US 3513933 A
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May 26, 1970 M. H. J. FAURE 3,513,933
MULTISKIRT GROUND EFFECT MACHINE Filed July 24, 1968 2 Sheets-Sheet 1 Fig.1
y 6, 1970 M. H. J. FAURE 3,513,933
MULTISKIRT GROUND EFFECT MACHINE Filed July 24, 1968 2 Sheets-Sheet 2 United States Patent Office 3,513,933 Patented May 26, 1970 3,513,933 MULTISKIRT GROUND EFFECT MACHINE Marc Henri Jean Faure, Saint-Maur-des-Fosses, France, assignor to Societe dEtudes et de Developpement des Aeroglisseurs Marins, S.E.D.A.M., Paris, France, a company of France Filed July 24, 1968, Ser. No. 747,217 Claims priority, appliizitiogggrance, July 27, 1967,
Int. (:1. B60v 1/16 US. Cl. 180-121 Claims ABSTRACT OF THE DISCLOSURE An air cushion vehicle comprising a movable skirtcarrier structure highly permeable to cushion supply fluid and connected to a rigid platform through a resilient suspension system which is immersed in the cushion fluid and designed for taking only a minor fraction (say, 5 to of the load, the major part being transmitted directly by cushion pressure to said platform owing to the high permeability of said skirt-carrier structure.
The present invention relates more particularly to a ground-effect machine of this kind, comprising at least one inner skirt bounding a central cushion and at least one outer skirt bounding a peripheral cushion, the latter being conveniently subdivided into a number of fragmentary cushions by partitions extending between the inner skirt and the outer skirt and which may be themselves stability skirts engaging more or less tangentially said inner and outer skirts.
With such vehicles, some difficulties are met which are due to the formation of a sort of tore-shaped vortex within a cushion, this tore-shaped vortex creating a vacuum zone in the latter and as a result a substantial decrease in the lift efficiency of the machine.
The troublesome influence of this tore-shaped vortex has been evidenced by Edwin E. Davenport in a technical note published in April 1961 by the N.A.S.A., No. D756, entitled Effects of geometric variations on lift augmentation of simple-plenum-chamber ground-effect models.
One of the objects of the present invention is to combat this detrimental phenomenon by the removal or at least the substantial reduction of this tore-shaped vortex.
Another object of the present invention is to decrease the apparent stiffness and the proper frequency of the vehicle in order to improve its dynamic stability characteristics, on account of the achievement of a negative variation ratio of cushion volume and pressure.
The present invention also allows decreasing the vertical accelerations to which the structure of the vehicle would be subjected upon displacements over uneven ground or waves.
It does this without transmissions and supply pipes, which simplifies the mechanic and aerodynamic design of the machine.
In accordance with the present invention, the ground effect machine comprises a movable skirt-carrier structure which is highly permeable to the cushion supply fluid and which is connected through a resilient suspension to a rigid part of the machine such as a platform, this resilient suspension, immersed in the cushion fluid, being designed for transmitting only a minor fraction of the load, most of which is transmitted directed by cushion pressure to said rigid part owing to the high permeability of said skirt-carrier structure.
In the accompanying drawings:
FIG. 1 is a schematic vertical section of a vehicle according to the present invention, taken along line I-I of FIG. 2;
FIG. 2 is a plan view of it from beneath;
FIG. 3 is a similar view showing a detail of the supply system;
FIG. 4 is a larger scale fragmentary section taken along line IVIV of FIG. 3;
FIG. 5 is a very schematic plan view of an embodiment with multilobed skirts.
The vehicle illustrated on FIGS. 1 to 4 comprises two frustocom'cal concentric skirts 1, 2 of flexible material having a bottom skirt diameter ratio in the range of 0.6 to 0.8, the taper of the outer skirt 1 being in excess of 10 to 20 compared with that of the inner skirt 2. Between these two concentric skirts 1 and 2, a number of skirts 3named stability skirts--extend radially; they are conical, with a 5 to 10 taper, of oblique axis, tangent to but not fast with the two concentric skirts 1-2. A minimum of three stability skirts 3 are required and there are six of them in the illustrated embodiment.
All these skirts 1-2-3 are hooked at their top to a light structure 4 which may be tubular. This assembly of skirts and structure has for instance a mass comprised between 4 and 8% of the total mass of the vehicle.
