Ships – Sail or control means therefor – Specific sail structure or arrangement
Patent
1987-01-02
1988-09-13
Barefoot, Galen
Ships
Sail or control means therefor
Specific sail structure or arrangement
114103, 114 392, 244 45R, B63H 904
Patent
active
047701137
DESCRIPTION:
BRIEF SUMMARY
This invention relates to airfoils, and especially to wingsail airfoils.
The wingsail systems with which the present invention is concerned are generally of the self setting type that are mounted freely for rotation about an upright axis. In a wingsail system with a multi-element wing comprising a leading element and a trailing element or flap positioned closely behind the leading element and pivotable to each side to form respective composite cambered configurations, the moment on the hinge of the flap due to airflow is considerable, and must be resisted if the cambered configuration is to be maintained. If a hydraulic ram is used to drive the flap and maintain its position, this necessitates use of a ram large enough to withstand the maximum moment likely to be encountered. A locking device may be employed in order to relieve the ram once the flap is fully deflected, but the hydraulic ram still has to be large in order to defect the flaps in a strong airstream.
Aircraft flaps incorporate devices such as rails and fixed pivots in order to alleviate any analogous problems, however this method is not easily adaptable for wingsail systems because, unlike aircraft flaps, the flap must be capable of deflection in both directions in order to operate on both tacks.
The present invention in one aspect is directed towards a method of assisting the flap to reach operating deflection.
Accordingly in one aspect the present invention provides a method of operating a self-trimming sailset comprising a wingsail having a leading airfoil, a trailing airfoil flap and a governor airfoil, the method comprising adjusting the angle between the governor and the leading airfoil so that the rig is trimmed to a position in which the forces opposing a movement of the flap in a particular direction are reduced, moving the flap in said direction, and then setting the governor to trim the sailset.
The forces may be reversed tending to aid movement of the flap in the particular direction.
The invention also relates to a control system for moving the flap of the self-trimming rig.
In a multi-element wingsail having a leading element and a trailing flap element it has been proposed to locate a slat at the trailing edge of the leading element, the slat extending towards the leading edge of the flap and being connected to it in some way so as to be correctly positioned to form a linear nozzle upon deflection of the flap. With a pivoted slat it is necessary in order for the slat to be operative on either tack for the slat to pass through the gap between the leading and trailing elements. If the connection between the slat and flap is a cable, which has advantages in terms of flexibility, then it may be subject to excessive wear, and also the mounting on the flap may be subject to fouling by the slat.
The present invention in another aspect is directed towards providing more durable cable connection and mounting and to easing the passage of the slat past the leading edge of the flap.
The type of sailset with which the invention is generally concerned is a multi-element, multiplane type, that is, it has a plurality of main thrust wings, each of the thrust wings being composed of at least two airfoil elements, usually a leading element and a trailing flap element. The thrust wings may be trimmed by a governor airfoil such as a tail vane.
It is often desired to stall the thrust wings, for example for running downwind. During stalling the airflow over the airfoil is eddying and turbulent, with the result that a downstream control such as a tail vane may become blanketed and be rendered less effective in controlling the trimming of the thrust wings in the proximity of stalling conditions.
The present invention in a further aspect is directed towards achieving reliable `in-stall` moment to assist maintenance of stall once entered.
Accordingly the present invention provides a wingsail system comprising a plurality of wings, each comprising a leading element and a trailing flap that can be deflected with respect to the leading element, and in which
REFERENCES:
patent: 2576294 (1951-11-01), Geraci
patent: 2996031 (1961-08-01), Easter
patent: 3587770 (1971-06-01), Flower
patent: 3844238 (1974-10-01), Murray
patent: 3911847 (1975-10-01), Worthing
patent: 3934533 (1976-01-01), Wainwright
patent: 3992979 (1976-11-01), Smith
patent: 4467741 (1984-08-01), Walker
patent: 4543899 (1985-10-01), Walker
"Walker Wingsail Project Rivals Japanese Experience", Motorship, vol. 65, No. 771, 10/1984, pp. 30-31.
Barefoot Galen
Salmon Paul E.
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