GB2068310A - Hovercraft propulsion unit with thrust reverser - Google Patents

Abstract

Ducted propulsion unit 18 of a hovercraft has a thrust reverser comprising a deflector 32 within the duct 22 and an outwardly openable door 48 for a side wall aperture 46. The deflector 32 moves between an inoperative position in an axial plane of duct 22 and an operative deflecting position extending obliquely across duct 22. Door 48 is coupled to deflector 32 by a link 60 so that it opens as the deflector moves to its operative position. Air driven down the duct by fan 26 is then deflected through aperture 46 and by the open door 48, to produce a rearward thrust component. With two propulsion units symmetrically arranged, selective operation of the thrust reverser of one or both units produces either a turning effect or a braking effect. For a single propulsion unit apertures 46 and doors 48 can be provided at both sides of the duct and the deflector can comprise independently operable pivoted flaps (Fig. 7, not shown) for selectively deflecting the air to one selected side for turning or to both sides for braking. <IMAGE>

Description

SPECIFICATION Hovercraft This invention relates to air cushion vehicles of the kind known as hovercraft.

For propulsion, hovercraft are generally provided with one or more propulsion units which commonly comprise a fan propeller disposed adjacent an air intake at the the forward end of an elongate duct that extends substantially horizontally in a fore and aft direction, this fan propeller serving to drive air down the duct to an air outlet at the rear end thereby to generate a forward thrust.

A practical problem associated with hovercraft is that of controlling reliably their direction of movement and of providing a high standard of manoeuvring ability and braking performance. Usually control is achieved by movable external rudder flaps which are generally provided at the rear end of the abovementioned duct type propulsion units. Also, the fan propellers of the latter may have variable pitch blades for controlling the propulsive force and for generating a reverse thrust for braking. With a plurality of such propulsion units positioned in a symmetrical arrangement on the craft, selective operation of the fan propellers to generate different proplusive forces resulting in an unbalanced thrust effort can also provide some measure of directional control, as can other kinds of aerodynamic control means designed to provide unbalanced drag forces.However, in practice many of the control systems presently used are rather complex and/or are not entirely satisfactory in that the movements of the hovercraft often still tend to be somewhat unpredictable and erratic and the manoeuvring ability and braking performance leaves much to be desired.

An object of the present invention is to provide improved means for controlling the movement of a hovercraft which can be more effective than or overcome disadvantages of prior art control arrangements.

The invention is specifically applicable to hovercraft having at least one propulsion unit of the duct type referred to and resides in a novel form of selectively operable air flow control means for such propulsion units.

More particularly, this selectively operable air flow control means provided by the invention comprises a deflector member which can be moved from an inoperative position into an operative deflecting position wherein it extends internally of the duct across the path of air flowing rearwardly along the duct downstream of the fan propeller and is effective in said operative deflecting position to deflect said air flow laterally towards a side wall portion of the duct, actuating means for controlling the movement and setting of said deflector member, an aperture in said side wall portion of the duct which aperture is provided with an outwardly openable closure member, and means for causing said closure member to open outwards in synchronism with moving the deflector member from its inoperative position to said operative deflecting position such that at least some of the internally deflected air flow is directed through said aperture and is further deflected by the open closure member to produce a rearwardly directed thrust component.

In preferred embodiments, the deflector member is in the form of a pivoted plate disposed within the duct adjacent to the side wall aperture so as to move angularly between an inoperative position lying in an axial plane and an operative deflecting position in which it extends obliquely across the width of the duct under the control, preferably, of a hydraulic actuator. Also, the closure member for the aperture is preferably in the form of a door pivoted about a vertical axis towards its rear edge so as to open outwardly and extend obliquely forwards when the deflector member is operative, this door being mechanically linked to the deflector member such that both members move in unison to ensure that the door opens at the same time as the deflector member is moved to is operative deflecting position.

Usually this air flow control means in accordance with the invention will be incorporated in a pair of propulsion units disposed symmetrically either side of the longitudinal axis of the hovercraft with the above-mentioned aperture and openable closure member being disposed in that side of the casing of each propulsion unit which faces outwardly of the craft. Then, by selective operation of the control means of one or both propulsion units either a turning effect or a braking effect can be produced as required.

