US3362494A - Ground effect machine wherein a constant air velocity is maintained in the duct from fan outlet to peripheral nozzle - Google Patents

Description

Jan. 1968 G. D. BOEHLER ETAL 3,362,494

GROUND EFFECT MACHINE WHEREIN A CONSTANT AIR VELOCITY I5 MAINTAINED IN THE DUCT FROM FAN OUTLET TO PERIPHERAL NOZZLE Filed Dec. 29, 1964 3 Sheets-Sheet 1 IN VE N TOR S, GABE/EL 0. 505/11. 5,? W/LL/AMF [OS/$46 mi/M, 54, 14 fwd/M ATTORNEYS INVENTORS,

ATTORNEYS 3,362,494 OCITY 1s BOEHLER ETAL 3 Sheets-Sheet 2 TO PERIPHERAL NOZZLE G. GROUND EFFECT MACHINE WHEREIN A CONSTANT AIR VEL MAINTAINED IN THE DUCT FROM FAN OUTLET Jan. 9, 1968 Filed Dec. 29, 1964 968 G. D. BOEHLER ETAL ,3

GROUND EFFECT MACHINE WHEREIN A CONSTANT AIR VELOCITY IS MAINTAINED IN THE DUCT FROM FAN OUTLET TO PERIPHERAL NOZZLE Filed Dec. 29, 1964 5 Sheets-Sheet 3 .o X m w 5 Wu. mm Mme M 0 w W M /m m m M firm 0 W B H w M Wm M m mm W ,w, m 1 m 4 T R Q y /A\)0 m m 1 w iwm n MJYFWN/B United States Patent ()fiice 3 ,352,494 Patented Jan. 9, 1968 GROUND EFFECT MACHINE WHEREIN A CON- STANT AIR VELOCITY IS MAINTAINED IN THE DUCT FROM FAN OUTLET T PERIPHERAL NOZZLE Gabriel ll). Boehler and William F. Foshag, Washington, D.C., assignors to Aerophysics Company, Washington, D.C., a corporation of the District of Columbia Filed Dec. 29, 1964, Ser. No. 421,878 14 Claims. (Cl. 180-7) ABSTRACT OF THE DISCLOSURE A ground effect machine in which a centrifugal fan is located centrally within a hollow body. The body defines a downwardly directed air discharge nozzle and an outwardly extending air passage establishing communication between the fan and the discharge nozzle. Air flow control vanes are disposed in the discharge nozzle with the lower ends of the vanes in vertical planes and the upper end portions thereof extending in angular relation to the lower ends and substantially parallel to the direction of air flow. The axial dimensions of the air passage decrease progressively in a radially outward direction from the fan at a rate to maintain the cross sectional area of said passage constant at all radial loctions, whereby to maintain the velocity of the air flow through the body until it is discharged downwardly from the body.

This invention relates to improvements in ground effect machines and more particularly to improvements in the means for supplying and maintaining the supporting air cushion of such a machine.

The type of vehicle referred to as a ground effect machine comprises a hollow body adapted to float on a cushion of air a short distance above the ground surface or a body of water and is provided with a power driven air impelling device such as a fan or compressor capable of forcing a sufficient quantity of air into the air cushion to support the body at its operational level above the supporting surface.

Among the major advantages of a ground effect machine is its ability to float at low altitudes on an air cushion, the creation and maintenance of which requires but a small fraction of the power that would be required to fly a vehicle of the same weight.

Ground effect machines have developed into several different types, of which the two principal types are the plenum chamber type and the peripheral jet type. The plenum chamber type involves a pneumatic body having a large internal cavity into which atmospheric air is forced by the fluid motor device, and in which the air when released becomes stabilized, converting energy of velocity or dynamic head incident to its being forced into the body into static pressure in the body cavity or plenum chamber. This static pressure raises the body above the supporting surface permitting the air to discharge under the lower peripheral edge of the body or under a flexible skirt depending from the lower edge of the body.

