US2773467A

US2773467A - Hydrofoil craft

Info

Publication number: US2773467A
Application number: US265551A
Authority: US
Inventors: David Z Bailey
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-01-09
Filing date: 1952-01-09
Publication date: 1956-12-11
Anticipated expiration: 1973-12-11

Description

Dec. 11, 1956 o. z. BAILEY HYDROFOIL CRAFT 4 Sheets-Sheet 1 Filed Jan. 9, 1952 8 INVENTOR.

Dqvid Z. Bailey BY 04m, yuan/r45 M &4?

TT EYS Dec. 11, 1956 D. 2. BAILEY 2,773,467

HYDROFOIL CRAFT Filed Jan. 9, 1952 4 Sheets-Sheet 2 v INVENTOR. David Z. Bailey BY ofawz yowwtclawdafi @440 ATTORNEYS Dec. 11, 1956 D. z. BAILEY 2,773,467

HYDROFOIL CRAFT Filed Jan. 9, 1952 4 Sheets-Sheet 3 40b FIG.4

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INVENTOR. .Dovid Z. Bailey BY v Warm/ 70W aadc/flcwo ATTORNEYS United States Patent HYDROFOIL CRAFT David Z. Bailey, Charlestown, R. I. Application January 9, 1952, Serial No. 265,551 7 Claims. (Cl. 114-66.5)

This invention generally relates to the control of Iongitudinal stability of water craft utilizing hydrofoil support for the purpose of reducing skin friction and displacement drag by raising the hull of the craft to a higher position with respect to the surface of the Water in which it travels. In a more particular aspect, this invention concerns not only control of longitudinal stability but also control of lateral stability.

A hydrofoil is a submerged surface mounted beneath the underside of a water-borne craft which provides an upward force component or lift when the craft has forward velocity with respect to the Water. If the velocity of the craft with respect to Water is sufficiently high, the lift exerted on the hydrofoil by the water may be sufficient to raise the entire hull above the surface of the Water, which is the desired form of travel for hydrofoil craft.

Hydrofoil craft are subject to certain disadvantages which are caused by the ever disturbed condition of the surface of almost every body of water. At a constant velocity of the craft with respect to the water, the lift force is a function of the angle of attack of the hydrofoil, i. e. angle between the water streamline and the chord line of the hydrofoil. Waves and similar disturbances produce changes in the angle of attack and the consequent change in lift tends to cause the craft to ride over the Waves and to maintain a constant height above the surface. Such variations in angle of attack result in highly inefficient operation of the hydrofoil from a hydrodynamic standpoint since they may result in stalling as Well as in wasted power in constantly raising and lowering the craft.

Moreover, the response of the craft to the surface configuration is always somewhat delayed, and therefore the upward reaction of the craft to a wave crest might raise the hydrofoil so near the surface of the following wave trough as to cause ventilation and serious loss of lift. Loss of lift can occur whenever the hydrofoil comes so close to the water surface that the flow of water over the hydrofoil tends to disturb the water surface.

My invention concerns principally a short period control system for hydrofoil boats which is designed to offset the effect of waves and similar disturbances sothat the craft tends to ride along an even level and so that the.

supporting hydrofoil maintains a constant angle of attack With the streamline. In a more particular aspect my invention also permits a long period control system for depth regulation which operates independently of the short period system to maintain or adjust operation to a selected mean depth. The long period system advantageously is laterally divided to provide independent control for port and starboard and thus also provide lateral stability.

In order to secure these ends, I provide in addition to the main hydrofoil a secondary or control hydrofoil mounted beneath the underside of the craft and free to assume an approximately streamline path both vertically and in pitch angle. The control hydrofoil is directly con- Patented Dec. 11, 1956 nected to the main hydrofoil so that the pitch angle of the main hydrofoil correspondingly ,and equally reflects changes in the pitch angle of the control hydrofoil induced by changes in the direction of flow of water past the control hydrofoil (short period system). In addition,

Figure 3 is an enlarged view of a control system ofan- 7 other craft identical to that shown in Figure l but also utilizing a system for controlling lateral stability coordinated with the long period stability control system.

Figures 4, 5, 6, 7, 8 and 9 describe a third craft identical to that in Figure 3, but also utilizing a system forvarying the lift coefiicient of the main hydrofoil.

Figure 4 is a plan view of a portion of the control system, while Figures 5 andv 6 are sectional elevations of the apparatus shown in Figure'4 taken along lines 5-5 and 6-6, respectively.

