WO2014195660A1

WO2014195660A1 - Flying platform

Info

Publication number: WO2014195660A1
Application number: PCT/GB2013/051489
Authority: WO
Inventors: Charl RANWELL
Original assignee: Cvr Limited
Priority date: 2013-06-06
Filing date: 2013-06-06
Publication date: 2014-12-11
Also published as: EP2892803A1

Abstract

A flying platform (100) includes a pilot platform (128); a set of rotor units (117), each said rotor unit including a respective rotor (122), and a motor (120) for rotating the respective rotor. It further includes a control arrangement (134) for a pilot (107) to control the motors of the rotor units and direction and yaw of the flying platform in use, and a set of landing supports (114). The rotor units are arranged around the pilot platform, such that in normal use, a said rotor unit is configured to act as an anti-torque rotor unit for a diagonally opposed said rotor unit.

Description

Flying Platform

The present invention relates to flying platforms.

A flying platform is an airborne vehicle with the major part of its manoeuvring performed by using the pilot's instinctive sense of balance to maintain the desired attitude, both in the hover and tilted towards the direction of travel. Called kinaesthetic control, it is most effective whilst standing up, as is the case with surfers and skiers.

The flying platform owes its origins to American inventor, Charles Zimmerman, who in the early 1940s explored the stability issues of a person balancing on a so-called thrust vector, and he found through experiments with standing on a tiltable platform that it was quite easy to remain stable in an upright position and he built and flew a rudimentary two-engined two counter- rotating propellers platform to convince the authorities. Zimmerman then developed a kinaesthetically controlled stand-on flying platform with the contra- rotating propellers enclosed in a single tube or duct, and six models were built by Hiller, the helicopter manufacturer. It was found that although the craft was stable and flew well enough, it couldn't elevate much above and outside of ground cushion effect due to being underpowered.

A major predicament with flying any single-engined aircraft is what happens when an engine fails. In a winged aircraft the pilot can glide to a safe landing field (provided he has enough height). In a conventional helicopter the pilot initiates a so-called autorotation where the main rotor's blade pitch is changed to allow the rotor to windmill freely thus allowing a controlled descent, and then when close to the ground, the pilot effects a blade pitch change the other way to obtain momentarily lift from the inertia in the turning main rotor and to thus reduce the rate of descent, and he then lands the helicopter.

If there is more than one engine then a single engine failure is in principle not that serious, especially with winged aircraft where the good engine or engines still provide forward thrust and thus lift from the wings. With helicopters the good engine continues providing power through a gearbox between the engines and the single main and tail rotors. However, the situation is more complicated with two engines and two main rotors since in such configurations the two rotors cancel out each other's anti-torque and so the gearbox has to allow both or either engine to continue to power both rotors.

Thus, even with small single-engined VTOL (Vertical Take Off and Landing) rotorcraft there has to be a mechanism to alter the blade pitch of the rotor plus a freewheeling clutch between rotor and engine to allow for autorotation in case of engine failure. If multi-engined, a gearbox is required for one or more rotors as discussed above. In all such cases this results in added weight and in complications in design, construction and operation.

A known solution to the problem of engine failure is to offer a ballistic emergency parachute, which allows the pilot to deploy a rocket-ejected emergency parachute to let the whole aircraft down in a slow descent in case of engine failure. However, a ballistic emergency parachute can only be used with sufficient height, and since it is designed to be used as a last resort, its operation usually results in major damage to the aircraft due to the still very hard landing. Furthermore, the parachute can drag the aircraft along the ground after landing in wind, causing more damage. Any aircraft with an engine-driven rotor or propeller on a vertical axis also has the issue of anti-rotating torque, i.e. in addition to the engine turning the rotor, there is a reactive force for the rotor to turn the engine (and resultantly the aircraft that it is attached to) the other way. With helicopters this is neutralised with either a horizontal axis tail rotor that acts against such main rotor anti- torque, or an additional vertical axis main rotor turning in the other direction, each main rotor thus cancelling out the other's anti-torque force. In the latter case the two main rotors can either be contra-rotating (on the same axis) or counter-rotating (on two axes).

Most personal VTOL craft, such as the flying platforms discussed above, have two contra- or counter-rotating propellers, each driven by an engine or both driven by one or more engines through a gearbox. Most flying platforms have the propellers contra-rotating below where the pilot stands.

There is the issue of yaw control, i.e. intentionally turning a two-rotor craft around its vertical axis. Using a rudder as with a winged aircraft only works if there is forward motion and thus airflow over the rudder, and since there is no tail rotor, there are only two methods that can be used: varying the power to one of the propellers in relation to the other, thus allowing the yaw due to its stronger torque force, or by using flap-like surfaces below the propellers to deflect the airflow.

Embodiments of the present invention are intended to address at least some of the abovementioned problems.

Embodiments of the flying platform described herein take into account the recent availability of light-weight high-powered engines for light aviation. Embodiments can be based on four such engines arranged on vertical axes in a square with each driving its own fixed ducted fan/propeller. This arrangement can allow redundancy, i.e. if one engine fails there are still three other engines to provide lift. Typically, two diagonally-opposed engines rotate in opposite directions to each other and are designed to work as a pair with each cancelling out the other's anti-torque.