The peripheral jet type of machine, to which the present invention relates, comprises a hollow body carrying power driven air delivering or impelling mechanism and having internal duct formations which direct the air into a downwardly directed jet which is of generally tubular conformation in plan extending around the lower peripheral edge portion of the body. The body may, if desired, be extended downwardly by a depending flexible skirt. In this type of machine, it is desirable to deliver the air into the body with a predetermined velocity energy and to maintain the velocity of the air flow through the body until it is discharged downwardly through the peripheral jet nozzle or nozzles.

In ground effect machines as heretofore known, air is delivered from the fan to the duct by means of a delivery passage or duct which also serves as an air diffuser. Diffusion is necessary to convert into pressure the high velocity kinetic energy of the flow from the fan discharge,

No such means has been devised to date to permit efficient diffusion, or in other words diffusion without material loss of energy. Diffusion losses are a main cause of reduced efiiciency of internal flow in ground effect machines.

Accordingly, a primary object of the invention is to incorporate into the internal flow system of the ground effect machine a radial delivery fan incorporating a diffuser which rotates with the fan in a manner to achieve the desired degree of diffusion of the air as it leaves the fan, such efficiency arising in large part because it takes place in the presence of a centrifugal field which creates a favorable pressure gradient so that the boundary layers adjacent the diffuser surfaces thin out rather than thickening incident to their radial outward movement.

It is a further object of the invention to achieve and maintain a maximum air pressure within the supporting cushion for a given power input. This is achieved by minimizing the reduction of the static air pressure of the air during its transmission from the fluid motor device to the cushion, by a novel formation of the air passage or conduit leading from the fan or impeller to the peripheral nozzle. Thus the said air passage is formed to minimize the diffusion of air between the centrally located fan or impeller and the discharge nozzle which surrounds and is spaced outwardly from the fan. This is done by decreasing the axial thickness of the encircling air passage as the dis-- tance from the rotational axis of the fan or impeller increases and in a manner to maintain the cross-sectional area of any given sector of said passage substantially constant at all radial distances from said axis.

It is a still further important object to minimize the rate of discharge of air from the cushion outwardly beneath the lower peripheral edge of the vehicle body, by removing from the air flow through the peripheral nozzle, the tangential or swirling flow components irnparted thereto by the rotating fan or impeller and such as would, if present, tend to effect a tangential outward flow of the air from beneath the lower peripheral edge of the vehicle skirt. Thus the nozzle functions to direct the air jet downwardly in a flow path, substantially all portions of which are either parallel to or, if desired, somewhat downwardly convergent with respect to the rotational axis of the impeller. In accordance with the invention, therefore, the downwardly directed jet tends to concentrate and maintain the pressurized cushion of air beneath the body while also contributing to the lifting effect on the body through the upward reaction of the air jet.

It is a further important object of the invention to provide flow controllers in a ground effect machine of the peripheral jet type here involved, for making possible the efficient utilization of peripheral jets or nozzles of other than circular shape in plan.

It is a further object to so position a flexible confining skirt at the outer edges of and contiguous to the peripherally arranged outlet nozzle so that the air issuing from the nozzle will, because of its viscosity, tend to adhere to and follow a downward path defined by the skirt, the flexible skirt serving in known manner to support the rigid body structure of the device at an increased elevation above the supporting surface and enabling it more easily to ride over and clear irregularities in such surface.

Still further objects and advantages will be made apparent by consideration of the following description and the appended claims in conjunction with the accompany ing drawings, in which:

FIGURE 1 is a top plan view of a ground effect machine illustrative of the invention.

FIGURE 2 is an enlarged diametrical cross-sectional view substantially on a plane indicated by the line 22 of FIGURE 1.

FIGURE 3 is a circumferential cross-sectional view substantially on a plane indicated by the line 33 of FIGURE 2.

FIGURE 4 is a fragmentary cross-sectional view substantially on a plane indicated by the line 4-4 of FIGURE 3.

FIGURE 5 is a cross-sectional view similar to FIGURE 2 but showing the device in operative condition with a depending flexible skirt attached.

FIGURE 6 is a top plan view of a compound vehicle supported by a plurality of ground effect machine units as shown in FIGURES 1 to 4 inclusive.

