US3369514A - Vehicle for operation over fluid surfaces - Google Patents

Description

Feb. 20, 1968 C. S. COCKERELL v VEHICLE FOR OPERATION OVER FLUID SURFACES 4 Sheets-Sheet 1 Filed Feb. 10, 1966 ll ini .llll illuA I! INVENTOE C S C OC KERELL BY W,Z %wz wad/Z227- ATTOFAEYS Feb. 20, 1968 c. s. COCKERELL 3,369,514

VEHICLE FOR OPERATION OVER FLUID SURFACES 7 Filed Feb. 10, 1966 4 Sheets-Sheet 2 IN VENTOP C. S. COCKERELL ATTORNEYS Feb. 20, 1968 c. s. C-OCKERELL 3,369,514

VEHICLE FOR OPERATION OVER FLUID SURFACES Filed Feb. 10, 1966 4 Sheets-Sheet s y o L k 5 0 2 I w, a L

0\ n* Lu 0 FLO Cfzinnm,f/zm 9 A TTOMYS Feb. 20, 1968 c. s. COCKERELL VEHICLE FOR OPERATION OVER FLUID SURFACES 4 Sheet s-Shet 4 Filed Feb 1.0, 1966 IN VEN TOR C. S. COCKERELL BY- 7 I Z (Ba/2mm ATTORNEYS 3,359,514 Patented Feb. 20, 1968 3,369,514 VEHICLE FOR OPERATION OVER FLUID SURFACES Christopher Sydney Cockerell, Bassett, Southampton, England, assignor to Hovercraft Development Limited, London, England, a British company Filed Feb. 10, 1966, Ser. No. 526,624 Claims priority, application Great Britain, Feb. 12, 1965, 6,299/ 65 13 Claims. (Cl. 114--67) ABSTRACT ()F THE DISCLOSURE A vehicle propellable over a fluid surface by two rotatable vanes of helicoidal form which, in operation, are normally immersed in the fluid to levels up to their axes of rotation. The vanes rotate in opposite directions and are so disposed that their components of thrust are directed towards each other. Deflector plates are disposed between adjacent ends of the vanes so as to convert axial thrust generated by the vanes into propulsive thrust. The angle between the rotational axis of each vane and the fore-and-aft axis of the vehicle may be varied in dependence on the relative speeds of the vehicle and the fluid, and the depth of immersion of the vanes may be regulated by vertical movement of the vanes relative to the vehicle body in response to changes in the local level of the fluid relative to said body.

The present invention relates to a vehicle for operation over a fluid surface; by the term fluid is meant more particularly a liquid such as Water, but it is to be understood that the term is intended to cover any material having a degree of flowability, such as mud, sand and light shingle. Hereinafter, reference will be made to water from time to time, and it is to be understood that the remarks made in respect of water will be applicable to other fluids as mentioned above.

One of the disadvantages of the screw porpeller is that the blades move in a plane which is substantially transverse to the desired direction of motion of the vehicle which they propel. This transverse movement of the blades in the fluid generates drag forces which are substantially symmetrically distributed about the screw propeller as a whole and have no utilisable resultant force.

It is an object of the present invention to provide a vehicle having a propulsion system which can utilise at least some of the drag forces between the propulsion system and the fluid.

According to the present invention, there is provided a vehicle for operation over a fluid surface and which is propella-ble thereover by at least one propulsion system comprising two vanes of helicoidal form, each vane being mounted for rotation about an axis extending substantially transverse to the fore-and-aft axis of the vehicle, the vanes being so disposed in relation to the body that, in operation, they are normally immersed to a level not exceeding the level of their axes of rotation, whereby, in operation the immersed parts of the vanes thrust against the fluid, the hands of the vanes and the senses of their rotation-s being chosen such that the thrusts of the vanes in directions transverse of the fore-and-aft axis will normally be oppositely directed.