According to a first aspect of the present invention there is provided a flying platform including or comprising:

a pilot platform;

a set of four rotor units, each said rotor unit including a respective rotor and a motor for rotating the respective rotor;

a control arrangement for a pilot to control the motors of the rotor units and direction and yaw of the flying platform in use, and

a set of landing supports,

wherein the rotor units are arranged around the pilot platform, such that in normal use, a said rotor unit is configured to act as an anti-torque rotor unit for a diagonally opposed said rotor unit,

wherein the rotor units are arranged as a two-by-two matrix formation around the pilot platform, wherein the rotors of the diagonally-opposed rotor units rotate in opposite rotational directions, wherein a first pair of said rotor units located at a front end of the flying platform rotate in a first rotational direction and a second pair of said rotor units located at a rear end of the flying platform rotate in an opposite rotational direction,

where, in use, the pilot kinaesthetically controls the direction of the flying platform in a horizontal plane by balancing and leaning in a desired direction and wherein the control arrangement is configured to allow the pilot to control yaw of the flying platform by independently controlling rotational speeds of the rotors of the first pair of rotor units and the rotors of the second pair of rotor units, and wherein the control arrangement is configured to allow the pilot to control vertical movement of the flying platform by decreasing or increasing rotational speeds of at least some of the rotors of the rotor units and the control arrangement includes a set of vertical control rotatable members, each said vertical control rotatable member configured to control the rotational speed of a respective said rotor unit for controlling vertical movement of the flying platform.

In some embodiments, the control arrangement can include a yaw control rotatable member, wherein rotation of the rotatable member in a first direction increases the rotational speed of the rotors of the first pair whilst decreasing the rotational speed of the rotors of the second pair, and vice versa. The rotatable member may have a neutral position that sets the rotors of all the rotor units to a same rotational speed.

An axis of rotation of the vertical control rotatable members may differ from an axis of rotation of the yaw control rotatable member, e.g. the axes may be perpendicular to each other.

The yaw control rotatable member may be substantially perpendicular with respect to the pilot platform. The yaw control member may have a non- parallel elongate member, e.g. a perpendicular handlebar. The vertical control rotatable members may be arranged along the handlebar. The vertical control rotatable members may be arranged so that a first set of the vertical control rotatable members are associated with the rotor units of the first pair and a second set of the vertical control rotatable members are associated with the rotor units of the second pair. The first set of vertical control rotatable members may be located towards a first end of the elongate member and the second set of vertical control rotatable members may be located towards a second end of the elongate member. The vertical control rotatable members in a said set may be arranged to normally rotate in a same direction (e.g. by friction), but may also be rotatable in different directions (e.g. overcoming the friction).

A said rotor unit may further include a duct at least partially surrounding the rotor of the rotor unit. A said duct may be generally cylindrical. At least an upper end of a said duct may be fitted with a filter or mesh. At least part of an upper lip of a said duct may curve outwardly and act as an aerodynamic lifting surface. A said rotor may comprise an uneven number, e.g. 5, of blades.

The flying platform may include a fuel tank for storing fuel for the motors. The fuel tank may be relatively wide compared to its depth. The fuel tank may be protected by means of a mesh cage or the like. The fuel tank may be located beneath, or form at least part of, the pilot platform.

The flying platform may include an alarm (audio and/or visual) for indicating failure of a particular said rotor unit. The flying platform may include a controller for attempting an in-flight restart of a failed said rotor unit.

The flying platform may further include an instrument panel. The instrument panel may include displays selected from a set including: RPM of the motors; pressure altimeter; GPS; speed; direction; moving map; motor cylinder head temperature; low fuel pressure visual warnings; low RPM visual and/or audio warnings; fuel contents gauge; battery charge gauge.

The flying platform may further include a cage or frame for, in use, protecting the pilot. The cage or frame may be at least partially fitted with a transparent screen. A pilot harness may be provided. The flying platform may further include a ballistic emergency parachute. The ballistic emergency parachute may be attached to the cage, e.g. to an upper part of the cage.

The flying platform may include a frame forming a collapsible undercarriage in the event of hard landing. The frame may comprise formations for supporting the rotor units and depending said landing supports. The frame may be formed of hollow tubing or the like.

The landing supports may comprise a set of wheels, skis or floats.

According to another aspect of the invention there is provided a flying platform controller substantially as described herein.

Whilst the invention has been described above, it extends to any inventive combination of features set out above or in the following description. Although illustrative embodiments of the invention are described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments. As such, many modifications and variations will be apparent to practitioners skilled in the art. Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mention of the particular feature. Thus, the invention extends to such specific combinations not already described. The invention may be performed in various ways, and, by way of example only, embodiments thereof will now be described, reference being made to the accompanying drawings in which:

Figure 1 is an upper view of an example flying platform in use;

Figure 2 is an underside view of the flying platform in use;

Figure 3 is an exploded diagram of some of the components of the flying platform;

Figure 4 illustrates how a control arrangement of the flying platform is used to control its motors;

Figure 5 details part of the control arrangement;

Figure 6 is an exploded diagram of part of the control arrangement;

Figure 7 details further components of the control arrangement.

Referring to Figures 1 to 3, an example flying platform 100 is illustrated. The platform includes a frame, shown generally at 101 , which is formed of bent and welded hollow chromoly steel tubing, which carries the other components of the flying platform, as well as providing the rigidity and strength in case of heavy landings. It will be appreciated that the frame shown is exemplary only and many variations are possible to its design and dimensions. Further, although steel tubing has advantages in terms of strength for weight, other materials could be used.

