WO2014195716A2

WO2014195716A2 - Hovercraft drive systems

Info

Publication number: WO2014195716A2
Application number: PCT/GB2014/051742
Authority: WO
Inventors: Malcolm Cox; Mark Downer
Original assignee: Griffon Hoverwork Ltd
Priority date: 2013-06-07
Filing date: 2014-06-05
Publication date: 2014-12-11
Also published as: WO2014195716A3; GB2516616A; GB2516616B; GB201310149D0

Abstract

A drive system for a hovercraft. The drive system includes at least one lift fan (8) for creating a pressurised cushion of air below the hovercraft and at least one propulsor (10) for generating forward thrust. The drive system also includes a primary motor (14) for driving either the lift fan or the propulsor, and a secondary motor (18) for driving the other of the lift fan and the propulsor. The primary motor (14) also generates energy to drive the secondary motor (18).

Description

HOVERCRAFT DRIVE SYSTEMS

Field of the Invention The invention relates to new configurations of drive systems for providing flows of air to lift, propel and steer a hovercraft.

Background

Hovercraft (known also as air-cushion vehicles) are craft that can travel over water and land on a cushion of air. Known hovercraft include a hull and a flexible skirt that extends around and downwards from the periphery of the hull, A lift fan is used to create a pressurised cushion of air below the hull, contained by the skirt. The craft is propelled forwards by one or more propuisors mounted on top of the hull, which typically include a driven propeller within a shroud. Typically the direction of travel is controlled either by using rudders mounted on the propulsor(s) to direct the flow of air from the propulsor(s) to steer the hovercraft or by using one or more propuisors that can be pivoted to change the direction of the air flow. The speed of the craft is typically controlled by varying the speed of the propeller of each propuisor and/or by controlling the angle of the blades of the propuisor propeller.

Known hovercraft drive systems typically include one or more piston or gas turbine motors that drive the lift fan and propuisors through mechanical drive linkages. In small craft, a single motor is often used to drive the lift fan and propulsor(s). This can result in complex mechanical linkages, particularly where multiple propuisors are used, and may place significant constrictions of the locations at which the lift fan and propuisors can be positioned on the hull. The use of a single motor can also to lead to inefficient running of the lift fan in the case where the speed of the hovercraft is varied by varying the motor speed. This is because as the motor speed is varied to control the speed of the hovercraft the speed of the lift fan will also vary, whereas a constant speed is best for efficient running of the lift fan. Larger craft tend to use separate motors for the lift fan and propuisors, which avoids at least some of the above problems but adds significantly to the weight of the hovercraft.

US 6,59 ,928 proposes an alternative drive system for a hovercraft lift fan and propuisors (referred to in this document as "thrust units") in which separate electric motors are used to drive the lift fan and each thrust unit. The motors are mounted directly on the lift fan and the airscrews of the thrust units, avoiding the need for any mechanical drive linkages. A central energy generator for powering the electric motors includes a turbine (or other combustion engine) and an electrical generator.

Summary of Invention A genera! aim of the present invention is to provide an improved drive system for a hovercraft. in a first aspect the invention provides a drive system for a hovercraft, the drive system comprising: at least one lift fan for creating a pressurised cushion of air below the hovercraft; at least one propulsor for generating forward thrust; a primary motor for driving said at least one lift fan; and a secondary motor for driving said at least one propulsor; wherein the primary motor also generates energy to drive the secondary motor. in an alternative aspect, the primary motor can drive the propulsor and the secondary motor can drive the lift fan.

The propulsor will typically include a propeller and the secondary motor is preferably mounted on the hub of the propeller to drive it directly without a gearbox. The propulsor is preferably mountable on the hull of the hovercraft in a manner that allows it to swivel, so that the direction of the air flow generated by the propulsor can be controlled by swivelling the propulsor in order to steer the craft, in some embodiments, multiple propulsors are provided. There may, for example be two propulsors mounted at the stern of the craft, one to either side, or alternatively mounted one at the stern and one towards the bow of the craft, in other embodiments more than two propulsors are used. Where multiple propulsors are used, each propulsor preferably has its own associated secondary motor, ail of which are powered by the primary motor.

By having separate drive motors for the lift fan and propulsor it is possible to drive the lift fan at constant or near constant speed, which is generally best for efficient running of the lift fan, whilst varying the speed of the propulsor motor to control the speed of the hovercraft However, by using a direct drive from the primary motor to either the lift fan or the propulsor, the overall system efficiency can be improved compared with a system of the type described in US 6,591 ,928 where electric motors are used for the lift fan and propulsor. The use of a direct mechanical drive also offers a weight and cost saving compared with an all-electric drive system.

