WO2008007147A1

WO2008007147A1 - Aircraft

Info

Publication number: WO2008007147A1
Application number: PCT/GB2007/050403
Authority: WO
Inventors: John Coakley
Original assignee: Hoverwing Limited
Priority date: 2006-07-13
Filing date: 2007-07-13
Publication date: 2008-01-17
Also published as: GB0613887D0

Abstract

An aircraft (10) comprising a rigid wing (12), a structure (18), a thrust producing means (16), and a pendulum (22) attached to said structure (18) at a pivoting end thereof, wherein the pendulum (22) is arranged to shift the centre of gravity of said aircraft (10) between at least first and second positions relative to a longitudinal centre line of the aircraft (10), and wherein in the first position the centre of gravity of said aircraft (10) is relatively far forward to provide a relatively fast flying mode and in the second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode.

Description

AIRCRAFT

The invention relates to aircraft. In particular, the invention concerns, but is not limited to, unmanned aircraft.

There is a need for unmanned aircraft to perform tasks such as surveillance, film-making or transport of small pay loads or, indeed, any task in which having a manned aircraft would be either uneconomical or unsafe. Typically, such aircraft may be remotely controlled either with a simple controller of the type used to pilot model aircraft, or with other more sophisticated means in which it may not be necessary to maintain line of sight contact with the aircraft. For some tasks it would be desirable to create an aircraft which as well as performing normal flying operations can approach and maintain a hovering position. It is well known that helicopters can approach and maintain a hovering position. However, problems exist because the remote control of helicopters in a hovering position is difficult to achieve. Furthermore, the noise levels and risk to safety caused by the exposed rotors of helicopters leads to problems in low-level flight applications such as film-making.

A well known prior art light aircraft designed for slow flying operations is the so-called "flying flea". The flying flea was invented by Henri Mignet in the 1930' s and has a tandem wing construction with both wings designed to generate lift, which is different from normal aircraft having conventional tail planes in which only the front wing is designed to generate lift. With a tandem wing aircraft the intention is for both the tail and lead wings to generate lift so that it can fly more slowly. However, normal wings tend to rotate or pitch forwards when lift is created, and so a balancing force is needed unless the moment can be reduced or eliminated.

Reflexed aerofoil sections are known for reducing or eliminating such forward pitch or rotation. Instead of curving progressively downwardly, the rear of the wing kinks back upwards at the trailing edge. This alters the lift distribution at the back of the wing to counteract the overall tendency to rotate forwards.

To enable an aircraft to fly conventionally as slowly as possible it is necessary to generate as much lift as possible from both wings.

No aerofoil can continue to generate lift at all speeds, and eventually every wing will stall. A conventional aircraft relies on its lead wing to produce all its lift, so when it stalls the nose drops and the aircraft will start to fall at increasing speed allowing the wing to recover its lift. During the stall, all control can be lost on the wing, leaving the aircraft with no roll control.

With the Mignet "flying flea" configuration where the lift is shared between lead and rear wings it is important that the lead wing stalls first. When it does so the rear wing will continue to create lift causing the nose to drop and the aircraft to recover. The Mignet configuration controls pitch by rotating the whole of the lead wing and can keep the lead wing at a higher angle to the relative airflow than the rear wing at slow speed, causing the lead wing to reach its stall point first. An additional advantage of the rotating lead wing is that when the aircraft starts to stall, the lead wing can be angled down slightly and therefore can recover much more quickly. When this happens the aircraft may lose some altitude but remains level and under full control because the control surfaces governing roll are on the rear wing, not the front wing. Further, the rear wing never stalls because the lead wing is designed to stall first, dropping the nose and causing the lead wing to recover before the rear wing can stall. This stall recovery mechanism results in a gentle nodding action known as "porpoising".

At slow speeds, the angle of attack of the lead wing is increased to give maximum lift, and the tendency of the lead wing to stall decisively before the rear wing is accentuated. This leads to an increase in pitch stability as the aircraft approaches a slowest flight speed.

At higher speeds, the angle of attack of the lead wing must reduce to maintain a level flight path otherwise too much lift will be created. This results in the lead and rear wings having similar angles of attack to the oncoming air resulting in the lead wing being less likely to stall first and thereby reducing stability.

The aforesaid problem was addressed by Mignet in the 1930s. Mignet decided to move the rear wing in the event that the rear wing begins to stall. However, this is difficult to achieve in unmanned aircraft where there is no pilot onboard who can feel the rear wing begin to stall and who can make the necessary adjustments to the rear wing .

Whilst the Mignet design is therefore very stable at slow speeds, it is not stable at higher speeds without an onboard pilot. Furthermore, the Mignet design cannot provide a true hover in a stable fashion.

It is an aim of preferred embodiments of the invention to provide a winged aircraft that is capable of stable flight at low speeds associated with Mignet style aircraft, and that is also stable at higher speeds. It is another aim of embodiments of the invention to provide an aircraft that is capable of hovering.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to a first aspect of the invention, there is provided an aircraft comprising a lead wing, a rear wing, a fuselage section and a thrust producing means such as an engine or motor, wherein the aircraft has a thrust to weight ratio of at least one and characterised in that a means is provided for shifting the centre of gravity of said aircraft between at least first through third positions relative to a longitudinal centre, nose to tail, line of the aircraft, wherein in a first position the centre of gravity of said aircraft is relatively far forward to provide a relatively fast flying mode, in a second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode, and in a third position the centre of gravity is positioned relatively far back to enable the aircraft to adopt a position in which the aircraft enters a hover mode in which a line of thrust of said thrust producing means is substantially vertical.

