US3168067A

US3168067A - Surface watercraft

Info

Publication number: US3168067A
Application number: US73790A
Authority: US
Inventors: Waldemar A Graig
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-12-05
Filing date: 1960-12-05
Publication date: 1965-02-02
Anticipated expiration: 1982-02-02

Description

Feb. 2, 1965 w; A'..GRA\IZG, 3,

SURFACE}; WATERCRAF'E Filed Dec. 5, 1960 3 Sheets-Sheet, 1

INVENTOR. WALDEMAR A- GRAIG VMFW ATTORNEY Eeb..-2, W. A. GRAIG 3,1

SURFACE WATERCRAFT Eild'Dec. 5,4960 3 Sheets-Sheet 2 INVEN TOR.

DEMAR A. GRAlG BY MXW ATTORNEY Feb. 2, 1965 w. A. GRAIG 3,168,067

SURFACE WATERCRAFT Filed Dec. 5, 1960 5 Sheets-Sheet 3 INVENTOR.

WALDEMAR A. GRAIG MFW ATTORNEY United States Patent 3,168,967 SURFACE WATERCRAFT Waldemar A. Graig, 729 Grand Ave, Dayton, Uhio Filed Dec. 5, rats, Ser. No. 73,790 12 Claims. or. iii-ens) This invention pertains to craft operating on the water surface, which are lifted by the dynamic forces generated by their motion. Such watercraft are usually equipped with one or more hydrofoils, air-foils, or other means producing dynamic sustentation.

The invention is particularly applicable to craft pro vided with aerodynamic wings, and also to craft equipped with downwardly extending hydrofoils for supplying sustentation, or lateral stabilization, or both.

The lifting properties of wings are too well known to warrant elaboration. On the other hand, support and/or lateral stabilization by downwardly extending hydrofoils, although not novel, will be described. A craft can be supported by port and starboard hydro-foils sloping down and outward, so that the foils of opposite boards converge toward the median plane in an open inverted V configuration known as anhedral. Their angles of attack are such as to produce in motion hydrodynamic forces acting up and outboard. At sufficient speed, the vertical lift components supply the required sustentation, while the horizontal components on port and starboard oppose each other and normally cancel out. If partially immersed, the foils also provide lateral stability, i.e., stability about the roll axis. In the event the craft should tilt, the unevenly immersed foils would produce a righting moment in consequence of the shift of the resultant hydrodynamic force.

By an expansion of this concept, the lifting and stabilizing means and functions can be disasssociated from each other. When sustentation is provided by independent means, the anhedral angle can be considerably increased, i.e., the inverted V closed up, and the lateral spread of the foils thereby conveniently reduced. The port and starboard foils can be established in strictly vertical planes, if the center of gravity of the craft is at sufiicient height above water.

Foil systems of the above type can be further modified in order to produce controlled banks. The modification consists in mounting the foils movably on the hull and subjecting them to control. By diiferential operation of the port and starboard foils (e.g., by lowering the foils on one side and lifting them on the other; or by changing differentially their angles of attack), the operator can destroy the balance between the port and starboard hydrodynamic moments and cause the craft to tilt. As the craft responds, the tilting moment decreases gradually and cancels out completely when the bank angle associated with the hydrofoil deflection has been reached.

