GB1599653A

GB1599653A - Form of windmill

Info

Publication number: GB1599653A
Application number: GB30383/77A
Authority: GB
Original assignee: Evans F C
Current assignee: Evans F C
Priority date: 1977-07-20
Filing date: 1977-07-20
Publication date: 1981-10-07
Also published as: BE869126A; DE2831731A1; FR2398195A1; NL7807654A

Description

(54) AN IMPROVED FORM OF WINDMILL (71) 1, FREDERICK CHARLES EVANS, a British subject, of Department of Physics, The University, St. Andrews, Fife, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to windmills for harnessing and converting wind power into useful energy.

It is known that vertical axis windmills of the drag or panemone type use pivoted blades in which the angle of attack is large and the airflow is fully stalled. In consequence, such machines cannot operate with a blade speed greater than wind speed. In the machine of my invention the blades produce lift, and consequently torque, under efficient aerodynamic conditions and can operate at blade speeds greater than wind speed.

A windmill according to the present invention has the advantages that, compared with existing designs of windmill, (i) it is very resistant to damage by storm-force winds, (ii) it is simple and economical to build in an efficient form, (iii) it requires no gearing to transmit power from the windmill which may be at an elevated position to machinery at a lower level, (iv) it does not require to be rotated in order to operate in winds of different directions and (v) it is self-starting.

Advantages (iii) and (iv) above are enjoyed by the present invention in common with other vertical-axis types of windmill. It is believed, however, that advantages (i) and (ii) are particular to the present invention.

According to the invention a windmill comprises a vertical shaft mounted for rotation about its longitudinal axis, a number of flat or aerofoil section blades each pivotally mounted for angular orientation about a longitudinal axis disposed parallel to the axis of rotation of the vertical shaft, supporting arms extending radially outwardly from the vertical shaft for supporting each blade and torque control means for controlling the angular orientation of the blades relative to the supporting arms. Counter-weights may be fitted to the blades in order to ensure that their orientation is not affected by centrifugal force, but is determined solely by the torque control device.The physical law obeyed by the torque control device may be varied to suit the application of the windmill, for example to make the windmill operate at a constant speed, to make it operate at a constant torque, or to maximise the total energy output for a particular range of wind speeds or loading conditions. The torque control may be used in association with fluidic logic for controlling the orientation of the blades in accordance with the wind speed and nature of the load to be driven. A windmill according to the invention permits the use of blades which do not require any twist, in contrast to propeller-type windmills.

The blades may be of aerofoil section for high efficiency, or they may simply be fiat sheets of material for low-cost applications.

A windmill according to the present invention has the features that the blades are free to pivot about a vertical axis, and that the motion about this axis is caused by the force of the wind. This gives the machine its selfstarting property and its speed-limiting capability. It also gives a greater component of force in the required direction for rotation and, in some conditions, a useful driving force for a greater proportion of the circle followed during rotation of the blades with the vertical shaft compared with windmills having fixed-pitch blades.

If desired, the blades may be only partially counter-balanced so that the centre of gravity of each blade is aft of the axis about which it is pivoted. In this way, the trailing edge of the blade will tend to swing out at high rotational speeds under centrifugal force to produce an air-brake effect which affords a way of limiting the speed of the windmill without relying on the feathering of the blades. Furthermore, the use of partially counter-balanced blades permits the designer to choose the tension and rate of the spring or other torque control so as to maximise power output at moderate wind speeds, and to set the limiting speed independently.

A windmill in accordance with the present invention will now be described by way of example with reference to the drawings accompanying the Provisional Specification in which: Figure 1 is a perspective of the windmill, and Figures 2(a) and 2(b) illustrate the principle of operation of the windmill.

Referring to Figure 1, the windmill has a vertical shaft 1, supporting arms 2 and blades 3. In this windmill, a torque control is in the form of a spring 4 extending between the arm 2 and the blade 3 as shown. Each blade is fitted with a counterweight 5. The vertical shaft is carried in suitable bearings, not shown. The power may be transmitted to any required form of load by connection to any part of the shaft. The load is not shown. The blades are given a symmetrical form of aerofoil section.

Figure 2 illustrates the principle of operation of the windmill for two cases, (a) when the speed of the blades is less than the wind speed and (b) when the speed of the blades is greater than the wind speed. In each case the direction and magnitude of the true wind is indicated by a solid arrow, and the directions and magnitude of the apparent wind at four points 1', 2', 3' and 4' in the cycle are indicated by dotted arrows. Referring to Figure 2(a), it can be seen that the wind is incident to the trailing edge of the blade at point 1' and is incident to the leading edge of the blade at point 3'. At all other points in the cycle the action of the wind in conjunction with the torque control it to turn the blade to a suitable angle of attack for it to produce lift under efficient aerodynamic conditions, in such a direction as to rotate the windmill clockwise in the plan view shown.At point 1' the blade swings over as indicated by the curved dotted arrow. Referring to Figure 2(b), the wind is incident to the leading edge twice per cycle, at points 1' and 3', and it is never incident to the trailing edge. At all other points the action of the wind is again to rotate the windmill clockwise as indicated by arrow-heads on the circle of revolution ofthe blades. In this case the angle of attack is always small, and these are the conditions under which a normal aerofoil section is most efficient.

