WO2008031174A1

WO2008031174A1 - Aerodynamic lifting device and airborne craft

Info

Publication number: WO2008031174A1
Application number: PCT/AU2007/001718
Authority: WO
Inventors: Christopher Kim Schlunke
Original assignee: Entecho Pty Ltd
Priority date: 2006-09-12
Filing date: 2007-11-09
Publication date: 2008-03-20

Abstract

A device useful for generating lift in airborne craft has a radial drum or drum rotor fan with an operating region intermediate the power loading ('y') asymptotic region and the disc loading ('x') asymptotic region of a power loading - disc loading characteristic for the lifting device. The drum rotor fan comprises a fan with a rotor, the rotor having a rotational axis and comprising a plurality of rotor blades disposed in an annular ring about the rotational axis and a driving means for the rotor such that, on operation of the driving means, lift is generated. A thrust vectoring means is advantageously included for directional control of vehicle incorporating the lifting device.

Description

AERODYNAMIC LIFTING DEVICE AND AIRBORNE CRAFT

This invention relates to aerodynamic lifting devices for airborne craft and the airborne craft employing such devices.

Powered airborne craft, manned and unmanned, may be capable of hovering in a stationary position while airborne. Such aircraft may range from craft which operate close to the ground relying on a cushion of air to those capable of free flight and vertical take off and landing. Craft operating close to the ground may be designed for transportation and recreational use whereas the free flight craft may operate at generally low altitudes compared to commercial aircraft and may be considered for applications including airport-to-downtown shuttle, home-to-office commuting, search and rescue and surveillance operations.

The most common craft that hovers close to the ground is the hovercraft which is generally a craft used for recreational and general transport and ferry duties. This craft has a number of disadvantages that have limited its penetration of markets for motorized recreational products and general transportation of personnel and goods.

One important limitation of such craft is the inability to operate over terrain with obstacles of significant size such as waves, boulders, riverbanks and the like because close contact must be made with the ground to avoid the leakage of the air cushion. Hovercraft rely on the static air pressure generated under the craft to maintain them above the ground. The skirt of the hovercraft is used to maintain this air pressure whilst allowing the craft to move. Any increase in the operating height of the hovercraft (resulting in a loss of air pressure under the skirt) is accompanied by an unrealistic horsepower requirement. A further notable limitation is the inability to develop significant lateral thrust for acceleration, braking, climbing gradients and changing direction with realistic horsepower requirements despite the use of separate fans for developing this lateral thrust. In general, the "footprint" of the hovercraft is acceptably small for its lifting capacity because the entire area under the craft and an appropriate peripheral skirt encapsulates an air cushion which can operate at sufficient pressure with low power requirements provided that the clearance between the grounds and the skirt is small so as to minimize air leakage. The most common and widely employed free flying vertical takeoff and landing (VTOL) craft that operates at higher altitudes is the helicopter. The success of this vehicle is due to the urgent need for this VTOL capability and the ability to achieve hovering flight with acceptable power consumption because of the very large amount of air that is contacted by the large diameter lightweight blade structure. The main undesirable characteristic of helicopters is the long rotating blades, which are a hazard to personnel and to the aircraft itself should they strike anything in the area and the very large footprint or minimum safe space requirements that these aircraft require, particularly during takeoff and landing.

Further undesirable characteristics include the requirement for a remotely mounted propeller to counteract torque reaction of the airframe to the drive of the main rotor, complicated and relatively fragile rotor blade attack-angle controls, high maintenance requirements and rotor blades which must be long, thin, and relatively light and thus are flexible and subject to fatigue problems. Add to this incomplete list of limitations the fact that failure of any one of these components is likely to have catastrophic consequences for the aircraft and all on board and it is evident that an alternative design is desirable.

In a craft free of ground effect, lift can be generated by the acceleration of a mass of air by a fan, propeller, wing, or other system. When a mass of air is changed from rest to a given velocity in a downward direction, an upwardly directed reaction force is produced. In general, the more air that is directed, the less power is required to produce a given lift. This defines the technical challenge which this invention attempts to address because increasing the volume of air generally involves an increase in the size of the craft as evidenced in the large diameter, high speed blades used in helicopters.

The rotor blades of a helicopter develop lift by accelerating air downward and parallel to the axis of its rotation (axially). The velocity of the tip of the rotor blade is typically set to a maximum that is close to sonic conditions (being approximately 1250 km/hr at sea level and normal temperatures) on the advancing blade when the helicopter is at maximum forward speed (typically helicopters are limited to forward speeds of about 320 km/hr, which means that the tip speed relative to the helicopter itself is of the order of 900 km/hr ie 250 m/s). The remainder of the blade must operate at a lower velocity proportional to its distance from the axis of the rotor. Unfortunately this non-uniform velocity along the blade means that significant blade length is underutilized despite varying the angle of attack and changing the aerodynamic profile along the length of the rotor blade because lift is proportional to the velocity squared. To compound the problems of the rotor, because the highest lift is generated at the highest velocity region, at the tip a very high bending moment is generated on this cantilevered structure. Further, to get the maximum lift from the rotor, the blade tip must operate at the highest permissible velocity close to sonic conditions, which means that considerable aero-acoustic noise is generated. Correspondingly the rotor diameter cannot be reduced because to generate the same lift, the velocity would have to increase beyond sonic conditions or some part of the operating envelope would have to be compromised.

Further, and within the class of airborne hovering craft capable of free flight, it would be a desirable object to achieve an increase in payload or lift at the same or reduced power in order to improve fuel efficiency and operating cost.

It is a further object of this invention to provide an aerodynamic lifting device for airborne craft such that such craft deliver performance characteristics superior to helicopters by generating superior lift capability and/or a reduced horsepower requirement from a lifting device with a smaller footprint.