Conceived for idealized conditions, the above arrangement can present in practice a serious inconvenience and even an outright safety hazard, which is remedied by the instant invention. The hydrofoil systems of the described nature will operate as stated only if the craft points straight in the direction of the relative water current, i.e., if it does not yaw. (By yaw one will understand such a condition whereby the longitudinal axis of the craft is at an angle to the relative water current. It is, of course, assumed here that the craft is of a symmetrical design and that the aforementioned foils are established at symmetric incidences. Unsymmetric craft are not discussed since their behavior can readily be understood by merely making the obvious correction which takes into account the peculiarity of their construction.) However, should the craft yaw, the angles of attack of the hydrofoils would be thereby altered. The angles would increase on one side and decrease on the other. This would result in an unexpected bank, which could only be corrected, if at all, by prompt control action. If the yaw angle exceeds the original incidence of the foils, the hydrodynamic force on one side is reversed; the automatic stabilizing action of the foils is lost; the control action becomes uneffective, or the operator can run out of control, or of time in his attempt to straighten out the craft. The gravity and frequency of this hazard will be appreciated considering that a substantial area of the craft is above water and is exposed to gusts and cross-winds. Depending on the speed, the wind could easily yaw a neutrally stable craft, by as much as 30, 45 and even more degrees. In the case of the previously suggested systems, the best one could do against such contingency would be to provide the craft with a powerful tail fin immersed in the water, and possibly supplemented with a rudder. Too often, such an arrangement would prove clumsy and only assuage the difficulty, since at best it would set the hull at a large angle to the relative wind, whereas operational considerations may require that the hull head straight into the relative wind.

It is therefore one object of the invention to provide in a craft of the type described, means whereby the downwardly extending hydrofoils assume assigned angles of at tack which are independent from any possible yaw of :the craft.

A further object of the invention is to provide means for substantially eliminating the forces fed into the control system by the bank regulating aforementioned hydrofoils.

Another object of the invention is to provide, in a watercraft of the type described, means for insulating the control system and the operator from the vibrations that could develop as a result of high frequency variations of the control forces.

A still further object of the invention is to provide means whereby airfoil borne watercraft may execute steep banks, without the tip of an airfoil contacting the water surface.

These and further objects of the invention will become more readily apparent from a reading of the description following hereinafter, and from an examination of the drawings, in which:

FIG. 1 is a frontal elevation of one embodiment of the invention as applied to a watercraft of the Hydrodyne or Grunberg type,

FIG. 2 is a side view of the embodiment of FIG. 1, partly in cross-section,

FIG. 3 is a cross-sectional view through the mechanism of the craft of FIG. 1 enabling the locking of the wing at any of its two alternate angles of incidence,

FIG. 4 is a schematic plan view of the same watercraft (wing removed),

FIG. 5 is a partial cross-sectional view of a portion of the bank regulating hydrofoil assembly,

FIG. 6 is a diagramatic layout of the bank regulating hydrofoil control mechanism, and

FIG. 7 is a side View, with cross-sections, of one of the bank regulating hydrofoils, indicating the means by which stabilization of the angle of attack of the hydrofoil is accomplished.

The watercraft of the invention is further described in connection with a Hydrodyne or Grunberg configuration, however, it will be understood by those skilled in the art to which this invention pertm'ns, that the invention is not limited to such particular configuration.

A hydrodyne in its best known embodiment, consists essentially of a hull; or other iioatable structure, a dynamic lifting device including rearwardly located main Patented Feb. 2, 1965 sustentation element(s) immersed in its operating fluid (either air or water) e.g. hydrofoils, airfoils, etc. and two laterally spaced planing surfaces or surface piercing hydrofoils; propulsive means, and a rudder. The planing surfaces have also been referred to as stabilizers. They are located forward of the crafts center of gravity. The main sustentation element is located in such relationship to the crafts center of gravity (usually aft of the latter) that its lift, together with all other forces, except those generated by the frontal stabilizers, creates a diving moment and presses the stabilizers against the water. The reacting hydrodynamic forces maintain the stabilizers on the water surface. Since the stabilizers glide at a practically constant level, variations in speed, or in gross weight, or in center of gravity location, or any other influence which may disrupt the balance either between the lift and weight,

or between the pitching moments, cause the craft to trim I about the stabilizers. The resulting change in angle of attack of the main sustentation means restores the balance. The craft always thus automatically seeks and achieves an attitude of longitudinal equilibrium, whereby the reseultant of all vertical forces, and the resultant pitching moment are reduced to zero. This arrangement with the main lifting system in the rear and the stabilizers in the front provides excellent longitudinm stability. The wide straddling of the frontal stabilizers in the hydrodynes above described version insures lateral stability.