The example embodiment has the following dimensions: width 2.26 m; maximum diagonal 2.74 m; overall height 2.53 m (excluding an optional ballistic emergency parachute); pilot "floor to ceiling" clearance 1 .98 m (6' 6"). It can therefore fit on a legal road trailer of maximum width 2.3 m, and the fuel filler is designed so that the craft can be tilted forward to lie horizontally without any spillage of fuel, nor any leakage from the battery which is sealed, nor seepage from the two-stroke engines (described below) which don't have carburettor float chambers or oil sumps. An optional separate wheeled dolly may be made available for the upper part of the structure to rest on. On its side, as mentioned above, the embodiment can also fit into a standard 3 m (10') length shipping container.

The frame 101 includes a square-shaped frame member 102. First 104A and second 104B cross-beams extend diagonally through the corners of the square-shaped member and further outwards. The frame further comprises four rotor unit-holding frame members 105A - 105D that are fixed to the square frame member and the cross-beams. These are arranged as a two-by-two matrix. For brevity, only one rotor unit-holding frame member 105A will be described in detail, but it will be understood that the construction of the other three is generally identical.

A lower circular frame member 106A of one of the rotor unit-holding frame members (the front-left from the perspective of a pilot 107 in the example) is fixed, e.g. by welding, to an outer end of the cross-beam 104A, as well as another point of that cross-beam within the border of the square frame member and two perpendicular points of the square frame member.

The rotor unit-holding frame member 105A further includes an inner vertical strut 108A, which extends upwardly from the point where the circular frame member 106A is fixed to the cross-beam 104A within the border of the square frame member 102. The rotor unit-holding frame member further includes an outer vertical strut 1 10A, which extends upwardly adjacent the point where the circular frame member is fixed to the end of the cross-beam. The two struts are connected to an upper circular frame member 1 12A, which has a greater diameter than the lower circular member. It will also be noted that the frame 101 is further reinforced by connections between the upper circular frames 1 12A - 1 12D.

The outer strut 1 1 OA has a foot portion 1 14A that depends below the lower circular frame member. There upper portion of this strut is angled by around 15^Q with respect to the foot portion. The strut can form part of a landing support. Parts of the frame can be considered as a collapsible and replaceable undercarriage structure that can prevent or minimise damage to the rest of the craft. In the example, a castoring wheel 1 16A is connected to the foot portion, but it will be understood that variations are possible, e.g. skis or floats could be used. At least one of the castoring wheels (e.g. the two front ones) can be locked in the forward position, thereby allowing the flying platform to be easily wheeled on to a trailer or into a container using two ramps.

Each of the four rotor unit-holding frame members 105A - 105D is fitted with a rotor unit 1 17A - 1 17D. Again, for brevity the components of only one rotor unit 1 17A will be described. The rotor unit includes a duct 1 18A, which is generally cylindrical in form, but has an upper diameter that is greater than its lower diameter, and is generally dimensioned so as to fit inside the rotor unit- holding frame member 105A. In the example, carbon fibre is used for the construction of the ducts to save weight. The upper lip 1 19A of the duct is curved outwardly and this can provide an aerodynamic lifting surface when propellers draw air into the duct, creating an airflow over the curve - this can be augmented if moving in a horizontal direction. The size and shape of the duct lips (and the fairings described below) have been designed for optimal performance so that the lift from the leading edge duct lips do not prevent the craft from being tilted in the direction of movement and limit its forward speed.

Light-weight high-powered engines are now available and ones designed and built for backpack-powered paragliders and for ultralight and microlight aircraft are used in the illustrated embodiment of the flying platform. The engines are air-cooled piston engines and run on a two-stroke cycle, and thus have comparably lower weight by elimination of four-stroke components such as valve trains and oil sumps and pumps, as well as hoses and radiators which would be required for water cooling. Due to the few moving parts, any vibrations at high speed are minimised. Since the engine 120A performs best at high RPM, and propellers at a lower RPM, a reduction belt drive 121 A or gearbox is used. Four F33 engines (produced by Gobler-Hirth of Germany) of 28 hp (21 kW) are used in the embodiment, each turning its own propeller through its own reduction belt drive.

The F33 engine 120A uses reduction belt drives rather than gearboxes and can run in both directions. Two-stroke engines have no valve train and they can thus easily be configured to run in either direction. Furthermore, the F33 engine has a carburettor with a membrane (diaphragm) and no float chamber, and it also has no oil sump, both of which would have posed a leak risk, and so it can be mounted vertically within the duct 1 18A.

The F33 electric start option has been chosen for the embodiment described herein for ease of use and to allow the pilot to attempt an in-flight restart in case of engine failure. An onboard battery 123 is used for starting and to power the electronic instruments. The battery is of the lithium polymer type with low weight and high capacity, and it is charged in flight by a 50 W generator on one of the engines.

Recently-developed metals and oils have overcome the historical two- stroke problems of heat-induced piston seizures and excessive exhaust smoke due to the oil being premixed with the fuel. Normal 95 octane motor vehicle petrol is used which is available everywhere, plus there is not then an issue with the impending disappearance of AVGAS fuel as is used by larger aviation piston engines.