It is a still further object of this invention that the fan geometry and powertrain used to achieve operation provide a convenient, stable and safe loadspace for manned and unmanned operation.

It is a still further object of this invention that the fan geometry provides for safer and quieter operation, including in areas where obstacles may be present and/or for operation close to the ground for extended periods.

With these objects in view, the present invention provides, in one aspect, an aerodynamic lifting device comprising an airflow generating means and a thrust vectoring means wherein the airflow from the airflow generating means acts on an inner side of the thrust vectoring means and wherein the device has an operating region intermediate the power loading ("y") asymptotic region and the disc loading ("x") asymptotic region of a power loading - disc loading characteristic for the lifting device. Such an aerodynamic lifting device may be used in airborne craft, particularly hovering craft, whether manned or unmanned.

The thrust vectoring means provides directional control of the device. The thrust vectoring means may be defined as a shroud. It may be flexible at least in part and may comprise a flexible portion, movement of the flexible portion resulting in thrust vectoring. The thrust vectoring means, or shroud may also be of varying flexibility comprising flexible and rigid portions.

The airflow or fluid flow generating means may take the form of a fan. The fan may be in the form of a rotor. Such a fan may be a radial drum fan or drum rotor fan. Such a fan may have the blades of the rotor parallel to the axis of rotation of the fan. The blades are advantageously of constant cross section along the length of the blades and have an aerodynamic profile comprising a leading edge, an increasing blade thickness reaching a maximum between the leading edge and a trailing edge, and a trailing edge thickness which is less than the leading edge thickness. The rotor may be driven by a hubless drive means. The fan may also incorporate further attributes of construction and geometry as described below. An aerodynamic lifting device comprising such a fan forms a further aspect of the invention. In a further related aspect, there is provided an aerodynamic lifting device having a radial drum or drum rotor fan for generating lift for the device which has an operating region intermediate the power loading ("y") asymptotic region and the disc loading ("x") asymptotic region of a power loading - disc loading characteristic for the lifting device.

The drum rotor fan may comprise a rotor having a rotational axis and comprising a plurality of rotor blades disposed in an annular ring about the rotational axis and a driving means for driving the rotor such that, on operation of the driving means, lift is generated. An aerodynamic lifting device comprising such a fan forms a further aspect of the present invention.

The blades may extend parallel to the rotational axis of the rotor. The blades advantageously occupy a region which has a radial depth which is small relative to the distance at which the blades are disposed from the rotational axis. Preferably, the blades occupy an annular region about the axis of the fan which has a radial extent that is less than 25% of the radial pitch of the blades. Preferably, the fan may be driven by a hub-less drive using a friction drive, belt, gear or other drive, wherein the fan is supported and guided for rotational motion at its periphery. This drive arrangement gives the flexibility of better packaging of the load/passenger space in the centre of the fan (i.e. there is no need for a central shaft to occupy this area) and also avoids the issue associated with out of balance rotational forces of a central drive shaft mounted drum rotor fan. The use of a hub-less drive arrangement for a drum rotor fan may be of particular benefit for fans used in ventilation or air-conditioning applications as a result of the packaging arrangement (which may allow for a particularly compact axial length of the fan/drive assembly which may be useful in certain applications) and/or the rotational balance benefits arising from the lack of a central drive shaft mounted fan, as discussed above.

Preferably, the air flow though the fan is managed in such a way that air enters the rotor at the radially innermost side, is acted upon by the rotor blades, is discharged at the radially outermost side of the rotor and is then re-directed in a generally axial (ie downward) direction.

Preferably, the blades have a longitudinal extent parallel to the rotor axis and the flow through them is primarily radial or perpendicular to the rotor axis, from the inner side of the annual ring to the outer side. In this way substantially the entire length of the blade operates at a similar velocity, generating the maximum amount of momentum in the air for minimum blade mass and minimum vehicle overall size. By avoiding the radially extending blades associated with the lifting craft in service at present, or disclosed in the patent literature, the optimum blade velocity and blade geometry can be utilized, and the size, cost and weight of the structure can be minimized. Further, the blades can be restrained at each end, or their upper and lower extent, by respective retaining rings or endplates that minimize the bending moment on the blade generated by the aerodynamic loads. This allows for a lighter blade structure, lighter vehicle structure and ultimately for the reasons noted above a reduced vehicle size. Preferably, the device includes a stator that has stator blades that are upstream and/or downstream of the rotor blades. Preferably, the stator produces a torque in the opposite direction to the torque on the rotor. Advantageously, the opposite torque produced by the stator is approximately equal in magnitude to the torque on the rotor.

Preferably, at least some of the stator blades are located upstream, that is at the radially inner side, of the rotor blades.

Conveniently, the stator blades can be designed and spaced apart so as to give some protection to the rotor blades from ingress of foreign materials, and/or prevent an operators limbs for coming into contact with the rotor blades.

The stator may comprise retaining means for the retention of downstream stator blades. The retaining means may comprise upper and lower retaining rings for these stator blades forming a diffuser duct such duct feeding air to a thrust vectoring means, air flowing through the diffuser duct generating a lifting force on a lifting face of the thrust vectoring means for generating a lifting force.

Respective facing surfaces of the retaining rings or restraining endplates may converge towards the radially outer side of the retaining rings or restraining endplates. Conveniently, the flow area at the inner side of the drum is approximately the same as the flow area at the outer side of the drum. The convergence of the retaining rings reduces the height of the flow area of the outer side of the drum, and since this area is at a greater radius than the inner side of the drum, the actual flow areas can be maintained approximately equal. It is believed that this arrangement provides an increase in lifting force on a lifting face of the thrust vectoring means.