FIGS. 1 and 2 generally show the invention as applied to a modified hydrodyne configuration. In FIG. 1 the line WLS indicates the water level in relation to the craft in a straightaway run at operational speed; whereas the line WLB indicates the water level in relation to the craft in a banked turn. In FIG. 2, the line WLM indicates the water level in relation to the craft at operational speed; whereas the line WLR indicates the water level with the craft in motion just before the take-off run is completed. The hull 1 has a propulsive system provided by the engine 6, driving a propeller 8, by means of appropriknown to have a lo ate transmissive means, e.g. a belt 7. The propeller operates within a duct or shroud 9. The propeller mount is a hollow structure streamlined into a vertical fin 10 which gives the hull the tendency to weatherc'ock into the relative wind. The main lifting system is provided by the airfoil or wing 5.

Whereas the best known hy-' drodyne configuration provided twin frontal stabilizers,

the version used in connection with the instantinvention employs only one such stabilizer 4, which is located astride the center plane. This stabilizer 4 contributes to the lift and provides longitudinal static stability, but it does not stabilize the craft laterally. Lateral stabilization is provided by the bank regulating hydrofoil means, including

hydrofoils

12 and 13 which are so arranged as to produce rolling moments acting in opposing directions. When the craft is not heeled and the hydrofoils are equally immersed, these rolling moments mutually cancel out. Should the craft tilt,.the depth of immersion of these hydrofoils becomes unevenand, a resulting moment develops opposing the tilt. By diiferentially controlling the depth of hydrofoils, the operator can induce the craft to bank to a desired degree, and thus cause it to turn.

The craft is also provided with an aerial rudder 11, to

supplement or counteract (as the case may be) the operation of the fin It A second rudder 18, when operating in water prior to take oif, serves as a steering means,

while the bank regulating hydrofoils have not yet become operational. At normal operational velocities, the rudder 18, no longer immersed, becomes inoperative.

The main sustentation element of the ,hydrodyne of FIGS. 1 and 2 is an airfoil wing 5 comprising two

panels

5 and 5". To achieve good maneuverability, this craft must be capable of sharp banks when turning. Yet, no winged water-craft has ever been conditionedfor such turns, since in a bank, the wings tip would come precariously close to the water long before an adequate. tilt angle has been reached. In accordance with the invention,

with high lift coefficients).

. to permit banking to the 1 take-off speed (i.e'. position R).

4 in order to permit tilt of the lifting surface, the wing panels are established either at a dihedral angle of a magnitude far above that which may have been previously suggested for watercraft; or the span of the wing is considerably reduced as compared with the wing span of other airborne vehicles of similar weight and speed; or else these two features are combined, to a greater or lesser extent, in the same watercraft.

I have found that watercraft may be provided with wings that are set at dihedral angles far exceeding the limit acceptable for an airplane. The divergent oscillations associated with such large dihedrals in aircraft are not experienced in a watercraft properly constructed in accordance with the teachings of this invention.

As an alternate or conjoint means, the wing span may be reduced as compared with other winged airborne watercraft of corresponding weightand speed. However, such reduction must be compensated either by an increase in wing depth (i.e. increase of chord length), in order that the wing area may remain unaltered; or alternately, the compensation is obtained by use of wings of reduced area operating at high angles of attack (which are associated Thesev two features of the wing, i.e. short span relative to its chord, and small area, can be combined. Both of these features are known to be detrimental to operational efiiciency of a wing. A wing of short span and large chord has a low aspect ratio span mean chord whichis known to increase the drag. A wing of small area which has to operate at a high angle of attack is defined as (lift to drag ratio). Hence, the short span proposed as option by the invention results in a wing of an unconventional planform or area.

As to wing areas, they may be made so small as to cause'the wing to operate at angles of attack removed only by a few degrees from the stalling angle. These three features, whether used separately or in any combination, need to beused only to such extent as is required desired angle.

