US3181636A - Ground effect machine having heave stability for traversing rough surfaces - Google Patents

Description

May 4, 1965 c. s. COCKERELL 3,181,636

GROUND EFFECT MACHINE HAVING HEAVE STABILITY Filed Sept; 29, 1960 FOR TRAVERSING ROUGH SURFACES 6 Sheets-Sheet 1 DIRECTION OF TRAVEL OF VEH/CLE Inveof'ar C. S. COCKEREL A lfarnzys May 4, 1965 FOR Filed Sept. 29. 1960 GROUND EFFECT q. s. COCKERELL 3,181,636

'IMACHINE HAVING HEAVE STABILITY TRAVERSING' ROUGH SURFACES 6 Sheets-Sheet 2 Invenf'or C. S. COCKCRELL M) May 4, 1965 c. s. COCKERELL 3,181,636

GROUND EFFECT MACHINE HAVING HEAVE STABILITY FOR TRAVERSING ROUGH SURFACES 6 Sheets-Sheet 5 Filed Sept. 29. 1960 FIG.6.

Inven C. S. Cocmsna 2a N m LL. WWW

flf/arneys May 4, 1965 FOR TRAVERSING ROUGH SURFA Filed Sept. 29. 1960 6 Sheets-Sheet 4 FIG.I4.

In VcnTo C, S. C oCKERELL.

c. -s. COCKERELL 3,181,636 i GROUND EFFECT MACHINE HAVING HEAV TABILITY 5 M, 42. plaza May 4, 1965 c. s. COCKERELL 3,181,636

GROUND EFFECT MACHINE HAVING HEAVE STABILITY FOR TRAVERSING ROUGH SURFACES Filed Sept. 29, 1960 6 Sheets-Sheet 5 FIGJS.

. 92 93 L Y/ M I [Fr/1 /////1 l\ \\Y/// 43\ \3] ,1 Q

94 FIG.I7A.

Inve 'far C. S. COCKL-ZRELL.

y 4, 1965 c. s. COCKERELL 3,181,636

GROUND EFFECT MACHINE HAVING HEAVE STABILITY FOR TRAVERSING ROUGH SURFACES Filed Sept. 29, 1960 6 Sheets-Sheet 6 FIG.I9.

Invenf'or C. S. COCKERELL.

United States Patent 3,181,636 GROUND EFFECT MACHINE HAVEJG HEAVE STABILITY FOR TRAVERSING ROUGH SURFACES Christopher Sydney Coclrerell, East Cowes, Isle of Wight, England, assignor to Hovercraft Development Limited, London, England, a British company Filed Sept. 29, I960, Ser. No. 59,306 Claims priority, application Great Britain, Oct. 2, 1959, 33,535/59 9 Claims. (Cl. 180-7) This invention relates to vehicles for travelling over land and/or water and which are supported above the surface of the land or water by one or more cushions of pressurized fluid.

In such vehicles means are provided for forming and maintaining a cushion or cushions of pressurised fluid beneath the vehicle, such means generally being adjacent to the periphery of the bottom of the vehicle.

The above described method of support is also applicable to a platform primarily intended to remain stationary, for example, for supporting a radar installation, and the term vehicle as used herein is to be understood as including, where the context permits, a platform.

The invention is concerned with the heave stability of the vehicle when travelling over rough water or over ground contoured in a similar manner. When the vehicle is travelling over rough water or ground, the path of the centre of gravity of the vehicle is determined by certain parameters, some of which are design parameters and others depend upon the speed of the craft, the length of the craft, and the height and spacing of the obstacles forming the rough surface. Dependent upon these parameters, such a path may be acceptable, but often the combinations of these parameters may result in an unacceptable path, due to such path exhibiting excessive heave, for example, a resonant condition or a path which is too far out of phase with the contours beneath the craft. These undesirable eifects may be reduced by an appropriate dynamic manipulation of some of the design parameters which determine the total upward thrust of the pressurised cushions at any one instant of time, thus enabling the total upward thrust to be varied.

It is well known that a rough surface, whether it be land or sea can be reproduced by the summation in appropriate phase and amplitude of a series of component waves superimposed upon one another. Thus although a Wave formation is in general the result of the superimposition of a number of individual wave formations of difierent length and height and speed of translation, it is permissible, in order to simplify the analysis, to consider simple formations first of short and then of long waves, it being known that a control system which is suitable for either separately will give a sat-isiiaotory performance when more than one is present, provided the amplitudes of the components in combination are within the maximum for which the control is designed.