A flexible inverted conical side-wall connects the outer circle 6 of the skirt-carrier structure 4 to the underface 7 of the vehicle structure properly speaking or platform 8, along a circle 9 which has a diameter 0.8 to 0.9 time that of circle 6 at the top of the outer skirts 1.
The skirt-carrier structure 4 is also connected to platform 8 through a resilient system 10 'which acts under compression and takes between 5 and 15% of the weight of the vehicle. The resiliency is determined so that the ratio between the daylight clearance h of the inner skirt 2 with respect to the ground and the height of the passage 11 between circle 12 which carries the inner skirt 2 and the underface 7 of platform 8, remains substantially constant irrespective of the load of the vehicle. The resilient suspension 10 between the skirt-carrier structure 4 and the platform 8 may be supplemented by hydraulic, pneumatic or friction damping devices, as described in US. specification No. 3,339,657.
Lift air discharged by one or more generators 13 flows directly into the central compartment 14 bounded by the vehicle underface 7 and the wall of the inner skirt 2. In order to facilitate supply of the stability skirts 3, flexible ducts 15 (FIG. 3) tap fluid from central compartment 14 towards these skirts 3.
A distribution grate 16 is fitted under the central subplenum 17 so that the flow is shared in conformity with a preselected law between the central compartment 14 and the peripheral compartments 18 bounded by the outer skirt 1, the inner skirt 2 and the stability skirts 3.
This grate 16 is conveniently fast with the skirt-carrier structure 4 and its displacement thereby gives rise to vibration damping by friction of air through its mesh.
Grate 16 has been illustrated as extending only above the central plenum chamber 14. It may however be extended so as to overlap also some or all of the peripheral 3 plenum chambers 18, with the exclusion of the stability skirts 3.
Small spaced stops 19 are fitted under the underface 7 of platform 8 for abutting circle 12 which carries inner skirt 2, in order that, at maximum load when the daylight clearance is nil, there always remains a passage from central compartment 14 towards peripheral compartments 18 and stability skirts 3: this passage will be about of the normal value at stabilised running.
During this stabilised running at normal load, the generator(s) 13 feed space 17 bounded by the underface 7 of platform 8 on the one hand, distribution grate 16 on the other hand, and lastly throttle 11 formed between the circle 12 of skirt 2 and the platform underface 7. In this sub-plenum 17 is obtained a static pressure to which conventional value 1 is attributed. In the lower central compartment 14, static pressure will then be about 0.9 because of the loss of head due to distribution grate 16, whereas pressure within the stability skirts 3 will reach 0.6 to 0.7 and within the peripheral compartments 18 it will be 0.5 to 0.6.
It is apparent that the flow from central compartment 17-14 enters peripheral compartments 18 both through the upper passage 11 and through the clearance h between the bottom of inner skirt 2 and the ground: this double circulation antagonizes formation of the detrimental toreshaped vortex mentioned above in the introduction.
Besides, a member 21 (see FIGS. 3 and 4) protruding from platform underface 7 extends around inner skirt 2 (except on the portions registering with the stability skirts 3 and their supply duct 15), enables the designer to define easily the desired law of variation of the air passage area for the peripheral plenum chambers 18 as a function of the displacement of the skirt-carrier structure 4. This law will be such that the sum of the lower and upper passage areas (cf. arrows f1 and f2) between the central plenum chamber and the peripheral ones will be equal to 1 to 3 times the passage area (cf. arrow f3) between the latter and the ambient medium.
If the load of the vehicle is doubled, there will be obtained roughly a pressure of 2 in the upper central compartment 17, of 1.9 in the lower central compartment 14, of 1.2 to 1.4 in the stability skirts 3 and of 1 to 1.2 in the peripheral compartments 18. The daylight clearance h will decrease according to the characteristics of the air generator(s) 13, but the hoverheight D of platform 8 above the ground will decrease much more (2 to times) by crushing of the resilient system 10 which will go on supporting 5 to of the load. Thus two of the results set forth in the introduction will be obtained:
Cushion volume decrease when pressure increases, due to closing up of skirt-carrier structure 4 and platform 8;
Efiicient suspension of the whole vehicle, although the resilient system 10 only takes a minor percentage of the load.
