AN AERIAL MACHINE

DESCRIPTION TITLE "An Aerial Machine" ^" TECHNICAL FIELD - This invention relates to a heavier-than-air machine which has a VTOL capability and more particularly but not exclusively to an aerial machine which utilises ground effect for support in certain modes o^"f operation. BACKGROUND ART

Various aerial machines having a VTOL capability have been proposed.

GB-A-1405737 discloses a heavier-than-air aircraft which is arranged so that, during normal forward propulsion, the total lift necessary to support the aircraft in the air is derived from the aerodynamic forces acting on the base of a flat fuselage inclined at a small angle of incidence to the horizontal, and which is capable of hovering as a result of lifting forces, at least equal to its total weight, produced by at least two lift producing engine units secured to the tips of sponsons or stub wings on each side of the fuselage. Such an aircraft will experience considerable stabilisation problems, especially on inclined surfaces off which it will tend to slide .

An article "Hybrid Heavy-Lift Airships Under Study" published in Aviation Week & Space Technology, June 21st, 1976, pages 48-52 discloses an airship, viz. a lighter-than-air aerial machine, which is a hybrid vehicle employing the buoyant lift of a large cigar-shaped helium-filled envelope in conjunction with the powered lift of four modified helicopters which are attached to the underside of the envelope - one forward and one aft on each side - by a rigid interconnecting structure. The buoyant weight of^" he envelope offsets essentially the entire empty weight of the vehicle, leaving the helicopter rotor thrust available for lifting the payload and manoeuvring the vehicle. Such a vehicle is liable to be subjected to negative lift because of the shape of the envelope.

Another known form of VTOL machine is a ground effect machine, usually known as a hovercraft, which comprises a load supporting platform having a substantially flat undersurface, and means for forming and maintaining a supporting air cushion under the undersurface by which the machine can be supported above an adjacent support surface. Such machines are notoriously unstable when operated at values of height/effective diameter (h/d) of 0.2 or more, and

OMH over sloping ground. Also they experience difficulties in maintaining their supporting air cushion when they need to traverse troughs or sudden dips and sharp rises in the support surface. An object of this invention is to provide an aerial machine having a VTOL capability which does not suffer from the various operational disadvantages of each of the craft or vehicles described above if and when it operates in an equivalent mode. DISCLOSURE OF THE INVENTION

This invention arises from an appreciation that the stabilisation system inherently incorporated in an airship can be adapted for incorporation in a heavier-than-air machine by fitting the heavier-than-air machine with an inflatable envelope which is somewhat smaller in size compared to the remainder of the machine than is the inflatable envelope of an airship, and which is too small to lift the machine. According to one aspect of this invention there is provided a heavier-than-air aerial machine comprising a body, means carried by the body for forming a stream of air which can be directed downwardly with respect to the body to provide at least a greater part of the aerodynamic-lift needed

OMPI for vertical take-off and landing and for hovering operation of the machine when laden; and an inflatable envelope which is mounted upon the body so that, when inflated, its volumetric centre is above the centre of gravity of the machine whereby to provide aerodynamic stabilisation for the machine.

According to another aspect of this invention there is provided a heavier-than-air aerial machine comprising a body having a substantially flat undersurface suitable for the formation thereunder of a supporting air cushion by which the machine can be supported above an adjacent support surface; means carried by said body for forming a stream of air directed downwardly with respect to said undersurface at at least two spaced locations whereby such a supporting air cushion can be formed; and an envelope filled with a gas which is lighter than air, the envelope being mounted upon the_body with its volumetric centre above the centre of gravity of the body.

Preferably said downwardly-directed air stream forming means are collectively capable of generating a thrust, the reaction to which will urge the machine to a height which is greater than the maximum height at which a supporting air cushion can

!R£Λι OMPI be maintained between said undersurface and said support surface, at least when the machine is only partly loaded.

