GB2094734A

GB2094734A - Steering air cushion vehicles

Info

Publication number: GB2094734A
Application number: GB8206895A
Authority: GB
Original assignee: Societe dEtudes et de Developpement des Aeroglisseurs Marins SEDAM SA
Current assignee: Societe dEtudes et de Developpement des Aeroglisseurs Marins SEDAM SA
Priority date: 1981-03-16
Filing date: 1982-03-09
Publication date: 1982-09-22
Also published as: FR2501606B1; CA1187915A; FR2501606A1; GB2094734B

Abstract

Means for controlling steering of an air cushion vehicle are formed by four vents (EV) supplied by withdrawing pressurized air from respective ones of two lateral regions, separated by a longitudinal wall 13, of the plenum chamber (D) of the vehicle. The vents (EV) eject air in a direction having at least one component directed from the lateral withdrawal region towards the opposite region. Apart from the direct effect (F(EV)) due to the air ejected by the vents, this particular arrangement creates a jet reaction (F(R)) and a hydrodynamic drag and when travelling on the ground, a frictional drag. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vehicles comprising air cushions The present invention relates to vehicles or machines comprising pressurized fluid cushions, also referred to as ground effect machines. Hereafter, in order to simplify the explanation, reference will be made solely to vehicles comprising air cushions, without this expression being limiting.

Vehicles comprising air cushions are already known of the type comprising a platform supporting the structure of the vehicle and whereof the lift is ensured by a lifting arrangement formed in particular of air cushions.

According to a particular embodiment, the air cushions which compose the base of the lifting arrangement are formed by flexible skirts defining a central cushion and a peripheral arrangement comprising a plurality of adjacent partitioned cells (or compartments).

The lifting arrangement may also comprise a diffusion chamber located between the platform of the vehicle and.the air cushions. This diffusion chamber forms a type of supply tank into which the fan discharges and since it is thus supplied with pressurized air, it in turn supplies the various air cushions directly or indirectly.

By way of example and in order to understand the present description fully, reference may be made to French Patent Application No. 79 23213fiXed on September 18th 1979 in the name of the Applicant.

The means for controlling steering intended to ensure manoeuvring of vehicles comprising air cushions of the previously described type are conventionally formed of aero-dynamic control means which comprise, in combination, screw-propellers and rudders and ailerons.

If, at cruising speed, these aerodynamic control means allow good manoeuvrability of vehicles comprising air cushions, on the other hand, at low speeds and in particular when the vehicle comprising air cushions is turning on approach and on the ground, these control means prove insufficient.

It has also been proposed to provide vehicles comprising air cushions with vents supplied with pressurized air and which eject the air towards the outside of the vehicle. These vents create forces by localized ejection of air withdrawn from the lifting arrangement.

However, the various arrangements of vents and methods of supplying the latter which have been proposed hitherto have not proved satisfactory. In particular, hitherto it has not been possible to utilize vents in order to obtain either an essentially transverse force or a torque with respect to the centre of gravity, whilst retaining a correct lifting power, which makes it possible to manoeuvre vehicles comprising air cushions easily and correctly.

For these reasons, there has been a tendency to abandon vents in favour of propellers and rudders and ailerons.

The present invention, which relates to vehicles comprising air cushions of the type comprising a lifting arrangement formed in particular by air cushions supplied with pressurized air through the intermediary of a diffusion chamber compartmentalized longitudinally in order to define two lateral chambers on either side of the longitudinal axis of the vehicle and a platform supported by this arrangement provides a solution to this problem of manoeuvrability by proposing providing said vehicles comprising air cushions with at least four vents emerging outside the vehicle and arranged in pairs respectively at the front and rear of the vehicle and symmetrically with respect to the longitudinal axis of the latter, each of the vents being supplied by withdrawing air from one of two lateral chambers defined by the partitioning of the diffusion chamber and said vents ejecting the air in a direction having at least one component directed from the lateral withdrawal region towards the opposite lateral region.

According to a first embodiment, the four vents are arranged so that their outlet sections are substantially in facing relationship in pairs respectively at the front and rear of the vehicle.

According to a second embodiment, two vents are arranged laterally on the vehicle and eject air towards the outside of the latter.

