This invention relates to aerofoils for wingsails.

Wingsails, used to propel marine or terrestrial vessels, generally require to be capable of operation on port or starboard tack. This may be achieved by having complex folding arrangements of asymmetrical aerofoils the camber of which can be reversed by extension and folding of separate sections. However the present invention is preferably utilised in wingsail systems that comprise a plurality of symmetrical aerofoil sections which can be angled with respect to one another to give cambered and slotted configurations and also self-setting configurations.

The invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic outline of an aerofoil according to the invention;

Figure 2 is a schematic outline of a slotted wing assembly according to the invention;

Figure 3 is a schematic outline of the wing of Figure 2 in a cambered configuration, and

Figure 4 is a schematic outline superimposing the aerofoil sections of Figures 1, 2 and 3.

Referring now to Figure 1, the aerofoil shown has a chord length C and a maximum thickness of 0.291 C- with a leading edge radius of 6.489% of C. The overall shape follows that of the table of ordinates Table 1.

% a1ong 1/2 Width % along 1/2 Width chord % of C chord % of C

0 0 20 14.01

0.5 2.66 30 14.54

0.75 3.24 40 13.2

1.25 4.28 50 10.74

2.5 5.94 60 7.95

5.0 8.27 70 5.22

7.5 9.93 80 2.9

10 11.13 90 1.1

• 100 0

Table 1

It will be seen from Table 1 that the maximum thickness occurs at approximately 30% along the total chord.

Referring now to Figure 2 the leading element 2 has a leading edge radius of 8.777% of its chord and a maximum thickness of 39.32% of its chord occurring at approximately 35% along the chord. The table of ordinates for this aerofoil shape is given in Table 2.

% along 1/2 Width % along 1/2 Width chord % of C chord % of C

0 0 35 19.661 0.5 3.002 40 19.57 0.75 3.772 45 19.22 1.25 4.88 50 18.52 2.5 6.934 55 17.55 5.0 9.655 60 16.28 7.5 11.586 65 14.728

10 13.34 70 12.973

15 15.71 75 11.033

20 17.42 80 8.865

25 18.6 85 6.618

30 19.31 90 4.476 100 2.247

Table 2

The trailing element 3 shown in Figure 2 has a leading edge radius of 10.625% of its chord with a maximum thickness of 30.42% of its chord occurring at approximately 25% along the chord from the leading edge. The table of ordinates for the profile is given in Table 3.

% along 1/2 Width % along 1/2 Width chord % of C chord % of C

0 0 45 12.0

0.5 3.232 50 10.629

0.75 3.935 55 9.209

1.25 5.044 60 7.789

2.5 6.93 65 6.423

5.0 9.5 70 5.14

7.5 11.19 75 3.92

10 12.488 80 2.87

15 - 14.13 85 1.893

20 14.98 90 1.082

25 15.21 95 0.473

30 14.9 100 0

35 14.2

40 13.22

Table 3

The aerofoil of Figure 1 may be regarded as a basic member of the preferred family of wingsail profiles. It comprises a relatively high leading edge radius when compared with aerofoils for aircraft, and thickens relatively rapidly to reach a 90% thickness zone that commences at about 20% of the chord and continues to about 40% of the chord, the aerofoil then narrowing into the trailing portion and curvature undergoing an inflexion.

The second member of the family, aerofoil 2 of Figure 2, has a leading edge curvature that matches with the leading edge of the aerofoil of Figure 1, but is modified into a more abrupt trailing edge with almost no curvature from about two thirds of the way along the chord. In the drawing the trailing edges are flat, in a more general case they may only be substantially flat and may have a slight curve or a slight inflexion. If reference is made to Figure 3 it will be observed that the trailing edge of the aerofoil 2 is provided with a slat 4 which acts to extend the trailing edge. In practice the trailing edge of the leading section may be truncated for the pivot mounting of the slat. Although the curvatures of the leading parts of aerofoils 1 and 2 match, the positions of maximum thickness and leading edge radius in percentages deviate because of the differing lengths of the trailing sections. In Figure 4 the trailing edge modification is shown in dotted outline.

The trailing aerofoil 3 of Figures 2 and 3 has a fatter leading edge portion, but from the point of maximum thickness matches with the trailing section of the aerofoil of Figure 1. The relatively rapid rise to maximum thickness makes the point of maximum thickness occur relatively sooner along the chord. In Figure 4 the leading edge modification for a trailing aerofoil is shown in chain dot outline.

For a single aerofoil, the 90% thickness zone extends over a range of approximately 17% to 33% of the chord, most preferably in the range of 23% to 27% of the chord. The 90% thickness zone may commence in the range of 10% to 25% of the chord and be contained within the range of 10% to 55% of the chord from the leading edge, most preferably being within the range 17% to 45%. The maximum thickness may lie in the range of 20% to 40% but preferably is in the range of 25% to 30% of the chord. The leading edge radius is preferably in the range of 5.5% to 7.5% of the chord, but may be in the range 5.5% to 12%.

In compound wings the leading section (disregarding any flaps or slats) preferably has a shortened tail section with no inflexion so that the 90% thickness zone starts at about 19% to 23% of the chord. The trailing section of compound wings preferably has a leading edge radius that lies in the upper end of the range as defined for single aerofoils.

Table 4 gives the approximate preferred ranges in terms of chord % for the three wingsail aerofoils described above. In compound wingsails it is possible to modify the curvature at the end that is adjacent another aerofoil, or to modify the overall curvature and compensate in the other aerofoil.

Foil 90% Zone 90% Zone Max. Thickness Max. Thickness LE range length position % radius

1 17%-45% 25% 30% 29% 6.4%

2 20%-55% 30% 35% 39% 8.7%

3 10%-35% 20% 25% 30% 10.6%

Table 4

Figures 2 and 3 represent an especially preferred compound wingsail according to the invention. The trailing element 3 is mounted on a boom or booms pivotable about an axis 5 on the chord of the leading element 2. Each of the main aerofoils 2 and 3 preferably have the same maximum thickness (although differing thickness is possible, the trailing section preferably having the larger thickness) of .170 C _TQT where C _TO τ is the total chord defined from the leading edge of the leading section to the trailing edge of the trailing section with the aerofoils aligned as in Figure 2. The leading element is shorter having a chord of .432C _TO τ ^an ^ the trailing section having a chord of .560C _Q r. with a space of

.008Cm _OT between the aerofoils. The slat 4 has a length .076C _TQT and in the fully cambered position shown in Figure 3 is deflected through 25° with an adjustment facility of 5.5°. The preferred fully cambered configuration deflects the trailing section through 42° with the pivot of the trailing section positioned about 2/3 of the way along the leading section: in Figure 3 it is .278c _TOT from the leading edge.

A main upright pivot axis for the compound wing passes through the zone of the centre of pressure of the leading element 2 and the wing is trimmed to the wind by an auxiliary aerofoil, normally a tail vane, which also has an aerofoil section in accordance with the invention. As the tail vane is usually a single aerofoil and does not have slats or an adjacent aerofoil it preferably has the leading and trailing profiles shown in Figure 1.