Should the machine be highly loaded, it can be operated at useful heights above a support surface as a conventional air cushion vehicle (or ground effect machine) , without depending peripheral flexible skirts, there being thrust fans which provide forward propulsion and an inflated envelope providing stabilisation. On the other hand, if lightly laden, the machine can rise substantially vertically through the range of heights at which it can operate with ground effect assistance, to free air operation in hover or forward flight due to vectored thrust from the thrust fans aided by the dynamic thrust generated by said downwardly-directed air stream forming means, whilst being stabilised by the inflated envelope.

Embodiment of this invention in a machine leads to there being inherent stability in the machine when operating in ground effect, VTOL, hovering, transitional forward flight and even in free unpowered vertical descent modes, due to the strategic placing and fixing of the bubble of gas (e.g. Helium) stored in the envelope which is placed either within the rigid structure of the machine with its volumetric

_OMPI_ IPO centre above the centre of gravity of the machine, or secured at a determinable height (meta centre) above the centre of gravity of the machine. The precise volume of the stabilising bubble depends on the size, all up weight and meta centre moment of the machine.

It is believed that the inercial mass offered by the bubble of gas in the envelope strongly resists the tendency of an otherwise unstable hovering platform to be displaced from the vertical, thus having a similar effect to a gyro stabilising system. The metal centre arm length is strictly related to the attendent aerodynamic/hydrodynamic and dynamic disturbing forces to which the machine is subjected. It can be shown that the stabilising value of an air bubble (depending on the meta centre arm length) can be in weight as low as 10 per cent of the all up weight of the machine, and, in the case of Helium, there is a considerable_ further weight reduction and consequent lowering of the engine horse power requirement. The principle of operation of a machine in which this invention is embodied differs from that of a conventional airship which employs a lifting gas to take up most of its weight.

Provision may be made for vertical and longitudinal displacement of the gas bubble for change of trim purposes.

It is believed that, by incorporating the features of this invention in a machine, the notorious instability inherent in ground effect machines such as those that are known as hovercraft, whan they are operated at values of height/effective diameter (h/d) of 0.2 or more, can be eradicated enabling the machine to ascend in ground effect to operational heights of h/d = 0.8 or higher, while remaining completely stable even over sloping ground, due to the jet effect. If the vertical thrust component is great enough the machine will go into free vertical flight completely stable.

The stabilising bubble may be separated into a number of external inflatable envelopes or units

(i.e. two or more), so placed that the combined centre of lift or inertia occurs at the required relationship to the centre of gravity of the machine. Such inflated units can be employed to act as wings capable of providing good aerodynamic lift in forward flight (with low drag around C. = 0.03) but which will also

offer maximum drag (around C. = 1.4) in free vertical

descent. These units have a variety of plan form shapes, such as circular, having an outer stiffening torus or tube, or delta-shaped, or may have a plain spindle shape which also offers minimum drag in forward flight and maximum drag in unpowered vertical descent. Momentum drag, which inhibits forwards operation of the machine in its ground effect modes, ceases to be effective when the machine operates at heights above that at which there is useful ground effect and supported by the dynamic vectored thrust of the fans alone.

DESCRIPTION OF THE DRAWINGS

Several machines in which this invention is embodied are now described, by way of example, with reference to the accompanying drawings, of which:— Figure 1 is a perspective view of one form of aerial machine in which this invention is embodied;

Figure 2 is a view from the front of the machine shown in Figure 1, and illustrating a controlled descent of the machine; Figure 3 is a perspective view of a gas-filled envelope for another form of aerial machine in which this invention is embodied;

Figure 4 is a perspective view of another form of gas-filled envelope for an aerial machine in which this invention is embodied; Figure 5 is a diagrammatic plan view of another form of aerial machine in which this invention is embodied;

Figure 6 is a diagram illustrating operation of the machine shown in Figure 5 in a ground effect mode of operation at a height too great for an air cushion to be formed and maintained to support it;

Figure 7 is a diagram similar to Figure 6 illustrating lift-off of the machine shown in Figure 6 from swampy ground;

Figure 8 is a diagram similar to Figure 7 illustrating another form of aerial machine in which this invention is embodied operating at a low height over a surface which is too uneven for a supporting air cushion to be maintained;

