The use of axial flow fans is known for both movable and stationary applications.

Examples of movable applications include aircraft such as helicopters and hovercraft and examples of stationary applications include power generation plant and wind tunnels. Fans for both applications, however, relay on airflow created by rotation of the fan to perform a specified function.

The efficiency of an axial flow fan depends primarily on its effective surface area, that is, the area swept by the fan blades on rotation thereof and available for unimpeded flow of the resulting airstream. Since conventional axial flow fans are powered by motors which drive the axial shaft of the fan, a certain proportion of the swept area is occupied by the motor or other mechanical device such as a gearbox or other transmission means, which restricts a portion of the airstream and reduces the efficiency of the fan. It follows that, for a given required airflow, either the fan must be larger than would otherwise be necessary or the fan must be driven faster. Conventionally-driven fans also suffer from the disadvantage that the driving force creates a reaction tendency for the structure mounting the motor to rotate in the opposite direction.

Prior proposals have been made for driving fans by mounting ramjets on the outer extremities of the blades thereof. However, such proposals have required the fan to be mounted in a tubular housing or structure with a secondary fan at one end to draw combustion air therethrough.

It is an object of the present invention to provide an axial flow fan which avoids the disadvantages of prior proposals.

According to one aspect of the invention, an axial flow fan comprises a fan matrix including radially-disposed blades terminating outwardly in a cylindrical wall and rotatably mounted in a support structure, two or more ramjets being mounted on the external surface of the wall and oriented to cause the thrust to rotate the fan matrix within the supporting structure.

The ramjets are disposed equi-angularly around the periphery of the fan matrix in such a way that the fan is balanced. For example, if two ramjets are utilised they are disposed diametrically of the matrix and if four are utilised they are disposed at 90° increments around the periphery of the matrix.

The supporting structure in which the matrix is rotatably mounted preferably comprises a central housing enclosing a hub bearing for the fan matrix. Radial struts may extend from the central housing above and/or below the fan blades and ramjets to an external annular cylinder so that the fan matrix, together with the ramjets, is rotatable within the cylinder.

Preferably, the ramjets are angled about a lateral axis so that they are tilted upwardly, whereby the exhaust from each ramjet has a downward flow pathway and the intake air is "clean"and not already oxygen-deficient from the other ramjet or ramjets. Preferably, an annular series of angled vanes, of the type used as stationary vanes in a turbine, is disposed within and attached to the cylinder, slightly below the ramjets, so that the exhaust impinges upon the vanes, thereby enhancing the forward thrust exerted by the ramjets, and is deflected axially of the fan. It is also preferred that the ramjets are mounted within housings which define at one end an intake for combustion air and at the other end an exhaust duct. The mouth of the air intake is preferably shaped and angled for optimum efficiency in collection of air, particularly in view of the fact that the flow of air through the fan will be substantially at a right angle to the plane of rotation of the fan and therefore to the direction of motion of the ramjets.

The fan blades may be of the variable pitch type and for this purpose may be pivotally mounted about longitudinal (that is, radial with respect to the fan matrix) support members extending between the central housing and cylindrical wall. Means for adjusting the pitch may be incorporated in the central housing and operated remotely via connection means located in a radial strut of the supporting structure. Similarly, fuel for the ramjets may be supplied from an external source via ducting in a radial strut to the central housing and thence via ducting in one or more of the fan blades to the ramjets, suitable seals being provided at junctions between moving and stationary parts.

Auxiliary starting means are provided for initially causing the fan matrix to rotate at a sufficiently high speed for the ramjets to begin operating. Thereafter, the rotation is self-sustaining provided that fuel is continually supplied. The shape of the ramjets'air intakes may be such as to increase the velocity of air into the combustion chamber, thereby reducing the minimum rotational speed of the matrix required for starting of the ramjets.

For starting purposes, the fan blades are preferably feathered to minimise their drag.

