US3545397A - Air-cushion vehicles and like craft - Google Patents

Description

United States Patent [72] Inv Thomas Andrews 50 Field ofSearch 1 14/67. 1; Cheltenham, England 180/116, 117, 119 [21] Appl. No. 808,014 [22] Filed March 17, 1969 [56] References Cited Continuation of Ser. No. 633,897, Apr. NI D STATES PATENTS 26,1967Jbandmd- 3,066,753 12/1962 Hurley et a1. 1 l4/67.l [45] Patented Dec. 8, 1970 [73] Assignee Dowty Technical Developments Limited Emmlfle"-Andrew Farrell Chelenhhm, Enghmd Armrney- Christensen. Sanborn & Matthews a British Company [32] Priority Mayr7, 1966 [33] Great Britain ABSTRACT: An air-cushion vehicle is provided with jet 3l No. 20327/66 ropulsion apparatus for propelling it across water. The apl P paratus may be retracted into the vehicle when its operation is 1 no longer required, to enable the vehicle to operate over sur- AIR'CUSHION VEHICLES AND LIKE CRAFT faces other than water. An engine which drives the apparatus 9 Claims lonrawing Figs also drives the lift fan of the vehicle and means are provided [52] U.S. Cl 114/67 for directional adjustment of the apparatus when operative to [5 l Int. Cl B63b 1/34 afford steering, braking and reversing the vehicle.

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AIR-CUSHION VEHICLES AND KE CRAFT This application is a continuation of Pat. application Ser. No. 633,897 filed Apr. 2o, l967,and now abandoned.

BACKGROUND OFTl-IE INVENTION 1. Field of the Invention i This invention relates to air-cushion vehicles and like craft.

2. Description of the Prior Art t In the complete specification of United Kingdom Pat. No. 968,381, there is disclosed in FIG. 8 a vehicle capable of travelling across water, having means whereby the pressure of the air in the space beneaththe vehicle body is raised, so that the body is supported above the water surface by a cushion of pressurized air, open propellers being provided fonpropulsion of the vehicle.

SUMMARY OF THE INVENTION apparatus of the reaction jet type and also apparatus of the.

ducted-propeller type.

Where such jet propulsion apparatus is of the hydraulic kind, it includes a pump capable of drawingin water through an intake opening and of discharging the wateras a propulsive j The jet propulsion apparatus or part thereof. may be retractable from the, position at a level below the air cushion to a stowed position within the vehicle, either withinthe air cushion, or above the air cushion, thereby to enable the vehicle then to operate over surfaces other than water.

When the jet propulsion apparatus is 'in its extended position itmay be angularly adjusted about a vertical or substantially vertical axis for directional control of the .vehicle. When the apparatus is turned through an angle of 180 about this axis, or when the direction of rotation of its rotor is reversed, it

is effective to reverse the direction of movement of the v ehicle, steering in reverse being achieved by. further angular movements of the apparatus about said vertical axis.

The pump of the apparatus may beof single-stage or multistage axial-flow-type, the rotor blading and/or the stator blading thereof being fixed,"or,.alternatively adjustable in pitch. Where the rotor blading is adjustable in pitch it may be displaceable from positive pitch to negative pitch for reverse operation or braking by the apparatus. In this case it wouldnot be necessary to turn the apparatus throughl80 to effect reverse operation or braking.

Where the pump portion of the hydraulic apparatus is fixed 'in the vehicle either within, or alternatively, above the aircushion, the intakeduct thereto and dischargeduct therefrom, may be extended from, or through and from, the air-cushion and into the water ,when' operation of the apparatus is I required. Thus in this case, only part of the apparatus is ex.-

more than one engine may be provided to power the apparatus or the apparatuses. r

The engine or engines may be so arranged as to drive a lift fan or lift fans housed within the vehicle, together with the jet propulsion apparatus or apparatuses. In particular, an engine may be vertically mounted in the vehicle and arranged to drive a lift fan mounted above it and also to drive a vertical shaft mounted below it which is connected to drive the pump of the jet propulsion apparatus. The fan, engine and drive shaft to the pump may all rotate about axes which are coincident. The

engine or engines may be of gas turbine type having power output shafts taken from both ends thereofcln this arrangement the engine, lift fan and jet propulsion apparatus form a power unit mounted and provided compactly within the vehicle.

