US 3195495 A
Description (OCR text may contain errors)
United States Patent 3,l5,495 HYDROFGIL BOAT @sear Erlandsen, Garden (Iity, N.Y., assignor to Thurston Erlandsen Qorporation, Sanford, Maine, a corporatien of Maine Filed Mar. 13, N63, Ser. No. 264358 3 Claims. (Cl. 114-665) This invention relates to new and useful improvements in hydrofoil design and more particularly seeks to provide a variable sweep arrangement of the hydrofoils for waterborne vehicles.
Stationary hydrofoils, to some extent, limit the efficiency of a hydrofoil boat by limiting its maximum efficiency over a wide speed range. If the stationary hydrofoils are generally transverse to the hull, there will be a relative high drag at high speeds, whereas if the stationary hydrofoils are swept back, there will be relatively small lift at low speeds. Hence, there is no one ideal planform or position for the hydrofoils of a high speed ratio (wide range) vehicle and operating efliciency is consequently lost at certain speeds in a hydrofoil boat having fixed planform hydrofoils.
It is, therefore, amongst the primary objects of the present invention to increase the efficiency of hydrofoil boats by varying the planform or position of the hydrofoils at varying speeds.
It is another important object of the present invention to enlarge the eflicient operational speed range of a water-borne vehicle by hydrofoil modification.
It is still another important object of the present invention to provide a water-borne vehicle having movable hydrofoils so that the same may be swept back at high speeds, extended transversely at low speeds and made to assume a variety of intermediate positions in order to have the best sweep angle at intermediate speeds for maximum operational efficiency.
With these and other objects and features in mind, the nature of which will be more apparent, the invention will be more fully understood by reference to the drawings, the accompanying detailed description and the appended claims.
In the drawings:
FIG. 1 is a diagrammatic plan view of a variable sweep hydrofoil in accordance with the present invention;
FIG. 2 is a diagrammatic vertical section through a boat equipped with the hydrofoils of FIG. 1; and
FIG. 3 is a graph plotting L/D in air (equivalent to lift over drag) against Mach number (speed) and Reynolds number with NACA foil 0012, chord1'=0", and C =0.4.
This invention, as illustrated, discloses a hydrofoil system mounted underneath a conventional hull l8, hydrofoils and 12 being mounted in housing 11 to pivot about points 14 and 16, respectively, as shown schematically in the drawings. The housing ll. is attached to and spaced from the hull by struts 9. The foils l0, l2. and the housing 11 are foil-shaped in cross-section to provide lift via well known hydrodynamic principles.
By reason of the foregoing construction, said hydrofoils may be made to assume a swept back position, a position which is most advantageous at high speeds. If the hydrofoils operate in the same plane, a portion of the base end of each hydrofoil may be arranged angularly of the remainder, as at 25 and 28, so they will not 0'0- 3,195,495 Patented July 20, 1965 struct each other when assuming the swept back position. The angle of sweep is shown at transverse to 45 behind transverse; but generally may be between about 10 in front to behind transverse, transverse being measured from the longitudinal axis of the hull. Foil it; (and dotted 3.2) is shown in slow transverse position, whereas 12 is shown in fast swept back position, although in operation, both would be in the same relative position.
At low speeds the same hydrofoils may readily be extended transversely of the hull to again assume a most advantageous lift position. For intermediate speeds, intermediate positions may be selected for said hydrofoils.
As will be seen from FIG. 3, the drag on an unswept airfoil of the particular design is constantly less on an unswept Wing up to about 0.6 Mach with the difference decreasing until they cross at about 0.63. However, on reaching 0.8 Mach, the drag on the unswept wing is more than double the 35 swept wing.
Since the basic principles of the dynamic forces eX- erted by a fluid on a foil moving therein are applicable to both air and water, both being fluids, the airfoil theory with proper adjustments, is applicable to hydrofoils.
The proportions, plus mechanical and structural considerations of the airplane wing render the overall advantage of the variable sweep wing as a dubious quantity in most cases. However, the hydrofoil wing is generally smaller, more compact and more heavily loaded than the airplane wing and, therefore, the structural, mechanical and weight penalties involved in introducing variable sweep are less critical for the hydrofoil boat. Thus, to take full advantage of minimum possible drag for a given lift, as applied to a high performance (i.e., wide range) boat, it is necessary to have a variable sweep wing.
The motive power for pivoting the hydrofoils may be derived from the power plant of the water-borne vehicle or from an independent power source, e.g. electrical or hydraulic. if the power plant of the vehicle is to be utilized, the hydrofoils may be readily linked by suitable gearing to the drive shaft for the boat propeller. They may, of course, be driven by conventional propeller, jet power, or other suitable propulsion means.
By providing a suitable system of gearing and clutches, the rotational moment of the drive shaft may be translated with minimum energy loss into the reversible linear movement required for the above described variations in hydrofoil position. An arrangement for locking the hydrofoils in any of the various possible positions therefor may readily and economically be combined with such gearing and clutches.
It may be seen from FIG. 3 that the optimum sweep angle of a particular hydrofoil is a function of the hydrofoil speed and other considerations. Hence, control of the sweep angle may be made automatic and as a function of hydrofoil speed. On the other hand, control may reside exclusively in the pilot and, of course, a dual system of controls may be provided.
Although the invention has been described in detail with respect to one preferred embodiment thereof, it will be understood by those skilled in the art, after reading this specification, that various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
1. In a water borne vehicle including a hull and a hydrofoil having continuous leading and trailing edges extending generally transverse to the longitudinalaxis of i through a variable sweep back angle Without braking the continuity of said leading and trailing edges whereby the plan view of said hydrofoil is continually changed with said pivoting. p I
' 2. he vehicle of claim 1 wherein said side sections are pivoted about a point on the proximal end thereof 7 positioned Within'the plan of said mid-section in such a manner that the saidleading and trailingledges of said ,side sections are always partly Within the plan of said amid-section.- I a 7 1 3. The vehicle of claim 1 wherein said pivotal angles of said side sections are between about 10 forward to 85 rearward of transverse, transverse being 90 from the longitudinal axis.
V ReEerences Cited by the Examiner V UNITED STATES PATENTS FERGUS' 's, MIDDLETON; Bi'iprary Examiner;