The problem can be illustrated by considering a number of varying operating conditions. Taking first when the vehicle is traversing plain waves, whose Wavelength is short compared with the length of the craft, then the integrated lift of its supporting cushion will remain very nearly constant, and so the path of the centre of gravity of the vehicle will be very nearly level, and the form of this path will be very little alfected by the speed of the vehicle. However, when the vehicle is slowly traversing plain Waves whose length is very long compared with the length of the vehicle, the vehicle will heave in phase with the wave so that the hover-height will be very nearly constant with respect to the mean height of the section of the wave beneath the vehicle in any one instant. Again,

3,18l ,636 Fate-rated May 4, 1965 when the vehicle is quickly traversing plain waves whose length is very long compared to the length of the vehicle, the vehicle will heave but the phase of its path will lag behind that of the wave so that its mean hover-height halfway down the wave will be greater than its mean hover-height when climbing the next crest. When the vehicle is traversing plain waves of intermediate length the vehicle will heave, in general, by less than the height of the waves, both the amplitude and the phase of this heaving path depending greatly upon the speed of traverse, the length of the craft and the natural period or periods in heave of the craft and its air cushion. In a further condition, when the vehicle is traversing plain waves of intermediate length and the frequency of encountering them is of the order of the natural frequency of the vehicle in heave, or a multiple of it, the vehicle is excited by the waves and a resonant condition is obtained, resulting in an amplitude of heave which may be far greater than the wave height.

In general, the fluid forming the cushion or cushions is air, and similarly, where fluid curtains are used to contain the cushion or cushions, these are also formed by air, and for convenience hereinafter this will be considered to be the case. However, other fluids, such as exhaust gases and Water or steam can be used particularly for forming the curtains.

The invention will be readily understood from the following description of various embodiments in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic vertical cross-section through a typical surface undulation showing the path followed by the centre of gravity of the vehicle without the application of the invention,

FIGURE 2 is a vertical cross-section of a vehicle embodying one form of the invention,

FIGURE 3 is a vertical cross-section of a slightly different form of vehicle embodying a similar form of invention as shown in FIGURE 2,

FIGURE 4 illustrates a modified form of the vehicle illustrated in FIGURE 2,

FIGURE 5 is a similar cross-section as in FIGURE 2 illustrating an alternative form of the invention,

FIGURE 6 is a similar cross-section as in FIGURE 3 illustrating the application of an alternative form of the invention as shown in FIGURE 3,

FIGURE 7 is a plan view of the vehicle as shown in FIGURE 2,

FIGURE 8 is a diagrammatic view of an apparatus for positively controlling the operations of the valves shown in FIGURES 2 to 6,

FIGURE 9 is a vertical cross-section of a vehicle similar to that shown in FIGURE 5, having an alternative fluid curtain system,

FIGURE 10 is a vertical cross-section of a vehicle sim ilar to that shown in FIGURE 4 illustrating a modification thereof,

FIGURE 11 is a diagrammatic partial cross-section of the bottom part of the vehicle embodying a further form of the invention,

FIGURE 12 is a modification of FIGURE 11,

FIGURE 13 illustrates a further modification of FIG- URE 11,

FIGURE 14 shows a further form of embodiment shown in FIGURE 11,

FIGURE 15 is a partial plan view of the detail of a flap as used in the various forms of the embodiment shown in FIGURES 11 to 14,

FIGURE 16 is a diagrammatic partial cross-section of the bottom of the vehicle having yet another embodiment of the invention,

FIGURES 17A and 17B illustrate diagrammatically a further embodiment of the invention,

periphery of a vehicle illustrating a further embodiment of the invention, and

FIGURE l9illustrates a modification of the. embodiment illustrated in FIGURE 18.

