FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A non-aerofoil fan blade, and fans with non-aerofoil blades, thereof
APPLICANTS:
Crompton Greaves Limited, CG House, Dr. Annie Besant Road, Worli, Mumbai -400030, Maharashtra, India, an Indian Company
INVENTOR:
Kusale Sarang Nagesh of Crompton Greaves Limited, Industrial Design Centre, Global R&D Centre, Bhaskara, Kanjur Marg (East) Mumbai - 400042, Maharashtra, India, an Indian National
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
This invention relates to the field of mechanical engineering, aerodynamics, and fluid dynamics.
Particularly, this invention relates to a non-aerofoil fan blade, and fans with non-aerofoil blades, thereof.
BACKGROUND OF THE INVENTION:
A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air or even liquid such as water. The fan consists of a rotating arrangement of vanes or blades which act on the air.
A ceiling fan is a mechanical fan, usually electrically powered, suspended from the ceiling of a room that uses hub-mounted rotating paddles to circulate air. Typically, a fan comprises a hub serving as a rotation center, and a plurality of blades disposed on the outer peripheral surface of the hub.
The basic function of a fan is to cause effective air flow. Rotations per minute characterize the speed of motor driving the fan, and hence, the fan speed itself.
In a ceiling fan, it is important that the air is blown downwards. Hence, the blades need to be characterized in a manner which enables this. The air circulated by the rotating movement of blades, induces evaporative cooling effect i.e. the sweat on the human body evaporates by the air movement, and the energy required for evaporation is taken from the body, and hence this phenomenon helps in reducing the temperature of human body and provides comfort. For a better evaporative cooling effect, the blades should be pitched to the right (if the motor spins anticlockwise) for downdraft.
Fan blades are characterized by terminologies such as aerofoil design, non-aerofoil design, pitch, leading edge, and trailing edge. An aerofoil is the shape of a wing or blade (of a propeller, rotor, or turbine) or sail as seen in cross-section. The leading edge is the part of the wing that first contacts the air. The trailing edge of an aerodynamic surface is its rear edge, where the airflow separated by the leading edge rejoins. The pitch is the angular edges of blades which is particularly important for effective movement of air. Shape of blades is crucial as the shape enables the blade to apply

pressure to air in front of it; and thus the air is forced downwards.
Ceiling fans may have a condition called as 'flapping of blades'. Blade flapping is the up and down movement of a rotor blade. It is important that this condition be reduced or eliminated from a safety perspective as well as from an efficiency and noise perspective.
Quality of fans is rated by parameters such as: ]) performance in moving air, effectively; 2) performance in moving air, quietly, 3) structural stability; and the like.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a fan blade to be used in a fan or motor which enables low speed operation, but ensures higher fluid flow.
Another object of the invention is to provide a fan blade to be used in a fan or motor which enables reduction in noise during its operation.
Yet another object of the invention is to provide a fan blade to be used in a fan or motor which eliminates 'flapping of blades'.
Still another object of the invention is to provide a fan blade to be used in a fan or motor which makes them structurally stronger.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a non-aerofoil fan blade being defined by at least a leading edge adapted to be coupled to a fan hub, at least a trailing edge adapted to be coupled to a fan hub, and at least a rounded tip adapted to mate said at least a leading edge with said at least a trailing edge, said rounded tip spaced apart from said fan hub, wherein:
a. said leading edge, characterised by a first set of curvature profiles comprising at least four
curvature profiles such that a first pre-defined curvature profile starting from said hub being a
relatively concave curvature profile, a subsequent pre-defined second curvature profile being a
substantially convex curvature profile, a subsequent pre-defined third curvature profile being a
relatively concave curvature profile, and a last pre-defined curvature profile being a convex
curvature profile;
b. said trailing edge, characterised by a second set of curvature profiles comprising at least two