FIGURE 7 is a side elevational view of the vehicle shown in FIGURE 6.

FIGURE 8 is a top plan view of a somewhat modified form of ground effect machine.

FIGURE 9 is a transverse cross-sectional view substantially on a plane indicated by the line 99 of FIGURE 8.

FIGURE 10 is a cross-sectional View substantially on a plane indicated by the line 10-10 of FIGURE 9, and

FIGURE 11 is a fragmentary cross-sectional view substantially on a plane indicated by the line 1l-11 :of FIGURE 10.

With continued reference to the drawings, the form of device shown in FIGURES 1 to 5 inclusive has a circular or annular body, generally indicated at 20, including an outer wall 21 having an annular depending skirt 22 of generally cylindrical shape and a flat top portion 23 joined to the upper edge of the annular portion by a suitable annular fillet. This outer wall is of strong, light weight construction and may be provided as a thin metal stamping or a resin and glass fiber laminate.

The top wall 23 is formed to define a concentric circular opening 24 surrounded by an upstanding annular spider rim 25 which, together with the opening 24, defines the upwardly opening air intake for the body and is firmly affixed to the top wall 23. The rim 25 may be of a suitable rigid though, if desired, hollow structure, which is preferably filled with a light-weight foam material such as a conventional plastic foam for purposes of reinforcement.

The spider, of which rim 25 is a part, comprises a central hub 26 and angularly spaced arms 27 extending radially from the hub to the rim 24 of the spider to interconnect the rim and hub in concentric relation.

A fan shaft 28 extends vertically through the hub 26 and is rotatably j'ournaled therein by suitable bearing means 29. A conventional power plant such as a gasoline engine (not illustrated) is operatively connected to the upper end of the shaft 28 so that the shaft may function to transmit a rotary driving force from the engine to a fan or impeller of the centrifugal radial flow type such as is generally indicated at 30. It will be seen that the fan is keyed on the shaft at 32 below the hub 26 and top wall 23 and within the hollow interior of the body, which thus functions to define the fan housing.

The fan 30 is of a known radial delivery type employing a rotating diffuser. Such a fan has characteristics which render it particularly usable in the combination illustrated. The fan has a hub 31 of generally frustoconical shape with an annular concave on its outer surface. The hub axially receives and is keyed on the shaft against relative rotation as by means of the key 32. A plurality of generally radial impeller blades 35 are affixed to the hub for rotation therewith at equally spaced angular intervals around the hub. Each blade comprises a thin, substantially, rigid flat vane extending in a radial plane of the hub and having one edge convexly curved at its intersection with the similarly ourved concave surface of the hub to which it is permanently secured. The outer edges of the blades are concavely curved in conformity with the curvature of an annular shroud 36 which surrounds and interconnects the outer ends of all blades. The upper edge of this shroud is rotatably received in an annular groove 36' in the lower face of the spider rim 25, concentrically to the air inlet opening defined by the rim 25. The blades 35 have substantially axially extending outer edges extending from the bottom outer circumference of the hub 31 parallel to the axis of shaft 28 just inwardly of the annular air outlet diffuser opening or port defined by and between the relatively spaced radially outwardly diverging diffuser rings 37 and 38, which in the form shown constitute radial extensions of the shroud 36 and the hub 31 respectively. No discharge scroll is employed with this type .of fan, so that the velocity of the air leaving the fan blades is not materially changed, the air being diffused between the two rotating of the diffuser rings, and discharged both radially and tangentially between the diffuser rings. Such diffusion of air, while subjected to centrifugal action of the rotating diffuser, creates a favorable pressure gradient so that the boundary layers adjacent the diffuser surfaces thin out incident to their outward movement.

