DESC:FIELD OF INVENTION
The present invention relates to ceiling fans. The present invention particularly relates to twisted blades whose cross section is thin airfoil and which is run by brushless DC (BLDC) electric motor or induction motor at reduced speeds. Further the present invention runs with lower energy consumption level providing larger air volumes than ceiling fans with traditional blades. Advantageously the present invention relates to a high efficient and cost effective aerodynamically twisted blade.

BACKGROUND OF INVENTION
Ceiling fans powered by electric motors have been used for years in circulating air. They typically have a motor within a housing mounted to a down rod that rotates a set of fan blades about the axis of the down rod. Their blades have traditionally been flat and oriented at an incline or pitch to present an angle of attack to the air mass in which they rotate. This causes air to be driven downwardly.

When a fan blade that extends generally radially from its axis of rotation is rotated, its tip end travels in a far longer path of travel than does its root end for any given time. Thus its tip end travels much faster than its root end. To balance the load of wind resistance along the blades, and the air flow generated by their movement, fan blades have been designed with an angle of attack that diminishes towards the tip.

It is reported in U.S. Pat. No. 6,039,541 that energy efficiency, i.e. air flow (CFM) per power consumption (watts) increases in fans built with blade design that has larger twist in degrees at its root end to a smaller twist or angle of attack at its tip end. So it will be advantageous to develop ceiling fans fitted with set of aerodynamically designed blades which will be able to deliver enhanced air flow producing less air cutting noise than conventional blades which is economical to manufacture.

The present invention has thin airfoil cross section with uniform thickness throughout the blade. The twist angles are different from theoretically calculated and they are arrived at experimentally for better performance. Manufacturing of aerodynamically designed blades with varying thickness along the length requires more expensive tooling and production rate is also low. The present invention overcomes this issue using the design of uniform thickness blades.

OBJECTS OF INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is the primary object of the present invention to provide a ceiling fan fitted with aerodynamically designed blades to move more air than fan fitted with conventional blades.

It is another object of the present invention to provide a ceiling fan fitted with blades that produce less air cutting noise than conventional blades.

It is another object of the present invention to provide a ceiling fan with blades having thin airfoil have a positive twist both at the hub and the tip.

It is another object of the present invention to provide a ceiling fan with blades whose chord length is tapered down from hub to the tip.

It is another object of the present invention to provide a ceiling fan with blades capable of delivering more air at slow speed.

It is another object of the present invention to provide a ceiling fan with blades that consume less power.

It is another object of the present invention to provide a ceiling fan fitted with aerodynamically designed blades combined with induction motor having improved service value compared to conventional blades constructed with induction motor.

It is another object of the present invention to provide a ceiling fan fitted with aerodynamically designed blades combined with brushless DC (BLDC) motor having improved service value compared to ceiling fans constructed with induction motor or BLDC motor having relatively flat blades.

It is another object of the present invention to provide a ceiling fan with aerodynamically efficient blades having aerofoil cross section suitable for the low speeds having continually varying twist blade angle in order to maintain an angle of attack required for the generation of optimum lift.

It is another object of the present invention to provide a ceiling fan with blades made of steel.

It is another object of the present invention to provide a ceiling fan with blades made of material such as aluminium, magnesium and engineering plastic.

It is another object of the present invention to provide a ceiling fan with aerodynamically efficient blades having aerofoil cross section suitable for the low speeds having continually varying twist blade angle with integrally formed shank.

SUMMARY OF INVENTION
Thus according to the embodiment of the present invention there is provided a High efficiency ceiling fan having one or more blade assembly for high air delivery in which each blade assembly comprises of a blade, a shank and plurality of rivets.
It is another aspect of the present invention, wherein the chord length and radius vary across the length of the blade.

It is another aspect of the present invention, wherein the shank is rigidly fitted with the blade by one or more rivets.

It is another aspect of the present invention, wherein the blade assembly has a hub angle and a tip angle.

It is another aspect of the present invention, wherein that for a fan of 1200mm sweep, the section 1 located at the shank end of the blade has a chord length 130mm to 140mm and is constructed with radius R1 which is in the range 200 mm to 210 mm.

It is another aspect of the present invention, wherein the section 2 located at a distance L2 from the shank end, which is approximately 126mm has a chord length 120mm to 130mm and is constructed with radius R2 which is in the range 210 mm to 220 mm.

It is another aspect of the present invention, wherein the section 3 located at a distance L3 from the shank end, which is approximately 228mm has a chord length 110mm to 120mm and is constructed with radius R3 which is in the range 260 mm to 270 mm.