Clutch means may be provided between each engine and its fan and/or each engine and its jet propulsion apparatus. Alternatively, gearboxes or variable speed transmissions, for example hydrostatic transmissions, may be provided between each engine and its fan and/or between each engine and its associated jet propulsion apparatus.

The precise arrangement of clutch means and/or gear-box and/or transmission depends upon the number of engines and the driving arrangement in each particular case.

Where the vehicle is not required to operate over surfaces other than water, the jet propulsion apparatus maybe the sole propulsion means, but in cases where the vehicle is required to operate over both water and other surfaces the jet propulsion apparatus is additional to other propulsion means. Such other propulsion means necessary, per.se,.for operation over surfaces other thanwater, may be in the form of a lifting skirt arrangement where, when so selected, some of the lift f an discharge is -directed through the lifted skirt for propulsion. Lifting skirts may be provided at positions around the sidewall of the vehicle for propulsion selectively in the forward, rearward or transverse directions.

Altematively, propulsion under such conditions may be achieved by the provision of an engine-driven airsc rew or airscrews. i i r I The jet propulsion apparatus or apparatuses may only be operative when the vehicle is crossingwater to supplement the propulsive effect of said other propulsion means. The jet propulsion apparatus maybe of contrarotating axialflow-type, the drive shaft from the respective engine driving the rotorsof the apparatusthrough bevel gearing arranged in the hub of the unit and between the rotors.

Retraction and extension of the jet propulsion apparatus may be effected by hydraulic jacks, or. the like, forming part of an hydrauliccontrol systemfor the vehicle The jet propulsion apparatus may be mounted upon a telescopic member coaxially arranged with respect to the drive shaft fromthe engine to the apparatus,.saicl jacks controlling the telescoping of this member for retraction and extension of the apparatus.cThe components of the telescopic member may be the means for transmitting steering controlling movements from a driver's control member to the jet. propulsion apparatus, or alternatively, steering means may be effective t endible' and retractable, but thewhole apparatus may be so adjustable about a vertical or substantially vertical axis as to afford directional controlof the vehicle.

Alternatively, where the pump portion of the apparatus is so fixed in the vehicle, the intake duct only may be extendible into the water and the discharge-duct so arranged as either to air. t

The vehicle may include either a single jet propulsion apparatus, or a plurality of apparatuses, the latter so arranged discharge into the water, or alternatively, to discharge into the I about the center line of the vehicle asto afford differential steering and reversing of the vehicle. i

The jet propulsion apparatus, or all of the jet propulsion apparatuses. may be driven by a single engine, or alternatively,

upon an angularly adjustable carrier member for the apparatus which isimmediately adjacent the apparatus, and in this case upon a beam member, which supports the carrier member, itself being raised and lowered by the jacks.

In the case where the pump of the jet propulsion apparatus ispermanently mounted within the structure of the vehicle above the air cushion, intake ducting to the pump and dischargeducting therefrom may be pivotally arranged with respect to the pump casing so that the ducting can be swung downwardly from a stowed position into an operative position ,below the air cushion. Suitable hydraulic jacks may be provided to afford such swinging movements of the ducting.

Where the jet propulsion apparatus does not use the water overwhich the vehicle is travelling as the motive fluid for its operation, the motive fluid may instead be gas derived from a gas turbine engine or engines which drive the lift fan or lift fans. The gas may alternatively be compressed air tapped from the engine compressor or discharged from an auxiliary compressor driven by that engine, or again may be exhaust gas discharging from the turbine section of the engine, the compressed air or gas discharging directly into the water over which the vehicle is travelling when suitable ducting is lowered through the air cushion into the water.

BRIEF DESCRIPTION OF THE DRAWINGS Of the 10 accompanying drawings:

FIG. 1 is a partly cutaway side elevation of an air-cushion vehicle in accordance with the first embodiment of the invention;

FIG. 2 is a view of the undersideof the air-cushion vehicle shown in FIG. 1;

FIG. 3 is a partly cutaway side elevation of an air-cushion vehicle in accordance with the second embodiment;

FIG. 4 is a view of the underside of the air-cushion vehicle shown in FIG. 3;

FIG. 5 is a transverse cross-sectional view of an air-cushion vehicle in accordance with the third embodiment of the invention;

- FIG. 6 is a view of the underside of the air-cushion vehicle shown in FIG. 5, but reduced in scale;

FIG. 7 is a transverse cross section of an air-cushion vehicle in accordance with the fourth embodiment of the invention;

FIG. 8 is an enlarged cross-sectional view of a part of the air-cushion vehicle shown in FIG. 7;

FIG. 9 is a partly cutaway side elevation of an air-cushion vehicle in accordance with the fifth embodiment of the invention; and

FIG. 10 is a transverse cross-sectional view of an air-cushion vehicle in accordance with the sixth embodiment of the invention.