The vehicle may be provided with fluid guide means having guide surfaces which project downwardly from the vehicle body and which are shaped for directing fluid moving transversely under the thrust of the rotating vanes in a direction rearwardly and substantially parallel to the fore-and-aft axis of the vehicle. The thrusted fluid will thus move rearwardly of the vehicle and provide a forward reaction for propelling the vehicle.

Because the vanes are mounted for'rotation about an axis which extends transversely to the fore-and-aft axis of the vehicle, drag forces acting on immersed parts of the vane-s, moving in a direction opposite to the direction of movement of the vehicle, will tend to prevent relative movement of the vanes and the fluid and the vanes will therefore grip the fluid: this grip contributes to the forward thrust on the vehicle. This is in contrast to the action of drag forces on a conventional screw-propeller, which only act in transverse direction and therefore tend to slow down the propeller without providing any useful propulsive thrust.

The fluid guide means may be disposed between the vanes, and the vanes are then normally arranged to be rotated in such senses that they thrust fluid generally towards each other.

Preferably, the pitch of the helicoidal (or helical) vanes increases in the direction in which the fluid is to be thrust: this ensures that as the fluid is thrust axially along each of the vanes, it is subjected to the ever increasing angle of attack of the vanes and is continuously accelerated as its progresses along the vanes.

The rotational axes of the vanes preferably converge towards the rear of the vehicle so that fluid is thrusted with a rearward component of motion.

The angle between the rotational axis of each vane and the fore-and-aft axis of the vehicle may be varied to suit the relative speed of the Vehicle and the fluid.

There may be at least one reaction blade attached to the body and arranged for impeding the passage of any fluid which is upwardly and forwardly projected by the helicoidal vanes, whereby to minimise thrust losses from forwardly projected fluid.

In order that the depth of immersion of the vanes may be regulated, each vane may be mounted for vertical movement relative to the vehicle body. The vertical movements of each vane relative to the vehicle body may be regulated by means which respond to changes in the local level of the fluid relative to the vehicle body. Signals from the level responsive means are preferably delayed, by suitable delaying means, in accordance with the forward speed of the vehicle relative to surface feature-s of the fluid (such as waves), whereby each of the vanes is vertically moved only when the vehicle has moved relative to the surface feature a distance substantially equal to the distance between the level responsive means and the vane.

Each vane may be formed from resilient material to minimise damage in the event of it striking an unyielding object, and additionally or alternatively, the vanes may each be formed from a number of vane elements which can be individually removed from the vane.

In a particular form the vehicle may be a gas cushion vehicle having means for forming and maintaining a cushion of pressurized gas beneath its body to support the body out of contact with the surface.

Some examples of vehicles in accordance with the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a gas cushion vehicle,

FIGURE 2 is a sectional plan view of part of the vehicle of FIGURE 1, taken on line IIII,

FIGURE 3 is a perspective view of the propulsion system of the vehicle of FIGURE 1, looking in the direction of arrow III of FIGURE 2,

FIGURE 4 is a perspective view of the rear of another gas cushion vehicle in accordance with the invention,

FIGURE 5 is a transverse sectional view of FIGURE 4, taken in the plane of line VV,

FIGURE 6 is a schematic diagram of a control system for the propulsion system of FIGURE 5,

FIGURE 7 illustrates the manner of assembly of a vane for use in the propulsion system of the vehicles of FIGURES 1 to 6,

FIGURE 8 is a sectional plan view corresponding to the view shown in FIGURE 2, but showing a modified form of propulsion system, and

FIGURE 9 is an underneath plan view of'a gas cushion vehicle in accordance with the invention, but having two of the propulsion systems shown in FIGURE 8.

In the drawings, an item which appears in more than one figure will be given the same reference numeral ineach figure.