Figure 9 is a diagram similar to Figure 8 illustrating operation of the machine shown in Figure 8 as it traverses a drop in the underlying surface, such as an escarpment or a waterfall, which it approached in its air cushion borne mode of operation;

Figure 10 illustrates operation of the machine shown in Figure 8 as it traverses a drop which is too deep for any form of ground affect support to be^'maintained until it approaches the bottom;

Figure 11 is a schematic view in perspective of a practical form of the machine that is shown in Figures 8 to 10, the machine being rectangular in planform, having four spaced axial flow lift fans and being shown in its air cushion borne mode of operation;

Figure 12 is a view similar to Figure 11 showing the machine set for operation at heights too great for an air cushion to be formed and maintained to support it; Figure 13 is a three-dimensional diagram illustrating operation of the lift fans of another form of machine in which this invention is embodied, when a.rectangular platform of the machine is oblique to the ground surface; and Figure 14 is a perspective view of another form of aerial machine in which this invention is embodied.

MODES FOR CARRYING OUT THE INVENTION

Figures 1 and 2 show an aerial machine having a wing 10 of delta low aspect ratio configuration. The wing 10 is constructed to contain on its underside, between that underside and a ground surface, a cushion of air which is maintained by air fed by a ^'lift fan or fans (not shown) through three spaced ports 14, 15 and 16, which are formed in the underside, whereby to provide aerodynamic lift by ground effect. The air discharged through each port 14, 15, 16 forms a column of air which is spaced from the columns of air issuing from the other two of the ports 14, 15 and 16 and which traverses the gap between, the underside and the ground surface.

A fuselage 17, elevators 18, fin 19 and rudder 20 are fitted to the wing 10. Two short stub wings 21 and 22 extend upwards from the fuselage 17 and diverge therefrom. Each stub wing 21, 22 carries a swivelling thrust fan 23, 24. The thrust fans 23 and 24 are operable to provide longitudinal propulsive thrust and vertical thrust when required. Also they are operable to effect rotation of the machine about a vertical axis.

Each stub wing 21, 22 carries a respective streamlined inflated pod 25, 26 at its end remote from the fuselage 17. Each pod 25, 26 is inflated with Helium. The lift fan or fans is/are housed within the fuselage 17 and are connected by suitable ducting to the ports 14, 15 and 16 and to an air intake 27 formed in the upper surface of the fuselage 17.

The machine rests upon a ground surface when the lift fans are not operating. When the machine is

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OMPI WlrO started up, air from the three columns -chat impinges upon the ground surface is directed into the space between the underside and the ground surface and forms an air cushion between the underside ana the ground surface. Initially the vehicle is lifted from the ground surface and supported above that ground surface by the air cushion, the pressure of air within the air cushion being relatively high. The machine is controlled against random rotary movement about its central axis that extends upwardly between the pods 25 and 26, by operation of the thrust fans 23 and 24. The machine will operate as an air cushion vehicle, supported above the ground by the high pressure air cushion formed between its underside and the ground surface, if it is so heavily laden that the thrust generated by the discharge of the three columns of air from the ports 14, 15 and 16 is insufficient to raise the machine above the ground surface by a distance which is greater than the maximum height of the underside above the ground surface at which an air cushion can be maintained by air discharged through the ports 14, 15 and 16. That distance is usually of the order of one fifth (1/5) of the effective diameter of the underside. Translational movement of the machine relative to the ground surface is effected by operation of the thrust fans 23 and 24.

The two bubbles of Helium that are contained within the interior of the pods 25 and 26 comprise inertial masses of lighter than air gas which are located with their volumetric centres displaced at a certain height above the centre of gravity of the machine. Those inertial masses resist any tendency for the body of the machine, when airborne, to depart from the attitude in which its central axis that extends upwardly between the two pods 25 and 26 is vertical, as they provide a restoring force tending to restore the machine to that attitude, due to the Archimedean principle.