Most preferably, the means for shifting the centre of gravity of said aircraft between at least first through third positions comprises a pendulum having a pivoted end and a free end, wherein the pivoted end is pivotally attached to the aircraft.

Preferably, the pendulum is pivotally attached to an underside of the aircraft.

The pendulum is preferably pivotally attached to a part of the aircraft situated between a lead chord line of the lead wing and a lead chord line of the rear wing. The part of the aircraft to which the pendulum is attached may comprise the fuselage.

Preferably, the pendulum is weighted at its free end by an attached mass which is a significant proportion of the overall aircraft weight.

Preferably, a payload is attached at the free end of the pendulum.

The payload is preferably pivotally attached to the free end of the pendulum. The payload may be capable of rotation about one or more axes of movement with respect to the free end of the pendulum.

Movement of the payload may be remotely controllable independent of movement of the pendulum.

Preferably, the payload comprises a camera, which may be a still or video camera.

Preferably, the pendulum is a two part pendulum comprising an upper pendulum portion pivotally linked to a lower pendulum portion, wherein the lower pendulum portion is pivotally linked at its upper end to a lower end of the upper pendulum portion.

Preferably, the pivotal linkage between the upper and lower pendulum portions is a spherical type joint linkage enabling movement of the joint in more than one axis.

Preferably, the pivotal linkage between the upper and lower pendulum portions is located approximately one third of the way down the entire pendulum length.

Preferably, in the first position the free end of the pendulum is held nearest to a nose end of the aircraft.

In said first position the free end of the pendulum may be held at a position forward of a nose end of the aircraft.

Means for holding the free end of the pendulum in the first position may comprise means provided adjacent to or at said nose end of the aircraft such as a latching means, a wire on a spool which may be wound in/out, a control arm, rod or piston, all of which may be remotely operated.

Preferably, in the case of a two part pendulum being employed, the pivotal linkage between the upper and lower pendulum portions is stabilised to prevent or limit relative movement between the two parts.

Preferably, in the first position the aircraft is capable of flying within a top speed range of operation. The top speed range of operation of the aircraft may be from approximately 20 to 40 knots.

Preferably, in said top speed range of operation the centre of gravity of the aircraft is positioned between 3/10^th and 4/10^th of the distance between a front and rear chord line of the lead wing.

Preferably, at an upper part of said top speed range the lead wing is arranged to be positively lift generating, whilst the rear wing is negatively lift generating. Preferably at lower parts of said top speed range both the lead and rear wings are arranged to be positively lift generating.

Preferably, in the second position the free end of the pendulum is allowed to depend downwardly freely from the aircraft during substantially level flight modes of the aircraft.

Preferably, in the second position and in the case of a two part pendulum being employed, the lower pendulum portion is arranged to be capable of swinging outside of the central longitudinal axis of the upper pendulum portion .

Preferably, movement of the lower pendulum portion is damped. Damping may be provided by friction in the pivotal linkage between the upper and lower pendulum portions .

Preferably, means for selectively stabilising the upper and lower portions of a two-part pendulum comprise a sheath which is capable of covering the pivotal linkage between the upper and lower pendulum portions and is longitudinally displaceable with respect to the upper pendulum portion.

The sheath preferably has a close fitting part which has an internal diameter that is slightly greater than the outer diameter of the upper and lower pendulum portions that it surrounds when stabilising the linkage.

The sheath preferably has a looser fitting flared part which is joined to the close fitting of the sheath, whereby when the looser fitting part is moved to be around the pivotal linkage between the upper and lower pendulum portions the lower pendulum portion is allowed a degree of freedom of independent movement.

Preferably, longitudinal displacement of the sheath along the axis of the upper pendulum portion is arranged to progressively bring the pivotal linkage between the upper and lower pendulum portions into the loose fitting part of the sheath when the pendulum is moved from the first to the second position such that in the second position a degree of independent movement of the lower pendulum portion is allowed.

Preferably, the lower portion of the pendulum is allowed to move away from the line of the upper portion of the pendulum by a maximum of 20 degrees.

Preferably, the close-fitting part of the sheath is an upper part thereof, whilst the loose fitting part is a lower part of the sheath. Preferably, the lower part of the sheath is at least in part conically shaped.

Preferably, movement of the sheath is provided by a control arm joined at its lower extent to the sheath and at its upper extent pivotally joined to the fuselage. Preferably, the pivot point of the control arm is positioned further toward the nose of the aircraft than the top pivot point of the upper pendulum portion.

Preferably, in use, the control arm acts such that when the pendulum is the first position the pivotal linkage between the upper and lower pendulum portions and the adjacent areas of the upper and lower pendulum portions are tightly shrouded by the close fitting part of the sheath so as to hold both the lower portion of the pendulum and the upper portion in line with one another.

Preferably, the control arm is arranged, in use, such that in the second position the sheath is raised along the line of the shaft to bring the loose fitting part of the sheath over the pivotal linkage between the upper and lower pendulum portions and the adjacent areas of the upper and lower pendulum portions.