' vehicle 10in accordance with the first embodiment includes a cabin section 11, a buoyancy section 12 and a skirt 13 around the side periphery of the vehicle attached to the lower portion of the buoyancy section. The zone 14 enclosed by the skirt forms an air cushion when the vehicle is operative. In conventional manner a centrifugal lift fan 15, which is mounted for rotation within the vehicle about a vertical axis 16, has an intake duct 17 opening thereto, fan discharge being directed through a suitably shaped plenum 18 into the zone 14 forming the air cushion.

The fan 15, and the air cushion produced in the zone 14, enables sufficient lift for the vehicle that the vehicle can operate over land or water surfaces with a small clearance between the lower edges of the skirt and these surfaces, propulsion in the ahead, astern or sideways directions being afforded by suitable respective lifting skirt portions arranged around the skirt. As shown, one lifting skirt portion 19 is provided at the front of the vehicle, a second lifting skirt portion 20 is provided on the starboard side of the vehicle, a third lifting skirt portion 21 is provided at the rear of the vehicle and a fourth lifting skirt portion 22 is provided on the port side of the vehicle.

All the lifting skirt portions are operable by hydraulic jacks, those jacks for operating the portions 19 and 21 being shown at 23 and 24in FIG. 1.

As the respective skirt portion is lifted, some of the air discharging from the centrifugal fan into the plenum 18 is allowed by that portion to pass to the exterior of the vehicle, and the vehicle is propelled across the surface in the appropriatedirection.

The fan 15 is driven by a gas turbine engine 25 vertically mounted in the vehicle. This engine has two output shafts, the first, 26, being directed upwardly and driving the fan 15 through a clutch 27, while the other, 28, is directed downwardly, both shafts having their axes coincident with the axis 16 of rotation of the fan. 1

The lower shaft 28 passes through a telescopic strut 29 the lower component 30 of which carries a beam 31. The beam is movable upwardly and downwardly with respect to the structure of the vehicle by a pair of telescopic hydraulic jacks 32 and 33, the cylinders of which are pivotally connected to the vehicle structure at 34 and 35 respectively, and the piston rods of which are pivotally connected to the beam at 36 and 37 respectively.

Mounted beneath the beam 31 upon a flanged portion 38 of the lower component 30 of the telescopic strut 29 in the manner such that it is angularly adjustable with respect to the beam in a horizontal plane, is a circular carrier member 39. This member is provided with a ring of teeth 40 around its periphery, the teeth being engaged by a worm 41 driven by an hydraulic motor 42 supported by the beam. The circular member 39 carries beneath it, rigidly secured thereto, an hydraulic jet propulsion unit 43 which includes a casing 44 in the form of a duct of circular cross section in which a pair of fixed pitch axial flow bladed rotors 45 and 46 are coaxially mounted for contrarotation. The lower drive shaft 28 which is also telescopic and which incorporates a clutch 47, drives the two rotors in contrarotational manner through suitable bevel gearing 48 provided in the hub section of the unit and between the two rotors.

The casing of the unit has an intake section 49 ahead of the first rotor and a discharge section 50 astern of the second rotor.

When the two jacks 32 and 33 are contracted as shown in FIG. 1 of the drawings, the beam 31 and thus the jet unit 43 are held in a stowed position in the vehicle, the lower clutch 47 then being disengaged, but when the jacks are simultaneously extended, the telescopic strut 29 is also extended and the beam 31 and jet unit 43 are lowered to a level below the air cushion 14 such that when the vehicle is operating over water the jet unit is fully immersed in the water. The lowered position of the jet unit is shown in dotted detail in FIG. 1 at 43'.

Hence, when the lower clutch 47 is engaged the jet unit is operative and the jet of water'discharging therefrom supplements the propulsive effect achieved by lifting of the respective skirt portion. Directional control by the jet of water is achieved by the operation of the hydraulic motor 42 which angularly adjusts the circular carrier member 39 and thus turns the jet unit.