Wings to generate lift may be mounted on the input airflow side. For example, upper face(s) of the inner and outer hub or stator of the fan which are disposed near the inlet or low pressure side of the fan may be contoured to function as wings and produce significant lift by developing high velocities and lower pressures near these surfaces. The reference to the inner and outer hub or stator is a reference to that part of the stator which is radially inward of the fan and radially outward of the fan respectively. An annular airfoil or airfoils may be deployed to improve lift while the craft is hovering while also functioning as a flow deflector to improve the radial flow into the stator and fan assembly. Desirably, this annular airfoil can also function as the upper restraint for the inner stator blades. Preferably, the input airflow side may include an upper inlet duct comprising one or more annular wings or guide vanes. Such upper inlet duct may be at least partially defined by a lip which is disposed around the most radially inward upstream circumference of the rotor of the drum rotor fan. Advantageously, said lip forms part of the annular airfoil which functions as an upper restraint for the inner stator blades. Further, advantageously at least part of said wings or guide vanes are disposed in an inlet region containing radially directed airflow.

Alternatively, or in addition to the inlet duct, an outlet duct comprising one or more annular wings or guide vanes is provided. Such outlet duct may be at least partially defined by a lip which is disposed around the most radially outward, downstream circumference of the rotor of the drum fan. Advantageously, the wings or guide vanes are disposed in an outlet region containing radially directed airflow. Preferably, those portions of the stator blades disposed above the upper inlet duct are contoured so as to provide approximately the same degree of circumferential acceleration to the airflow at the inlet to the rotor blades as that provided by the portion of the stator blades which are disposed below the upper inlet duct. Advantageously, this can be achieved by the use of a "twister" portion at the upper end of the stator blade. This feature is particularly beneficial for airflow which emanates from a region at a radius close to the radius of the inlet of the rotor blades and above the top of the rotor blades as this air does not traverse the same radial extent of the inlet stator blade and is not provided with the same degree of circumferential acceleration as air which enters the stator blades at their lower extent and therefore traverses the complete radial extent of the stator blade.

Preferably, the twister portion of the inlet stator blade comprises an upper portion which is displaced circumferentially at its radially outer extent relative to a portion of the blade below said upper portion. In either case of an inlet duct or an outlet duct, the corresponding lip may be contoured to develop lift.

Preferably, in the case of an inlet duct, the lip extends over and radially beyond the upstream facing edge of the rotor blades. In the case of an inlet duct, the corresponding lip may have the associated wings to generate lift disposed about it, both upstream and downstream and radially inward of said lip.

In operation under such circumstances, air flow would be directed radially inwardly and flowing over the top of the lip, then downwardly and around the most radially inward part of the lip and then radially outward under the lip and towards the rotor blades.

Preferably, the upper inlet duct comprises stator blades that correspond to stator blades disposed below the upper inlet duct. In either case of an inlet duct or an outlet duct, the corresponding lip may have the associated wings disposed about it, both upstream and downstream and radially outward of said lip. Preferably, the wings develop positive lift.

Alternatively, and somewhat counter intuitively, even when design constraints dictate that such wings will develop negative lift, they are still to be advantageously applied in order to provide guidance of the air around the lip to enhance the performance of said fan or enhance the overall lifting performance of the device.

The wings may form an aerodynamic slot by being spatially disposed to each other and/or the associated lip. The aerodynamic slots would desirably be configured to accelerate the boundary layer over said wings and prevent or delay separation of the air stream from the lifting surfaces.

Preferably, said aerodynamic slots are greater than one/one hundredth of the chord of said wings and less than one/tenth of the chord of said wings. Using a radial drum or drum rotor fan as means to generate thrust for an airborne vehicle places high demands on the rotor blades.

Advantageously, the fan blades have aerodynamic profiles. The fan blades may be contoured so that the aerodynamic lifting forces acting on the blades are approximately opposite in magnitude, and direction to the centrifugal forces acting on said blades in use. Advantageously, the aerodynamic loading on a blade of the rotor is in opposite direction to the centrifugal loading on the blade. The blades may take the form of known aerodynamic wing profiles such as the NACA series of profiles. The blades may be contoured by varying at least one of the group consisting of chord length, blade thickness, radial position, camber and camber position. Such contouring provides advantages including fan efficiency, noise, the ability to operate satisfactorily with differing inlet air velocities and different angles of attack, and reduced mass of the blades construction for a given working duty.

The geometry of such blades may include (but is not limited to) a forward facing (concave face towards the direction of rotation) with the blade including a leading edge (relative to the direction of rotation) forward of the trailing edge (relative to the direction of rotation). Blade thickness may reach a maximum between the leading edge and the trailing edge. Trailing edge thickness is less than leading edge thickness.

Conveniently, the blades are of a constant cross-section.

Preferably, such blades are of composite or metallic material. Blades may be manufactured by an extrusion process as commonly used in the aluminium or plastics industry.

Alternatively, the blades may be manufactured by wire cutting a blank which may then be coated by tape and/or fibre and resin for reinforcing and protection of the blank shape.

Accordingly, fans employing such blades form another aspect of the present invention. In this aspect, fans - such as drum rotor fans - suitable for ventilation or other purposes may comprise blades as above described.

Application for fans of this type may arise, for example, in the mining industry. In addition, the blade contour aspect of the invention would have benefits for any fluid dynamic device utilising radial drum or drum rotor style fans or pumps. Radial outflow of air from the drum rotor fan is desirably converted to pressure in a suitably shaped duct formed beneath an outer hub thereby maximizing the lift generated by the process. The increase in pressure which occurs through the blades of the fan as a result of the acceleration of the airflow by the blades, may be optimized by the design of a radial duct provided downstream of the fan. The radial duct directs the flow downward and optimizes the pressure field developed downstream of the fan to generate the maximum lift.