Referring to FIGURES l and 2, there is shown a gas cushion vehicle 10 for operation over a fluid surface 11, in this case a water surface. The gas cushion vehicle 10 comprises a body 12 beneath which a cushion 13 of pressurised air is formed to support the body 12 out of contact with the water surface 11. The air which is to form the air-cushion 13 is initially induced through an intake 14 by a compressor 15 driven by a motor 16 and pressurised by the compressor 15 before being fed beneath the body 12 through a number of ducts 17. The air forming the air-cushion 13 is confined beneath the body 12 byv a flexible wall or skirt 18 at the front and sides of the cushion13 and by an inflated wall 19 at the rear of the cushion 13. The flexible wall 18 is of the type disclosed in co-pending application Ser. No. 566,948, filed July 21, 1966, and generally comprises a succession of chute-like pieces of flexible material which downwardly extend from the bottom periphery of the body 12 and abut each other under the inflating action of the aircushion 13 and thereby form a boundary for the cushion 13. The inflated wall 19 is of the type disclosed in copending application Ser. No. 316,852, filed Oct. 17, 1963, now Patent No. 3,291,237, and generally comprises a piece of flexible material which depends from two parallel lines of attachment to the bottom of the body 12 which extend between the opposite rear ends of the flexible wall 18, the space between the bottom of the body between. said parallel lines of attachment and the depending material being supplied with pressurised air so that the material is inflated to form a rear boundary to the cushion 13.

The vehicle 10 is propellable over the surface 11 by means of a propulsion system, generally indicated by reference 20, disposed beneath the rear of the body 12 and aft of the'inflated wall 19.

From FIGURE 2, it will be seen that the propulsion system 20" comprises two vanes 21 of helicoidal form. mounted for rotation about respective axes 22 or 23 which extend transversely to the fore-and-aft axis 24 of the vehicle 10. In normal operation, the vanes 21 are so disposed in relation to the body 12 that they are normally immersed no further than their axes of rotation 22 or 23; the means for regulating the degree of immersion of the vanes 21 will be described below.

The axes of rotation 22, 23 converge towards the rear. of the vehicle 10 and intersect on the fore-and-aft axis 24: thus, when the vanes 21 are rotated in the appropriate sense, they each thrust water towards the fore-and-aft axis 24 with a component opposite to the corresponding component of thrust of the other vane 21 and with a rearward component parallel to the fore-and-aft axis 24. The vanes 21 are made as similar as possible, except that their helices are of opposite hands when assembled in the propulsion system 20, so that when they are rotating at the same speed, they generate substantially equal thrust. The pitch of the helix of each vane 21 increases along the vane 21 in the direction of the fore-and-aft axis 24 so that water, which is thrust along the vane 21 is subjected to an ever-increasing angle of attack of the vane 21 so that the water is constantly accelerated by the vane 21. The vanes 21 are each supported at their axially outermost ends in bearings (not visible in the drawings) which also support the power output shaft (also no vis ible) of a hydraulic motor 25, and at'their axially innermost ends in bearings 26 attached to guide plates 27. The hydraulic motors may be of any of the well-known types. The guide plates 27 are disposed on each side of a centre plate 28 extending along the fore-and-aft axis 24. Each guide plate 27 has a surface 29 facing its respective vane 21 which is shaped for smoothly directing water which is thrust towards it by the vane 21 in a rearward direction, so that as much as possible of the trans verse momentum of thrusted water will be changed intorearward momentum: the forward propulsion force generated by. the vanes 21 will be equal to the change in rearward momentum of the thrusted water. The guide plates 27 rearwardly taper towards the bearing plate 28, and the latter has a rudder 30 vertically pivoted to its rear end so that the vehicle 10 can be steered.

The forward thrust of thevanes 21 is communicated to the vehicle body 12 by inner thrust bars 31 attached to the guide plates 27 and outer thrust bars 32 attached to the carcasses of the hydraulic motors 25, and the thrust bars 31, 32 are secured to a thrust bearing frame (not shown) in the body 12. The position of vanes 21 in relation to the body 12 is determined by inner vertical stays 33 connected between the body 12 and the guide plates 27 and outer vertical stays 34 connected between the body 12 and the carcasses of the hydraulic motor 25.