The body generally designated 20 may be formed in any suitable manner to define therein the space for housing the fan, as well as the peripheral downwardly directed jet nozzle 42 which surrounds the fan in spaced relation thereto, and the radial air passage or duct P which delivers the air with undiminished velocity from the fan to the nozzle. In the present instance, these several features are defined jointly by the outer shell, consisting of the top wall 23 and rigid skirt 22, in conjunction with a circular plate or diaphragm 40 which is rigidly and concentrically affixed within the body by the flow control blades or members 50 in spaced relation to its top wall 13 and skirt 20. It will be readily apparent that this plate cooperates with the rest of the body in jointly defining a housing for the fan as Well as the radially extending air duct P around the fan to receive the air flowing outwardly from the fan and to deliver same into the downwardly directed jet nozzle 42 which also is jointly defined by the cooperating members. The plate 40 has a preferably smooth flat lower face in the plane of the lower edge of skirt 20 to ride on the air cushion formed therebeneath. The plate 40 is provided with a central opening in which is disposed a thrust bearing 41 in which the reduced diameter lower end portion of shaft 28 is journaled. The outer perpihery of plate 40 is uniformly spaced from the annular skirt 22 to therewith define the annular nozzle 42 through which the downwardly directed annular jet is discharged. It will be noted that the plate 40 is provided with an upwardly presented annular rim or bolster formation 43 extending around its radially outer portion. This rim presents an outer surface 44 of cylindrical shape concentric to the skirt 22. The inwardly converging frustoconical surface 46 of the plate or diaphragm 40 thus cooperates with the lower surface of the flat housing top 23 in defining the annular air passage P surrounding the fan and extending radially outwardly from the fan to the upwardly presented entrance to the encircling peripheral jet nozzle 42. The outwardly converging relationship of the upper and lower surfaces of the air duct or passage thus defined is such that the air passage P has a cross-sectional area which remains substantially uniform at all radial locations between the fan outlet and the discharge nozzle entrance. To put it another way, as the distance outwardly from the fan increases with a consequent increase in circumferential dimension of the passage, the thickness of the passage in an axial direction undergoes a compensating decrease to thus maintain the circumferential crosssectional area of the passage or of any sector thereof, substantially constant at all radial locations between the periphery of the fan and the entrance to the downwardly directed annular nozzle 42.

The nozzle 42 is in effect a continuation, and therefore a portion of the passage P, and its total cross-sectional area will preferably be equal to that of the passage P at any selected radial location of the latter. This characteristic of the air passage P achieves the desired function of maintaining the velocity of the air substantially uniform and undiminished during its movement from the fan into the upwardly directed entrance to the annular nozzle 42 defined between the outer wall 84 of the diaphragm and the skirt wall 22 of outer housing 20. There are no bafiles or guides in the annular air passage P of this embodiment and the surfaces which define said passage are made as smooth as practical to avoid loss of any material portion of the velocity energy of the air by friction, turbulence, compression or expansion.

The diaphragm or plate 40 may obviously be formed of a minimum weight commensurate with the strength required of it, being if desired formed of a substantially rigid and strong outer hollow shell filled and reinforced with a conventional plastic foam.

For eliminating from the outwardly flowing air the tangential or swirling component of flow imparted thereto by the rotating fan or impeller, there are provided a plurality of flow control vanes or air straighteners 50 which are preferably located at substantially equal angular intervals around the annular nozzle 42. These flow control vanes will desirably comprise thin plates of metal or other suitable material capable of being bent or curved to take a permanent set and are curved in a manner such as illustrated in FIGURE 4, with their upper end portions inclined reversely to the rotation of the fan 30 to be disposed parallel to the direction of air flow. From their upper end portions, the blades approach a vertical disposition toward their lower edges, thus to substantially eliminate the tangential component of flow resulting from the swirling action of the air, so that when the air leaves the annular nozzle in the form of an annular jet, it Will be directed downwardly in a substantially vertical direc tion, or if desired may have a slight inward inclination toward the rotational axis of the fan. In any event, elimination of the swirling or circling motion of the air, and thus of its tangential flow component, will eliminate any tendency of the air to escape from the air cushion beneath the vehicle because of any component of motion existing therein at the time of its discharge from the annular nozzle. Thus the air jet is discharged with minimum loss of energy. It will be appreciated that there should be provided a sufiicient number of the vanes 50 to subdivide the annular nozzle 42 into a suitable number of nozzle segments of appropriate length to effectively achieve the foregoing function.