By providing a progression in the amount of freedom allowed to the pivotal linkage between upper and lower pendulum portions a degree of ironing out of unwanted oscillations or perturbations in the craft as a whole and has been found to occur which can provide good pitch and roll stability.

Damping means for damping movements of the lower pendulum portion within the loose fitting part of the sheath may be provided and may comprise a foam layer within the loose-fitting part.

Preferably, in the second position the aircraft is capable of flying within a slow to medium speed range of operation. The slow to medium speed range of operation of the aircraft may be from approximately 18 to 25 knots.

Preferably, in said slow to medium speed range of operation the centre of gravity of the aircraft is positioned between 6/10^th and 8/10^th of the distance between a front and rear chord line of the lead wing.

Preferably, throughout said slow to medium speed range both the lead and rear wings are positive lift generating.

Preferably, below the bottom end of said slow to medium speed range the lead wing of the aircraft will stall before the rear wing, such that the rear wing positively rotates the aircraft about its pitch axis to force the nose down and therefore reduce the angle of attack of the lead wing causing a porpoise or nodding action to maintain stability and control.

Preferably, the wing configuration of the aircraft is a tandem wing configuration - most preferably a Mignet configuration.

Preferably, the lead wing is a reflexed wing design. The lead wing may be a NACA 127115 wing.

Preferably, the lead wing is pivotally attached to the rest of the aircraft, such that the entire lead wing may be pivoted front/back to alter its angle of attack.

The rear wing may be a Clarke YH section.

Preferably, the aircraft is an unmanned aircraft.

Preferably, the aircraft is a remotely controlled aircraft.

Preferably, the aircraft is provided with control systems to automatically control the positioning of the pendulum and angle of attack of the lead wing according to airspeed of the aircraft.

Preferably, the aircraft is provided with control systems to automatically control the positioning of the pendulum according to whether a desired mode of operation corresponds to high to medium, slower airspeeds or hover mode . According to a second aspect of the invention, there is provided an aircraft comprising a rigid wing and structure, a thrust producing means such as an engine or motor, and a wherein a pendulum is provided which is fixed to said structure at a pivoting end thereof and is arranged for shifting the centre of gravity of said aircraft between at least first and second positions relative to a longitudinal centre, nose to tail, line of the aircraft, wherein in a first position the centre of gravity of said aircraft is relatively far forward to provide a relatively fast flying mode and in a second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode.

Preferably, the aircraft has a thrust to weight ratio of at least one and the pendulum is positionable in at least first to third positions, wherein in the third position the centre of gravity is positioned relatively far back to enable the aircraft to adopt a position in which the aircraft enters a hover mode in which a line of thrust of said thrust producing means is substantially vertical .

The aircraft rigid wing may comprise a lead wing of the aircraft.

The structure may comprise an underside of the rigid wing, or may comprise a fuselage section of the aircraft.

The aircraft may further comprise a rear wing.

According to a third aspect of the invention, there is provided an aircraft comprising a rigid wing, a structure, a thrust producing means, and characterised by a means to shift the centre of gravity of said aircraft between at least first and second positions relative to a longitudinal centre line of the aircraft, wherein in a first position the centre of gravity of said aircraft is relatively far forward to provide a relatively fast flying mode and in a second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode.

According to a fourth aspect of the invention, there is provided a film-making platform from which a camera is arranged to film scenes from the air, wherein the platform comprises an aircraft according to either the first, second or third aspects of the invention and, wherein the camera is pivotally attached to a free end of the pendulum to command a large field of view.

The skilled man will appreciate that any of the preferred features of the first aspect may be combined with features of the second and/or third aspects where such combinations are technically feasible

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows a preferred embodiment of the invention in schematic side view illustrating a forward flight mode;

Figure 2 is another schematic side view illustrating a the aircraft in forward flight mode; Figure 3 is a schematic view illustrating the aircraft in hover mode from a first angle;

Figure 4 is a schematic view illustrating the aircraft in hover mode from a second angle;

Figure 5 is a schematic view illustrating an embodiment of the aircraft in slow flight mode;

Figure 6 shows an aerofoil section and the exemplary placement of centre of gravity of the aircraft in fast and slow flying modes; and

Figures Ia-Ic show a preferred variant of a pendulum for use with the aircraft.

Referring initially to Figures 1 and 2, there is shown an aircraft 10 in forward flight mode. The aircraft 10 is shown arranged along a nose-to-tail centre line N T and comprises a lead wing 12, a rear wing 14, ducted fans 16i, I62 for providing forward thrust, a fuselage 18, rudders 20i, 2O2, a pendulum 22 pivotally attached to the underside of the aircraft, landing/take off wheels 24_X, 24₂ and tail wheels 26i, 26₂. The lead wing 12 is pivotally attached P to the rest of the aircraft 10 by support struts 13 attached to shroud portions of the ducted fans I61, I62.