Figure 7 is a horizontal section of another portion of the third'craft, while Figure 8 is a vertical section of the apparatus shown in Figure 7 taken along line 8--8 in Figure 7. Figure 9 is a front view shown partially in section of the apparatus shown in Figures 7 and 8 taken at line 9-9 in Figure 8.

Referring to Figures 1 and 2 of the drawings, the reference numeral 1 represents a hydrofoil water craft embodying a simple illustration of my invention. Hydrofoil craft 1 comprises a hull 2 of conventional shape having mounted thereon, by means of hollow supporting strutsv 3 and horizontal beam 4, a main hydrofoil 5. Struts 3' and hydrofoil 5 are of streamline cross-section so as to reduce frictional drag through the water as much as possible. Hydrofoil 5 is pivoted to struts 3 at points 6.

. The craft is provided with a rudder assembly 7 comprising a tiller 8, strut rudder 9 and stabilizer hydrofoil 10. Preferably, stabilizer hydrofoil 10 is of adjustable pitch angle, by means of sheave 11 and line 12 which is,

streamline cross-section passes downwardly through an aperture 14 in craft 1 and terminates at its lower end below the underside of the craft 1. Control hydrofoil 15 is mounted in front of strut 13 by lever arm 16 which is fixed at end 17 to control hydrofoil 15 and pivoted to strut 13 at point 18 intermediate the length of arm 16.

Strut 13 is supported by a second lever arm 19 lying in the same vertical plane as, and parallel to, lever arm 16. Lever arm 19 is pivotally mounted to craft 1 at point 20 and is pivotally connected to the upper portion of strut 13 at point 21 intermediate the length of arm 19. A third lever arm 22, lying in the same vertical plane as, and parallel to, lever

arms

16 and 19, is pivotally connected at its end 23 with strut 13. The pivot point 23 lies on the imaginary line determined by

points

21 and 18. Lever arm 22 is pivotally connected at its other end with craft 1 at point 24A which is determined by the point of intersection of arm 22 With an imaginary line passing through point 20 parallel to the imaginary line determined by

points

21 and 18. The

free ends

24 and 25 of lever arms 19 and.16, respectively, are linked by connecting rod 26 which is parallel to the imaginary line determined by

points

21 and 18. Lever arm 19 is connected at point 20 by direct axle connection with sheave 27. The length of lever arm 16 from pivot point 25 to the forward tip of control hydrofoil 15 must be substantially less than the distance on lever arm 19 between

pivot points

20 and 24.

The pitch of hydrofoil is controlled by cable 28 which is wound over sheave 29 mounted to beam 4 and is fastened to hydrofoil 5 at point 30 on the leading surface point 31 on the trailing surface. Preferably, the sheave and line arrangement is duplicated at each end of hydrofoil 5. Cables 28 pass down through the centers of hollow struts 3. Sheaves 29 are mounted on a common axle '32 which traverses beam 4 of craft 1. Sheave 33 is mounted on axle 32 in line with sheave 27 and has a diameter twice that of sheave 27. Forward of sheave 33 and in line with it is positioned sheave 34 which is suitably mounted to the deck of craft 1 and which is rotatable by crank 35.

Cable 36 attached to pulley block 37 and pulley block 38 passes around sheave 27. A continuous cable 39 is passed from the. underside of sheave 33 to the underside of pulley sheave 40 mounted in pulley block 37, from the upper side of pulley sheave 40 to the underside of sheave 34, from the upper side of sheave 34 to the underside of pulley sheave 41 mounted in pulley block 38 and from the upper side of pulley sheave 41 to the upper side of sheave 33.

Figure 2 illustrates more clearly the mechanism by which the control hydrofoil operates to vary the pitch angle of main hydrofoil 5.

If, for example, there is a downward velocity of the boat or an upward velocity of the water due to some disturbance such as the crest of a Wave passing control hydrofoil 15, then there is an increase in lift on control hydrofoil 15 because the effective angle of attack of the control hydrofoil is increased. The added lift will cause control hydrofoil strut 13 to rise with respect to the boat thereby causing

lever arms

22 and 19 to rotate about their forward pivots 24A and 20, respectively. By means of connecting rod 26, lever arm 16 is made to rotate in a similar manner and to decrease the angle of attack until hydrofoil 15 assumes a new equilibrium position with respect to the water flowing past it. Such equilibrium position is, of course, approximately a streamline position with just sufficient angle of attack to exert enough lift to support the free weight of strut 13 and its associated lever arm mechanism. The dotted line position in Figure 2 illustrates such a new equilibrium point caused by a downward velocity of the boat or an upward velocity of the water. It will be observed that inherently the movement imparted to control hydrofoil 15 by its supporting structure, as hydrofoil 15 moves from one equilibrium position to another in following a streamline path, is about a pivot axis which extends horizontally and which is located forward of control hydrofoil 15 transversely passing through the intersection A of an imaginary line through pivots and 24a with an imaginary line passing through

pivots

18 and 25.

