GB1601369A

GB1601369A - Variable geometry blade

Info

Publication number: GB1601369A
Application number: GB4673477A
Authority: GB
Original assignee: Coventry City Council
Current assignee: Coventry City Council
Priority date: 1978-05-24
Filing date: 1978-05-24
Publication date: 1981-10-28

Description

(54) VARIABLE GEOMETRY BLADE (71) We, COVENTRY CITY COUNCIL, of the Council House, Earl Street, Coventry, CVI. 5RR. West Midlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention has reference to angularly rotatable blades of aerofoil cross section and has for its object to provide a construction of blade in which the geometry is variable according to its speed of angular rotation in order to present an optimum angle of attack of the blade along the length of the latter in relation to the flow of air or other fluid medium in which the blade is operated, especially where a series of radially arranged blades (i.e. a windmill) is driven by an air or like flow.However, the invention also has practical application where the arrangement is such that air or other medium is driven by a series of the radial blades acting as a fan or impeller. These and other practical advantages of the invention will be apparent from the following disclosure.

According to this invention an angularly rotatable blade has at least one mass attached to, or arranged to act upon, spar structure of the blade whereby on the mass being subject to centrifugal force as the blade is angularly rotated, the spar structure is subject to distorting forces by the mass which effect twisting of the blade about its longitudinal axis.

In practice construction and arrangements may be as follows, reference being had to the accompanying drawings in which: Figure 1 is a cross sectional view of an aerofoil blade embodying the invention as viewed from the blade tip towards its axis of angular rotation.

Figure 2 is a view in the direction of the arrow W of Figure 1, and Figures 3 and 4 are cross sectional views similar to Figure 1 but each showing a modified arrangement.

Referring to Figures 1 and 2 the blade 1 of aerofoil cross section and of hollow interior construction is shown provided with a pair of spaced apart spar members 12, 13 extending for substantially the length of the blade i.e.

through the usual internal ribs 11 of the latter. The axis of angular rotation of the blade 1 is indicated at R and the direction of wind acting on the blade at W, i.e. where the blade forms part of a windmill, e.g. for driving a generator or pump. D indicates the direction of motion of the blade.

For the purpose of this invention and attached to each spar 12, 13 by means of an arm 4 is a mass 2, 3, the masses 2, 3 being arranged one each side of the blade 1 in a balanced manner. The arms are shown extending substantially perpendicular from the corresponding surface of the blade 1 or, as indicated at 2a, 3a in Figure 2, they may have some inclination towards the axis R of angular rotation of the blade.

The arrangement is such that as the blade 1 or each such blade of a windmill is angularly rotated, the masses 2, 3 are subject to centrifugal force, the extent of outward movement of the masses away from the axis R depending on the speed of rotation.

The effect of such outward movement of the masses 2, 3 causes the spars 12, 13 to be progressively bent against their - inherent resilience and in a direction parallel to their depth, the resulting displacement causing twisting of the blade as indicated in chain dotted lines at 11 in Figure 1.

As a result the angle of twist of the particular portion of the blade 1 is varied to suit the prevailing speed of angular rotation in an automatic self-adjusting manner so that an optimum or substantially constant angle of attack is maintained for maximum efficiency in converting the energy of the wind into mechanical energy.

Although the centrifugal force acting on the masses 12, 13 is proportional to the square of the speed of angular rotation of the blade 1, a good approximation can be obtained in practice whereby, within suitable limits, the angle of twist of the blade substantially corresponds to the speed of rotation.

In order to avoid the use of external masses, an arrangement is shown in Figure 3 in which a mass 20 is accommodated within the hollow interior of the blade 1 and is shown connected by an arm 24 to a rear spar 113 in relation to the leading edge L of the blade. This spar 113 is linked at 25 to a front spar 112 which is inclined to the rear spar 113. On centrifugal movement of the mass 20 away from the axis of rotation R the rear spar 113 is progressively bent forward, i.e. towards the leading edge L and, by the link 25, imparts similar bending movement to the front spar 112 but in a direction perpendicular to its plane of inclination. The resulting displacement of the front spar 112 causes twisting of the blade 1 in the manner indicated in chain dotted lines at 11. In this case the spars 112, 113 are bent in directions normal to their planes and not crosswise as in Figure 1.