If the loading of the machine is such that the thrust generated by the downwardly-directed columns of air emerging from the three ports 14, 15 and 16 is greater than that merely necessary to form and maintain an air cushion between the underside and the ground surface, the machine will be urged upwardly away from the ground surface beyond the maximum height at which an air cushion can be maintained between it and the ground surface. When the air cushion first dissipates, the machine will be supported above the ground by the combination of the reaction to the thrust of the downwardly-directed columns that emerge

OMPI from the three ports 14, 15 and 16 as well as up thrust due to recirculation of air that is deflected upwardly from the ground surface to the undersurface where it is further deflected downwardly again, there being a momentum exchange between the upwardly directed air that strikes the underside and thereby generates an up thrust augmenting the thrust due to the downwardly-directed columns of air emerging from the ports 14, 15 and 16. There will also be a certain, relatively small amount of lift provided by the inflated pods 25 and 26.

Eventually the machine will reach a height at which there is no significant up thrust by recirculation of air deflected upwardly from the ground surface to strike the underside of the machine. That height is usually approximately equal to the effective diameter of the underside. The machine will be solely dependent upon lift due to the reaction to the thrust of the downwardly-directed columns of air that emerge from the three ports 14, 15 and 16 augmented by lift due to the Helium by which the pods 25 and 26 are inflated and lift from the wing 10 and from the structure of the pods 25 and 26, which serve as an extension of the wing 10. The machine can take off with a conventional short run, being supported above the ground surface by the air cushion, instead of a conventional undercarriage, until sufficient forward speed is established for all lift to be transferred to the wing surfaces, at which time the lift fan(s) may be stopped, so that momentum drag from lift fan operation is avoided.

During free flight, the machine is stabilised by the action of the two bubbles of Helium contained within the pods 25 and 26 as discussed above. A conventional landing approach can be made from such free flight with a final flare out to power vertical descent, as is illustrated in Figure 2. The machine can make a safe controlled vertical landing even if only one of the three columns of air that emerge from the ports 14, 15 and 16 should be generated, due to some failure in the system that generates the three columns of air. This is because, in such a descent, asymmetric thrust is offset by the restoring couple due to the effect of the two bubbles of Helium contained in the pods 25 and 26. In the event of failure of all the fans, the machine can make a controlled glide descent in the conventional manner by a suitable adjustment of the elevator 18. In an extreme case, on nearing the ground surface, if there

- tJ lΛ should be only a restricted landing patch available (i.e. a clearing in a wood), the machine can flare out and go into vertical descent, landing with an acceptable contact speed, this manoeuvre being made possible by the stabilising effect of the bubbles of Helium contained in the pods 25 and 26 and manipulation of the elevator 18.

The underside, although being substantially flat, is formed with a shallow concave form with a depending peripheral projection. This arrangement has the advantage that the underside will afford additional parachute drag characteristics which are effective, without risk of the machine becoming aerodynamically unstable, because of the stabilising effect of the two bubbles of Helium contained in the pods 25 and 26.

Various alternative forms of pods inflated with a lighter than air gas may be employed in place of the pods 25 and 26 to provide the restoring couple by the Archimedean effect as described. It is not essential for there to be two pods, a single pod arranged with its geometrical centre vertically above the centre of gravity of the machine may be used. Such a pod may be elongate, conveniently cigar-shaped. Alternatively an inflated ring structure which may be closed by intervening sheeting, such as is shown in Figure 3, may be employed, or a delta-shaped structure comprising two cigar-shaped pods joined together at one end and spaced apart at the other end with intervening sheeting enclosing the overall structure may be employed as shown in Figure 4.

The cushion forming fans may be mounted outside the perimeter of the load carrying platform that forms the downwardly concave undersurface instead of being housed within the body as described above with reference to Figures 1 and 2. Such an arrangement is illustrated diagrammatically in Figure 5 which shows a circular platform 10A with two pairs of diametrically-opposed axial flow fans 28 and 29, 28A and 29A mounted thereon. One of the pairs of diametrically-opposed fans .may be omitted. The platform 10A need not be circular, any suitable form, such as rectangular as shown in Figures 8, 9 and 10, may be used. Operation of the machine is basically the same as described above.

