EP0073589B1

EP0073589B1 - Improvements in and relating to wingsail craft and wingsails therefor

Info

Publication number: EP0073589B1
Application number: EP82304256A
Authority: EP
Inventors: John Graham Walker
Original assignee: Walker Wingsail Systems Ltd
Current assignee: Walker Wingsail Systems Ltd
Priority date: 1981-08-22
Filing date: 1982-08-12
Publication date: 1986-03-26
Also published as: JPH02162191A; FI77420B; EP0073589A1; PT75448B; ES275247U; DE8237177U1; JPH0631069B2; DE3270117D1; AU560143B2; FI77420C; FI822833A0; PT75448A; DE8223561U1; FI822833L; AU8714982A; KR840001087A; ES275247Y; CA1185487A

Description

Field of Invention

This invention concerns wingsail craft and particularly the mounting, construction and balancing of wingsails.

Background to the Invention

It is known to construct a craft typically a ship, having a so called wingsail in which the sail is formed as a more or less rigid aerofoil section as in an aircraft wing. In such arrangements it is usual to mount the sail on the vessel about an approximately vertical pivot axis. This pivot axis normally comprises a single lower bearing about which the wingsail is rotated in order to adjust the trim angle of the sail to the wind.
In both servomechanically rotated and tail trimmed wingsails, it is desirable to minimise the trimming work needed. For this reason the axis of the trim bearing is usually arranged to pass through the narrow zone in which the centre of pressure of the sail is found in the normal working range. However, for most cambered and high thrust sections this zone will lie approximately 35% back from the leading edge, while even in symmetrical sections it will be some 25% back from the leading edge. Its vertical position is approximately at the half height for wingsails of rectilinear design, while simple geometrical constructions are commonly used to locate the zone vertically for wingsails of tapered or elliptical shape.
The strongest part of the wingsail, most suitable for mating with the vertical bearing assembly, is usually a Dbox leading edge section, which may occupy only the leading 20% perhaps of the total wingsail chord.
In the case of a wingsail having two elements, it is normally assumed that the leading element is the principle strength member.
Many wingsail propulsion sets need to be carefully balanced about their vertical or near vertical axes of rotation to enable optimum control of angle of attack to be achieved, and the invention is in part concerned with wingsail balancing.
In complex wingsails, composed of two or more elements hinged or otherwise connected, three distinct types of conformation may be obtained:

These are:-
- Symmetrical and all-in-line,
- Cambered for port tack sailing, and
- Cambered for starboard tack sailing.

Such a sailset may be balanced about a vertical or near vertical axis by a mass mounted on the leading edge of the leading sailset section, as exemplified by British Patent GB-A-1375192. This type of construction offers an alternative solution to the problem of balancing with minimum trimming work.
The actual construction of a wingsail or the various elements of a multiple element wingsail is important, in that weight and strength are of primary importance. The invention is therefore also concerned with the actual construction of a wingsail and of the elements which make up a multiple element wingsail.

The Invention

According to one aspect of the present invention there is provided a wingsail of symmetrical single or multiple element design having a principal region of strength extending over substantially the height of the sail in the or one of the elements and located, for example, adjacent the leading edge of the element, and which is arranged to be mounted in a craft by means of a bearing at the bottom of the sail, the bearing defining an axis of pivoting of the sail or sail element, wherein the axis of pivoting of the sail assembly is arranged to pass through the centre of pressure zone; characterised in that said axis of pivoting is arranged to be intersected by at least a part of the principal region of strength at a point at which the sail element is to be attached to the bearing so that the latter will be attached at a point of maximum strength.
Using this aspect of the invention ensures a strong and reliable mounting for the wingsail enabling pressure balancing to minimise trimming work.
According to another aspect of the present invention there is provided a wingsail of multiple element design having a leading sail section and a trailing sail section pivoted thereto, and a balancing mass is mounted on the leading edge of the leading section; characterised in that the balancing mass is mounted on a boom pivotally mounted to said leading edge to pivot relative to the leading sail section in the same rotational sense as the trailing sail section in order to maintain equilibrium, and a locating means is provided to link the balancing mass with the trailing sail section.
This aspect of the invention provides an alternative solution to the same problem by means of mass balancing.
The locating means may comprise a pair of wire stays, a mechanical linkage using a pushpull rod, or hydraulic means or the like, in which the final balance position is assured by a fixed or manually adjustable ratio system or by a servo loop which may include a computing link. Where a computer is incorporated the latter may be supplied with information relating to the sailing conditions and the craft to allow the computer to compute the optimum balance position.
A subordinate aspect of the invention concerns a wingsail element for use in the above described pressure or mass balanced wingsail assembly, which is constructed in a conventional manner using spars and ribs which latter define the aerofoil section, and lie broadly in the direction of air flow, the ribs being constructed from moulded glass reinforced plastics (GRP) material, and wherein each rib includes at least one side flange which subtends over part of its length an angle which is greater than 90° to the remainder of the rib, to facilitate the removal of the rib from a mould, and the angle and said part of the rib are selected so that the flange angle corresponds to the angle of rake of the edge of the sail with which it is to cooperate.
Preferably the flange angle reduces to 90° where it is to be attached to a spar or the like.
The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 illustrates a wingsail craft,
Figures 2 and 3 illustrate wingsail constructions embodying the first aspect of the invention,
Figures 4, 5 and 6 illustrate a twin element sailset in the three different modes,
Figures 7 and 8 illustrate locating means according to the second aspect of the invention applied to such a sailset,
Figure 9 illustrates this aspect of the invention applied to a sailset in which the leading sailset section is hinged to the trailing sailset section,
Figure 10 is a perspective view of an open tray section the sides of which form the flanges of a rib, for a wingsail,
Figure 11 is a detail of the side of the rib of Figure 10,
Figures 12 and 13 show parallelogram shaped wings which may be employed in practice of the invention, and
Figure 14 is a cross section on the centre line of a forwardly raked sail element.