The fuselage 18 connects the main parts of the aircraft together and has a forked type construction comprising left and right hand sections I81, I82 having the rudders 20i, 2O₂ at one end thereof and which connect together in a wishbone type formation at the other end to a main fuselage part I83 rearwardly of and between the ducted fans I61, I62. The left and right hand fuselage sections I81, I82 have a cut-away section located forwardly of the leading edge of the rear wing 14 to enhance airflow and ensure that the rear wing has a maximum lift generating area. Adjacent to where the two halves of the wishbone formation join together, the fuselage main part I83 forms a support structure for carrying the pivoting end of the pendulum 22. At the free-end of the pendulum 22 a payload 30 (typically a camera) is provided.

There is a need within the film-making industry, and in other areas of human activity to provide unmanned aircraft with are capable of flying within a range of speeds including hovering. There is also a need to provide an arrangement in which an airborne camera may be positioned upon an unmanned aircraft so as to give a virtually unrestricted view towards the ground, no matter what attitude the aircraft may assume, and regardless of air speed etc. With this in mind, preferred embodiments of the invention are arranged so as to be able to fly in a number of different modes, namely: a medium to high speed mode; a slow speed flying mode; and a hovering mode.

As has already been mentioned, Mignet type designs show very good stability for medium to slow flying situations, but cannot achieve a stable full hover mode. Another drawback of the Mignet design is that at higher speeds, the whole Mignet design can become unstable. This instability is because at higher speeds the lead wing' s 12 angle of attack needs to reduce to maintain level flight or it will actually create too much lift resulting in the lead 12 and rear wing 14 having similar angles of attack to the oncoming air and the lead wing 12 being less likely to stall first. This instability problem was recognised by Mignet during the 1930' s when the flying flea design planes showed a tendency to crash. The problem was solved to an extent at that time by providing a mechanism for moving the rear wing in the event of commencement of a stall. However, without a pilot onboard it is difficult to recognise the onset of such a stall and to react accordingly.

The inventor has solved the high-speed stall problem of the Mignet wing by providing an arrangement in which the centre of gravity is shifted forwards so that the lead wing 12 has to run a higher angle of attack to carry it while the rear wing 14 runs a lower angle of attack with little or no lift. The angle-of-attack difference between the wings is restored. Referring now especially to Figures 1 and 2, this shifting forward of the centre of gravity is shown, by the pendulum 22 and its associated payload 30 being maintained in a forward facing direction so as to bring the centre of gravity of the aircraft to within a 30% - 40% displaced distance from the lead chord of the main wing 12 (please see Figure 6 for a visual explanation) .

By positioning a relatively significant weight in the form of the payload 30 on the end of pendulum 22 (for instance, for an aircraft weighing 5kg, a typical payload at the end of pendulum 22 may add an extra 2kg to give a total weight of approximately 7kg) movement of the payload provides an effective shift in the total centre of gravity of the aircraft so as to give an arrangement in which the aircraft may maintain stability as it flies faster. The typical speed range for the forward flying "medium to fast" mode may typically be between 22 knots airspeed and a given maximum speed (of at least, say, 40 knots) . By providing the payload 30 with a hinged connection H to the pendulum arm 22, a suitably weighted payload may automatically be arranged so that the payload maintains a stable position with regard to the ground over which the aircraft is flying. In other words, if the payload 30 were a camera then suitable arrangement of the hinges H can automatically arrange for the camera to be (for instance) ground facing. Of course, it is also possible to provide arrangements in which the directional orientation of such a camera may be independently remotely controlled by, for instance, servo motor mechanisms using an operator controlled arrangement, or a automated control system. Also, whilst a simple swinging hinge mechanism is shown, other arrangements may be provided such as gimble arrangements giving a 360° possibility for range of control by remotely controlled servo mechanisms etc. It will be noted that by having the camera as payload 30 in the position shown in Figures 1 and 2 the camera is relatively clear of the structure of the aircraft and so commands a potentially large field of view.

It will be appreciated that for faster flying, the thrust of the engines 16i, I62 will be at the medium to maximum settings, and that the angle of attack of the lead wing 12 (which has no control surfaces - but instead constitutes one large control surface in itself) is still relatively great compared to the rear wing, which by now will run a lower angle of attack with little or no lift. The front wing will still stall first, thereby ensuring the stall recovery mechanism already discussed.

Whilst the illustrations do not show any detail of any mechanism for altering the angle of attack of the lead wing 12, it will be appreciated that this may be provided in a number of different possible ways. For instance, servo controlled mechanisms may be provided associated with hinge connections P or, control arms, ram arrangements, wire and pulley arrangements, for instance, could be provided linked to the main part of the fuselage I83 so as to provide the necessary movements. Of course, other suitable arrangements are within the realm of the skilled man and could just as easily be applied to provide the necessary movement without departing from the scope of this invention.

Similarly, with regard to moving the pendulum 22 and maintaining it in the forward position, such control could, for instance, be provided by servo mechanisms housed within the main portion I83 of the fuselage and those arrangements could be geared and/or, for instance, a control line on a rotatable spool could be provided toward a forward end of the fuselage 18 so as to reel the pendulum 22 into the position shown in Figures 1 and 2. Other means that could hold the free end of the pendulum in the first position adjacent to or in front of a nose end of the aircraft 10 may comprise a remotely controlled latching/unlatching means, control arm, rod or piston arrangements etc, all of which may be remotely operated.

