surfaces are concave and upper blade surfaces convex-
More specifically, the invention provides in a first aspect a combined
ceiling fan and light fitting having a plurality of fan blades, wherein:
each blade is pivotally mounted so as to be pivotable about an upright
pivot axis of the blade between a stowed position and a deployed position;
each blade when in its stowed position lies within a specified radius
from an upright fan rotation axis and above a light fitting portion and has an
air
moving portion that in the deployed. position of the blade extends beyond said
specified-radius; and
each blade is generally elongate and arcuate wherf seen in plan view
and in its stowed position extends peripherally within said specified radius
between its pivot axis and a tip end of the blade and partially overlies a
neighbouring one of the blades in its own stowed position;
the-combined ceiling fan and light fitting characterized in that:
(a) each blade initially rises in height above a datum height with increasing
distance along the blade from its pivot axis end so that the blade when
in its stowed position overlies the pivot axis end of the neighbouring
blade in its own stowed position and
(b) with increasing distance from a pivot axis end of the air moving portion
towards the tip, end of the blade the leading edge of the air moving
portion first increases in height above the said datum height and then
turns downwardly whereby to limit the height of the tip end above the
datum height.
The term "neighbouring blade" here means a blade that is first found by
moving peripherally forward (i.e. in the direction of fan rotation) from one
blade.
The phrase "turns. downwardly" here does not necessarily mean that
with increasing distance toward the tip end from such turning down the blade
begins to actually descend. Rather it means that the blade increases in height
at a lesser rate than before the turning down, which may still be positive
although that is not to preclude a zero or negative rate of height increase.
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Thus, the leading edge of the air moving portion of each blade may
have a peak height above the datum height at a position between the pivot-
axis end of the air moving portion and the tip end of the blade.
Further, the height above the datum height of the leading edge of the.
air moving portion may decline from said peak height with increasing distance
.
along the leading edge toward the. tip end of the blade.
The "specified radius" may be approximately a radius of a light fitting
portion that is comprised in the combined ceiling fan and light fitting and
located below the blade and that is of circular shape when seen in plan view..
The "datum heig.ht may, purely for example, be the height of an upper
surface of a horizontal platelike member to which each of the blades is
pivotably mounted as in the case of the construction described by Villella.
The air moving portion of each blade may have a trailing edge that
when seen in plan view is approximately, a circular arc which when the blade
is in its stowed position said is substantially centred on the fan rotation
axis-
This-arrangement allows effectively use of the available. space above a light
fitting portion that is round when seen in plan view.
Preferably, for each blade when in its stowed position the radial
distance between the leading and trailing edges of the air moving portion
reduces progressively (i.e. the blade tapers as seen in plan view) from a.
maximum value partway along the length of the air moving portion towards
the blade tip end. .
More preferably, when all blades are. in their stowed positions there is
for each blade a.first point on the leading edge of its air moving portion
where
the blade overlies its neighbouring blade which first point when seen in a
notional radial plane including the fan rotation axis lies at a greater radius
than
a second point in the same notional plane that is on the leading edge of the
overlain neighbouring blade.
Still more preferably, the said first point may be at a height above the
datum height not exceeding the height of the said second point.
These arrangements can enhance the compactness of stowage of the,
blades.
It is preferred that the air moving portion of each blade has in the
deployed position of the blade a maximum angle of incidence to the horizontal
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at a'position partway along the air moving portion the angle of incidence
decreasing with increasing distance from that position of maximum incidence
towards the tip end of the blade.
Preferably also, the air moving portion has a positive angle of incidence
5 to the horizontal at its pivot-axis end. .
The position partway along the air moving portion of each blade at
which its incidence to the horizontal is a maximum when the blade is in its
deployed position may be radially inboard of a position at which the blade
chord measured along an arc centred on the fan rotation.axis is at a maximum
value. It is thought (but.not asserted) that this feature may smooth the
distribution of downward thrust on the air along the blade, so reducing
induced drag on the blade.
Although adaptable to other numbers of blades, for example three or
five, the number of blades is preferably four with the blades' pivot axes
being
spaced 90 degrees apart from each other peripherally.
That section- of each blade between its pivot axis and its tip end when
the blade is in its stowed position may subtend an angle of about 160 to 170
degrees at the fan rotation axis. Values in this range allow reasonable blade
areas within the available stowage space above the light fitting portion, but
without at any point requiring the stacking of more than two blades. This
assists in obtaining compact blade stowage.
Preferably, each blade pivots through an angle of about 180 degrees to
move from its stowed position to its deployed position. This gives a
satisfactory blade-swept area for a given blade size.
Preferably, the air moving section of each blade is upwardly cambered
(i.e.concave downwards) between its leading and trailing edges when seen in
cross-section on a cylindrical surface centred on the fan rotation axis and
intersecting the air moving section at a radius between the specified radius
and the blade tip end.