curvature profiles such that a first pre-defined curvature profile starting from said hub being a substantially concave curvature profile, and a last pre-defined curvature profile being a substantially convex curvature profile;
c. at least a midsection curve, characterized in that, said midsection curve being defined by a third
set of curvature profiles, said midsection curve further being defined as a locus of midsection
points such that on any curve joining at least a point on said leading edge to at least a point on
said trailing edge, a midsection point is encountered which is the point where drastic change in
curvature occurs;
d. said fan blade comprising different sectional profiles at different radii, each of said different
sectional profiles being characterized by a different curve index; and
e. said fan blade comprising different sectional profiles at different radii, each of said different
sectional profiles being characterized by.a different thickness index.
According to this invention, there is also provided a fan with at least a non-aerofoil blade being defined by at least a leading edge adapted to be coupled to a fan hub, at least a trailing edge adapted to be'coupled to a fan hub, and at least a rounded tip adapted to mate said at least a leading edge with said at least a trailing edge, said rounded tip spaced apart from said fan hub, wherein:
a. said leading edge, characterised by a first set of curvature profiles comprising at least four
curvature profiles such that a first pre-defined curvature profile starting from said hub being a
relatively concave curvature profile, a subsequent pre-defined second curvature profile being a
substantially convex curvature profile, a subsequent pre-defined third curvature profile being a
relatively concave curvature profile, and a last pre-defined curvature profile being a convex
curvature profile;
b. said trailing edge, characterised by a second set of curvature profiles comprising at least two
curvature profiles such that a first pre-defined curvature profile starting from said hub being a
substantially concave curvature profile, and a last pre-defined curvature profile being a
substantially convex curvature profile;
c. at least a midsection curve, characterized in that, said midsection curve being defined by a third
set of curvature profiles, said midsection curve further being defined as a locus of midsection
points such that on any curve joining at least a point on said leading edge to at least a point on
said trailing edge, a midsection point is encountered which is the point where drastic change in
curvature occurs:
d. said fan blade comprising different sectional profiles at different radii, each of said different
sectional profiles being characterized by a different curve index; and

e. said fan blade comprising different sectional profiles at different radii, each of said different sectional profiles being characterized by a different thickness index.
Typically, said first pre-defined curvature profile is defined by a first pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.
Typically, said second pre-defined curvature profile is defined by a second pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.
Typically, said third pre-defined curvature profile is defined by a third pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.
Typically, said fan blade comprises a dual blade profile curvature, in that, said fan blade is geometrically divided into two parts: a first half part from said hub towards a middle point leading towards said rounded tip being a forward profiled section; and a second half part from said middle point till said rounded tip being a backward profiled section.
Typically, said midsection curve is an imaginary curve.
Typically, said midsection curve comprises a top midsection curve being defined by a locus of midsection points on an operative top surface of said fan blade.
Typically, said midsection curve comprises a bottom midsection curve being defined by a locus of midsection points on an operative bottom surface of said fan blade.
Typically, said fan blade comprises different sectional profiles at different radii; each of said different sectional profiles is characterized by a different curve index, each of the indexes is defined in accordance with a pre-determined shape profile derived from seagulls' wings.
Typically, said fan blade comprises different sectional profiles at different radii; each of said different sectional profiles is characterized by a different curve index, each curve index is defined by a locus of points characterized by a pre-defined equation or co-ordinate pattern.
Typically, said fan blade comprises different sectional profiles at different radii; each of said different sectional profiles is characterized by a different thickness index, each of the indexes is defined in accordance with a pre-determined shape profile derived from seagulls' wings.