The movement of lever arm 19 in response to such changes in the equilibrium position of hydrofoil 15 causes sheave 27 to rotate, which rotation is translated into a change of position of pulley blocks 37 and 38 by means of cable 36. In ordinary operation crank 35 is secured in one position so that sheave 34 remains stationary. Hence, the movement of pulley blocks 37 and 38 causes a corresponding rotation in sheave 33 due to the movement of cable 39 induced by such change in position of pulley blocks 37 and 38. Since sheave 33 has twice the diameter of sheave 27, it is displaced through an angular change equal to the angular displacement of sheave 27. Sheave 33 causes sheaves 29' to rotate equally since they are connected by common axle 32' and thus the motion of hydrofoil 15 is communicated directly and equally to hydrofoil 5, thus causing its lift to, decrease,

thereby tending to offset the effect of the downward velocity of the craft or upward velocity of the water which induced the change in position of hydrofoil 15 and to maintain hydrofoil 5 at a constant angle of attack with the streamline.

However, the short period system which I have just described is not complete. I have found it is also necessary to provide a mechanism for independently adjusting to new boat velocities or to allow for vertical accelerations. In addition, the boat might slowly sink or rise due to inability of a small change in lift on the control hydrofoil 15 to move the control system because of the friction in the system. When it is desired to change the vertical position of the craft with respect to the water, it is necessary to rotate main hydrofoil 5 while maintaining control hydrofoil 15 in the same position. This is accomplished by providing an independent mechanism for adjusting the pitch angle of main hydrofoil 5 without affecting the pitch angle of control hydrofoil 15. That is, a means is provided to adjust the phase relation between the pitch angles of control hydrofoil 15 and main hydrofoil 5.

In the craft illustrated in Figures l and 2 such an independent control mechanism is crank 35 and sheave 34 which are coordinated with the operation between

sheaves

27 and 33 by

pulleys

37 and 38. Thus, changing the position of crank 35 causes sheave 34 to rotate. Such rotation is translated to sheave 33 and thereby to main hydrofoil 5. The position of control hydrofoil 15, of course, is entirely independent of such operation and is not elfected by it.

The long period system, that is, the independent control of the phase relation between the pitch angles of the control and main hydrofoils, is more usefully controlled by automatic rather than by human response. While the pilot is able to control the craft shown in Figure l, the adjustment of crank 35 is difficult at best. Moreover, the pilot will not always react fast enough and will have difliculty in judging the degree of correction needed.

It is best, therefore, in the interests of safety to effect the change in pitch angle relation by utilizing a conventional depth senser which measures the depth at the hydrofoil or some other convenient point based on the conversion of hydrodynamic energy into electrical energy. For example, a Pitot static tube with static pressure holes advantageously is arranged with a resistance type strain gauge (or a slide wire and piston) so that the resistance of the strain gauge is a function of the static pressure at the holes. An electrical control circuit is governed by the strain gauge and is adjusted so that operation may be set for any desired actual depth at the point of measurement. The electrical control circuit is used to energize a motor which is geared to drive sheave 34 in accordance with deviations from the desired depth.

It should be noted that the short period system not only remains unaffected by changes in the phasing of the pitch angles of main hydrofoil 5 and control hydrofoil 15, except insofar as such changes may momentarily require a readjustment of control hydrofoil 15 to a new equilibrium position, but also hydrofoil 15 is only negligibly affected by the pitching moment of hydrofoil 5 since pivot points 6 are located approximately at the ends of the theoretical line across the span of hydrofoil 5 about which all force components are exerted, thus the reaction load is carried principally by pivot points 6, and since a considerable mechanical advantage exists between hydrofoil 15 and hydrofoil 5.

The utilization of such a long period system facilitates control of lateral stability as Well as longitudinal stability. That is, the main hydrofoil may be divided by a central strut into two sections each independently controlled for desired depth by a Pitot tube located at the lower end of the adjacent outside strut. Each main hydrofoil continues to be controlled in the same degree by the control hydrofoil.

