GB2098943A

GB2098943A - Lift and propulsion installation of air-cushion vehicle

Info

Publication number: GB2098943A
Application number: GB8116013A
Authority: GB
Original assignee: DO G PK I EXPERI
Current assignee: DO G PK I EXPERI
Priority date: 1981-05-26
Filing date: 1981-05-26
Publication date: 1982-12-01
Also published as: GB2098943B

Abstract

A lift and propulsion installation of an air-cushion vehicle comprising an axial fan 2 installed in the entrance portion of an annular duct 1 divided by a cylindrical splitter 8 into external and internal annular passages 9 and 10. The external passage 9 is communicated through a diffuser 5 and a box 6 with an air cushion A, and the internal passage 10 is communicated with a thrust nozzle 11 having a reverse-steering device having pivoted rudders 13 and reversing blades 12. The fan 2 has two rows of blades 17 and 18. Each first row blade 17 is of fixed incidence and has at its peripheral portion 19 a cambered section disposed before the entrance into the external passage 9, and its radially inner portion 21 has a symmetrical flat profile disposed before the entrance into the internal passage 10. The second row blades 18 are of variable incidence and are installed before the entrance into the internal passage 10. Straightening blades 25, 26 are provided. <IMAGE>

Description

SPECIFICATION Lift and propulsion installation of air-cushion transport vehicle The present invention relates to air-cushion transport vehicles and more particularly to a lift and propulsion installation of an air-cushion transport vehicle.

The present invention may suitably be used in the development of air-cushion transport vehicles, for example, air-cushion craft, self-propelled transport plafforms and like apparatuses, in which are supporting a vehicle above the bearing surface the use is made of pressurized air delivered into the cushion, and the translatory motion is effected due to a reactive thrust provided by the ejected air stream.

In many countries the air-cushion transport vehicles find various applications in different branches of economy. Factors which restrain further application of such vehicles are the following: large overall sizes and mass of installations equipped with fans generating pressurized air for producing the reactive thrust and filling the air cushion, and also the complexity of mechanisms which ensure regulation of the amdunt of pressurized air delivered into the air cushion and reactive thrust nozzle.

The overall sizes and mass of these installations are mainly dictated by the required output and pressure of pressurized air and respectively by the design of a fan providing the delivery of pressurized air.

Production of light lift and propulsion installations of reduced overall sizes necessitates the use of highly efficient axial fans, in which regulation of the air delivery and air pressure is accomplished by turning the blades of the fan wheel.

Used nowadays throughout the world are installations of various types, in which generation of pressurized air and its delivery to the air cushion and to the reactive thrust nozzle are effected in a single unit. Such units are known as lift and propulsion installations of air-cushion transport vehicles.

Known to the prior art is a lift and propulsion installation for air-cushion craft (cf., for example, a magazine "Air-Cushion Vehicles", No. 45, 1966, pp. 33-39), comprising a centrifugal fan installed in a spiral casing. From the spiral casing part of the pressurized air is delivered to the air cushion while the other part is directed into the nozzle for producing the reactive thrust.

However, due to their design features the centrifugal fans have large overall sizes and produce less pressurized air in comparison with axial fans. Therefore, the lift and propulsion installations equipped with centrifugal fans are not economical and cannot ensure a high traveling speed of air-cushion vehicles.

Known in the prior art is a lift and propulsion installation with an axial fan (cf., for example, British Patent No. 1,306,687, cl. B60 V 1/100, February 14, 1973) disposed in a duct, in which there is installed a cylindrical splitter dividing the space after the axial fan into two annular passages, the external annular passage being communicated with an air-cushion and the internal annular passage, with a reactive thrust nozzle. A wheel of this fan is provided with a splitter ring arranged concentric with the fan axis, thereby dividing the blade passages into internal and external ones, and is registered in diameter with the cylindrical splitter. The splitter ring serves as a support for the fan working blades.

The turning mechanism of the blades of the internal passage is accommodated in the hub of the fan wheel.

However, such a fan wheel may be used only at a relatively slow rotative speed thereof due to a low mechanical strength of the fan wheel caused by the necessity to arrange movable supports of the blades of the internal passage in the splitter ring and to fasten the blades of the external passage.

Therefore, such a fan wheel, when used in a small-size installation, fails to ensure an ample delivery of pressurized air which reduces the travelling speed of an air-cushion transport vehicle equipped with the herein described lift and propulsion installation.

The present invention seeks to eliminate the aforesaid disadvantages.

The invention essentially aims at developing such a design of a lift and propulsion installation for an air-cushion transport vehicle, which will allow the reactive thrust to be substantially increased and more economically regulated, with the installation overall sizes reduced due to the alteration of the design of an axial fan wheel.