The change in area of this radial duct in the direction of the airflow increases by no more than 1.5 times from inlet to exit and decreases by no less than 0.5 times from inlet to exit. It is also an aspect of this invention that the mean flow path length of this radial annular flow path may vary from the minimum possible length that deflects the air through 70 degrees to 110 degrees up to 3 times this length. The radial duct may be in the form of a shroud or skirt constructed from a flexible material that surrounds the drum rotor fan and deflects the airflow to provide a compact lightweight means for directional control of the craft. This is to be contrasted to the skirt of a conventional hovercraft which simply maintains a close contact with the ground rather than providing a means to deflect the airflow to provide thrust and directional control of the craft. The radial duct or shroud may have a circumference disposed outwardly from the radial drum fan.

Preferably, an outer shroud is used to re-direct the air discharged from the fan.

Preferably, the shroud has an air discharge area which is in the range of 0.5 to 2.0 times that of the discharge area of the fan. Preferably, the discharge area of the shroud is approximately equal to the discharge area of the fan.

The fan discharge area is equal to the height of the blades multiplied by the dimension of the outer circumference of the fan. The discharge area of the shroud may be in the form of an annulus which is in a plane perpendicular to the axis of the fan (ie a horizontal plane in the case of a vertical axis fan). Preferably, the radius of the outer part of this annulus is approximately equal to the outer radius of the fan plus the height of the fan blades.

Preferably, the shroud transitions between an upper most region proximate to the upper portion of the fan to a discharge region in a aerodynamically efficient manner. By using a smooth transition, the air flowing out of the fan does not undergo unnecessary energy losses as it flows to the discharge of the shroud.

An actuation means may be used to move all or part of the shroud relative to the stator assembly. Preferably, movement of all or part of the shroud results in a change in the position of the centre of action of the lifting forces when projected in a horizontal plane. Alternatively, or in addition, movement of all or part of the shroud results in a change in direction of the resultant thrust vector acting on the craft. Movement of the centre of action of the lifting forces results in a tilting of the craft about its centre of gravity. The tilting action results in the thrust vector changing direction and propelling the craft in the direction of the tilt.

A further means of producing lift when close to the ground, effective in takeoff and landing, is "Ground Effect." This is roughly equivalent to creating a zone of very slight compression in the air between the vehicle and the ground and using that pressure applied to the lower projected area of the vehicle to help support said vehicle. This ground effect becomes stronger as the ground is approached and becomes negligible as the vehicle lifts away from the ground. The ground effect is also utilised in combination with the other lifting aspects by deploying said flexible flow deflecting duct at a distance which is sufficiently close to the ground to generate significant additional lift when it may be required for take-off or very high payloads. In this case the flexible flow deflecting duct effectively acts in a similar capacity as the skirt of a hovercraft.

In a further embodiment of this invention, there is provided an airborne lifting device comprising: a vertical axis fan with a plurality of blades whose axes are also vertical or near vertical disposed at a distance from said axis, said blades occupying an annular region which has a radial extent which is small relative to said distance and generating primarily radial airflow; a stator assembly that comprises an inner load carrying hub and lifting surfaces, stator blades that are radially inward and/or outward of said fan blades; and a thrust vectoring means.

The thrust vectoring means may take the form of an outer shroud that incorporates upper and/or lower aerodynamic lifting surfaces. This shroud is used for directional control and may enable a variety of maneuvers for an airborne craft employing the airborne lifting device.

Preferably, the vertical axis or drum rotor fan comprises vertical or near vertical blades which may have constant cross section. The fan may include an upper retaining ring for said blades and a lower retaining ring, said rings forming a diffuser duct in conjunction with said shroud for the purposes of generating the maximum pressure over the largest horizontally projected area of the lower lifting face of the shroud for generating a lifting force. The shroud may be flexible or be of varying flexibility in selected directions or regions and may be constrained at its inner and/or outer periphery. Shroud constraints may be moved by an operator or controller as a thrust vector to effect directional control of a craft employing the lifting device. The retaining rings or restraining endplates may have facing surfaces that converge towards the radially outer-side of the rings to form the diffuser duct. Advantageously the degree of convergence of the retaining ring faces is such that the flow area into the drum rotor fan is approximately the same as the flow area at the exit of the drum rotor fan The fan may be driven by a ring on the rotor, such as the lower retaining ring, using a friction drive, belt, gear or other drive, such drive being provided by a source of power disposed near the said retaining ring or radially further inboard toward the centre of said load carrying hub.

Conveniently, the fan may be supported for rotation by bearings disposed between, and bearing against, the upper and/or lower retaining rings.

The stator may be mounted inboard of the rotor and so as to provide a support for the payload. Aerodynamic device(s) or surfaces providing lift may be mounted on the input airflow side of the rotor and may form part of a retaining ring which supports the blades of the stator. An inner hub of the stator may incorporate an upper payload carrying and lifting surface and may have a load space beneath it. Radial dimensions of said inner hub, stator blades, fan blades and outer shroud are advantageously minimized to generate the smallest possible footprint while still creating sufficient lifting surface area and sufficient airflow at a low enough pressure to minimize the power required for lift. In contrast to the practice of using axial flow fans (as in helicopters) for generating lift, there is provided a radial flow fan lifting device in which blades of limited radial dimensions are adopted to create a static load carrying space in the centre of the craft such that craft overall dimensions are minimized for a given lifting capacity. Further, the rotor blades are thereby positioned in a fixed radial location so that the total length of all the blades in the rotor assembly operate at a similar and optimized velocity to accelerate the largest amount of air over suitably disposed adjacent lifting surfaces thereby minimizing the horsepower required to generate lift within a small vehicle envelope. Further, the fan geometry provides operation of airborne craft with competitive lift/power performance with a much reduced footprint or weight/area ratio when compared to current craft. At the same time, the fan geometry provides a convenient central stable safe load space for manned and unmanned operation. A manned airborne craft such as a VTOL craft, having the above described lifting device preferably comprises an operator area for housing an operator and operator controls for maneuvering the airborne craft. The operator area may be disposed such that, in operation, the centre of gravity of the operator is at or below the uppermost extremity of the rotor blades and further located such that the operator has a clear line of sight over the top of the fan.