It is to be appreciated that it is desirable to ensure that the vanes 21 are immersed no further than the level of their rotational axes 22, 23 since ,parts of the vanes 21 above the axes 22, 23 will generate thrusts in opposite directions to those generated by parts of the vanes 21 below the axes 22, 23. In the extreme case where the vanes 21 are completely submerged, the useful net thrusts of the vanes would be very small, if not substantially zero. In

most cases it is likely that the greatest propulsive efficiency (over water) is obtained when the lowest 10-20% of the vanes 21 are immersed.,Although, in practice, it would be preferable to immerse the vanes 21 up to the level of the lowest 40%. Accordingly, where the vehicle 10 is to travel over a surface 11 which will be reliably smooth (for example, a sheltered stretch of water) the vertical stays 33, 34 are fixed relative to the axes of rotation 22, 23 of the vanes 21.

The hydraulic motors 25 are supplied with hydraulic fluid through a feeding duct 35 and a return duct 36 with hydraulic fluid from separate hydraulic pumps 39,

and the lattermay be driven by separate motors 40, or by a single motor which is differentially connected to the pumps 39: by this means, the hydraulic motors 25 may be driven independently of each other, so that, for example, one vane 21 may be stopped whilst the other is rotating, to provide improved manoeuverability of the vehicle 10 at low speeds when the rudder 30 is less effective. It is also contemplated that by the provision of a suitable gearbox (not shown) between the motor 40 and the hydraulic pumps 39, the vanes 21 may be rotated to provide rearward thrust for driving the vehicle 10 backwards or for increasing the manoeuverability thereof and furthermore that the vanes21 may be so rotated that they both thrust fluid in the same transverse direction.

During the rotation of the vanes 21, some water will be upwardly and forwardly projected by the vanes 21. The momentum of this projected water, more particularly the forwardly projected water, is usefully harnessed by a reaction blade 41, shown in FIGURE 3, which surrounds the forward and upper regions of each vane 21, and is attached to the carcass of the corresponding hydraulic motor 25. and the guide plate 27. The reaction blades 41 impede the forward passage of the water and thereby communicate the momentum thereof to the body 12. There may be more than one reaction blade 41 for each vane 21 and they may take shapes other than the depicted in FIGURE 3.

If the vehicle It is to operate over surfaces 11 which will not be reliably smooth, it is desirable to be able to vertically adjust the position of the axes of rotation 22, 23 of the vanes 21 relative to the body 12 so that if, for instance, the distance between the water surface 11 and the body 12 should decrease as the vehicle passes over the crest of a wave, the vanes 21 can be raised to prevent immersion above the level of the axis of rotation 22 or 23. FIGURE 4 shows diagrammatically the propulsion system 2% of FIGURES 1 to 3 modified so that the vanes 21 can be raised or lowered relative to the body 12.

It is desirable that the two vanes 21 should be vertically movable independently of each other to take account of the differing surface conditions which might obtain on each side of the vehicle since the separate means for vertically moving each of the vanes 21 are similar, only the means for vertically moving one of the vanes 21 will be described, it being understood that the remarks made apply to both of said means.

It will be seen that the inner and outer thrust bars 31, 32 are horizontally pivoted at 42 to a thrust-bearing frame 4-3, and the inner and outer vertical stays 33, 34 for vane 21 are connected above the vane 21 by a cross beam 44. The cross-beam 44 is pivotally supported by two links 45 which are pivotally connected to respective piston rods 46 of two hydraulic jacks 47. The hydraulic jacks are hydraulically connected in parallel by a duct 48 supplying hydraulic fluid to the lower chamber of each jack 47 and a duct 49 supplying hydraulic fluid to the upper chambers. If hydraulic fluid is supplied to the jacks 47 via duct 48, and allowed to escape from the jacks 48 via duct 49, the cross beam 44 will be raised, and with it, the vertical stays 33, 34 and the vane 21 supported thereby, and all the moving parts will pivots about pivot 42. If hydraulic fluid is supplied to the jacks 47 via ducts 49, and allowed to escape from the jacks 47 via ducts 48, the vane 21 will be lowered. In a modification (not shown) the hydraulic jacks 47 may be pivotally connected to the body 12 so that the pivotal connections between the piston rods 46, the links 45 and the cross-beam 44 may be dispensed with.