Figure 6 illustrates the recirculation mode, which has been described briefly to explain how the machine shown in Figures 1 and 2 is supported when it has been lifted above the height at which an air cushion can be maintained but not so high as to prevent

^• "** * there being any ground effect support for it. Figure 6 shows that each fan 28, 29 of the machine shown in Figure 5 directs a column of air downwardly outside the perimeter of the platform 10A. When the column of air strikes the ground surface 12 it spreads in all directions from the point of contact. Some of the air is deflected into the space between the concave undersurface and the ground surface 12 where it meets air deflected inwardly in the opposite direction from the column of air formed by the diametrically-opposite fan 28, 29. The two streams of air that meet below the centre of the concave undersurface interact to form an upwardly flowing column of air which flows up and strikes the undersurface of the concave undersurface at its centre. That upwardly moving column of air is deflected .by contact with the underside and diverges outwardly in all directions towards the radially outer perimeter of the concave undersurface where it is deflected downwardly again by the downwardly curved perimeter of the undersurface and returned towards the ground surface 12.

Use of axial flow fans located outside the perimeter of the underside and above the lowermost surface of the machine (as shown in Figure 6) leads to the fans being sufficiently remote from the ground

OM?I surface 12 as to minimise the risk of the fans stalling due to back pressure and no flow conditions. Furthermore, as illustrated in Figure 7, axial flow fans 28 and 29 so located can enable lifting thrust to be generated and maintained above swampy ground of the kind over which conventional air cushion vehicles are liable to be stuck fast without an air cushion being generated.

Figure 8 shows that a craft in which the present invention is embodied can be arranged so that an air cushion is maintained over the kind of rough uneven surface which usually make it impossible to maintain an air cushion of conventional air cushion vehicles. This is due to the recirculation effect generated by the spaced separate columns of air generated by the axial flow fans with which the kind of vehicle illustrated in Figures 5, 6 and 7 are fitted.

Figures 9 and 10 show that, when a machine in which the present invention is embodied is operated in its ground effect mode and approaches a sudden drop such as an escarpment or waterfall, it remains stable and does not topple over the edge. This is due to the effects of the stabilising bubble or bubbles and also to the fact that, as is illustrated in Figure 9 , the

IRE31 OMPI portion of the machine that projects beyond the sudden drop can be supported by a form of ground effect due to recirculation as described above even though it would be at a height above the ground surface below it that is greater than the maximum height at which an air cushion can be maintained. Figure 10 shows that the machine moves above the sharp edge substantially horizontally and then descends gradually until it comes close to the lower ground surface where it bounces upon an air cushion that is formed between its underside and that surface, and by which it is supported for further movement over that lower surface.

Figures 11 and 12 illustrate a practical form of machine having the basic layout that is shown diagrammaticaly in Figures .8 to 10. The main body 31 of the machine is generally rectangular. Two pairs of axial flow fans 28 and 29, 28A and 29A are arranged each adjacent to a respective corner of the rectangular body 31. The major part of the upper half of the machine comprises an inflated generally rectangular mattress 32 which is inflated with a lighter than air gas, such as Helium. The mattress 32 is supported upon the main body *31 by extensible linkage mechanisms 33 such that it can be moved to a

-fTJ JEΛ OMPI location in which it is spaced above the main body 31 by extension of the mechanism 33. The machine is arranged in the condition shown in Figure 11 for the mode of operation in which it is supported on an air cushion, the extensible linkages 33 being contracted so that the mattress 32 is in its lower position and the machine in its most compact streamline mode.

When the machine transfers from its air cushion supported mode to the higher mode in which it is supported above the ground by ground effect due to recirculation, and from which it moves into free flight, the linkages 33 are extended to support the mattress 32 spaced above the main body 31; as shown in Figure 12. The mattress 32 serves as the stabilising pod.