FIGURE 5 illustrates a ground effect machine of FIG- URES 1 through 4 modified by the addition thereto of a flexible skirt 51 of air-impervious flexible sheet material surrounding and depending from the lower edge of the annular rigid skirt or wall 22. Such a flexible skirt increases the operating height of the machine above the supporting surface and facilitates its negotiation of uneven terrain in known manner. Also, because of the tendency of the outwardly and downwardly flowing air jet to adhere to its inner surface, the skirt 51 assists in defining an air curtain for effectively confining the air cushion against lateral spreading and dispersion.

FIGURES 6 and 7 illustrate a mode of employing a plurality of the ground effect devices such as illustrated in FIGURE 5 for support of a vehicle, including a central hollow elongated body 55 for carrying passengers or cargo. This body has at its forward end a shield 56, behind which is the pilots cockpit provided with suitable controls (not shown) for operation and navigation of the vehicle. At its rear end, the body provides a mounting 57 for a propeller 58 exemplifying a suitable means for imparting a forwardly directed thrust to the vehicle. In

this embodiment, there are provided four ground effect devices or units such as shown in FIGURE 5, these being designated A, B, C and D respectively. These are preferably located in symmetrical relation to the longitudinal axis of the vehicle body. The body 55 is supported on these devices by suitable frame assemblies as shown in 60, and power is supplied to the fans of the several devices by individual power shafts such as 61, it being understood that these may be operatively connected to the respective fan shafts 128 in suitable manner.

In the modified form of the ground effect machine illustrated in FIGURES 8 to 11 inclusive, the construction and arrangement is similar to that illustrated in FIGURES 1 through 4 except for the shape of the body portion, the shape of which is here selected to illustrate the adaptability of the invention for use with a body of any desired noncircular configuration or plan, as for instance one which is oval or elliptical instead of circular. Thus the rigid outer body member has a flat top wall 121 with a marginal rounded fillet 122 from which depends the elliptical skirt wall 123. The top wall has a central opening surrounded by reinforced rim or boss 124 of the spider 125, the hub 126 of which supports the bearing 129 through which the fan shaft 128 is journaled. A centrifugal or radial flow fan 130, as employed in earlier embodiments, is mounted on the shaft below the housing 126 and the lower end of the shaft is journaled in a bearing 141 supported in a central opening in the bottom plate or diaphragm 140. The plate is of the same general shape and functions in substantially the same manner as that in the preceding embodiments, thus providing a continuous downwardly directed peripheral nozzle 142 into which the output of the fan is delivered through the air passage P which encircles the fan and establishes communication between the fan and the said nozzle throughout 360, around the rotational axis 128 of the fan. As in the preceding embodiment, this air passage P is formed so that any selected sector thereof has a constant cross-sectional area, regardless of the radial distance from the shaft 128 at which said area is measured (it being understood that the cross section here referred to will be transverse to a radial plane bisecting said sector).

Air flow control vanes or plates extend across the annular air duct or passage P near its juncture with the downwardly directed annular nozzle 142 and, in addition to the plan form shape of the device, constitute a major feature of difference between the modified form of the device shown in FIGURES 8 through 11 as contrasted to the form thereof shown in preceding figures.

As particularly shown in FIGURES 9, l0 and 11, the vanes 150 extend substantially vertically or parallel to the fan axis 128, and have air deflector portions 150' projecting radially into and extending generally axially across the outer portion of the air passage or duct 142 which encircles the fan and occupies all space between the fan and the noncircular or generally elliptical nozzle 142. These deflector portions 150' are curved in a direction counter to the rotational direction of the fan and generally in alignment with the air flow at their respective locations in the passage 142, to deliver this flow between the depending vertical vanes 150 where the latter extend downwardly through the nozzle 142, thereby eliminating the swirling movement of the air as it flows through the nozzle and directing it vertically downwardly so that when it issues from the nozzle it will have no swirling or tangential component.

The curvature of the extensions or deflector portions 150' and the spacing of the vanes 150 are such as to provide an even distribution of the air around the nozzle 142 and a substantially uniform velocity of the air around the entire perimeter of the nozzle.