The windmill of the present invention is self-starting from rest because torque is produced in the same direction in cases (a) and (b).

In the event of a very strong wind, the blades tend to feather to a very small angle of attack, so that the wind resistance is reduced.

In emergency, the torque control may be disconnected, either manually or automatically, so that all the blades will point directly into the wind and the wind resistance of the whole structure will be very small.

WHAT I CLAIM IS: 1. A windmill comprising a vertical shaft mounted for rotation about its longitudinal axis, a number of flat or aerofoil section blades each pivotally mounted for angular orientation about a longitudinal axis disposed parallel to the axis of rotation of the vertical shaft, supporting arms extending radially outwardly from the vertical shaft for supporting each blade and torque control means for controlling the angular orientation of the blades relative to the supporting arms.

2. A windmill according to Claim 1 including means for counterbalancing each blade so that angular orientation of the blades is substantially unaffected by centrifugal force during rotation of the windmill.

3. A windmill according to Claim 1 including means partially counterbalancing each blade so that the centre of gravity of each blade is disposed aft (when considered relative to the direction of rotation thereof with the vertical shaft) of the vertical shaft) of the pivotal axis of the blade.

4. A windmill according to Claim 1, 2 or 3 wherein the torque control is spring, hydraulic, pneumatic or electro-mechanical mechanism.

5. A windmill according to any preceding claim wherein the blades are of aerofoil cross-section.

6. A windmill according to any one of Claims 1 to 4 wherein the blades are of rectangular flat sheet from.

7. A windmill constructed and arranged substantially as hereinbefore described with reference to and as shown in the drawings accompanying the provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. example with reference to the drawings accompanying the Provisional Specification in which: Figure 1 is a perspective of the windmill, and Figures 2(a) and 2(b) illustrate the principle of operation of the windmill. Referring to Figure 1, the windmill has a vertical shaft 1, supporting arms 2 and blades 3. In this windmill, a torque control is in the form of a spring 4 extending between the arm 2 and the blade 3 as shown. Each blade is fitted with a counterweight 5. The vertical shaft is carried in suitable bearings, not shown. The power may be transmitted to any required form of load by connection to any part of the shaft. The load is not shown. The blades are given a symmetrical form of aerofoil section. Figure 2 illustrates the principle of operation of the windmill for two cases, (a) when the speed of the blades is less than the wind speed and (b) when the speed of the blades is greater than the wind speed. In each case the direction and magnitude of the true wind is indicated by a solid arrow, and the directions and magnitude of the apparent wind at four points 1', 2', 3' and 4' in the cycle are indicated by dotted arrows. Referring to Figure 2(a), it can be seen that the wind is incident to the trailing edge of the blade at point 1' and is incident to the leading edge of the blade at point 3'. At all other points in the cycle the action of the wind in conjunction with the torque control it to turn the blade to a suitable angle of attack for it to produce lift under efficient aerodynamic conditions, in such a direction as to rotate the windmill clockwise in the plan view shown.At point 1' the blade swings over as indicated by the curved dotted arrow. Referring to Figure 2(b), the wind is incident to the leading edge twice per cycle, at points 1' and 3', and it is never incident to the trailing edge. At all other points the action of the wind is again to rotate the windmill clockwise as indicated by arrow-heads on the circle of revolution ofthe blades. In this case the angle of attack is always small, and these are the conditions under which a normal aerofoil section is most efficient. The windmill of the present invention is self-starting from rest because torque is produced in the same direction in cases (a) and (b). In the event of a very strong wind, the blades tend to feather to a very small angle of attack, so that the wind resistance is reduced. In emergency, the torque control may be disconnected, either manually or automatically, so that all the blades will point directly into the wind and the wind resistance of the whole structure will be very small. WHAT I CLAIM IS:

1. A windmill comprising a vertical shaft mounted for rotation about its longitudinal axis, a number of flat or aerofoil section blades each pivotally mounted for angular orientation about a longitudinal axis disposed parallel to the axis of rotation of the vertical shaft, supporting arms extending radially outwardly from the vertical shaft for supporting each blade and torque control means for controlling the angular orientation of the blades relative to the supporting arms.