It will be appreciated that alternatives to the F33 engines may be used. For instance, engines such as the range produced by Austrian manufacturer, Rotax, use reduction gearboxes and these can fairly easily be modified to provide the present requirement of two engines turning propellers clockwise, and two anti-clockwise. If the gearbox is modified then the engine can be mounted horizontally if required. Electric motors are also in development for aircraft and can provide the power required, both for winged and rotorcraft. The flying platform described herein is well suited for four electric motors each turning their own ducted propeller. An important design factor in all engine configurations is the engine's power vs. its weight (of itself plus of the fuel it requires) because, unlike conventional aircraft where the engine is used for horizontal motion and lift is obtained from airflow over the wings, an engine for the flying platform has to lift its weight vertically and have additional upwards thrust available to be used for the craft's weight and the payload.

A propeller 122A with spinner is driven by the engine 120A. Preferably, the number of blades on the propeller is uneven (five in the example), as this can help eliminate any in-duct resonance. A wire mesh grid 124A is fitted over the top of the duct 1 18A to prevent airborne debris and limbs from being drawn into the ducts when the engine 120A is running.

One reason for use of the ducts 1 18A - 1 18D is safety: the ducts can protect the propeller blades from damage and bystanders close by from injury by the blades (both issues are major considerations in flying conventional rotorcraft with unprotected blades). Then, due to inter alia blade tip losses being eliminated by using a duct, a 40% greater efficiency over same sized non-ducted propellers is obtained. This allows for a smaller craft, and also with the blade protection mentioned above, it means being able to get into tighter spaces and overhangs than any rotorcraft with unprotected blades. Furthermore, noise is reduced compared to conventional helicopters since smaller diameter propellers have lower propeller tip speeds. Also, the ducts shield the engine and propeller sound. A possible disadvantage of using ducts is the added weight but the use of carbon fibre mitigates this. Also, the walls of the ducts are relatively thin since they are not used to give rigidity to the structure or to carry any load.

Fairings 126A - 126D are used for streamlining between the ducts and also to provide additional lift in whichever horizontal direction the craft is moving. As with the ducts, the fairing walls are thin except where generating lift, and they have no inside walls to further save weight. In the example craft, there are four fairings, each one fitted between adjacent pairs of ducts 1 18A - 1 18D, but it will be understood that the number, location, design and dimensions can be varied. Carbon fibre material is used for the fairings, as well as the propellers and spinners, but, again, it will be understood that other materials could be used.

The flying platform 100 further includes a fuel tank 128, which, in the example, is of the self-sealing bladder type. The tank has a cross-shape, with scooped lines extending between its points and is designed so that the four rotor units 1 17A - 1 17D are arranged equidistantly around it. The tank is contained in a protective steel mesh cage 130 to help it remain intact in case of a crash. The upper surface of the tank and the cage also form the platform on which the pilot 107 stands in use. This eliminates the requirement for, and the added weight of, a separate platform, and the mesh surface prevents the pilot from slipping on the platform surface in wet weather. However, it will be understood that in alternative embodiments, the pilot platform could be formed differently.

In use, the fuel tank 128 can be fitted in/adjacent the centre of the craft 100, with the rotor units 1 17A - 1 17D surrounding it, thereby minimising changes to the centre of gravity with varying quantities of fuel. Because the tank is wide and relatively flat, the fuel doesn't slosh around much and so that also little effect on the centre of gravity. Furthermore, unlike other known flying platforms where the pilot stands above the duct, the illustrated embodiment is designed so that the pilot platform is between the ducts 1 18A - 1 18D, and this, combined with the fuel tank below, gives a much lower centre of gravity, thereby reducing a tendency for the craft to topple over.

One point of the four points of the tank 128 (the one that is at the rear of the flying platform 100 from the perspective of the pilot 107) has a fuel filler pipe 131 attached to it. The pipe has a screw on cap 131 A which can easily be reached for refilling when standing next to flying platform. The pipe is positioned at the rear end of fuel tank so that when flying platform is tilted forward for transport or storage, the fuel does not leak from the filler.

A pilot safety cage 140, formed of tubular steel or the like, may also be provided, which can help protect the pilot 107 in the event of a roll over. It will be appreciated that the cage shown is exemplary only and alternative designs are possible. At least one transparent panel, e.g. of Perspex, may be provided for the cage to help shield the pilot. The illustrated cage includes an attachment point 142 at its apex for connection of an optional ballistic emergency parachute. An optional pilot harness (not shown) may also be attached to the upper frame. The wearing of a full-face crash helmet with visor by the pilot may be encouraged.

When assembled, a handlebar 134 is pivotably connected to a front portion 143 of the tubing that forms the safety cage 140 by means of a downwardly-extending vertical stem 132. An instrument panel 136 is also fixed to the tubing portion 143. Instruments are positioned on the panel to allow the pilot to easily identify which instruments and switches belong to each of the four engines 120A - 120D. All instruments, switches and warning lights are waterproof, and the following are examples of the type which can be fitted on the panel:

• Flight: Conventional pressure altimeter; GPS giving speed, direction and navigation with moving map (including controlled airspace awareness) • Engine (times four): RPM gauges; Cylinder head temperature (CHT) gauges; Low fuel pressure visual warnings; Low RPM visual and audio warnings, including indicator for which side twistgrip controls the affected engine; Combined magneto selectors and start switches

• Avionics: VHF radio; Mode S transponder

• Other: Fuel contents gauge; Battery charge gauge; Master all- engines kill switch with safety cover (in case of deployment of the optional ballistic emergency parachute); Pull toggle for ballistic emergency parachute deployment, with safety cover attached to upper parts of the frame 101 .