This is attained by that in a lift and propulsion installation of an air-cushion transport vehicle, comprising an axial fan installed in an annular duct and provided with a wheel disposed at the entrance portion of the annular duct at the exit of which is arranged a diffuser and a box pneumatically associated with the axial fan, and disposed internally in the annular duct is a cylindrical splitter dividing this annular duct into external and internal annular passages, the external annular passage being communicated through said box with the space of an air-cushion, whereas the internal annular passage being communicated with a thrust nozzle provided at its exit with a reverse-steering device including pivoted rudders and reversing blades arranged after the fan wheel, according to the invention the fan wheel has two rows of blades and each blade of the first row is provided at its peripheral portion with a wing-like curved profile disposed before the entrance into the external annular passage, whereas its lower portion has a symmetrical flat profile disposed before the entrance into the internal annular passage, the blades of the first row being fixedly secured on a hub of the fan wheel and the blades of the second row being installed on the same hub before the entrance into the internal annular passage and adapted to be turned each about its radial axis, straightening blades are installed at least in one of the annular passages after the working blades.

Such an embodiment of the wheel blades ensures a sufficient strength thereof and simple construction which permits the wheel to be rotated at a high peripheral speed, thereby providing a greater delivery of pressurized air and a suitable reactive thrust, with the overall sizes of the lift and propulsion installation essentially minimized. Owing to the turning of the working blades of the second row, made wing-like through the entire length, the economic regulation of the developed thrust is attained.

The hub of the fan wheel may suitably be made in the form of a bushing with cylindrical and conical portions smoothly changing into one another, and the blades of the first row may be arranged on the cylindrical portion of the bushing, the diameter of which is equal to 0.2-0.3 of the wheel outside diameter in the plane of a disc defined by the first row blades, and the blades of the second row may be installed on the conical portion of the bushing with the exit diameter equal to 0.3-0.5 of the wheel outside diameter in the plane of a disc defined by the second row blades.

Such a construction of the bushing and said relative dimensions thereof make it possible to obtain high values of the efficiency factor which provides for obtaining a greater air delivery at a relatively small outside diameter of the fan wheel.

It is preferred that the inside diameter confining the wing-like portion of the first row blades and the outside diameter of the second row blades be in register with the diameter of the annular duct and should comprise 0.75-0.90 of the outside diameter of the fan wheel in the plane of a disc defined by the first row blades.

Such a ratio of the annular duct diameter makes it possible to ensure the delivery of a rational amount of air through the external annular passage to the air cushion and to obtain a greater delivery of air through the internal annular passage to provide a respective value of the reactive thrust.

The cylindrical splitter may conveniently be arranged over the wheel blades of the second row to confined the external passage which makes it possible to increase the pressure of air delivered through the external annular passage to the aircushion space.

The straightening blades may be installed either after the working blades of the first row in the external annular passage or after the working blades of the second row in the internal annular passage, or after the working blades of the first and second rows in the external and internal annular passages, respectively.

Due to such installation of the straightening blades the pressure of air delivered through the external annular passage into the air-cushion space will be raised and the pressure of air delivered from the internal annular passage to the nozzle will be raised which will correspondingly increase the developed reactive thrust.

To enable the invention to be fully understood the embodiment thereof will now be described with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates a vertical section of a lift and propulsion installation of an air-cushion transport vehicle, according to the invention; Fig. 2 is a horizontal section of Fig. 1; Fig. 3 is a section taken on the line Ill-Ill of Fig. 1; Fig. 4 is a section taken on the line IV--IV of Fig. 1.

A lift and propulsion installation of an aircushion transport vehicle, according to the invention, comprises an annular duct 1 (Fig.) at the entrance portion of which is installed an axial fan wheel 2 with a spinner 3 disposed thereafter and a drive system 4 mounted before the fan wheel 2. Provided at the exit portion of the annular duct 1 is a diffuser 5 (Figs. 1, 2) connected with a box 6 (Fig. 1) which pneumatically communicates with the space of a skirt 7 bounding the area of an air cushion A.

Installed internally in the box 6 and the diffuser 5 is a cylindrical splitter 8 which divides the spaceafter the fan wheel 2 into an external annular passage 9 restricted by the annular duct 1 and the cylindrical splitter 8, and an internal annular passage 10 restricted by the cylindrical splitter 8 and the spinner 3.

The external annular passage 9 is pneumatically in communication with the skirt 7 through the box 6 while the internal annular passage 10 (Figs. 1, 2) is connected at its exit with a reactive thrust nozzle 11. Blades 12 serving for reversal of the air stream are installed on the side walls of the nozzle 11 and pivoted rudders 13 for effecting the directional control of a transport vehicle are arranged at the nozzle exit.

