GB2169663A

GB2169663A - Windmill blade

Info

Publication number: GB2169663A
Application number: GB08432768A
Authority: GB
Inventors: Gordon Proven
Original assignee: Proven Engineering Products Ltd
Current assignee: Proven Engineering Products Ltd
Priority date: 1984-12-29
Filing date: 1984-12-29
Publication date: 1986-07-16
Also published as: GB2169663B; GB8432768D0

Abstract

A propylene windmill blade having a hub portion 7 and a blade portion 6 which are interconnected through a resilient angled crease hinge 6,7,8, whereby application of an increasing centrifugal force in a direction outwardly along the blade caused by increased speed of rotation of the windmill, results in an alteration of the pitch of the blade through blade rotation about the angled creases. <IMAGE>

Description

SPECIFICATION Windmill blade This invention relates to a windmill blade.

With the depletion of the world's mineral resources alternative sources of energy have become more popular, and one of these is wind power. It has been proposed to erect large windmills having wind-driven blades connected with generators for producing electricity. However, the large variations in wind speed have necessitated the incorporation of pitch variation for the blades so that a generally constant blade rotation is approximated.

Such pitch variation has hitherto been achieved by providing mechanical spring linkages between the hub of the windmill and the blades, the linkages being pivotal to alter the blade pitch.

According to the present invention there is provided a windmill blade having an inner portion and an outer portion interconnected through a hinge whose axis is angled with respect to the main axis of the outer portion of the blade, the inner portion of the blade being normally in a plane at an angle to the plane of the outer portion, the arrangement being such that an increasing force applied to the blade in a direction along the main axis of the blade portion causes rotation of the outer portion about the hinge, said rotation resulting in an alteration in the pitch of the outer portion.

Preferably a second hinge is provided with its axis at an angle to the axis of the first hinge whereby said increasing force causes rotation about both hinges simultaneously.

Preferably also the blade is formed from a single piece of material which is preferably resilient. The material may typically be plastics, for example polypropylene, or spring steel.

The hinge is preferably resilient so that when the applied force is reduced the blade returns to its original pitch. The blade is then self-adjusting in pitch in each direction.

The hinge or hinges may be arranged so that said increasing applied force causes elongation of the overall blade, resulting in alteration of pitch, while reduction of said applied force causes the blade to retract in overall length.

The blade may be single or may be integral with a further blade or further blades, for example by all integral blades together being of unitary construction.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a windmill having blades of the present invention; Figure 2 is a front view of a central part of a blade of the present invention; Figure 3 is a side view corresponding to Fig. 2; and Figure 4 is a section on A-A of Fig. 1.

Referring first to Fig. 1, a windmill 1 for generating electricity has a support post 2 secured to the ground through a base plate 3, the post 2 having mounted on it a rotatable director 4 with a tubular housing. An electrical generator is mounted within the housing 5 and connected to wiring which runs through the director 4 and post 2 and thence to a location- where electricity is required. The generator is on a rotatable shaft which carries at the end four blades 6. In use the director 4 ensures that the blades 6 are always disposed in a direction for rotation by the wind.

Referring now to Fig. 2, the blades 6 are in pairs each pair being connected through a hub 7 having a through hole 11 for mounting on the rotatable shaft. Each pair of blades 6 and hub 7 are formed from a single piece of polypropylene which is capable of flexing as a hinge while maintaining substantial rigidity along its length. Each blade 6 has a double hinge formation adjacent the hub 7, the hinges being formed by providing three creases 8, 9, 10 in the blade 6 across its width at desired angles. The creases 8, 9, 10 are disposed so that in front view (Fig. 2) the creases 8 and 10 are parallel to one another while the crease 9 forms a diagonal between them; however, all three creases 8, 9, 10 are out of plane with respect to one another as can be seen in Figs. 3 and 4.

The main portion 6A of each blade is nonplanar as it twists along its length to provide a differential angle of attack to the wind, as in a conventional windmill blade.

The effect of the creases 8, 9 and 10 is that as the blades 6 are driven round by the wind they experience centrifugai force in an outward direction, and this force tends to "straighten out" the creases 8, 9, 10, to allow the blade 6 to elongate. This straightening-out effect increases with increasing wind force, and the creases are so angled that as they straighten out they cause the pitch of the blade 6 to alter. Thus an increasing wind force results in pitch alteration which shows the rate of rotation of the blades 6.

The polypropylene of the blades 6 is resilient so a decrease in wind speed results in the creases 8, 9, 10 returning towards their original attitude, with automatic adjustment of the blade pitch to ensure faster rotation of the blades 6.

Thus the blades 6 rotate at a generally constant speed regardless of wind speed.

Modifications and improvements can be made without departing from the scope of the invention. For example, more or less than three creases can be provided as required; the centre of gravity of the blade may be disposed forward of the blade axis; the centre of effort may be rearward of the blade axis; damping may be provided for the creases 8, 9, 10, such as by reinforcement of the polypropylene; and the blades 6 may be secured to a separate non-intregral hub through a hinge arrangement.

The blade 6 is preferably arranged to rotate at a speed whereby the blade outer ends travel at 6 to 8 times the average wind speed.

Claims

1. A windmill blade having an inner portion and an outer portion interconnected through a hinge whose axis is angled with respect to the main axis of the outer portion of the blade, the arrangement being such that an increasing force applied to the blade in a direction along the main axis of the blade causes the outer portion to rotate on the hinge around the main axis of the blade, resulting in alteration of the pitch of the outer portion of the blade.

2. A windmill blade according to Claim 1, wherein the hinge is resilient so that on reduction of the applied force the hinge returns to its original attitude.

3. A windmill blade according to Claim 1 or 2, wherein the first and second portions of the blade adjacent the hinge are in planes which are angled to one another and application of said increasing force causes the angle between the planes to decrease.

4. A windmill blade according to Claim 1, 2 or 3, wherein the hinge is arranged so that application of said increasing force causes elongation of the overall blade length.

5. A windmill blade according to any one of the preceding Claims, wherein the blade is of unitary construction.

6. A windmill blade according to any one of the preceding Claims, wherein a second hinge is provided with its axis at an angle to the axis of the first hinge whereby application of said increasing force causes rotation on both hinges simultaneously.

7. A windmill blade according to Claim 6, wherein the first and second hinges are mutually out-of-piane.

8. A windmill blade substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

9. A windmill having a blade according to any one of the preceding Claims.