US3162166A

US3162166A - Variable sweep hydrofoil

Info

Publication number: US3162166A
Application number: US261910A
Authority: US
Inventors: Eugene H Handler
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-02-28
Filing date: 1963-02-28
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

Dec. 22, 1964 E. H. HANDLER 3,

VARIABLE SWEEP HYDROFOIL Filed Feb. 28, 1963 2 Sheets-Sheet 1 INVENTOR Eugene h. Hand/er AGENT Dec. 22, 1964 E. H. HANDLER 3,162,166

VARIABLE SWEEP HYDROFOIL.

Filed Feb. 28, 1963 2 Sheets-Sheet 2 PUMP United States Patent Ofi 3,162,166 Patented Dec. 22, 1964 3,162,166 VARIABLE SWEEP HYDRUFGIL Eugene H. Handler, Keusington, Mi, assignor to the United States of America as represented by the Secretary of the Navy Filed Feb. 28, 1963, Ser. No. 261,910

' 3 Claims. (Cl. 114-665) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention pertains generally to a hydrofoil system for supporting a water-borne craft and in particular the invention relates to a variable-sweep hydrofoil by which an appropriate angle of sweep-back, aspect ratio and foil section may be selected as a function of speed.

A hydrofoil is a surface provided below the hull of a water-borne craft which provides an upward force component of lift when the craft has forward velocity with respect to the water. The lift exerted on the hydrofoil by the water is suilicient to raise the hull of the craft above the surface of the water when the velocity of the craft is of proper magnitude.

It is well known in the design of high speed boats that the performance of such craft can be greatly improved by the use of hydrofoils. Many hydrofoil craft in the past, however, exhibited certain disadvantages. The prior art foil systems are often quite complex; in one common type, for example, each foil support has thereon three or four foils in generally vertical alignment. Such an array is heavy, expensive and may require extensive maintenance. In addition, the low speed resistance of chevron and/ or ladder systems are excessive since both low and high speed foils are immersed. Furthermore, if the latter have super-cavitating sections, their resistance will be extremely high. Additionally, during high speed operation when utilizing the ladder type arrangement of foil support, theuppermost or low speed foils are clear of the water, thus being carried along as dead weight. Also, both the large foils and the series of generally vertically supported foils present problems of storage when the ship is in port.

The present invention obviates the aforementioned disadvantages by providing a craft with variable sweep foils. The under side of the hull is provided with symmetrically spaced support struts, the lower ends of which rotatably mount the foils of the instant invention. The foils are aligned with the minimum chord fore-and-aft for the low speed phase of the acceleration run or low speed cruise. In this configuration, the foil has maximum aspect ratio, a term which may be defined as the ratio of span to average chord. In addition, the low speed position is specifically designed to have a sub-cavitating cross-section.

As the hydrofoil boat speed is increasedfthe foil is rotated to a position giving the desired chord/thickness ratio and sweep. The angle of rotation in the simplest case is 90, giving maximum aspect ratio and chord/thickness ratio for low speed and minimum aspect ratio and chord/thickness for high speed.

Therefore, objects and features of this invention are the provision of hydrofoil systems for water-borne craft in which foil configuration may be optimized for any desired speed within the crafts capabilities.

- provision of a novelhydrofoil system by means of which Further objects and features of this invention are the smooth transition from low speed to high speed is achieved.

Further objects and features of the invention include the provision of a hydrofoil system having rotatable foils, the variable configuration of which eliminates force and moment discontinuities due to the onset of, cavitation.

Additional objects and features of this invention are the provision of structural arrangements for hydrofoil craft of such nature and character as to minimize weight due to the minimization of foil surfaces and the simpli fication of design and associated equipment.

Other objects and features and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side view of the craft in motion illustrating the elevation of the hull above the Water surface and further illustrating the foils of the instant invention rotated to the high speed position;

FIG. 2 is a top plan view of the craft in FIG. 1, illustrating the symmetrical paths of rotation of the variable sweep foils of the instant invention from the high speed position through 90 to the low speed position;

FIG. 3 is a front elevation view of the craft of FIG. 1;

FIG. 4 is a sectional view with parts broken away of a rotatable foil and actuating mechanism therefor taken substantially along the line 44 of FIG. 2; FIG. 5 is a transverse sectional view with parts broken away of the foil, the foil supporting strut and the rotation actuation mechanism taken substantially along the line 5-5 of FIG. 4;

FIG. 6 is a top plan view of a typical foil showing the general configuration thereof;

FIG. 7 is a sectional view of a foil taken substantially along the line 7-7 of FIG. 2 in which the cross-section of the foil is optimized for low speed with regard to water flow past the foil from right to left;

FIG. 8 is a sectional view of the foil taken substantially along the line 8-8 of FIG. 3 in which the cross-section of the foil is optimized for high speed with regard to fiow of water past the foil from right to left; and FIG. 9 is a view similar to FIG. 7 of a typical aft foil showing the optional reduced-thickness, cross-sectional configuration.