The fan wheel 2 (Fig. 1) comprises a hub 14 which is made in the form of a bushing with cylindrical and conical portions 15 and 16 smoothly changing into one another.

The fan wheel 2 has the first row of working blades 17 with an outside diameter D, and the second row of working blades 18 with an outside diameter D2. The blades 1 7 have their peripheral portion 1 9 made in the form of a wing-like curved profile 20 (Fig. 3) disposed along the radius before the entrance into the external annular passage 9 (Fig. 1), whereas a lower portion 21 of the blade 1 7 has a symmetrical flat profile 22 (Fig. 4) and is disposed in the space before the entrance into the internal annular passage 10 (Fig. 1) The blades 17 of the first row are fixedly secured on the cylindrical portion 15 of the bushing, having a diameter d1. Each blade 18 of the second row is installed on the conical portion 16 of the bushing and adapted to be turned about its radial axis 23 with the aid of a turning mechanism 24 internally arranged in the hub 14.

At the exit the portion 1 6 of the bushing has a diameter d2.

In an optimal case the diameter d1 of the cylindrical portion 1 5 comprises 0.2-0.3 of the outside diameter D, in the plane of a disc defined by the first row blades 1 7. The conical portion 1 6 of the bushing makes it possible to preclude separation of the air stream flowing around the blades 18 of the second row at large angles of their setting when the diameter d2 at the exit of the bushing comprises 0.3-0.5 of the outside diameter D2 in the plane of a disc defined by the second row blades 18.

Such relative values of the diameters d, and d2 of the bushing provide for obtaining the maximum possible delivery of air through the internal annular passage 10.

Depending on the required values of pressure and amount of pressurized air to be delivered through the external annular passage to the aircushion A, a diameter d3 of the cylindrical splitter 8 may be selected within 0.75-0.90 of the outside diameter D, of the fan wheel 2 in the plane of disc defined by the first row blades 17.

In this case the diameter d3 is selected at the design stage depending on a preassigned travelling speed and configuration of the surface above which the air-cushion transport vehicle is to travel. For example, for travelling above an even smooth surface (ice, hard-surfaced area) the value of the diameter d3 may be taken about 0.90.

In this case a small amount of air required for the air cushion A will be delivered through the external annular passage 9. At the same time, the energy of the drive system 4 will be spent to a greater extent for delivery of a greater amount of air into the internal annular passage 10 to ensure respectively a greater value of the reactive thrust and a higher travelling speed of the transport vehicle supported by the air cushion A.

If a transport vehicle supported by the aircushion A is intended for travelling above an uneven surface (rough water, hammocks of ice), then the value of the diameter d3 may be equal approximately to 0.75. In this case a greater amount of air will be delivered into the internal annular passage 9 due to which the volume of the air cushion A will be increased and the conditions for travelling of the transport vehicle supported by the air cushion A, above an uneven surface will be improved.

In other cases the value of the diameter d3 may be within the above-mentioned range of 0.75 to 0.90, depending on the conditions in which an air-cushion transport vehicle is to be employed.

A correctly selected value of the diameter d3 ensures the optimal conditions for motion of an air-cushion transport vehicle with the minimum expenditure of energy of the drive system 4 transmitted to the fan wheel 2.

The inside diameter confining the wing-like portion of the first row blades 1 7 and the outside diameter D2 of the second row blades 18 are approximately equal and less than the inside diameter d3 of the cylindrical splitter 8 by the value of a radical clearance ensuring the possibility for the blades 1 8 to rotate inside the cylindrical splitter 8. Such an arrangement of the cylindrical splitter 8 over the second row blades 18 makes it possible to improve the delivery of air through the external and internal annular passages 9 and 10 due to elimination of flow of the air streams between the annular passages 9 and 10.

To obtain a higher pressure of air in the external annular passage 9, straightening blades 25 are arranged after the peripheral portion 19 of the first row blades 1 7.

To increase the pressure of air in the internal annular passage 10, straightening blades 26 may be arranged after the second row blades 1 8.

The lift and propulsion installation of an aircushion transport vehicle operates in the following manner.

The drive system 4 rotates the fan wheel 2 with blades 1 7, 18 due to which air is drawn in the annular duct 1 and passes to the first row blades 17 (Fig. 1). The peripheral portion 19 of these blades acting by the wing-like profile 20 on the air flow imparts to it the energy from the drive system 4 with the result that the air flow acquires a whirl velocity and then is straightened by the straightening blades 25 which contributes to a rise of the static pressure of pressurized air delivered intdthe external annular passage 9.