This positioning of the operator provides a number of benefits. The centre of gravity of the craft is at least 0.3 times the craft diameter below the intersection of the line of action of the lifting forces when the craft is tilted at an angle of 45 degrees. Firstly, the operator is located in a safe position within the craft structure because the significant energy must be expended in the event of an impact by deforming the shroud rotor, stator and inner hub before there is any intrusion into the operator's cockpit.

Advantageously, the driving means for the rotor is configured such that the inside of said rotor is not occupied by rotating components that would intrude into the free load space thereby made available. The driving means may include a friction or belt drive, a gear drive, a chain drive or an inductive or magnetic drive. A belt drive may incorporate a belt which has teeth on the outer side which engage in a driving pulley mounted on an engine or motor, an idler pulley that changes the direction of the belt so as to create sufficient wrap angle on said driving pulley, and a flat side on said belt that drives an outer rim of an annular flange that is connected to said rotor blades.

A particular advantage of the aerodynamic lifting device and airborne craft of the present invention is the lesser noise compared to helicopters and other similar craft. For a craft capable of carrying a human operator, a rotor diameter of approximately two (2.0) meters may be employed. The rotor blade tip speed may be advantageously set to a maximum of below 100 m/s. In an experimental model being developed by the applicant the maximum blade tip speed has been set to approximately 50 m/s with good results. This enables a comparatively low disc loading which enables a better power loading. This blade tip speed can be compared to a typical helicopter blade tip speed which is discussed earlier in this specification. The blade tip speed criteria apply also to the drum rotor fan described above, that fan being adaptable to various applications other than airborne craft.

The fan, aerodynamic lifting device and airborne craft of the present invention may be more fully understood from the following description of preferred embodiments thereof made with reference to the accompanying drawings in which:

Fig. 1 is a graph of power loading vs disc loading which indicates the calculated lift performance and power requirements of a range of helicopters and an aerodynamic lifting device according to the invention. A curve, which indicates the performance indicated by the momentum equation, is also shown along with a similar curve that predicts the performance of a helicopter that is just capable of hovering with no additional horsepower available for climbing or for operation at higher altitudes.

Fig. 2 is a diagrammatic half sectional view of an embodiment of the invention that indicates the primary lifting surfaces of the aerodynamic lifting device of the invention.

Fig. 3 is a diagrammatic half sectional view of the aerodynamic lifting device compared to a rotor blade lifting mechanism used by a helicopter scaled to demonstrate the size benefits of this invention.

Fig. 4 is a sectional view of an airborne craft in accordance with a preferred embodiment of the invention that indicates the primary lifting surfaces of the aerodynamic lifting device of the invention.

Fig. 5 is a schematic drawing of an airborne craft in accordance with the preferred embodiment of this invention shown in Fig. 4.

Fig. 6 is a sectional view of the airborne craft of Fig. 5 that shows the flexible shroud or thrust vector in an offset position with the lower rigid ring displaced to effect a change in direction.

Fig. 7 provides images of a flexible shroud thrust vector for the airborne craft of Figs. 4 to 6 shown in various positions. Fig. 8 is a sectional view showing the disposition and geometry of the rotor blades and inlet stator blades for a radial drum fan employed in preferred embodiments of aerodynamic lifting device and airborne craft of the present invention such as shown in Figs. 4 to 7. Fig. 9a is a sectional view showing the use of an upper inlet duct and an outlet duct and associated wings and slots in a second embodiment of aerodynamic lifting device and airborne craft of the present invention having a diameter of approximately 600 mm and adapted for unmanned operation. Fig. 9b is a detail of Fig. 9a showing the diffuser duct configuration. Fig. 10 shows a partial isometric view of the inlet stator blades of the aerodynamic lifting device shown in Fig. 9a.

Fig. 11 is a sectional view of the airborne craft shown in Fig 9a showing two alternative positions of the shroud.

Referring to Fig. 1 , there is shown a power loading ("y") vs disc loading ("x") characteristic conventionally used in the field of helicopter design and showing operating points for helicopters using long rotating blades in accordance with current practice. These points assist in defining an operating region for current hovering craft which corresponds to a region in which power loading asymptotes and which may be described as the power loading or y asymptotic region 270. Intermediate this region and the disc loading or x asymptotic region 290 lies an intermediate region 300 forming the design envelope for airborne hovering craft forming one aspect of this invention. The intermediate region 300 may also be defined, by way of more specific example, as an operating region in which an aerodynamic lifting device or airborne craft (referred to as a "Hoverpod" aircraft) has a band of disc loadings or weight per unit of lift area from 10 to 30 Ib/sq ft as shown on the horizontal, or "X" axis, while also operating within the band of power loading or weight per unit horsepower from 3 to 13 Ib/hp as shown on the vertical, or "Y", axis. This mix of characteristics is developed as a result of the radially compact design described with reference to Fig. 4. Such combination of characteristics allows for the lowest horsepower, the smallest size or the maximum useful payload or a desirable combination of any or all of these.