Referring now to Figure 5, there is shown a slow flying mode of the aircraft 10, which may apply to bring about stable flight within a slow to medium airspeed range. In this mode, it can be seen that the pendulum 22 has been released from the forward position so as to hang down from the main part I83 of the fuselage 18 and to bring the centre of gravity of the aircraft more positively between the lead wing 12 and rear wing 14. Here, referring to Figure 6, the centre of gravity of the plane may be between 60% and 80% displaced distance from the front to rear chord of the lead wing. In this arrangement, stable flying within the range of 18 to 25 knots (for instance) is achievable and the effective configuration is a Mignet style arrangement. It will be noted that in this arrangement, the payload 30 is well clear of any parts of the aircraft 10 and is particularly nicely positioned for filming operations as it is unlikely that any parts for the aircraft would disturb the field of view of a camera mounted in this position.

With the pendulum 22 in the position shown in Figure 5, the aircraft 10 relies more on the rear wing 14 to create lift than when the pendulum 22 is in the forward position. Doing this does lessen stability to a certain extent - the rear wing 14 is closer to stalling first - but this configuration generates more lift overall, enabling slower flight. At this lower air speed the lead wing 12 can run right up close to its stall angle, thereby just preserving the aircraft's porpoise mechanism stability. Reducing airspeed below the slowest sustainable forward flying speed (for instance decreasing or cutting the throttle settings from an 18 knot slow flying speed) will result in a controlled descent with the aircraft gently descending and porpoising rather than stalling and this position may be recovered at any time by increasing the throttle setting.

Analysis shows that when wishing to transition from the slow flying mode to the fast flying mode, as the pendulum is moved forward from the position shown in Figure 5 to the position shown in Figures 1 and 2, the aircraft can fly faster and still maintain a positive angle of attack difference between lead and trailing wing to maintain stability. Indeed, at higher speeds the rear wing 14 may produce some downward lift, meaning that the aircraft may at some speeds convert from a stabilised Mignet type higher speed flight mode to a conventional airplane type arrangement.

Referring now to Figures 3 and 4, there is shown a configuration in which the aircraft has made a transition from slow flight to full hover. In the preferred embodiment, each three bladed prop of the ducted fans 16i, I62 is capable of delivering 5.9kg of thrust unshrouded, but 7.7kg of thrust once shrouded in the ducts. The aircraft as a whole, including the 2kg payload weighs around 7kg and, therefore, with twin fans a thrust-to- weight ratio of well over one is guaranteed.

As the pendulum 22 is swung rearwardly and the lead wing 12 pitched to its maximum (which it will be during the slowest flying modes) the aircraft automatically flies upward into a near hover, which is almost stabilized as the pendulum 22 moves beneath it. Maintenance of the full hover mode (in which the nose of the aircraft points vertically upward and the pendulum 22 hangs vertically downward) may be maintained with a simple auto pilot system for providing an automated sequence of adjustments to throttle, lead wing angle and pendulum settings or can be maintained by fine pilot control. As the aircraft as a whole is relatively light the aircraft can be maintained at a low level hover without producing huge amounts of downdraft and, therefore, it is eminently suitable for providing close-up filming of actors etc on location without causing large air disturbances.

The aircraft is unusual in that it pitches up through almost 90° in flight. With any type of aircraft used in film-making, it is of course vital to secure the camera payload in such a way that it can see all around without being blanked by the fuselage 18 and in such a manner that it is kept relatively level. By providing the camera as the payload of a pendulum 22, such matters are automatically ensured and, with correct damping, the pendulum may also work to isolate the aircrafts motion from the camera.

Referring now to Figure 6, which has already been referred to with regard to placement of centre of gravity, it will be noted that the aerofoil section is what is known as "reflexed". This means that instead of curving progressively downward, the top of the wing kinks back upwards at the trailing edge. This creates a small amount of down force at the back of the main wing 12 to counteract forward rotation. It also has the side effect of reducing overall lift, so a deeply cambered shape to the wing is necessary to retrieve that lost lift.

With a Mignet tandem wing configuration, the lead wing 12 is very dominant and unless virtually all forward rotation is cancelled out the trailing wing won't be able to provide lift. If it did so then the entire aircraft would somersault forward. Particular aerofoil sections being utilized at the moment for the purposes of the present invention include an NACA 127115 reflex lead wing coupled to a Clarke YH section rear wing (both known wing section types) . This combination is found to provide good lift generation from both wings, without forward rotation at all required operating speeds.

In the adopted Mignet-style configuration of wings, the whole of the lead wing rotates fore and aft to control the aircrafts pitch angle. Analysis has been able to show that the slower the aircraft 10 flies, the steeper the lead wing needs to be held at and, surprisingly, the more stable the entire aircraft becomes. As the lead wing's angle of attack is increased to give maximum lift for the slower speeds, so its tendency to stall decisively before the rear wing is accentuated - leading to an increase in pitch stability as it approaches its slowest level flight speed.

Figures 7a through 7c show a modified design of pendulum which has been found to be particularly apt for use with the present invention.

Whilst in all of the preceding Figures, a solid pendulum shaft 22 has been shown, in preference this shaft actually itself has an auxiliary pivot point "B". By providing an auxiliary pivot point intermediate a top pivot connection "A" and the payload 30, the pendulum 22 is able under certain circumstances to split into upper 22U and lower 22L pendulum portions, with the lower portion 22L being separated from the line of thrust of the fan motor units 16i, I62 when the aircraft 10 is in hover mode. By enabling movement of a lower pendulum portion 22L off the line of thrust, instabilities found in hover mode may be compensated for, and this separation mechanism has also been found to increase stability in the low speed flying mode.