If the vehicle is travelling forwardly over the water and a rapid stop is required, the rearward skirt portion 21 is dropped and the forward one 19 is lifted, but at the same time the jet unit is rapidly turned through to afford direction of the jet forwardly thereby effecting braking under water. This same controlling function affords reverse movement of the vehicle, steering in reverse being achieved by appropriate angular adjustment of the jet unit in the horizontal plane.

When the vehicle approaches a beach and is required to travel over land, the jet unit 43 is retracted by contraction of the jacks 32 and 33, and propulsion over land occurs under the propelling effect achieved solely by lifting of the appropriate portion of the skirt.

The hydraulic jacks 32, 33, the hydraulic motor 42 and means (not shown) for operating the clutches 27 and 47 are all included as components of the hydraulic system of the vehicle, suitable control valves (not shown) being provided for selective control of these components.

Suitable control valves (also not shown) are also provided for controlling the jacks which operate the lifting skirt portions, suitable means being provided for correlation in the operation of these valves with the hydraulic motor 42.

The' above installation enables a single large power unit to be used without over complicated drives and gearing, giving a very compact and stowable unit.

Referring now to FIGS. 3 and 4 of the drawings, the second embodiment comprises an air-cushion vehicle 60, which like the construction of the first embodiment includes a vertically mounted gas turbine engine 61 having two output shafts 62 and 63, the upper shaft 62 incorporating a clutch 64 and driving a fan whose discharge is directed through a suitably shaped plenum 66 into the air-cushion zone 67.

Lifting skirt portions are provided in a manner similar to th construction of the first embodiment, but only two of these 68 and 69 are shown inFIG. 3, together with their operating jacks 70 and 71. e The lower shaft 63 from the engine incorporates a clutch 72 and is arranged to drive an hydraulic jet propulsion unit 73 which includes apair of axial flowbladed rotors 74 and75 coaxially mounted for contrarotation.

However, unlike the construction of the first embodiment, instead of extending and retracting the jet propulsion unit 73 as a whole, the pump portion 76 thereof is rigidly secured to thevehicle structure at a level above the level of the lower edge periphery of the skirt portions. Since the pump portion 76 is fixed in the vertical sense, the drive shaft 63 thereto is of nontelescopic type. However, an intake duct 77 of cranked form is secured to the inlet side of the pump casing and a discharge duct 78, also of cranked form, is secured to the outlet side of the pump casing. When the jet unit 73 is inoperative, these ducts are stowed in a vertical position above the plane of the pump as indicated in dotted detail at 77 and 78'.

in FIG. 3, having been moved there by the contraction of operating jacks 79 and 80. Thecylinders of the jacks 79 and 80 are pivotally connected at 81 and 82 respectively to a rotatable carrier member 83 suitably mounted within the structure of the vehicle asto be rotatable about the axis 84 of rotation of the fanand engine. Such rotation is afforded by an hydraulic motor 85 whose drive shaft carries a worm 86 which meshes with a pinion 87 fast with the carrier member 83.

When the jet unit 73 is required to be operative, the jacks i 79 and 80 are extended simultaneously thereby to cause the ducts 77 and 78 to pivot downwardly about axes coincident with the rotational axis of the pump 76. Such downward movement is through the air-cushion zone 67, and beyond it,

so that when the cranked ducts are fully extended with their inlet and outlet respectively in their lowermost positions as shown in full lines in FIG. 3 of the drawings, the inlet and outlet are completely immersed in the water over which the vehi cle is travelling. Subsequentoperation of the lower clutch 72 i to its engaged position bringsthe jet unit into operation and water is discharged as a jet to assist in the propulsion of the vehicle. p c c In order to effect steering of the vehicle when the jet unit is operative, the hydraulic motor85 is operated to turn the carribraking of the vehicle and also reverse movement of the vehicle, further adjustment of the carrier member when in reverse providing steerability in reverse.

Such steering, braking and reversing under the control of the jet unit can be effected in conjunction with the operation of the lifting skirtportions and, as with the construction of the first embodiment, the hydraulic system of the vehicle includes control valve means for correlation in the operation of the jacks operating the lifting skirt portions, the hydraulic motor 85 and the clutch 72. l l y When it is required to beach the vehicle, and thereafter operate it over land, the lower clutch 72 is disengaged and the intake and discharge ducts 77 and 78 are retracted by contraction of the jacks 79 and 80. Thereafter, operation of the vehicle can occur .under the control of the lifting skirt portions only. e

. Referring now to FIGS. 5 and 6 of the drawings, in the third As with the constructions of the two previous embodiments lifting skirt portions are provided around the periphery of the air-cushion wall, a first lifting portion 108 being provided at the forward end of the vehicle, a second lifting skirt portion 109 being provided at the rear of the: vehicle, while third and fourth lifting portions are provided at 110 and 111 on the starboard and port sides of the vehicle.