As will be described in more detail in the following description, the effect of the vents corresponding to the previously described arrangement of the present invention, is divided into two elements. The first element or direct effect is proportional to the quantity of movement of the jet of air from the vent, whereas the second element or secondary effect is in turn divided into two components, one corresponding to the creation of a jet reaction and the other to hydrodynamic drag, when manoeuvring on water, due to tilting of the vehicle. This secondary effect is a function of the flow of air withdrawn from the lifting arrangement and thus of the number of vents used and of the characteristics of the latter.

Further advantages and characteristics of the present invention and in particular the special arrangement of the different vents, will become apparent on reading the ensuing detailed description referring to the accompanying drawings given as non-limiting examples and in which: Figure l is a cross-sectional view of a vehicle comprising air cushions according to the present invention, along a section plane passing in the vicinity of the vents and showing diagrammatically the direct effect and the reaction effect of the jet due to the vents, Figures 2 and 3 are respectively a cross-sectional view and a plan view of a vehicle comprising air cushions, illustrating diagrammatically the hydrodynamic effect due to tilting of the vehicle, Figure 4 is a diagrammatic plan view of a vehicle comprising air cushions, according to a particular embodiment of the present invention, Figures 5 and 6 are a diagrammatic plan view and a view along the section plane bearing the reference VII-VII in Figure 5 of a vehicle comprising air cushions according to another embodiment of the present invention.

The vehicle comprising air cushions illustrated in the various drawings comprises a platform G sup ported by air cushions defined by flexible skirts, this type of cushion being well known per se. Two fans V shown diagrammatically in the drawings are arranged symmetrically on either side of the longitudinal axis A-A of the vehicle comprising air cushions and supply the lifting arrangement located below the platform G with pressurized air. For vehicles comprising air cushions which strictly speaking do not have a longitudinal axis, such as vehicles comprising air cushions formed by a structure having a substantially circular horizontal section, the term longitudinal axis A-A will be understood to mean an axis passing through the centre of the vehicle comprising air cushions and parallel to the direction of travel of the latter.

The lifting arrangement comprises a diffusion chamber D located just below the platform G and defined by a wall p in its lower and side portions.

This diffusion chamber which receives the pressurized air from the fans V supplies the various air cushions directly or indirectly.

According to a particularly advantageous embodiment, such as that which will be described in more detail in the following description, the diffusion chamber D is partitioned longitudinally by means of a vertical partition 13 dividing this diffusion chamber D into two separate lateral regions, on either side of the longitudinal axis A-A of the vehicle comprising air cushions.

According to an equally known embodiment, the air cushions are formed by a central enclosure 100 and a peripheral arrangement formed by a juxtaposition of cells C. Each of these cells C is constituted by a lobe (forming part of the outerwall on the vehicle) which surrounds a partitioned skirt F laterally.

The improvements provided by the presentinven- tion will now be described and in particular the method of supplying the vents and the effects induced by the latter, as well as various advantageous arrangements. The vents EV according to the present invention are supplied by withdrawing pressurized air from one of two lateral regions of the diffusion chamber D of the vehicle defined on either side of the longitudinal axis A-A of the vehicle comprising air cushions, as shown in Figure 1.

Since the circulation of air has been shown diagrammatically by various arrows in thin line in the drawings, it is apparent that the vents EV eject air in a direction having at least one component directed from the lateral withdrawal region towards the opposite region. Thus, according to the embodiment illustrated in Figure 1, the vent EVG shown on the left of the drawing withdraws air from the left-hand lateral region of the diffusion chamber D of the vehicle comprising air cushions and ejects air towards the right-hand lateral region ofthevehicle, or towards the region opposite the withdrawal region.

The air is directed from the withdrawal region of the diffusion chamber D as far as the outlet orifice of the vents EV by means of pipes 10 of suitable shape and cross-section. The section of passage of the air in the pipes 10 is controlled by means of flaps 12 shown diagrammatically in the drawings, which are controlled from the pilot's station on the vehicle comprising air cushions.

The various effects due to the vents will now be described in more detail.