It is also preferred for efficient air moving that the air moving section of
each blade has a rounded leading edge and a sharp trailing edge over at least
part of its along-blade length when seen in cross-section on a cylindrical
surface centred on the fan rotation axis and intersecting the air moving
section at a radius between the specified radius and the blade tip end.
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The minimum height difference between each blade and its
neighbouring blade when the blades are in their stowed positions may
advantageously occur approximately where the blade overlies its
neighbouring blade. If an overlying. blade sags slightly, as may be the case
with blades moulded from certain plastics if left unused for some time, this
arrangement has been found to support the outer part of the blade reasonably
well once contact between a blade and its underlying neighbour has been
made.
The invention provides in another aspect a combined ceiling fan and
light fitting having a plurality of elongate and arcuate planform blades that
can
move pivotally about upright axes between firstly stowed positions above a
light fitting enclosure and secondly deployed positions in which the blades
extend outwardly beyond the light fitting, characterized in that leading edges
of the blades when in their deployed positions firstly rise with increasing
radius beyond the light fitting enclosure first and thereafter are cranked
downwardly.
In this aspect, when the blades are in their stowed positions each blade
overlies a part of its neighbouring blade which part is received in a gap
above
the light fitting enclosure and below the underside of the overlying blade
said
gap existing by virtue of the cranked shape of the overlying blade.
Each blade may be pivotally mounted to a rotating platelike member
with said gap lying above said platelike member.
In a third aspect the invention provides a combined ceiling fan and light
fitting having air moving blades that in use exhibit. gullwing dihedral. It is
thought that such a dihedral form may be advantageous in itself even apart
from its ability to enable compact stowage of retracting blades. "Gullwing
dihedral" is to be taken as meaning that a lifting blade or wing rises between
its root end and a point or region along its length toward its tip end and
then
either falls, remains level or rises more slowly.
In a further aspect the invention provides a combined ceiling fan and
light fitting having a plurality of fan blades, wherein:
each blade is pivotally mounted so as to be pivotable about an upright
pivot axis of the blade between a stowed position and a deployed position;
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each blade when in its stowed position lies within a specified radius
.from an upright fan rotation axis and above a light fitting portion and has
an air
moving portion that in the deployed position of the blade extends. beyond said
specified radius; and
5. each blade is generally elongate and arcuate when seen in plan view
with concave and convex sides and in its stowed position extends peripherally
within said specified radius between its pivot axis and a tip end of the
blade,
characterized in that
(a) each. blade when deployed is so positioned that -a concave side of the
blade faces forward in the blade's direction of rotation and so that a
radially outer-portion of the blade's length extends both outwardly and
forwardly;
(b) there is a first position partway along the air moving portion of
the blade at which the blade's chord as measured in a peripheral
direction has a maximum value and a second position partway along
the air moving portion of the blade at which the blade has a maximum
positive angle of incidence to-the horizontal; and
(c) the first position is at a greater radius than the second position.
That is, the distributions of incidence and chord disclosed herein are
believed advantageous in themselves apart from the issue of blade stowage.
The invention further provides a blade adapted for use in fan/lights as
disclosed.
It is explicitly intended that the specific four-blade embodiment
described in detail below be taken to be a claimable aspect of the invention
both as to the proportions of the blades and their relative positions when in
their stowed and operating positions.
The invention is preferably applied in fanlights having certain features
of the construction described in International Patent Publication WO
20071006096 (based on International Patent Application No.
PCT/AU2006/000981 by Joe Villeila).
In a still further aspect of the invention there is further provided a
fan/light comprising a plurality of retractable fan blades, wherein:
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each said blade is pivotally mounted to a fan-member that is rotatable
about an upright fan rotation axis so that said blade is pivotable between a
retracted position and an operating position about an upright blade pivot axis
of said fan member;
each said blade has an elongate'and generally arcuate air moving
blade portion that when said blade is in the retracted position of said blade
lies within a space bounded by:
(a) an inner cylindrical surface coaxial with said fan rotation axis and
touching an inner edge of said blade portion;
(b) an outer cylindrical surface coaxial with said fan rotation axis and
touching,an outer edge of said blade portion;
(c) a first radial plane containing said fan rotation axis-and said blade
pivot
axis; and
(d) a second radial plane containing said fan rotation axis and that touches
a tip of the, blade,
so that associated with- every point on said blade portion is an angle
theta being an angle between said first radial plane and a radial plane
containing the fan rotation axis and that point; and
within_a continuous section of the blade portion that lies between said
first and second radial planes, said inner edge increases in height above a
datum height with increasing theta, and a radial projection of said inner edge
onto a cylindrical surface coaxial with said fan rotation axis is concave
downwards.
Preferably, within said continuous section of said blade said inner edge
increases in height above said datum height with increasing theta until a
maximum value of the inner edge height is first reached at a point thereon
whose value of theta is less than the value of theta at the blade tip.