Figure 3 is a close-up view of the central portion of a hydrofoil craft similar to that shown in Figure 1 but which also utilizes a system of lateral stability control. In the figure, the parts not shown are identical with those in Figure 1. Where I have used the same numbers, it is to be understood that the same part is intended. Also in the designation of the parts I have utilized the suffix a to designate all the parts which are specific to the port side of the craft and the suflix b to designate all the parts specific to the starboard side of the craft where such parts are symmetrically disposed on both port and starboard.

It will be noted that the craft illustrated in Figure 3 utilizes an identical control system as the craft shown in Figure 1. However, from pulley blocks 37' and .38 to

hydrofoils

5a and 5b the system is divided into two corresponding halves, each half corresponding in operation to the operation between pulley blocks 37 and 38 and hydrofoil 5 of craft 1 in Figure 1. Craft 1' is provided with a central strut 3 which divides main hydrofoil 5 into two

sections

5a and 5b. The use of the central strut permits control of. each main hydrofoil 5a and 512 by passing cables 28a and 281; through the central strut rather than requiring the need of an axle 32 and additional sheaves 29 as in Figure 1.

Pulley blocks 37' and 38 each carry a pair of pulley sheaves, 40a and 40b, and 41a and 41b, respectively. Sheave 34 of Figure 1 is replaced by two independently mounted

sheaves

34a and 34b which are driven by electric motors 42a and 4212 through screw drive transmissions 43a and 43b, respectively. Motors 42a and 42b are controlled by the hydrostatic pressure at Pitot static tubes 44a and 44!), respectively, mounted in struts 3. Sheave 33 of the craft in Figure 1 is replaced by a pair of independently mounted double grooved sheaves 45a and 45b.

Continuous cables

39a and 3% are substituted for single cable 39 of the craft in Figure 1. Thus cable 39a traverses sheave 45a, pulley sheave 40a, sheave 34a and pulley sheave 41a in the same manner that cable 39 traverses sheave 33, pulley sheave 40, sheave 34 and pulley sheave 41, respectively, in Figure 1. Cable 39b is correspondingly mounted about sheave 45b, pulley sheave 40b, sheave 34b and pulley sheave 4111, respectively.

Cables

28a and 28b attached to

hydrofoils

5a and 5b, respectively, are passed through the second groove of sheaves 45a and 4512, respectively, and are housed within hollow center strut 3.

As the craft is passing through the water, disregarding for the moment the operation of the two long period control systems, any change in position in control hydrofoil 15 is transmitted to pulley blocks 37 and 38' as in the operation of the craft in Figure 1. So long as the two long period systems are inoperative,

sheaves

34a and 34b remain stationary and therefore hydrofoils 5a and 5b are caused to change their pitch angle in exactly the same amount as control hydrofoil 15 is changed by whatever disturbance moves it.

However, as soon as either side of the craft changes in depth from the desired and selected depth of operation, the change in static pressure of the Pitot static tube energizes operation of its corresponding lateral control system. For example, assume that the port side of craft 1 sinks due to a change in the loading of the craft, the increase in hydrostatic pressure measured at Pitot tube 44a causes motor 42a to turn sheave 34a so as to increase the pitch of hydrofoil 5a in the same manner that rotation of sheave 34 changes the pitch in the craft in Figure l, and thus returns craft 1 to an even keel, motor being de-energized when the desired depth is again attaiued. This same action, of course, is eifective on both port and starboard and operates to maintain the craft on an even keel as well to control the desired depth of operation as in Figure 1. During turning operations the pilot can change the desired depth for each side todifferent values and thus obtain the necessary bank for turning.

The same type of long'period control system may be coordinated. to vary the mean camber of the hydrofoil. Figures 4, 5, 6, 7, 8 and 9 illustrate a modification of the device shown in Figure 3 for effecting such a change in mean camber of the main hydrofoils. Where I have used the same numbers, the same parts are intended as in Figures 3 and 1, and their operation will be identical with that of the operation in Figure 3. Also, the use of the subscripts a and b has been retained with the same meaning as in Figure 3.