The first effect or direct effect produces a force (F(EV)) proportional to the quantity of movement of the jet of air from the vent, this force (F(EV)) is shown diagrammatically in the drawings by the arrow drawn in thick line bearing the reference F(EV), this force (F(EV)) is directed in opposition to the jet of air ejected through the vent, its value may be determined by the following relationship: F(EV) = 2.k.S.P(EV) in which k designates the coefficient of contraction of the outlet of the jet from the vent EV, S designates the outlet section of the vent, P(EV) designates the relative pressure of the air at the outlet of the vent EV.

For a given air pressure in air cushions, the geometry of the pipes 10 and of the ejection orifices of the vents EV will be easily determined in order to obtain a rate of flow and ejection speed providing a suitable quantity of movement of the jet of air.

Furthermore, as can be seen from Figure 1, the withdrawal of airfrom the lifting arrangement brings about tilting of the machine which causes dissymetry of the escape flow of air and of the flying height at the periphery of the air cushions. This second effect on the one hand causes the creation of a jet reaction and on the other hand the creation of hydrodynamic drag on water or ground friction.

The value of the force F(R) due to the jet reaction may be determined by the following relationship: F(R) = 2k'. (h2L2p2-h1L1p1) in which K' designates the coefficient of contraction of the air at the foot of the skirts, h designates the flying height of the skirts, Ldesignatesthe length of the cushion, p the relative pressure of the air at the outlet of the skirts, the indices 1 and 2 being respectively assigned to the side where the air for the vent is withdrawn and to the opposite side, as shown clearly in Figure 1.

This force (F(R)) due to the jet reaction is illustrated diagrammatically in Figure 1 by the arrow drawn in thick line bearing the reference (F(R)), this force is directed in opposition to the jet of air escaping from the bottom of the skirts on the higher side of the vehicle comprising air cushions.

It will be understood that the special arrangement of the vents EV according to the present invention, consisting of ejecting airfrom the vents in a direction starting from the withdrawal side towards the opposite edge makes it possible to obtain a force (F(EV)) due to the direct effect and a force (F(R)) due to the jet reaction which have the same direction, thus their effects are added together, which makes it possible to achieve maximum efficiency of the vents. Furthermore, as shown diagrammatically by the cross ruled region in Figures 2 and 3, the tilting of the machine due to the withdrawal of air from the lifting arrangement causes a difference in drag at the bottom of the skirts between the left-hand side and the right-hand side of the vehicle comprising air cushions, when manoeuvring on water.The value of the force T shown diagrammatically in the drawings by the arrow drawn in thick line bearing the reference T and due to this difference in drag (T1-T2) on either side of the longitudinal axis A-A may be expressed by a simplified relationship of the form T = T1 - T2 = k"V2L (h2 - h) in which the indices 1 and 2 correspond, as previously, respectively to the side where the air for the vent is withdrawn and to the opposite side, k" corresponds to the coefficient of friction and V corresponds to the speed of movement of the vehicle comprising air cushions on land or on water.Consequently, it will be understood that the resultant force T of this difference in drag at the bottom of the skirts, illustrated diagrammatically by the arrow drawn in thick line bearing the reference Tin Figure 3, causes a rocking momentum Mwith respect to the centre of gravity of the machine. Thus, the two secondary effects, the jet reaction (F(R)) and the hydrodynamic drag (T), induced by the tilting of the cushion, increase the efficiency of the direct effect (F(EV)) of the vent EV.

The arrangement of the ejection orifices, outside the machine, is determined with respect to the centre of gravity of the vehicle in order to induce a system of forces and momentum suitable for controlling the manoeuvrability of the machine.

The various arrangements of the vents EV according to the present invention will now be described in more detail in particular with reference to Figures 4 to6.

Figure 4 shows a first embodiment of a vehicle comprising air cushions according to the present invention, comprising four vents EV arranged in pairs respectively at the front (EVAVG and EVAVD) and at the rear (EVARG and EVARD) of the vehicle comprising air cushions, on either side of the longitudinal axis A-A and whereof the outlet sections are respectively substantially in facing relationship. The various pipes 10 supplying the vents of the vehicle have not been shown in this drawing, but it should naturally be considered that these pipes 10 withdraw pressurized air from a lateral part of the diffusion chamber D of the vehicle comprising air cushions and direct this pressurized air to the outlet orifice of the vents EV which eject the air in a direction having at least one component directed from the lateral withdrawal region towards the opposite region.