FIGURE 5 is an elevational view of a vertical section through the two adjacent inner vertical stays 33 of FIG- URE 4 showing how the inner vertical stay 33, and hence all the parts attached thereto are maintained in correct relative alignment.

The adjacent vertical stays 33 are provided with vertical grooves 50 on their adjacent facing surfaces, and a number of bearing rollers 51 are disposed between the stays 33 with their horizontally opposite peripheries received in the grooves 50. The bearing rollers 51 are rotatably mounted in a bearing plate 52 which is retained in position only by the frictional engagement of the bearing rollers 51 with the stays 33 in the grooves 50. The frictional engagement of the rollers 51 and stays 33 is maintained by means of strong tension springs 53 provided on each side of the bearing plate 52, and which urge the stays 33 towards each other. The tension springs 53 act on the stays 33 through ball jointed connectors 54 received in sockets 55 formed in the stays 33. The sockets 55 are formed partly by the main body of each of the stays 33 and partly by a plate attached on the main body of each stay 33, the plate also presenting the groove 50 towards the opposite stay 33. The lower end of the bearing plate 52 is attached to the centre plate 28.

In case the stays 33 should become widely separated, suitable hinged stops (not shown) are provided which extend between the stays 33 through a long vertical slot in the bearing plate 52 to prevent the latter falling out between the stays 33. 7,

FIGURE 6 illustrates schematically a quick response control system generally indicated by reference 56 which will control the position of one of the vanes 21 relative to the body 12 as the level of the water surface 11 varies relative to the body 12 so as to substantially maintain an optimal degree of immersion of the vane 21. A similar system 56 is used to control the position of the other of the vanes 21.

The control system 56 comprises a sonic radar apparatus 57 which directs pulses of sonic waves downwardly from the front of the vehicle 10 onto the surface 11 over which the vehicles 10 is to pass. The surface 11 reflects back the pulses of sonic waves, and the radar apparatus 57 measures the time lag between the transmission of each pulse and the receipt of its reflection. An electric signal is generated in line 58 corresponding to the said time lag, and thus corresponding with the distance of the surface 11 below the radar apparatus 57 at the time of measurement. Since the vertical movements of the vanes 21 at the rear of the vehicle 10 must take place after a time delay which decreases with increasing forward speed of the vehicle 10, it is necessary to time modulate the signal in line 58. The time modulation is performed in a delaying apparatus 59in accordance with a vehicle water relative speed signal in line 60 set by a pitot head 61 in the water. The modulated distance signal from delaying apparatus 59 in line 62 represents the desired vertical position of the vanes 21 which should be achieved by the time the vehicle 10 has so advanced that the vanes 21 are in the position at which the corresponding sonic pulses were received by the radar apparatus 57. In order to establish whether the vertical position of the vanes 21 must be changed from their present vertical position, the signal in line 62 is compared in a comparator 63 with a position signal generated by a position indicator 64 connected to the piston of one of the jacks 47. The output signal in line 65 from comparator 63 is an error signal representing the necessary vertical movement of the vanes 21. The error signal is fed to an amplifier 66, and the amplified error signal is converted to a mechanical error movement by for example, a solenoid 67. The solenoid 67 is mechanically coupled to two normally open valves 68 and 69 in a hydraulic circuit, and the mechanical coupling between the solenoid 67 and the valves 68, 69 is such that a positive error signal will move only one of the valves, say valve 68 from its maximum open position, and a negative error signal will move only the other valve, in this case, valve 69, from its maximum open position.