According to another aspect of the present invention, an axial flow fan of the type described includes arrays of imbricated slats forming a louvred surface disposed respectively on each side of the fan matrix, the slats of each array being independently angularly adjustable to alter the direction of the intake and/or outlet air passing through the fan matrix. The arrays of slats are preferably rotatable about the axial fan axis. The louvred surfaces formed by the slats are closed or shut when the slats are in the imbricated position and are progressively and selectively openable as the slats are angularly adjusted from the imbricated position.

According to yet another aspect of the present invention, the annular supporting structure in which the axial flow fan is housed is mounted within an aircraft fuselage, preferably for pivotal movement between positions which facilitate transitional lifting force and propulsion force. For the purpose of forwards propulsion, the aircraft fuselage is preferably bifurcated towards the tail to allow unobstructed passage of airflow from the fan.

Referring to the aspect including imbricated slats, preferably the slats are pivotally mounted for rotation about their longitudinal axis to allow 90° of movement from a closed position, for example parallel to the fuselage when fitted in an aircraft, in order to maintain the optimum aerodynamic efficiency of the aircraft in forward flight, to an open position, for example orthogonal to the fuselage and preferably continuing a further angle of rotation, preferably from 45° upwards, for example 60°.

When thrust from the axial flow fan is not required, it follows that the fan blades will be stationary or feathered and the slats will be parallel to the fuselage (closed position). In the open position the slats will allow air to ingress and exit freely.

Preferably the arrays of inlet and outlet slats can be rotated about their longitudinal axis independently of each other so that, by way of example, when the inlet slats are at a right angle to the fuselage or angled to a certain degree toward the front of the aircraft, the outlet slats can be angled such that the thrust from the axial flow fan is vectored in a direction to lift the aircraft vertically or assist or maintain forward flight.

Preferably at least the outlet slats are mounted within an annular cylindrical structure, preferably with bearing means for rotation about the axis of the axial flow fan and within the confines of the fan outlet. This allows the downforce generated by the axial flow fan to be vectored rearwardly to assist or maintain forward flight or be directed laterally to achieve sideways movement or counter the yawing effect associated with vertical lift aircraft. The cylindrical structure may be rotated mechanically by means of, for example, a rack and pinion means.

A beam member may be mounted centrally to span the annular cylindrical structure. The beam member may be disposed at a right angle to the rotatable slats. The slats are thus divided into two sectors, one sector on either side of the beam member. The beam member may have bearing means to accept inner slat-carrying shafts, outer slat-carrying shafts being journalled in bearing means disposed on the inner wall of the cylindrical structure.

The slats may be rotated about their shafts by means of a slide bar carried on the beam member and having camming grooves formed therein, the grooves accommodating cam followers carried by the slats to effect rotation of the slats on sliding of the bar. The cam followers preferably comprise rollers.

It follows that when the slidably mounted bar is moved to a pre-determined position along the beam member, the pivotally mounted slats will rotate about their axis to the required fixed position.

The slidably mounted bar may be moved longitudinally by, for example, a hydraulic or electromechanical linear actuator.

Referring to the aspect of the present invention in which the annular supporting structure, in which the axial flow fan is housed, is pivotally mounted within an aircraft fuselage, the annular supporting structure is preferably carried between trunnion means suitably located on either side of and aligned transversely to the longitudinal axis of the aircraft. The aircraft fuselage may have a bifurcated configuration, the supporting structure being carried between the bifurcated parts thereof. The supporting structure may be carried in each wing of an aircraft.