As stated above when a vehicle is traveling over an undulating surface, or when a vehicle is hovering over water with waves flowing beneath it, the effect of the variation in height, or clearance, between the bottom of the vehicle and the surfacewill depend upon the wave length of the undulations compared with the length of the vehicle. Where the wave length is a sub-multiple of the vehicle length, the vehicle will maintain a substantially level course, rising and falling only whenencountering isolated taller crests or deeper troughs of suchundulations. At the other extreme, where the wave length is several times the length of the vehicle, the vehicle will follow the profile of the undulations without undue vertical accelerations cushion, the air being supplied to the port 3 from a duct 5. In FIGURE 3 the cushion is contained peripherally by a flexible downward projecting peripheral member 6, air being blown into the space occupied by the cushion through a port 7 from a duct 8 in the bottom of the main body of the vehicle, existing air escaping beneath 'the downward projecting member'6. Inboth vehicles, one way valves 9 and 10 are provided which in their normal position close ports or ducts 11 through the downward projecting members '4 and 6. The valves 9, at the front of the vehicles, open inwards towards the cushion, while the valves 10, at the rear of the vehicles, open outwards. The valves 9 and 10'ma'y, of course, be loaded or biased toa ward their normally closed positions in any suitable manbeing imposed on the vehicle. I have found that the range of wave lengths at which unacceptable vertical accelerations may occur generally lies very roughly between 1 and 2 /2 times the length of the vehicle, and if provision can be made to cause the vehicle to follow a modified path having a reduced height variation for this range of wave lengths, the undue vertical accelerations which would otherwise occur can be reduced to an acceptable value, or

even almost prevented. a FIGURE 1 illustrates diagrammatically. the profile of an undulating surface, the wavelength being of the order of twice the vehicle length, together with an indication of the path which would normally be followed by the centre of gravity of the vehicle, As described hereinafter, the undulating surface will be considered as being waves in water although it willbe appreciated that the invention is applicable to a vehicle travelling over other surfaces hav-' ing similar characteristics such as sand dunes and the like.

Line A represents the profile of a wave andthe chain dotted line B is the path followed by the centre of'gravity of a vehicle which would normally occur. At the'positions indicated at C, D and E the height is that which it is, intended to operate the vehicle, that is the cushion volume. and mean pressure and the curtainheight, areat their correct or datum values. It will be seen that as the centre,

of gravity of the vehicle passes pointC the height of the vehicle relative to the surface increases beyond the mean. and there is a corresponding increase in cushion volume which causes a decrease in cushion pressure below the mean. This increase in volume andthe; accompanying decrease in cushion pressure results in a decreased upward thrust from the vehicle which continues until the centre. of gravity of the vehicle reaches point D.- As the centre of gravity passes point D, the height of the vehicle decreases below the mean, with a corresponding decrease in cushion volume and an increase in pressure beyond the mean, and an increase in upward thrust, until pointE is reached. The variations in upward thrust causeyariations of the lift exerted from the vehicle which cause, vertical accelerations which may be quite large.

To reduce or prevent these variations inlift with the resultant variations in upward thrust, the variations in cushion pressure are reduced or prevented. Thus, for ex.-v

ample, by' providing additional air to the cushion for the period the centre of gravity of the vehicle is travelling from C to D, and by theextracting air from the cushion for the period the vehicle is travelling from D to E, its

to hereinafter as such. The air curtain 2 flows down-1 ner, as by springs (not shown). If the pressure of the cushions 1 falls below theatmospheric, theffront valves 9 open and admit air to the cushion, reducing the loss ,of lift and the normal result of the downwarddropof the vehicle. Similarly, when the pressure of the cushions 1 exceeds the predetermined value, rear valves 10 open to allow the escape of some of thecushion forming air to atmosphere. It is advisable to provide a series of ports or ducts 11 as shown in FIGURE'7 described below to enable large flows of air to' take place.

As indicated above, the effect on the vehicle of variations in the pressure of the cushion and in resultant thrust on the vehicle bottom is exactly the same when the vehicle is stationary and hovering over water with waves flowing therebeneath as when the vehicle is travelling over an undulating surface, whether thatsurface be stationary or moving. 7 a

Assuming that the vehicle is hovering, when the crest of a wave passes 'therebeneath and causes the vehicle to move'upwards, there is an overshootingeffect due to the inertia of the vehicle whichproduces a decrease in cushion pressure. With a sufficiently fast movementand steepness ofthe wave, the cushion pressure can fall below atmospheric pressure, whereupon the vehicle becomes subject to a downward force which accelerates the vehicle downwards; As the vehicle moves downwards, the volume of the cushion starts to decrease and the cushion pressure will'start to increase. When the vehicle has dropped to a height above the surface of the wave equivalent to the normal hoverheighh'the cushion pressure will be' normal and the vehicle will have reached its maximum downward velocity. As the vehicle continues to drop, the clearance and the cushion volume will decrease with a'corresponding increase in cushion pressure, which increase in pressure slows down the vertical movement of the vehicle until it is finally arrested. Since the increase in pressure is proportional to the decreasein clearance, the rise in cushion pressure is relatively rapid. Forexam'ple, assumingv that the normal'clearance or hoverheight of the vehicle is 12', an initial decrease in clearance of 6" doubles the cushion pressure, a further decrease of only 3" doubles the pressure again, whilea still further doubling of pressure occurs for only another 1 /2"v decrease in clearance. It