As shown in FIG. 1, the wing 5 is rotatively mounted about a transverse'axis K-K, so that the wings angle of incidence can be altered. Alternately, the wing panels may be rotatively mounted about individual axes which are substantially parallel to their respective spans. The wing is locked in either of two alternate positions T or R (see FIG. 2 wherein the port wing panel is represented in two alternate positions by an outline of its root section projected on the hull). The higher incidence position is provided when operating at better than The wing is locked into low incidence position T when the craft is at rest or during the take-elf run.

The axis of rotation KK of the wings may conveniently be formed by the wings own spar 41 (see FIG. 2), or by a special axle joining the wings two panels. Any conventional operating means such'as electric or hydraulic actuators can be provided for repositioning of thawing from one angle of incidence to the other. The actuating cylinder may be attached to the fuselage with 1ts piston attached to the Wing, at some distance from the axis of rotation KK.' The actuator may conyeniently be controlled by the operator to move the wing into position'T or R. Alternate provisions for wing tilting are discussed hereinafter.

An arrangement for locking of the wing in the. selected position is shown diagrammatically in FIG. 3. A plate 16 is made integral with, or fastened to, the hull 1. A

plate 17 is an integral part of, or is fastened to, wing 5. The plate 16 is provided with a hole 1?, and the plate 17 is provided with two

holes

20 and 21. Either the hole 20 or the hole 21 in the plate 17 is alternatively placed into alignment with hole 19 in plate 16 when it is desired to lock the wing 5 into position R or T, respectively. A stud 22 is loaded by a spring 24 and serves as a locking lug. The shoulder 23 on stud 22 serves as a stop. Stud 22 can be retracted by the operator against the spring pressure. For example, the stem 25 may be operated by solenoid 50.

The axis of rotation K-K is located aft of the center of pressure of the wing. Hence, when the craft is in motion, the aerodynamic forces produce a moment which urges the Wing to rotate toward a higher angle of incidence. The take-oft" run starts with the wing locked at low angle of incidence so as to reduce the take-off drag. In this position T, the

hole

21 and 19 are in alignment and the stud is in locked position. The wing is kept in position T until the take-01f speed has been approached or reached, at which time the stud is retracted from hole 21. After the wing has been unlocked, the aerodynamic forces rotate the wing into a higher angle of incidence position. As the position R is reached, the wing plate 17 encounters the stop 117 with the holes 19 and 2G in alignment. The stud 22 is now released, it snaps into locking position.

At rest, in the absence of substantial aerodynamic forces, the wing 5 can be easily brought into low incidence position by retraction of the stud 22 and by tilt of the wing panel, either manually or by action of a spring, or by any other appropriate method.

The described selective setting of the wing permits compensation for the high trim angle assumed in the take-off stage of the run. The temporary reduction of wing incidence during take-off permits the craft to develop less drag, accelerate faster, take off on less power and requires a shorter run. Although helpful, this arrangement is not essential.

An alternate or conjoint means for reducing take-off drag may be optionally provided by the hydrofoil 26 which can be secured to the hull 1 slightly below its bottom. This hydrofoil helps to lift the hull at slow speed, long before the wing 5 has developed the required lift. The hydrofoil 26 thus assists the take-off, helping as it does to keep the hull above water and thus eliminating the water resistance that otherwise would be encountered by the hull. Also, it reduces the trim angle of the craft, thereby reducing the drag coefficient at take-off. The hydrofoil 26 is shown as being rigidly secured to the hull, but it can also be secured to a retractable support somewhat in the manner of the landing gear of an aircraft.

Both of the above described means of reducing the drag at take-off may be either alternatively or concurrently provided on the same craft.