Thus, according to the embodiment illustrated in this Figure 4, the vents (EVAVG and EVARG) located on the left-hand side of the vehicle are supplied by with drawing air from the left-hand lateral region of the diffusion chamber D and eject the air towards the right-hand side of the vehicle and conversely; furthermore, the vents arranged in pairs at the front (EVAVG,EVAVD) and at the rear (EVARG,EVARD) of the vehicle eject the air substantially in the direction of their counterpart since their sections are in facing relationship in pairs.

Furthermore, as can be seen from Figures 1 and 2, each of the two vents (EVAVG,EVAVD) located at the front of a vehicle comprising air cushions ejects air in such a manner as to direct the jet above the vent located in facing relationship so as to prevent blocking of the jet by the latter. Similarly, in order to prevent blocking of the jet of air emitted by one of the rear vents (EVARG,EVARD) by the vent which is symmetrical with respect thereto, each of the latter will be arranged so that the jet of air emitted has at least one component directed towards the rear of the vehicle comprising air cushions.

On the other hand, it will be noted that in the configuration of crossed vents, the force created by the ejection of air at the outlet of a vent (EVAVG, EVAVD) induces a transverse momentum which tends to tilt the cushion further and which amplifies the secondary effects described above.

The use of one of these four front vents (EVAVG, EVAVD) or rear vents (EVARG, EVARD) makes it possible to create a lateral force and a momentum with respect to the centre of gravity of the vehicle comprising air cushions. The use of two lateral vents (EVAVG and EVARG, OR EVAVD and EVARD) makes it possible to create essentially a lateral force, which is particularly advantageous at the time of a lateral approach of the vehicle, for example with respect to a quay.

In addition, where two lateral vents are used (EVAVG and EVARG, or EVAVD and EVARD) located on the same side of the vehicle and ejecting in the same direction in order to create a lateral or transverse resultant force which corresponds to the sum of the direct effects of the vents and of the jet reaction of each of said front and rear vents, the drag T is exerted on the side where the air is withdrawn in order to supply the two vents and thus creates a rocking momentum tending to rotate the machine towards this withdrawal edge. Thus, the resulting system of the transverse forces and of the rocking momentum tends to move the machine diagonally; this effect may be used for steering the vehicle against the wind or on a slope, which is the desired aim in most cases.

The use of two vents arranged diagonally (EVAVG and EVARD, or EVAVD and EVARG) essentially allows the creation of a momentum used for example in order to effect a change of direction of the vehicle through 180 . On the contrary, the use of four vents allows deflation of the lifting system and controlled friction of the skirts on the ground by creating a force of adhesion on the latter, without it being necessary to interfere with the normal running of the fans.

Furthermore, with the anchoring to the ground obtained in this way, the possibilities of use of conventional propellers and rudders are preserved and increased even substantially.

Finally, Figures 5 and 6 show a second embodiment according to the present invention, in which two vents (EVAVG and EVAVD) are arranged laterally on the outside of the vehicle comprising air cushions and at the front of the latter. Each of these two vents ejects pressurized air towards the outside of this vehicle comprising air cushions, in a direction opposed to the region for withdrawing air in the diffusion chamber D. Two other vents (EVARG and EVARD) are located at the rear of the vehicle, on either side of the longitudinal axis A-A and eject air in a manner similar to the two rear vents shown in Figure 4.

Figure 6 shows diagrammatically the pipes 10 which withdraw air from the diffusion chamber D of the vehicle comprising air cushions and convey the latter to the front vents (EVAVG and EVAvo). Thus, the vent (EVAVD) shown on the right of the vehicle is supplied with pressurized air by the pipe 10 which withdraws the air from the left-hand part of the diffusion chamber D and vice versa. This vent (EVAVD) shown on the right of the drawing ejects air towards the right of the vehicle comprising air cushions, namely in a direction starting from the (left-hand) lateral region for withdrawing air towards the (right-hand) opposite lateral region.