By way of example one way in which the invention may be carried out will be more particularly described with reference to the accompanying drawings wherein: Figure 1 is a side view of a hovercraft having a pair of duct type propulsion units provided with air flow control means in accordance with one embodiment of the invention; Figure 2 is a plan view of the hovercraft of Fig. 1; Figure 3 is a diagrammatic horizontal sectional view through one of the propulsion units of the hovercraft of Fig. 1 showing an internal deflector member therein set in an operative deflecting position; Figure 4 is a view similar to Fig. 3 but showing the deflector member set in an inoperative position; Figure 5 is a transverse cross-section on line V-V of Fig. 4; Figure 6 is a view taken along line VI-VI of Fig. 3 showing the configuration of the deflector member; and Figure 7 is a further diagram similar to Fig.

4 showing a modification.

Referring to the drawings, the hovercraft designated generally by the reference 10 has a superstructure 1 2 above a deck 14 beneath which is a conventional hull and flexible skirt structure 16, and towards the rear it has a pair of propulsion units 1 8 disposed symmetrically either side of the superstructure and of the longitudinal axis of the craft.

Each propulsion unit 1 8 comprises a generally cylindrical open-ended casing or nacelle 20 providing an internal elongate duct 22 extending substantially horizontally in a fore and aft direction and within this duct adjacent the air intake opening 24 at the forward end is a motor driven fan propeller 26 adapted to drive air down the duct to an air outlet 28 at the rear end thereby to generate a forward thrust for propelling the craft.

At the rear end in the air outlet 28 there is provided a pair of conventional angularly movable vertically-disposed rudder flaps 30, 30, operable through a suitable control linkage (not shown) for normal guiding of the craft. In accordance with the invention, however, each propulsion unit 1 8 is further provided internally with a deflector member which, in this embodiment, is in the form of a deflector plate 32 pivotally mounted in the casing 20 in the manner of a butterfly valve by trunnion bearings 34, 36, for angular movement about a central vertical axis intersecting the longitudinal axis of the duct 22.

This deflector plate 32 has a somewhat oval or elliptical configuration with a rectangular extension portion 38 at one end as shown in Fig. 6, and it may conveniently be composed of glass fibre reinforced plastics material for lightness and strength with metal channel member 40, 42, attached thereto which carry the trunnion bearing shafts 41 and 43 at top and bottom respectively.

In its normal inoperative position, as shown in Fig. 4, the deflector plate 32 lies in an axial plane along the duct so that it does not obstruct or significantly affect air flowing axially down the duct. As hereinafter described, however, it can be moved angularly into an operative deflecting position as shown in Fig.

3 in which it extends obliquely across the interior of the duct 22 in the path of air flowing axially rearwards.

It will be seen from the drawings that on the side which is presented outwardly of the craft the casing 20 of each propulsion unit 1 8 is shaped to provide a flattish side wall portion 44 of the duct in which there is formed, adjacent the deflector plate 32, a window aperture 46 provided with an openable closure member in the form of a door 48 hinged at 50 along its rear vertical edge so as to open angularly outwards as shown in Fig. 3.

This door 48 has a somewhat U-shaped configuration in vertical cross-section, as seen in Fig. 5, provided by inwardly extending horizontal top and bottom plates or flanges, 52a and 52b respectively, of substantially triangular or sector shape which cover the triangular gap top and bottom between the casing 20 and the main panel 49 of the door 48 when the latter is open. When the door 48 is in its closed position these plates or tlanges 52a and 52b are accommodated within the interior of the duct 22.

It is so arranged that the door 48 is in its closed position when the deflector plate 32 is in its inoperative position as seen in Fig. 4, but when the deflector plate 32 is moved to its operative deflecting position as seen in Fig.

3 the door 48 is automatically caused to open in synchronism with the deflector plate movement, this being achieved in this embodiment by a mechanical connecting link 60 between these two members.

Thus, the deflector plate 32 and the door 48 move in unison and they mutually cooperate in controlling the propulsive air flow when the deflector plate is moved away from its inoperative position such that, at least in the fully operative position in which the deflector plate extends obliquely across the full width of the duct and the door 48 is open to its maximum extent at a forwardly inclined angle as indicated in Fig. 3, most of the air flowing down the duct 22 is deflected by the deflector plate 32 so as to be directed through the window aperture 46 and is then further deflected by the door 48 especially the main panel 49 thereof which at its inner hinge end lies closely adjacent the extension portion 38 of plate 32, thereby to emerge in a generally forwards direction producing a rearwardly directed thrust component as well as a lateral thrust component.The top and bottom plates or flanges 52a and 52b are however important for guiding the air flow and reducing spillage in an upwards and downwards direction.

It will be appreciated that this deflection of the propulsive air flow is effective to influence and control the movement of the hovercraft.