The means for lateral stabilization at controllable bank angles include port and

starboard hydrofoils

12 and 13, which extend downwardly into the water. In side view, these hydrofoils are arranged at a considerable angle to the vertical (i.e. with sweepback, or sweepforward), as shown in FIG. 2. The hydrofoils are rotatably mounted about their respective axes MM and NN (see FIG. 4), and can be differentially controlled by the operator, so as to cause the hydrofoil means on one side to bite deeper into the water, and the hydrofoil means on the other side to move up. Since this produces a rolling moment, the craft banks until it assumes an attitude corresponding to that immersion of the hydrofoils at which their rolling moments mutually cancel out. (Of course, it is assumed that the craft is not subject to an extraneous heeling moment. Otherwise, stability is achieved at a bank angle corresponding to such immersion of the port and starboard foil which yields a rolling moment equal and opposite to the upsetting heeling moment.) Conversely, should the craft, for some fortuitous reason, bank away from the position where both hydrofoils stabilize it, a restoring moment will be instantly created to reestablish the proper bank.

As indicated above, the orientation in azimuth of the components of the craft immersed into the water need not be necessarily conditioned by the orientation of the components operating in the air and vice versa. Often, the orientation of the former must be governed by the direction of the relative water current, while the orientation of the latter must be governed by the relative air current. These conflicting requirements are met by employing pivoted connections between those components of the watercraft which are affected by the contrariety of said requirements. The pivoted connections are so arranged as to allow said components to orient themselves independently of one another, and in accordance with their own respective needs. Thus, as shown in FIG. 2, the heel of the frontal stabilizer 4 may be rotatably mounted so as to align itself with the relative water current, independently of the orientation of the hull. Similarly, the port and starboard hydrofoil means providing lateral stabilization are pivotally mounted to rotate about axes associated with variations of the hydrofoils angle of attack (i.e., associated with pitchwise rotations); and furthermore the hydrofoil means are automatically stabilized at angles of attack which produce hydrodynamic forces acting in outboard direction, as stated earlier in this specification. The angles of attack may either be so stabilized as to remain constant under all operational conditions; or optionally, the angle-of-attack stabilization means can be so constructed (as will be shown) as to render the angle of attack dependent on the foils depth of penetration below water, or on some other judiciously selected parameter. But under no condition are the hydrofoil means allowed to partake in the crafts yaw, if any; except only for such slight lag which can develop in the process of angle of attack adjustment to its assigned value. (Such lag could be the consequence of friction in the bearings, or of damping action, etc.) In summary, the port and starboard lateral stabilization means are stabilized at lift producing angles of attack assigned to them, which are substantially independent from any possible yaw of the craft.

An example of hydrofoil means stabilizing the craft about its roll axis and answering the above description is shown on FIGS. 2 and 7. In this example, the port hydrofoil means for lateral stabilization (duplicated on starboard by a symmetric means) consist of two

hydrofoils

12 and 39, arranged in tandem, and joined by a connecting structure 40. This assembly is free to rotate about axis AA. Sulficient room is allowed about the assembly, so that it may not be obstructed in its displacements compensating for the yaw of the craft. The foils 12 and 39 are disposed relative to each other and their common axis of rotation AA in the same manner as the wing and horizontal tail surface of an airplane are disposed relative to each other and the airplanes central principal transverse axis of inertia. (The latter axis does fully correspond to axis AA, since the airplanes pitching motion is such as if the craft was hinged about the aforesaid axis of inertia.) The behaviour of the hydrofoil assembly is essentially determined by the immersed portions of the foils which act and interact exactly in the manner of an airplanes wing and horizontal tail. Thus, the angle of attack of the assembly (and hence of the foils) is totally defined by the immersed portions of

foils

12 and 39, i.e., by their respective profiles, incidences, areas, distances from the common axis of rotation, aspect ratios, and other, secondary factors the effects of which are well understood by those conversant with the art; and just as an airplane can be designed and trimmed for stable operation at a desired lift-generating angle of attack, so does compliance with the same well established rules permit stabilization of the

foils

12 and 39 at angles which are independent from the angle at which the craft arenas? happens to be oriented with reference to the relative water current.