Typically, said fan blade comprises different sectional profiles at different radii; each of said different sectional profiles is characterized by a different thickness index, each thickness index is defined by a locus of points characterized by a pre-defined equation or co-ordinate pattern.
Typically, said leading edge is the thickest; said trailing edge is the thinnest; and said midsection thickness lying between said leading edge thickness and said trailing edge thickness.
Typically, for any curvature from any point on said trailing edge to any point on said leading edge, a corresponding midsection point is thicker than said point on said trailing edge but is thinner than said point on said leading edge.
Typically, each of said different sectional profiles comprises at least a set of transition points, where curvature transition occurs for any curve from at least a point on said leading edge to at least a point on said trailing edge., said transition at least a set of transition points being defined by a locus of points which is said midsection curve.
Typically, said midsection curve comprises a top midsection curve being defined by a locus of midsection points on an operative top surface of said fan blade and said fan blade characterised, in that, a curvature from at least a point on said trailing edge to at least a point on said leading edge is a convex curvature profile on an operative top surface with the top most point of this convexity being a transition point and located on said top midsection curve.
Typically, said midsection curve comprises a bottom midsection curve being defined by a locus of midsection points on an operative bottom surface of said fan blade and said fan blade characterised. in that, a curvature from at least a point on said trailing edge to at least a point on said leading edge is a concave curvature profile on an operative bottom surface with the bottom most point of this concavity being a transition point and located on said bottom midsection curve.
Typically, each of said cross-sectional comprise at least a point on said leading edge, at least a point on a trailing edge, at least a point on a top midsection curve of said midsection curve, and at least a point on a bottom midsection curve of said midsection curve.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
This invention will now be described in relation to the accompanying drawings, in which: Figure 1 illustrates a bottom view of the fan blade;

Figure 2 illustrates an elevation view of the fan blade;
Figure 3 illustrates a side view of the fan blade;
Figure 4 illustrates a top view of the fan blade, of this invention, along with a fan hub;
Figure 5 illustrates various cross-sectional profiles of the fan blade, of this invention, in relation to the plurality of arcs of various radii marked in Figure 4 of the accompanying drawings;
Figure 6 illustrates a perspective view from top side of the fan blade;
Figure 7 illustrates velocity vectors of air delivery;
Figure 8 illustrates velocity variations across the fan;
Figure 9 illustrates pressure contour on top surface of blade;
Figure 10 illustrates pressure contour on bottom surface of blade; and
Figures 11 and 12 illustrate structural analysis of the blade.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a non-aerofoil fan blade, and fans with non-aerofoil blades, thereof.
Figure 1 illustrates a bottom view of the fan blade, of this invention. The angular arrow depicts direction of angular displacement of the fan blade in order to exert a downward thrust.
Figure 2 illustrates an elevation view of the fan blade, of this invention.
Figure 3 illustrates a side view of the fan blade, of this invention.
Figure 4 illustrates a top view of the fan blade, of this invention, along with a fan hub. A plurality of arcs of a circle are marked along the blade, with each arc being defined a radius.
Figure 5 illustrates various cross-sectional profiles of the fan blade, of this invention, in relation to the plurality of arcs of various radii marked in Figure 4 of the accompanying drawings.

Figure 6 illustrates a perspective view from top side of the fan blade, of this invention.
Reference numeral (10) refers to fan hub.
In accordance with an embodiment of this invention, there is provided a fan blade with a leading edge (12), characterized in that, said leading edge is defined by a first set of curvature profiles. This first set of curvature profiles may be characterized by at least four curvature profiles such that: 1) the curvature profile extending from the fan hub 10 to section C is a relatively concave curvature profile; 2)the curvature profile extending from section C until the section E is a substantially convex curvature profile; 3) the curvature profile extending from section E until the section F is a relatively concave curvature profile; and 4) the curvature profile extending from section F until a tip 18 is a convex curvature profile.
In accordance with another embodiment of this invention, there is provided a fan blade with a trailing edge (14), characterized in that, said trailing edge is defined by a second set of curvature profiles. The second set of curvature profiles may be characterized by at least two curvature profiles such that: 1) the curvature profile extending from the fan hub 10 until section E is a substantially concave curvature profile; 2) the curvature profile extending from section E until the tip 18 is a substantially convex curvature profile.
Typically, the leading edge (12) and the trailing edge (14) of the blade meet in a rounded tip (18).
Typically, the sections C, E, F are crucial sections and are defined as follows:
Section C is defined by a first pre-defined radius, from hub centre, and provides points on the
leading edge (12) as well as on the trailing edge (14).
Similarly, Section E is defined by a second pre-defined radius, from hub centre, and provides points on the leading edge (12) as well as on the trailing edge (14). Similarly, Section F is defined by a third pre-defined radius, from hub centre, and provides points on the leading edge (12) as well as on the trailing edge (14).
In accordance with yet another embodiment of this invention, there is provided a fan blade with a midsection curve (16), characterized in that, said midsection curve is defined by a third set of curvature profiles. The midsection curve is an imaginary curve which is defined as a locus of midsection points such that on any curve joining at least a point on the leading edge to at least a point on the trailing edge, a midsection point is encountered with is the point where drastic change in curvature occurs.