To illustrate the above, if a rigid pendulum were considered and the aircraft was in the hover mode as shown in Figures 3 and 4, then a sharp disturbance to the aircraft 10, such as a crosswind blowing the centre line of the aircraft away from the vertical, can cause the aircraft to simply topple from the sky, as all the forces of the aircraft are directed along one line, i.e. along the fuselage line and none of them are able to provide a correctional force. However, if an extra pivot point "B" is provided in the pendulum 22, then a force knocking the fuselage away from the vertical will cause the freely pivoting bottom pendulum portion 22L to swing away from the line of thrust and provide a corrective force to the fuselage to bring it back into the vertical line.

It has been found that by providing this extra pivot point "B" approximately one third distance from the top of the pendulum and to damp movement of the bottom pendulum portion 22L with respect to the upper pendulum portion 22U is particularly effective.

Of course, it is not always desirable for the extra pivot point to be in action. Particularly with regard to the higher speed forward flying modes during which the aircraft 10 flies in the manner of a conventional aircraft any active pendulum action would be dangerous and some means of stabilizing the extra pivot point "B" must be provided.

One particularly simple and effective mechanism for selective stabilisation of the lower pendulum portion 22L and the pivot point "B" is shown in Figures 7a through 7c. In these Figures, the upper and lower portions 22U, 22L of the pendulum shaft 22 are shown, along with a conical sheath 32 and an actuating arm 34. The area of the fuselage that the pendulum joins to at the top is shown in the Figures, but the rest (as well as the payload 30 and the lowermost extent of the lower pendulum portion 22L) is omitted for reasons of clarity. Here, the uppermost end of the upper pendulum portion 22U is pivotally attached to fuselage 18 by means of a top pivot point "A", whilst the lower pivot point "B" (which is a spherical type pivot point) connecting the upper 22U and lower 22L pendulum portions is (as mentioned previously) located approximately one third of the way down the entire pendulum length. The control arm 34 is joined at its lower extent to an upper part 32U of sheath 32 and at its upper extent s joined to the fuselage 18 at pivot point "C" which is positioned further toward the nose of the aircraft 10 than the top pivot point "A" of the pendulum 22. The control arm arrangement 34 acts such that when the pendulum is in a forward position, as shown in Figure 7a, the pivot point B and the adjacent areas of the upper 22U and lower 22L pendulum portions are tightly shrouded by a close fitting part of the sheath 32, so as to hold both the lower portion 22 of the pendulum and the upper portion 23 in line with one another. Referring now to Figure 7b, the situation is shown where the pendulum depends downwardly from the fuselage section 18. In this case, because of the situation of the control arm 34 with regard to the pendulum portions 22U, 22L, the sheath 32 is raised along the line of the shaft so as to expose the lower pivot point B within a flared portion 32f, which will allow a degree of movement of the lower portion of the pendulum 22L away from the line of the upper portion of the pendulum 22U. As can be seen then from Figure 7c, further movement of the pendulum 22 to the rearward position in which hover is approached, provides a greater deal of exposure and, therefore, freedom for movement of the lower portion of the pendulum 22L, with respect to the upper part 22U. The maximum amount of freedom of movement of the lower pendulum 22L of away from the central axis of the upper pendulum portion is fixed by the sheath to be around 10 to 20 degrees (preferably about 15 degrees) . The progression in the amount of freedom allowed to the joint "B" and the lower pendulum portion 22L provides a degree of ironing out of unwanted oscillations or perturbations in the craft as a whole and has been found to provide good pitch and roll stability.

It has also been found to be useful in the configurations shown in Figures 7b and 7c (i.e. those of relatively slow speed forward flight where the pendulum is hanging practically directly downward and of hover mode) to provide means for damping movement of the lower pendulum portion within the sheath 32. Damping within the restricted range of movement allowed by the flared sheath portion 32f, may be provided by surrounding the main line of the pendulum shaft 22 held within the sheath 32 with a soft foam type insulation. This stops the pendulum from moving too quickly or producing oscillations and thereby further helps to stabilize the aircraft. In an alternative, the pivot joint "B" may be designed to have a certain amount of inherent friction or resistance to movement which may in itself provide sufficient damping.

The above description discloses the basic arrangements for producing an aircraft capable of forward flight in a quasi-conventional aircraft mode, forward slow flying in a Mignet type mode and hovering flight. Such an aircraft is particularly apt for use within the film-making industry, but may be useful in any number of areas of activity.

Whilst the aircraft discussed is an unmanned aircraft, the teachings of the invention may be extended to apply to the area of manned flight and the invention is not limited by any weight or speed ranges discussed herein unless it is otherwise specifically stated as such.

It will be appreciated by the skilled man that many different ways may be found for varying the design of the aircraft without departing from the scope of the present invention .

To augment pitch and roll control in hover, elevators (not shown) may be included on either side of the rear wing .