Within said continuous section and for theta values greater than the
smallest value at which said inner edge has its maximum height above said
datum height, the height of said inner edge may decrease with increasing
theta. This particular embodiment corresponds to the preferred embodiment
described in detail herein.
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In such a fan/light the other preferred features proportions and relative.
positioning of the blades as described herein may also be applied, including
as to the blade trailing edge shape.
Further features, preferences and inventive concepts are disclosed in
the following detailed description and appended claims.
In this specification, including in the appended claims, the word
"comprise" (and derivatives such as "comprising", "comprises" and
"comprised") when used in relation to a set of integers, elements or steps is
not to betaken as precluding the possibility that other integers elements or
steps are present or able to be,included.
In order that the invention may be. better understood there will now be
described, non-limitingly, preferred embodiments of the invention as shown in
the attached Figures, of which:
Figure 1 is a perspective view from above of a fan/light with retractable
fan blades according to the invention, shown with its blades deployed to their
operating positions;
Figure 2 is a perspective view from below of the fan/light shown in
Figure 1 with its blades deployed to their operating positions;
Figure 3 is a perspective from above of the fan/light,shown in Figure 1,
now with its fan blades shown in their folded, non-operating positions;
Figure 4 is a perspective view from below of the fan/light shown in
Figure 1, with its fan blades shown in their folded, non-operating positions;
Figure 5 is a plan view of the fan/light of Figure 1, with its fan blades
shown deployed to their operating positions;
Figure 6 is a.plan view of the fanlight of Figure 1, with its fan blades
shown. in their folded, non-operating positions;
Figure 7 is a side view of the fan/light of Figure 1, with its fan blades
shown deployed to their operating positions;
Figure 8 is a side view of the fan/light of Figure 1, with its fan blades
-shown in their folded, non-operating positions;
Figure 9 is a perspective view from below of a subassembly of a
fan/light with retractable fan blades described in International Patent
Publication No. WO 2007/006096 by Villella;
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Figure 10 is a schematic plan view of the fanlight shown in Figure 1
showing one blade In both deployed and retracted positions and the other
blades in retracted positions and chain-dotted lines only;
Figure 11 is a schematic plan view of the fan/light shown in Figure 1
5 with all blades shown in chain-dotted lines in retracted positions and one
blade also shown in its deployed position the view further showing positions
of
a set of cylindrical surfaces intersecting, and located at radially spaced
stations along, the extended.blade;
Figure. 12 is a set of sections (labeled a - I) on radial planes as defined
10 in Figure 10 of retracted blades. of the fan/light shown schematically; in
Figure
10;
Figure 13 is a graph of heights above a datum height of inner and outer
edges of a blade of the fan/light shown in Figure 1, as a function of
circumferential position when the blade is in a retracted position;
'15 Figure 14 is a graph of radial distance between inner and outer edges
of a blade of the fan/light shown in Figure 1, as a function of
circumferential
position when the blade. is in a retracted position;
Figure 15 is a graph of heights above a datum height of inner and outer
edges of all blades of the fan/light shown in Figure 1-, as a function of
circumferential position when the blades are in their retracted positions;
Figure 16 is a set of cross-sections of the extended blade shown in
Figure 11 taken on planes tangential to the arcs shown therein an numbered
1 to 8;
Figure 17 is a graph of an angle of incidence to the horizontal of the'
extended fan blade shown in Figure 11 as a function of radial position on the
blade; .
Figure 18 is a graph of the chord.of the extended- blade shown in
Figure 11 as a function of radial position on the blade.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
30. . Figures 1 to 8 show a fan/light 10 according to the invention. Fan/light
10 has a non-rotating bowl-like translucent enclosure 12 in which is mounted
at least one electric lamp (not shown), and is supported from a ceiling by a
tubular support 13 in known manner. Fan/light 10 also has fan blades 1, 2, 3
and 4 that are rotatable by an electric motor (not shown) about an upright
axis
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15'coaxial with tubular support 13. The electric motor and the lamp are
operable separately or together from a source of electric power that is
supplied through the tubular support 13. The motor is of a known type, widely
used in ceiling fans, that has a rotating external casing (not shown) with a
central cavity in which is received the tubular support 13. Enclosure 12 is
circular in plan view, centered on. axis 15.
Blades 1 - 4 each extend outwardly to the operating positions shown in
Figures 1, 2, 5 and 7 when the motor is switched on, and retract (fold) into
positions shown in Figures 3, 4, 6 and 8 when the motor is switched off. The
sense of rotation is as.shown by arrow 7. Each one of blades 1 - 4 is
pivotally
supported on a blade support plate 14 that supports and rotates with blades 1
- 4, is disc-shaped, is coaxial with the rotation axis 15 of the motor and is
secured to the motor's casing. A decorative dust cover 18 is secured on the
support 4 above the blades 1 - 4 when they are in the folded positions shown
in Figures 3, 4, 6 and 8.