Preferably, rotating means, for example rotary actuators, can be suitably mounted to the trunnion means, whereby, when the fan matrix axis is at a right angle to the longitudinal axis of the aircraft fuselage, that is to say the efflux of air from the axial flow fan is directed in a downward direction, a vertical lift capability is possible and when the fan matrix axis is rotated towards the longitudinal axis of the aircraft fuselage, a gradual transition from vertical lift to forward flight can be achieved as the efflux of air from the fan is directed rearwardly. Fuel supply, variable pitch fan blade control and fan starting capability can be accessed through tubular trunnion means.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings of which:- Figure 1 is a plan view of a fan according to the first aspect of the invention; Figures 2 is a cross section along the line A-A of Figure 1; Figure 3 is a cross section along the line B-B of Figure 1; Figure 4 is a plan view of the supporting structure of the fan of Figure 1; Figure 5 is a cross section along the line C-C of Figure 4; Figure 6 is a plan view of the fan matrix and ramjet housings of the fan of Figure 1; Figure 7 is an oblique view of an array of slats for use in the second embodiment of the invention; Figures 8 and 9 show the slats of Figure 7 in the closed position; Figure 10 shows a plan view of the slats of Figures 7 to 9 in the open position, showing axial fan blades behind; Figures 11,12 and 13 show the mechanism for controlling the pitch angle of the slats; Figure 14 shows the underside of an aircraft with variable pitch slats open and laterally disposed; Figure 15 shows the underside of the aircraft of Figure 14 with the slats open and diagonally disposed; Figure 16 shows an oblique diagonal top view of an aircraft with variable pitch slats closed and laterally disposed; Figure 17 shows a plan view of the aircraft of Figure 16 with the slats open and laterally disposed; Figure 18 shows a plan view of a bifurcated-fuselage aircraft with a rotatable axial flow fan mounted therein; Figure 19 shows an oblique diagonal top view of the aircraft of Figure 18; and Figures 20 to 22 show side views of the aircraft of Figures 18 and 19 with the rotatable axial flow fan axis disposed respectively at a right angle, a 45° angle and parallel to the longitudinal axis of the aircraft.

Referring firstly to Figure 1, an axial-flow fan is shown generally at 10 and consists of a fan matrix including fan blades 11 the outer edges of which abut the inside wall of an annular cylindrical ring 12 (see also Figures 2 and 6). The fan blades 11 are of the variable pitch type and are pivotable about shafts 13 which extend between a central hub 14 and the ring 12. Ramjets 15 (Figures 2 and 3) are mounted in housings 16 attached to the outside wall of the cylindrical ring 12; the housings define air intake scoops at their front ends 17, considered in relation to the direction of rotation of the fan, and exhaust ducts at their rear ends 18. The ramjets and housings are mounted at an angle so that their thrust is directed to have a rearward and a downward component, as illustrated in Figure 3.

The hub 14 of the fan matrix is rotatably carried by a shaft 19 journalled in bearings 20 located in a streamlined axial housing 21 from which extend radial upper 22 and lower 23 struts to an outer annular cylindrical wall 24. Fixed to the inside of the wall 24 are angled vanes 25 (see in particular Figures 4 and 5). The vanes are so arranged that the thrust from the ramjets impinges upon them.

One of the struts 22 carries a fuel line 26 which communicates via a seal 27 in the housing 21 with a passageway 28 formed in the hub 14 and radial lines 29 formed through the fan blades with the ramjets. The fuel, once fed to the hub, is urged to the ramjets by centrifugal force, once the fan matrix is revolving. A variable pitch control shaft 30 is carried within one of the struts 23 and controls a variable pitch mechanism 31. A starter motor 32 is contained within the housing 21.

In use, the fan blades are feathered and the starter motor is caused to initiate rotation of the fan matrix. When the matrix has attained a suitable peripheral speed, that is, when incoming air is compressed in the combustion chambers by the ram effect to a sufficient extent, the fuel is admitted to the combustion chambers and combustion takes place. The peripheral speed then increases further, the starter motor is disengaged and stopped, and the fan operation is self-sustaining. The fan blades may then be adjusted to the required pitch to create the necessary air flow. Exhaust cases from the ramjets impinge on the vanes 25 to enhance the efficiency of the fan and are deflected generally axially and away from the intake air region of the ramjets.

