Background

The present invention is a reversible camber airfoil that can be used to power a vehicle such as a boat, etc. Prior art conventional sails have very low efficiency due to a lack of thickness, and therefore have a large amount of resistance to the wind; this resistance results in the boat or other vehicle "heeling" over in a strong wind.

Early attempts at producing a three-dimensional sail were only marginally successful because the sails were symmetrical; since a sail for a boat has to accommodate wind over either bow, the only known way to achieve this capability was with a symme¬ trical airfoil even though it was known that asymmetric airfoils were better.

Later attempts to produce an asymmetric reversible camber airfoil were also not very successful for several reasons. In some cases the airfoils were not very thick and thus were not very efficient at low wind speeds. In other cases the airfoils were comprised of a large number of moving parts which were subject to wearing out or breaking under severe conditions. In some cases the airfoil had an outer surface that was made up of interfitting pieces, with the result that freezing rain could get between the pieces and effectively "weld" it into a non- reversible asymmetric airfoil. Objects of the Present Invention

Accordingly, it is an object of the present invention to provide a reversible camber asymmetric airfoil having high ef¬ ficiency at low wind speeds.

It is a further object to provide such an airfoil that has a minimum of moving parts.

It is a further object to provide such an airfoil where the moving parts are large and sturdy.

It is a further object to provide such an airfoil which is not affected by ice buildup on its outer surface. Summary

Briefly, the present invention is a reversible camber asym¬ metrical airfoil comprised of a pivotable front member, a

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pivotable rear member, and a flexible outer covering. The front and rear members cooperate to form the contours of the suction surface of the airfoil; the pressure surface is formed by the flexible outer covering alone. The flexible outer covering en¬ closes all moving parts, protecting them from ice and dust in addition to assuming the desired airfoil shape. The pivotable front and rear members are linked by means which synchronizes their movements. Brief Description of the Drawings

Figure 1 is a cutaway perspective view of the airfoil of the present invention.

Figure 2 is a closeup of the front and rear pivotable mem¬ bers. Description of the Preferred Embodiment

The present invention is a reversible camber airfoil 10 as shown in cutaway perspective in Figure 1. It comprises a frame covered by a flexible outer covering or member, the frame com¬ prising a series of pivotable front members 11 and pivotable rear members 12. All front members 11 are preferably, but not necessarily, enclosed in rigid front shell 14, and all rear mem¬ bers 12 are preferably, but not necessarily, enclosed in rigid rear shell 16. The purpose of shells 14 and 16 is to provide a smooth even surface for flexible outer member 18 to slide upon as the camber is reversed, as will be explained later.

Front members 11 and rear members 12 are linked to each other by means which synchronizes their movement such that they pivot in unison but in opposite directions; this is illustrated in Figure 2 as a set of meshing gear teeth 20, but may be of any other type of linkage that allows the desired movement.

When front members 11 are in a first position rear members 12 are in a corresponding first position that is determined by gear teeth 20 or other synchronizing means. When front members 11 are moved from this first position forming an airfoil having a first camber to a second position forming an airfoil of the opposite camber, rear members 12 assume a corresponding second position. If they are linked by gear teeth as shown, the teeth must be relatively long since when the front and rear members are at one extreme of motion or the other their line of contact

is not the same as it is when they are aligned with each other (i.e., when they are exactly between the two extremes of tra¬ vel). The teeth must be long enough to accommodate this differ¬ ence in the line of contact.

Flexible outer member 18 is fastened to the airfoil only at its trailing edge; it may be glued or otherwise fastened to the trailing edge of rigid rear shell 16. Once it is fastened to rear shell 16, the amount of slack in flexible outer member 18 is one of the factors that determines the thickness of the re¬ sulting airfoil section; a large amount of slack produces a thick airfoil, and a small amount of slack produces a thin air¬ foil.

It may be necessary to provide vertical support for the front of flexible member 18, otherwise it may sag in front and not work properly. This can be done for example by attaching cross members 34, either flexible or rigid, to the inside of flexible member 18 as shown in Figure 2 such that cross members 34 project through slots in shell 14 and rest on front members 11. Cross members 34 will support the weight of flexible member 18 yet will allow it to form a reversible camber airfoil shape v/hen front and rear members 11 and 12 are pivoted.

Front ■nembers 11 pivot about vertical member 22, and rear members 12 pivot about vertical member 24. Vertical members 22 and 24 are rigidly fastened to turntable 26 at the bottom, and are supported by guy wires (not shown) that are attached to a similar turntable at the top (not shown) . These guy wires help transmit the force generated by the airfoil to the vehicle it is mounted on, just like the stays in a sailboard.