It will be noted that depending on the depth to which these foils penetrate below water, the parameters which influence the angle of attack may, or may not, vary. For example, assuming the

foils

12 and 39 to be held by the controls in a fixed position, each to be of constant profile along the span, as well as of constant chord and incidence (no twist), and to be parallel to axis A-A, the factors which govern the angle of attack of the assembly do not substantially vary with the draught. Hence, the angle of attack remains substantiallyconstant. On the otherhand, in a hydrofoil system so built that any one of the above conditions is not met, the angle of attack will change in a predictable manner as the foil system penetrates deeper or moves out of the water. The foil system of FIG. 7 illustrates this feature. Foil 12 tapers from root to tip, considerably more than does foil 39; thus the ratio of the immersed areas of the two foils undergoes variation with the draught,zwhile the other parameters remain ubstantially constant. Because of this, the hydrofoils 12-39 while being consistently stable, achieve stability at variable angles which are fully determined by the extent of their immersion. These angles constitute a built-in feature of the structure. In the case of FIG. 7, the angle of attack grows with the draught, due to the fact that foil 12 is mounted at a higher incidence than foil 39 (according to the classical rules followed in associating wing and tail). The advantage of thi arrangement is that as long as the craft is on even keel and the lateral stabilization means are engaged but slightly in the water, the hydrofoils attack the water at low angle of attack producing minimal drag, but when one of the hydrofoil assemblies bites deeper into the water, i.e., when action is demanded from the systems, their stabilizing effect is augmented by the appropriate variations of their angles of attack, in which'case the penalty in drag is V justifiably increased. 7

By contrast with FIG. 7, the

foils

12 and 39 in FIG. 2 are both tapered in a substantially mutually compensating manner. Assuming the other parameters to be constant, the lateral stabilization means of FIG. 2 operate at constant angles of attack, regardless of their immer sion. In both figures the foil are completely unconcerned with the directional orientation of hull 1. Other means can be provided to accomplish the purpose of sta' bilizing the angle of attack. Thus, for example, foil 39 could be located ahead of foil 12, which would be some,

what analogous to the canard arrangement of the horizontal tail surface of an airplane. The stabilization of

hydrofoils

12 and 13 may be achieved Without adding such tail surfaces by use of self-stabilizing (autostable) hydrofoils. Known foil sections (profiles) exist which stabilize themselves at predeterminable angles of attack. These sections are employed in tailless airplanes, and the same sections could be used for the hydrofoil 12 of the invention, in which case no adjunction of foil 39 would be needed.

When a lateral stabilization means such as the one here considered is arranged to function at a substantially constant angle, the thereby created hydrodynamic force acts always in a substantially constant direction F (which has a rearward tilt due to its drag component). This case is.

illustrated in FIG. 4 by the arrows F and F pertaining to the port and starboard stabilizers.

It is known that the torque produced by a force about an axis, depends upon the orientation of the force relative to the axis. When the force vector and the axis are parallel, or more generally, are coplanar, no torque is created about the axis. All other conditions being equal, the greater the deviation from coplanarity, the greater is the torque. With this in mind, and in order to moderate the torque forces feeding into the control system shown in FIG. 6, the axes of rotation MM and NN of the port and starboard stabilizing systems are set substantially in a common plane with the hydrodynamic forces produced by the respective hydrofoils, so that in plan view they appear as shown in FIG. 4, i.e. parallel or approximately parallel to the respectivedirections F and P In those instances where the directions F and F are not necessarily constant (e.g., when the angle of attack is made to vary with the draught of the lateral stabilization system), it is still feasible to minimize the torque by orienting appropriately the axes of rotation MM and NN. In other instances, one may deliberately choose to retain some little torque in the control system. Hence, by the term substantial co-planarity or substantial parallelism, as appears herein and in the claims hereinafter, is meant such orientation of the items in question that it would require only a small angular displacement of less than 15 of one of them in order to become strictly parallel or co-planar, as the case may be.