In use, the flying platform 100 is mainly kinaesthetically controlled, i.e. by the standing pilot 107 balancing and leaning in the relevant direction for movement in the horizontal plane (left, right, forward, backward or any combination thereof). The only other controls normally required are for movement in the vertical plane (up and down), and for yawing (rotating in the vertical axis). Although the illustrated embodiment is designed for transporting one person in a standing position, it will be understood that variations are possible. For example, embodiments for carrying one or more passenger in addition to the pilot, with the passenger(s) either seated or standing behind the pilot, are possible. Further, a seat or other rest for the pilot so that he/she is not fully standing at all times may also be offered, provided that this does not impair their ability to control the craft kinaesthetically.

The control system of the flying platform 100 is simple yet very effective, and avoids the complication of flaps for yawing. Referring to Figure 4, where forward direction of the craft from the pilot's perspective is shown by arrow 400, the control system allows the pilot 107 to use the handlebar 134 in the manner of a motorbike handlebar for directional control. The handlebar includes a horizontal cylindrical member 402. Each end of the horizontal member includes a twistgrip, and each twistgrip is split into two halves: 404A, 404B on the left- hand side and 404C, 404D on the right-hand side. The handlebar and twistgrips are linked to the throttle controls of the four engines 120A - 120D via a mixer mechanism described below.

As illustrated by arrows 406A, 406B in Figure 4, the pair of engines 120A, 120B located at the front end of the flying platform 100 both rotate their respective propellers (not shown) clockwise. The pair of engines 120C, 120D located at the rear end both rotate their respective propellers anti-clockwise. Thus, diagonally-opposed engines (i.e. 120A and 120D; and 120B and 120C) rotate in opposite directions to each other and are designed to work as a pair, each cancelling out the other's anti-torque.

Each of one twistgrip's halves is linked to the throttle controls of such a pair of engines (as will be described below in detail): the two outer halves 404A, 404D are linked to the front engines 120A, 120B (left outer twistgrip half 404A to the left front engine 120A, and right outer twist grip half 404D to right front engine 120B), and the inner halves 404B, 404C to the throttle controls of the rear engines 120D, 120C, respectively.

For yaw control, the pilot 107 turns the handlebar 134 in a conventional manner to the left or right, which correspondingly increases the revolutions per minute (RPM) of two of the engines that are rotating in the same direction (i.e. either the front pair 120A, 120B, or the rear pair 120C, 120D), and decreases the RPM of the other two. Such variations in RPM are slight and the resultant forward or backward tilting imbalance caused by more upwards thrust from one set of engines compared to the other, can be corrected kinaesthetically by the pilot. When the handlebar is returned to a middle neutral position then the four engines all revert to running at the same RPM. The flying platform 100 uses fixed blade pitch propellers 122 and so here power effectively equates to RPM, and since each propeller is driven by its own engine 120, yaw control can be achieved simply by increasing or decreasing the relevant engines' RPM.

Each of the twistgrip halves 404 is individually linked to the throttle control of each of the engines 120, and for up and down movement of the flying platform 100, both twistgrips (all four halves) are simply rotated together by the pilot in the same direction so as to facilitate less or more RPM and thereby upwards thrust to all four engines. This is similar in orientation to a motorbike's twistgrip throttle, i.e. rotating it rearwards to increase RPM and vice versa, but for the flying platform all twistgrips are turned together in the same direction.

The two halves (404A, 404B and 404C, 404D) of a twistgrip have been designed so that there is friction between them; they normally operate and remain together due to this friction, but one half can be adjusted in relation to the other half to trim out slight power imbalances between the two engines controlled by that pair of halves. This friction may be due to the type of material used for the grip halves, or a pattern or the like on their abutting surfaces. Although the illustrated embodiment uses twistgrips on a rotatable handlebar, which has benefits in terms of simplicity of construction and costs, it will be understood that alternative control mechanism could be used, e.g. switches, buttons or levers that communicate in a wired or wireless manner with engine throttle controls, joysticks, etc. Also, not all controls need to be mounted on the controller.

An important feature of the four-engined design and its handlebar/twistgrips and kinaesthetic control system is the ability to recover safely from an engine failure without the need for a ballistic emergency parachute. If, for example, the left front engine 120A suddenly failed in normal flight, the craft 100 would tilt in that direction due to the loss of RPM (upwards thrust) from it. The first reaction of the pilot 107 would be to instinctively lean towards the right rear to compensate kinaesthetically. The craft will also yaw to the right on its vertical axis due to a reduction in the failed engine's anti-torque power, and the pilot would usually automatically turn the handlebar towards the left to correct the yaw (using the power from the other non-failed engines). The pilot would then immediately throttle back on (both halves of) the left twistgrip 404A, 404B, as much as is necessary to maintain a level attitude, since by doing so it reduces the power of the right rear engine 120D of the pair which is causing the unwanted tilt and yaw.