The primary motor is preferably an internal combustion engine. It may, for example, be a gas turbine or a reciprocating piston engine, in the latter case it may be a spark ignition or a compression ignition engine, for example a compression ignition diesel engine or a gas fuelled engine.

The secondary motor, which is powered by the primary motor, may be a hydraulic motor, an air motor or an electric motor for example. in order to generate the energy for the secondary motor, the system may further include a generator that is driven by the primary motor. Where the secondary motor is a hydraulic motor, this generator can be a pump to provide a pressurised supply of hydraulic fluid to drive the secondary motor. Where the secondary motor is an electric motor, the generator is an electric generator. Where the secondary motor is an air motor, the generator is an air compressor, in any of these cases, there is no need for any mechanical drive linkages between the primary motor and the secondary motor. Rather, all that is required are power transmission components (e.g. fluid pipes or electric power cables).

The system may further comprise an energy store for storing energy generated by the primary motor (and associated generator) that can be used subsequently to power the secondary motor. For example, in the case where the secondary motor is an electric motor, one or more batteries may be provided to store electrical energy generated by an electric generator driven by the primary motor. This storage may also be achieved using capacitors. Where the drive is achieved through pressurised fluid, the energy may be stored in an accumulator. in the case where the primary motor is an internal combustion engine, the system preferably also includes a fuel reservoir (e.g. one or more fuel tanks) from which fuel can be supplied to the engine.

Conveniently, in the case where the primary motor drives the lift fan, the primary motor, lift fan and generator, optionally along with the energy store and fuel reservoir can be provided as a single module that can be assembled and subsequently installed in the hull of a hovercraft as a unitary assembly.

Accordingly, in a second aspect, there is provided a lift fan module for a hovercraft, the module comprising: a hovercraft lift fan; a primary motor; a drive linkage through which the primary motor drives the lift fan; and a generator that is driven by the primary motor; wherein the lift fan, primary motor, drive linkage and generator are mounted to one another to provide a unitary assembly that can subsequently be installed in a hovercraft hull.

The module may further comprise an energy store, for example one or more batteries, that also forms a part of the unitary assembly.

The module may further comprise a fuel reservoir, for example one or more fuel tanks, that also forms a part of the unitary assembly.

The components of the module may be mounted directly on one another or may be mounted on one another via one or more support structures, for example support frames.

Particularly in the case where the lift fan module includes all of the components necessary for its operation, advantageously it becomes possible to build and test the module "on the bench" before it is installed in the hovercraft. This can reduce build time by allowing construction of these units to be carried out in parallel to construction of the hovercraft hull. The self-contained nature of this module also means that it can be easily removed from the hovercraft for maintenance. If desired, a replacement module can be installed in the craft whilst the original module is undergoing maintenance, thus improving craft availability. it will generally be necessary to cool the primary motor, especially in the case where it is an internal combustion engine. Where the lift fan is located adjacent to the primary motor, for example as part of the lift fan module described above, the flow of air created by the lift fan can be used (directly or indirectly) to cool the motor. For example, in the case where the lift fan is a centrifugal fan having a volute through which the lift air is expelled, the wall of the volute may be used as part of a heat exchanger for cooling the motor, for example by passing engine cooling water in conduits alongside or within the volute wail.

The propulsor and the secondary motor that drives it may also conveniently be provided as a module that can be assembled prior to installation on the hovercraft. in a third aspect, the invention provides a method used in constructing a hovercraft, the method comprising: assembling a lift fan module comprising: a hovercraft lift fan; a primary motor; a drive linkage through which the primary motor drives the lift fan; and a generator that is driven by the primary motor; assembling at least one propuisor module comprising: a propuisor; and a secondary motor for driving the propuisor; providing a hovercraft hull; and installing the assembled lift fan module and at least one assembled propuisor module on the hovercraft hull.

Conveniently, taking this approach, the hull can be constructed at the same time as the lift fan and propuisor modules are being assembled, reducing the overall hovercraft build time.

In further aspects the invention provides a hovercraft comprising the drive system of the first aspect above and/or the lift fan assembly of the second aspect above.

Brief Description of the Figures

An embodiment of the invention is described below by way of example with reference to the accompanying figures, in which: Fig. 1 is a schematic sectional view across the width of a hovercraft having a drive system in accordance with an embodiment of the present invention;

Fig. 2 is a partial schematic sectional side view of the hovercraft shown in fig. 1 ;

Fig. 3 is a schematic of the drive system for the hovercraft shown in fig. 1 ;

Fig. 4 is a schematic of an alternative drive system for the hovercraft shown in fig. 1 ; Figs. 5a, 5b and 5c schematically show alternative motor cooling arrangements making use of the lift fan volute; and Fig. 6 is a schematic longitudinal sectional view of another hovercraft having a drive system in accordance with another embodiment of the invention in which there are two lift fan modules.