FIGS. 5, 6 and 7 illustrate the bank regulating mechanism. The hydrofoil 12 extends at its upper end into a cylindrical shank 27, which is rotatably mounted within bearings 29 in a hollow cylinder 28. The latter is secured at to a shaft 30, which penetrates into the hull 1, where it is rotatably held within

bearings

31 and 42. Shaft 30'is arranged in the direction indicated in FIG. 4 by line MM. Shaft 30 terminates at its end opposite to hydrofoil 12 in a bevel gear 32. The latter meshes with gear 33 which is keyed to shaft 34. The shaft 34 is rotatably mounted in bearings 35 (only one of which is shown). Theshaft 34 extends in the plane of symmetry of the craft towards the control station, where it is geared (as shown), linked, or otherwise connected to the operators controls 70. The hydrofoil 13 is mounted in the same manner and is kinematically related to the gear 33 by the shaft 30' and gear 32'.

As indicated previously, depending on the angle at which the shafts 30 and 30' are located, the hydrofoils may or may not produce torque about said shafts. When torque is present, the shaft 34 is subjected to the difference between port and starboard torques. High frequency variations of this differential torque could be objectionable. Such variations are suppressed by the dampers 36 and 36'. These dampers may be'of any well known construction. For example, a dashpot may be connected in the usual manner to axis 30. A similar 'damper-36can be installed on shaft 30'. Shaft 34 may be spring loaded by

springs

37 and 38 which act as a centeringmeans, i.e. they urge both hydrofoils to set themselves at equal sweepbacks.

The differential control of port and starboard hydrofoils is achieved by the operation of the shaft 34. The steering effort of the operator is dependent on the orientation of axes MM and NN, and the stiffness of-the

springs

37 and 38.

The shape of foil 12 on FIG. 7 is dictated by structural as well as operational considerations. The effect of foil 12 taper on the behavior of the hydrofoil system 12-39 has been reviewed earlier in this specification. As to the structural viewpoint, the taper increases the foils strength, thanks to increased root thickness. This is beneficial since the bending moments grow toward the root. If need be, the strength can be further improved by varying the profile along the foils span, changing it from a thin to a thick section. For the-sake of the argument it may be realistically assumed that at the tip the foil has an NACA 0007 rofile (cross-section 74), while the section 72 at the root is of NACA 0035 profile. (Thus, the thickness of one section is equal to 7% of the chord; the other section is 35% thick.) Assuming that the taper is in the ratio of 2 to 1, the actual thicknessstood that many modifications and rearrangements of parts can be made without departing from the spirit and scope of the invention.

What I claim is:

1. In a craft operating on water and supported in motion by means developing dynamic lift forces, lateral stabilization means on the craft including port and starboard downwardly extending hydrofoil means, each producing hydrodynamic forces tending to heel the craft toward the opposite side; said hydrofoil means being rotatively held in supports affording rotary freedom about axes associated with pitchwise rotations and being provided with angle of attack stabilization means for automatic stabilization of said hydrofoil means at their assigned lift producing angles of attack and preventing the hydrofoil means from partaking in any possible yaw of the craft.

2 In a craft of claim 1 each hydrofoil means and its angle of attack stabilization means comprising two hydrofoils joined together by a connecting structure, said hydrofoils being mounted in tandem and disposed relative to each other and to said rotary axis in the same relationship as an airplanes Wing and horizontal tail surface are disposed relative to each other and to the airplanes central principal transverse axis of inertia.

3. In a craft of claim 1 each of said hydrofoil means and its angle of attack stabilizing means comprising a hydrofoil of autostable profile disposed about its rotatory axis in the same manner as the wing of a tailless airplane is disposed relative to the latters central principal transverse axis of inertia.

4. A craft of claim 1 including: kinematic couplings between the craft and the supports of the hydrofoil means providing for freedom of raising and lowering movements of the hydrofoil means; and controls for differentially moving the port and starboard hydrofoil means whereby the operation of the controls regulates the angle of bank of the craft at which lateral stability is achieved.