By selectively operating the deflector plate of one or other of the two propulsion units 18, the craft can be caused to turn either to port or starboard and it has been found that the turning circle can be extremely small, much smaller than that usually expected with conventional aerodynamic control means. Alternatively, by operating together the deflector plates of both propulsion units a very efficient braking effect can be obtained with both units producing a reverse thrust.

In that in the operative position the door 48 of each propulsion unit projects outwardly at a forwardly inclined angle into the external airstream this will of course increase drag which in itself will produce a braking effect, but it should be understood that the principal factor contributing to the efficiency of the arrange ment described in accordance with the invention for controlling the movement of the craft is not the change in drag characteristics but is the deflection of the propulsive air flow.

In the embodiment described, the movement and setting of the deflector plate 32, and hence of the door 48, is controlled by actuating means comprising an hydraulic cylinder actuator 56 which is incorporated in an electro-hydraulic control system and which is operatively-connected to an arm 58 fixed to the lower bearing shaft 43 which extends below the casing 20 as indicated in Fig. 5.

When in operation the deflector plate 32 is moved away from its inoperative position it will be apparent that it is liable to be acted upon by heavy unbalanced forces from the air flow, especially under conditions of relatively high speed motion of the craft. Nevertheless, it has been found that hydraulic control, as provided by an electrically operated hydraulic control system as mentioned, is suitable for regulating the movement with a satisfactory degree of stability and can enable the problems associated with smoothly controlling the deflector plate movement under operational conditions to be overcome. To relieve some of the air pressure acting on the deflector plate, however, it can also be beneficial to provide a number of small holes therein towards the leading edge, as indicated at 62 in Fig. 6.

If desired, instead of a mechanical linkage between the door 48 and deflector plate 32 each member could be driven by separate actuators with common or linked control means arranged so that they are energised simultaneously so as to operate in synchronism. It could also be possible for the deflector plate to be arranged to move slidably between inoperative and operative positions, and it will be understood that many other modifications in the structural details and arrangements of the embodiment herein specifically described may be made with the scope of the invention.

The air flow control means of the invention may moreover be adapted to suit hovercraft having a single duct type propulsion unit which may be arranged to lie in the vertical longitudinal axial plane of the craft, and one way of carrying out this modification is indicated in the diagrammatic view of Fig. 7.In this case, it will be seen that the duct 22 is provided with two openable doors 48a and 48b closing window apertures 46a and 46b at opposite sides and the deflector member is composed of a number of separate flap sec tions 32a, 32band 32e each mounted on its own pivot 70a, 70b or 70c and having its own actuator (not shown) so as to be independently operable so that they can be moved in different combinations to give a deflection to a selected one side or to both sides in conjunction with an opening movement of the appropriate door or doors.The doors 48a and 48b in this arrangement are also conveniently provided with their own actuators, acting on their pivot mountings 50a and 50b, and the required combination of movements can be brought about by selective interlock means in the operating system for the actuators which again may be electrically controlled hydraulic actuators. Thus, it may be arranged so that if the craft is required to turn in one direction, door 48a is opened and deflector flap elements 32a and 32c are moved to a corresponding appropriate deflecting position, if the craft is required to turn in the opposite direction, door 48b is opened and deflector flap elements 32band 32care moved to a corresponding different deflecting position, and if braking is required both doors 48a and 48b open and both flap elements 32a and 32b move into opposite deflecting positions in a V-shaped configuration.

Claims (14)

1. A hovercraft having at least one propulsion unit which includes a casing defining an elongate duct extending substantially horizontally in a fore and aft direction and a fan propeller disposed adjacent an air intake at the forward end of said duct, this fan propeller serving to drive air down the duct to an air outlet at the rear end thereby to generate a forward thrust, characterised in that said propulsion unit is provided with selectively operable air flow control means comprising:: (a) a movable deflector member arranged to be moved between an inoperative position in which it presents a minimal impedance or obstruction to air flowing axially rearwards along the duct and an operative deflecting position in which it extends internally of the duct across the path or air flowing axially rearwards along the duct downstream of the fan propeller and is then effective to deflect said air flow laterally towards a side wall portion of the duct casing, (b) actuating means for controlling the movement and setting of said deflector member, (c) an aperture in said side wall portion of the duct casing, (d) an outwardly openable closure member for closing said aperture, and (e) operating means for causing said closure member to open outwards in synchronism with moving the deflector member from its inoperative position to said operative deflecting position such that at least some of the internally deflected air flow is directed through said aperture and is then further deflected by the open closure member to produce a rearwardly directed thrust component.