. should therefore be evident that, even though the cushion pressure may dropbelow atmospheric pressure, the vehicle itself will not drop down onto the surface of the,

water, but its downward movement will be arrested by the very much increased cushion pressureproduce'd during the Idroppingmovement, which pressure will then accelerate the vehicle upwards.

As pointed out below,'the only material difference between conditions when the vehicle is travelling over an undulating surface and when it is hovering over water with waves flowing beneath it, is that whenithe vehicle is wardly from an annular supply port 3 formed in the bot-i :tom of 'the' downward projecting peripheral member 4 which also peripherally contains .thelupper portion of the moving it-is possible to take advantage of;the. head pressure produced at the front of the vehicle was to feed'air to the cushion before its pressure drops below atmospheric pressure. There may also be aregion of subat'rnospheric pressure at the rear -of the vehicle whichcan be utilized'to facilitate the flow of airout of the cushion when its pressure increases above a predetermined value.

The objective of the present invention is thus to reduce the vertical accelerations imposed on the vehicle by reducing the variations in cushion pressure. This is accomplished by admitting air to the cushion when the pressure rops below atmospheric, and by releasing air from the cushion when the pressure goes above some predetermined value, whereby the vertical movements of the vehicle are damped or leveled out.

Such a system as shown in FIGURES 2 and 3 reduces to some extent the pressure variations and the path of the centre of gravity of the vehicle is slightly modified from that shown in FIGURE 1, but variations in cushion pressure and thus lift will still occur. This is partly due to the fact that no air is admitted to the cushion until it is below atmospheric pressure. A further improvement can be obtained if it is arranged to admit air to the space occupied by the cushion 1 before the pressure drops below atmospheric. A source of high pressure is thus required. Still further improvement is possibl'= if it is arranged to exhaust air from the cushions to a region of reduced pressure. In the vehicles as shown in FIGURES 2 and 3, these improvements can readily be achieved when the vehicles are in motion as the pressure at the front of the vehicle is above atmospheric, whilst the pressure at the rear of the vehicle is slightly sub-atmospheric.

The vehicles shown in FIGURES 2 and 3 have the dis advantage that a substantially rigid downward projecting member, comprising the whole of the member 4 in FIG- URE 2 and a comparatively large part of the member 6 in FIGURE 3, must be provided, increasing the height of the structure.

To avoid this, ducts or ports 12 can be formed in the main body of the vehicle as shown in FIGURE 4. In this example, ducts 12 are formed in the periphery of the vehicle, valves 13 being provided in the ducts acting in a similar manner to the valves 9 and of FIGURES 2 and 3. Although FIGURE 4 illustrates a modification of FIGURE 2 a similar modification can also be made to FIGURE 3.

An alternative arrangement is to provide ducts through the body of the vehicle, the ducts serving both for the influx and efiiux of air, controlled by a valve capable of opening either way. Such an arrangement is illustrated in FIGURES 5 and 6, the vehicle shown in FIGURE 5 being similar to that shown in FIGURE 2, whilst the vehicle shown in FIGURE 6 is similar to that shown in FIG- URE 3.

In the vehicle shown in FIGURES '5 and 6 the duct 15 is formed in the main body 16 of the vehicle, communicatiilg at one end with the space occupied by the cushion 1, and at the other end with the surrounding atmosphere. Two valves 17 normally close the ducts 15 under the action of springs 18 and can rotate one way or the other, as indicated by the dotted lines 19 to allow air to flow into or out of the cushion space. Valves 17 can be so controlled by springs 8 that there is restricted pressure range over which they remain closed. It will be seen that in FIG- URE 5 the supply port 20 need only project slightly below the bottom of the vehicle or may be flush with the bottom surface. Similarly, in FIGURE 6 the downward projecting member 21 need not be as long as member 6 in FIG- URE 3. Instead of one large duct 15 being provided a number of smaller ducts can be used.