Both good engines in the opposite diagonally-opposed pair (i.e. right front

120B and left rear 120C in this example) would still be functioning normally and would not be creating unwanted tilt or yaw as they run at the same RPM and rotate in opposite directions to each other. The right twistgrip 404C, 404D could then be used to increase the RPM of both of these engines together to counteract any overall loss of lift due to the failed engine 120A. Depending on the weight of the pilot, fuel level and engine performance (which decreases with increased altitude), the craft 100 may start descending as its height may not be able to be maintained by only the two good engines operating at maximum RPM, and with the other unaffected engine also providing upwards thrust but not fully since the resultant tilt and yaw from the failed engine may then not be controllable by leaning and using the handlebar. But even so, the pilot has time to plan his landing and the craft will not be falling out of the sky.

The engine instruments on the panel 136 are arranged so that the pilot can easily identify which engine has failed, and in addition to the RPM and other gauges' indications, a warning light can indicate to the pilot which side's twistgrip needs to be throttled back. An audible alarm may also sound. The power to the failed engine is accordingly also reduced by the actions described above, i.e. throttling back on the left twistgrip, which is good practice as that engine may not have totally failed and could be surging which then makes it more difficult to maintain a level attitude. Once the pilot has the craft settled down, an in-flight restart of the failed engine can be attempted. The above discussion and pilot actions, of course, apply to any of the engines failing and only one example is discussed. Good airmanship dictates landing immediately as is practical if only relying on three engines to remain airborne, since if another engine fails, especially if not in the same pair as the already failed engine, there is no other means of staying aloft. For this scenario, or if the fuel runs out in flight, provision has can be made to install a ballistic emergency parachute unit as an option.

Even though the vertical axes of the four engines 120A - 120D are offset from the centre of the craft 100, variations of one engine's RPM in relation to the others (intentionally using the handlebar, or inadvertently due to engine failure) can still cause a yawing moment, mainly around the centre of gravity and thus the centre vertical axis, and any other resultant horizontal movement of the craft due to the offset can be controlled kinaesthetically.

The linkages to the throttles of the four engines 120A - 120D from the four rotating twistgrip halves 404A - 404D, and from the handlebar 134 turning left or right, use the known mechanically operated Bowden cables, which make the control system very simple and very effective. There is a complication as the throttle linkages from the twistgrips and from the handlebars need in a sense to be "mixed" together: the pilot can at times be operating both the twistgrips and the handlebars at the same time. The mixer mechanism described below is based on the fact that for a Bowden cable, either the inner cable, or the outer cable housing, or both, can be moved in relation to each other (normally, the outer housing is fixed and only the inner cable moved).

Figures 5 and 6 show components of the handlebar in assembled and exploded views, respectively. Figure 5 shows the components from a viewpoint generally opposite to a pilot's perspective, whilst Figure 6 shows the components rotated clockwise by around 1 10^Q with respect to Figure 5. As can be seen in Figure 6, the upper area of a substantially central portion of the horizontal cylindrical member 402 of the handlebar 134 includes a fixed cylindrical stub 602 that has a central bore that is pivotably fitted to the vertical stem 132 of the handlebar 134, and through which an axle 604 (shown partially in Figure 6 and detailed below) also passes. The horizontal member is hollow and includes a set of four outer slots 606A - 606D, arranged as two spaced- apart pairs towards its ends, and a set of four inner slots 608A - 608D, arranged in two close pairs each side of the cylindrical stub.

The first left-hand side outer slot 606A is located beneath the outer half 404A of the left-hand twistgrip. The twistgrip half 404A cooperates with a throttle control component 61 OA, which comprises a rotatable horizontal bar 612A. The left-hand end of this bar has a vertical protrusion 614A fixed to it. When assembled, this protrusion extends through the slot 606A. When a user rotates the twistgrip half 404A, the protrusion 614A and the bar 612A also rotate. The right-hand end of the bar 612A of the control component has a curved member 616A fitted on it, extending outwardly from the upper end of a vertical strut 617A.

As can be seen in Figure 5, when assembled, the curved member 616A protrudes through the left-hand inner slot 608B. The curved member 616A includes a channel in which an inner portion of a Bowden cable 504A is located. The end of the Bowden cable is fixed to the end of the curved member 616A. The rotatable horizontal bar 612A is connected to this Bowden cable and so rotation of twistgrip half 404A as discussed above, can result in the Bowden cable 504A being pulled. As the bar 612A is rotated by the twistgrip, the vertical member 614A and strut 617A are moved together so that the curved member 616A is moved around the horizontal member 402. The other end of the Bowden cable is connected to the throttle of the front left-engine 120A and so, as mentioned previously, the RPM of that engine can be controlled by rotation of the twistgrip half.

In a similar manner, the second left-hand outer slot 606B is located beneath the inner left-hand twistgrip half 404B. A protrusion 614B of a throttle control component 61 OB, which is fitted on the left-hand end of a bar 612B, extends through that slot 606B. The other end of the bar includes a curved component 614B that, when assembled, extends through the left-hand inner slot 608A in a similar manner to how the curved component 616A extends through the slot 606B, as described above. The longer bar 612A fits coaxially through a bore 613 that runs through the shorter bar 612B. An inner portion of other Bowden cable 504B is housed within the channel of this curved member. The right-hand components 610C - 610D and slots 606C - 606D, 608C - 608D are arranged in a similar manner with respect to inner portions of Bowden cables 504C - 504D, respectively. This allows the twistgrip halves 404A, 404B, 404C, 404D to control the throttles of engines 120A, 120D, 120C, 120B, respectively, as discussed previously, typically for controlling the height of the flying platform 100.