Pivoting of blades 1 - 4 on blade support plate 14.is respectively about
axes 21, 22, 23 and 24 parallel to the axis 15 of rotation of the motor. When
the motor is switched on, blades 1 - 4 pivot outwardly under the influence of
centrifugal force, pivoting around their respective pivot axes 21 - 24, until
the
operating positions shown in Figures 1, 2, 5 and 7 are reached. When the
motor is switched off, blades I - 4 are retracted to their stowed positions as
shown in Figures 3, 4, 6 and 8, again pivoting about their respective axes 21 -
24..
In international patent No. publication WO 2007/006096 (based on
International Patent Application No. PCT/AU20061000981 by Villella), which is
incorporated herein in its entirety by reference, there is described a
fan/light
generally in accordance with the above principles and arrangement, albeit
with three blades instead of the four blades 1 - 4 of fanlight 10. The present
invention in its preferred embodiment is made-in accordance with the
. principles and arrangement set out in Villella's disclosure save for the use
of
the four blades 1 - 4 instead of three.
In particular, synchronization of the pivoting movement of blades 1 -4
and their retraction, may be by means of a simple adaptation to four blades of
the approach disclosed by Villella, now briefly described. Figure 9 (similar
to
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Figure 7 of Villella's publication) shows a subassembly 30 of Villella's
fan/light
comprising a motor 34, blade support plate 36 and three blades 31, 32 and
33. (Note: The item numbers used` herein to describe subassembly 30 are not
the same as those used in the cited Villella publication.) Blade support plate
-36 is ring shaped and secured to motor 34 (of the rotating casing type
previously mentioned) so as to rotate therewith in its own plane.
Secured below blade support plate 36 is a sun gear 38. (The term "sun
gear" is here used as it is in the art of so-called planetary gearing systems,
where it refers to a gear that meshes with a number of "planetary" gears
arrayed around its periphery.) Sun gear 38 is coaxial with the motor 34 when
support plate 36 is mounted to motor 34, and is able to rotate about its axis
relative to support plate 36. Meshing with sun gear 38 are planetary gears 41,
42 and 43, each of which rotates as its associated one of blades 31 - 33
pivots between its stowed and operating positions. Each of gears 41 - 43 is
secured to a short shaft (not visible) that passes downwardly from its
associated one of blades 31 - 33 and can rotate within support plate 36. The
.gears 41 - 43 are equispaced around the periphery of sun gear 38 and are
themselves all at the sane radius as each ether from the rotation axis 35 of
motor 34. The effect of this arrangement is that provided blades 31 - 33 are
identical and identically positioned in their working positions relative to
support
plate 36, they will be kept synchronized always when they pivot between their
operating and retracted positions.
To retract blades 31 - 33 when motor 34 is switched off, coil springs 44
are provided. One end of each spring is secured to a formation 46 depending
from support. plate 36 and the other end is secured to a formation 48
depending from sun gear 38. Coil springs 44 are arranged to be intension
when blades 31 - 33 are in their retracted position and are extended as
centrifugal force urges blades 31 - 33 out when motor 34 is started. When
motor 34 is stopped, springs 44 urge sun gear 38 to rotate relative to support
. plate 34 so as to retract the blades 31 - 33.
For further information on, and options relating to, this arrangement for
blade synchronization and retraction, refer can be made.to the cited
publication of Villella.
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The way to adapt this arrangement to the four blades 1 - 4 of the
embodiment of the present invention here described will be readily apparent
to persons skilled in the art. There would be provided four planetary gears
(not shown, but equivalent to gears 41 - 43) instead of three, equispaced
around the sun gear (not shown, but equivalent to sun gear 38) and each
associated with one blade.
In the following description, it will be assumed that blades 1 - 4 are
pivotally mounted to support plate 14 essentially similar. to support plate 36
and synchronized and retracted in the same way as blades 31 - 33 of
subassembly 30. However, it is emphasized that the aerodynamic design of
blades 1 - 4 and the way that they "nest" together when retracted are by no
means limited to this particular fan/light construction.. The configuration
and
arrangement of blades 1 - 4 could be applied to fan/lights of other
constructions and to fans requiring retractable blades and without any
lighting
capability.
The blades 1 - 4 and their arrangement in fan/light 10 will now be
described. Blades 1 - 4-are intended to provide fan/light 10 with a useful
balance between satisfactory air-moving performance, compactness when the
blades are in their stowed (i.e. retracted or folded) position, together with
a
diameter of the translucent enclosure 12 that is large enough to provide a
reasonably diffuse lighting effect. The blades 1 - 4 are intended to lie
substantially above the translucent enclosure 12 when retracted. In the
embodiment shown and described herein, the enclosure 12 has a diameter
that is about 39% of the-overall diameter. of fanlight 10 with its blades 1 -
4
extended for operation. The diameter of the hub of a conventional ceiling fan
or fan/light without retractable blades is typically smaller than 39% of the
overall diameter over the blades. The larger the diameter of enclosure 12 for
a
given overall diameter, the easier it is to meet the requirement of compact
folding, with blades 1 - 4 above enclosure 12, but the more difficult it is to
provide satisfactory air moving performance at normal fan rotational speeds.