FIGURE 7 illustrates diagrammatically the relative position of the ducts 11 to the vehicle illustrated in FIG- URE 2. Ducts 11 are positioned at the front and the rear of the vehicle as shown. The air for the formation of the air curtain 2 enters through intakes 22, being forced by the propellers 23 into the duct 5. A plan view of the vehicle shown in FIGURE 3 will be very similar, the difference being that the air from the propellers 23 is fed to duct 8 instead. Again the plan form of the vehicle as illustrated in FIGURES 5 and 6 is similar to that of FIG- URE 7.

The valves 9, III, 13 and 17 of FIGURES 27, instead of being spring biased or controlled, may be positively actuated by a device or devices controlled, for example, by cushion pressure. Such a device is shown diagrammatically in FIGURE 8. An hydraulic control valve illustrated generally at 39, controls the flow of pressurised oil from supply inlet 31 to either side of the piston 32 mounted in a cylinder 33. Piston 32 is connected by a suitable linkage 34 to a valve 35 which corresponds to the valve 17 of FIGURES 5 and 6. The cushion pressure I" is fed to an inlet 36 of the control valve 30. Springs 37 on either side of the piston tend to maintain the piston in central position, in which the valve 35 is closed.

In operation, variations in cushion pressures are fed by inlet 36 to the control valve 30, oil being supplied to one side or the other of piston 32. The piston moves in the cylinder, rotating a valve 35 one way or the other. On return of the cushion pressure to normal the oil supply to cylinder 33 is cut off and both sides of the piston open to exhaust, whereupon the springs 37 return the piston to its central position closing the valve 35.

Where the valve 35 needs to move only in one direction, as for example in FIGURES 2, 3 and 4, only a single-sided piston 32 is required.

FIGURE 9 illustrates the application of the invention to a vehicle having a more complex form of air curtain, such as described in patent specification of co-pending application Serial No. 837,428, filed September 1, 1959, and since abandoned. In such curtain systems, at least part of the curtain forming air is recovered through recovery ports formed at the bottom of the vehicle, inboard of a supply port. This vehicle is similar to the vehicle illustrated in FIGURE 5, the air recovered through the recovery ports 40 being re-energised and recirculated back to the supply port 3.

In a vehicle having an air curtain system, such as in FIGURE 2, 4, 5 and 9, it is possible to reduce the mass flow of the curtain at any convenient position, e.g. at the rear of the vehicle, thus weakening it, when the pressure of the cushion tends to rise above the predetermined pressure. Air from the cushion can then escape beneath the curtain. This is illustrated diagrammatically in FIGURE 10. A mass flow of air through the supply port 43 can be varied locally by a sliding flap 44. In the example shown, fiap 4-4 at the rear of the vehicle, on the right of FIGURE 10 is restricting the How of air to the part of the supply port 43 at the rear, locally weakening the curtain of air 45. Air from the cushion is able to flow out beneath the air curtain as at 46. One or more additional air curtains may be formed beneath the vehicle to subdivide the cushion, as shown dotted at 48.

It will be apparent from the foregoing description of various embodiments in the invention that the invention seeks to reduce, prevent or even reverse variations in vertical thrust due to the variations in cushion pressure, which would otherwise occur, when traveling over waves and obstacles of similar profile. Thus, when the vehicle leaves a crest of the obstruction and travels over a trough,

the cushion pressure is maintained, as by the valves 9.

in FIGURES 2 and 3, at a pressure above that which would normally occur, up to the mean pressure, or may be even increased above the mean. However, the curtain height is greater than normal at this time and may not be capable of containing the required cushion pressure. Conversely, when the vehicle after traveling over a trough encounters a rising face of an obstacle, the cushion pressure is maintained, as by the valves 10 in FIG- URES 2 and 3, at a pressure below that which would normally occur, down to mean pressure, or may be even ecreased below the mean. At this time, however, the curtain height is lower than normal and is capable of maintaining and will tend to maintain a cushion of pressure above the mean.

, The application of the variation of themass flow of the curtain forming air is similar to the variation of mass flow asdescribed above, with reference to FIGURE 10. Servo motors 47, are provided to operate the flaps 44, 'in combination with the above described variation of mass flow for the admission of air to, and exhausting of air from, the cushion again controlled by variations in cushion pressure.