Typically, there is a top midsection curve which is defined by the locus of midsection points on the operative top surface of the fan blade. Typically, there is a bottom midsection curve which is defined by the locus of midsection points on the operative bottom surface of the fan blade.
The fan blade has a dual blade profile curvature, in that, it is divided into two parts: first half part from the hub towards a middle point leading towards the rounded tip being a forward profiled section; and the second half from the middle point till the rounded tip being a backward profiled section.
In accordance with still another embodiment of this invention, the fan blade defined by the leading edge (12) and the trailing edge (14) comprises different sectional profiles (A, B, C, D, E, F) at different radii; each different sectional profile being characterized by a different curve index; each of the indexes being defined in accordance with a pre-determined shape profile derived from seagulls' wings. The curvature changes are defined by a locus of points characterized by a predefined equation or co-ordinate pattern.
In accordance with still another embodiment of this invention, the fan blade defined by the leading edge (12) and the trailing edge (14) comprises different sectional profiles (A. B, C, D, E, F) at different radii; each different sectional profile being characterized by a different thickness index; each of the indexes being defined in accordance with a pre-determined shape profile derived from seagulls' wings. The thickness changes are defined by a locus of points characterized by a predefined equation or co-ordinate pattern.
Typically, the leading edge is the thickest; the trailing edge is the thinnest; and the midsection thickness lies between the leading edge thickness and trailing edge thickness. For any curvature from any point on trailing edge to any point on the leading edge, the midsection point is thicker than the point on the trailing edge but is thinner than the point on the leading edge.
As seen in Figure 5 of the accompanying drawings, reference numerals A, B, C, D, E, and F depict variations in curvature and thicknesses in the cross-sectional profile which characterize the blade profile of this invention. In each of the profiles a transition point is observed. Each of the transition points is a locus of points which is the midsection curve (16). Typically, there is a top midsection curve and a bottom midsection curve. Typically, from a point on the trailing edge to a point on the leading edge, there is a convex curvature profile on the operative top surface. The top most point of this convexity is a transition point and location on the top midsection curve (16). Typically, from a point on the trailing edge to a point on the leading edge, there is a concave curvature profile on the

operative bottom surface. The bottom most point of this concavity is a transition point and location on the bottom midsection curve (16). Therefore, each of the cross-sectional profiles A, B. C, D, E, and F (Figure 5) comprise one point on the leading edge, one point on the trailing edge, one point on the top midsection curve, and one point on the bottom midsection curve.
In accordance with a non-limiting exemplary embodiment, the fan blade has a cross-section curve, which is medium in size at hub (10) side (@ radius 100mm from axis of rotation); it narrows till radius equals 158mm (from axis of rotation), and then it goes on increasing till middle (@ radius 300 mm), and then goes on decreasing up to tip (18) (the span of the fan blade ends at radius 600mm). In the first mid section the blade profile curve is forward and in second mid section (From mid to tip) the blade profile curve is backward and the tip is rounded merging smoothly the leading edge and trailing edge.
According to the prior art, ceiling fan can be categorized into two types:
(1) High speed (300 to 400 RPM) High air delivery (Above 210 m3/min)
(2) Low speed (below 300 RPM) and low air delivery (below 200 m3/min)
The type (1) fans are generally used in tropical climate and hot Coastal areas where the High Air flow is the prime requirement.
The type (2) fans are generally used in dry climate or cold climate or in closed environments with air-conditioning units. These fans are only for air circulation purpose.
Typically, the fans, of the current invention, are operated in low speed (below 280 RPM) and deliver high air flow (above 215 m3/min). Thus, this fan creates less noise as compared to the High speed high air delivery fans (type 1)
In the prior art, the fan blades are thin so there are chances that they vibrate at higher speed(s). This phenomenon is known as 'flapping of blades'. It occurs due to tip size and high linear velocity at tips. This 'flapping' also creates noise which causes discomfort to humans. The blade of the current fan is structurally stronger; so it eliminates the flapping phenomenon. This blade is also narrow at the tip side which helps in reducing flapping.
Figure 7 illustrates velocity vectors of air delivery.
Figure 8 illustrates velocity variations across the fan. The red area shows maximum velocity. The green area shows intermediate velocity.