Fans according to the invention may be incorporated into hovercraft, vertical and short take-off and landing aircraft, either in an air-foil section thereof such as a wing or into a fuselage.

With reference to Figure 7 onwards, Figure 7 shows arrays of slats 71,72 disposed respectively on each side of a beam member 73 which extends diametrally across an annular support 74 which is mounted within the deflected exhaust stream of ramjets mounted on fan blades, as described with reference to Figures 1 to 6. Radially-disposed support struts 75 are secured to an outer annular cylindrical wall 76, whereby the support 74, struts 75 and wall 76 define a series of arcuate slots 76A through which pass hot exhaust gases from the ramjets. The slats 71,72 are journalled at their respective ends in bearings carried by the beam member 73 and by step formations 77 attached to the inner wall of the annular support member 74. The slats are shown in the fully-open position, whereby high pressure air from the fan passes through the array of slats and exits axially of the annular support.

Figure 8 shows the slats 71,72 in the fully-closed position, in which adjacent slats are in an imbricated relationship. Figures 9 and 10 are plan views, in which the slats are shown in the fully-closed position in Figure 9 and in the open position in Figure 10, revealing the fan blade assembly, as described with reference to Figures 1 to 6, behind.

With reference to Figures 11 to 13, the slats 71, shown in cross section, are journalled at 78 in the beam member 73 to which is attached a slidable bar 79. The bar is formed with camming slots 80 in which are engaged cam follower rollers 81 attached to respective slats 71. As shown in Figure 11, the slidable bar has been moved fully to the left and the camming action as between the slots 80 and the cam followers 81 has caused the slats to rotate in an anticlockwise direction to adopt the closed, fully imbricated, position in which the tapered ends are in overlapping and abutting relationship, whereby the faces of the slats present upper and lower planar surfaces. In Figure 12, the slidable bar has been moved to the right and the slats have moved in'a clockwise direction to adopt a fully-open position; in Figure 13, the bar has been moved further to the right and the slats have rotated further in a clockwise direction to adopt an open arrangement where the exhaust gases are vectored laterally to the right as shown. A multi-directional vectored thrust capability is thereby provided; optionally, some of the high pressure air from the axial flow fan can be ducted to various nozzle outlets suitably located on the airframe of the aircraft to provide controlled stabilising means. Furthermore, each array of slats 71,72 may be journalled at their inner ends in separate, independently-operable slide bars 79, whereby a bilateral contra-vectored thrust may be provided.

Figures 14 and 15 show how the slats may be rotated about the axis 90 of the fan to provide multi-directional vectored thrusts the slats being orthogonal to the longitudinal axis of the aircraft 91 in Figure 14 and at an oblique angle thereto in Figure 15. As shown, the slats are mounted in the exhaust stream from the fan and therefore need to be formed from a suitable heat-resistant material but, as shown in Figures 16 and 17, slats may also be provided on the inlet side of the fan.

Figures 18 and 19 show how the fan and slats may be pivotably mounted as an assembly in a cylindrical support 92 between trunnions in a bifurcated air frame configuration 93, in which the trunnion axis Y-Y is orthogonal to the longitudinal aircraft axis X-X. As shown in Figure 19, the aircraft has vertical tail fins 94 attached to the inner side of each wing constituting the bifurcated arrangement and an elevated tailpane 95, whereby exhaust from the fan has an unobstructed rearwards pathway when the support 92 is in the position for imparting a forwards propulsion force, as shown in Figure 22.

Figures 20 to 22 illustrate how an assembly of axial flow fan and slats, mounted in an annular housing supported on trunnion axis Y-Y as in Figures 18, can be rotated about that axis to provide downward thrust (Figure 20), thrust angled rearwardly and downwardly (Figure 21) and rearwardly directed thrust (Figure 22). In this way, the invention provides thrust which can be vectored from a direction in which it assists take off of the aircraft through transitional positions to a position providing forward movement of the aircraft.