GB2271615A

GB2271615A - Windmills.

Info

Publication number: GB2271615A
Application number: GB9221539A
Authority: GB
Inventors: John Stanley Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-10-14
Filing date: 1992-10-14
Publication date: 1994-04-20
Also published as: GB9221539D0

Abstract

A rotor 1, mounted to rotate about a vertical axis, has four arms 2 carrying sails 3 at their ends. The sails are in the form of rectangular flat panels which are pivotally secured to the rotor for movement between positions which they are respectively flat against the arms and perpendicular to the arms. The panels can so pivot between first positions in which they present broad (high drag factor) faces to the wind, and second positions in which they present narrow (low drag factor) edge faces to the wind. <IMAGE>

Description

WINDMILLS This invention relates to the mounting of sails on a rotor for wind-powered rotation.

In anemometers it is common to mount a series of cup-shaped sails upon a rotor. As air passes over the anemometer greater air resistance is provided by those cups whose concave sides face the incident air flow than by the cups whose convex side faces the incident air flow. The resulting imbalance of forces causes rotation of the rotor.

The net energy output from each cup-shaped sail is dependent upon the difference between the force of the air flow upon the concave cup side during its driving run and the force required to push the convex side of the cup through the air flow during its return run.

Since the difference in drag offered by the concave and convex sides of each cup is relatively small, the net energy output of the rotor is also small.

According to the present invention, a sail providing a high drag factor face and a low drag factor face is pivotally mounted on a rotor so that during a return leg in each rotation of the rotor, when the sail is moving against the incident air flow, the sail is pivoted to present its low drag factor face to provide a lower drag to the air flow than that provided by presentation of the high draft factor face during a driving leg in the rotation of the rotor.

The sail becomes pivoted relative to the rotor on which it is mounted so that during the return leg a greatly reduced drag is presented to the air flow.

Restraining means may be provided to limit the movement of the sail about its pivot to any suitable angle.

Four sails may conveniently be mounted on the rotor but any suitable number may be used.

The rotor axis may be vertical or at any other suitable inclination.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which shows a plan view of a vertical shaft rotor with four sails mounted according to the invention.

A rotor 1, rotatable about a vertical axis, comprises four rotor arms 2 at right-angles to each other. Adjacent to the end of each arm 2 a sail 3, in the form of a flat panel, is attached to the arm 2 by a pivot 6 along one edge of the sail, the sail extending beyond the arm in both axial directions. The sail is formed of a rectangular board formed of canvas on a wooden frame and comprises a broad (high drag factor) face 4 and a narrow (low drag factor) face 5 at right-angles to each other. Each sail can move on its pivot 6 about an axis parallel to the rotor axis through an angle of substantially 900 between a first pivotal position in which the sail lies flat against the arm and the broad face 4 is substantially parallel to the arm and a second pivotal position in which that face is substantially perpendicular to the arm.

Restraining means in the form of a string 7 attached at one end to the rotor arm intermediate the pivot 6 and the rotor axis and at the other end to the sail restrains the angular movement of the sail about its pivot. In this embodiment, sail rotation is limited to 900.

Damping means may also be provided for the movement of the sail.

With the wind air flow emanating from a position of 0 , a driving leg for each rotation of the rotor occurs between 0 and 1800 and a return leg between 1800 and 3600.

During the driving leg, the incident air flow maintains each sail 3 in its first pivotal position, the air flow forcing the sail 3 against its arm 2 and the high drag factor face 4 being substantially parallel to the arm. The maximum driving force on the sail occurs as the arm passes through 900 at which point the high drag factor face 4 is perpendicular to the incident air flow.

As the arm passes through 1800 the air flow gets behind the sail and swings the sail out to its second pivotal position; the string 7 prevents the sail rotating more than 900 about its pivot. As the arm subsequently passes 2700 it is the low drag factor face 5 which is perpendicular to the incident air flow. Finally, as the arm moves between 2700 and 3600 the air flow acts upon the sail 3 to turn it back around its pivot 6 to its first position.

Claims

1. A windmill in which a sail providing a high drag factor face and a low drag factor face is pivotally mounted on a rotor so that during a return leg in each rotation of the rotor, when the sail is moving against the incident air flow, the sail is pivoted to present its low drag factor face to provide a lower drag to the air flow than that provided by presentation of the high drag factor face during a driving leg in the rotation of the rotor.

2. A windmill according to claim 1 comprising a plurality of such sails pivotally mounted on the rotor and uniformly distributed about the axis of the rotor.

3. A windmill according to claim 2 comprising four sails pivotally mounted at 900 intervals about the rotor axis.

4. A windmill according to any one of claims 1 to 3 in which the rotor is arranged to rotate about a vertical axis.

5. A windmill according to any one of claims 1 to 4 in which the or each sail is arranged to pivot through an angle of 900 on the rotor in moving between presentation of its high and low drag factor faces.

6. A windmill according to any one of the preceding claims in which the or each sail is in the form of an elongate panel arranged to pivot on the rotor about an axis extending longitudinally of the panel.

7. A windmill substantially as hereinfore described with reference to the accompanying drawing.