The hydraulic circuit comprises two oppositely acting hydraulic pumps 70, 71 which are preferably driven by a common motor. The hydraulic pumps 70, 71 are in operation'at all times when the vehicle 10 is operating, and they pump hydraulic fluid through a common duct 72 and then around separate ducts, including the valves 68, 69 in hydraulic subcircuits 73, 74 respectively. The resistance to flow in the subcircuits 73, 74 is made as small as possible by providing large diameter short-length ducting. The intake side of pump 70 and the output side of pump 71 are connected to respective sides of the pistons in the jacks 47 through restricted diameter ducts 75, 76 respectively.

Assuming that the signal passed to solenoid 67 is a positive error signal, valve 68 will close (fully or partially) while valve 69 will be unatfected; Thus the flow in subcircuit 73 will be reduced or shut off and the fluid output of pump 70 will be directed through the high resistance duct 75 to the lower side of the pistons in the jacks 47. The pistons will be raised and the vane 21 will be correspondingly elevated. Some of the fluid on the upper sides of the pistons will pass back to the pump 70 via high resistance duct 76. As the vane 21 is elevated, the position signal generated by position indicator 64 will change and as the desired vertical position of the vanes 21 is approached, the error signal produced in line 65 by comparator 63 will approach zero.

Should the error signal reaching solenoid 67 be a negative" error signal, valve 69 only will close fully, or partially, and pump 71 will pump fluid through duct 76 to the upper side of the pistons of the jacks 47 and will receive fluid from the lower sides thereof. Thus the pistons will be lowered and the vane 21 will also be lowered. The changing position signal from position indicator 64 will operate in comparator 66 on the signal in line.65 to reduce the error signal as the vane 21 is lowered.

Although the control system 56 described above is electro-hydraulie, equivalent mechanical or pneumatic systerns will be apparent to those skilled in the art.

Referring now to FIGURE 7 each vane .21 is formed from a number of vane elements 78 including a hollow stub shaft 79 having an internal keyways 80'. The vane elements 78 are assembled in the vane 21 by threading them onto a keyed power shaft 81 which is supported at one end in the bearings of the hydraulic motor 25 (see FIGURE 2) and at the other end in the bearings 26. The vane elements 78 are axially secured on the power shaft 81 by the housing (not shown) of the said bearings,

vane ele'ment(s) 78 in question will resiliently deflect.

until the unyielding object is passed.

As the vehicle increases its speed relative to the water surface 11, the efliciency of the vanes 21 falls oif for a given angle of their axes of rotation 22, 23 relative to the fore-and-aft axis 24, and it becomes desirable to vary this angle so that the angle between the rotational axes 22, 23 is reduced as the speed increases so that the efliciency can be maintained.

In FIGURE. 8, the previously described previously de-. scribed propulsion system of FIGURE-4 has been modified by forming the thrust frame 43 in two parts 83, 84 which are connected at their inner ends by a verticalpivot 85. The outer ends of the frame parts 83, 84 are connected to a fixed frame 86 of the vehicle body 12, by vertical pivots 87, 88 and a hydraulic jack 89 is provided between the pivot 85 and the fixed frame 86 for moving the vertical pivot 85 relative to the fixed frame 86. The thrust bars 32 are linked to the frame parts 83,84 by universal joints 90, 91 of known type, and to the carcasses of the hydraulic motors by vertical pivots 92, 93. The bearings 26 of the vanes 21 are also vertically pivoted at 94 to the guide plates 27, and the inner vertical stays 33 are rotatably mounted on the tops of the guide plates 27. The lifting jacks 47 are fixed in the vehicle body 12 and their pivoted links 45 allow relative horizontal movement between the body 12 and the lifting beam 44. Thus if the jack 89 is extended, the adjacent ends of the inner thrust bars 31 are pushed rearwardly with respect to the fixed frame 86. The bearings 26 also move rearwardly and the angle between the axes 22, 23 of the vanes 21 and the fore-and-aft axis 24 of the vehicle 10 is decreased.