A range of from about 36% to about 42% for the above ratio is believed to be
possible by straightforward adaptation of the blade shapes as described
herein, but a figure in the region of 38% to 40% is preferred..
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The geometry of blades 1 - 4 will be described below by reference to
quantities and sections defined in Figures 10 and 11. In the schematic plan
view of Figure 10, enclosure 12 is represented simply by its circular outer
peripheral edge 26. Blades 1 - 4 are all shown in outline in their retracted
positions, blade I in solid lines and the others in chain-dotted lines, and
blade
1 is also shown in solid lines in its deployed position. Blades 1 - 4 are
substantially identical to each other and are generally scimitar-shaped, i.e.
of
arcuate form so as to lie, when retracted, within the enclosure peripheral
edge
26 and around the motor (not shown but centred on axis 15). The pivot axes
21 - 24 are adjacent to root ends 51 - 54 respectively (Figure 11) of blades I
- 4 and in their retracted position the blades 1 - 4 extend clockwise to tips
(free ends) 61 - 64 respectively. Item numbers with the postscript "a" are for
blade 1 in its deployed position and item numbers with the postscript "b" are
for blade I in its retracted position.
Blades 1 - 4 of fan/light 10 are shown (by arrow 7) as rotating
clockwise when seen from above. It is to be understood however, that
counter-clockwise rotation could equally well be chosen, in which case the
term "counter-clockwise" would be applicable where in the present description
clockwise" now appears, including in the definitions given below of the terms
"next blade" and "previous blade". (Note that for counter-clockwise rotation,
the blades would be made of opposite hand to blades 1 - 4, as it is preferred
that each blade's leading edge be its concave one.)
In relation to. any given one of blades 1 - 4, the term "next blade" refers
to the blade whose pivot axis is 90 degrees in the rotation direction (here
clockwise) from the pivot axis of the given blade, and the term "previous
blade" refers to the blade whose pivot axis is 90 degrees in a counter-
direction opposite to the rotation direction (i.e. counter-clockwise here)
from
the pivot axis of the given blade. Thus, in relation to blade 1, the next
blade is
blade 2 and the previous blade is blade 4. The blade shape will be described
mainly by reference to blade 1 for convenience, noting that blades 1 - 4 are
substantially identical.
To show how blades 1 - 4 are arranged relative to each other in nesting
fashion when retracted, it will be convenient to use sectional views on radial
planes, Le, planes that include the fan axis 15. Such a plane 42 is shown in
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Figure 10 and is shown to be at an angle 6 (theta) to a similar plane 44 that
includes both axis 15 and axis 21 of blade 1.
For discussion of the blade shape from the point of view of
aerodynamic characteristics when in the deployed position, it will be useful
to
5 consider blade sections taken on surfaces that are cylindrical, coaxial with
fan
axis 15, and located at stations radially spaced apart along a blade. Arcs
numbered 1 to 8 in.Figure 11 indicate such stations on blade 1. Stations I and
8 are respectively at radii of 39% and 97% of the overall fan radius (i.e.
substantially at the edge of enclosure 12) with stations'2 - 7 radially
10 equispaced between stations 1 and 8.
Each'of blades 1 - 4 pivots through 180 degrees between its retracted
and operating positions. From axis 21 to tip 61, representative blade 1 when
retracted extends from theta = 0 degrees to theta = approximately 168
degrees. The angle 166 degrees is chosen to be close to, but below, 180
15 degrees so as to provide a blade 1 whose tip 61 is well clear of enclosure
peripheral edge 26 when blade.1 is deployed, but with no more than two of
blades 1 -.4 overlapping each other- at any point when the blades are
retracted. This is important in keeping the overall height of the group of
blades
1 - 4, when retracted,'to a compactly small value. Note that if tip 61 where
at
theta = 180 degrees, all three of blades 1, 2 and 3 would overlap at theta =
180 degrees.
As can be seen in Figures 1, 5 and 7, representative blade 1 has two
distinct portions, namely a root-end portion 80 and a blade portion 82 which
in
the operating position extends outwardly of peripheral edge 26 of enclosure
25. 12 and is aerodynamically shaped to facilitate air movement. Blade portion
82
is supported cantilever-fashion from blade portion 80 which is pivotably
secured to blade support plate 14. In the preferred embodiment, portions 80
and 82 are formed as a single part, for example by injection molding in a
suitable plastics material.