2. A hovercraft according to Claim 1 wherein the deflector member is in the form of a pivoted plate disposed within the duct and arranged to move angularly, under the control of said actuating means, between said inoperative position in which it lies in an axial plane and said operative deflecting position in which it extends obliquely across the width of the duct adjacent said side wall aperture.

3. A hovercraft according to Claim 2 wherein said actuating means includes a hydraulic actuator which provides a power drive source.

4. A hovercraft according to Claim 1, 2 or 3, wherein said operating means comprises a mechanical linkage operatively interconnecting the deflector member and the closure member such that they both move in unison thereby to ensure that the closure member opens at the same time as the deflector member is moved to its operative deflecting position.

5. A hovercraft according to Claim 1, 2 or 3, wherein the closure member for closing the aperture is in the form of a door pivoted about a vertical axis proximate its rearmost edge so as to open outwards and extend obliquely forwards when the deflector member is in its said operative position.

6. A hovercraft according to Claim 5 wherein said door comprises a main panel with inwardly extending horizontal flanges for covering the gap at top and bottom between the duct casing and said main panel when the door is open.

7. A hovercraft according to Claim 5 or 6, wherein said operating means comprises a mechanical linkage operatively interconnecting the door and deflector member such that both move in unison thereby to ensure that the door opens at the same time as the deflector member is moved to its operative deflecting position.

8. A hovercraft according to any one of the preceding claims, wherein said propulsion unit is one of a pair of substantially identical propulsion units disposed symmetrically either side of the longitudinal axis of the hovercraft, each propulsion unit being provided with selectively operable air flow control means as hereinbefore defined with the aperture and openable closure member of the latter being disposed in that side of the duct casing of each propulsion unit which faces laterally outwards of the craft so that by selective operation of the air flow control means of one or both propulsion units either a turning effect or a braking effect can be produced as required.

9. A hovercraft having a propulsion unit which includes a casing defining an elongate duct extending substantially horizontally in a fore and aft direction in the vertical longitudinal axial plane of the craft and which also includes a fan propeller disposed adjacent an air intake at the forward end of said duct, this fan propeller serving to drive air down the duct to an air outlet at the rear end thereby to generate a forward thrust, characterised in that said propulsion unit is provided with selectively operable air flow control means comprising:: (a) a movable deflector member arranged to be moved between an inoperative position in which it presents a minimal impedance or obstruction to air flowing axially rearwards along the duct and a selected operative deflecting position in which it extends internally of the duct across the path of air flowing axially rearwards along the duct downstream of the fan propeller and is then effective selectively to deflect said air flow laterally towards one or each of opposite side will portions of the duct casing, (b) actuating means for controlling the movement and setting of said deflector member, (c) an aperture in each of said opposite side wall portions of the duct casing, (d) a laterally outwards openable closure member associated with each said aperture for closing the latter, and (e) operating means for causing a selected one of or both said closure members to open outwards in synchronism with moving the deflector member from its inoperative position to a said operative deflecting position such that at least some of the internally deflected air flow is directed through one or both said apertures and is then further deflected by the open closure member associated therewith to produce a rearwardly directed thrust component.

1 0. A hovercraft according to Claim 9, wherein each said closure member is in the form of a door pivoted about a vertical axis proximate its rearmost edge so as to open outwards and extend obliquely forwards when the deflector member is in a respective said operative position.

11. A hovercraft according to Claim 10, wherein said operating means comprises hydraulic actuators controlled selectively to operate in synchronism with a hydraulic actuator arrangement which provides a power drive source of the actuating means for controlling the movement and setting of said deflector member.

12. A hovercraft according to Claim 9, 10 or 11, wherein the deflector member is composed of a plurality of pivoted flap sections disposed within the duct and arranged to be independently operable so as selectively to move angularly, under the control of said actuating means, between said inoperative position in which they all lie in an axial plane and a selected said operative deflecting position in which a combintion of said flap sections extends obliquely across the width of the duct in the region of said side wall apertures.

1 3. A hovercraft according to Claim 12, wherein said actuating means includes a separate hydraulic actuator for controlling each flap section.

14. A hovercraft having propulsion units provided with selectively operable air flow control means substantially as herein before described and illustrated with reference to Figs. 1 to 6 of the accompanying drawings.

1 5. A hovercraft having a propulsion unit provided with selectively operable air flow control means substantially as hereinbefore described and illustrated with reference to Fig.

7 of the accompanying drawings.