Patent Application
20220063765
N/A
The invention relates to personal hydrofoil watercraft used for utility or recreation. Said craft may be used in flat waters or for surfing waves or boat wakes. Said craft may be propelled, by surfing the surface of a wave or ocean swell, by towing with a kite, towed by a boat, self propelled with a motor, or human propelled using a leg pumping technique.
The majority of successful personal hydrofoil designs are based on the design originally described in U.S. Pat. No. 7,232,355 by Wooley. This hydrofoil design has been extensively used for personal kite powered hydrofoils as well as towing behind a boat. The most popular use is with the rider standing on a board, rather than seated as described by Wooley. The Wooley design is passively stabilized by the downward force provided by the stabilizer, in a configuration which is identical to that used in conventional aircraft. Steering and height control are achieved by weight shifts of the rider. Augera in U.S. Pat. No. 9,789,935 describes such a configuration optimized for stand up paddling in the surf Langelaan describes the use of this hydrofoil configuration in conjunction with an electrically powered immersed prop drive attached to the hydrofoil in U.S. Pat. No. 9586659 B2. Shane in U.S. Pat. No. 7,021,232 describes a human powered hydrofoil with a different configuration and stabilization method.
The present invention is a personal hydrofoil surfboard design that has a wing with a reflexed mean camber line. This type of wing has a low negative pitching moment, zero pitching moment or even positive pitching moment. The present invention greatly improves the controllability and ease of use of the hydrofoil. The hydrofoil is much more stable than conventional designs at high speed when the angle of attack may be negative and conventional wings will suddenly develop negative lift. Moreover, the balance point does not shift forward or back as the foil is loaded and unloaded during foot transitions as it does in conventional designs. This makes it much easier to tack and jibe the hydrofoil. These attributes allow a hydrofoil of the present invention to be stable and yet highly responsive. Additionally, the low pitching moment of the reflexed wing allows the use of the hydrofoil without a stabilizer if that is desired.
To my knowledge, a reflexed airfoil has never been used in hydrofoil applications and is rarely used in aviation. It is exclusively used in tailless flying wing designs, which require pitch stability without the use of a stabilizer. Reflexed airfoils provide less lift per wing area than conventional airfoils and therefore are not used in conventional aircraft configurations. It is surprising and unexpected that. wings with reflex camber lines have a very significant benefit when used on hydrofoils, and most surprisingly that this benefit is present on hydrofoils equipped with a stabilizer.
The current invention consists of a support platform generally shaped as a surfboard. A streamlined strut is rigidly attached to the bottom of the support platform at the center line and approximately 70% of the way back from the front of the board. The strut can be detachable from the board for ease of transportation. The strut extends downward and is typically 40 to 110 cm long. A wing with a reflexed mean camber line may be attached directly to the strut, but typically, a fuselage is rigidly attached to the bottom of the strut, typically using bolt fasteners, and is aligned with and parallel to the long axis of the support platform. A one piece, strut/fuselage component may also be used. A wing with a reflexed mean camber line and providing upward lift is attached to the front of the fuselage. The wing area is typically 300 to 3000 sq cm. A stabilizer is rigidly attached at the aft of the fuselage and has an area typical between 175 and 500 sq cm. The stabilizer is set at an angle of attack less than that of the wing and provides a stabilizing down force during hydrofoil flight. The force configuration of the wing and stabilizer is that used on conventional airplane designs, where the center of mass of the airplane is in front of the center of lift of the main wing and the stabilizer provides a balancing down force. The stabilizer angle is typically 0 to −5 degrees with respect to the wing. If a lifting foil section is used for the stabilizer, this foil section will be upside down with respect to the wing, since down force is desired. A canard wing configuration could also be used and is also a subject of the current invention. In a canard configuration the stabilizer will be mounted in front of the wing and will provide up force as is typical in canard aircraft. Using a wing with a reflexed mean camber line, without a stabilizer, is also a subject of the present invention.
The airfoil of the main wing has a reflexed mean camber line which results in a pitching moment that is slightly negative, zero or even positive. The pitching moment on typical airfoils such as the SD7037 is about −0.08 at zero degrees of angle of attack (AOA). Airfoils of the current invention such as the Eppler 335 have pitching moments of −0.02 at an AOA of zero and positive pitching moments at positive AOA.
The foil sections typically used in tailless flying wing aircraft may be used. The HQ 34, NACA 24112, and Eppler 335 are typical examples. The distinguishing characteristic of a reflexed wing is that its mean camber line has an inflection point. Conventional airfoils have downward facing concave, mean camber lines. Reflexed airfoils have downward facing concave mean camber lines at the forward portion of the wing, and upward facing concave mean camber lines at the rear portion of the wing. In layman's terms the trailing edge of the wing is oriented upward rather than downward as in a conventional wing. This is illustrated in
It is appreciated that a reflexed airfoil may also be used with a swept back wing with wing washout to make the pitching moment even more positive. Using swept back wings with a reflexed airfoil, which also have washout in the wing tips, is also a subject of the present invention.
The wing thickness may be between 5% to 35% of the chord. Wings with thicknesses of 8% to 18% of the chord length are preferred.
The invention and its assembly and operation may be further understood from the following description of the preferred practices thereof, which are shown by way of example in the accompanying drawings, wherein:
Turning now in greater detail to the appended drawings,
The current invention may also be practiced without stabilizer (6) by simply omitting it. In this case the fuselage (4) may be truncated behind the strut (3) attachment area.
The present invention is a personal hydrofoil surfboard comprised of a rigid elongated platform to support a human rider, at least one wing, at least one wing having a reflex camber line, and a connecting means between said elongated platform and said wings. Said wings are situated beneath and rigidly connected to said elongated platform via a connecting means.
In a canard configuration, a wing having a reflexed mean camber line will be rigidly attached to rear of the fuselage and will provide an upward force, and a stabilizer wing will be rigidly attached to the front of the fuselage and will provide an upward force.
Accordingly, while the preferred embodiments have been shown and described in detail by way of example, further modifications and embodiments are possible without departing from the scope of the invention.