Description of Embodiment

Figs. 1 and 2 show a hovercraft having a central hull 2, sidebodies 4 extending from either side of the hull 2, one on the left and one on the right, and a conventional skirt 8 attached to the outboard sides of the sidebodies 4 and to the bow and stern of the hull 2. Between them the hull 2, sidebodies 4 and skirt 6 form a plenum for a cushion of air on which the hovercraft rides. Air is supplied to the plenum by a centrifugal lift fan 8 and propulsion for the hovercraft is provided by a shrouded propeller 0 mounted towards the stern of the craft. The lift fan 8, propeller 10 and their drives are ail carried on the hull 2. in this example, as shown schematically in fig. 3, the lift fan 8 is driven (via a belt drive 12) by a diesei engine 14. The engine 14 exhausts in to the cushion air. The diesel engine 14 also drives an electric generator 16. Electrical energy from the generator 16 is transmitted to an electric motor 18 mounted in the hub of the propeller 10 to drive the propeller. in an alternative arrangement, shown schematically in fig. 4, the propeller 10' of the propuisor unit may be driven by the diesei engine 14' (via a belt drive) and the lift fan 8' driven by an electric motor 18' powered by a generator 16' that is driven by the diesei engine 14'. in the example shown in figs. 1 to 3, the diesei engine 14, lift fan 8 and generator 18 are provided as a single module, mounted to one another on a module frame 20, which can be installed in the hull 2 and subsequently removed from the hull 2 as a single unit. Also mounted on the frame are a battery 22 for storing electrical energy from the generator (e.g. to provide electrical power to the hovercraft and energy for starting the engine) and a fuel tank 24 from which fuel is supplied to the diesei engine 14.

The volute of the centrifugal lift fan incorporates cooling elements for the engine. These elements may be conventional automotive cooling matrices inserted into the fan volute or may take the form of fluid-filled passages built into the walls of the fan volute. This construction avoids the need for separate engine cooling arrangements, thus helping to minimise the overall dimensions and weight of the lift fan module. Rejecting engine heat to the flow of cushion air in this manner not only saves on power that would normally be expended on a separate cooling fan but also increases the volume of cushion air. The heating of the lift fan volute (including the fan intake) may also be exploited to reduce the build-up of ice during operations over water in cold climates. Three exemplary cooling arrangements are shown in figs, 5a to 5c.

More specifically, fig. 5a a conventional radiator 32 is located in the outlet of the volute 30. Air passing through the radiator 32 cools engine coolant that flows through the radiator. The arrangement shown in fig. 5b is similar but in this case the radiator 32' is mounted obliquely within the volute 30. With this arrangement there it is possible to have a larger radiator surface area exposed to the volute airflow than is possible with the arrangement of fig. 5a, increasing the cooling capacity. The arrangement shown in fig. 5c takes a different approach by using a double wailed volute 30'. Engine coolant flows through the cavity 34 between the two wails of the volute 30', either filling the cavity or, alternatively within pipes 38 housed in the cavity 34. Heat transfer from the engine coolant to the volute air flow is through the inner volute wall 38. To increase the effectiveness of this heat transfer the surface area of the inner volute wall is preferably increased by the addition of fins 40 that project from this wall into the volute. The cooled fluid may be liquid or air (as in the case of a charge-air cooler).

The shrouded propeller 10 used for craft propulsion is, as noted above, driven by an electric motor 18 that is powered indirectly by the diesei engine 14. The electric motor 18 is variable speed and reversible to control the speed of the craft. By reversing the direction of rotation of the motor 18 and hence the direction of rotation of the propeller 10 it is possible to quickly slow the craft or move it in reverse.

A propulsor unit, including the propeller 10, its shroud and mount for mounting the unit on the hull can be swivelled about a vertical axis to control the direction of air expelled from the propeller to steer the craft. This avoids the need for a rudder. The swivelling motion of the propulsor unit can be driven by another electric motor that is also powered by the diesei engine driven generator. Further, if the swivelling mount is configured to allow rotation about horizontal axes, the propulsor may be tilted to provide hovercraft control in roll or pitch thus avoiding the need for elevators. Freed from the constraints of mechanical transmissions and if considered useful, the propulsor may also be bodily raised or lowered.

The electric motors for the propeller drive and the swivelling of the propulsor unit are controlled by one or more motor control units 50, which receive inputs from operator controls (not shown) that the pilot uses to control the speed and direction of the craft. The hovercraft illustrated in figs. 1 and 2 is a relatively small passenger craft that has a single lift fan 8 and a single propulsor unit 10. The principles of the invention are, however, also applicable to larger craft using a greater number of propulsor units (i.e. two or more) for propulsion and steering of the craft and/or multiple lift fans. For example, fig. 6 shows a craft in which two lift fan modules 60, 62 are installed. Each module has the same components as the single module described above, including a diesel engine, a generator, batteries and a fuel tank. There are two propulsor units 64 (only one is seen in the figure) mounted on the rear of the craft, side-by-side, both driven by their own hub-mounted electric motor. In this example, the generator of the forward lift fan module 60 drives one of the propulsor units 64 and the generator of the aft lift fan module 62 drives the other propulsor unit. Alternatively both generators may feed into a shared power supply for both of the propulsor units.