Figure 9 illustrates pressure contour on top surface of blade. The leading edge and trailing edge record relatively higher (yellow area) pressures than the remainder (green area).
Figure 10 illustrates pressure contour on bottom surface of blade. The hub edge records relatively lesser (yellow area) pressures than the tip edge (red area).
Figures 11 and 12 illustrate structural analysis of the blade of this invention.
The technical advancement of the current invention lies in specific changes in curvature and thickness along the blade profile; which curvature changes being defined by a locus of points characterized by a pre-defined equation or co-ordinated pattern, and which thickness changes being defined by a locus of points characterized by a pre-defined equation or co-ordinated pattern. Further, the forward and backward curvature forming dual curvature across the fan blade also contributes to technical advancement.
According to a non-limiting exemplary embodiment, a first fan blade was developed which had similar structure of the fan of the current invention, but with uniform thickness at every point. A second fan blade was developed which had a structure defined in accordance with the embodiments of the current invention. It was observed that air flow from the first fan blade was relatively less smoother as compared to the second fan blade. The air flow delivery, of the first fan blade, was 186 m3/min at 230 RPM. It was further observed that the air flow for the fan and fan blade of the current invention is relatively better and smoother. Also, the air flow delivery, of the second fan blade, was relatively greater at 217 m3/min at 234 RPM. Therefore, at comparable rate of angular displacement, air flow delivery of the current fan blade, with varying thicknesses, scored better than the prior art fan blade with uniform thickness.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A non-aerofoil fan blade being defined by at least a leading edge adapted to be coupled to a
fan hub. at least a trailing edge adapted to be coupled to a fan hub, and at least a rounded tip
adapted to mate said at least a leading edge with said at least a trailing edge, said rounded tip
spaced apart from said fan hub. wherein:
a. said leading edge, characterised by a first set of curvature profiles comprising at least
four curvature profiles such that a first pre-defined curvature profile starting from said
hub being a relatively concave curvature profile, a subsequent pre-defined second
curvature profile being a substantially convex curvature profile, a subsequent pre
defined third curvature profile being a relatively concave curvature profile, and a last
pre-defined curvature profile being a convex curvature profile;
b. said trailing edge, characterised by a second set of curvature profiles comprising at least
two curvature profiles such that a first pre-defined curvature profiJe starting from said
hub being a substantially concave curvature profile, and a last pre-defined curvature
profile being a substantially convex curvature profile;
c. at least a midsection curve, characterized in that, said midsection curve being defined by
a third set of curvature profiles, said midsection curve further being defined as a locus of
midsection points such that on any curve joining at least a point on said leading edge to
at least a point on said trailing edge, a midsection point is encountered which is the point
where drastic change in curvature occurs;
d. said fan blade comprising different sectional profiles at different radii, each of said
different sectional profiles being characterized by a different curve index; and
e. said fan blade comprising different sectional profiles at different radii, each of said
different sectional profiles being characterized by a different thickness index.
2. The non-aerofoil fan blade as claimed in claim 1, wherein said first pre-defined curvature profile being defined by a first pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.
3. The non-aerofoil fan blade as claimed in claim 1, wherein said second pre-defined curvature profile being defined by a second pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.
4. The non-aerofoil fan blade as claimed in claim 1, wherein said third pre-defined curvature profile being defined by a third pre-defined radius, from hub centre, providing points on said