As stated above the necessity for the control according to the invention decreases as'the length of the wave increases, in that'with very long waves undue accelerations will not be generated if the vehicle is allowed to follow their contour.

-The variation of vertical thrust, or lift, produced by the cushion can also be obtained by varyingthe area of the cushion. For example, if thecushion pressure has decreased and it is desired to reduce, or prevent,,the loss of vertical thrust which would otherwise occur, this can be done by increasing the effective area of the cushion,

such as by moving the air curtains outwards or by providing a further curtain out-board of the existing curtain. The converse applies when it is desired to prevent or reduce the increase in vertical thrust which would otherwise occur on an increased cushion pressure. Various ways of varying the efiective cushion area are described below. a f a FIGURE 11 shows a simple arrangement in which two supply ports 54 and 55 are supplied with air by ducts 56 and 57 respectively. A hinged flap 58 is mounted at the junction-of the two ducts 56 and 57,:the position of the flap controlling the amount of air fed from a compressor by a duct 59, which enters each of ducts 56 and. 57. By rotating the flap'one way, anti-clockwise in FIG- URE 11, the amountof air flowing tothe inner-air cur- .tain'is reduced and that flowing to the outer air curtain is. increased. This leads to an increase in pressure of the secondary cushion which is' formed between the 'two air curtains and thus increases the effective area of the main cushion. Reverse rotation of the flap has the reverse elfectl FIGURES 12 .and 13 are variations of the shown in FIGURE 11. In these examples the outer air curtain is formed from two supply ports 60 and 61, fed by two ducts 62 and-63 respectively, the inner. air curtain being formed from a single supply port' 64 fed by a duct 65. A hinged flap 66 operates to vary'the air fiow to'the two ducts 63 and 65, the air flow tothe duct 62 being separate. Operation of the flap varies the relative air system gPorts 88 and 89 are postioned in the plate 85 so that when.

flow to the two supply ports 61 and 64 with the above described efie'ct. In FIGURE12 the ducts 62 and 63 are raised so that air from the compressor flowing along the duct flows smoothly into the duct 65. In FIGURE 13 the ducts'62 and 63 are not raised and a curved guide is formed from two supply ports, the outer air curtain by supply ports 70 and 71 fed by ducts 72 and .73 and the inner air curtain by supply ports 74 and 75 fed by ducts 76 and 77 respectively; In each pair of ducts the outer duct 72 and 76 is wider than the inner duct. A hinged 8 her, only the relative flows to the outer ducts 72 and '76 being varied. V I a In the arrangements as shown in FIGURES 11 to 14, where the flap or valve is circular it must be made of flexible material or sectors of stifi material with radial joints of flexiblematerial as shown in FIGURE 15, which is a plan view'bf a suitable flap for use in FIGURE 13. FIGURE 16 illustrates diagrammatically an alternative method of varying relative flows of air to the supply ports, using a sliding flap or plate. A flat plate is mounted on the bottom surface of the vehicle, arranged to slide inwardly and outwardly over-the supply ports 86 and 87. The supplyports 86 and 87 are much wider in the radial direction than is normally the case, i.e., in comparison with the supply ports of FIGURES 11-14, and the sliding I plate :85 is provided with ports 88 and 89 which act as the actual ports through which the curtain forming air issues. The ports 88 and 89 are slightly wider than normal ports, being sufiiciently wider for the issue of the maximum additional air it is intended should be transferred.

the plate is in its central position the outer edge of the port 88 is slightly outside the outer edge of the port 86 and the inner edgeof port .89 is slightlysinside the inner edge of port 87, the unobstructed widths of the ports 88 and 89 being the correct widths for the formation of normal curtains. Air is fed to the ports via a duct 90 and it will be seen that the movement of the plate 85 in or out will vary the relative flows of air out of ports 88 and 89. Vanes may be provided in the wide ports 86 and 87. Whilst the flap plate is shown as being fitted inside the bottom of the vehicle, it can readily 'be fitted on the outside, but is liable to be damaged. Again, the relative positioning's of the wide and narrow ports can be reversed, the narrow ports 88 and 89 being formed in the bottom of the vehicle and the wide ports 86 and 87 being formed in the sliding plate 85.