In a noncircular body such as here shown, the curvature of different flow control vanes, or rather of the air deflector portions 150 thereof, will vary in accordance with such factors as differing air flow directions and velocities at their respective locations, differing distances from the fan axis, and the like. Notwithstanding this, by appropriate adjustment of the individual blade curvatures, the air jet discharged throughout the entire nozzle 142 may be directed accurately downwardly and substantially free of any tangential or outward component. Thus, in accordance with the invention, it is possible and practical to achieve efficient operation even of a noncircular discharge nozzle.

While preferred embodiments of the invention have been described and illustrated herein, it is to be understood that the scope of the invention is not limited to the embodiments specifically so illustrated and described, but that the invention is subject to obvious further variation and modification such as will be obvious to those skilled in the art from the teachings contained herein. Accordingly, the drawings and description herein are to be considered merely illustrative in nature and by no means as limitative.

Having thus described our invention, we claim:

1. In a ground effect machine, a hollow outer body having an open bottom, a diaphragm secured in said hollow body and marginally spaced therefrom to provide a downwardly directed annular air discharge gap of substantially constant width around the outer edge of said diaphragm, a power shaft disposed centrally of and journaled in said hollow body and said diaphragm, said hollow body having an air inlet opening therein surrounding said shaft, and a centrifugal fan mounted on said shaft between said hollow body and said diaphragm and provided with upper and lower flat diffuser rings, said hollow body and said diaphragm providing an annular air passage surrounding said fan and having a substantially constant cross-sectional area at all radial locations outwardly from said fan to said air discharge gap to maintain the velocity of the air from said fan substantially constant until the air leaves said discharge gap.

2. In a ground effect machine a hollow outer body having an annular skirt wall and a top wall joined to the upper edge of said skirt wall, a flat diaphragm secured in said hollow body substantially flush with the bottom edge of said skirt wall and having its peripheral surface spaced from said skirt wall to provide an annular air discharge gap of substantially constant width around said diaphragm, air guide vanes extending across said annular gap at predetermined intervals therearound and secured to said skirt wall and said diaphragm, a centrally located power shaft extending through said top wall and journaled in said top wall and said diaphragm, said top wall having an air inlet opening surrounding said shaft, and a centrfugal fan mounted on said shaft between said top wall and said diaphragm and having fiat radially projecting diffuser rings above and below the air discharge area thereof, said outer housing and said diaphragm providing around said fan an annular air passage chamber having a substantially constant cross-sectional area at all radial locations between said fan and said air discharge gap.

3. In a ground effect machine, a hollow outer body having a top wall and an annular skirt wall depending from the top wall, a diaphragm disposed within said hollow body with its bottom surface substantially flush with the bottom edge of said skirt wall, said diaphragm being spaced from said skirt wall to provide an air discharge gap of substantially constant width extending entirely around said diaphragm, air guide vanes extending across said annular gap and having air guiding curved portions, a centrifugal fan disposed centrally of the space between said diaphragm and said top wall and having upper and lower rotatable diffuser rings extending radially from the air discharge area of the fan, and an annular bolster formation on the upper surface of said diaphragm shaped to provide an annular air chamber of substantially constant cross-sectional area at all radial locations around said fan and providing a smooth turn from said fan downwardly through said air discharge gap.

4. The combination defined in claim 3 wherein said air discharge gap has an area substantially the same as the air discharge area of said fan.

5. A ground effect machine comprising a hollow body structure having a centrifugal fan centrally located therein and defining a downwardly directed air discharge nozzle of uniform cross-sectional size and shape disposed marginally around its lower periphery, and an outwardly extending air passage establishing communication between the said fan and the said discharge nozzle, in combination with air flow control vanes disposed at relatively spaced intervals in said discharge nozzle, with the lower end portions of said vanes disposed in vertical planes, the upper end portions thereof extending in a plane in angular relation to said lower end portions and substan' tially parallel to the direction of air flow at their respective locations.