Referring first to Figures 7, 8 and 9 to illustrate the change in hydrofoil structure, it will be noted that Figure 8 is a cross-section taken through hydrofoil 5'a looking toward center strut 3'. Hydrofoil 5a is divided spanwise into two principal sections. Main span 46a is a wedge shaped piece extending through three-quarters of the cord line of hydrofoil 5a. The first quarter of hydrofoil 5a is a sharp pointed circular arc nose flap 47a. Leading edge (nose flap) 47a is movably fixed to main span 46a by spring steel strip 49a and stretched rubber strip 48a.

Referring now to Figures 4, 5 and 6 which illustrate the adjustment in the pulley system to accommodate a control system of the flap angle, it will be seen that the system of Figure 3 has been duplicated. However, an additional pair of symmetrically disposed systems have been added, so that each pulley block 37" and 33 now carries 4 pulley sheaves instead of 2 as in Figure 3. To motor driven

sheaves

34a and 34b have been added additional sheaves 51a and 51b, respectively, of three times the diameter of sheaves 34a and 3411. Double grooved sheaves a and 45b have been combined with additional elements to produce compound sheaves a and 50!), respectively Sheave 50a, working from inside out, comprises double grooved sheave 45a which is axially mounted to rotate freely, groove edged plate 57a which is pivotally connected on pin 58a with sheave 45a, link 59a which is pivotally connected with plate 57a by pin 60a, and outside sheave a which is pivotally connected to link 5911 by pivot pin 61a. Outside sheave 56a is single grooved, is axially mounted to rotate freely, and is of the same diameter as sheave 45a. The distance of pivot pin 58a from the center of sheav 45a is equal to the distance between pivot pins a and 61a on link 59a. The distance of pivot pin 61a from the center of sheave 5'6a is equal to the distance between

pivot pins

58a and 60a on plate 57a. Sheave 50b is, of course, the symmetrical counterpart of sheave 50a.

In the cable and pulley connection arrangement cable 54a is continuous and passes from the bottom of sheave 56a to the bottom of pulley sheave 52a, from the, top of pulley sheave 52ato the top of sheave 51a, from the bottom of sheave 51a to the bottom of pulley sheave 53a and from the top of pulley sheave 53a to the top of sheave 56a.

Figure 4 is an elevation view of the arrangement of all four cables 39:! and 39b, and 54a and 54b. Figure 5 is a cross-section taken along line 55 in Figure 4 and shows exclusively the arrangement of cable 54a which is a duplicate of the arrangement of cable 54b. In Figure 5 sheave 56a is partially cut away to show the internal arrangement of compound sheave 50a.

Figure 6 is a section through Figure 4 along line 6-6 and shows exclusively the arrangement of cable 3%. In Figure 6 double sheave 45b is partially cut away to show the internal arrangement of parts in compound sheave 50b which in all respects is a mirror image of sheave 50a.

Control cables

28a and 28b which control main hydrofoil spans 46a and 461') are wound over the second grooves of sheaves 45a and 45b, respectively, and pass down through central strut 3'.

Control cables

62a and 7 62b which adjust the flap angles of flaps 47a and 47b, respectively, pass over grooved plates 57a and 57b, respectively, and also are fed downwardly through central strut 3.

Referring now to Figures 7, 8 and 9, it will be noted that main span 46a is bolted to a plate 55a and pivoted on pin 63 to strut 3. Span. 46b is similarly pivoted.

Cables

28a and 28b are fastened to the ends of

plates

55a and 55b, respectively, and thus translate the motion of control hydrofoil 15 to the

main span hydrofoils

46a and 46b as before (Figure 3 Flap

angle control cables

62a and 62b are connected to the ends of

plates

64a and 64b, respectively, which are bolted at their forward ends to nose flaps 47a and 47b and are pivoted on

pins

65a and 65b to plates 55a and 551;, respectively, the point of pivot being adjusted in the illustrated case at the quarter cord distance and along the upper surface of the foil.

Referring back to Figures 4, and 6, for the moment, each of grooved plates 57:: and 57b is formed having opposite arcuate edges about pivot pins 58a and 58]), respectively, as centers. Each of pivot pins 58:: and 58b is located in its respective plate 57a or 57b so that one such arcuate edge is constructed with three times the radius of the opposite arcuate edge. Thus the por tion of each of cables 62a and 6212 leading to the forward edge of each of

plates

64a and 64b, respectively, will be moved through onethird the distance through which the other end of the cable moves, as each of plates 57a and 57b is rotated about pivot pin 58a and 5811, respectively. It will be apparent that each of plates 57a and 57!) has the same angular geometry as each of

plates

64a and 65b, and thus angular motion about

pivot

58a or 58b is duplicated about

pivot

65a and 65b, respectively, while angular motion about the central axes of

sheaves

50a and 56b is duplicated about pin 63.