In order to reverse the camber of airfoil 10 it is neces¬ sary to cause front members 11 and rear members 12 to pivot about vertical members 22 and 24 respectively. This can be done by any means but is illustrated in Figure 1 by a rack and pinion gear arrangement. Rack 28 is fixed to front member 11 and pinion gear 30 is fixed to the shaft of reversible motor 32 which is fixed to rear member 12. When motor 32 is energized it causes front member 11 and rear member 12 to move relative to each other, and gear teeth 20 on both synchronize the motion. Since all front members are in a first shell and all rear

members are in a second shell, they will all move as a unit and it is not necessary to have such a rack and pinion arrangement on each pair of front and rear members. If they are not in a shell, it will be necessary to have a rack and pinion arrange¬ ment for each pair of front and rear members. Reversible motor 32 may be either an electric or a hydraulic motor; alterna¬ tively, double acting hydraulic cylinders could also be used to reverse the camber of airfoil 10.

Alternatively, it may be preferable to have front members 11 fixed to vertical member 22 and rear members 12 fixed to ver¬ tical member 24 and to have vertical members 22 and 24 rotat¬ ably mounted on turntable 26. Then, to reverse the camber of airfoil 10 vertical members 22 and 24 would be rotated about their axes. Since the motion of front members 11 and rear members 12 is synchronized, it may be possible to rotate only one of vertical members 22 and 24 to reverse the camber of air¬ foil 10.

Turntable.26, which is mounted on the vehicle that is pow¬ ered by airfoil 10, is necessary so that airfoil 10 can be pro¬ perly aligned with the wind. If the vehicle that airfoil 10 is mounted on is moving north and the wind is out of the east, then the leading edge of airfoil 10 will have to be pointed to the east. If the wind should shift and come out of the west, then airfoil 10 will have to be rotated by rotating turntable 26 so that its leading edge is pointed to the west; at the same time the camber will have to be reversed, so that the airfoil's "lift" is always directed to the north.

At present the only method known of designing a reversible camber airfoil of the present invention is an empirical one. An outline of the desired airfoil is drawn, then the front and rear members are drawn as in Figure 2. After the front and rear mem¬ bers are synchronized by means of gear teeth or otherwise, the length of flexible outer member 18 is determined. As stated earlier, the length of flexible outer member 18 is one of the factors that determines the thickness of airfoil 10 (the other obviously is the thickness of front and rear members 11 and 12) . The longer it is the more that front and rear members 11 and 12

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can pivot to either position, thereby creating a thicker air¬ foil.

As shown in Figure 2, front members 11 and rear members 12 are symmetrical about their centerlines. Further, when they are at one extreme of travel or the other to form an-airfoil, the rounded part of the front members 11 forms the leading edge and the first portion of the contours of the curved or suction sur¬ face of the airfoil, while the corresponding side of rear mem¬ bers 12 forms the remainder of the contours of the curved or

_ suction surface of the airfoil. The flat or pressure surface of the airfoil is formed by flexible member 18 which is stretched taut. Thus the shape of the curved or suction surface of the airfoil is determined by the contours of front members 11 and rear members 12 when flexible outer member 18 is stretched over them, and the flat or pressure surface results from the fact that flexible member 18 is unsupported from a point just slightly downstream from the leading edge to the trailing edge and is stretched taut between these two points.

Operation of the airfoil of the present invention is as follows. If airfoil 10 is on a boat and the boat changes course so that the wind direction changes from the port bow to the starboard bow, the entire airfoil will have to be rotated by means of turntable 26 (which is preferably operated by an elec¬ tric or hydraulic motor, not shown) so that the leading edge of airfoil 10 is pointed into the wind. At the same time motor 32 will be energized to reverse the camber of airfoil 10 so that it continues to produce "lift" in the forward direction.

As front members 11 and rear members 12 pivot from one position to the other, flexible outer member 18 becomes loose at the midpoint of their travel; it is prevented from sagging by cross members 34, whose sole function is to support it at this time. When front members 11 and rear members 12 reach the new position, flexible member 18 is stretched taut again.

Thus it can be clearly seen that all moving parts of re¬ versible camber airfoil 10 are enclosed within flexible member 18; this has several advantages. One advantage is that the moving parts are protected from dust and ice, resulting in

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greatly increased reliability and operating lifetime. Another advantage is that if the vehicle is exposed to icing conditions, ice that builds up on the outside surface of flexible member 18 will be broken off when the camber is reversed because all of the contours of the airfoil will be changed.

Furthermore, the present airfoil allows for considerable flexibility in its design. The thickness of the airfoil is a function of the shapes of front and rear members 11 and 12 and of the length of flexible outer member 18, which means that the final design can be tailored to fit a given set of conditions.

Obviously airfoil 10 should be as light and strong as possible, which means that all components except flexible outer member 18 should be made of aluminum or other lightweight metal or of a fiber reinforced composite. Flexible outer member 18 should be of a material that is flexible, light in weight, and does not stretch; suitable materials are fiber glass and synthetics such as Kevlar. Flexible outer member 18 may also be coated on both sides with Teflon, so that ice buildup can be more readily removed and so that it will slide more easily on shells 14 and 16.

SUBSTITUTE SHEET

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