To augment yaw control in hover, thrust may be transferred between fans. It will also be appreciated that where specific arrangements with regard to actuating and controlling movement of the various controlled elements of the aircraft (e.g. pivoting of the lead wing 12, movement and retention of the pendulum 22) have been discussed, the invention is not limited to such arrangements and that such arrangements may be substituted with obvious alternative arrangements available to the skilled man without departing from the scope of the invention.

Further, whilst the arrangements are described in relation to a tandem wing aircraft, it is possible that the invention may also be exploited in other aircraft such as mono-wing designs or tri-wing designs.

Whilst the description refers to use of the invention in unmanned film-making applications, it will be appreciated that the invention is useful in many types of activity. Another good example of where the invention may be particularly advantageous is in airborne surveying/scanning where buildings may be inspected and their dimensions and details recorded. Data gathered from such exercises can be used in virtual reality environments, such as gaming to provide faithful virtual reproduction of real life scenes.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. An aircraft (10) comprising a lead wing (12) a rear wing (14), a fuselage section (18) and a thrust producing means (16), wherein the aircraft (10) has a thrust to weight ratio of at least one;

characterised by:

a weight transferring means (22) arranged to shift the centre of gravity of said aircraft (10) between at least first through third positions relative to a longitudinal centre line of the aircraft (10), wherein in the first position the centre of gravity of said aircraft (10) is relatively far forward to provide a relatively fast flying mode, in the second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode, and in the third position the centre of gravity is positioned relatively far back to enable the aircraft (10) to adopt a position in which the aircraft (10) enters a hover mode in which a line of thrust of said thrust producing means (16) is substantially vertical.

2. The aircraft of claim 1, wherein, the weight transferring means comprises a pendulum having a pivoted end and a free end, wherein the pivoted end is pivotally attached to the aircraft.

3. The aircraft of claim 2, wherein the pendulum is pivotally attached to an underside of the aircraft.

4. The aircraft of claim 2 or claim 3, wherein the pendulum is pivotally attached to a part of the aircraft situated between a lead chord line of the lead wing and a lead chord line of the rear wing.

5. The aircraft of any of claims 2 to 4, wherein the pendulum is weighted at its free end by an attached mass which is a significant proportion of the overall aircraft weight .

6. The aircraft of any of claims 2 to 5, wherein a payload is attached at the free end of the pendulum.

7. The aircraft of claim 6, wherein the payload is pivotally attached to the free end of the pendulum.

8. The aircraft of claim 6 or claim 7, wherein the payload is capable of rotation about one or more axes of movement with respect to the free end of the pendulum.

9. The aircraft of any of claims 6 to 8, wherein movement of the payload is remotely controllable independent of movement of the pendulum.

10. The aircraft of any of claims 6 to 9, wherein the payload comprises a camera, which may be a still or video camera.

11. The aircraft of any of claims 2 to 10, wherein when the centre of gravity is in the first position the free end of the pendulum is held nearest to a nose end of the aircraft.

12. The aircraft of any of claims 2 to 10, wherein when the centre of gravity is in the first position the free end of the pendulum may be held at a position forward of a nose end of the aircraft.

13. The aircraft of any of claims 2 to 12, wherein the pendulum is a two part pendulum comprising an upper pendulum portion pivotally linked to a lower pendulum portion, wherein the lower pendulum portion is pivotally linked at its upper end to a lower end of the upper pendulum portion.

14. The aircraft of claim 13, wherein the pivotal linkage between the upper and lower pendulum portions is a spherical type joint linkage enabling movement of the joint in more than one axis.

15. The aircraft of claim 13 or claim 14, wherein the pivotal linkage between the upper and lower pendulum portions is located approximately one third of the way down the entire pendulum length.

16. The aircraft of any of claims 13 to 15, wherein the pivotal linkage between the upper and lower pendulum portions is stabilised to prevent or limit relative movement between the two parts.

17. The aircraft of any of claims 13 to 16, wherein when the centre of gravity is in the second position the lower pendulum portion is arranged to be capable of swinging outside of the central longitudinal axis of the upper pendulum portion.

18. The aircraft of claim 17, wherein movement of the lower pendulum portion is damped by friction in the pivotal linkage between the upper and lower pendulum portions .

19. The aircraft of claim 13 to 18, wherein means for selectively stabilising the upper and lower portions of the two-part pendulum comprises a sheath which is capable of covering the pivotal linkage between the upper and lower pendulum portions and is longitudinally displaceable with respect to the upper pendulum portion.

20. The aircraft of claim 19, wherein the sheath has a close fitting part which has an internal diameter that is slightly greater than the outer diameter of the upper and lower pendulum portions that it surrounds when stabilising the linkage.

21. The aircraft of claim 20, wherein the sheath has a looser fitting flared part which is joined to the close fitting of the sheath, whereby when the looser fitting part is moved to be around the pivotal linkage between the upper and lower pendulum portions the lower pendulum portion is allowed a degree of freedom of independent movement .

22. The aircraft of claim 21, wherein longitudinal displacement of the sheath along the axis of the upper pendulum portion is arranged to progressively bring the pivotal linkage between the upper and lower pendulum portions into the loose fitting part of the sheath when the pendulum is moved from the first to the second position such that in the second position a degree of independent movement of the lower pendulum portion is allowed.

23. The aircraft of any of claims 13 to 22, wherein the lower portion of the pendulum is allowed to move away from the line of the upper portion of the pendulum by a maximum of 20 degrees.

