Ships – Sail or control means therefor – Specific sail structure or arrangement
Patent
1984-04-06
1986-09-09
Blix, Trygve M.
Ships
Sail or control means therefor
Specific sail structure or arrangement
244203, 244210, 244 1R, 340966, B63H 906, B64C 1316
Patent
active
046102132
DESCRIPTION:
BRIEF SUMMARY
This invention relates to rigid sails and in particular to monitoring wind pressure and/or flow conditions in the vicinity of such sails.
The type of sailset to which this invention is applicable generally comprises one or more rigid aerofoils, each of which is constructed in the form of a wing (as of an aircraft) although the fabric from which it is made may be different to the fabric of aircraft wings. Usually the cross-section of the aerofoil will be symmetrical but asymmetric cross-sections are not excluded. The aerofoils are mounted to rotate about upright axes which may pass through the aerofoil or be remote from it and connected for example by a boom. Trimming of the sailset is achieved by rotating one or more of the aerofoils about its axis. Sailsets of this type are described in the published European Patent Applications 61291 and 77205.
During sailing there is a constant need to select the angle of attack for the aerofoils that gives the required thrust, which may be a varying percentage of the maximum available thrust, and to protect the sailset and vessel from the excessive forces of high winds. Additionally it may be desired to incorporate specialised systems that modulate the trimming action, for example to maintain a constant angle of heel while sailing or, when the vessel is moored, to minimise warp tension, roll, send etc.
In order to provide an automatic or semi automatic system that responds to the prevailing conditions and the input direction and thrust demands, it is desirable to monitor the precise wind and flow conditions in the vicinity of the aerofoil.
Accordingly the invention provides a sailset comprising at least one rigid aerofoil and including at least one pair of pressure tappings arranged to give an indication of the state of airflow in the vicinity of the aerofoil surface.
The invention is now described by way of example with reference to the accompanying drawings in which:
FIGS. 1a-1c illustrate schematically the flow conditions around an aerofoil sailset at the onset of stalling;
FIG. 2 shows an aerofoil section with pressure tapping points in accordance with the invention,
FIG. 3 shows schematically in section, an aerofoil sailset with an alternative arrangement of pressure tapping points in accordance with the invention, and
FIG. 4 shows schematically a flow sensing and stall warning device in accordance with the invention.
For the avoidance of doubt, the terms lift, drag and thrust have the following relationship. Lift is the crosswind force, drag is the downwind force and thrust is the vector sum of lift and drag.
Referring to FIG. 1, an aerofoil sailset is represented in sectional view. The sailset consists of a leading sail element 1 that will generally be pivoted about an upright axis passing through the aerofoil, and a trailing sail element 2 that will generally be pivoted about an upright axis that is carried by the leading sail element 1 and passes through the leading sail element towards its trailing edge. The trailing element 2 is attached to its axis by booms which permit the trailing element to be swung from one side of the leading element 1 to the other in mirror image configurations. A slat or flap may be attached to the trailing edge of the leading element 1 in order to enhance the aerodynamic slot configuration formed between the two elements. The elements 1 and 2 constitute the principal sail of the sailset and the whole assembly may be rotated by the action of a tail vane (not shown).
In FIG. 1a the wind, indicated by the arrow, is incident to the leading element 1 at an angle of -10.degree. and the air flow around the aerofoils is smooth and `attached` with the exception of a small separated wake 3a at the trailing edge of the trailing section 2, on its low pressure side. The presence to a significant degree of this separated wake signals the onset of stalling and as the degree of stalling increases the separated wake moves further along the aerofoil towards the leading edge (i.e. the separation occurs earlier in the airflow) as represented in FIGS. 1
REFERENCES:
patent: 2237306 (1941-04-01), Hood
patent: 2440198 (1948-04-01), Green
patent: 2523481 (1950-09-01), Rabenhorst
patent: 2635152 (1953-04-01), Dyche, Jr.
patent: 3006187 (1961-10-01), Wilkenson
patent: 3304778 (1967-02-01), Stuart
patent: 3654807 (1972-04-01), Deskey
patent: 4027533 (1977-06-01), Pretto
patent: 4350314 (1982-09-01), Hoadley
Blix Trygve M.
Corl Rodney
Young & Thompson
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