This decrease in angle would be appropriate to an increase in speed of the vehicle 10. The jack 89 is contracted to increase the angle as the speed of the vehicle 10 decreases.

The movements of the jack 89 may be automatically governed by speed signals generated by the pitot head 61 (FIGURE 6). Thus, in one arrangement (not shown) the initial static and total pressure head signals from the pitot head 61 are communicated to opposite sides of a diaphragm which controls the setting of a variable electrical URE 8. One of the propulsion systems 20 is disposed beneath the rear of the vehicle 10 as in the embodiments of FIGURES 1 to 8, whilst the other propulsion system 20 is disposed within the space for the air cushion 13. One

(or both) of the propulsion systems v2t) may be mounted on a rotable turret, as indicated at 96, so that the propulsive thrust can be applied to the vehicle 16 in any desired direction, thus improving the manoeuverability of the vehicle.

The propulsion systems described may be incorporated in vehicles other than gas cushion vehicles without departing from the scope of the present invention.

1 claim:

1. A vehicle for operation over a fluid surface and which is propellable thereover by at least one propulsion system comprising two vanes of helicoidal form, said vehicle having a fore-and-aft axis and a body,-means mounting each vane for rotation about an axis which extends substantially transversely of the fore-and-aft axis of the vehicle, means connecting said mounting means to said body, said mounting means serving, in operation, to maintain the vanes immersed in the fluid to a level no deeper than the level of the axes of rotation of said vanes, driving means operatively connected to said vanes for rotating said vanes about their axes of rotation, whereby, in operation, the immersed parts of each vane thrust against the fluid, the hands of the vanes and the senses of their rotations being so selected that the thrusts of the vanes in directions transverse of said fore-an-aft axis are normally oppositely directed, and fluid guide means projecting downwardly from the vehicle between the helicoidal vanes, said fluid guide means having guide surfaces towards which fluid will be thrust by the vanes in operation and comprising means for rotatably mounting adjacent ends of said vanes, said guide surfaces being so shaped as to direct said thrusted fluid substantially in a desired direction relative to the vehicle body, and the driving means, in operation, normally rotating the vanes so that, they thrust fluid generally towards each other.

2. A vehicle according to claim 1 including at least one reaction means for each vane which is attached to the body above the respective vane, each reaction blade having a portion adapted for arresting fluid which is forwardly and upwardly flung, in operation, by the rotating vanes, whereby to reduce thrust losses from forwardly projected fluid.

3. A vehicle according to claim 1 in which said mounting means for said vanes are pivotally connected to said connecting meansso as to be pivotally movable relative to the connecting means in a substantially horizontal plane, there being extensible means attached at one end to the vehicle body and at the other end to said connecting means adjacent said pivotal connections, whereby a change in length of said extensible means will cause. a change in an angle defined by the rotational axis of each vane and said fore-and-aft axis of the vehicle.

4. A vehicle for operation over a fluid surface and having a fore-and-aft axis and a body and which is propellable thereover 'by at least one propulsion system comprising two vanes of helicoidal form having respective axes of rotation which extend substantially transversely of the fore-and-aft axis of the vehicle and which converge towards the rear of the vehicle, each of said vanes being rotatably mounted at one axial end in a fluid guide member downwardly projecting from the vehicle body between the two vanes and at the other axial end in bearings, the pitch of each of the helicoidal vanes increasing from said one axial end towards said other axial end, the vanes being so mounted in relation to the body that, during operation, they will be immersed in the fluid to a level no further than the level of their axes of rotation, and driving means operatively connected for rotating said vanes in such senses that, in normal operation, they will each thrust fluid towards the fluid guide member in a direction having a component which is parallel to the fore-and-aft axis of the vehicle, the fluid guide member having guide surfaces facing each of said vanes and which are shaped for directing thrusted fluid from said vanes in a desired direction.