It is another aspect of the present invention, wherein the section 4 located at a distance L4 from the shank end, which is approximately 329 mm has a chord length 100mm to 110mm and is constructed with radius R4 which is in the range 235 mm to 245 mm.

It is another aspect of the present invention, wherein the section 5 located at a distance L5 from the shank end, which is approximately 431 mm has a chord length 90mm to 100mm and is constructed with radius R5 which is in the range 195 mm to 205 mm.

It is another aspect of the present invention, wherein the section 6 located at a distance L6 from the shank end, which is approximately 511 mm has a chord length 85mm to 95mm and is constructed with radius R6 which is in the range 180 mm to 190 mm.

It is another aspect of the present invention, wherein for a fan of 1200mm sweep the hub angle is in the range 18º to 22º, preferably 20º.

It is another aspect of the present invention, wherein for a fan of 1200mm sweep tip angle is in the range 8º to 13º, preferably 10º.

It is another aspect of the present invention, wherein the material of the blade is selected from steel, aluminium, magnesium and engineering plastic.

It is another aspect of the present invention, wherein the thickness (t) of the blade (1a) made of aluminium/ magnesium is in the range 0.8mm to 1.2mm, preferably 1mm.

It is another aspect of the present invention, wherein the thickness (t) of the blade (1a) made of engineering plastic is in the range 2.0mm to 4.0mm.

It is another aspect of the present invention, wherein the thickness (t) of the blade (1a) made of steel is in the range 0.4mm to 0.6mm.

It is another aspect of the present invention, wherein for a fan of 1200mm sweep the length (L) of the blade assembly is in the range 515mm to 520 mm.

BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 of the drawing schematically illustrates a ceiling fan.
Figure 2 of the drawing schematically illustrates the blade assembly of a ceiling fan.
Figure 3 of the drawing schematically illustrates the hub angle of the blade assembly according to the present invention.
Figure 4 of the drawing schematically illustrates the tip angle of the blade assembly according to the present invention.
Figure 5 of the drawing schematically illustrates the view of the blade sections according to the present invention shown superimposed on each other.
Figure 5a of the drawing schematically illustrates the detail of the sections of the fan blade according to the present invention.
Figure 6 of the drawing schematically illustrates the sectional view of first section of the blade according to the present invention.
Figure 7 of the drawing schematically illustrates the sectional view of second section of the blade according to the present invention.
Figure 8 of the drawing schematically illustrates the sectional view of third section of the blade according to the present invention.
Figure 9 of the drawing schematically illustrates the sectional view of fourth section of the blade according to the present invention.
Figure 10 of the drawing schematically illustrates the sectional view of fifth section of the blade according to the present invention.
Figure 11 of the drawing schematically illustrates the sectional view of sixth section of the blade according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
As in figure 1, the ceiling fan according to the present invention is fitted with blade assembly (1) comprising aerodynamically designed blades (1a) combined with brushless DC (BLDC) motor (2) having improved service value as compared to ceiling fans constructed with induction motor or BLDC motor having relatively flat blades. In order to deliver more air at slow speed operations of the fan, the aerofoil cross section of the blades (1a) is constructed with continually varying twist blade angle. The aerofoil construction of the blades enables minimizing the air cutting noise than conventional blades. The blades (1a) are airfoil construction and has positive twist angle both at the hub (1b) and the tip (1c). As shown in figure 2, the chord length of the blades is tapered down from hub to the tip and is varying continuously. In order to maintain an angle of attack required for the generation of optimum lift at low speeds the aerofoil blades also constructed with continually varying twist angle.

The blades (1a) are made of material such as steel, aluminium, magnesium and engineering plastic.

As in figure 1, the ceiling fan has plurality of fan blade assembly (1), a BLDC motor (2), a down rod (3) and canopies (4). In order to make the ceiling fan more attractive the canopies (4) and down rod (3) are designed to suit the profile of the BLDC motor (2). The ceiling fan may be provided with as many number of blade assembly for example 3, 4 or 5 as per the requirement.

In a preferred embodiment shown in figure 1, the ceiling fan is constructed with three number of blade assembly (1). The blade assembly (1) are mounted on the hub of the BLDC motor (2) which is a rotating member. The blade assembly (1) comprises blade (1a) and shank (1d) and the length (L) of the blade assembly (1) is in the range 515mm to 520 mm. For enhanced air delivery the blades (1a) of the ceiling fan is constructed with aerofoil shape as shown in figure 3. The fan blade (1a) shown in figure 3 pertains to a ceiling fan of 1200mm sweep. The ceiling fan blade (1a) has a first end which is the tip (1c ) end and a second end which is hub(1b) end. The fan blade is aerofoil cross section and the blade assembly (1) is constructed with hub angle (A1) which is in the range 18º to 22º, preferably 20º and tip angle (A2) which is in the range 8º to 13º, preferably 10º.