By separating the drives for the propulsor unit propeiler(s) and the lift fan(s) in the manner proposed it becomes possible to drive the lift fan at constant or near constant speed, as is desired, whilst modulating the speed and even direction of the propeller to accelerate or decelerate the craft. This approach also avoids complex mechanical drive linkages that would be required if the propulsor unit(s) and lift fan(s) were to be driven by a single motor. The modular nature of the lift fan units and propulsor units provides benefits in terms of craft design and assembly, as well as offering easier maintenance and replacement of these units.

Various variations and modifications to the specifically described example are possible within the scope of the invention. For example, whilst the illustrated examples make use of diesel piston engines as the primary motor, other types of engine are envisaged for use with the invention, including gas fuelled piston engines and gas turbines. Similarly, the skilled person will appreciate that there are alternatives to the electric motors that exemplify the secondary motor, including for instance air motors and hydraulic motors.

Claims

Claims:

1 . A drive system for a hovercraft, the drive system comprising: at least one lift fan for creating a pressurised cushion of air below the hovercraft; at least one propulsor for generating forward thrust; a primary motor for driving one of said at least one lift fan and said at least one propulsor; and a secondary motor for driving the other of said at least one lift fan and said at least one propulsor; wherein the primary motor also generates energy to drive the secondary motor.

2. A drive system according to claim 1 , wherein the propulsor is driven by the secondary motor and includes a propeller, the secondary motor being mounted on the hub of the propeller to drive it directly without a gearbox.

3. A drive system according to claim 1 or claim 2, wherein the propulsor is mountable on the hull of the hovercraft in a manner that allows it to swivel, so that the direction of the air flow generated by the propulsor can be controlled by swivelling the propulsor in order to steer the craft.

4. A drive system according to any one of the preceding claims, comprising multiple propulsors, each propulsor having its own associated secondary motor, all of which are powered by the primary motor.

5. A drive system according to any one of the preceding claims, wherein the primary motor is an internal combustion engine.

6. A drive system according to any one of the preceding claims, wherein the secondary motor is a hydraulic motor, an air motor or an electric motor.

7. A drive system according to any one of the preceding claims, further comprising a generator that is driven by the primary motor to generate power to drive the secondary motor.

8. A drive system according to claim 7, further comprising an energy store for storing energy generated by the generator.

9. A drive system according to any one of the preceding claims, further comprising a fuel reservoir for the primary motor.

10. A lift fan module for a hovercraft, the module comprising: a hovercraft lift fan; a primary motor; a drive linkage through which the primary motor drives the lift fan; and a generator that is driven by the primary motor; wherein the lift fan, primary motor, drive linkage and generator are mounted to one another to provide a unitary assembly that can subsequently be installed in a hovercraft hull.

1 1 . A lift fan module according to claim 10, further comprising an energy store that also forms a part of the unitary assembly.

12. A lift fan module according to claim 10 or claim 1 1 , further comprising a fuel reservoir that also forms a part of the unitary assembly.

13. A drive system according to any one of claims 1 to 9 or a lift fan module according to any one of claims 10 to 12, wherein the lift fan is a centrifugal fan having a volute through which the lift air is expelled and the volute is used as part of a heat exchanger for cooling the motor.

14. A drive system or a lift fan module according to claim 13, comprising one or more conduits for engine coolant that pass alongside or within the volute wall.

15. A drive system or a lift fan module according to claim 14, wherein the conduit(s) for the engine coolant are provided by a radiator mounted within the volute.

16. A drive system or a lift fan module according to claim 14, wherein the volute has a double wall and the conduit(s) is within the wall.

17. A method used in constructing a hovercraft, the method comprising: assembling a lift fan module comprising: a hovercraft lift fan; a primary motor; a drive linkage through which the primary motor drives the lift fan; and a generator that is driven by the primary motor; assembling at least one propulsor module comprising: a propulsor; and a secondary motor for driving the propulsor; providing a hovercraft hull; and installing the assembled lift fan module and at least one assembled propulsor module on the hovercraft hull.

18. A hovercraft comprising a drive system according to any one of claims 1 to 9 or 13 to 16.

19. A hovercraft comprising at least one lift fan module according to any one of claims 10 to 16.

20. A hovercraft according to claim 19, comprising at least two lift fan modules according to any one of claims 10 to 16.