Description of the Drawings

Figure 1 shows a sailing craft A having a wingsail B pivotally mounted in a bearing assembly C.for rotation about an axis D.
In Figure 2, two wingsail assemblies have been shown superimposed, both having the same centre of pressure zone E, in which one has been drawn in chain dotted outline as a simple rectangle, and the other in solid outline as a parallelogram. The two sail assemblies have the same height, area and centre of pressure position.
The strong leading edge member F, shown cross hatched, is arranged, by correct choice of forward sweep angle, so that its lower end is located exactly over the position of the bearing assembly C, whilst the axis D of the bearing C still passes through the centre of pressure zone E. The strong leading edge member is provided with a flange or other arrangement to mate with the shaft or other rotating element of the bearing assembly.
In wingsails of multielement design, it may be preferred that the second or other element of the aerofoil section shall contain the strong spar member. Figure 3 shows a double element of such a wingsail configuration. Here the leading element 1 is hinged to the trailing main strength element 2 by hinge assemblies 3. The centre of pressure zone of this complex assembly is at E, and as before, to minimize trimming work, the approximately vertical axis D of the bearing C is arranged to pass through this zone.
In this case, the main strength member of the wingsail is the leading edge 7 of the trailing element 2 shown cross hatched. This is now arranged so that its lower end falls into the best relationship for strong and reliable mating of the bearing assembly by raking the entire assembly aft as shown.
The design is arrived at by starting with the rectilinear design, positioning the centre of pressure zone on the bearing axis and then replacing the rectangle with a parallelogram of the same height and area, whose angle brings the base of the main spar conveniently over the bearing.
While this aspect of the invention has been described for simplicity with reference to parallel, constant chord wingsails, it is nonetheless applicable to wingsails of tapering or curvilinear outline.
Figures 4, 5 and 6 show a twin section sailset where 11 is the leading sail section and 12 is the trailing section, hinged to 11 along an axis 13. The whole sailset is mounted to the vessel in this case via element 11 on a vertical or near vertical axis 14, about which the sail is trimmed to the wind.
In the all in line case, the sailset is balanced about the axis 14 by a mass 15 mounted on a boom 16 pivoted to the leading edge of the leading section 11 at a pivot 17.
In the port tack sailing case, illustrated in Figure 5 it will be seen that a new balance may be achieved by moving the weight around in a clockwise manner until equilibrium is restored.
Figure 6 shows the opposite tack case.
In accordance with the second aspect of the invention the location of the balance weight in an approximately horizontal plane is achieved by a pair of wire stays, as shown in Figure 7.
To this end a streamlined structure having two fins 18, 19 is rigidly fixed to the base of the leading section 11 of the sailset. A pair of pulleys 20, 21 are carried by the fins around which wires 23 and 24 pass. The wires are connected to the trailing section 12 at lugs 25, 26 and to the counterweight boom at lugs 27 and 28. Spring elements 29, 30 in the wires maintain wire tension. Dotted lines 22 show the trailing section 12 fully deflected.
When the trailing section 12 is moved relative to 11 in order to develop camber, say in the clockwise direction in the plan view drawn, wire 23 pulls the counterweight to the correct position to maintain balance. In this case wire 24 maintains tension. The opposite action will occur on anticlockwise rotation.
Figure 8 shows alternative versions of the lugs 25, 26. The alternative lugs shown at 31 and 32 are slotted to allow fine adjustment of the balancing effect.
In some wingsail designs the trailing section 12 is mounted on the vessel via the axis 14, and the leading section 11 is then hinged to the trailing section 12. Figure 9 shows such a case. Here an end plate structure 33 broadly similar in principle to the structure 18, 19 of Figure 7 carries the counterweight boom pivot 17.
The pivot 13 between 11 and 12 could also be mounted on 33, but for reasons of bending moment optimisation is more likely to be mounted on separate hinge arms 34, working through clearance slots in 11. Wires 35 and 36 are now connected at one end via lugs 27, 28 to the counterweight boom and at the other end to adjustable lugs 31, 32 on the leading section 11. The wires adjust the position of the counterweight to maintain balance.
While bracing wires such as 23, 24 and 35, 36 are illustrated, the same action of broadly horizontal movement of the counterweight may also be achieved by:

A mechanical linkage using a pushpull rod, or
Hydraulic or other means in which the correct final balance may be assured either by a fixed or manually adjustable ratio system, or by a servo loop which may incorporate a computer link.

Figure 10 shows a simple form of moulding envisaged for use in production of a wingsail to be used in practice of the invention, in the form of an open tray section where the sides of the tray 39, 40 form the flanges of the rib. For ease of release from a simple one piece mould, such mouldings should preferably be arranged with a draft angle greater than 0 as shown in Figure 11. Such an angle can make the fixing of the skin of the aerofoil to the rib difficult to achieve. However, if the wing is parallelogram shaped, as shown in Figures 12 and 13 the draft angle may be utilised.
Figure 14 is a centre line section through a raked forward sail element such as is shown in Figure 12 where a leading edge member 41, a main spar 42 and a trailing edge 43 are connected by a typical leading edge rib 44 and a typical trailing edge rib 45.
It will be noted that, because this is a swept forward design, the leading edge rib 44 is fitted with its flanges upwards, while the trailing edge rib 45 is fitted with its flanges downwards. The draft angle of the mould is made equal to the desired forward rake angle at leading edge and trailing edge, but is gradually reduced to zero so that the flange of each rib is at 90° to the web in the immediate vicinity of the main spar 42.
By varying the draft angle in this way along each rib the rib flanges will in general be coplanar with the skin for ease of skin attachment, whilst the mould and moulding techniques are kept simple and reliable.
In the case of raked back wingsails, as in Figure 13, then the leading edge rib elements will be fitted flange down and the trailing edge ribs will be fitted flange up.
In the case of multielement wings, where each element has its own broadly aerofoil shaped section and main spar, the ribs will be fitted as described above in each individual element, as if it were a complete wing.

Claims

1. A wingsail (B) of symmetrical single or multiple element design having a principal region of strength (F, 7) extending over substantially the height of the sail in the or one of the elements (1, 11; 2, 21) and located, for example, adjacent the leading edge of the element, and which is arranged to be mounted in a craft by means of the bearing (C) at the bottom of the sail, the bearing defining an axis of pivoting (D) of the sail or sail element, wherein the axis of pivoting of the sail assembly is arranged to pass through the centre of pressure zone (E); characterised in that said axis of pivoting (D) is arranged to be intersected by at least a part of the principal region of strength (F, 7) at a point at which the sail element (1,11; 2, 12) is to be attached to the bearing (C) so that the latter will be attached at a point of maximum strength.

2. A wingsail of multiple element design having a leading sail section (11) and a trailing sail section (12) pivoted thereto, and a balancing mass is mounted on the leading edge of the leading section; characterised in that the balancing mass (15) is mounted on a boom (16) pivotally mounted to said leading edge to pivot relative to the leading sail section (11) in the same rotational sense as the trailing sail section (12) in order to maintain equilibrium, and a locating means (23, 24) is provided to link the balancing mass with the trailing sail section.

3. A wingsail assembly as set forth in claim 2 wherein the locating means comprises a pair of wire stays (23, 24).

4. A wingsail assembly as set forth in claim 2 wherein the locating means comprises a mechanical linkage incorporating a pushpull rod.

5. A wingsail assembly as set forth in claim 2 wherein the locating means comprises hydraulic means.

6. A wingsail assembly as set forth in claim 2 wherein the final balance position is assured by a fixed or manually adjustable ratio system or by a servo loop which may include a computing link.

7. A wingsail as set forth in any of claims 1 to 6, wherein the or each sail element is constructed of spars and ribs which define an aerofoil section, wherein the ribs are made of moulded glass reinforced plastics (GRP) material, characterised in that each rib (44, 45) includes at least one side flange (39,.40) which subtends over part of its length an angle greater than 90° to the remainder of the rib, to facilitate the removal of the rib from a mould, and the angle and said part of the rib are selected so that the flange angle corresponds to the angle of rake of the edge of the sail with which it is to cooperate.

8. A wingsail as set forth in claim 7 wherein the flange angle reduces to 90° where it is to be attached to a spar (42).