In operation, when the long period control system is stationary, it will be seen that any motion in hydrofoil 15 is directly translated equally to both

main spans

46a and 46b of

hydrofoils

5a and 5b. By the same motion each of

sheaves

56a and 56b will be caused to move through the same angle of rotation as double sheaves 45a and 45b and hence plates 57a and 57b will also exhibit the same degree of turn about the axial lines of

sheaves

56a and 45a, and 56b and 45b, respectively. Since plates 57a and 57b rotate through the same angle as sheaves 45a and 45b and

sheaves

56a and 56b, re spectively, and since cables 62a and 62]) are substantially parallel to

cables

28a and 28b, the flap deflection angle of

hydrofoils

5a and 5b remains substantially constant.

However, when the long period system of either side is caused to operate, due to the geometry of the system, the flap angle is given three times the effect and in an opposite direction as the main hydrofoil span. Assume, for example, that it is desired to increase the lift of hydrofoil 5a, this is done by increasing its angle of attack by energizing motor 42a which causes its associated

sheaves

51a and 34a to rotate at a slow rate of speed. Assuming that control hydrofoil 15 remains in a stationary position, this rotation will cause cable 54:: to rotate three times as much as cable 390 since sheave 51a has three times the diameter of sheave 34a. Moreover, the movement of the

cables

39a and 54a will be in opposite directions. Since the geometry of plate 57a is such that it is pivoted with respect to sheave 45a at the same relative point as nose flap plate 64a is with respect to main span plate 55a, the opposite and threefold angular rate of movement induced in plate 64:: will cause nose flap 47a to be deflected downwardly with a flap deflection three times as great as the increase in pitch of span 460.

It will be obvious to those skilled in the art that certain changes other than those I have suggested may be made in the described water craft. For example, hydrofoil 15 may be positioned aft of strut 13. Its operation will produce identical results. However, it should be remembered that the water disturbance created by strut 13 will, in a degree, reduce the sensitivity of hydrofoil 15. For that matter, hydrofoil 15 can be placed with its associated support mechanism aft of the main hydrofoil. The same objections however can be made against the desirability of such practice. One convenient alternative arrangement is to place strut 13 and connecting rod 26 inside central strut 3' with a slit .in the leading edge of strut 3' to allow lever arm 16 to move up and down hold ing hydrofoil 15 out ahead.

The pulley assemblies above decks may readily be replaced by equivalent mechanical linkages, for example, by cranks and a connecting rod having an adjustable connection such as a slidable pivot point. Or lever arm 19 might turn an axle which drives the rotor of a selfsynchronous motor having its stator connected in parallel to the stator of another self-synchronous motor, both having their rotors connected to a common A. C. supply, which second motor would be used to drive axle 32. Or an angularly responsive electrical mechanism, such as a self-synchronous transmitter, might be positioned at pivot point 25 utilizing a seWo mechanism to produce equal changes in hydrofoil 5, or

hydrofoils

5a and 5b, as the case may be. In such cases, phase adjustment could be made either electrically by known methods or by a mechanical system involving a transmission and clutch. Along the same idea the pulley and cable arrangements of the craft shown in Figure 3 and of the craft shown in Figures 49 may be substituted by obvious mechanical and electrical equivalents.

It will be noted that I have omitted any description of a propulsion system. I contemplate the use of any of the marine propulsion systems utilized in hydrofoil type craft. In particular, air propulsion is extremely well adapted to hydrofoil craft as it provides minimum disturbance of the water passing the hydrofoils.

I claim:

1. In a water craft having a main hydrofoil pivotally supported below the level of the underside of the craft which hydrofoil is inclinable to provide an upward force component by dynamic action with the water when the craft has forward velocity with respect to the water, the improvement which comprises a control hydrofoil; an approximately vertically positioned strut passing downwardly through the craft, free to move in approximately vertical directions with respect to the craft, and terminat ing at its lower end beneath the underside of the craft; a first lever arm lying in approximately the fore and aft direction of said craft, fixed at one end to said control hydrofoil, and pivotally connected at a point intermediate its length with the lower end of said vertical strut; a second lever arm lying in the same vertical plane as, and parallel to, said first lever arm, pivotally connected at one end with said craft, and pivotally connected at a point intermediate its length with the upper portion of said vertictal strut; a third lever arm lying in the same vertical plane as, and parallel to, said first and second lever arms, pivotally connected at one end with said vertical strut along the imaginary line determined by the pivotal connections of said first and second lever arms with said strut, and pivotally connected at its other end with said craft at the point determined by its intersection of the imaginary line passing through the pivotal connection of said second lever arm with said craft parallel to the imaginary line determined by the pivotal connections of said first and second lever arms with said strut; a connecting rod parallel to the imaginary line determined by the pivotal connections of said first and second lever arms with said strut, and pivotally connected at its ends with the free ends of said first and second lever arms; linkage connecting said control hydrofoil and said main hydrofoil, whereby changes induced in the angular position of said control hydrofoil are reflected by corresponding changes in the angular position of said main hydr0- foil; and means independent of the angular position of said control hydrofoil for varying the phase relation of the angular positions of said control and main hydrofoils. I 2. In a water craft having a mainvhydrofoilpivotally supported below the level of the underside of the craft 10 strut, and pivotally connected at itsother endwithsaid craft at the point determined by its'intersection of theimag inary linepassingithrough'the pivotal connection of said second lever arm with saidcraftparallel to the imaginary line determined by the pivotal connections of said first and second lever arms with said strut; a connecting rod paral which hydrofoil is inclinable to provide an up ward force component by dynamic action with the water when the craft has forward velocity with respect to the Water and which main hydrofoilis divided into an independent port hydrofoil and an independent starboard hydrofoil; the improvement which comprises a control hydrofoil; an approximately vertically positioned strut passing downwardly through the craft, free to move in approximately vertical directions with respect to the craft,'and'terminat ing at its lower end beneath the underside of the craft; a first lever arm lying in approximately the fore and aft direction of said craft, fixed at one endto said control hydrofoil, and pivotally connected at a point intermediate its length with the lowerend ofsaid'fvertical strut; a second lever arm lying in the same vertical plane as, and parallel to, said first lever arm, pivotally connected at one end with said craft, and pivotally connected at a point intermediate its length Withthe .upper portion of said vertical strut; a third lever arm lying in the same vertical plane as, and parallel to, said first and second lever arms, pivotally connected at one end with said vertical strut along the imaginary line determined by the pivotal connections of said first and second lever arms with said strut, and pivot-ally connected at its other end with said craft at the point determined by its intersection of the imaginary line passing through the pivotal connection of said second lever arm with said craft parallel to the imaginary line determined by the pivotal connections of said first and second lever arms with said strut; a connecting rod parallel to the imaginary line determined by the pivotal connections of said first and second lever arms with said strut, and pivotally connected at its ends with the free ends of said first and second lever arms; linkage connecting said control hydrofoil and each of said main hydrofoils, whereby changes induced in the angular position of said control hydrofoil are reflected by corresponding changes in the angular positions of each of said main hydrofoils; and a pair of means independent of the angular position of said control hydrofoil, one for varying the phase relation of the angular positions of said control and said port main hydrofoils, and the other for varying the phase relation of the angular positions of said control and said starboard main hydrofoils.

3. In a water craft having a main hydrofoil pivotally supported below the level of the underside of the craft which hydrofoil is inclinable to provide an upward force component by dynamic action with the Water when the craft has forward velocity with respect to the water and which main hydrofoil is divided into an independent port hydrofoil and an independent starboard hydrofoil; the improvement which comprises a control hydrofoil; an approximately vertically positioned strut passing downwardly through the craft, free to move in approximately vertical directions with respect to the craft, and terminating at its lower end beneath the underside of the craft; a first lever arm lying in approximately the fore and aft direction of said craft, fixed at one end to said control hydrofoil, and pivotally connected at a point intermediate its length with the lower end of said vertical strut; a second lever arm lying in the same vertical plane as, and parallel to, said first lever arm, pivotally connected at one end with said craft, and pivotally connected at a point intermediate its length with the upper portion of said vertical strut; a third lever arm lying in the same vertical plane as, and parallel to, said first and second lever arms, pivotally connected at one end with said vertical strut along the imaginary line determined by the pivotal connections of said first and second lever arms with said lel to the imaginary line determined byv the pivotal con-v nections 'of said first and second lever arms with said strut, and pivotally connected at its ends with the free ends of said first and second lever arms; linkage connecting said control hydrofoil and each of said main hydrofoils, whereby changes induced inthe angular position of said control hydrofoil are reflectedby corresponding changes in the angular positions of each of said main hydrofoils; a first pair of means independent of the angular position of said, control hydrofoil, one for varying the phase relation of the angular positions of said control and said port main hydrofoils, and the other for varying the phase relation of theangular positions of said con-. trol and saidstarboard main hydrofoils; and a second pair of means independent of the angular position of said control hydrofoil, coordinated with said first pair, one

for varying the mean camberof said port main hydrofoil, and the other for varying the mean camber of said,

starboard main hydrofoil.