Figure 5 also shows components that assist with allowing the rotation of the handlebar 134 to control the yaw of the flying platform 100, as discussed above. A housing 502 is attached to a substantially central portion of the handlebar. The housing includes a bearing arrangement (described below) that allows the handlebar to turn left or right. An inner change bar 508 (having a squared U-shape, i.e. an elongate portion with an arm extending perpendicularly each of end) is connected to the outer housings 505B and 505C of the two inner Bowden cables 504B and 504C. An outer bar 510 (similar in shape, but greater in dimensions than the inner change bar) is connected to outer housings 505A and 505D of the two outer Bowden cables 504A and 504D. As will be described below, these handlebar change bars are rotated on coaxial shafts by a bevel gear mechanism within the housing 502. The outer housings 505 of the Bowden cables (shown in their neutral positions in Figure 5) can be pushed/pulled by movement of the handlebar change bars.

Figure 7 shows the gear arrangement contained with the housing 502.

Figure 7 shows the components from a similar viewpoint to Figure 5, i.e. from the perspective of an onlooker looking towards the front of the flying platform, and not from the pilot's perspective. The vertical axle 604, which is located within and fixed to the vertical stem 132 of the handlebar 134, has a bevel gear 704 fixed to its lower end. This gear cooperates with a left-hand bevel gear 706A and a right-hand bevel gear 706B. The left-hand bevel gear is mounted on an inner coaxial shaft 708, which runs in bearings (not shown) on the gear housing. The ends of the outer change bar 510 are fixed to this shaft. A first portion 71 OA of an outer coaxial shaft is mounted on a portion of the inner shaft, running from inside the right-hand arm of the outer change bar to the inside of the left-hand bevel gear 706A. A second portion 710B of the outer coaxial shaft is located between the outside of the bevel gear 706A and the inside of the other arm of the outer change bar. Respective arms of the inner change bar 508 are fixed to the first and second portions of the outer coaxial shaft. The right-hand bevel gear is mounted on (the first portion of) the outer shaft.

The inner change bar 508 includes a bore 712C at its left-hand corner (adjacent its left-hand arm) and another bore 712B at its right-hand corner. The outer change bar 510 includes a bore 712D at its left-hand corner and another bore 712A at its right-hand corner. The outer housings 5054A - 505D of the Bowden cables 504A - 504D pass through bores 712A - 712D, respectively. Thus, when the inner change bar is moved up/down (by virtue of the handlebar being rotated left/right) then outer housings 505B and 505C are pulled/pushed, resulting in the RPM of the front pair of engines 120A and 120B being increased/decreased. Similarly, when the outer change bar is moved up/down (by virtue of the handlebar being rotated right/left) then the outer housings 505D and 505A are pulled/pushed, resulting in the RPM of the rear pair of engines 120C and 120D being decreased/increased.

Embodiments of the flying platform can be used for various applications. A non-exhaustive list of examples includes: leisure (e.g. outdoor recreation and exploration, sport flying); commercial (e.g. pylon and pipeline inspection, agriculture, park and wildlife management, aerial photography, sporting event control, news reporting, cargo lifting); emergency and rescue (e.g. patrol, search, first on the scene response, fire fighting forward control); security and defence (e.g. one-person transport, reconnaissance, surveillance). The ability of embodiments to be able to get into small spaces and overhangs, and being quieter is an important advantage in helicopter emergency medical services (HEMS). As embodiments of the flying platform described herein can safely fly in between and land on top of buildings and on single lane streets in city centres, which conventional helicopters cannot do, they offer unprecedented first on the scene response and medical treatment within the "golden hour" by the pilot/paramedic. The castoring wheels can easily be interchanged with small skis, again allowing unmatched first on the scene response on ski slopes where the craft can land on snow in small clearings between trees. Similarly, floats can be fitted for landing on water, facilitating seaside and lakeside first on the scene response. The reduced acquisition and operating cost of the flying platform compared to a HEMS helicopter is another major advantage.

Claims

1 . A flying platform (100) including:

a pilot platform (128);

a set of four rotor units (1 17), each said rotor unit including a respective rotor (122) and a motor (120) for rotating the respective rotor;

a control arrangement (134) for a pilot (107) to control the motors of the rotor units and direction and yaw of the flying platform in use, and

a set of landing supports (1 14),

wherein the rotor units are arranged around the pilot platform, such that in normal use, a said rotor unit is configured to act as an anti-torque rotor unit for a diagonally opposed said rotor unit, and wherein the rotor units (120A - 120D) are arranged as a two-by-two matrix formation around the pilot platform (128) and the rotors (120A, 120D) of the diagonally-opposed rotor units (1 17A, 1 17D) rotate in opposite rotational directions,

wherein a first pair of said rotor units (1 17A, 1 17B) are located at a front end of the flying platform (100) and rotate in a first rotational direction, and a second pair of said rotor units (1 17C, 1 17D) are located at a rear end of the flying platform rotate in an opposite rotational direction,

where, in use, a pilot (107) kinaesthetically controls direction of the flying platform (100) in a horizontal plane by balancing and leaning in a desired direction, and wherein the control arrangement (134) is configured to allow the pilot (107), in use, to control yaw of the flying platform (100) by independently controlling rotational speeds of the rotors (122A, 122B) of the first pair of rotor units (1 17A, 1 17B) and the rotors (122C, 122D) of the second pair of rotor units (1 17C, 1 17D), and

wherein the control arrangement (134) is configured to allow the pilot (107), in use, to control vertical movement of the flying platform (100) by decreasing or increasing rotational speeds of at least some of the rotors (122) of the rotor units (1 17), and wherein the control arrangement (134) includes a set of vertical control rotatable members (404), each said vertical control rotatable member configured to control the rotational speed of a respective said rotor unit (1 17) for controlling vertical movement of the flying platform (100).