Hydraulic jacks are provided for operating the lifting skirt portions, those associated with the portions 110 and 111 being shown at 112 and 113in FIG. 5.' a

Clutches 114 and 115 are provided in the drive shaft 116 and 117 to the fans 104 and 108 respectively, while telescopic driveshafts 118 and 119 are respectively taken downwardly in FIG. 5 from the engines 101 and 102 to hydraulic jet propulsion units 120 and 121 respectively.

As with the construction of FIGS. 1 and 2, the jet units 120 and 121 are bodily retractable and extendible, but instead of having their own beam members and their own retraction jacks they are mounted beneath a common beam member 122 itself suspended from telescopic struts 123 and 124. Two transversely spaced jacks 124 and 126 are provided for effect- .ing extension and retraction of the common beam and in this way both jet units are extendible and retractable simultaneously. However, each jet unit has its own hydraulic motor 127 and 128 for rotating a respective circular carrier member 129 and 130 for directional control of each jet unit.

Since the jet units 120 and 121 are provided on either side of the center line of the vehicle, differential steering of the vehicle is afforded. In particular, for rapid turning movements, the full turning of one jet unit with respect to the other can with advantage be employed.

In operation of the air-cushion vehicle, when the vehicle is required to operate over water, the jacks 125 and 126 are extended so that the jet units 120 and 121 are lowered to a level below the air-cushion zone 107 of the vehicle. Then clutches 131 and 132 in the drive 1l8and 119 are engaged so that power is transmitted to the jet units 120 and 121 and propulsion of the vehicle occurs over the water by the now operating and fully immersed jet units. Such operation can be supplemented by the lifting of that lifting skirt portion appropriate to the direction of travel of the vehicle.

When it is required to beach the vehicle and operate over land, the jacks 125 and 126 are contracted and the jet units 120 and 121 are simultaneously lifted to their stowed positions as shown in FIG. 5 within the air-cushion zone 107, whereuembodiment an air-cushion vehicle 100 has two separate engines 101 and 102arranged ,on either side of its center line 103, each engine driving its own fan 104, 105 respectively, the discharge from both fans'being directed intoua common plenum 106 which opens into an air-cushion zone107.

pon the clutches 131 and,132 are disengaged and operation of the vehicle can continue under the control of the lifting skirt portions alone.

Referring now to FIGS. 7 and 8 of the drawings, an aircushion vehicle in accordance with the fourth embodiment includes a single engine 141 whose first output shaft 142 incorporates a clutch 143 and drives a single lift fan 144 whose discharge is directed through a plenum 145 again into an air-cushion zone 146. i

As with the constructions of the previous embodiments, the skirt or wall of the air-cushion zone is provided with lifting portions, two of which are shown at 147 and 148, each operated by their respective hydraulic jacks 149 and 150.

The lower drive shaft 151 from the engine 141 incorporates a clutch 152, and the arrangement difiers from those of the previous embodiments in that instead of the engine driving a single jet propulsion unit, it is instead arranged to drive two jet propulsion units 153 and 154.

As shown in full lines in FIGS. 7 and 8, the jet units 153 and l 154 are mounted on struts 1 55 and 156, themselves pivotally mounted at .157 and 158 upon a carrier member 159 mounted upon the structure of the vehicle and above the air-cushion zone 146. In the positions shown in full lines the jet units are positioned at a level below the .air cushion 146 but are retractable to the positions shown at 153' and 154' by the operation of hydraulic jacks 160 and 161.

As shown in FIG. 8, the piston rods 162 and 163 of the hydraulic jacks 160 and 161 are provided with toothed rack portions 164 and 165 which rn e'sli'with gear teeth 166 and 167 formed at the upper end portions of the struts 155 and 156 respectively. Linear movement of the piston rods 162 and 163 in the jack-contracting direction thus moves the struts 155 and 156 through an angle of 90 to the retracted position shown above the air cushion 146.