When the air flow moves through the portion of the passage 9 provided with the diffuser 5 the velocity of the air flow drops and its static pressure rises. From the passage 9 with the diffuser 5 the pressurized air is delivered to the box 6, wherefrom it is directed to the skirt 7 and then, into the air cushion A which supports a body 27 of the transport vehicle above a bearing surface 28.

The lower portion 21 of the blades 17 having the symmetrical flat profile 22 serves as streamlined struts passing air to the working blades 18 of the second row with minimum aerodynamic losses.

The blades 1 8 impart the energy from the drive system 4 to the air flow and after straightening of the air flow by the straightening blades 26, the air passes into the internal annular passage 10 wherefrom it is directed into the nozzle 11.

When passing from the nozzle 11 at a preset velocity, the air produces the reactive force which propels the body 27 of a transport vehicle above the bearing surface 28.

The exit velocity of air ejected from the nozzle 11 is governed by the angle of the blades 1 8.

When the blades 1 8 are turned through a greater or smaller angle (Fig. 4) with the aid of the mechanism 24 (Fig. 1), the amount of air and its velocity at the exit from the nozzle 11 will increase or decrease, respectively. Any variation in the air velocity at the exit from the nozzle 11 causes a respective variation in the reactive force produced by the air stream due to which the travelling speed of the body 27 of a transport vehicle moving above the bearing surface 28 is increased or decreased.

If it is required to change the direction of motion of an aircushion transport vehicle the rudders 13 should be turned to alter the direction of the reactive jet. For manouvering in reverse the rudders 13 are turned to direct the air stream from the nozzle 11 through the blades 12 (Fig. 2) to the side of reversal.

Thus the disclosed design of a lift and propulsion installation and the basic ratios heretofore described make it possible to increase the travelling speed of an air-cushion transport vehicle, with the overall sizes of a lift and propulsion installation minimized in comparison with the prior art installations.

Claims

1. A lift and propulsion installation of an aircushion transport vehicle, wherein an axial fan is installed in an annular duct and provided with a wheel disposed at the entrance portion of the annular duct; at the exit of the annular duct arranged are a diffuser and a box pneumatically associated with the axial fan; a cylindrical splitter is disposed internally in the annular duct to divide it into an external annular passage and an internal annular passage, the external annular passage being communicated through the box with the space of an air cushion and the internal annular passage being communicated with a thrust nozzle provided at its exit with a reverse-steering device having pivoted rudders and reversing blades installed after the axial fan wheel; the axial fan wheel has two rows of blades and each blade of the first row is provided at its peripheral portion with a section having a wing-like curved profile disposed before the entrance into the external annular passage, whereas its lower portion has a symmetrical flat profile disposed before the entrance into the internal annular passage; the blades of the first row are fixedly secured on a hub of the fan wheel, while the blades of the second row are installed on the same hub before the entrance into the internal annular passage and adapted each to be turned about its radial axis; straightening blades are installed at least in one of the annular passages after the working blades.

2. A lift and propulsion installation as claimed in Claim 1, wherein the hub of the fan wheel is made in the form of a bushing with cylindrical and conical portions smoothly changing into one another, the blades of the first row being arranged on the cylindrical portion of the bushing the diameter of which is equal to 0.2-0.3 of the outside diameter of the fan wheel in the plane of a disc defined by the blades of the first row, while the blades of the second row are installed on the conical portion of the bushing with an exit diameter equal to 0.3-0.5 of the outside diameter of the fan wheel in the plane of a disc defined by the second row of the blades.

3. A lift and propulsion installation as claimed in Claim 2, wherein the inside diameter confining the wing-like profile of the blades of the first row and the outside diameter of the blades of the second row are in register with the diameter of the cylindrical splitter and comprise 0.75-0.90 of the outside diameter of the fan wheel in the plane of a disc defined by the first row of the blades.

4. A lift and propulsion installation as claimed in Claims 1, 2, 3 wherein a cylindrical splitter is arranged over the blades of the second row of the fan wheel, thereby confining the external annular passage.

5. A lift and propulsion installation as claimed in Claim 1, wherein the straightening blades are installed after the working blades of the first row in the external annular passage.

6. A lift and propulsion installation as claimed in Claim 1, wherein the straightening blades are installed after the working blades of the second row in the internal annular passage.

7. A lift and propulsion installation as claimed in Claim 1, wherein the straightening blades are installed after the working blades of the first and second rows in the external and internal annular passages, respectively.

8. A lift and propulsion installation substantially as herein described with reference to and as illustrated in the accompanying drawings.