GB2098668A - Windmill rotor - Google Patents

Abstract

The rotor (10) comprises radial spars (111-116) to each of which is attached a sail (121-126) provided with centrifugal means (181 etc.) to increase the pitch of said sail with an increase in rotor speed and to reduce the pitch with a reduction in speed. <IMAGE>

Description

SPECIFICATION Improved windmill and rotor therefore This invention relates to awindmill and more ospeciallyto a rotor for a windmill said rotor having a plurality of sails. One such windmill is the well known Cretan windmill of polygonal outline that is always attended in use since it requires that the sails be furled when high wind speed are involved so that the rotor does not destroy itself. The Cretan type of windmill now finds favour in a modern form and the present invention seeks to provide such a windmill with automatic speed control.

According to one aspect of the present invention there is provided a rotor for a windmill said rotor comprising a plurality of radial spars to each of which is attached a sail that is provided with means that is able to increase or coarsen the pitch of said sail commensurably with an increase in the rotational speed of the spar when the rotor is in use and to reduce the pitch with a reduction in the rotational speed of the spar.

According to another aspect of the invention there is provided a windmill having a rotor as described above.

The invention will be more fully understood from the following description given by way of example only with reference to the figures of the accompanying drawings in which Figures 1A, 1B are respectively a front elevation and side elevation in 3rd angle orthographic projection of a rotor of a windmill, to a reduced scale.

Figures 2A, 2B are respectively a side elevation of a windmill with the rotor of Figures 1A, 1 B in position and Figure 2B is a sectional plan taken on section station BB of Figure 2A.

Figure 3 is a schematic to an even more reduced scale of the windmill of Figure 2A in its operational position (full lines) and its lowered position (chain dotted lines) for adjustment and servicing.

Referring now specifically to the several figures of the drawings, in Figures 1A, 1B a hexagonal rotor shown generally at 10 has six radial spars 111, 112, 113 etc. each having a sail 12,, 122, 133 etc. and a peripheral pre-stretched polyester rope 13.

Afront hub plate 14, and a rear hub plate 142 bolted with eighteen bolts, such as that shown at 15, form a suitably rigid structure for rotation about the axis AA1 which is aligned along bowsprit 16 from the outer end 1 6A of which come six tie ropes 17 to the respective peripheral end (see Figure 1 B) of their respective radial spars 111, 112, 113 etc. Each spar 111, 112, 113 etc. carries a centrifugal weight 181, 182, 183 etc. in the convenient form of a cantilever arm pivoted at ?9s, 192, 193 etc. It is to be noted that sail 1 is actuated by arm 182 from spar 112 and so for the others mutatis mutandis.The weight may be considered to be concentrated at the centre of the arm as shown on arm 181 at M1 giving the well known value for the generated centrifugal force in rotation of M, r2 where is the radius of M1.

Each arm (181 for example) is urged at itsextrem- ity (18E) toward the hub by elastic cord 20, tethered at 211 to adjustment member 22 and restrained by sheet231 tethered at 24, via pulley 25, to one peripheral end S, of triangular sail S, having ends Si, S2, S3; ends S2, S3 being on a spar.

Consider now the operation of arm 18r (the other arms 182,183 etc. acting in unison). The rotor rotates under the wind velocity as it is kept into the eye of the wind by vane 26 on tail strut 27 and slewing bearing shown generally at 28 (Figure 2A).

The arm 18, is subject to centrifugal force and at a certain value it moves about its pivot point 19, in the direction of arrow R1 for anti-clockwise rotation viewed from the front and looking onto the front extremity of the bowsprit. As it moves about its pivot so the sheet 231 is lengthened to allow the sail to coarsen its pitch; point S1 moving out of the plane of rotation of the rotor so that the line Si, S2 of the sail moves to change angle a1 toa2 until under certain conditions of high rotational speed a2 approaches a right angle and the rotor is prevented from over speeding since the sails are feathered, as shown at F1, F2 in Figure 1 B.This movement of the sail to coarsen pitch with increase of rotor speed is continuously varied (alto a!2 ) so that as the wind speed increased any accelerating torque is reduced. In operation a satisfactory intermediate position of the sail is generally adopted and a form of effective automatic rotational speed control thereby effected.