5. A vehicle according to claim 4 in which there is provided at least one reaction blade for each vane, the reaction blades being attached to the body above the respective vanes and each having a portion shaped to arrest fluid which has been forwardly flung, in operation, 'by the rotating vane, whereby to reduce thrust losses from forwardly projected fluid.

6. A vehicle according to claim 5 in which the fluid guide member and the said bearings are pivotally attached to the body for pivoting ovement about a horizontal axis whereby the vanes are capable of vertical movement, there being means operative on the vanes which regulate the vertical movement of the vanes in response to changes in the level of fluid relative to the vehicle body.

7. A vehicle according to claim 6 in which the fluid level responsive means comprises a radar device attached to the vehicle body above the fluid surface and which is disposed relative to the body for transmitting radar signals towards said surface, and for receiving reflections of said radar signals from said surface.

8. A vehicle according to claim 7 in which a rudder portion is pivoted to the rear end of the guide member for horizontal pivotal movement for steering the vehicle over the fluid surface.

9. A vehicle according to claim 7 in which said mounting means for said vanes are pivotally connected to said connecting means for pivotal movement in substantially horizontal directions, there being extensible means having opposite ends which are respectively connected to the body and said connecting means adjacent said pivotal connections of said vanes, said extensible means being operable to extend substantially horizontally whereby to change an angle defined between the rotational axis of each vane and said fore-and-aft axis of the vehicle,

10. A vehicle according to claim 8 having means for forming at least one cushion of pressurised gas beneath the body for supporting the body above the surface, and means for laterally bounding said cushion of pressurised g 11. A gas cushion vehicle for operation over a fluid surface and having a body, means for forming at least one cushion of pressurised gas beneath the body and means for laterally bounding said cushion of pressurised gas,

said vehicle being propellable over said fluid surface by at least one propulsion system comprising two vanes of helicoidal form having respective axes of rotation which extend substantially transversely of the fore-and-aft axis of the vehicle and which rearwardly converge, said vanes each being rotatably supported at one axial end in a fluid guide member which downwardly proje 'cts from the vehicle body between the two vanes, and in bearings at the other axial end, the pitch of each vane increasing along its rotational axis in a direction away from said bearings to said fluid guide member, the fluid guide member and the said bearings being horizontally pivoted to the body whereby the vanes can move vertically, means responsive to the local level of the fluid surface relative to the body to regulate vertical movement of said vanes to maintain each vane immersed in the fluid no further than the level of its rotational axis, driving means for rotating each vane so that it will normally thrust fluid towards fluid guide surfaces on said fluid guide member, said fluid guide surfaces being shaped to direct thrusted fluid substantially in a desired direction, there being at least one reaction member for each vane attached to the body and extending adjacent the respective vane, said reaction member being disposed so as to arrest any fluid which is forwardly and upwardly flung, in operation, by the vane whereby to reduce thrust losses from forwardly projected fluid.

12. A vehicle according to claim 11 including speed responsive means operative to generate signals indicative of the speed of the vehicle relative to the fluid, delaying means connected to receive said speed-indicative signals and to receive level-indicative signals from said level responsive means, said delaying means serving to transmit said level-indicative signals to means for vertically moving each of said vanes after a delay which varies in indirect proportion with the relative speed of the vehicle.

13. A vehicle according to claim 11 in which each vane is pivotally mounted at each axial end relative to the vehicle body for substantially vertical pivotal movement, there being extensible means connected in a substantially horizontal plane at one end to the body and at the other end to the guide member of each vane, whereby a change in the length of said extensible means causes a change in the angles defined between said fore-and-aft axis of the vehicle and respective axes of rotation of the vanes.

References Cited UNITED STATES PATENTS 772,384 10/1904 Smith 1'154l 2,702,516 2/1955 Tinker -l6 3,130,702 4/1964 Fischer 114---66.5 3,250,239 5/1966 Garate 11519 3,276,415 10/1966 Laing 11516 3,288,236 11/1966 Padial 11467 ANDREW H. FARRELL, Primary Examiner.

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