leading edge as well as on said trailing edge.
5. The non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising a dual blade profile curvature, in that, said fan blade being geometrically divided into two parts: a first half part from said hub towards a middle point leading towards said rounded tip being a forward profiled section; and a second half part from said middle point till said rounded tip being a backward profiled section.
6. The non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve is an imaginary curve.
7. The non-aerofoil fan blade as claimed in claim I, wherein said midsection curve comprising a top midsection curve being defined by a locus of midsection points on an operative top surface of said fan blade.
8. The non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve comprising a bottom midsection curve being defined by a locus of midsection points on an operative bottom surface of said fan blade.
9. The non-aerofoil fan blade as claimed in claim 1. wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different curve index, each of the indexes being defined in accordance with a predetermined shape profile derived from seagulls' wings.
10. The non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different curve index, each curve index being defined by a locus of points characterized by a pre-defined equation or co-ordinate pattern.
11. The non-aerofoil fan blade as claimed in claim 1. wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different thickness index, each of the indexes being defined in accordance with a predetermined shape profile derived from seagulls' wings.
12. The non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different thickness index, each thickness index being defined by a locus of points

characterized by a pre-defined equation or co-ordinate pattern.
13. The non-aerofoii fan blade as claimed in claim 1, characterised, in that said leading edge being the thickest; said trailing edge being the thinnest; and said midsection thickness lying between said leading edge thickness and said trailing edge thickness.
14. The non-aerofoil fan blade as claimed in claim 1. characterised, in that for any curvature from any point on said trailing edge to any point on said leading edge, a corresponding midsection point is thicker than said point on said trailing edge but is thinner than said point on said leading edge.
15. The non-aerofoil fan blade as claimed in claim 1, characterised, in that each of said different sectional profiles comprising at least a set of transition points, where curvature transition occurs for any curve from at least a point on said leading edge to at least a point on said trailing edge, said transition at least a set of transition points being defined by a locus of points which is said midsection curve.
16. The non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve comprising a top midsection curve being defined by a locus of midsection points on an operative top surface of said fan blade and said fan blade characterised, in that, a curvature from at least a point on said trailing edge to at least a point on said leading edge is a convex curvature profile on an operative top surface with the top most point of this convexity being a transition point and located on said top midsection curve.
17. The non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve comprising a bottom midsection curve being defined by a locus of midsection points on an operative bottom surface of said fan blade and said fan blade characterised, in that, a curvature from at least a point on said trailing edge to at least a point on said leading edge is a concave curvature profile on an operative bottom surface with the bottom most point of this concavity being a transition point and located on said bottom midsection curve.
18. The non-aerofoil fan blade as claimed in claim 1. characterised, in that each of said cross-sectional comprise at least a point on said leading edge, at least a point on a trailing edge, at least a point on a top midsection curve of said midsection curve, and at least a point on a bottom midsection curve of said midsection curve.