Referring now to the drawings and in particular to FIGS. 1, 2 and 3, an embodiment of the hydrofoil system of the invention is shown mounted on a generally con-v ventional boat 10 having a hull 12 driven by a propeller 14, which propeller is mounted on shaft 16 connected to a suitable source of power (not shown). Directional control of thecraft is maintained by manipulation of rudder 18 in the conventional manner.

In accordance with this invention the hydrofoil system comprises a pair of forward hydrofoils 2t), 22 and a pair of aft hydrofoils '24, 26 rotatably mounted on supporting struts Z1, 23, 25 and 27-, respectively, which are secured to boat hull 12. These supporting struts are constructed in the general form of an airfoil in order that drag resistance may be reduced to a minimum. As may be seen in FIG. 3 the foils are secured to the craftvat an angle of sufficient dihedral to promote stability.

FIGS. 4 and 5 illustrate a representative mechanism suitable for imparting rotational movement to said foils about the ends of the supporting struts. A typical foil;

supporting strut, member 23 comprises a primary load carrying frame 30 enclosed by a foil shaped housing 31. Frame 30 is a hollow structure terminating-in a stepped bore for bearing surface32 and an outwardly extending flange 33. An upwardly extending column 34 issecured to the upper surface of the foil and is received within'the hollow frame 30. The column is provided adjacent the opposite directions.

foil with. a bearing surface 35 of such dimensions as to rotatably engage the lower stepped bore bearing surface 32 of saidframe. Appropriate seals 32a as, for example, O-rings are provided between the bearing surfaces in order to exclude ambient sea water from within frame 39. Column 34 may be further axially supported within. the frame 30 at its upper end 38 by sleeve 39 concentrically arranged within frame 3th The upper surface of the foil is further provided with an annular collar 36 concentrically positioned about column 34. Frame flange 33 'is slidably retained within said collar thereby retaining the foil in rotative sliding abutment with the end of the strut support frame. Foil 22 is therefore retained in freely rotatable condition on the end .of frame 36 in both radial and axial directions by column 34 and the abutting association of flange 33 with collar 35. v.

Rotative motion may be imparted to the foil by any one of a number of instrumentalities. One such system is shown in FIGS. 4 and 5. An internal ring gear 42 is secured to the top of column 34 by bolts 43 and is engaged and driven by pinion 44. The pinion may be powered by any suitable means as, for example, a hydraulic motor 45 conveniently located within frame 39. The pump for the motor and necessary controls for directing foil movement are conveniently placed within the boat and may be driven by means of a power take-off from the boat power plant. In order that the foils may be maintained inany desired position, instrumentalities such as an accumulator, pump bypass and holding valves, or a mechanical one-way drive gear system may be used. In addition, the pump is reversible to accommodate bidirectional operation of the foils.

become apparent to those skilled in the art. Ring gear 42 is provided on its exterior surface with an abutment 46 which is engageable with either of two blocks 47 mounted within frame 30, thus limiting rotation of the ring gear, column and foil to 90 for purposes disclosed hereinafter. Housing 31 is provided with a removable panel or door 48 for access to the foil rotation mechanism located therewithin.

Referring now to FIGS. 2, 6, 7 and 8, the hydrofoils of the instant invention are rotatable about their supporting struts from positions having transverse axis AA through 90 to positions having transverse axis BB. In this manner, a single foil may be provided with a configuration with regard to one axis which is optimized for low speed and, in addition, a configuration along an other axis beneficial for high speed. To this end the foils of the instant case are formed with a sub-cavitating crosssection, FIG. '7, having. minimum chord fore-andaft for the low speed phase of the acceleration run or low speed 'eruise- This low speed configuration, having transverse axis A'A, is illustrated in FIG. 2n the dotted lines. In this position, the foil has maximum aspect ratio as well as 'chord/ thickness ratio, both of which are desirable featuresfor achieving the optimum relationship of lift to resistance at low speeds. V V

As the hydrofoil'boatspeed is increased, the foil :may be rotated through a sequence of positions in order'that i the desired sweep and chord/thickness ratiomay be ob tained. When top speed is reached the foil has been rotated through 90 thereby presenting a foil configurationin which BB isthetransverse axis as shown in FIGS. 1, 2, 3 and 6. In this position both the aspect ratio and the chord/thickness ratio have been minimized :a's'shown .in FIG. 8.

In order to maintain 'symmetry' and to stabilize the motion of the boat, opposing pairs of foils are rotated in FIG. 2 illustrates the preferred inward [rotation of

foils

26 and 22 from high speed positionstothose locations better adapted for lowspeeds.

Rotation from. low speed to high speed positions is achieved in-tlie opposite manner, foil 20 being rotated Numerous alternatives for achieving desired foil rotation may be used as will outwardly counter-clockwise and foil 22 being rotated outwardly clockwise to the position shown in FIG. 2.