Referring to Figure 4 front and rear spars 102, 103 of the blade 1 are part of a box spar structure 10 of the latter and forwardly and rearwardly disposed masses 32, 33 within the hollow interior of the blade are connected by corresponding arms 34 to diagonally opposite corners of the box structure 10. By such an arrangement and on centrifugal movement of the masses 32, 33 warping forces are applied to the box structure 10 which again effects twisting of the bade 1 in accordance with its speed of angular rotation.

In the embodiments of the invention herein described and shown in the drawings, the centrifugal action of the mass of masses 2, 3, 20 or 32, 33 is such as to provide an appropriate angle of twist of each portion of the blade 1 where the latter is driven by wind or similarly by the action of relatively moving air or the like. However, the arrangement of the mass or masses may be such that on increase in the speed of angular rotation of the blade 1, the angle of attack is reduced to e.g. a feathered position This applies in particular where a radial series of the blades operate as a fan for driving air up to a required speed of rotation of the fan and thereafter ceases to drive the air or at least only drives it at a reduced rate.

Such an arrangement has practical application in the case of a fan associated with a cooling radiator of an internal combustion engine especially of a motor vehicle and particularly where the fan is driven by the engine.

Thus at a low or idling speed when ram air flow through the radiator is non-existent or negligible i.e. where the vehicle is stationary or only moving slowly, the angle of attack of the blade is such as to effect cooling air flow through the radiator, but as engine speed increases (with forward movement of the vehicle) the driving action of the fan decreases to or towards a feathered condition of each blade as ram air flow increases. Particularly in the case of a cooling or other fan, the mass or masses may be suitably connected or arranged to act upon spar structure of each blade of a moulded construction of fan e.g.

in suitable plastic material.

In a further practical application of the invention, the centrifugal action of the mass or masses may be such as to cause overtwist of the or each blade 1 so that it has a governing action on the speed of angular rotation e.g. in the case of a windmill.

Mass balancing of the blades may be effected to counteract blade flutter.

WHAT WE CLAIM IS:- 1. An angularly rotatable blade having at least one mass attached to, or arranged to act upon, spar structure of the blade whereby on the mass being subject to centrifugal force as the blade is angularly rotated, the spar structure is subject to distorting forces by the mass which effect twisting of the blade about its longitudinal axis.

2. An angularly rotatable blade according to claim 1 wherein the or each mass is connected by an arm to the spar structure of the blade.

3. An angularly rotatable blade according to claim 1 or 2 wherein the or each mass is situated externally or internally of the blade.

4. An angularly rotatable blade according to claim 1, 2 or 3 wherein the or each mass when subject to centrifugal force due to angular rotation of the blade is arranged to impart distorting forces on the spar structure against the inherent resilience of the latter and in a direction parallel to its depth whereby the resulting displacement thereof causes twisting of the blade about its longitudinal axis.

5. An angularly rotatable blade according to claim 1, 2 or 3 wherein at least one said mass, when subject to centrifugal force due to angular rotation of the blade is arranged to impart distorting forces on the spar structure against the inherent resilience of the latter and in a direction substantially normal to its depth whereby the resulting displacement thereof causes twisting of the blade about its longitudinal axis.

6. An angularly rotatable blade according to claim 1, 2 or 3 wherein the or each mass when subject to centrifugal force due to angular rotation of the blade is arranged to impart warping forces on the spar structure whereby the resulting displacement thereof causes twisting of the blade about its longitudinal axis.

7. An angularly rotatable blade according to claims 2, 3 and 4 wherein a pair of masses externally situated one at each side of the blade are each connected by an external arm to a corresponding member of a pair of spar members of the spar structure whereby on the masses being subject to centrifugal force due to angular rotation of the blade, the spar members are bent in a direction parallel to their depth and in an opposite manner so