When the jet units 153 and 154 are in their extended operable positions, fully immersed in the water beneath the aircushion vehicle, the clutch 152 is engaged, drive to the jet units from the engine 141 beingthrough the single shaft 151 when the clutch 152 is engaged.

The shaft 151 is provided with a bevel gear 168 which is in mesh with bevel gears 169 and 170 contained within the interior of the carrier member 159. The bevel gear 169 is fast with a shaft 171 which drives the jet unit 153, while the bevel gear 170 is fast with a shaft 172 which drives the jet unit 154. The drive to the jet unit ,153-is similar to the drive to the unit 154, the latter further including abevel gear 173 carried at the end of the shaft 172 remote from the bevel gear 170 and engaging a bevel gear 174 with which another bevel gear 175 meshes. The bevel gear 175 is fast with a shaft 176 which passes through the strut 156 and which at its end portion remote from the gear 175 carries a further bevel gear 177 I which drives the contrarotating bladed rotors of the jet unit .As with the constructions of the previous embodiments, means are provided, but not shown, in the present embodiment to afford adjustment of the jet units in a horizontal plane for directional control of the vehicle and also for effecting braking or movement in reverse. Again, as with the previous embodiments it is intended that movement of the vehicle under the operation of the jet propulsion units can be assisted by propulsion under the effect of the lifting skirt portions.

Referring now to FIG. 9 of the drawings, an air-cushion vehicle .190 in accordance with the fifth embodiment of the invention includes a single engine 191 of gas-turbine type having a single drive shaft 192 incorporating a clutch 193. The drive shaft 192 is connected to drive a fan 194 whose discharge is directed through a plenum 195 to an air-cushion zone 196.

Again, the vehicle is provided with lifting skirt p'ortions one of which is shown at 197, but unlike the constructions of the previous embodiments, no second drive shaft is taken to hydraulic :jet propulsion apparatus, but instead the jet pipe 198 of the gas turbine engine is turned through an angle of 90 and connects with a cranked jet propulsion duct 199 itself capable of being rotated about an axis 200 under the control of an hydraulic jack 201.

In the full lines, shown in the drawing the cranked jet propulsion duct 199 is positioned so that its outlet is at a level below the air-cushion zone 196 and with the vehicle over water is totally immersed in the water.

Thus in operation of the gas turbine epgine 191, the fan 194 provides the air for the air-cushion zone 196 while the exhaust gases discharging from the engine jet pipe 198 pass into the duct 199 and are discharged therefrom intothe water as a propulsive jet. Such propulsion of the vehicleby a gaseous jet may be the sole means for effecting movement of the vehicle across the water, or alternatively it may be assisted by the operationv of whichever lifting skirt is appropriate to the required direction of movement.

Although not shown in the drawing, means are provided for adjusting the direction at which the gases are discharged from the cranked jet propulsion duct to afford steerability and/or reverse operation of the vehicle.

When it is required to operate the vehicle over land, the jack 201 is extended and the cranked jet propulsion duct 199 is moved about the axis 200 to the retracted position substantially above the air-cushion zone 196 as shown in dotted lines at 199" in the drawing. in this position the outlet of theduct 199 aligns with another ducti202provided in the vehicle structure which directs the exhaus} gases from the engine 191 into the air-cushion Zone 196.

Operation of the vehicle overland surfaces is thereafter afforded under the controlof the appropriate lifting skirt portion.

Referring now to FIG. 10 of the drawings, an air-cushion vehicle 210 in accordance with the sixth embodiment of the invention, includes a single engine 211 having a first output shaft 212 and clutch 213 through which a lift fan 214 is driven. The discharge from the fan again is directed into a plenum 215 which opens into an air-cushion zone 216. Again, the peripheral skirt 217 of the vehicle is provided with portions as at 218 and 219 which can be lifted for propelling the vehicle in an appropriate direction.

The lower output shaft 220 from the engine incorporates a clutch 221 and drives a bevel gear 222, itself in mesh with bevel gears 223 and 224 themselves respectively fast upon shafts 225 and 226 extending transversely to port and starboard of the vehicle. The shafts 225 and 226 are arranged to drive hydraulic jet propulsion units 227 and 228, themselves respectively carried on outrigger struts 229 and 230 pivotally mounted at 231 and 232 upon the vehicle.