24. The aircraft of any of claims 13 to 23, wherein movement of the sheath is provided by a control arm joined at its lower extent to the sheath and at its upper extent pivotally joined to the fuselage. Preferably, the pivot point of the control arm is positioned further toward the nose of the aircraft than the top pivot point of the upper pendulum portion.

25. The aircraft of claim 24, wherein in use, the control arm acts such that when the pendulum is the first position the pivotal linkage between the upper and lower pendulum portions and the adjacent areas of the upper and lower pendulum portions are tightly shrouded by the close fitting part of the sheath so as to hold both the lower portion of the pendulum and the upper portion in line with one another.

26. The aircraft of claim 24 or claim 25, wherein the control arm is arranged, in use, such that in the second position the sheath is raised along the line of the shaft to bring the loose fitting part of the sheath over the pivotal linkage between the upper and lower pendulum portions and the adjacent areas of the upper and lower pendulum portions.

27. The aircraft of any of claims 2 to 26, wherein when the centre of gravity is in the second position the free end of the pendulum is allowed to depend downwardly freely from the aircraft during substantially level flight modes of the aircraft.

28. The aircraft of any of claims 2 to 27, wherein the aircraft is provided with control systems to automatically control the positioning of the pendulum and angle of attack of the lead wing according to airspeed of the aircraft .

29. The aircraft of claim 28, wherein the aircraft is provided with control systems to automatically control the positioning of the pendulum according to whether a desired mode of operation corresponds to high to medium, slower airspeeds or hover mode.

30. The aircraft of any preceding claim, wherein in the first position the aircraft is capable of flying within a top speed range of operation from approximately 20 to 40 knots.

31. The aircraft of claim 30, wherein in said top speed range of operation the centre of gravity of the aircraft is positioned between 3/10^th and 4/10^th of the distance between a front and rear chord line of the lead wing.

32. The aircraft of claim 30 or claim 31, wherein at an upper part of said top speed range the lead wing is arranged to be positively lift generating, whilst the rear wing is negatively lift generating, and at lower parts of said top speed range both the lead and rear wings are arranged to be positively lift generating.

33. The aircraft of any preceding claim, wherein in the second position the aircraft is capable of flying within a slow to medium speed range of operation from approximately 18 to 25 knots.

34. The aircraft of claim 33, wherein in said slow to medium speed range of operation the centre of gravity of the aircraft is positioned between 6/10^th and 8/10^th of the distance between a front and rear chord line of the lead wing.

35. The aircraft of claim 33 or claim 34, wherein throughout said slow to medium speed range both the lead and rear wings are positive lift generating.

36. The aircraft of any of claims 33 to 35, wherein below the bottom end of said slow to medium speed range the lead wing of the aircraft will stall before the rear wing, such that the rear wing positively rotates the aircraft about its pitch axis to force the nose down and therefore reduce the angle of attack of the lead wing causing a porpoise or nodding action to maintain stability and control.

37. An aircraft (10) comprising a rigid wing (12), a structure (18) and a thrust producing means (16);

characterised by:

a pendulum (22) attached to said structure (18) at a pivoting end thereof, wherein the pendulum (22) is arranged to shift the centre of gravity of said aircraft

(10) between at least first and second positions relative to a longitudinal centre line of the aircraft (10), and wherein in the first position the centre of gravity of said aircraft (10) is relatively far forward to provide a relatively fast flying mode and in the second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode.

38. The aircraft of claim 37, wherein the aircraft (10) has a thrust to weight ratio of at least one and the pendulum (22) is further arranged to shift the centre of gravity of the aircraft (10) to a third position, wherein in the third position the centre of gravity is positioned relatively far back to enable the aircraft (10) to adopt a hovering position in which a line of thrust of said thrust producing means (16) is substantially vertical.

39. A method for controlling an aircraft (10) comprising a thrust producing means (16);

characterised by the step of:

transferring the centre of gravity of the aircraft (10) between at least first through third positions relative to a longitudinal centre line of the aircraft (10), wherein in the first position the centre of gravity of said aircraft (10) is relatively far forward to provide a relatively fast flying mode, in the second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode, and in the third position the centre of gravity is positioned relatively far back to enable the aircraft (10) to adopt a hovering position in which a line of thrust of the thrust producing means (16) is substantially vertical.

40. A method for controlling an aircraft (10) comprising a thrust producing means (16);

characterised by the steps of:

attaching a pendulum (22) to a structure (18) of the aircraft (10) at a pivoting end thereof; and

transferring the centre of gravity of said aircraft

(10) between at least a first position and a second position relative to a longitudinal centre line of the aircraft (10) by pivoting the pendulum (22), wherein in the first position the centre of gravity of said aircraft (10) is relatively far forward to provide a relatively fast flying mode and in the second position the centre of gravity is positioned relatively centrally to provide a relatively slow flying mode.

41. The method of claim 40, wherein the aircraft (10) has a thrust to weight ratio of at least one and the step of transferring the centre of gravity further comprises transferring the centre of gravity of the aircraft (10) to a third position, wherein in the third position the centre of gravity is positioned relatively far back to enable the aircraft (10) to adopt a hovering position in which a line of thrust of said thrust producing means (16) is substantially vertical.