Root end portion 80 comprises a plate 84 that lies above and,
approximately parallel to support plate upper surface 46. A hole 86 in plate
84
permits a stub shaft (not shown) to pass through it and through to the
underside of support plate 14 to be secured there to a planet gear (not shown)
of the blade synchronization mechanism as described previously. Root end
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portion 80 further comprises a blade end plate formation 88 whose function is
to provide a suitably strong connection between portions 80 and 82'with'blade
portion 82 inclined at an angle of incidence to plate 84 (see below).
Figure 12 shows a set of 12 radial sections (i.e. on planes 42) of
representative blade I and its next and previous blades 2 and 4 in their
retracted positions, each section being labeled with its correct value of
theta
for blade 1. Radii from fan axis 15 increase to the right in.sections (a) to
(I). In
each section, blade support plate 14 is shown, with its outer edge 90 at the
same lateral position on each page to facilitate comparison between the
sections. Outer edge 90 lies radially just within but is close to the
enclosure
peripheral edge 26 (not shown in Figure 12).
Sections (a) to (c) of Figure 12 show how portion 80 of blade 1
transitions to the cantilevered air-moving portion 82.
As can be best seen, in Figure 10, outer edge 94 of portion 82 of
1.5 representative blade 1 is very close to a circular arc except near the
rounded
tip 61, that arc being centred on fan axis 15 when blade 1 is retracted and
having. a.radius very close to the radius of enclosure peripheral edge 26.
Accordingly outer edge 94 of portion 82 of blade 1 lies at almost exactly the
same radius as the outer edges of next and previous blades 2 and 4, except
near tip 61, as shown in sections (d) to (1) of Figure 12.
Figure 10 and sections (a) to (f) of Figure 12 show that previous blade
4 overlies representative blade 1 between theta = 0 degrees and slightly Iess
than theta = 90 degrees, but without contact between blades I and 4.
Between theta = 90 degrees and theta = 165 degrees (sections (g) to (1))
blade 1 itself overlies next blade 2, without contact between blades 1 and 2.
Figure 13 is a graph showing the heights of inner edge 92 and outer
edge 94 of representative blade 1 above surface 46 of support plate 14 as a
function of angle theta. Inner edge 92 is higher than outer edge 94 for a
given
value of theta, consistently with blade I having an angle of incidence to the
horizontal so as to move air downward when deployed (see below). Absolute
height figures are used.in Figure 13, for a fanlight 10 having an overall
swept
diameter with blades 1 - 4 deployed of 1200mm:
Figure 14 is a graph showing the radial distance between inner edge
92 and outer edge 94 of representative blade 1 when in its retracted position
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as a function of angle theta. Absolute radial distances are used in Figure 13,
for a fan/light 10 having an overall swept diameter with blades 1,- 4 deployed
of 1200mm. The curve between data points has not been extended to the
data point for theta = 165 degrees because that point is affected by rounding
of tip 61:
Figure 15 is a graph showing the same data as Figure 13, but now for
all of blades 1 - 4, in. their respective peripheral angle (theta) positions.
The
initials "LE" and "TE" are used for inner and outer edges 92 and 94
respectively in Figure 15, because the inner edge of a blade is its leading
edge and the outer edge is its trailing edge, when in the deployed position.
Note that the blade pivot axes 21, 22, 23 and 24 are at angles theta of 0
degrees, 90 degrees, 180 degrees and 270 degrees, respectively.
Figure 12 - 15 together illustrate how blades 1 - 4 in their retracted
positions "nest" compactly together without any two blades contacting each
other. It has been found that the arrangement shown can also give
satisfactory air moving performance.
As illustrated by the edge heights in Figures 13 and 15, representative
blade 1 rises smoothly from its pivot axis 21 (at theta = 6 degrees) to a
point
(at about theta = 90 degrees) where it must overlap and clear the next blade
2. However, instead of continuing further upward at the same rate towards its
tip 61, blade I ceases to rise any higher, as shown by the leveling off and
then decreasing of the height of inner edge 92 with increasing theta. This
arrangement limits the overall height 96 (Figure 12) above support plate 14 of
the group of blades 1 - 4 when retracted. The maximum value of height 96
occurs for representative blade 1 at about theta 105 degrees.
It will be noted in Figure 13 and 15 that, after remaining approximately
constant between about theta = 90 degrees and theta = 120 degrees, outer
edge height 94 increases again beyond about theta = 120 degrees. As can be
seen from sections 6) to (1) in Figure 12 , and from the slight protrusion of
blade 1 shown in Figure 4, this optional feature means that some slight
sacrifice of compactness in the blade nesting arrangement is incurred
(although without any increase in overall height 96), it is believed to be
aerodynamically desirable, as set out later herein, and so is preferred.