The aerofoil shaped blade comprises curved profile formed with varying radius at various sections across the length of the bade. In figure 5a, location of 6 sections of the blade is illustrated. The section 1 located at the shank end of the blade assembly has a chord length 130mm to 140 mm and is constructed with radius R1 which is in the range 200 mm to 210 mm. The section 2 located at a distance L2 from the shank end, which is approximately 126mm has a chord length 120mm to 130 mm and is constructed with radius R2 which is in the range 210 mm to 220 mm. The section 3 located at a distance L3 from the shank end, which is approximately 228 mm has a chord length 110mm to 120 mm and is constructed with radius R3 which in the range 260 mm to 270 mm. The section 4 located at a distance L4 from the shank end, which is approximately 329 mm has a chord length 100mm to 110 mm and is constructed with radius R4 which is in the range 235 mm to 245 mm. The section 5 located at a distance L5 from the shank end, which is approximately 431 mm has a chord length 90mm to 100 mm and is constructed with radius R5 which is in the range 195 mm to 205 mm. The section 6 located at a distance L6 from the shank end, which is approximately 511 mm has a chord length 85mm to 95 mm and is constructed with radius R6 which is in the range 180 mm to 190 mm.

In an embodiment the thickness (t) of the aerofoil shaped blade made of aluminium/ magnesium is in the range 0.8mm to 1.2mm, preferably 1 mm.

In an another embodiment the thickness (t) of the blade made of engineering plastic is in the range 2.0mm to 4.0mm.

In yet another embodiment the thickness (t) of the blade made of steel is in the range 0.4mm to 0.6mm.

The aerofoil shaped profile with non-uniform optimized twist angle provides higher air delivery even at slow speed working of the fan. The optimum speed of the ceiling fan fitted with the aerofoil shaped blade is in the range 250 RPM to 270 RPM and capable of delivering more than 230 m3 air per minute.

Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention. ,CLAIMS:WE CLAIM
1. High efficiency ceiling fan having one or more blade assembly (1) for high air delivery in which each blade assembly (1) comprising:
a blade (1a);
a shank (1d);
plurality of rivets (1e);
wherein the chord length and radius vary across its length of the blade;
wherein the shank (1d) is rigidly fitted with the blade (1a) by one or more rivets (1e);
wherein the blade assembly has a hub angle (A1) and a tip angle (A2) and
characterised in that for a fan of 1200mm sweep:
the section 1 located at the shank end of the blade has a chord length 130mm to 140 mm and is constructed with radius R1 which is in the range 200 mm to 210 mm;
the section 2 located at a distance L2 from the shank end, which is approximately 126mm has a chord length 120mm to 130 mm and is constructed with radius R2 which is in the range 210 mm to 220 mm;
the section 3 located at a distance L3 from the shank end, which is approximately 228 mm has a chord length 110mm to 120 mm and is constructed with radius R3 which is in the range 260 mm to 270 mm.;
the section 4 located at a distance L4 from the shank end , which is approximately 329 mm has a chord length 100mm to 110 mm and is constructed with radius R4 which is in the range 235 mm to 245 mm;
the section 5 located at a distance L5 from the shank end , which is approximately 431 mm has a chord length 90mm to 100 mm and is constructed with radius R5 which is in the range 195 mm to 205 mm and
the section 6 located at a distance L6 from the shank end, which is approximately 511mm has a chord length 85mm to 95 mm and is constructed with radius R6 which is in the range 180 mm to 190 mm.

2. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein for a fan of 1200mm sweep the hub angle (A1) is in the range 18º to 22º , preferably 20º.

3. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein for a fan of 1200mm sweep tip angle (A2) is in the range 8º to 13º, preferably 10º.

4. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein the material of the blade (1a) is selected from steel, aluminium, magnesium and engineering plastic.

5. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein the thickness (t) of the blade (1a) made of aluminium, magnesium is in the range 0.8mm to 1.2mm, preferably 1mm.

6. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein the thickness (t) of the blade (1a) made of engineering plastic is in the range 2.0mm to 4.0mm.

7. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein the thickness (t) of the blade (1a) made of steel is in the range 0.4mm to 0.6mm.

8. The high efficiency ceiling fan having one or more blade assembly (1) as claimed in claim1, wherein for a fan of 1200mm sweep the length (L) of the blade assembly (1) is in the range 515mm to 520mm.