Referring to Fig. 2, there is shown a diagrammatic representation of the aerodynamic lifting device for an airborne hovering craft 100 incorporating the aerodynamic lifting device of the present invention. The airflow generating means is a radial drum fan with rotor 977 shown in the Figure. The thrust vectoring means is a shroud 15, a portion of which is shown in the Figure. Lift generated by the low pressure on the upper surfaces shown at 177, 277, and 377 may be optimised by optimizing the shape of these surfaces. The geometry of the shroud 15 may also be optimised, particularly in the region of surface 177 and annular area (please check) 14. For example, an air foil shape may be adopted for surfaces 177 and 377. Portion or all of shroud 15 may be flexible to promote the shroud's role as a thrust vectoring means or thrust vector providing directional control for the airborne craft 100.

An airflow guide, 6, which may be a separate annular ring, with an aerodynamic cross section that may also function as a retainer and end plate for the stator blades, is also desirably incorporated. Flow guide 6 may have a shape optimized to generate maximum lift through the development of the maximum pressure difference between its upper and lower surfaces. Flow guides similar to flow guide 6, placed above and attached to surface, 777, and to surface, 877, which is part of the lower end plate of the rotor, 977, are may also be provided. Optimum duct dimensions are selected, as desired, for the input airflow side as formed by the annular inlet area, 101 , the vertical cylindrical areas, 11 , 12 and 13, defined by the stator vane height at inlet, the rotor vane height at inlet, and the rotor vane height at exit respectively and the annular exit area, 14.

Referring to Fig. 3, there is shown a diagrammatic representation of the lifting surfaces of the aerodynamic lifting device of Fig 2, and the lifting surfaces of a helicopter rotor blade with comparable lifting capability. It can be seen that the radial dimension 107 for the aerodynamic lifting device of the invention is significantly less than the radial dimension 207, which is the radius of the rotor disk of the helicopter.

Referring to Fig 4, there is shown an airborne craft incorporating a radial drum rotor fan 2 airflow generating means, having a rotor 19 with a plurality of vertically extending blades 3, arranged in an annulus disposed at a distance 4, from the rotational axis 5 of rotor 19, said blades being disposed in an annular region having a radial extent or width 6, which is small relative to radial distance 4. The blades 3 extend downward and parallel to the rotational axis 5 of rotor 19. This construction thereby creates a useful load space inside the fan 2 and minimizes the mass of the fan 2 to provide the maximum useful load weight, and to avoid excessive gyroscopic and accelerating and decelerating forces on the rotor 19. This construction also allows the inlet area to the fan 2 to be maximized thereby minimizing the velocity that needs to be induced in the incoming air to generate the desired amount of lift.

Fan 2 generates a primarily radial airflow 7 which does not impart any axial momentum to the air to generate lift through the rotor 19 as is the case with helicopters. Such construction allows the complete axial length of the rotor blades 3 to be utilized to develop said velocity and therefore to develop maximum pressure beyond the fan 2 exit. This means that maximum use is made of the fan blade 3 length and mass in contrast to the inefficient use made of conventional helicopter blades of the prior art.

A stator assembly 8, comprises an inner load carrying hub 9, with lifting surfaces 10 and 10a, a plurality of stator blades 111 , and an upper stator blade retaining ring 121 , with upper and lower lifting surfaces 131 and 141 , and an outer shroud 15, that incorporates upper and lower lifting surfaces 16 and 17 and acts as a thrust vector. The stator assembly 8 provides an approximately equal and opposite torque to the rotor 19. Fan blades 3 have a constant cross section, and may be retained within the rotor 19 by an upper rotor blade retaining ring, 18, and a lower rotor blade retaining ring 119. Retaining rings 18 and 19 form a diffuser duct in conjunction with shroud 15 for the purposes of generating the maximum pressure over the lifting surface 17. Lower blade retaining ring 119 has an outer friction or drive face that can be driven by the back of a toothed belt, a flat belt, or other drive means.

Referring to Fig. 5, there is shown an airborne craft 200 of a preferred embodiment of the invention, which can be used in a wide variety of applications. Fig. 5 indicates the use of a shape for the central load carrying space 120 that provides a cockpit operating area for the operator 155 while maximizing the area available for airflow into the drum rotor fan 255 which acts as the airflow generating means. In particular, the horizontal annular area defined by the cockpit 155 and the upper annular retaining ring for the stator 355 that could control the air entry to the fan is held to the maximum and the volume available for the operator is allowed to grow vertically and radially above this plane to provide more load space without compromising airflow into the fan 255.

The flexible shroud 455, acting as thrust vector, is shown in a forward deflected position as may be used to effect directional control as by a braking or reversing maneuver for airborne craft 100.

Referring to Fig. 6, there is shown an outer shroud for airborne craft 200 which incorporates an inner edge 166 that is fixed to a grill and/or vane sub assembly 466; a relatively flexible airflow guide portion, 266; and a relatively rigid outer rim portion, 366, and means for connecting said rigid outer rim to a means for an operator to control the position of the said outer rim 366 relative to the said fixed inner edge 166 such that the airflow guide 266 and outer rim 366 create a smooth surface that vectors the airflow in a desirable way to assist with maneuvering of the airborne craft 100. Referring to Fig. 7, there is shown a preferred embodiment of airborne craft 400 that shows the flexible shroud 415 in three positions, as achieved by control of airflow so as to cause the airborne craft 100 to accelerate forward, brake or reverse backward, or move laterally as would be required to go around a comer. Referring to Fig. 8, there is shown a preferred embodiment of the geometry of the rotor blades 800 and stator blades 900. The rotor blades 800 are attached to upper and lower annular retaining rings (not shown) and rotate in the direction indicated by 801. The rotor blades 800 are in the form of a aerodynamic wing profiles in the NACA series of profiles and have a leading edge 810 with a defined radius, a trailing edge 820 the thickness of which is less than the leading edge, a forward face 830, and a back face 840. Air flows from the radially inner side of the rotor blades 850 and is accelerated by the stator blades 900 in the circumferential direction towards the oncoming leading edges 810 of the rotor blades 800. Such geometry creates an aerodynamic force on the rotor blades which is in opposition (ie radially inward) to the centrifugal forces acting on the rotor blades as a result of their rotation about the rotor axis in use.