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Figure 13 can be interpreted as a partial picture of blade 1 as it would
appear if projected on an imaginary cylindrical surface coaxial with fan axis,
with that surface then being laid flat. It is apparent that blade 1 in such a
picture resembles a gull wing, or an aircraft wing with a particular form of
varying dihedral, firstly rising with increasing distance from its root end
and
from a certain point rising no further or at a lesser rate towards its tip
end.
Figure 15 shows that the inner edge height 92 of representative
blade 1 becomes lower than the leading' edge height of its next blade 2 for
values of theta greater than about 150 degrees. This can be seen in sections
(k) and (I) of Figure 12. -It does not mean that there is contact between
blades
1 and 2 because the reduction in radial width of blade 1 means, that inner
edge'92 of blade 1 is radially outward of the corresponding edge of blade 2.
In addition to folding neatly, the blades 1. - 4 must move air downwards
reasonably efficiently when deployed and rotating about fan axis 15, so. the
shapes of blades 1 - 4 as they affect air movement will now be discussed.
The arcs in Figure 11 that are numbered 1 - 8 represent a set of spaced apart
cylindrical surfaces coaxial with axis-15 and radially spaced apart. Although
the downward air flow through fan/light 10 will not in general be precisely
axial
(i.e. parallel to axis 15) and therefore occur on such surfaces, a reasonable
ZO way to discuss blade shape is by reference to the intersections with the
cylindrical surfaces 1 - 8 of representative blade 1 when in its deployed
position.
It is also helpful in the following discussion of the representative blade
I when it is deployed to make mention of values of the angle theta that was
Z5 used above in describing its geometry when retracted. Theta is in effect a
measure of position along the scimitar-shaped blade 1. In Figure 11, there is
shown a non-physical point 101 that if blade 1 were to be retracted would fall
on axis 15, and that when blade 1 is deployed is displaced by 180 degrees
from axis 15 about the blade pivot axis 21. The value of angle theta
30 corresponding to a particular feature on deployed blade 1 can be found
using
the schematic plan view of Figure 11 by constructing firstly a line joining
point
101 to the feature in question and secondly a line 102 joining point 101 and
passing through axes 21, 15 and 23. Theta is the angle between these two
lines.
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Figure 16 shows cross sectional views of blade I taken on chords 100
(see-Figure 10) that are tangent to the cylindrical surfaces of stations 1 to
8..
These are close approximations to the shapes of the cylindrical surfaces of
intersection between stations 1 to 8 and blade 1, as. those surfaces would
appear if laid flat. In the sections of Figure 16, blade 1 moves right to
left, so
the leading edge 92 and trailing edge 94 are positioned as shown. Although
trailing edge 94 is of course not straight in reality, the views in Figure 16
are
so positioned that the trailing edge 94 in all-sections is. vertically aligned
to
facilitate comparisons among them.
Figure 17 is a graph showing alpha (a), the angle of incidence to the
horizontal of representative blade 1 at stations 2 to 8, the meaning of alpha
being illustrated in the section for station 7 in Figure 16. The values of
alpha
plotted in Figure 17 are not taken from the approximate sections of Figure 16,
but are estimates of the. values that would be obtained in the manner shown if
the sections of Figure 16 were laid-flat developments of the true surfaces of
intersection between the cylindrical surfaces numbered 2 to 8 and blade 1.
Figure 18 is a graph showing values of the true chord (i.e. distance
measured directly from leading edge.92 to trailing edge 94) of blade I at
intersections with the cylindrical surfaces numbered 1 to B. The chord values
are not taken from the approximate sections of Figure 16, but are estimates of
the values that would be obtained if the true surfaces of intersection between
blade 1 and the cylindrical surfaces numbered 1 to 8 were obtained and laid
flat.
It has been found that fan/light 10 with blades 1 - 4 having the
geometry shown does move air reasonably satisfactorily despite the'
comparatively large ratio of the diameter of enclosure 12 to the overall
diameter swept by the deployed blades 1 - 4 and the scimitar-like shape (in
plan view) of the blades.
Generally, the blades 1 - 4 thrust air downward (and themselves
experience a corresponding reactive lifting force) as they rotate. The
effectiveness of a blade in this (for a given speed of rotation) is. believed
to be
dependent on, at least, its aerofoil-type cross sectional shape, its incidence
to
the horizontal, its size (for example its chord as measured from leading edge
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to trailing edge), the distribution of these along the blade's length (span)
and
its shape as seen in plan view.
As seen in the cross-sections of representative blade 1 in Figure 16,
blades 1 - 4 have. an aerofoil-type cross-sectional shape, being cambered so
5' that their lower faces are concave and their upper faces are convex. Their
leading edges (eg leading edge 92 of representative blade 1) are rounded and
their trailing edges (eg edge 94 of representative blade 1) are sharp.
Generally, blades 1 - 4 are preferred to have cambered aerofoil sections.