2. A flying platform according to claim 1 , wherein the control arrangement includes a yaw control rotatable member (134), wherein rotation of the rotatable member in a first direction increases the rotational speed of the rotors (122A, 122B) of the first pair of rotor units (1 17A, 1 17B) whilst decreasing the rotational speed of the rotors (122C, 122D) of the second pair of rotor units (1 17C, 1 17D), and vice versa when the rotatable member is rotated in a opposite direction.

3. A flying platform according to claim 2, wherein the rotatable member (134) has a neutral position that sets the rotors (122A - 122D) of all the rotor units (1 17A - 1 17D) to a same rotational speed.

4. A flying platform according to claim 1 , wherein an axis of rotation of the vertical control rotatable members (404) differs from an axis of rotation of the yaw control rotatable member (134).

5. A flying platform according to claim 4, wherein the axes of rotation are perpendicular to each other.

6. A flying platform according to claim 4 or 5, wherein the yaw control rotatable member (134) is substantially perpendicular with respect to the pilot platform (128).

7. A flying platform according to claim 6, the vertical control rotatable members (404) are arranged along a handlebar (402) that is a perpendicular handlebar (402) to the yaw control member (134).

8. A flying platform according to claim 7, when dependent upon claim 4, wherein the vertical control rotatable members (404) are arranged so that a first set of the vertical control rotatable members (404A, 404D) are associated with the rotor units (1 17A, 1 17B) of the first pair of rotor units, and a second set of the vertical control rotatable members (404, 404C) are associated with the rotor units (1 17D, 1 17C) of the second pair of rotor units.

9. A flying platform according to claim 8, wherein the first set of the vertical control rotatable members (404A, 404B) are located towards a first end of the handlebar (402) and the second set (404C, 404D) of the vertical control rotatable members are located towards a second end of the handlebar.

10. A flying platform according to claim 9, wherein the vertical control rotatable members (404A, 404B) in a said set are arranged so as to normally rotate in a same direction (e.g. by friction), but can also be rotatable in different directions (e.g. by overcoming the friction).

1 1 . A flying platform according to any one of the preceding claims, wherein a said rotor unit (1 17) further includes a duct (1 18) at least partially surrounding the rotor (122) of the rotor unit.

12. A flying platform according to claim 1 1 , wherein a said duct (1 18) is generally cylindrical.

13. A flying platform according to claim 12, wherein at least an upper end of a said duct (1 18) is fitted with a filter or mesh (124).

14. A flying platform according to claim 12 or 13, wherein at least part of an upper lip of a said duct (1 18) curves outwardly and acts as an aerodynamic lifting surface.

15. A flying platform according to any one of the preceding claims, wherein a said rotor (122) comprises an uneven number, e.g. 5, of blades.

16. A flying platform according to any one of the preceding claims, including a fuel tank (128) for storing fuel for the motors (120).

17. A flying platform according to claim 16, wherein the fuel tank (128) is relatively wide compared to its depth.

18. A flying platform according to claim 16 or 17, wherein the fuel tank (128) is be protected by means of a mesh cage (130).

19. A flying platform according to any one of claims 16 to 18, wherein the fuel tank (128) is located beneath, or form at least part of, the pilot platform.

20. A flying platform according to any one of the preceding claims, further including an alarm (audio and/or visual) for indicating failure of a particular said rotor unit (1 17).

21 . A flying platform according to any one of the preceding claims, further including a controller for attempting an in-flight restart of a failed said rotor unit (1 17).

22. A flying platform according to any one of the preceding claims, further including an instrument panel (136).

23. A flying platform according to claim 22, wherein the instrument panel (136) includes displays selected from a set including: RPM of the motors; pressure altimeter; GPS; speed; direction; moving map; motor cylinder head temperature; low fuel pressure visual warnings; low RPM visual and/or audio warnings; fuel contents gauge; battery charge gauge.

24. A flying platform according to any one of the preceding claims, further including a cage (140) or frame for, in use, protecting the pilot (107).

25. A flying platform according to claim 24, wherein the cage (140) or frame is at least partially fitted with a transparent screen.

26. A flying platform according to any one of the preceding claims, further including a pilot safety harness.

27. A flying platform according to any one of the preceding claims, further including a ballistic emergency parachute.

28. A flying platform according to claim 27, when dependent upon claim 24, wherein the ballistic emergency parachute is attached to the cage (140).

29. A flying platform according to any one of the preceding claims, further including a frame (101 ) forming a collapsible undercarriage in the event of hard landing.

30. A flying platform according to claim 29, wherein the frame (101 ) comprises formations (106) for supporting the rotor units (1 17) and depending said landing supports (1 14).

31 . A flying platform according to claim 29 or 30, wherein the frame (101 ) is formed of hollow tubing.

32. A flying platform according to any one of the preceding claims, wherein the landing supports (1 14) comprise a set of wheels, skis or floats.