The use of one ofthesefourfrontvents (EVAVG or EVvo) or rear vents (EVARG or EVARD) makes it possible to create a momentum with respect to the centre of gravity of the vehicle. The use of two lateral vents (EVAVG and EVARG or EVAVD and EVARD) allows the creation essentially of a momentum which can be used for example for carrying out a rotation of the vehicle comprising air cushions corresponding to a substantial change of direction of the latter. The use of two vents located diagonally (EVAVG and EVARD or EVAVD and EVARG) makes it possible to create a lateral force. Finally, the use of four vents allows deflation of the air cushions and controlled friction of the skirts as has been described previously.

It will be noted that in the case of a diffusion chamber partitioned longitudinally by means of a vertical partition 13, as has been described previously, the action on the air cushions is considerable and the tilting effect is accentuated. In fact, the air supplying the vents is withdrawn from the lifting air of a lateral compartment, thus in the case of operation of the vent, the air remaining for the lift of the corresponding side is slight and tilting of the apparatus is all the greater. Thus, the two secondary effects, the jet reaction (F(R)) and the hydrodynamic drag (T) are increased.

Furthermore, it should be noted that the air used for the operation of the vents EV is taken from the diffusion chamber D of the vehicle, when the latter is travelling at low speed, which is consequently in no way troublesome.

The arrangement of the ejection orifices, the air pressure in the cushions as well as the geometry of the pipes 10 and of the said ejection orifices will be easily determined as a function of the rate of flow and ejection speed, thus of the quantity of movement of the jet desired in order to determine, with respect to the centre of gravity of the vehicle, a system of forces and momentum suitable for con tolling the latter.

In the case of a breakdown of a conventional lateral propeller, the thrust of the remaining propellers creates a troublesome considerable rocking momentum. This momentum may be advantageously counter-balanced within the scope of the present invention by the use of the vents in the configuration producing a momentum, either by using one vent ortwo vents located diagonally according to the embodiment of Figure 4, one vent or two lateral vents according to the embodiment of Figures 5 and 6.

Furthermore, said vents EV can be used in order to create leakages of air in the lifting arrangement for the purpose of reducing variations of the output of the fans flying on waves and thus to reduce the pressure variations in the air cushions in order to reduce vertical accelerations.

In this case, the air ejected by the vents may be orientated towards the rear in order to recover the quantity of movement for increasing the propulsion force. For this purpose, a device for orientating the jet could be located at the outlet of the vents.

It will thus be understood that the present invention facilitates any manoeuvres whether on the ground into the wind or with a slope, or on water and this is even for approaches and movements in a very restricted and cluttered space and in the case of a breakdown.

Tests have shown that for vehicles comprising air cushions provided for example with four vents EV according to those illustrated in Figure 4, the use of two of the latter located on the same side of the machine (EVAVG and EVARG or EVAVD and EVARD) makes it possible to achieve a force equal to approximately 1% of the weight of the machine for an output, in the two vents, representing approximately half the total output of the fans.

Naturally, the present invention is not limited to the embodiments which have been described, based on which other forms and methods of construction can be provided without diverging from the scope of the present invention.

Claims

1. Avehicle comprising air cushions ofthetype having a lifting arrangement formed in particular by air cushions supplied with pressurized air by the intermediary of a diffusion chamber partitioned longitudinally in orderto define two lateral chambers on either side of the longitudinal axis of the vehicle, a platform supported by this arrangement, characterised in that the means for controlling steering comprises at least four vents emerging outside the vehicle and arranged in pairs respectively at the front and rear of the vehicle and symmetrically with respect to the longitudinal axis of the latter, by the fact that each of the vents is supplied by withdrawing air from one of two lateral chambers defined by partitioning the diffusion chamber and by the fact that the said vents eject air in a direction having at least one component directed from the lateral withdrawal region towards the opposite lateral region.

2. A vehicle comprising air cushions according to claim 1, characterised by the fact that the four vents are arranged so that their outlet sections are substantially in facing relationship in pairs respectively at the front and at the rear of the vehicle.

3. A vehicle comprising air cushions according to claim 1, characterised by the fact that two vents are arranged laterally on the vehicle and eject air towards the outside of the latter.