Representative blade 1 has positive incidence to the horizontal (and is
10 of cambered aerofoil cross-section) near its pivot end where, when
deployed,
it crosses the enclosure peripheral edge 26, and this is believed to be one
factor in its air-moving performance. This positive incidence (alpha greater
than zero) is apparent in the section numbered 1 in Figure 16.
It is thought desirable that the lift distribution (and the consequent
15 distribution of air moving effect) along the length of a blade should be
generally smoothly varying and in particular that there should be no strong
concentration of the effect close to the outer (tip) end. Such a concentration
is
thought to produce a tendency for high pressure air below the tip area to
"leak" upward over the tip end (61 in representative blade 1) to the area
20 above the tip area, merely agitating the air locally (and wasting power)
rather
than moving. it bodily downward. Therefore, the distribution of incidence
angle
alpha shown in Figure 17 shows that the peak blade incidence of about 20
degrees is at about the radius of station 3 (see Figure 11) and smoothly
decreases with increasing radius to about 10 degrees at station 8. (Station 3
corresponds very approximately to theta = 60 degrees.)
The incidence distribution shown in Figure 17 is due in part to the
optional upsweeping of the blade trailing edge beyond about theta 120
degrees that was discussed above. Although a slightly more compact nesting
of blades 1 - 4 is achievable if this upsweeping is not incorporated, it does
appear to be beneficial to the blades' performance due to its effect on the
incidence distribution achieved.
A further way to influence the lift distribution along the blade is by
control of its width (chord) distribution. If one imagines a scimitar shaped
blade of constant width along its length (for example for all values of the
theta)
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deployed in the way shown for blades 1 - 4 in Figure 11, an effect of the
scimitar shape would be that the blade chord, as measured in the
circumferential direction with the blade deployed, would be highest at the
blade tip and root end and lower therebetween. To offset this effect and so
limit the tendency to concentrate the lifting effect at the tip and root ends,
blades 1 - 4 are not of constant width. Referring to Figure 14, the blade
width
as seen in plan view) is greatest at about theta = 90 degrees 'and
progressively reduces towards the tip end (61 for representative blade 1). As
can be seen in Figure 11, theta = 90 degrees corresponds approximately to
station 5. This reduction serves the dual purposes of compact nesting of the
blades when retracted (as discussed above) and obtaining the desired blade
lift distribution.
Figure 18 shows the blade chord increasing from a minimum in the
region of stations 2 and 3 before failing away at station 8 due to tip
rounding.
However, the rate of increase in chord with radius is less than it would be if
the blade width did not vary with angle theta in the way described herein. See
also Figure 16, where the alignment-of the sections numbered 1 to 8 on the
page allows the distribution of chord with radius to be seen.
As mentioned above the blades may be made conveniently by injection
20.. molding.in suitable plastics materials. As unobtrusiveness is a desired
feature
of fan/lights according to the invention, one way of enhancing this is to
provide
that the blades be formed from a transparent or at least translucent material.
This feature is believed to be inventive in itself.
Although the blade stowage arrangement and method described herein
provides for stowage of the blades without contact between blades, the
described stowage positions of the blades are such that slight sagging of one
blade so as to contact another may not cause failure to deploy. It will be
noted
in Figure 12 that the sectional view showing the smallest clearance between
blade 1 and its next blade 2 is section (g), corresponding to theta = 90
_ 'degrees. This is thought to be a suitable position for minimum clearance
and
so for first contact between blades 1 and 2 to occur if after a period of
stowage without fan use, blade 1 should sag slightly. It is thought that after
such contact between blades 1 and 2, the tendency to further sagging would
be limited and the moment arm about axis 21 of any friction. force due to
blade
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coritact less than for contact between tip 61 of blade I and the underlying
blade 2, thus, limiting the possibility of a failure of blade 1 to deploy on
fan
startup.
The possibility of blades that are comparatively thin. (so that they may
sag over time if not used) also means that the blades when in use may flex
upwardly-toward their tip ends. This can it is believed advantageously dire ct
air slightly more outwardly as well as downwardly than if the blades were
rigid.
The particular shape of the translucent lower section 9 of enclosure 2 is
by no means the only possible one. Even a shape that is not of the circular
shape in plan, as shown in the Figures 1 to 7 could be used as an alternative
aesthetic choice.
A further invention will now be disclosed..In fan/lights such as those
described by Villella in his aforementioned PCT application, the "sun gear"
may comprise a single member to which toothed segments are secured for
engagement with the "planet gears", instead of a complete gear. This
possibility, which it has been found can reduce manufacturing costs arises
because suitable sun and planet gear proportions can be chosen which do not
require the sun gear. to rotate far enough during deployment and retraction
for
any one tooth thereof to encounter more than one planet gear.
It will be readily apparent to persons skilled in the art that many other
variations and choices can be made to the fan/light described above without
exceeding the scope of the invention as stated.