The spaced columns of air formed by the axial flow lift fans' of each of the machines shown in Figures 1 to 12 tend to stabilise the machine when it is operating in ground effect. This effect is illustrated in Figure 13 which shows a rectangular main platform 51 comprising a rectangular peripheral framework 52 surrounding a removable rectangular load carrying pallet 53 and having four axial flow fans 28, 28A, 29 and 29A located each in a respective downwardly-opening chamber formed at a respective

When the platform 51 is oblique to the ground surface 12, the downwardly-directed air column 34-37 generated by each of the fans 28, 28A, 29 and 29A strikes the ground surface 12 at an angle to the vertical. Upon impact with ground surface 12, the air of each column 34-37 spreads in all directions along the ground surface 12. The deflected air that flows towards another of the columns of air (say from the column 34 towards the column 35) meets air deflected from that other column 34-37 and cooperates therewith to form a respective upwardly-directed column of air 41-44 substantially midway between those two downwardly-directed air columns. The upwardly-directed column 41-44 that is below the part of the platform 51 that is nearest to the ground surface 12 (viz. column 41 in Figure 13) counters the destabilising effect on the platform 51 of the two adjacent air columns (viz. columns 42 and 44 in Figure 13) whilst the opposite air column (viz. column 43 in Figure 13) misses the platform 51. Hence the resultant effect of the upwardly-directed columns 41-44 on the platform 51 is a stabilising couple which

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OMPI tends to right the platform 51 and restore its attitude where it is substantially parallel to the ground surface 12.

Where the machine is provided with two pairs of axial flow fans 28 and 29, 28A and 29A arranged at equi-angularly spaced locations around and outside the periphery of a circular platform (as shown in Figure 5) or at or adjacent to the corners of a rectangular platform (as shown in Figures 8 to 13) , it is convenient to provide each fan 28, 29, 28A, 29A with its own respective engine. Also it is convenient to interlink the control systems of the two engines that drive the fans of each pair of fans 28 and 29 or 28A and 29A that are located at diametrically or diagonally opposed locations with respect to the platform or body. The interlinked pairs of control systems, which conveniently are linked electrically or by other means, are arranged so that, in the event of failure of any one of the engines, the interlinked diametrically or diagonally opposed engine is shut down automatically so that further operation of the machine is on the basis of the other pair of engines and fans only.

Figure 14 shows a machine having a stabilising pod 54 which is an inflated envelope

O PI W1P similar to that shown in Figure 4 and which, being provided with a pair of tail fins, serves as a delta-shaped aerofoil or wing of the machine. The pod 54 is mounted on the top of a body 55 comprising a cabin structure 56 and a tail section 57. Although the underside of the cabin structure 56 may be flat it is not designed to contain an air cushion between itself and a ground surface which supports the machine. The machine is designed as a free flight machine which can hover either in or out of ground effect. The whole of the undersurface of the machine, including that formed by the wing or pod 54 which has a substantially greater planform area than the body 55, cooperates with the ground to provide ground effect support for the machine when the machine is close enough to the ground.

Although it is possible that the machine could be made to fly if provided with a single engine mounted rotatably in the body 55 just aft of the cabin section so that it can be directed downwardly for vertical take-off and landing and for hovering, and directed aft for forwards propulsion in free flight, it is thought that two such engines or one engine driving two spaced fans will be required in practice to provide effective ground effect support in the

ON--PI ground effect mode. Hence the machine shown in Figure 14 is provided with two engines, one on either side of the cabin section 56. One of the engines is shown at 58 in Figure 14. Air may be tapped from the lift engines and ducted to laterally-opening jets formed at the aft end of the tail section, control flaps being provided for selectively opening such jets in a chosen lateral direction so that tapped air emerges therefrom to provide directional control in yaw. A machine provided with an inflaited pod filled with air would obtain a degree of stabilisation from that pod but an air filled envelope would not significantly improve stabilisation of an air cushion supported vehicle at heights at which that vehicle is liable to be aerodynamically unstable. A lighter than air gas, such as Helium, is preferred to aiir because it provides more usable stabilisation. In addition it provides some lift.

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