19. A fan with at least a non-aerofoil blade being defined by at least a leading edge adapted to be
coupled to a fan hub, at least a trailing edge adapted to be coupled to a fan hub, and at least a
rounded tip adapted to mate said at least a leading edge with said at least a trailing edge, said
rounded tip spaced apart from said fan hub, wherein:
a. said leading edge, characterised by a first set of curvature profiles comprising at least
four curvature profiles such that a first pre-defined curvature profile starting from
said hub being a relatively concave curvature profile, a subsequent pre-defined
second curvature profile being a substantially convex curvature profile, a subsequent
pre-defined third curvature profile being a relatively concave curvature profile, and a
last pre-defined curvature profile being a convex curvature profile;
b. said trailing edge, characterised by a second set of curvature profiles comprising at
least two curvature profiles such that a first pre-defined curvature profile starting
from said hub being a substantially concave curvature profile, and a last pre-defined
curvature profile being a substantially convex curvature profile;
c. at least a midsection curve, characterized in that, said midsection curve being defined
by a third set of curvature profiles, said midsection curve further being defined as a
locus of midsection points such that on any curve joining at least a point on said
leading edge to at least a point on said trailing edge, a midsection point is
encountered which is the point where drastic change in curvature occurs;
d. said fan blade comprising different sectional profiles at different radii, each of said
different sectional profiles being characterized by a different curve index; and
e. said fan blade comprising different sectional profiles at different radii, each of said
different sectional profiles being characterized by a different thickness index.
20. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said first predefined curvature profile being defined by a first pre-defined radius, from hub centre, providing points on said leading edge as welt as on said trailing edge.
21. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said second predefined curvature profile being defined by a second pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.
22. The fan with at least a non-aerofoil fan blade as claimed in claim 1. wherein said third predefined curvature profile being defined by a third pre-defined radius, from hub centre, providing points on said leading edge as well as on said trailing edge.

23. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising a dual blade profile curvature, in that, said fan blade being geometrically divided into two parts: a first half part from said hub towards a middle point leading towards said rounded tip being a forward profiled section; and a second half part from said middle point till said rounded tip being a backward profiled section.
24. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve is an imaginary curve.
25. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve comprising a top midsection curve being defined by a locus of midsection points on an operative top surface of said fan blade.
26. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve comprising a bottom midsection curve being defined by a locus of midsection points on an operative bottom surface of said fan blade.
27. The fan with at least a non-aerofoil fan blade as claimed in claim 1. wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different curve index, each of the indexes being defined in accordance with a pre-determined shape profile derived from seagulls' wings.
28. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different curve index, each curve index being defined by a locus of points characterized by a pre-defined equation or co-ordinate pattern.
29. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different thickness index, each of the indexes being defined in accordance with a pre-determined shape profile derived from seagulls' wings.
30. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said fan blade comprising different sectional profiles at different radii; each of said different sectional profiles being characterized by a different thickness index, each thickness index being defined by a locus of points characterized by a pre-defined equation or co-ordinate pattern.

31. The fan with at least a non-aerofoil fan blade as claimed in claim 1, characterised, in that said leading edge being the thickest; said trailing edge being the thinnest; and said midsection thickness lying between said leading edge thickness and said trailing edge thickness.
32. The fan with at least a non-aerofoil fan blade as claimed in claim 1, characterised, in that for any curvature from any point on said trailing edge to any point on said leading edge, a corresponding midsection point is thicker than said point on said trailing edge but is thinner than said point on aid leading edge.
33. The fan with at least a non-aerofoil fan blade as claimed in claim 1, characterised, in that each of said different sectional profiles comprising at least a set of transition points, where curvature transition occurs for any curve from at least a point on said leading edge to at least a point on said trailing edge, said transition at least a set of transition points being defined by a locus of points which is said midsection curve.
34. The fan with at least a non-aerofoii fan blade as claimed in claim 1, wherein said midsection curve comprising a top midsection curve being defined by a locus of midsection points on an operative top surface of said fan blade and said fan blade characterised, in that, a curvature from at least a point on said trailing edge to at least a point on said leading edge is a convex curvature profile on an operative top surface with the top most point of this convexity being a transition point and located on said top midsection curve.
35. The fan with at least a non-aerofoil fan blade as claimed in claim 1, wherein said midsection curve comprising a bottom midsection curve being defined by a locus of midsection points on an operative bottom surface of said fan blade and said fan blade characterised, in that, a curvature from at least a point on said trailing edge to at least a point on said leading edge is a concave curvature profile on an operative bottom surface with the bottom most point of this concavity being a transition point and located on said bottom midsection curve.
36. The fan with at least a non-aerofoil fan blade as claimed in claim 1, characterised, in that each of said cross-sectional comprise at least a point on said leading edge, at least a point on a trailing edge, at least a point on a top midsection curve of said midsection curve, and at least a point on a bottom midsection curve of said midsection curve.