Referring to Fig. 9a, there is shown a rotor 800a, a stator 900, the stator having an inner hub 901 and an outer hub 902. Stator blades 903 are provided at the radially outermost part of the inner hub. An upper inlet duct 910 is defined in part by an annular lip 920. The lip 920 forms part of the outer hub 902 of the stator and houses the top of the rotor 800a. Lip 920 extends over and radially beyond the upstream facing edge of rotor blade 800 (see also Fig. 9b for more detail). The lip 920 is surrounded by and forms part of an airfoil 921 which is contoured to provide positive lift when air flows over the airfoil 921 and passes into the upper inlet duct 910. It may also be seen that lip 920 overlaps upper retaining ring 960 for rotor drum 1000, this allowing a smooth transition of the airflow into the rotor 800a (see also Fig. 9b for detail). The upper inlet duct also comprises a set of wings 903, 904 separated by a slot 905.

Fig. 9a also shows an outlet duct which contains a wing 301 having a slot 302 between it and the lower retaining ring 303 of the rotor drum 1000. The facing surfaces of the retaining rings 960 and 303 may converge towards the radially outer side of the rings 960 and 303 to form a diffuser duct 970 - which acts in conjunction with shroud 915 to assist airflow through the diffuser duct 970 to generate maximum pressure over the lower lifting face 916 of the shroud 915 to generate lift. The diffuser duct 970 geometry is also observable from the lesser length of rotor blade 800 on its radially outward side in comparison to its length on the radially inward side of the blade 800. This is shown in detail in Fig. 9b. Referring to Fig. 10, there are shown stator blades 903, an upper inlet duct

910 and an edge 930 which contacts the upper lip (not shown) in the region between the two dotted lines 920 representing the upper lip.

Fig. 10 also shows an airstream 940 entering the upper inlet duct 910 in a radial direction and a subsequent airstream 942 deflected in a partially tangential direction by the twisted surface of the upper part of the stator blades 944 and the camber of the lower part of the stator blades 946.

Referring to Fig. 11 , there is shown a neutral position of the shroud 1115 and an actuated deflected position 1116 (in dotted lining) for an airborne craft 1110. A resultant force 1117 acts through the centre of gravity 1118 when shroud 1115 is in the neutral position. Actuation of the shroud 1115 to the deflected position 1116 results in a change in the position of the centre of action of the lifting forces to 1120 due to movement in location of the resultant force to 1126. This results in a torque being produced about the centre of gravity and the craft rotating in this direction. The resulting tilt of the craft thus vectors the thrust such as to propel the craft laterally. Once the desired level of tilt has been achieved, the shroud 1115 is actuated to maintain the desired level of tilt.

Modifications and variations of the fan, aerodynamic or airborne lifting device and airborne craft of the invention may be apparent to skilled readers of this disclosure. Such modifications and variations are deemed within the scope of the present invention.

Claims

CLAIMS:

1. A drum rotor fan for generating a fluid flow wherein the blades of the rotor are parallel to the axis of rotation of the fan, are of constant cross-section along the length of the blades, and wherein the blades have an aerodynamic profile comprising a leading edge, an increasing blade thickness reaching a maximum between the leading edge and a trailing edge, and a trailing edge thickness which is less than the leading edge thickness.

2. A drum rotor fan as claimed in Claim 1 wherein, in use, the aerodynamic loading on a blade of the rotor is in opposite direction to the centrifugal loading.

3. A drum rotor fan as claimed in Claims 1 or 2 wherein the fan blade surfaces are of a composite material.

4. A drum rotor fan as claimed in Claims 1 , 2 or 3 whereby the rotor fan is driven by a hubless drive means.

5. A drum rotor fan as claimed in any of Claims 1 to 4 wherein the blades are retained at their upper and lower extent by respective retaining rings, said rings forming a diffuser duct wherein the respective facing surfaces of the rings converge towards the radially outer-side of the rings.

6. A drum rotor fan as claimed in any of Claims 1 to 5 wherein the blade tip speed, at maximum operating speed, is less than 100 m/s.

7. A drum rotor fan as claimed in Claim 6 wherein the blade tip speed, at its maximum operating speed, is approximately 50 m/s.

8. A drum rotor fan as claimed in any of the preceding claims wherein the drum rotor fan is used as part of a ventilation or air-conditioning system.

9. An aerodynamic lifting device comprising an airflow generating means and a thrust vectoring means wherein the airflow from the airflow generating means acts on an inner side of the thrust vectoring means and wherein the device has an operating region intermediate the power loading ("y") asymptotic region and the disc loading ("x") asymptotic region of a power loading - disc loading characteristic for the lifting device.

10. An aerodynamic lifting device of claim 9 wherein the thrust vectoring means provides directional control of the device.

11. An aerodynamic lifting device of claim 9, wherein the thrust vectoring means comprises a flexible portion, movement of the flexible portion resulting in thrust vectoring.

12. An aerodynamic lifting device of claim 11 , wherein a vertical lifting force is produced and wherein movement of at least part of the flexible portion results in a change in the position of the centre of action of the lifting forces when projected in a horizontal plane.

13. An aerodynamic lifting device as claimed in any one of Claims 9 to 12, inclusive, wherein the airflow generating means comprises a drum rotor fan as claimed in claim 1.