The details of the drive gear to both jet units 227 and 228 are similar but only that for the unit 227 is shown in the drawing. The shaft 225 is provided with a bevel gear 233 at its extremity remote from the bevel gear 223, the gear 233 meshing with a bevel gear 234 which meshes with a bevel gear 235 fast with a shaft 236 which extends through the interior of the strut 229. At its end portion remote from the gear 235, the shaft 236 is provided with a bevel gear 237 which meshes with bevel gearing 238 arranged within the hub of the unit 227 for driving the bladed rotors thereof in contrarotational manner.

Hydraulic jacks 239 and 240 are provided upon the vehicle, the piston rods 241 and 242 thereof having teeth thus to form a rack engageable with pinion teeth 243 and 244 formed at the upper end portions of the struts 229, 230 respectively.

In the extended position shown in full lines in the drawing the jet units 227 and 228 are totally immersed in the water over which the vehicle is travelling, at a level well below the air-cushion zone 216.

However, when it is required to discontinue the operation of the jet units 227 and 228, the clutch22l is disengaged and the jacks 239 and 240 are extended so that the struts 229, 230 and the jet units 227 and 228, carried thereby, are moved upwardly about the pivotal mountings 231 and 232 respectively to their stowed positions shown in dotted detail at 227' and 228'.

Thus the embodiment of FIG. 10 shows that the invention is in no way limited to jet propulsion apparatuses being lowered from a position above the air cushion, through the air cushion to the water beneath it, because by being mounted on the outrigger struts 229 and 230 there is no necessity for the units 227 and 228 to pass through the air-cushion zone during their extension or retraction.

By the invention, when an hydraulic jet unit or hydraulic jet units are operative, a relatively large amount of engine power can be absorbed by the jet units due to their relatively large pumping capacity. For example, one-third of the power is absorbed by the fan and two-thirds by the jet unit. Hence, when the vehicle is travelling over water, relatively high speed water propulsion is achieved.

ln larger air-cushion vehicles, particularly, high propulsion speeds have not been easy to achieve hitherto because very large diameter airscrews or a largenumber of smaller diameter airscrews have been necessary to provide the very high propulsive thrusts required. Large diameter airscrews have given rise to mechanical problems, such as blade bending and vibrations clue to the large thrusts upon them, while the larger number of smaller diameter airscrews have complicated the driving arrangements, involving an excessive amount of gearing and shafting, all of these with attendant noise objections.

However in other embodiments of the invention, instead of using lifting skirts for purposes of propulsion, an airscrew may be used for propulsion over land, or again both lifting skirts and an airscrew or airscrews may be used.

The present invention, whilst accepting propulsion by lifting skirts and/or airscrews for the ,purpose of beaching and travelling over land, nevertheless affords high speed operation over water by applying highly efficient jet propulsion at a level below the air cushion. Since such vehicles are required more often to operate over water expanses, jet propulsion is immediately available whenever it is needed, but is instantly withdrawable when land is approached.

Considering the drag characteristics of the vehicle in relation to the thrust characteristics of the airscrews or of the air discharged through liftingskirts, and in relation also to the thrust characteristics of the jet unit, then due to the fact that the jet unit characteristics improve with increasing forward speed while the air propulsion characteristics decline somewhatwith increasing forward speed, there is a point, when the vehicle is at speed, at which the jet unit thrust commences to becomereally useful and effective in the function of propelling the vehicle across water. Below this point in forward speed, the jet unit can thus be inoperative as it adds little or no useful effect to airscrew or lifting skirt propulsion. How ever, above this vehicle speed point the ram effect gives sufficient pressure tocope with cavitation and the jet unit is very efficiently operative and is sufficiently effective to give such additional propulsive effect under conditions where significantly higher vehicle speeds could not otherwise have been expected from operation of the airscrew or lifting skirt alone. Thus, in most applications of the invention jet propulsion would not be required for operation in the lower speed range of the vehicle,but above for example cruise speed,.or again at cruise speed and above it, the jet propulsion apparatus is necessarily brought into operation to achieve such higher speeds unattainable by air propulsion alone.

By reducing the need for airscrews, or by, their elimination altogether, problems of airscrew blade erosion due to salt water spray are reduced, or removed altogether.

Although in the embodiments above described with reference to the drawings provision is made for bringing the discharging jets into orout of effective operation with respect to the water, in other embodiments where the air-cushion.

vehicles are never required to operate over beaches or land,

, hydraulic jet units or portionsthereof may be extended permanently, or substantially so, into water at a level beneath the level of the air cushion.