It will be understood that air is deflected from the inner air curtain system to the outer air curtain system when it is desired to increase the effective area of the cushion to offset any decrease, in cushion pressure. The vehicle would normally be arranged tooperate with the pressure of the secondary'cushion formed between the air curtain sys'tems at, for example, half the pressure of the main cushion. It would then be'possible to increase the vertical thrust above the normal, or to increase the vertical thrust that would otherwise obtain, by raising the pressure'of the.

' 17A and 17B illustrate diagrammatically such a method for movingthe position of a port relative to the bottom of the vehicle; The normal narrow port through which the air curtain is formed is replaced by a wide port 91. Mounted over the port is a slidable flap plate 92 having a narrow port 93. Port 93 is equivalent to the normal port 1 formed in the bottom of the vehicle'in the previously described vehicles, and where the air issuing through it forms a primary air curtain, port 93 is in the form of an annulus or is aseries of ports in annular configuration. As shown valve member 78, formed from two parallel flaps, 78a

and 78b, is'mounted at the junction of the ducts, movement of the valve member varying the flow of air into, the

outer duct of each air curtain forming system. Air passesbetween the parallel flaps 7 8a and 7 812 into the inner duct 73 of the outer air curtain system andflows below the valve into the inner duct 77 of the inner air curtain sysin FIGURE 17A, the port 93 is-in its central position. By moving the plate in or out, in a general radial direction, the position of the portand thus the curtain can bevarled. Ifthe port 93 is moved inwards towards the centre of the vehicle as shown in FIGURE 17B, the edge of the cushion will be moved inwards which will have. the effect of reducing the area of the cushion. Conversely moving the port 93 outwards away from the centre of the vehicle has the effect of increasing the area of the cushion. The movable plate 92 is easily provided for straight portions of the ports at the bottom of the vehicle; where the. Ports are tem. The air flow into each of the inner ducts73 and 77 I is virtually unafiected by any movement of the valve mem-,

curved, it will be necessary to provide for the plates to slide one over the other as they are mov in andput to allow for the variation in circumferential distance. Vanes 94 may be provided in the wide port 91.

An alternative method of varying the effective area of the cushion, as applied to curtain systems in which at least part of the curtain forming air is recovered, is illustrated in FIGURE 18. A supply port 100 is formed in the bottom of the vehicle at the periphery and a recovery pont 101 is also formed in the bottom of the vehicle slightly inboard of the supply port 100. A further recovery port 102 is formed in the bottom of the vehicle spaced further inboard than the first recovery port 101. The recovery ports 101 and 102 communicate via ducts 103 and 104 respectively with a common recovery duct 105. A sliding vane 106 is mounted between the two recovery ports and acts to vary the opening of the ports. In operation, air issues from the supply port 100, and some of the curtain forming air is recovered through recovery port 101, further air being recovered through recovery port 102. The sliding vane 106 can completely close either of the recovery ports, and if, for example, the outer recovery port 101 is closed then the cushion extends, effectively, only as far as the inner recovery port 102. Similarly, if the inner recovery port 102 is closed, the cushion extends as far as the outer recovery port 101. A graduation of the effective cushion area between these two limits can be obtained by varying the sliding vane 106.

FIGURE 19 illustrates a method of cushion area variation similar to that shown in FIGURE 18, a rotatable vane 107 being provided to vary the relative amounts of air recovered through the recovery ports 101 and 102, instead of sliding vane 106.

As described above, when the vehicle is quickly traversing plain waves whose length is very long relative to the length of the vehicle, the vehicle is liable to become out of phase with the waves, overshooting at the crests and for at least part of the downward going faces, and undershooting at the troughs and for at least part of the upward going faces of the waves. Under such conditions it is possible that the vehicle will meet obstacles such as small waves imposed on the long Waves, which it would normally miss, but which due to the decreased height at certain positions in its path it will hit. This can be prevented if means are provided, for example, for increasing the mass flow of the curtain forming air or increasing the cushion area so that the vehicle will tend to be maintained at its correct height. The converse will apply on the downward going slope of the wave and the mass flow of the curtain air or the cushion area can be reduced at these times.

I claim:

1. A vehicle for travelling over a surface comprising a body, means for forming and maintaining a cushion of pressurised fluid beneath said body by which said vehicle is at least partly supported above said surface as it travels thereover, and means carried by said body for reducing unacceptable vertical accelerations of said body, said means including means responsive directly to variations in the volume of said cushion from a predetermined value for automatically supplying fluid to and releasing fluid from said cushion and thereby reducing the variations in vertical thrust on the vehicle produced by variations in the cushion pressure resulting from said variations in volume of the cushion.