This last feature constitutes one of the basic characteristics of the present invention. It derives from the fact that the skirt-carrier structure 4 and the distribution grate 16 are highly permeable to the cushion supply fluid discharged by the fan(s) 13, so that the resilient suspension system 10 interposed between the movable structure 4 and the rigid platform 8 is immersed in cushion fluid, and cushion pressure, disregarding small losses of head, applies directly to the underface 7 of platform 8. The situation would of course have been quite different, had the skirtcarrier structure 4 been a fluidtight closure for the cushions, subjected to their pressure and transmitting the resultant effort to platform 8 through the resilient suspension system 10 which would then be exposed to open air, as in the case of the devices described in the last mentioned specification, wherein the suspension system takes practically the whole load.
Quiet to the contrary, suspension 10 of the device of the invention only takes, as stated, a minor fraction of the load about 5 to 15%.
In addition, it reduces the stiffness and the proper frequency of the vehicles, as well as the vertical accelerations on waves and uneven ground.
If the vehicle tilts, pitch and roll stability is ensured by pressure increase in the peripheral compartments 18 getting closer to the ground and pressure decrease in those moving away therefrom. Thanks to the resilient system 10, the slant of the vehicle platform 8 is from 2 to 5 times larger than that of the bottom plane of the skirts. Therefore the attitude changes of the vehicle on uneven ground will be smaller than the changes in slope of the ground.
Computations and tests carried out show that the vehicle can take centering variations of 4 to 6% of its dimensions before the outer skirt 1 engages the ground, these values rising to 15 to 20% before the vehicle collapses on one side.
In the embodiment of FIGS. 1 to 4, the case has been considered of a generally disc-shaped vehicle with skirts of circular planform. In the case of elongated vehicles, the invention is applicable without difliculty.
Thus, FIG. 5 shows the skirt-carrier structure 4" of an elongated vehicle with multilobed skirts having flexible planar sheets 20 separating the various lobes. If the number of sheets 20 is important, it is possible to do without stability skirts 3 or to reduce their number, the partitioning between the inner skirt 2 and the outer skirt 1 being then sufficient to ensure pitch and roll stability of the vehicle.
1. A multicushion ground effect machine having a platform or like rigid portion designed to hover above a supporting surface with the interposition of pressure fluid cushions, comprising a movable structure highly permeable to cushion fluid extending under said platform in spaced relationship and defining therewith a supply manifold, a plurality of cushion containing skirts depending from said movable structure and carried thereby, the space bounded by said skirts communicating directly with said manifold through said highly permeable structure, cushion pressure fluid generating means discharging into said manifold, and a resilient suspension system extending between said platform and said skirtcarrier structure, inside said supply manifold and immersed in pressure fluid, said resilient suspension system being designed for taking only a minor fractionof the weight of the machine and transmitting the same to said platform while the major part of said weight is transmitted directly to said platform by cushion pressure exerted thereon through said highly p ermeable skirtcarrier structure.
2. Machine as claimed in claim 1, wherein said cushion containing skirts comprise at least one inner skirt adpated for containing a central cushion, at least one outer skirt adapted for containing a peripheral cushion, and partition means extending between said inner and outer skirts for subdividing said peripheral cushion into a plurality of fragmentary cushions.
3. Machine as claimed in claim 2, wherein said partition means comprises at least one stability skirt engaging substantially tangentially said inner and outer skirts.
4. Machine as claimed in claim 2, further comprising a fluid distribution grate extending across the communication between said supply manifold and the space bounded by said inner skirt.
5. Machine as claimed in claim 4, wherein said distribution grate is fast with said movable skirt-carrier structure.
6. Machine as claimed in claim 4, wherein said distribution grate extends over at least some of the fragmentary peripheral cushions.
7. Machine as claimed in claim 1, further comprising spacer means interposed between said platform and said skirt-carrier structure for limiting the stroke of said skirtcarrier structure towards said platform, whereby said supply manifold has a width which cannot decrease beyond a minimum value.
8. Machine as claimed in claim 1, wherein said skirtcarrier structure comprises a light-weight frame made of tubular sections.
9. Machine as claimed in claim 1, further comprising shaped protrusions extending from said platform and cooperating with said movable skirt-carrier structure, to define therewith variable-area passages in said supply manifold, as said skirt carrier structure moves relatively to said platform.
10. Machine as claimed in claim 1, wherein said resilient suspension system is designed for taking from about 5% to about 15% of the total weight of the machine.
6 References Cited UNITED STATES PATENTS A. HARRY LEVY, Primary Examiner US. Cl. X.R.