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. a mass 20 is accommodated within the hollow interior of the blade 1 and is shown connected by an arm 24 to a rear spar 113 in relation to the leading edge L of the blade. This spar 113 is linked at 25 to a front spar 112 which is inclined to the rear spar 113. On centrifugal movement of the mass 20 away from the axis of rotation R the rear spar 113 is progressively bent forward, i.e. towards the leading edge L and, by the link 25, imparts similar bending movement to the front spar 112 but in a direction perpendicular to its plane of inclination. The resulting displacement of the front spar 112 causes twisting of the blade 1 in the manner indicated in chain dotted lines at 11. In this case the spars 112, 113 are bent in directions normal to their planes and not crosswise as in Figure 1. Referring to Figure 4 front and rear spars 102, 103 of the blade 1 are part of a box spar structure 10 of the latter and forwardly and rearwardly disposed masses 32, 33 within the hollow interior of the blade are connected by corresponding arms 34 to diagonally opposite corners of the box structure 10. By such an arrangement and on centrifugal movement of the masses 32, 33 warping forces are applied to the box structure 10 which again effects twisting of the bade 1 in accordance with its speed of angular rotation. In the embodiments of the invention herein described and shown in the drawings, the centrifugal action of the mass of masses 2, 3, 20 or 32, 33 is such as to provide an appropriate angle of twist of each portion of the blade 1 where the latter is driven by wind or similarly by the action of relatively moving air or the like. However, the arrangement of the mass or masses may be such that on increase in the speed of angular rotation of the blade 1, the angle of attack is reduced to e.g. a feathered position This applies in particular where a radial series of the blades operate as a fan for driving air up to a required speed of rotation of the fan and thereafter ceases to drive the air or at least only drives it at a reduced rate. Such an arrangement has practical application in the case of a fan associated with a cooling radiator of an internal combustion engine especially of a motor vehicle and particularly where the fan is driven by the engine. Thus at a low or idling speed when ram air flow through the radiator is non-existent or negligible i.e. where the vehicle is stationary or only moving slowly, the angle of attack of the blade is such as to effect cooling air flow through the radiator, but as engine speed increases (with forward movement of the vehicle) the driving action of the fan decreases to or towards a feathered condition of each blade as ram air flow increases. Particularly in the case of a cooling or other fan, the mass or masses may be suitably connected or arranged to act upon spar structure of each blade of a moulded construction of fan e.g. in suitable plastic material. In a further practical application of the invention, the centrifugal action of the mass or masses may be such as to cause overtwist of the or each blade 1 so that it has a governing action on the speed of angular rotation e.g. in the case of a windmill. Mass balancing of the blades may be effected to counteract blade flutter. WHAT WE CLAIM IS:-

1. An angularly rotatable blade having at least one mass attached to, or arranged to act upon, spar structure of the blade whereby on the mass being subject to centrifugal force as the blade is angularly rotated, the spar structure is subject to distorting forces by the mass which effect twisting of the blade about its longitudinal axis.

that twisting of the blade is effected about its longitudinal axis.

8. An angularly rotatable blade according to claim 7 wherein each external arm is substantially perpendicular to the corresponding surface of the blade or inclined thereto.

9. An angularly rotatable blade according to claims 2, 3 and 5 wherein a mass situated within the blade is connected by an arm to one member of a pair of spar members of the spar structure, which spar member is linked to the other spar member whereby on the mass being subject to centrifugal force due to angular rotation of the blade, each spar member is bent in a direction substantially normal to its depth so that twisting of the blade is effected about its longitudinal axis.

10. An angularly rotatable blade according to claim 9 wherein the trnsverse direction of the other spar member is inclined to that of the first mentioned spar member and to the surfaces of the blade.

11. An angularly rotatable blade according to claims 2, 3 and 6 wherein a pair of masses situated within the blade are connected by corresponding arms to diagonally opposite corners of spar structure of box form whereby on the masses being subject to centrifugal force as a result of angular rotation of the blade the spar structure is subject to warping forces so that twisting of the blade is effected about its longitudinal axis.

12. An angularly rotatable blade when substantially as herein described with reference to Figures 1 and 2 or Figure 3 or Figure 4 of the accompanying drawings.

13. An angularly rotatable blade according to any of the preceding claims wherein the mass or masses is or are such that the blade is twisted during angular rotation to present an optimum or substantially constant angle of attack to relatively moving air flow or the like driving the blade or a series thereof or where the air or the like is driven thereby.

14. An angularly rotatable blade according to any of claims 1 to 13 wherein the mass or masses is or are such that on increased speed of angular rotation of the blade the angle of attack is reduced e.g. to a feathered position.

15. An angularly rotatable blade according to any of claims 1 to 13 wherein the mass or masses is or are such that on increased speed of angular rotation of the blade the latter is over-twisted so as to increase the angle of attack in obtaining a governing action on the speed of angular rotation of the blade or a series thereof.

16. An angularly rotatable blade according to any of claims 1 to 6, 9 to 11 and any of claims 13 to 15 appedant thereto wherein the or each mass is incorporated in a moulded construction of the blade.

17. A windmill or fan have radially arranged angularly rotatable blades according to any of the preceding claims.