Aft foils 24 and 26 may be of similar configuration to, and may be rotated in a similar manner as, their forward counterparts. It may be desirable, however, to provide the aft foils with a configuration of reduced thickness, shown in FIG. 9, so as to delay separation of flow and the consequent deterioration in stability. Although the directions of rotation of the aft foils are identical to those of the forward foils, the need for rotation may be decreased or eliminated if the aft foils are used primarily for longitudinal stabilization. In this use the onset of cavitation would not seriously affect the aft foils left which has been minimized in accordance with their function as stabilizers.

In operation, with the hull of the boat resting on the surface of the water prior to acceleration, the hydrofoils are rotated to the positions shown in dotted lines in FIG. 2 having minimum chord fore-and-aft and maximum aspect ratio. As the craft accelerates, the foils are rotated outwardly in order that the optimum lift/resistance relationship may be maintained by permitting an appropriate angle of sweep-back, aspect ratio and foil section to be selected as a function of speed. As the craft obtains top speed, at which the hull is supported above the surface of the water by the foils, the foils will be rotated to those positions shown in FIG. 2 wherein the chord fore-and-aft is maximized, resulting in minimum aspect ratio and chord/ thickness ratio.

It will be apparent from the foregoing description that the provision of variable sweep hydrofoils for a waterborne craft in the manner taught herein achieves the objectives of optimizing foil configuration for any desired speed within the capabilities of the craft. Another benefit of the instant invention is realized in economics of initial cost, maintenance and weight by virtue of the simplifiedsystem and the decrease in number of foil surfaces over those required in the prior art. A further advantage is the elimination of force and moment discontinuities due to the onset of cavitation as well as a smooth transition from low to high speed.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. For example, the angle of rotation from low speed alignment to high speed alignment for purposes of illustration was chosen to be However, optimum foil alignment in any given specific situation may define an angle of rotation of different magnitude than 90. Optimum angle determination would be dependent upon foil shape, size and attitude, as well as the craft velocity and the properties of the fluid, e.g., fresh water or salt water. The precise plan view of the foils depends upon the sections chosen for it; that is, for example, whether the cross-section is sub-cavitating or super-cavitating, and whether the foils are to be used for longitudinal stabilization.

It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A waterborne craft comprising a hull,

a hydrofoil system including at least a pair of symmetrically located hydrofoil supports extending generally downwardly from said hull,

variable sweep hydrofoils, each hydrofoil having a foilshaped cross-scetionabout each of two substantially v perpendicular axes, continuously immersed during operation and rotatably secured to said supports,

-, said hydrofoils having effective aspect and chord/ thickness 'ratios which vary as a function of the angle of sweep of said hydrofoils,

I control means in said craft operatively connected to said hydrofoils toset the foils to any selected intermediate sweep angle between two predetermined limits,

thereby to provide at any given speed within the speed range of the craft a hydrofoil sweep angle which optimizes the lift/resistance ratio for that particular speed. 2. In the craft according to claim 1, said hydrofoil system comprising pairs of hydrofoils and supporting struts longitudinally spaced along said craft, the aft hydrofoils being thinner than the forward hydrofoils whereby separation of flow may be delayed thereby maintaining stability of operation of the hydrofoil system. 3. The craft according to claim 2 wherein said pairs of hydrofoils and struts comprise one hydrofoil positioned on the starboard side of said craft and the other hydrofoil symmetrically located on the port side of said craft and References Cited by the Examiner UNITED STATES PATENTS Dawson 244105 Barkla 114-665 Wendel 114-665 Follett 114--66.5 Headrick et a1 114--66.5 Smith 11466.5

15 FERGUS s. MIDDLETON, Primary Examiner.

Claims

1. A WATERBORNE CRAFT COMPRISING A HULL, A HYDROFOIL SYSTEM INCLUDING AT LEAST A PAIR OF SYMMETRICALLY LOCATED HYDROFOIL SUPPORTS EXTENDING GENERALLY DOWNWARDLY FROM SAID HULL, VARIABLE SWEEP HYDROFOILS, EACH HYDROFOIL HAVING A FOILSHAPED CROSS-SECTION ABOUT EACH OF TWO SUBSTANTIALLY PERPENDICULAR AXES, CONTINUOUSLY IMMERSED DURING OPERATION AND ROTATABLY SECURED TO SAID SUPPORTS, SAID HYDROFOILS HAVING EFFECTIVE ASPECT AND CHORD/ THICKNESS RATIOS WHICH VARY AS A FUNCTION OF THE ANGLE OF SWEEP OF SAID HYDROFOILS, CONTROL MEANS IN SAID CRAFT OPERATIVELY CONNECTED TO SAID HYDROFOILS TO SET THE FOILS TO ANY SELECTED INTERMEDIATE SWEEP ANGLE BETWEEN TWO PREDETERMINED LIMITS, THEREBY TO PROVIDE AT ANY GIVEN SPEED WITHIN THE SPEED RANGE OF THE CRAFT A HYDROFOIL SWEEP ANGLE WHICH OPTIMIZES THE LIFT/RESISTANCE RATIO FOR THAT PARTICULAR SPEED.