In this case also the jet units may be the sole propelling means and the fan of the vehicle used only for lift.

Although in the first three embodiments the blading of the jet units is of fixed. pitch, in alternative embodiments of the invention the blading of the jet units may be of variable pitch with accompanying suitable pitch-controlling mechanisms. In this case the rotor blading may be movable from positive pitch into negative pitch for reverse operation or braking by the unit or units. Thus it would not be necessary to turn the units through 180 to effect reverse operation or braking,

As an alternative to the arrangement in some of the embodiments of turning the jet units about a vertical axis for tion, the motive fluid in that case: being the exhaust gases derived from the gas turbine engine which drives the lift fan.

lclaim:

I. An air-cushion vehicle including, in combination, a vehicle structure, air-cushion zone-defining means formed therewith, an engine, a compressor separate from said engine, drive means coupling the engine to the compressor so that upon operation of the engine the compressor charges said zone with air under pressure, and means, affording the vehicle reversing, in other embodiments the jet units are turnable about a vertical axis for steering, but for reversing, the direction of rotation of the rotor or rotors of the jet unit is reversed by suitable changeover gearing in the drive to the unit.

Although in the second embodiment above described the pump portion of the hydraulic jet propulsion apparatus is fixed in the vehicle and both the intake duct and the discharge duct of the apparatus are retractable from their operative positions, in other embodiments the intake duct only is retractable while the discharge duct is so arranged as in some embodiments to discharge into the water, or in other embodiments to discharge into the air.

jet propulsion, which is disposed, in plan view, within the periphery of the air-cushion zone and which includes a duct, at least the outlet portion of said duct being movable between an operative position in which it is positioned below said zone, and an inoperative position within the vehicle, said duct when in said operative position, during operation of the vehicle over water, so discharging beneath the water as at least to assist in the propulsion of the vehicle across the water, and the compressor, engine and drive means all rotating about axes which are coincident.

2. An air-cushion vehicle including a main vehicle structure, an engine, air-cushion zone-defining means formed with said structure and chargeable by air supplied thereto under pressure by a compressor driven by said engine, wherein the improvement comprises the provision of ducting taken from the exhaust sectionof the engine, which isso mounted with respect to the vehicle that when the vehicle is operating over water, part of the ducting at least is immersible in the water so that engine exhaust gases are discharged into the water to at least assist in the propulsion of the vehicle across the water, the air-cushion zone being at all times fully charged by air dur' ing such propulsion across water.

j 3. A vehicle as claimed in claim 12, wherein said engine is a gas turbine engine and said ducting is displaceable from its immersed position to a position above the water in which it directs the exhaust gases into the air cushion.

4. In combination, a vehicle having first conduit means defining an opening in the bottom thereof and an enginedriven compressor unit thereon for discharging a stream of pressurized gas through the opening in the bottom, which impinges on the surface therebelow to form a cushion of air under the vehicle that rises it above the surface, and jet propulsion apparatus for use in propelling the vehicle over the surface, including a second conduit means separate from the first conduit means and defining a fluidtransfer duct having an outlet thereon which is operatively disposed below the opening in the bottom of the vehicle for discharging a jet of pressurized fluid from the outlet; and fluid intake means connected with the compressor engine to collect and deliver the exhaust gases therefrom to the duct.

Again, although in certain of the embodiments hereinbefore mounted above 5..The combination according to claim 4 wherein the vehicle is operable over water and the outlet of the duct is immersible below the surface of the water during propulsion.

6. The combination according to claim 5 wherein alternatively, the duct is retractable to a level above the bottom of the vehicle.

7. An air-cushion vehicle including a main vehicle, structure, a gas turbine engine mounted within the structure with a generally. vertical rotational axis, air-cushion zone-defining means formed with said structure and chargeable by air supplied thereto by a compressor driven by said engine, the compressor and engine being disposed in line with the compressor the engine, ducting which extends downwardly from the exhaust section of the engine and which includes a cranked outlet duct section which can be swung about an axis disposed generally fore and aft of the vehicle engine exhaust gases are discharged into the air-cushion zone.

9. An air-cushion vehicle according to claim 8, wherein when said outlet duct section is in the retracted position it is in alignment with a fixed duct section mounted in the vehicle structure and arranged to discharge within the air-cushion zone.

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