6. A ground effect machine comprising a hollow body structure, a centrally located radial flow fan housed in said hollow body for rotation about a vertical axis and having a peripherally continuous radially outwardly directed discharge port, said housing defining an upwardly axially directed central air intake opening, and a downwardly axially directed continuous air discharge nozzle spaced outwardly radially from and completely surrounding said fan discharge port, said body structure further defining a radially extending circumferentially continuous air flow passage radially interconnecting and circumferentially coextensive with both said discharge port and said discharge nozzle, in combination with air flow control vanes disposed at relatively circumferentially spaced intervals around the hollow interior of said body, the lower end portions of said vanes being located in said nozzle in radial planes parallel to the rotational axis of the fan, other portions of said vanes being inclined to extend substantially parallel to the direction of the air flow from said fan in their respecive localities, said other portions merging smoothly with the said lower portions to eliminate the swirling movement from said air flow prior to its discharge from the said nozzle.

7. A ground effect machine as defined in claim 6 in which said discharge port is defined by an air diffuser rotatably carried by said fan.

8. A ground effect machine as defined in claim- 6 in which said nozzle is concentric to the rotational axis of said fan.

9. A ground effect machine as defined in claim 6 in which said vanes include portions curved about axes parallel to but respectively displaced from the rotational axis of the fan, the curvature of said last mentioned portions of the vanes increasing with the radial distance of said other end portions from the rotational axis of said fan.

10. A ground effect machine comprising a hollow body structure, a centrally located radial flow fan supported in said structure for rotation about a vertical axis and having a peripheral radially outwardly directed discharge port extending continuously therearound concentrically to the said axis, said body structure defining an axially upwardly directed central air intake opening for said fan, a downwardly axially directed continuous air discharge nozzle spaced radially outwardly from and concentrically to said discharge port of the fan, and a radially extending circumferentially continuous air flow passage radially interconnecting and circumferentially coextensive with both said discharge port and said nozzle, the axial dimension of said passage decreasing progressively in a radially outward direction from said discharge port of the fan at a rate to maintain the cross-sectional area of said passage constant at all radial locations.

11. A ground effect machine as defined in claim 10 in which said cross-sectional area of any given sector of said passage is equal to the cross-sectional area of the corresponding segment of the nozzle of said sector.

12. A ground elTect machine comprising a hollow body structure, a centrally located radial flow fan supported in said structure for rotation about a vertical axis and having a peripheral radially outwardly directed discharge port extending continuously therearound concentrically to the said axis, said body structure defining an axially upwardly directed central air intake opening for said fan, a downwardly axially directed continuous air discharge nozzle spaced radially outwardly from and concentrically to said discharge port of the fan, and a radially extending circumferentially continuous air flow passage radially interconnecting and circumferentially coextensive with both said discharge port and said nozzle, the axial dimension of said passage decreasing progressively in a radially outward direction from said discharge port of the fan at a rate to maintain the cross sectional area of said passage constant at all radial locations, in combination with air flow control vanes disposed at relatively circumferenti-ally spaced intervals in said nozzle, the portions of said vanes adjacent the lower discharge end of said nozzle extending in radial planes parallel to the rotational axis of the fan, and other portions of said vanes being reversely inclined with respect to the rotation of the fan to extend substantially parallel to the air flow from said fan in their respective localities, said inclined portions of the vanes respectively merging smoothly with the lower end portions thereof to eliminate the swirling motion from said air flow prior to its discharge from the nozzle.

13. A ground efiect machine as defined in claim 12 in which said nozzle and said vanes are disposed concentrically to the rotational axis of said fan, and said other portions of the vanes are uniformly curved.

14. A ground eifect machine as defined in claim 12 in which said nozzle and said vanes are disposed eccentrically with respect to said rotational axis of the fan and in which the inclination of said other portions of the vanes decreases as their distance from the said rotational axis increases.

References Cited UNITED STATES PATENTS 3,107,071 10/1963 Wessels --7 3,127,863 4/1964 Tinajero 180-7 X 3,150,731 9/1964 Franklin et al. 180-7 A. HARRY LEVY, Primary Examiner.

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