The rotor may rotate either clockwise or anticlockwise, the arm will still give effective speed control since it will always be moved by centrifugal force in the direction of arrow R1.

A simple geometrical evaluation of the movement of point S1 of the sail shows that the arm 181, ideally is to be of sufficient length to allow S1 to obtain the feathered position F1 F2; any reduction in its length 11 Figure 1 A will reduce the ability of al a2 becoming a right angle. In a rotor of 3 m diameter a rotor speed of 50 r.p.m. will allow the arm 181 to move in the direction of arrow R1 and a rotor speed of 100 r.p.m.

will allow the sail to approach the feathered condition.

The slewing bearing shown generally at 28 has three co-operating parts forming a sandwich. A top plate 28T, a bottom plate 28B and an intermediate plate 28 containing in each of a plurality of radial closed slots (generally six) a free right cylindrical roller 28R made of a material such as a long-chain synthetic polymeric amide for example that is known under the name of Nylon 66.

The plates 28T 28B are of good quality marine plyboard faced on their co-operating juxtaposed surfaces with formica as shown at 28F and held together rotationally by a suitable central bush. The slewing bearing in use takes rain water and this acts as a lubricant.

A boxed-in portion 29 also made from marine board houses for example an electrical alternator (not shown). The support tower shown generally at 30 is made of struts 31 all less than the radius of the rotor. The tower has a hinge point 32 and the release of a single bolt at33 enables the tower to be rabated into the position shown in chain-dot lines in Figure 3.

For a three metre diameter rotor a suitable tower is of height4.7m.

The length of each rotor spar, that is to say its radius is the greatest linear dimension of any unitary member of the windmill of the invention. For exam ple with a rotor of 3m diameter the radius is 1.5m and all struts (unitary members) of the tower are less than 1 .5m. This enables the whole windmill to be broken down into a kit of parts and placed in a box of about 1.5m length for ready transport to any part of the world where the windmill may quickly be assembled by unskilled labour.

A rotor of the invention at 3m diameter can produce at a wind speed of 7.5 m/s for example a power output in 0.45 kilowatts as shown from the well known equation.

kw = 0.00012 D2V3 kw = 0.00012 x 32 x 7.53 kw = 0.00012 x 9 x 421.8 kw = 0.45 kw.

Claims (1)

1. A rotor for a windmill, said rotor comprising a plurality of radial spars to each of which is attached a sail that is provided with means that is able to increase or coarsen the pitch of said sail commensurably with an increase in the rotational speed of the spar when the rotor is in use and to reduce the pitch with a reduction in the rotational speed of the spar.

2. The rotor as claimed in claim 1 wherein the pitch may be so coarsened that each sail approaches the feathered position.

3. The rotor as claimed in claim 1 or claim 2 wherein centrifugal means on a radial spar allows a sheet attached to a sail to lengthen with an increase in the rotational speed of the spar and to shorten with a decrease in the rotational speed of the spar.

4. The rotor as claimed in claim 3 wherein the centrifugal means is an arm pivoted at one extremity directly or indirectly to a spar and restrained at the other extremity by an elastic cord in opposition to the movement of said other extremity under centrifugal force generated when the spar is rotated to allow a sheet to lengthen and shorten with increase and decrease of rotational speed of the spar.

5. The rotor as claimed in any preceding claim wherein each said sail is of triangular form tethered at two points only on its spar.

6. The rotor as claimed in any preceding claim wherein the form of rotor is hexagonal.

7. The rotor of any preceding claim for rotation into the wind on a slewing bearing comprising a top plate, a bottom plate and an intermediate plate each plate made from marine board, the juxtaposed inner faces of the top and bottom plate being faced with formica and the intermediate plate carrying rollers made from a long-chain synthetic polymeric amide such as nylon, the three plates being held rotationally together by a bush.

9. Awindmill for rotor as claimed in claim 8 wherein the windmill is assembled from unitary parts, each part being of a length less than the said radius of a spar.

10. A kit of unitary parts from which a windmill as claimed in claim 9 may be constructed.

11. A rotor constructed and arranged substantially as hereinbefore described and as shown in Figures 1A 1B ofthe accompanying drawings.

12. Awindmill constructed and arranged substantially as hereinbefore described and as shown in Figures 2A 2B and 3 of the accompanying drawings.