4. In a water craft having a main hydrofoil pivotally supported below the level of the underside of the craft which hydrofoil is inclinable to provide an upward force component by dynamic action with the water when the craft has forward velocity with respect to the water; the improvement which comprises a control hydrofoil; means supporting said control hydrofoil below the level of the underside of the craft, said control foil being movable about a horizontally extending pivot axis forward of said control foil whereby said control hydrofoil assumes an approximately streamline path through the water beneath the surface thereof when said craft has forward velocity with respect to the water; linkage connecting said control hydrofoil and said main hydrofoil, whereby changes induced in the angular position of said control hydrofoil are reflected by corresponding changes in the angular position of said main hydrofoil; and means independent of the angular position of said control hydrofoil for varying the phase relation of the angular positions of said con-trol and main hydrofoils.

5. In a water craft having a main hydrofoil pivotally supported below the level of the underside of the craft which hydrofoil is inclinable to provide an upward force component by dynamic action with the water when the craft has forward velocity with respect to the water and which main hydrofoil is divided into an independent port hydrofoil and an independent starboard hydrofoil; the improvement which comprises a control hydrofoil; means supporting said control hydrofoil below the level of the underside of the craft, said control foil being movable about a horizontally extending pivot axis forward of said control foil whereby said control hydrofoil assumes an approximately streamline path through the water beneath the surface thereof when said craft has forward velocity with respect to the water; linkages connecting said control hydrofoil and each of said main hydrofoils, whereby changes induced in the angular position of said control hydrofoil are reflected by corresponding changes in the angular positions of each of said main hydrofoils; and a pair of means independent of the angular position of said control hydrofoil, one for varying the phase relation of the angular positions of said control and said port main hydrofoils, and the other for vary-ing the phase relation of the angular position of said control and said starboard main hydrofoils.

6. In a water craft having a main hydrofoil pivotally supported below the level of the underside of the craft which hydrofoil is inclinable to provide an upward force component by dynamic action with the water when the craft has forward velocity with respect to the water and which main hydrofoil is divided into an independent port hydrofoil and an independent starboard hydrofoil; the improvement which comprises a control hydrofoil; means supporting said control hydrofoil below the level of the underside of the ,craft, said control foil being movable about a horizontally extending pivot axis forward of said control 'foil whereby said control hydrofoil assumes an approximately streamline path through the water beneath the surface thereof when said craft has forward velocity with respect to the water; link-ages connecting said control hydrofoil and each of said main hydrofoils, whereby changes induced in the angular position of said control hydrofoil are reflected by corresponding changes in the angular positions of each of said main hydrofoils; and a pair of means independent of the angular .position of said control hydrofoil, one for varying the phase relation of the angular positions of said control and said port main hydrofoils, and the other for varying the .phase relation of the angular position of said control and said starboard m-ainhydrofoils; and a second pair of means independent of said control hydrofoil coordinated with said first pair, one for varying the mean camber of said port main hydrofoil and the other for varying the mean camber of said starboard main hydrofoil.

7. f lm afwater craft having a main hydrofoil pivotally supported below thelevel of the underside of the craft; the improvement which comprises a control hydrofoil; means supporting said control hydrofoil below the level of the underside of the craft, said control foil being movable about a horizontally extending pivot axis forward of said control foil whereby said control hydrofoil assurnes an approximately streamline .path through the water beneath the surface thereof when said craft has tor-ward velocity with respect to the water; and linkage connecting said control hydrofoil and said main hydrofo'i'l, whereby changes induced in the angular position of said control hydrofoil are reflected by corresponding changes in the angular position of said main hydrofoil.

References Cited in the file of this patent UNITED STATES PATENTS 1,186,816 Meacham June 13, 1916 2,387,907 Hook Oct. 30, 1945 2,584,347 Hazard v Feb. 5, 1952 2,603,179 Gardiner July 15, 1952 FOREIGN PATENTS 516,651 Great Britain J an. 8, 1940