14. The device of claim 9 wherein the thrust vectoring means is a shroud.

15. The device of claim 9 wherein the thrust vectoring means is a shroud which is flexible at least in part.

16. The device of any one of claims 9 to 15 inclusive wherein disc loading of the device ranges between 10 and 30 Ib/ft² and the power loading of the device ranges between 3 to 13 Ib/hp.

17. An airborne craft comprising an aerodynamic lifting device having a rotor drum fan for generating lift for the device which has an operating region intermediate the power loading ("y") asymptotic region and the disc loading ("x") asymptotic region of a power loading - disc loading characteristic for the lifting device.

18. The airborne craft of claim 17 wherein the craft is manned.

19. The airborne craft of claim 17 wherein the rotor drum fan comprises a rotor, the rotor having a rotational axis and comprising a plurality of rotor blades disposed in an annular ring about the rotational axis and a driving means for driving the rotor such that, on operation of the driving means, lift is generated.

20. The airborne craft of claim 17 wherein the operator area is disposed such that a centre of gravity of the operator is at or below the uppermost extremity of said rotor blades.

21. An aerodynamic lifting device comprising a rotor drum fan with a rotor, the rotor having a rotational axis and comprising a plurality of rotor blades disposed in an annular ring about the rotational axis said blades extending substantially parallel to said rotational axis of the rotor wherein the radial depth of said rotor blades is less than 25% of the radial pitch of the blades, and a driving means for the rotor such that, on operation of the driving means, lift is generated.

22. The aerodynamic lifting device of claim 21 further comprising a thrust vectoring means for re-directing airflow from the fan in a downward direction.

23. The aerodynamic lifting device of claim 22 wherein the thrust vectoring means provides directional control of the device.

24. The aerodynamic lifting device of claim 21 comprising a stator that has blades upstream and/or downstream of the rotor blades.

25. The aerodynamic lifting device of claim 24 wherein the stator produces an opposite torque to the rotor.

26. The aerodynamic lifting device of claim 21 comprising upper and lower retaining rings for said rotor blades forming a diffuser duct and a thrust vectoring means, air flowing through the diffuser duct generating a lifting force on a lifting face of said thrust vectoring means for generating a lifting force.

27. The aerodynamic lifting device of claims 21 or 24 wherein said blades are of a constant cross-section.

28. The aerodynamic lifting device of claim 21 wherein said rotor is driven on its periphery by a ring on the rotor.

29. The aerodynamic lifting device of claim 21 wherein said rotor is driven on its periphery by a friction drive.

30. An airborne lifting device comprising: a vertical axis fan with a plurality of blades whose axes are also vertical or near vertical disposed at a distance from said axis, having a radial depth which is small relative to said distance and generating primarily radial airflow; a stator assembly that comprises an inner load carrying hub and lifting surfaces; and a thrust vectoring means for directional control of the device.

31. The airborne lifting device of claim 30, wherein stator blades are provided radially inward of said fan blades and about the fan axis.

32. The airborne lifting device of claim 31 wherein the radial extent of the stator blades is small relative to said distance from said axis.

33. The airborne lifting device of claim 30 wherein said thrust vectoring means is an outer shroud that incorporates upper and lower aerodynamic lifting surfaces.

34. The lifting device of any one of claims 17, 21 , or 30 wherein said fan has an input airflow side, and wings to generate lift are mounted on said input airflow side.

35. The lifting device of any one of claims 21 to 34 wherein said blades are contoured so that the aerodynamic lifting forces acting on the blades are approximately opposite in magnitude and direction to centrifugal forces acting on the blades in use.

36. The lifting device of claim 30 wherein upper face(s) of the inner and outer hub or stator of the fan which are disposed near the inlet or low pressure side of the fan are contoured to function as wing(s).

37. The lifting device of claim 36 wherein wing(s) function as a flow deflector to improve the radial flow into the stator and fan assembly.

38. The lifting device of claim 37 wherein the wings functions as the upper restraint for the stator blades.

39. The lifting device of any one of claims 34 or 36 to 38 wherein the input airflow side includes an upper inlet duct comprising one or more annular wings or guide vanes.

40. The lifting device of claim 30 wherein the device includes an upper inlet duct which is at least partially defined by a lip which is disposed around the most radially inward upstream circumference of the fan.

41. The lifting device of claim 40 wherein said lip forms part of the annular airfoil which functions as an upper restraint for the stator blades.

42. The lifting device of any one of claims 39 to 41 wherein at least part of said wings or guide vanes are disposed in an inlet region containing radially directed airflow.

43. The lifting device of any one of claims 30 to 42 including an outlet duct comprising one or more annular wings or guide vanes.

44. The lifting device of claim 43 wherein said outlet duct is at least partially defined by a lip which is disposed around the most radially outward, downstream circumference of the rotor of the rotor drum fan.

45. The lifting device of claim 43 or 44 wherein the wings or guide vanes are disposed in an outlet region containing radially directed airflow.

46. The lifting device of claim 31 or 35 wherein stator blades located in the upper inlet duct are contoured to provide approximately the same degree of circumferential acceleration to the airflow at the inlet to the rotor blades as that provided by the stator blades which are disposed below the upper inlet duct.

47. The lifting device of claim 40 or 44 wherein, in either the case of an inlet duct or an outlet duct, the corresponding lip is contoured to develop lift.

48. The lifting device of any one of claims 40 to 47 wherein, in the case of an inlet duct, the lip extends over and radially beyond the upstream facing edge of the rotor blades.

49. The lifting device of any one of claims 40 to 48 wherein, in the case of an inlet duct, the corresponding lip has wings to generate lift disposed about it, both upstream and downstream and radially inward of said lip.

50. The lifting device of any one of claims 34, 36, 37, 38, 39, 42, 43, 45 or 49 wherein the wings form an aerodynamic slot by being spatially disposed to each other and/or the associated lip.