5. In the craft of claim 4 said couplings including rotative mountings for said supports to provide for rotations of the port and starboard hydrofoil means about transverse axes substantially coplanar with the hydrodynamic forces generated by the respective hydrofoil means.

6. A craft of claim 2 including: kinematic couplings between the craft and the supports of the hydrofoil means providing for freedom of raising and lowering movements of the hydrofoil means; and controls for differentially moving the port and starboard hydrofoil means whereby the operation of the controls regulates the angle of bank of the craft at which lateral stability is achieved.

7. A craft of claim 3 including: kinematic couplings between the craft and the supports of the hydrofoil means providing for freedom of raising and lowering movements of the hydrofoil means; and controls for differentially moving the port and starboard hydrofoil means whereby '10 the operation of the controls regulates the angle of bank of the craft at which lateral stability is achieved.

8. In craft of claim 6 said couplings including rotative mountings for said supports to provide for rotations of the port and starboard hydrofoil means about transverse axes substantially coplanar with the hydrodynamic forces generated by the respective hydrofoil means.

9. In a craft of claim 7 said couplings including rotative mountings for said supports to provide for rotations of the port and starboard hydrofoil means about transverse axes substantially coplanar with the hydrodynamic forces generated by the respective hydrofoil means.

10. In the craft of claim 4, said kinematic couplings including dampers operatively connected thereto to absorb any vibrations created by the hydrofoil means and transmittable to the controls.

11. In a craft of claim 1 said angle of attack stabilization means being arranged to impart the angles of attack a substantially constant value.

12. In a craft of claim 1 said angle of attack stabilization means being arranged to impart the angles of attack a value which is dependent on the depth of immersion of the respective hydrofoil means.

References Cited in the file of this patent UNITED STATES PATENTS 1,223,616 Riecks Apr. 24, 1917 1,410,876 Bell et a1. Mar. 28, 1922 1,728,937 Kemp Sept. 24, 1929 1,776,336 Rohrbach Sept. 23, 1930 1,776,700 Pegna Sept. 30, 1930 2,139,303 Greg Dec. 6, 1938 2,167,143 Thompson July 25, 1939 2,194,596 Henter Mar. 26, 1940 2,210,935 Giliberty Aug. 13, 1940 2,365,205 Martin Dec. 19, 1944 2,511,607 Turnquist June 13, 1950 2,914,014 Carl et al Nov. 24, 1959 2,980,047 Korganoff et al Apr. 18, 1961 2,997,260 Locke Aug. 22, 1961 3,014,674 Strawn Dec. 26, 1961 FOREIGN PATENTS 96,322 Australia Mar. 10, 1924 411,197 France Apr. 6, 1910 413,115 France May 19, 1910 651,279 France Oct. 8, 1928 717,054 France Oct. 13, 1931 150,858 Great Britain Sept. 16, 1920 282,108 Great Britain July 12, 1928 493,373 Great Britain Oct. 6, 1938 587,317 Great Britain Apr. 22, 1947 814,173 Great Britain June 3, 1959 420,825 Italy May 6, 1947 469,300 Italy Feb. 22, 1952

Claims

1. IN A CRAFT OPERATING ON WATER AND SUPPORTED IN MOTION BY MEANS DEVELOPING DYMAMIC LIFT FORCES, LATERAL STABILIZATION MEANS ON THE CRAFT INCLUDING PORT AND STARBOARD DOWNWARDLY EXTENDING HYDROFOIL MEANS, EACH PRODUCING HYRODYNAMIC FORCES TENDING TO HEEL THE CRAFT TOWARD THE OPPOSITE SIDE; SAID HYDROFOIL MEANS BEING ROTATIVELY HELD IN SUPPORTS AFFORDING ROTARY FREEDOM ABOUT AXES ASSOCIATED WITH PITCHWISE ROTATIONS AND BEING PRO-