2. A vehicle for travelling over a surface comprising a body, teams for forming a cushion of pressurised fluid beneath said body by which said vehicle is at least partly supported above said surface as it travels thereover, means for containing said cushion including a portion of the vehicle body, and means carried by said body for reducing unacceptable vertical accelerations of said body, said 'rneans including means responsive directly to variations in the pressure of said cushion relative to the pressure of the atmosphere around the vehicle for automatically supplying air from the atmosphere to said cushion and releasing air from said cushion to the atmosphere and thereby reducing the variations in vertical thrust on the vehicle produced by said variations in the cushion pressure.

3. A vehicle as claimed in claim 1 wherein said first mentioned means includes means for forming at least one curtain of fluid which at least partly forms and contains the cushion of pressurised fiuid.

4. A vehicle as claimed in claim 2 wherein said lastrnentioned means includes at least one opening in the body of the vehicle providing communication between said cushion and the atmosphere, and a flap mounted in said opening operative in response to variations in the cushion pressure for admitting air into the cushion when the cushion pressure decreases, and releasing air from the cushion when the cushion pressure increases, from a predetermined pressure.

5. A vehicle as claimed in claim 4 including power operating means for operating the flap.

6. A vehicle as claimed in claim 2 wherein said lastmentioned means includes openings in the body of the vehicle at the front and rear thereof providing communication between said cushion and the atmosphere, a flap for admitting fluid into the cushion positioned in the opening at the front of the vehicle, and a flap for releasing fluid from the cushion positioned in the opening at the rear of the vehicle.

7. A vehicle as claimed in claim 1 wherein said first mentioned means includes means for forming at least one curtain of fluid which at least partly forms and contains the cushion of pressurised fluid, and wherein said lastmentioned means includes means responsive to variations in the cushion pressure for varying at least locally the mass flow of the fluid forming the curtain, said last-mentioned means being so constructed and arranged as to decrease the mass flow when the cushion pressure tends to increase and to increase the mass flow when the cushion pressure tends to decrease, whereby fluctuations in cushion pressure are reduced.

8. A vehicle as claimed in claim 7 wherein said curtrain-forming means further includes at least one supply port formed in the bottom of the vehicle, and wherein the means for varying the mass flow of fluid forming the curtain includes at least one movable member for varying the width of the supply port.

9. A vehicle as claimed in claim 8 wherein the means for varying the mass flow of fluid forming the curtain further includes power operating means responsive to variations in the cushion pressure for moving said movable member.

References Cited by the Examiner UNITED STATES PATENTS 1,123,589 l/15 Porter. 2,567,392 9/51 Naught. 2,751,038 6/56 Acheson. 2,838,257 6/58 Wibault. 3,042,129 7/62 Wade 7 FOREIGN PATENTS 219,133 11/58 Australia. 1,238,499 7/60 France.

OTHER REFERENCES Popular Science, July 1959, pages 51, 52, 53, 54, 55, 194.

A. HARRY LEVY, Primary Examiner. PHILIP ARNOLD, Examiner.

Claims (1)

1. A VEHICLE FOR TRAVELLING OVER A SURFACE COMPRISING A BODY, MEANS FOR FORMING AND MAINTAINING A CUSHION OF PRESSURIXED FLUID BENEATH SAID BODY BY WHICH SAID VEHICLE IS AT LEAST PARTLY SUPPORTED ABOVE SAID SURFACE AS IT TRAVELS THEREOVER, AND MEANS CARRIED BY SAID BODY FOR REDUCING UNACCEPTABLE VERTICAL ACCELERATIONS OF SAID BODY, SAID MEANS INCLUDING MEANS RESPONSIVE DIRECTLY TO VARIATIONS IN THE VOLUME OF SAID CUSHION FROM A PREDETERMINED VALUE FOR AUTOMATICALLY SUPPLYING FLUID TO AND RELEASING FLUID FROM SAID CUSHION AND THEREBY REDUCING THE VARIATIONS IN VERTICAL THRUST ON THE VEHICLE PRODUCED BY VARIATIONS IN THE CUSHION PRESSURE RSULTING FROM SAID VARIATIONS IN VOLUME OF THE CUSHION.

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